Fundamentals of Motors

Fundamentals of Motors 5/05 FOM

Fundamentals of Motors Table of Contents Electrical and Magnetic Basics................................................................ 1-2 Fluid Flow versus Electron Flow............................................................. 1-2 Electro Magnetism........................................................................ 1-2 Single and Three Phase Power............................................................. 1-4 Torque, Horsepower and Speed............................................................... 1-5 Torque.................................................................................. 1-5 Speed................................................................................... 1-5 Horsepower.............................................................................. 1-5 Relationship of Torque, Speed and Horsepower............................................... 1-6 NEMA................................................................................... 1-6 Speed versus Torque and Current........................................................... 1-6 Motor Basics................................................................................ 1-8 Frame Size.............................................................................. 1-8 NEMA Motor Enclosures................................................................... 1-8 Service Factor and Duty Cycle.............................................................. 1-10 Efficiency................................................................................ 1-10 Types of Motors.............................................................................. 1-11 Three Phase AC Motors................................................................... 1-11 Explosion Proof........................................................................... 1-11 Single Phase AC Motors................................................................... 1-12 DC Motors............................................................................... 1-15 FOM Fundamentals of Motors 1-1

Section 1 General Information Motor Fundamentals consists of four chapters: Electrical and Magnetic Basics Torque, Horsepower and Speed Motor Basics Type of Motors Electrical and Magnetic Basics Electrical motors use magnetism and induction to change electrical energy to mechanical energy. It is therefore important to understand electrical and magnetic fundamentals. Fluid Flow versus Electron Flow Electricity flows through conductors (wire) much the same as liquid flows through tubing or pipes. Electricity is measured in Amps, Volts and Watts and may be compared to liquid flow as shown in Table 1 1. There are similarities in the relationships of pressure, flow and energy. Table 1 1 Unit Fluid FLow Electrical Flow Media Water Electrons Pressure PSI (Pounds per Square Inch) Volts Flow Gallons Amps Energy Gallons per minute Watts Ohms Law In electrical circuits, the relationship between voltage (electrical pressure), current (electron flow) and resistance (resistance to electron flow) is stated as ohms law: I E I = Amperes (AMPS) E = Volts R R = Resistance (Ohms) Therefore, if the voltage across the motor changes, either amps or ohms has also changed. Electro Magnetism Magnetism can be produced by applying electricity to a coil of wire. The wire is wrapped around an iron core. When current flows through the wire, Magnetic lines of force (called magnetic flux, from North pole to South pole) are produced, Figure 1-1. Figure 1-1 Electro Magnetism When a wire is moved through a magnetic field, electric current is produced in the wire. This is known as induction and is the principle of operation for an AC or DC motor generator. The relationship of magnetic flux and current flow in a wire (amps) is shown in Figure 1-2. Figure 1-2 Motor Generator Wire Amps North South Magnetic FLux Wire Movement 1-2 Fundamentals of Motors FOM

When the wire is moved up through the magnetic field, electric current flows in one direction in the wire. When the wire is moved down through the magnetic field, electric current flows in the other direction. This relationship is shown in Figure 1-3. Figure 1-3 Electro Magnetic Generator Simplified Alternator: (AC Generator) The magnetic field is being moved through the wires rather than the wires moving through the magnetic field. A complete current path is established to the Light by the wires that are rotating through the magnetic field. The current and voltage produced lights the Light bulb shown in Figure 1-4. Figure 1-4 Simple AC Generator Slip Rings Stator Rotor Brushes Sine AC Generator As the magnetic field makes one revolution through the wires, a complete sine wave of voltage is produced. This means that both positive and negative voltages are produced and the speed of the wires moving through the filed determines the frequency of the AC voltage, Figure 1-5. Figure 1-5 AC Sine Wave Generator FOM Fundamentals of Motors 1-3

Simplified DC Generator The DC generator works very much the same as the AC alternator. Brushes are in contact with the commutator and each full rotation produces two pulses. Figure 1-6 DC Generator Basic DC Generator Operation FIgure 1-7 illustrate how the voltage signal is produced during one complete revolution of the DC Generator. As the wires rotate through the magnetic field, the brushes that are in contact each half of the commutator switch to the other half of the commutator at the 180 degree points ( B and D ). This changes the polarity of the signal that is produced. In this case, two positive pulses are produced for each 360 degree rotation of the rotor. Figure 1-7 DC Generator Operation Single and Three Phase Power AC Frequency Figure 1-8 shows the relationship of single phase AC Voltage and AC Current. Notice that the current lags slightly behind the voltage. Frequency is the number of cycles per second, called hertz. 60 Hz (hertz) = 60 cycles per second. The green waveform shown in Figure 1-8 is called a sine wave. Figure 1-8 AC Voltage and Current Relationship Three Phase AC Power Three phase AC power consists of three individual voltages that are synchronized with each other. These are Phase A, Phase B and Phase C voltages shown in Figure 1-9. Figure 1-9 Three Phase AC Power Phase A Phase B Phase C + 1-4 Fundamentals of Motors FOM

Rotating Magnetic Field A rotating magnetic field is produced in the stator (stationary coils of wire in the motor). The 3 phase power applied to the stator causes the rotor (rotating part of the motor) to move which converts the electrical energy to mechanical energy. Torque, Horsepower and Speed Torque Torque is the twisting force applied to the load as shown in Figure 1-10. Although we think of horsepower when selecting a motor, the load actually sees Torque supplied by the motor. Standard units of measure are: lb in (inch pounds), lb ft (pound feet), oz in (ounce inches) and nm (newton meters). Torque is a measured force at a specified distance. Torque = Force X Distance Figure 1-10 Torque Speed The rotational speed of the magnetic field within the motor is called the Synchronous Speed. It is approximately the no load motor speed. The synchronous speed varies by motor design but generally depends upon the number of motor poles and the operating frequency of the AC voltage, Figure 1-11. Figure 1-11 Synchronous Speed Horsepower Horsepower is a measure of the rate at which a motor or drive can produce work. A 1hp motor can produce 33,000 lb ft of work in one minute of time. Figure 1-12 Horsepower Illustration 16.3 2000 33 1000 FOM Fundamentals of Motors 1-5

Relationship of Torque, Speed and Horsepower Putting it all together. There is a relationship between a motor s Horsepower (hp), Torque and Speed. Figure 1-13 Torque, Speed & Horsepower Relationships Torque (lb ft) x Speed hp 5252 Torque (lb in) x Speed hp 63025 OR hp x 5252 Torque (lb ft) Speed Rules of thumb: Torque (lb in) hp x 63025 Speed As speed decreases, torque increases! As Torque increases so does the amount of required current! NEMA Full load torque for common motor speeds at 1 hp are: 1hp = 1.5 lb ft of Torque @ 3450RPM 1hp = 3.0 lb ft of Torque @ 1750RPM 1hp = 4.5 lb ft of Torque @ 1200RPM 1hp = 6.0 lb ft of Torque @ 850RPM National Electrical Manufactures Association. NEMA was established to provide a common standard for the electrical industry. Baldor and other motor manufacturers build their motors to the MG 1 specifications. Specifications also include: Enclosures, Insulation Classes, Frame sizes, Energy Efficiency and Nameplates According to NEMA a nameplate must include the following as a minimum: Mfg. Type and frame design. HP output Time Rating ( Duty Cycle ) Max. Ambient Temp Insulation system designation Frequency 50 or 60 HZ Number of phases Voltage Full Load Amps Code Letter for locked rotor KVA Efficiency This can be used as a guide to obtain needed information about the application so the correct motor may be selected. Speed versus Torque and Current This is a standard for Speed/Torque curve for a three phase AC induction motor. 1-6 Fundamentals of Motors FOM

Locked Rotor Torque is the torque the motor produces with full voltage applied and the load is stationary. It is torque available to break the load away from its rest position. Also called starting torque and breakaway torque. Pull Up Torque the lowest point on the Torque/Speed curve for a motor that is accelerating a load to full speed. The lowest point may be the locked rotor point for some motors. Also called pull in torque. Breakdown Torque the maximum amount of torque that is available from the motor shaft. When a motor operates at full voltage and maximum speed, the load is increased until the maximum torque is reached. Also called pull out torque. Full Load Torque the rated continuous torque the motor can provide without overheating within it s time rating. Also called rated torque. NEMA Design A, B, C and D motor comparisons. Design B is the most common three phase design used. NEMA provides standardized ratings for starting and torque characteristics and the amount of slip of a motor. See Figure 1-14. Figure 1-14 NEMA Design A, B, C and D Comparisons NEMA Torque Design Summary Something to Know: Slip & Heat Slip is loss of potential energy that shows up as heat. Slip is the difference between synchronous speed and full load speed. Design D motors have more losses from the stator, so more heat is produced. Starting Locked Rotor Breakdown NEMA Design Percent Slip Current Torque Torque Medium Medium High Maximum 5% Applications: Normal starting torque for fans, blowers, rotary pumps, B unloaded compressors, some conveyors, metal cutting machine tools, miscellaneous machinery. Slight speed change with load. Medium High Medium Maximum 5% Applications: High inertia starts, such as large centrifugal plowers, fly C wheels, and crusher drums. Loaded starts, such as piston pumps, compressors and conveyors. Slight speed change with changing load. Medium Extra High Medium 5% or More Applications: Very High inertia and loaded starts. Also, considerable D variation in load speed. Punch presses, shears and forming machine tools. Cranes, hoists, elevators, and oil well pumping jacks. Torque Types for Motors For higher starting torque applications, Design C or D motors should be used. FOM Fundamentals of Motors 1-7

Motor Basics Frame Size NEMA standardized the motor frame size that allows motors to be interchangeable regardless of the manufacturer. Three Generations 1. Prior to 1952 Original 284 2. 1952 to 1965 U frame 284U 3. 1965 to present T frame 284T NEMA frame size Designation. NEMA Motor Enclosures Two digit 56 56 = shaft height in 1/16 inch increments, 56/16 = 3.5 inches (Base to shaft center) IEC motors (metric) measure the shaft height in millimeters. For example, an 80 frame would have an 80 millimeter shaft height. Three digit 284T 28 = shaft height in 1/4 inch increments, 28/4 = 7 inches (Base to shaft center) 4 = Relative frame length (6 is a longer frame than 4) Common Frame Size Variations (suffix letter appears after frame size, ie. 56C) C Face mount D Flange mount S Short Shaft with smaller shaft diameter than standard T 1964 generation U 1952 1964 era Y Special mounting configuration Z Special Shaft longer, larger, holes, threads, etc. US Voltage Ratings 3 Phase Industrial Power Sources; 240 480 600 VAC 3 Phase Motors Prior to 1965; 220 440 550 VAC 1965 to present; 230 460 575 VAC 1-8 Fundamentals of Motors FOM

Voltage Drop As current leaves it s source and travels through wires to the load, the resistance of the wire and connections causes voltage drops across the wire or connections. This reduces the voltage available at the load. Because voltage drop affects motor performance, voltage and current should be measured at the motor, not at the fuse/breaker box. Figure 1-15 illustrates voltage drops at various parts of the circuit. Notice the reduced voltage at the lamp. Figure 1-15 Insulation Class NEMA also classifies the insulation used inside the motor. Centigrade and Fahrenheit Comparison FOM Fundamentals of Motors 1-9

Service Factor and Duty Cycle Service Factor Is a measure of the overload capacity designed within the motor. This service factor should only be used if other factors are within nameplate ratings (such as ambient temperature and voltage). Service factor for a motor should not be used when the altitude for the application exceeds 3300 ft (1000 meters). A SF of 1.15 means a motor is capable of running at 115% of rated load with out exceeding temperature rise limits. Other common SF are 1.0 and 1.25 Duty Cycle Motors are rated for Continuous or Limited (timed) Duty. Most motors are rated Cont. Duty Efficiency Efficiency is the percentage of the input power that is actually converted to work output (motor shaft). Output Power (kw) Efficiency Input Power (kw) 1kW = 1.34 hp Nameplate lists Nominal Efficiency There is also a Minimum Efficiency Standard versus Energy Efficient Electric Consumption by Motors In industry, electric motors consume more electricity than any other item. Operating Cost versus Purchase Price Rule of Thumb: (Assume 24 hour operation @ $0.05/kWh) It costs about $1 per horsepower per day to operate a motor. 1-10 Fundamentals of Motors FOM

Types of Motors Three Phase AC Motors Squirrel Cage Induction Motors These motors meet many of the requirements found in industry. Because of their simple construction, low maintenance cost, and versatility, these motors are used most often. They have good speed characteristics and can be easily reversed. Three Phase AC Motor Parts: Inverter Ready Super E Motors ISR Inverter Spike Resistant Wire is used in all Baldor AC Motors. EXXON/Mobil POLYREX "EM Grease Baldor Inverter Duty Motors Meet all requirements of NEMA MG 1 part 31 Speed Range 1000:1 (except explosion proof) TENV or TEBC Matched Performance with Baldor controls Class H Insulation Thermostats in windings C Face standard 1024 PPR Encoder (2 styles) Vector, Inverter Explosion Proof These are specially designed AC squirrel cage induction motors. Explosion Proof motors are designed for use in the presence of combustible gasses and vapors. These are required to be constructed so that gas vapor air explosions that occur within the motor will not ignite surrounding gas vapor air mixtures. Joints are machined with close tolerance, metal to metal contact, with adequate flame paths to arrest any propagation of flame or hot gas from inside the enclosure to the surrounding atmosphere. Explosion Proof Parts Explosion Proof Cutaway View FOM Fundamentals of Motors 1-11

Single Phase AC Motors Types of AC Single Phase Motors Shaded Pole Split Phase Capacitor Start Induction Run Capacitor Start Capacitor Run Permanent Split Capacitor Repulsion Start Induction Run Single Phase Voltages Single phase motors larger than 5hp are normally 230VAC only. Single phase motors smaller than 5hp are normally 115/230VAC. Shaded Pole Motor The shaded pole motor will operate loads that are very easy to start. It has low starting torque from 50 to 75 % of the normal full speed torque. Typical applications are found on small fans used on home appliances and computer fans. Baldor does not build these type of motors. Split Phase Motors Split phase motors are wound to divide the incoming current into two parts during the starting phase. The run or main winding consists of many turns of low resistance, large diameter wire. The auxiliary winding (sometimes called the start winding) consists of fine wire with high resistance. This causes a shift in the magnetic field that is needed to start the motor. A switch disconnects the auxiliary start winding when the run RPM is reached. 1-12 Fundamentals of Motors FOM

Capacitor Start Induction Run These motors are similar to split phase motors, except a capacitor is connected in series with the start winding. The capacitor causes the current phase shift between the run and start windings. A centrifugal switch mounted in the endbell of the motor disconnects the start winding when the run RPM is reached. This is the most common single phase motor used in industry. The start capacitor is an electrolytic type that has a time rating. All capacitors of this type cannot be Online all the time. Capacitor Start Capacitor Run Similar to the capacitor start induction run motor except an electrolytic capacitor is used with the start winding to start the motor and an oil filled capacitor is used with the run winding to run the motor. The run capacitor reduces the line current required to run the motor. The capacitor (unlike the oil electrolytic) is not time rated and may be Online all the time. This motor type may be found in many farm duty applications. Permanent Split Capacitor The permanent split capacitor motor uses the same oil filled type capacitor for starting and running (no switch). This motor type is used in fan applications. FOM Fundamentals of Motors 1-13

Repulsion Start The repulsion start induction run motor has a start winding similar to the single phase motor except it has a wound armature with a commutator similar to the DC motor. Starting torque develops through the interaction of the rotor current and single phase stator. As the motor is running, the commutator is removed from the circuit and the motor operates as a single phase induction motor. This motor type is used in hard to start applications and is the most expensive single phase design. Comparison of Motor Parts 1-14 Fundamentals of Motors FOM

DC Motors DC Motor Parts Types of DC Motors Permanent Magnet Wound Field Series Wound Shunt Wound Compound Wound Permanent Magnet DC Motors Permanently magnetized materials create the magnetic field (instead of an electromagnetic Stator winding). This type of motor has a straight line sped torque curve. This design is used in adjustable speed applications normally less than 5hp. Armature voltages are commonly 90VDC and 180VDC. Series Wound DC Motors Field coils are series connected to the armature. As the load is reduced, current decreases and this results in a weaker magnetic field. This causes the motor speed to increase. The high torque at low speeds makes these motors ideal for electric vehicle applications. Rated voltages are commonly 12, 24, 48, 72 or 96 VDC (multiples of 12VDC). Shunt Wound DC Motors Field coils are connected in parallel with the armature. This motor type has the flattest speed torque curve of wound stator design and is ideal for conveying applications. However, this motor type does not perform well under heavy overload conditions. This design is used in adjustable speed applications. Can be wound for very special applications. These have both armature and field rated voltages (ie. 90VARM/100VFIELD). FOM Fundamentals of Motors 1-15

Compound Wound DC Motors A combination of series and parallel windings are used. One filed coil is in series with the armature and the other is in parallel with the armature. This motor develops more starting torque than a shunt wound motor and has less speed variation under load than the series wound type. Compound wound motors are used in fans and pumps. Rated voltages are commonly 115VDC or 230VDC. Benefits of Permanent Magnet DC Motors Stable Magnetic field Higher stall torque More efficient use of electricity Reduced frame size for a given output. Very durable Only two wires required Lowest (perceived) cost Benefits of Wound DC Motors Can be wound to meet extremely specific operating characteristics, especially for speed control and over speeding. They are the only type of DC motor available in some torque ranges. Overview of Motors Characteristics DC Motors Change in voltage produces a change in speed. Change in current produces a change in torque. AC Motors Change in input frequency produces a change in speed. Change in current produces a change in torque. 1-16 Fundamentals of Motors FOM

BALDOR ELECTRIC COMPANY P.O. BOX 2400 Fort Smith, AR 72902 2400 (479) 646 4711 Fax (479) 648 5792 www.baldor.com Baldor Electric Company FOM Printed in USA 5/05

Fundamentals of Motors Name: Branch Address: Phone: email Address: 1. What is the largest user of electricity in industry? Light bulbs Computers Electric Motors Electric Pencil Sharpeners 2. Since Fluid flow and Electrical flow can be compared, what is the pressure or PSI in Fluid flow most like? Electrons Volts Amperes Watts 3. When a wire is moved through a magnetic field nothing happens. True False 4. In an AC system frequency is known as voltage change. True False 5. A rotating magnetic field within the stator of an AC motor is called the speed of the motor? 6. An AC motor has stationary and rotating parts. The stationary part of an AC motor is called the. The rotating part of the AC motor is called the. Fundamentals of Motors Questions 1

7. For every one horsepower, a 1750 RPM motor will develop approximately lb ft of Torque at full load. 3 33 333 3333 8. NEMA stands for... National Engineering Managers Association National Electrical Manufacturers Association National Electrical Manufacturing Association National Electrical Motor Association 9. Locked Rotor torque is also called Starting Torque. True False 10. In a DC motor, a change in voltage changes motor speed. current changes motor speed. hertz changes motor speed. temperature changes motor speed. 11. The higher the insulation class letter the greater the amount of heat the insulation can withstand before breaking down. True False 12. Service Factor is a measure of the overload capacity of a motor. If a motor is used in Denver, Colorado (5,200 ft) it is OK to use it s service factor to determine overload capacity. True False 2 Fundamentals of Motors Questions

13. Where is an explosion proof motor used? 14. What is the most common NEMA winding design of three phase motor used in industry? 15. What is the most popular motor for industry? Capacitor Start, Induction Run Motors. Split Capacitor Motors Wound Field DC Motors Shaded Pole Motors 16. What are the alternate names for the Conduit box on a motor. (Check all that apply). Terminal Box Breaker Box Junction Box End Bell Assembly 17. Split Phase AC Motors have only one set of windings. True False 18. Wound DC motors can be wound to meet extremely specific operation characteristics. True False 19. Why is avoiding a large voltage drop important in motor applications? Fundamentals of Motors Questions 3

Section 1 General Information 20. A customer has a three phase conveyor application. What type of motor would you supply and why? 21. What data would you need to know before selecting the motor for the application? Return your completed form to: Baldor Electric Company Marketing Dept. P.O. Box 2400 Fort Smith, AR 72902 2400 Attn: Director of Education 4 Fundamentals of Motors Questions

Fundamentals of Drives 5/05 FOD

Fundamentals of Drives Table of Contents Basics...................................................................................... 2-2 AC Motor Speed.......................................................................... 2-2 AC Motor Poles........................................................................... 2-2 Frequency............................................................................... 2-2 Synchronous Motor Speed................................................................. 2-2 Full Load Speed.......................................................................... 2-3 Slip..................................................................................... 2-3 Torque and Horsepower Formulas........................................................... 2-3 2 Wire Control Circuits..................................................................... 2-3 3 Wire Control Circuits..................................................................... 2-3 Load Types.............................................................................. 2-4 Motor Starters............................................................................... 2-5 Full Voltage Starting...................................................................... 2-5 Reduced Voltage Starting.................................................................. 2-5 Adjustable Speed AC Controls................................................................ 2-7 Multi Speed AC Motors.................................................................... 2-8 Feedback................................................................................ 2-8 Inverter Control........................................................................... 2-9 Dynamic Braking.......................................................................... 2-10 Line Regenerative Braking................................................................. 2-10 Output Ratings........................................................................... 2-11 Vector Control............................................................................ 2-11 Encoderless Vector Control................................................................. 2-12 Feedback Devices............................................................................ 2-13 Encoder................................................................................. 2-13 Resolver................................................................................. 2-13 DC Motor Controls........................................................................... 2-14 DC SCR Control.......................................................................... 2-14 PWM DC Control......................................................................... 2-14 DC Power Supply Types................................................................... 2-15 Feedback for DC Control................................................................... 2-16 Terminology................................................................................. 2-16 FOD Fundamentals of Drives 2-1

Section 1 General Information Basics AC Motor Speed AC Motors are essentially constant speed motors. The speed of the magnetic field is determined by the line frequency and the arrangement of the stator windings (number of magnetic poles). AC Motor Poles The number of pole pairs (north and south electromagnetic poles) are determined by how the stator windings are constructed. Figure 2-1 AC Induction Motor Poles A C B B C Frequency A Frequency of the AC Line is determined by the number of positive and negative cycles occur per second. Motor designs are based on the voltage and frequency specified. Frequency is normally 60 or 50Hertz. Figure 2-2 Three Phase AC Voltage Waveform Phase A Phase B Phase C + Synchronous Motor Speed Synchronous Motor Speed is the speed at which the magnetic field within the motor (stator) rotates. This is also approximately the no load rotor speed. Synchronous speed (see Table 2 1) is determined by the number of poles and operating frequency. More poles provide more torque but slower speed. Table 2 1 Poles 60Hz Speed (synchronous) 50Hz Speed (synchronous) 2 3600 RPM 3000 RPM 4 1800 RPM 1500 RPM 6 1200 RPM 1000 RPM 8 900 RPM 750 RPM The formula to calculate synchronous rotation speed is: 120 AC Frequency RPM Number of Poles 2-2 Fundamentals of Drives FOD

Full Load Speed The full load motor speed is approximately the motor speed when the motor is producing full torque. It is also called the base speed or running speed of the AC motor. Table 2 2 Poles 60Hz Speed 50Hz Speed (synchronous) (full load) (synchronous) (full load) 2 3600 RPM 3450 RPM 3000 RPM 2850 RPM 4 1800 RPM 1725 RPM 1500 RPM 1440 RPM 6 1200 RPM 1140 RPM 1000 RPM 960 RPM 8 900 RPM 860 RPM 750 RPM 720 RPM Slip Slip is the difference between a motor s synchronous speed and full load speed. As the load increases, motor speed is reduced slightly to move the load. Large motors tend to have less slip than small motors. High efficiency motors tend to have low values of slip. 3 5% slip for motors less than 10hp and 1% for motors greater than 75hp. Table 2 3 Motor hp Running RPM Slip RPM Percent Slip 1/2 1725 RPM 75 RPM 4.0% 100 1760 RPM 40 RPM 2.2% 200 1780 RPM 20 RPM 1.1% Torque and Horsepower Formulas Here is the relationship of Torque and Horsepower. Torque HP X constant Where: HP = Horsepower, S = Base Speed S constant = 5252 (for torque in lb ft) 2 Wire Control Circuits An example of a 2 Wire control circuit is shown in Figure 2-3. Figure 2-3 2 Wire Control When water reaches a preset level, the float switch closes and the pump motor runs. When the water level decreases to a preset level, the float switch opens and the pump motor stops. Another example of a 2 wire control is a light switch. Close the switch and the light goes On. Open the switch and the light goes Off. L1 Float Switch 2 Wire controls are inexpensive but have a major draw back. When the switch is closed and the motor is running then power is lost, the motor stops. When power is restored, the motor will immediately start running (switch is still closed). This can be extremely dangerous in many applications. 3 Wire Control Circuits An example of a 3 Wire control circuit is shown in Figure 2-4. Figure 2-4 3 Wire Control L1 Momentary contacts are used so that if power is lost and restored, the motor will not operate. Closing the Start Start switch energizes the M contactor to start motor operation Stop and the M contact across the start switch is closed (sealing M contact of the M contactor relay. The motor is connected across L1 and L2 and continues to run until power is lost M (sealing contact opens) or one of the three Stop switches is pressed. When a Stop switch is pressed, the motor connection to L1 is lost and the motor stops. 3 wire control is much safer if power is lost and restored. M OL OL L2 L2 L1 L2 L3 M OL T1 T2 T3 Three Phase Motor L1 L2 L3 M OL T1 T2 T3 Three Phase Motor FOD Fundamentals of Drives 2-3

Load Types Loads are generally divided into three categories: Variable Torque, Constant Torque and Constant Horsepower. Figure 2-5 Variable Torque Variable torque loads have characteristics requiring low 100 % HP & Torque torque at low speeds and increased torque as speed is 80 increased. Examples of variable torque loads are fans, and centrifugal pumps. 60 40 Torque 20 HP Constant torque loads have characteristics where torque is constant regardless of motor speed. Examples of constant torque loads are conveyors, extruders, mixing applications and positive displacement pumps. % Speed 50 100 Figure 2-6 Constant Torque % HP & Torque 100 Torque 80 60 HP 40 20 % Speed 50 100 Figure 2-7 Constant Horsepower Constant horsepower loads require reduced torque as motor speed is increased. 100 % Torque Examples of constant horsepower loads are drill presses, lathes, milling machines and winding equipment. 80 60 % HP Note: A constant horse- power load is easily identified when either the diameter of the tool or the load is changed. 40 20 100 % Speed 200 2-4 Fundamentals of Drives FOD

Motor Starters A starter controls two important characteristics of a motor: The motor current (torque produced by the motor) and the frequency of the voltage applied to the motor (motor speed ). Motor starters can be Full Voltage Starters or Reduced Voltage Starters. Full Voltage Starting Full voltage starters are also called across the line starters. Full AC line voltage is applied directly to the motor. Typically full voltage starting is used for squirrel cage induction motors. This results in starting current of up to 600% of full load current and from 200 400% of full load torque. (See Table 2 4 that compares inrush current and torque for different starter types). This can cause mechanical and electrical stress on the motor. Table 2 4 Inrush Current Starter Type Inrush Amps % Torque % Across the Line 400 700% FLA 150 400% FLT Resistor 65% FLA 42% FLT Part Winding 50% FLA 50% FLT Wye/Delta 60% FLA 60% FLT Auto Transformer 50/60/80% FLA 50/60/80% FLT Solid-State Soft Start 10 100% FLA 10 100% FLT * Depends on Motor Design Reduced Voltage Starting Reduced voltage starting methods include: Part Winding, Primary resistor, Wye Delta, Auto Transformer and Solid State Soft Starter. Figure 2-8 Part Winding Starter Part winding starters use two motor windings. Power is applied to only one winding to achieve reduced voltage starting. Normal current is approximately 70% and torque is approximately 50% of locked rotor full voltage condition. After a time delay, power is applied to the second winding that brings the motor to full speed and torque. Limitations of Part Winding Starters are: Maintenance of electro mechanical contacts. Initial starting torque is not adjustable to load condition. Special motor and starter are required. Transition from initial start to full winding operation is stepped instantaneously causing mechanical and electrical stress. FOD Fundamentals of Drives 2-5

Figure 2-9 Primary Resistance Starter Primary resistance starters insert power resistors to reduce voltage to the motor. After starting, the resistors are removed and full voltage is applied to the motor. Limitations of Primary Resistance Starters are: Maintenance of electro mechanical contacts. Transition from initial start to full voltage operation causes mechanical and electrical stress. Stop Start A T.C. M A M O.L. Thermal Cut Out M L1 L2 L3 M A M A M A Resistors O.L. O.L. O.L. T1 T2 T3 Motor Figure 2-10 Wye Delta Starter Wye Delta motors are specifically wound for use with a Wye Delta starter. The motor is started in the Wye configuration to achieve reduced voltage starting. Current and torque are approximately 2/3 of locked rotor values. After a time delay, the windings are switched to delta configuration to bring the motor to full speed and torque. Limitations of Wye Delta Starters are similar to other reduced voltage starters. Figure 2-11 Auto Transformer Starter Auto transformer starting uses a standard AC induction motor. The starter may have up to three taps usually 50%, 65% and 85% of full voltage. Reduced voltage starting is accomplished by selecting the desired voltage tap. After a time delay, the starter will switch to full voltage. There are thermal limitations with the auto transformer that limits the number of starts per minute. L1 L2 L3 S S S R R R T2 T1 T3 AC Motor 2-6 Fundamentals of Drives FOD

Figure 2-12 Solid State Soft Starter Solid state soft starter controls use solid state switching devices (SCR or Silicon Controlled Rectifiers) to produce a linear voltage increase to the motor. Solid state starting eliminates switching transients that cause mechanical and electrical stress for the motor. There are no inherent limitations to the number of starts in a period of time. Adjustable Speed AC Controls AC Motors are designed to run at one speed at rated voltage. To control the speed of an AC motor application, a speed reduction gearbox, pulleys, sprockets or other devices must be used. Figure 2-13 Gearbox or Pulley Adjustable Speed Devices FOD Fundamentals of Drives 2-7

Multi Speed AC Motors A multi speed AC motor has one or more windings allowing for multi speed operation. Most operate as two speed motors. Three and four speed motors are not common but available. Multi speed motors are normally single voltage. Single winding motors are designed to be connected for speeds based on 2:1 ratio. For example, at 60Hz speeds of 3450/1750 RPM or 1750/850 RPM are available. 4:1 ratios are available but not as common. Two winding motors are designed so that available speeds are not necessarily on a 2:1 ratio. For example, two winding motor full load speeds could be 1750/1140 RPM or 3450/850 RPM. When ordering multi speed motors, be sure to specify the number of windings (one or two windings) torque characteristic (variable torque, constant torque, constant hp) and voltage rating. Adjustable Speed Control To adjust the speed of an AC induction motor you must adjust the frequency and to adjust the torque you must control the current to the motor. Figure 2-14 Control Selection Chart Must Control the Motor s Speed and Torque Must control motor starting Soft Start Adjustable Speed Control DC SCR Inverter Vector Must control position Servo Vector Feedback Open Loop: There is no speed or shaft position feedback from the motor to the control in an open loop system. Closed Loop: A feedback device mounted on the motor provides speed and shaft position information to the control. Most common feedback devices are tachometers, resolvers and encoders. 2-8 Fundamentals of Drives FOD

Inverter Control An inverter control adjusts the speed of an AC induction motor. The inverter adjusts the frequency and voltage of the output power that is applied to the motor. It is an open loop control and does not monitor motor speed or position. Internally the control converts fixed voltage, fixed frequency AC line power to DC power that is stored in capacitors. This is done by the Converter section of the control. The DC Bus voltage is approximately 1.4 times the RMS AC line voltage (230VAC line voltage will produce 322 volt DC bus voltage). The DC bus voltage is then converted to a PWM (Pulse Width Modulation) 3 phase AC signal to be applied to the motor. The way that the PWM signal is controlled adjusts the frequency and voltage applied to the motor. Figure 2-15 Inverter Control Converter Inverter L1 L2 L3 + DC Bus T1 T2 T3 Logic Circuits Logic Circuits Three Phase Motor Control Circuits SCR PWM signal has the a series of positive and negative pulses for it s output signal. The width of each pulse changes with the amplitude of the voltage it represents. A very narrow pulse represents a lower voltage than a wider pulse. Figure 2-16 illustrates the PWM signal and the corresponding AC motor voltage waveforms. All pulses are the same amplitude but their width changes to control motor voltage. The frequency of the motor voltage is controlled by the frequency of the positive and negative transitions of the PWM signal. Figure 2-16 PWM Signal Capacitor Transistor Carrier Frequency changes pulse rate Motor Output PWM Voltage Narrow pulse widths produce less power to the motor Output Current Carrier Frequency changes pulse rate Output Frequency Output Frequency PWM signal pulses occur at the rate of the Carrier frequency or the switching speed of the Inverter section transistors. For inverters this is adjustable between 1kHz and 15kHz. A 2kHz carrier frequency has more audible noise than an 8kHz carrier frequency but the 8kHz produces more losses (heat). The resulting motor current is a three phase signal whose frequency is determined by the positive and negative transitions of the PWM signal. If the PWM signal changes from positive going to negative going 40 times each second, the output frequency to the motor is 40Hz. The frequency of the output to the motor is generally adjustable from 10 to 400Hz. FOD Fundamentals of Drives 2-9

Audible Noise Low carrier frequencies typically produce audible noise from the motor windings. Increasing the carrier frequency will reduce the audible noise. The trade off is reduced output current from the inverter due to increased power losses within the power devices themselves, increased motor heating and faster application of the current into the winding. Figure 2-17 Volts per Hertz Ratio For a motor to be able to output the desired torque VAC at each frequency (speed) it is necessary to apply the optimal motor voltage at each frequency. The 460 ratio of this Motor Voltage to Motor Frequency is called Volts per Hertz ratio. 306 The ratio for a 460VAC inverter with a 60Hz motor is 7.67 Volts/Hz. If the output frequency is 40Hz, the output voltage is then 40x7.67=306VAC. Hz 40 60 Dynamic Braking When a motor is stopped faster than it would coast to a stop, the motor becomes a generator. It produces power which must be sent back to the power line (Regenerative Mode) or it must be dissipated as heat. To dissipate the extra energy, a resistor called a dumping resistor or Dynamic Brake resistor is used. During a stop, the DC bus voltage increases and is automatically switched to the dynamic brake resistor for dissipation so the bus voltage remains relatively constant. A dynamic brake is simply to dissipate heat during load deceleration, it does not hold the load at zero speed. A mechanical fail safe brake is required if Holding Torque is required at zero speed. The mechanical brake must be wired directly to the power line, not through the control. If the brake were connected to the control, because of varying voltage the control may not provide enough power to release the mechanical holding brake. Figure 2-18 Dynamic Brake and Mechanical Brake Dynamic Brake Resistors Mechanical Brake Assembly Line Regenerative Braking The excess power produced during braking periods can be put back on the incoming AC. The excess DC power on the bus must be converted to AC power and synchronized and be in phase with the 60Hz utility power. This requires an additional converter section and is more expensive. 2-10 Fundamentals of Drives FOD

Output Ratings Motor torque is directly related to the current applied to the motor. Load conditions may require greater or reduced torque (motor current) as conditions change. The average current required by the load is within the Continuous Operating Area if the control. Peak torque available (for starting and other changing load conditions) is generally 150% to 200% of the continuous output rating. Figure 2-19 Inverter Output Rating Chart Vector Control Like the inverter, a Vector control adjusts the speed of an AC induction motor. The vector adjusts the frequency and current of the output power that is applied to the motor. An encoder feedback device is used with the vector control to monitor motor speed. This creates a closed loop control system that continuously calculates motor speed and adjusts the motor signal to increase or decrease speed and current to match changing load demands. The vector control provides more precise control than an inverter. Full motor torque is available independent of speed (including zero speed). Internally the control converts fixed voltage, fixed frequency AC line power to DC power that is stored in capacitors. This is done by the Converter section of the control. The DC Bus voltage is approximately 1.4 times the RMS AC line voltage (230VAC line voltage will produce 322 volt DC bus voltage). The DC bus voltage is then converted to a PWM (Pulse Width Modulation) 3 phase AC signal to be applied to the motor. The way that the PWM signal is controlled adjusts the frequency and voltage applied to the motor. The vector control uses a complex algorithm to separately control motor excitation current called flux current and torque producing load current. Figure 2-20 Vector Control Converter Inverter L1 L2 L3 + DC Bus T1 T2 T3 Logic Circuits Logic Circuits Three Phase Motor Encoder Control Circuits FOD Fundamentals of Drives 2-11

The vectors microprocessor calculates magnetizing current and torque producing current values and vectorially adds them and this current value is applied to the motor. This value of motor current produces optimal speed/torque control of the load. The algorithm maximizes motor torque while minimizing motor heating. Figure 2-21 Torque Components Magnetizing Current C A Rotor Stator É ÉÉ ÉÉ É É É 90 B Torque Current The vector ratings are illustrated in Figure 2-22, compare it s ratings with those of the inverter (Figure 2-19). A vector control has more precise control of the motor and allows full motor torque to be available at zero speed. This provides torque control (Vector) rather than speed control (Inverter) and a wider range of operating speeds. Figure 2-22 Vector Output Rating Chart Encoderless Vector Control The encoderless vector control is also called sensorless or open loop vector control. This control uses an adaptive vector algorithm to calculate motor currents and provide torque control. The control monitors motor current and voltage and calculates rotor and stator flux signals, calculates motor speed based on these signals and controls the motor. In other words, the motor itself becomes the speed sensor. Figure 2-23 Encoderless Vector Control Current Signals I d I q Voltage Signals V d V q Adaptive Motor Model Motor Speed L M L 1 Slip R s Inductance, Resistance, and Slip Signal 2-12 Fundamentals of Drives FOD

Feedback Devices A feedback device attached to the motor provides feedback information to the vector control. The device provides angular position and speed information to the control. Encoder The encoder feedback device is a photo optical device that produces pulses as the motor shaft rotates. The encoder is constructed to produce two channels of pulses (A and B) and a once per revolution marker pulse (C) channel. The control receives this data and can precisely calculate motor shaft position, speed and direction of rotation. Figure 2-24 Encoder Operation Resolver Code Disk C B A Three Light Sensors Light Beams Three Light Sources A B C 0 1024 Pulses Per Revolution 0123 Quadrature Quadrature 0 1 2 3 A 0 1 1 0 B 0 0 1 1 Time Pattern Repeats 1024 Times per Revolution A resolver looks like a motor, it has a shaft, windings and electrical connections. More properly, it is a revolving transformer. A signal from the rotor winding is induced into it s stator winding. This output signal varies according to the angle of the rotor windings relative to the armature windings. A resolver and associated electronics, provides information about the speed, direction and position of the motor shaft that the resolver is connected to. Resolvers do this without parts that wear out (like DC tachometer brushes). A resolver is more rugged and may be operated at higher temperatures than an encoder. Figure 2-25 Resolver Operation R2 R1 S3 S1 S2 S4 SIN+ SIN COS+ COS REF+ REF (Common) FOD Fundamentals of Drives 2-13

Table 2 5 Features of Feedback Devices Feature Tachometer Encoder Resolver What it measures Speed Position, can derive speed Position, can derive speed Location On motor shaft On motor shaft or lead screw On motor shaft Output Continuous voltage proportional to Digital signal (On/Off) Sinusoidal (sine and cosine) signal speed (analog) Precision ±1% set speed, no position information Depends on number of encoder lines Depends on sample rate of microprocessor (control) Ruggedness Good. Brush wear, ripple, change in output with temperature Fair. Susceptible to shock, vibration, dirt and dust Best. No internal electronic parts, withstands greater temperatures Cost Low. (But no position information) Mid Range. Digital output works well with controls. Highest. Requires additional electronics to process complex sinusoidal signals. DC Motor Controls DC motor controls respond to feedback signals to generate proper DC voltage and current to control the DC motor and regulate motor performance. DC Voltage controls motor speed, DC Current controls motor torque. The actual motor signal from the control may be DC or a PWM signal like the inverter. DC SCR Control The DC SCR motor control is the least expensive control type for motor control applications. The speed demand determines the conduction of the SCR (silicon controlled rectifier) devices that convert the AC line power to DC motor power. The more speed required, the more conduction is required from the SCR devices. The SCR devices automatically turn off when the AC waveform crosses through zero volts. By controlling when each SCR turns on, the amount of DC power produced is controlled. The polarity of the DC voltage determines motor direction. The SCR s can be arranged for half wave or full wave rectification. Full wave rectification provides the most power to the motor. Figure 2-26 DC SCR Conduction Operation VAC 1 A 1 B 2 A VDC VDC VAC 2 B 1 A 1 B 2 A 2 B 3 A 3 B VAC A B VDC VDC Natural Commutation Single Phase Full Wave Three Phase Full Wave PWM DC Control A PWM control are the most sophisticated DC motor control. Like the Inverter, incoming AC line power is rectified to DC power that is stored in capacitors. This is done by the Converter section of the control. The DC Bus voltage is then converted to a PWM (Pulse Width Modulation) signal. The PWM signal is filtered and the DC voltage is applied to the motor. Dynamic braking or Regenerative braking considerations also apply to DC controls. Figure 2-27 PWM DC Control Operation VAC PWM Output Filtered DC To Motor 2-14 Fundamentals of Drives FOD

DC Power Supply Types NEMA (National Electrical Manufactures Association) was established to provide a common standard for the electrical industry. NEMA defines typical DC power supplies in it s specification MG1 12.62. Baldor DC rated motors are designed to operate from type K power supplies for the 90 and 180 volt motors. 240 and 500 volt motors are designed for type C power supplies. Many designs also operate from type D power supplies. Power Supply A Designates a DC Generator or Battery. Figure 2-28 NEMA Power Supply Types Power Supply A DC Gen. + Power Supply K Power Supply K Designates a single phase full wave power supply. A1 A2 A1 A2 Power Supply C Designates a Three Phase, Full Wave Power Supply. Power Supply C Power Supply D Power Supply E Power Supply D Designates a Three Phase, Half Wave Power Supply. Power Supply E Designates a Three Phase, One Way Power Supply. A1 A2 A1 A2 A1 A2 Figure 2-29 DC SCR Rated Motor FOD Fundamentals of Drives 2-15

Feedback for DC Control DC Controls can use Armature, Tachometer or Encoder Feedback to measure motor speed. For encoder feedback, see Figure 2-24. Figure 2-30 Armature Feedback Armature feedback senses the armature current and this feedback signal is used to correct the motor speed. Most SCR DC Controls have a speed regulation of 1% of base speed with armature feedback. A tachometer is a motor that operates in a reverse manner. The rotating shaft of the tachometer is attached to the motor shaft and rotates with it. As it rotates, a voltage is induced in the stator of the tachometer. The voltage is proportional to to speed and direction of the motor. Tachometers are rated in terms of rated voltage, ripple voltage and linearity. Tachometers are rated as volts per thousand RPM (ie 50volts per 1000RPM). 10VDC Summing Junction Feedback Voltage Controller 0V Figure 2-31 Tachometer Feedback Brush Assembly Tach Armature Error Signal Tach Magnet Terminology Speed/Torque Regulation Base Speed The speed at which a motor delivers rated voltage (for DC motors) or rated frequency (for AC motors). Set Speed The desired operating speed set by the operator at the control. Speed Regulation The percentage of base speed change between full load and no load speed given as: No Load Speed Full Load Speed % Regulation X100 No Load Speed 2-16 Fundamentals of Drives FOD

BALDOR ELECTRIC COMPANY P.O. BOX 2400 Fort Smith, AR 72902 2400 (479) 646 4711 Fax (479) 648 5792 www.baldor.com Baldor Electric Company FOD Printed in USA 5/05

Fundamentals of Drives Name: Branch Address: Phone: email Address: 1. We know in an AC motor more poles mean more Torque. What is the trade off? Smaller size Larger shaft Slower speed More Heat 2. AC Motors are essentially constant speed motors. True False 3. What are the two most important concepts to know when controlling AC motors? (Select 2 answers). To control the torque, you must control the current. The motor rotates. You must overvoltage the motor. To vary the speed, you must vary the power line frequency. 4. What type of load has the characteristic where the amount of torque required is the same regardless of speed? Constant Horsepower Constant Torque Variable Torque Variable Horsepower Fundamentals of Drives Questions 1

5. Limitations of part winding starters are. Select all that apply. Can produce more than full load torque at start Maintenance of electo mechanical contacts You must have a special motor and starter The transition from initial start to full winding operation is instantaneous 6. Full voltage starting of AC squirrel cage induction motors can result in starting currents up to % of full load current. 7. Solid State Soft Starts can only produce 2 starts per minute. True False 8. An inverter adjusts to control the speed of an AC motor. 9. Multi speed motors, designed for use without a control have one or two windings. True False 10. The rate at which the PWM pulses are produced is called the carrier frequency. True False 11. What two types of current are added in a vector control? (Select 2 answers). Torque Current Over Current Flux Current DC Current 12. is the industry standard optical feedback device used with a vector motor and control? 13. An Encoderless vector control uses the control as a speed sensor. True False 2 Fundamentals of Drives Questions

14. Encoderless Vector controls offer better performance then a closed loop vector control. True False 15. Which is not a type of feedback used with DC motors and controls. Armature Servo Encoder Tachometer 16. Base speed is the speed you set on the control. True False 17. With DC drives, a change in voltage changes speed. True False 18. A DC control performs which of the following? (Select all that apply). Rectify incoming AC power to DC power Control the amount of current to the motor Control the pay scale Respond to feedback signals 19. When we say that a control is Line Regenerative, what do we mean? 20. What is a vector control? 21. How is a vector control different than an inverter? Fundamentals of Drives Questions 3

Return your completed form to: Baldor Electric Company Marketing Dept. P.O. Box 2400 Fort Smith, AR 72902 2400 Attn: Director of Education 4 Fundamentals of Drives Questions

Fundamentals of Servos 7/05 MIFOS

Fundamentals of Servos Table of Contents Servo Specifics............................................................................... 3-2 Servo Terminology............................................................................ 3-3 Servo Motor Benefits.......................................................................... 3-5 PMDC Servo Motor............................................................................ 3-5 Brushless Servo Motors........................................................................ 3-6 Feedback Devices............................................................................ 3-7 Tachometer.............................................................................. 3-7 Encoder................................................................................. 3-7 Resolver................................................................................. 3-8 Hall Sensors............................................................................. 3-8 Pulse Width Modulation........................................................................ 3-9 MIFOS Fundamentals of Servos 3-1

Section 1 General Information Servo Specifics A Servo is a system of devices used to control the position, direction and/or the speed of a load. These devices are normally a Control, Motor and Feedback device. Within this guide, we will call the control a Servo Control, the motor a Servo Motor and the feedback device can be a resolver or an encoder. A Servo drive is a control and motor. Servo s are used in applications where there s a lot of starting and stopping. Where motor direction is frequently reversed. The changes in speed or position are rapid almost instantaneous. In a potential servo application, it s the need for movement that will first attract your attention. Open and Closed Loop Systems An open loop system, the control provides voltage and current to the motor and hopes that the motor is going in the correct direction and the correct speed. There is no feedback signal to inform the control that the proper motion has taken place. This system is not self correcting. A closed loop system the control provides voltage and current to the motor so it will go in in the correct direction and the correct speed. A feedback signal from the motor or load are returned to the control. The feedback signals are compared to the desired setpoints and the signal to the motor is changed to correct any system errors. The feedback signal (return signal) provides the means to monitor the motor or process. Feedback allows a closed loop system to perform more complex tasks with greater precision than an open loop system. Servo applications require tight control over position and velocity, or both. Tight control that customers are not able to get from other drive types (Inverter, Vector or DC controls). Those loads are typical large horsepower motors and heavy loads that create large inertia that cannot be quickly accelerated, stopped or reversed. Some examples of these applications are: Packaging, where the load must be positioned for form/fill/seal and wrapping applications. Textiles, where a plotter cutter must be accurately positioned according to the pattern and cutting table. Robotics, where the robot arm must be positioned in X Y Z coordinates. Each X, Y and Z motion axis requires a separate Servo Control and Motor. Figure 3-1 Open Loop and Closed Loop System Open Loop System Closed Loop System Feedback signal Input Power Motor Power Input Power Motor Power Servo Control Servo Control 3-2 Fundamentals of Servos MIFOS

Tight Velocity control Servos provide tight control over speed, ± 0.1 % of set speed, for example. A servo responds to the feedback signal and change speeds within a matter of milliseconds. Velocity control is important in applications such as: Semiconductor industry, where silicon wafers are spun out to evenly distribute the coating. Laboratory applications like centrifuges and blood analyzers where products must be spun at exact speeds for the desired separations. Both Velocity and Position control The majority of applications require some degree of control over both velocity and position. Automatic fastening application such as tightening caps on tubes of toothpaste or tightening nuts on automobiles, are primarily concerned with velocity and torque. But there is a positioning component to these operations, as well. Your customers may want their positioning applications performed within a controlled time frame for maximum productivity. So the packaging, textile, and medical applications previously discussed could also have a velocity component. Servo Terminology Load Servo Motor DC Servo Motor Brushless Motor Servo Control Feedback Power Supply The work being moved by the servo drive. The part of the servo drive that provides the motion. Servo motors are built to have the low inertia and fast response. There are brush type and brushless servo motors. A DC PM motor has a stationary stator field that is produced by permanent magnets. A second field, the rotor field, is set up by passing current through stationary brushes and a commutator on the rotating rotor assembly. The rotor field rotates in an effort to align itself with the stator field, but at the appropriate time (due to the brushes and commutator) the rotor field is switched. The feedback device may be either a tachometer, encoder, or resolver. A brushless servo motor could be DC or AC but has no brushes for commutation. The feedback device effectively determines whether it is considered DC or AC, since this dictates the control scheme. The feedback device may be either Hall sensors, encoders, or resolver. The part of the servo drive that monitors or controls the amount of power applied to the motor. This will control how fast the motor rotates. For example: with more voltage supplied, the motor will rotate fast; with less voltage supplied, the motor will rotate slowly. A servo control commands the motor to move to a position at a specific speed. The control continuously monitors the feedback signal. If the feedback signal indicates the motor position or speed is not correct, the control changes the signals to the motor to correct the motor s speed or position. A feedback device (located within the motor) generates a signal that s sent back to the control. Tachometers, Hall effect, encoders, and resolvers are examples of feedback devices for servo systems. The power supply converts AC power to DC power. MIFOS Fundamentals of Servos 3-3

The servo drive controls speed or velocity only. To command the machine to go to a specific position, a means of monitoring position must be added. The positioner monitors the machine position and is typically called a Motion Controller which is a programmable device. Figure 3-2 Control System Components Servo Axis Programmable Motion Controller represents the brains of this package. It monitors position. The user writes a program to accomplish a task i.e. run at a certain speed to a specific position. This program is stored in the memory of the Programmable Motion Controller. The user interface can be a PC (that is used to develop the software program) or an HMI panel to display results. The motion controller monitors the position and velocity of each servo axis. To control the machine position, it sends corrections to each axis so the load is moved to the correct position at the correct speed. Acceleration and deceleration of each load must also be precisely controlled. A Network (CAN or Ethernet etc.) is normally used to allow system elements to provide additional inputs and outputs (I/O) and to provide communication or system monitoring. 3-4 Fundamentals of Servos MIFOS

Servo Motor Benefits An AC motor can be connected across the line to run at a fixed speed to operate a compressor, a grinder or other machine. You expect and you get a certain performance. Likewise, take any PMDC motor and connect it to a servo control and you get a certain performance, but not the same performance you would get with a servo motor. What makes a servo motor ideal for many applications? A servo motor must be used with a control and feedback device. The feedback device provides position information to the control so that the load can be accurately controlled. The following are benefits of using servos: Smaller size for a given amount of output torque, a servomotor has a smaller rotor diameter, thus a smaller housing diameter. This makes it easy to fit servomotors into tight confining locations. But the prime reason for smaller size is for lower rotor inertia. Weighs less a servomotor is smaller, thus it weighs less. This is important in applications that move a load that includes the servomotor the smaller the servomotor, the smaller, less power required to move it. More performance servomotor have a higher speed capability and a higher peak or acceleration capability, thus offering wider performance range. This improves the machine s performance empowering it to produce more parts. Faster lower rotor inertia means faster acceleration, faster positioning, thus improving a machine s throughput. By making the machine faster, it can increase the number of parts produced, and increasing production helps to reduce part costs. Highly accurate accurate parts means better quality and less part rejects. This saves money, improving the bottom line of the facility. High efficient servomotors are by design to be highly efficient, to have a high efficient power conversion factor, making the best use of power/energy. Controllability motors used in closed loop applications offer very high controllability, reducing reject rate, improving the quality of the parts being produced. Rapid positioning servos have the capability to accelerate faster, run at higher speeds, and get into position faster. This improves the machines productivity. Uses power only when on servos use power only when commanded to move to a position. Then power to the servo motor is usually turned off. PMDC Servo Motor (Permanent Magnet DC Motor) This is a motor designed for incrementing (start stop) applications. This motor has a stator field that is produced by permanent magnets. This is a stationary field (as opposed to the AC stator field which is rotating). The second field, the rotor field, is set up by passing current through a commutator and into the rotor assembly. The rotor field rotates in an effort to align itself with the stator field, but at the appropriate time (due to the commutator) the rotor field is switched. In this method then, the rotor field never catches up to the stator field. Rotational speed (i.e. how fast the rotor turns) is dependent on the strength of the rotor field. In other words, the more voltage on the motor, the faster the rotor will turn. Since the stator field is generated by permanent magnets, no power is used for field generation. The magnets provide constant field flux at all speeds. Therefore, linear speed torque curves result. This motor type provides relatively high starting, or acceleration torque, is linear and predictable, and has a smaller frame and lighter weight compared to other motor types and provides rapid positioning. Figure 3-3 DC Servo Motor Components Termination Tachometer Encoder Tach Brushes Tach Magnets Commutator Motor Brushes Rotor MIFOS Fundamentals of Servos 3-5

Brushless Servo Motors Servo drives are closed loop systems. The feedback device is normally built into the servo motor as shown in Figure 3-4. Figure 3-4 Brushless AC Servo Motor Components Terminal Box Feedback Rotor Permanent Magnet Bearing Mounting Face Feedback Stator Stator Laminations Windings A brushless AC servo motor includes a resolver or encoder feedback as standard. Power is applied through the terminal box to the stator windings. As power flows through the stator, it sets up a magnetic field which interacts with the permanent magnets on the rotor. The interaction of these two result in rotation of the motor shaft. The rotor races to catch up and align with the magnetic poles of the stator windings. However the resolver informs the control about the location of the rotor assembly. Just before the rotor catches up, the control will switch power to another winding. Now the rotor must race to catch up with another winding. This is called commutation. By electronic commutation, power is switched from winding to winding, and shaft rotation continues. The resolver must be aligned (similar to timing on your car) to the rotor s back emf. Brushless servos are available as either DC brushless or AC brushless. The feedback device effectively determines whether it is considered DC or AC, since this dictates the control scheme. The feedback device may be either Hall sensors, encoders, or resolver. With Hall sensor feedback, the three phase brushless motor is powered by energizing two of the three motor windings at a time. There are six different commutation sections for one mechanical revolution, and with in each commutation section, a DC level of power is applied. The amount of DC applied is directly proportional to the desired operating motor speed. Thus the term DC brushless. With resolver or encoder feedback, a sinusoidal waveform is applied on the motor windings. Thus the term AC brushless. The advantage of this technology is that, for the same torque (compared to DC brushless), the AC brushless will require less current. Therefore a smaller control may often be used in the application. This becomes possible since the motor has a three phase sinusoidal winding being powered by a three phase sinusoidal current waveform. Advantages of brushless technology include higher speed capability, higher torques in a smaller package, much lower inertia (thus faster acceleration capability), and of course, long reliable maintenance free life in the application. There are different motor configurations. Some may be motor and resolver, others may be motor and encoder or motor and Hall Effect Device. Brakes may also be incorporated internally within the motor housing. 3-6 Fundamentals of Servos MIFOS

Feedback Devices A feedback device attached to the motor provides feedback information to the servo control. The device provides speed and/or angular position information to the control. Tachometer Encoder A tachometer is shown in Figure 3-3. Tachometers are used to indicate speed. Their output is a DC voltage proportional to speed. Tachometers resemble a miniature motor, the faster the shaft is turned, the larger the DC voltage that is developed. The output voltage will be positive or negative depending on direction of rotation. Voltage Constant Also may be referred to as voltage gradient, or sensitivity. This represents the output voltage generated from a tachometer when operated at 1000 RPM, i.e. V/KRPM. Sometimes converted, and expressed in volts per radian per second, i.e. V/rad/sec. Ripple Also may be called voltage ripple, or tachometer ripple. Since tachs are not really an ideal device, and design and manufacturing tolerances enter into the product, we should be concerned with deviations from the norm. In an analog tach, when the shaft is rotated, a DC signal is produced, as well as an amount of an AC signal, this is noise and can be measured as RMS or Peak to Peak ripple expressed as a percent of the average DC level. Linearity The ideal tachometer would have a perfect straight line for voltage vs speed curve. Linearity is a measure of how far away from perfect this is. Linearity is measured by driving the tach at various speeds, while measuring both speed and output voltage. The reversibility error is the difference between CW and CCW voltage constants expressed as a percentage of the nominal. The encoder feedback device is a photo optical device that produces pulses as the motor shaft rotates. The encoder is constructed to produce two channels of pulses (A and B) and a once per revolution marker pulse (C) channel. The control receives this data and can calculate motor shaft position, speed and direction of rotation. Some encoders have Hall signals to provide commutation for a brushless servo motor. Figure 3-5 Encoder Operation Code Disk C B A Three Light Sensors Light Beams Three Light Sources A B C 0 1024 Pulses Per Revolution 0123 Quadrature 0 1 2 3 A 0 1 1 0 B 0 0 1 1 Time Pattern Repeats 1024 Times per Revolution MIFOS Fundamentals of Servos 3-7

Resolver A resolver looks like a revolving transformer. An AC reference voltage is applied onto windings R1 and R2. This AC reference voltage is then coupled to the secondary windings by transformer action (S1 and S3 and S2 and S4). The amplitude of the signal picked up by the secondary winding depends on the angle between the primary and secondary. In other words, this output signal varies according to the angle of the rotor windings relative to the armature windings. A resolver and associated electronics, provides information about the speed, direction and position of the motor shaft that the resolver is connected to. Resolvers do this without parts that wear out (like DC tachometer brushes). A resolver is more rugged and may be operated at higher temperatures than an encoder. Figure 3-6 Resolver Operation R2 S2 Hall Sensors R1 S3 S1 S4 SIN+ SIN COS+ COS REF+ REF (Common) Hall Sensors provide commutation information to the control. For electronic commutation to work, the Halls must be timed properly to the motor s back emf. The output of the Hall sensor is a DC level. Nominally +12 VDC is supplied. As a permanent magnet is passed by the Hall sensor, and the magnetic field changes the Hall switches from Off to On. As an example, the Hall would be On for 90 mechanical degrees, then Off for 90 degrees. This repeats for the remainder of the 360 degrees rotation. Figure 3-7 Hall Sensor Operation Hall Sensors PC Board Magnet Mounting Ring Clamp Mechanical Degrees Electrical Degrees Hall Leads 0 30 60 90 120 150 180 210 240 270 300 330 360 0 60 120 180 240 300 360 420 480 540 600 660 720 Hall Signals Table 2 1 Comparison of Feedback Devices Feature Hall Sensor Encoder Resolver What it measures Speed Position, can derive speed Position, can derive speed Output Digital Signal (On/Off) Digital signal (On/Off) Sinusoidal (sine and cosine) signal Ruggedness Good. No parts to wear. Fair. Susceptible to shock, vibration, dirt and dust Best. No internal electronic parts, withstands greater temperatures Cost Lowest Medium. Digital output works well with controls. Low. Requires additional electronics to process sinusoidal signals. 3-8 Fundamentals of Servos MIFOS

Pulse Width Modulation A Servo control adjusts the speed and direction of a servo motor. It is a closed loop control and continuously monitors motor speed, direction and position. Internally the control converts fixed voltage, fixed frequency AC line power to DC power that is stored in capacitors. This is done by the Converter section of the control. The DC Bus voltage is approximately 1.4 times the RMS AC line voltage (230VAC line voltage will produce 322 volt DC bus voltage). The DC bus voltage is then converted to a PWM (Pulse Width Modulation) 3 phase AC signal to be applied to the motor. The way that the PWM signal is controlled adjusts the frequency and voltage applied to the motor. Figure 3-8 PWM Control Converter OUTPUT L1 L2 L3 + DC Bus T1 T2 T3 Logic Circuits Logic Circuits Three Phase Motor Control Circuits PWM signal has the a series of positive and negative pulses for it s output signal. The width of each pulse changes with the amplitude of the voltage it represents. A very narrow pulse represents a lower voltage than a wider pulse. Figure 3-9 illustrates the PWM signal and the corresponding AC motor voltage waveforms. All pulses are the same amplitude but their width changes to control motor voltage. The frequency of the motor voltage is controlled by the frequency of the positive and negative transitions of the PWM signal. The rate at which the PWM pulses are produced is called the carrier frequency. SCR Capacitor Transistor Figure 3-9 PWM Signal Carrier Frequency changes pulse rate Motor Output PWM Voltage Narrow pulse widths produce less power to the motor Output Current Carrier Frequency changes pulse rate Output Frequency Output Frequency MIFOS Fundamentals of Servos 3-9

If the PWM signal changes from positive going to negative going 40 times each second, the output frequency to the motor is 40Hz. The frequency of the output to the motor is generally adjustable from 0 to 500Hz. Figure 3-10 PWM Stepper Operation PWM Output Motor Current 3-10 Fundamentals of Servos MIFOS

BALDOR ELECTRIC COMPANY P.O. BOX 2400 Fort Smith, AR 72902 2400 (479) 646 4711 Fax (479) 648 5792 www.baldor.com Baldor Electric Company FOS Printed in USA 7/05

Fundamentals of Servos Name: Branch Address: Phone: email Address: 1. What type of application would servos be used in? Positioning Constant Speed Constant horsepower Constant torque 2. What is a closed loop system? A system with no feedback device A system which shares no information A system that uses a local area network A system with a feedback device to monitor the process 3. What is electronic commutation? Mechanical switching resulting from the use of a copper commutator Switching of power from winding to winding through electronic switches Aligning the resolver to the motor s EMF 4. Linear speed torque characteristics are the result of what? Superior engineering design High power permanent magnets Use of feedback devices 5. A resolver provides sine and cosine output waveforms. True False Fundamentals of Servos Questions 1

6. An encoder provides a train of output pulses; counting these pulses can provide position information. True False 7. The main advantage of a servo system over other AC motor controls is (select all that apply) Precise control of motor speed Precise control of motor position Precise control of motor torque Precise control of line frequency 8. A servo system always consists of a control, motor and feedback device. True False 9. The rate at which the PWM pulses are produced is called the carrier frequency. True False 10. A tachometer is a good feedback device because it provides speed and direction feedback and can be used for commutation for brushless motors. True False 11. A tachometer is like a DC generator. The faster it spins, the more DC voltage it produces. True False 12. The encoder can provide commutation for a brushless servo motor if the encoder has Hall signals. True False 13. Name 3 benefits of servos. 1. 2. 3. 2 Fundamentals of Servos Questions

14. Brushless servo motors are available as AC or DC brushless types. True False 15. A resolver is the least expensive feedback type because it is an analog device. True False 16. Hall sensors rely on a field to operate the Hall switches. 17. What part of a control system is programmed by the user? Operator Interface Network Input/Output Motion Controller Servo Control 18. What is the torque of a 3hp, 1750RPM motor? (Hint: Remember Fundamentals of Motors) 36 lb in 72 lb in 108 lb in 144 lb in 19. What applications may require a velocity control? (name three) 1. 2. 3. 20. A servo system is an open loop system. True False 21. When selecting a motor for an application, what factors should you consider to decide whether or not to use a servo system? Fundamentals of Servos Questions 3

Return your completed form to: Baldor Electric Company Marketing Dept. P.O. Box 2400 Fort Smith, AR 72902 2400 Attn: Director of Education 4 Fundamentals of Servos Questions

Fundamentals of Speed Reduction 5/05 FOG

Fundamentals of Speed Reduction Table of Contents Speed Reducer Types............................................................................. 1-2 Introduction................................................................................... 1-2 Gear Basics................................................................................... 1-3 Gear Ratio................................................................................ 1-3 Torque................................................................................... 1-4 Horsepower............................................................................... 1-4 I/O Shafts................................................................................ 1-4 Comparison of Gear Types...................................................................... 1-6 Introduction to Speed Reducers.................................................................... 1-7 Speed Reducer Mounting....................................................................... 1-7 Parallel Shaft and Right Angle Reducers.......................................................... 1-8 Speed Reducer Nomenclature................................................................... 1-9 Input Connections.............................................................................. 1-10 Gearing Types................................................................................. 1-11 Helical Speed Reducers.................................................................... 1-11 Worm Gear Speed Reducers................................................................ 1-11 Worm Helical Speed Reducers............................................................. 1-11 Planetary Speed Reducers...................................................................... 1-11 Speed Reducer Ratings........................................................................ 1-12 Speed Limits.............................................................................. 1-13 Load Capacity............................................................................. 1-13 Thermal Limits............................................................................ 1-13 efficiency................................................................................. 1-13 Torque Rating............................................................................ 1-13 Power Rating............................................................................. 1-13 Service Factor............................................................................ 1-14 OHL..................................................................................... 1-14 FOG Fundamentals of Speed Reduction 1-1

Section 1 General Information Introduction Gears and gear drives have been used for over 3000 years and are among the earliest forms of power transmission. They are used in pairs to transmit power between two or more shafts without slipping. Gears can be used to change both speed and direction of rotation. They are used in a wide verity of applications from the tiny gears used in watches & toys to giant 100 foot diameter gears used in radar antennas. There are two classifications of Gears: Open or enclosed gearing. Open gearing is supplied loose (unassembled), the machine builder incorporate a set or multiple sets into the design. Enclosed gearing is assembled and supplied as a gearbox, speed reducer or a gearmotor. Figure 1-1 Speed Reducers Enclosed Gearing Enclosed Gearing is assembled and supplied as a gearbox, speed reducer or a gearmotor. These devices come in a variety of sizes, shapes and drive configurations. Figure 1-2 Gear Types Gears come in many sizes and shapes. They all share common characteristics, however, they also have significant differences to allow their use in a wide range of applications. Gears are grouped into five basic design categories: Spur, Helical, Bevel, Hypoid and Worm. They are also grouped according to the orientation of the shaft they are mounted, either parallel or at right angle. Generally, shaft orientation, efficiency and speed determine which type should be used. 1-2 Fundamentals of Speed Reduction FOG

Gear Basics Gear Teeth Mesh 20 10 Gear Ratio 10 9 8 7 6 5 4 3 2 1 1 2 Various gear types are shown in Figure 1-2. Consider the first type, the spur gear. This is perhaps the most widely used because it is simple and inexpensive. In Figure 1-3 we see the basic characteristics of operation or application. Figure 1-3 Gear Ratio The teeth are designed to mesh together, or to be in contact with each other. For the teeth to perfectly mesh, they must be the same size and have the same geometric shape. If the gears have the same number of teeth, they are the same diameter. Number of teeth of a gear determines the speed increase or decrease of the driven gear. If a gear has fewer teeth it must then be smaller in diameter. If a gear has a greater number of teeth it must be larger in diameter. The drive gear and the driven gear have a relationship. This relationship is called a ratio which is the ratio of the number of teeth of each gear. A drive gear with 10 teeth makes one revolution and the driven gear with 20 teeth only makes one half revolution in the opposite direction. The diameter of each gear determines the gear ratio of the drive gear to the driven gear. Input RPM Ratio 2:1 3 4 5 6 Drive Gear Rotates 8 Teeth Driven Gear Rotates 8 Teeth 7 8 9 10 Output RPM 2 1 If the Drive gear has 10 teeth and the driven gear has 20 teeth, the gear ratio is 2:1. This means the speed of the driven gear half the speed of the drive (input) gear. If the larger gear becomes the drive gear, the ratio is then 1:2 so the smaller driven gear rotates twice as fast as the larger drive gear. Reversing drive power is not possible with all gearing types. Rotation direction is opposite in this example. If the drive gear rotates Clockwise, the driven gear rotates counterclockwise. The direction of the driven gear can be reversed by adding an idler gear that is in contact with both gears. Drive Gear Drive Gear Idler Gear Driven Gear Opposite Rotation Driven Gear Same Rotation Gear Ratio When two gears mesh together one is the drive gear. The drive gear is driven by a motor, a gasoline engine or even a simple hand crank. The power from the drive source is transferred to the driven gear. There are many forces acting upon each gear and bearings etc. so the power transfer is not 100% efficient. Heat is a normal by product of the work being done by the energy transfer. The amount of power that a gear system can handle is measured in terms of horsepower and torque. FOG Fundamentals of Speed Reduction 1-3

Torque Torque is the rotational or twisting force applied to the load as shown in Figure 1-4. Although we think of horsepower when selecting a motor, the load actually sees Torque supplied by the motor. Standard units of measure are: lb in (inch pounds), lb ft (pound feet), oz in (ounce inches) and Nm (newton meters). Torque is a measured force at a specified distance. Torque = Force X Distance Figure 1-4 Torque Horsepower Horsepower is a measure of the rate at which a motor or drive can produce work. A 1hp motor can produce 33,000 lb ft of work in one minute of time. This is equal to lifting one ton (2,000 lbs.) 16.5 feet, or 1,000 lbs., 33 feet in one minute. Figure 1-5 Horsepower Illustration 16.3 2000 33 1000 I/O Shafts Typically, a gear has a shaft mechanical attached to it. gear configurations have their shafts parallel with each other or at 90 to each other. Figure 1-6 shows these relationships. Figure 1-6 Input/Output Shaft Relationships Parallel shafts Some examples are: Spur Gears Helical Gears Planetary Gears Right Angle shafts Some examples are: Bevel Gears Hypoid Gears Worm Gears Spur Gearing The spur gear set is the simplest to design Gear and manufacture. The spur gear and Pinion pinion both have teeth cut straight across the width of the gear face. The gear set transmits rotary motion and torque from one parallel shaft to another. It is widely used where rotational velocities and torques are relatively low, and cost is an important consideration. Normally, the gear and pinion (smallest gear is always considered the pinion) rotate in opposite directions. If the parallel shafts must rotate in the same direction an idler gear is used between gear and pinion. The rack and pinion is a variation of the spur gear in which the gear (rack) is flat rather than round. The rack and its round pinion convert rotation to linear motion or vice versa. 1-4 Fundamentals of Speed Reduction FOG

Helical Gearing Helical gear teeth are cut at helixes (teeth are oriented at an Straight Helical Herringbone angle) rather than straight lines across the gear face. This creates smoother and quieter operation. Meshing teeth of two gears come into gradual contact. They are able to carry more load than spur gears. Helical gears operate at higher speeds as compared with spur gearing. Unlike spur gears, which produce only radial loads, helical gears also produce thrust load. The greater the helix angle, the greater the thrust load. Bearings that are able to hand thrust must be used. Double helical or herringbone design with opposing helix angles cancel thrust loads. Worm Gearing Worm gears look different and operate differently than other gear types. These gears are called a worm and a wheel, although terms like worm gear and gear are often used to describe the two components. Worm gear sets work similar to a screw. When you turn a screw into a tapped hole, the screw moves up or down depending on the direction the screw is turned. Worm gears use this principal. The worm pushes the wheel into rotation. Worm gears use a sliding action. Due to the sliding action, worm gear sets are not as efficient as spur, helical or bevel gear sets. The efficiency range is typically 40% 90%. This means more power is needed to do the same job as a more efficient spur, helical or bevel gear set. However, one revolution of the input shaft only moves the driven gear one tooth. So if the driven gear has 40 teeth, a 40:1 ratio results. Straight Bevel Gearing Bevel gears look different and operate differently than other gear types. They transmit power between shafts that intersect at 90 degrees, but are sometimes used on shafts at other angles. The teeth are cut into surfaces that are angular or conical. There are four basic types, straight, zerol, spiral and skew tooth. The teeth are tapered with the widest part on the outer edge. Since the teeth are straight, as the two gears rotate together their teeth are in complete contact with each other. This means a straight bevel gear is generally noisy and vibrates as compared to some gear types. Spiral Bevel Gearing (& Hypoid) Spiral bevel gears have teeth that are spirals. The spiral angle of the teeth provides the same benefit as helical gears. The teeth do not come in complete contact at one time and more teeth contact each other at the same time. They also produce more thrust load than straight bevel gears. Spiral bevel gears must be positioned accurately or they will not work properly and produce noise and premature gear wear will result. Hypoid gears are similar to Spiral Bevel Gears except that the axes of the shafts do not intersect (allowing both shafts to be supported at both ends). Zerol Bevel Gearing Zerol bevel gears are similar to spiral bevel gears. The difference is the zerol bevel gear angle is set to zero degrees. They operate similar to straight bevel gears. However they are less noisy since their teeth do not slap together. They do not have as much load capacity as spiral bevel gears. Skew Tooth Bevel Gearing Skew tooth bevel gears are typically used when large gears are required. Generally, they are 30 inch in diameter or larger. They have most of the same characteristics as spiral bevel gears. Spiral bevel gears will operate more smoothly than a similar skew tooth bevel gear. FOG Fundamentals of Speed Reduction 1-5

Comparison of Gear Types Gear Type Advantages Disadvantages Spur Gearing Inexpensive to manufacture Efficient Does not produce thrust loads Noisy, produces vibration Can only be mounted on parallel shafts Helical Gearing Less noise and vibration (than spur gear) Greater torque capacity than spur gear Can be used on right angle shafts More costly than spur gear Does produce thrust loads Bevel Gearing See Worm Gearing See Worm Gearing Spiral Gearing See Worm Gearing See Worm Gearing Worm Gearing Quiet operation Handles shock load extremely well High ratios available in a single reduction Inexpensive to manufacture Produces heat Low efficiency 1-6 Fundamentals of Speed Reduction FOG

Introduction to Speed Reducers A speed reducer converts the rotational speed from a power source (electric motor) to a useable torque and RPM for a load. A speed reducer is an enclosed gearing box that uses gear types that were described in the beginning of this document along with an exclosure, bearings, seals and lubricants to form a complete assembly. The primary tasks of a Speed Reducer is to: Increase or Reduce Speed. Increase or Reduce Torque. Change Rotation Direction. Figure 1-7 Inside Look at a Speed Reducer Housing A speed reducer is an arrangement of gears in an enclosed housing. The reducer housing also contains shafts, bearings, lubrication and other small parts. The gears are mounted on shafts that are support by bearings. Reducers come in a wide range of shapes and sizes to accommodate a board range applications. Speed reducers are called by names such as reducer, gearbox, Worm Gearing shown gear reducer, gear drive or enclosed gear drive. The name speed reducer comes from the most common use of the gearbox, to reduce the speed at the input shaft to a usable speed at the output shaft. Another use is to change the torque. A speed reducer will increase the input torque if the speed is reduced, it will decrease the torque if the speed is increased. Another common use is to change the rotation direction of the shafts. Clockwise/Counter Clockwise or change direction to an angle as in a right angle gearbox. A speed reducer can also be used to change the direction of rotation. Odd number of stages (spur and helical sets) such as 1, 3 & 5... the output rotation is opposite input rotation. Even stages 2, 4, 6... input and output rotation are equal. Speed reducers using worm, bevel or hypoid gears other factors may determine if the input and output shafts rotate in the same direction. Speed Reducer Mounting Speed reducers have advantages over other means of reducing speed, one advantage is variety of mounting. A speed reducer is mounted in one of three ways, foot mounted, flange mounted or shaft mounted. Mounted means how the gearbox is attached. The speed reducer must be attached so it does not move while it is transmitting torque. Figure 1-8 Foot Mounted Foot mounted or base mounted reducers have either a hole that a bolt will pass through or have tapped holes where the reducer is mounted to the machine and the bolt passes through the frame into the reducer. This is the most common type of reducer. FOG Fundamentals of Speed Reduction 1-7

Figure 1-9 Flange Mounted Flange Mounted or face mounted reducers as the name implies, have a flange on the output of the reducer. Most often, this type of reducer will support the weight of the reducer and the motor and is usually bolted directly to the application. The mounting holes are usually centered around the output shaft. The flanges purpose is to support the reducer and hold it in place. A flange also prevents the gearbox from turning when the motor and reducer are energized. Figure 1-10 Shaft Mounted or Hollow Bore Shaft mounted or hollow bore reducers are mounted directly to the driven shaft. The driven shaft passes through the output shaft of the reducer that is hollow. This type of reducer is ideal as it eliminates the need for pulleys, belts, chains and sprockets. Safety guards are also eliminated with type of reducer and take up the lease amount of space. A possible disadvantage to using a shaft mounted reducer is that it may become difficult to remove the reducer from the application. The two shaft surfaces become stuck through a process know as fretting corrosion. This is cause by small movements between the two surfaces. The shafts become bonded to each other. The more movement there is between the shafts the worse the condition becomes. Applications that cycle on and off and have shock loads are more susceptible to fretting corrosion. With shaft mounted reducers a torque arm or reaction arm must be used. Since the speed reducer and motor are directly connected to the driven shaft, there is nothing to prevent the speed reducer and motor from rotating once they are energized. Torque Arm The most import factor about the mounting position is lubrication. The level needs to be high enough to allow all components to get sufficiently lubricated. Some reducers have vent plugs or breathers. Vents allow the pressure inside and outside the reducer to equalize. If too much pressure builds inside the reducer, the seals can fail prematurely. This will allow oil to leak from the reducer. The vent plug is usually mounted in the highest position as determined by the mounting position. Mounting position also affects the speed reducer s efficiency. Some mounting positions require the reducer to almost complete filled with oil. As the gears turn they must plow through the oil. The more the gears are submerged in oil, the harder they have to work. This type of lost is known as churning losses. Since the gears are churning the oil creating heat in the speed reducer, energy is wasted. Oil seal location is also another consideration concerning mounting position. In vertical application with the motor below the reducer, the weight of the oil presses down on the seal, which will increase the seal wear. Whenever possible, it is most advantageous to select a speed reducer mounting position that requires the least amount of lubrication and one that keeps the seals above the reducer s oil level. 1-8 Fundamentals of Speed Reduction FOG

Speed Reducer Nomenclature AGMA The American Gear Manufacturers Association is composed of member companies who manufacture speed reducers, enclosed gear drives, open gearing, and gear type shaft couplings, and an equally large number of technical members (domestic and foreign) who use these products or supply tools, machines, or other products to the gear industry. Together, they establish standards to help standardize the design and application of gear products. Axial Movement Endwise movement of input or output shafts, sometimes called endplay, is usually expressed in thousandths of an inch ( 1 / 1000 or 0.001 ). Back Driving This is the converse of self locking. It is difficult to predict the back driving capability of a speed reducer. Worm gear reducers are not intended to be used as speed increasers. Backlash Rotational movement of the output shaft when holding the input shaft stationary and rotating the output shaft alternately clockwise and counter clockwise. Backlash may be expressed in thousandths of an inch ( 1 / 1000 or 0.001 ) measured at a specific radius at the output shaft. Center Distance On a single reduction reducer, this is the distance between the center lines of the input and output shafts. Shaft center lines may be parallel or at right angles to one another. The center distance of multiple stage reducers usually refers to the lowest speed stage (last reduction). Greater center distances have greater torque capabilities. Efficiency The amount of output power of the reducer as compared to the amount of input power. It is usually stated as a percentage. Fretting Corrosion Input Horsepower The amount of power applied to the input shaft of a reducer by the prime mover. It is often used as a selection basis for power transmission components, and it appears in the rating tables of drive manufacturers published data. Input horsepower ratings represent the maximum amount of power that the reducer can safely handle. Output Horsepower The amount of power available at the output shaft of a reducer. Due to losses caused by inefficiency, output horsepower is always less than input horsepower. Mechanical Rating The maximum power or torque that a speed reducer can transmit based on the strength and durability of its components. Reducers typically have a safety margin of two to three times their mechanical rating. This is so the reducer can withstand momentary overloads during start up or other brief overload conditions. Mounting Position The relationship of the input and output shafts relative to the floor line. Overhung Load A force applied at right angles to the input or output shaft of the reducer, beyond its outermost bearing. The overhung load creates loads that the bearings must be able to support without damage. Ratio The ratio of a drive is based on the relationship of its input shaft speed to its output shaft speed. It is commonly expressed as a proportion. Self Locking Baldor worm reducers, under no conditions, should be considered to hold a load when at rest. Service Factors The service factor is a multiplier applied to the known load, which redefines the load in terms of operating conditions. It can also reduce ratings, thus redefining the rating in accordance with drive conditions. The service factor is usually applied to the speed reducer, but it can also be applied to the nameplate rating of the prime mover. Thermal Rating The maximum power or torques that a speed reducer can transmit continuously, based on its ability to dissipate heat generated by friction, is its thermal rating. Thrust Load Forces imposed on a shaft parallel to the shaft axis is called thrust load. It is often encountered on shafts driving mixers, fans, blowers, and similar applications. When thrust load acts on a speed reducer, be sure that the thrust load rating of the reducer is high enough that its shafts and bearings can absorb the load. Torque A twisting effort exerted around an axis is called torque. It is the product of a force and its distance from the axis around which the force acts. FOG Fundamentals of Speed Reduction 1-9

Parallel Shaft and Right Angle Reducers Generally speaking there are two groups of speed reducers, Parallel Shaft and Right Angle. These descriptions refer to the relationship between the input and output shafts of the reducer, there is really no such thing as a Left Angle speed reducer. Usually, a speed reducer s output shaft will be at a 90 angle (right angle) or parallel to the input shaft. Parallel shaft Parallel shaft, in line, offset parallel and concentric speed reducers as they are called, share the same common traits. All have output shaft that run parallel to the input. An offset parallel speed reducer s output shaft is not in line with the input shaft. It can be offset left, right, up or down. As their names imply, in line and concentric speed reducers input and output shaft are in the same line. Right Angle Right Angle speed reducers are usually available with right, left or double output shafts. They are also available with hollow bores for shaft mounting. Input Connections Speed reducers need an input shaft rotation to have output shaft rotation. An electric motor, internal combustion engine, hydraulic motors, air motors or even a hand cranks can drive a reducer. The most common drive is the electric motor. For an electric motor to power a speed reducer it must be connected to the reducer. There are three common connection methods. 1. Motors output shaft is connected to a solid input shaft of the reducer. 2. Motors C face is connected to a flange on the speed reducer. 3. The motor is part of the speed reducer (Gearmotor) Solid Input Shaft Connection Solid Input shaft connection are made by either connecting the motors shaft to the reducers input shaft with a shaft coupling or by using a belts and pulleys. The reducer and motor are usually base mounted. Another option for this type of connection is called Scoop mounting. The motor is mounted to a base that is permanently mounted to the reducer. The scoop acts as a base for the motor. Flanged Input Connections Flanged input connections are made through the use of an input flange that accepts the motors input. NEMA C face flanges are common in the US. There are generally two types. Quill type Quill type reducer has a hollow input shaft. This shaft is designed to accommodate the motors shaft diameter. It is usually an integral part of the reducers first stage gearing (pinion or worm depending on the type of reducer). The term Quill comes from the period in which feather pens were dipped into ink for writing. The quill (feather) was dipped into an inkwell to get ink. The motor is in effect is dipped into the reducers hollow input shaft. As with the shaft mounted reducer, a disadvantage to using this type of reducer is fretting corrosion. The motor and gearbox can become stuck together making it difficult to replace one or the other. Coupling type Coupling type reducer is similar to the solid input shaft design. A flange is used to connect to the motors c face and a jaw type coupling is used between the motor and reducer. The flange usually adds considerable length to the reducer/ motor arrangement. As an advantage this arrangement handles shock loading much better than the quill reducer. The jaws absorb the shock and can be replaced. This makes this reducer ideal for reversing application and frequent starts and stops. Gearmotors Gearmotors generally do not have input shafts, quills or couplings. The motor and speed reducer are design to be integral (connected to each other). The gearmotor will have an input pinion or worm mounted directly to the motors output shaft. The gearmotor has fewer components and is generally less expensive and takes up less space as compared to a speed reducer/motor combination. With a gearmotor you know what your output torque and speed are going to be. 1-10 Fundamentals of Speed Reduction FOG

Gearing Types Speed reducers and gearmotors are also put into groups based on the type of gears used. Different gears will have advantages and disadvantages. Some gear types are better suited for certain applications than other gear types. Helical Speed Reducers Helical speed reducers use helical gearing as the name implies. They usually have shafts that are parallel or concentric to the motors shaft. Helical speed reducers are very efficient and can have multiple gear stages. Each gear stage will have an efficiency range of 97% to 99%. This means a speed reducer having up to three stages can be as high as 97% (99% x 99% x 99%) efficient. Properly lubricated and applied, a helical speed reducer can have infinite life. Helical gears do not wear when properly applied. It is most important to ensure that the load does not exceed the reducer s rating. Shock loads should also be considered when selecting helical speed reducers, using proper service factoring will help eliminate early gear failure. Worm Gear Speed Reducers Worm gear speed reducers use worm gears and have an output shaft that is at a right angle to the input shaft. They are the most common type of speed reducer used in low power ratings (generally below 10 hp). Worm gear speed reducers have the advantage of being produced in large gear ratios, up to 100:1 can be obtained in a single reduction. The down side is they are not very efficient. An efficiency range from 40% 90% is very common, this is a result of the sliding action of the worm gear set. The higher the ratio, the lower the efficiency. A worm gear set having a ratio of 5:1 can be 90% efficient, where as, a 100:1 might be 40% efficient. RPM will also affect the efficiency, the higher the input speed the greater the efficiency. Worm gear speed reducer can also be built in multiple stages for increased ratios. 3600:1 is possible with a double worm gear set; the efficiency is extremely poor however. A typical 60:1 gear set may have an efficiency of 69%, multiply that by 2 (69% x 69%) and you have an efficiency of 47%. This means you would need a 2 hp motor to produce the power needed for 1 hp application. Their center distance usually categorizes worm gear speed reducers. The center distance of a worm gear speed reducer is the distance between the input shaft and output shaft. Worm gear speed reducers having greater center distances will have greater load (torque) carrying capacity. In general, speed reducers having the same center distance, will have similar load carrying capacity. Worm gears handle shock loads better than helical. Worm Helical Speed Reducers Worm Helical speed reducers offer some advantages of both helical and worm gears. They are more efficient than standard worm gear speed reducers, however, they are not as efficient as an all helical reducer. They are efficient because they generally use smaller (lower) more efficient worm ratios on the input or high speed and a highly efficient helical ratio the final output stage. Planetary Speed Reducers Planetary speed reducers always have concentric output shafts. They usually have 5 gears to produce a ratio. Planetary speed reducers tend to be very strong and handle shock loads because they have more teeth in contact at the same moment. 3 Planet Gears Sun Gear or Pinion Gear Ring Gear Planet Carrier Plate Figure 1-11 Planetary Speed Reducers The pinion gear (often called the sun gear) is in contact with three to four planet gears at one time. The load on the sun gear is shared by three or four meshes instead of one as in a standard pair of gears. Planetary speed reducers must be built to precise standards. If not, the loads may not be shared equally and failure will result. The precision required in machining and assembly increases the overall cost as compared to other types of gearing. FOG Fundamentals of Speed Reduction 1-11

Speed Reducer Ratings Ratings for speed reducers depend on several factors. The mechanical and thermal capacities of the individual gears are the main factors. The housing, bearings, keys and bolts are also contributing factors. Selecting a speed reducer involves considering a number of different ratings, capacities and limits. Speed reducers are rated in terms such as power, speed, torque, service factor and overhung load (OHL) to name a few. Figure 1-12 shows how ratings are listed in a catalog specification sheet. Figure 1-12 Speed Reducer Selection Table Ratio The ratio of speed of the input shaft compared to the output shaft. Input RPM Normal rated operating RPM to drive the input shaft. Output RPM Normal rated operating RPM of the output shaft (when input shaft is at normal RPM). Input HP Maximum rated hp of drive power. Output HP Maximum rated load hp at rated input hp. Output Torque Maximum rated torque provided at the output shaft. Overhung Load Overhung load capacity of the output shaft (statement of bearing capability). Described in detail later in this section. Output Shaft Thrust Load A force imposed on the output shaft parallel to the axis or the shaft axis is called thrust load. Maximum Input Speed Maximum rated operating RPM to drive the input shaft. 1-12 Fundamentals of Speed Reduction FOG