3. What are the sensors used in engine management system? (N/D 2011) Airflow sensor Ford-type MAP sensors Hall effect and AC excited sensors

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2 (Other possible questions) 1. List out the drawbacks of traditional design approach. (N/D 2012) The drawbacks of traditional design approach are: Less flexible Less accurate More complicate mechanism in design It involves more components and moving parts 2. What is the role of an opto-isolator in robot control? (N/D 2012) TRIAC opto-isolator consists of LED and TRIAC. If the input of the LED is 1, it glows and activates the TRIAC to conduct the current to the solenoid valve. Otherwise, TRIAC will not conduct the current to the solenoid. 3. What are the sensors used in engine management system? (N/D 2011) Airflow sensor Ford-type MAP sensors Hall effect and AC excited sensors 4. How is a traditional design of flow control in a large pipe improved by mechatronics design? (N/D 2010) A traditional design of flow control system in large pipe line can be improved by using fluid flow sensors such as venture meter, turbine flow meter, etc., along with servo motor controlled valves. 5. Automatic camera is a mechatronics system Justify. (N/D 2010) A typical mechatronics system should have some of the basic elements such as actuators, sensors, signal conditioning elements, digital logic systems, software, display devices, etc., As the automatic camera has all those elements, it is considered as mechatronics system. 6. Compare traditional design with mechatronics design. (A/M 2010) 7. What are the mechatronics elements used in an automatic camera? (N/D 2007) The various mechatronics elements in an automatic camera are:

3 Auto-focussing mechanism control Aperture drive Shutter drive Mirror drive Lens position encoder Lens drive Film advance mechanism control 8. What are the advantages of using a microprocessor in the place of a mechanical controller for a carburettor of an automobile? (A/M 2008) The advantages of using a microprocessor in the place of a mechanical controller for a carburettor of an automobile are: Micro processor controller is more accurate in terms of supplying proper mixture air fuel ratio based on the variation of load. It also avoids detonation by getting feedback from the knock sensor placed in the engine block. It involves fewer components and moving parts and hence less wear and long life. 9. Identify the sensor, signal conditioner and display elements in the Bourdon pressure gauge. (N/D 2008) Sensor Bourdon tube Signal conditioner Mechanical linkages Display elements Pointer and scale 10. List out the seven modules of mechatronics design approach. (N/D 2009) Need for design Analysis of problem Preparation of specification Generation of possible solution Selection of suitable solution or evaluation Production of detailed design Production of working drawing Implementation of design 11. What is meant by timed switch? (N/D 2009) The device which is used to start the pulse applied, check the timer whether it is ON or OFF condition and timer should be in OFF condition before triggering is called timed switch. 12. How is a traditional design of temperature control of domestic central heating system improved by mechatronics design? (A/M 2006) The traditional design of the temperature control for a central AC system involves a bimetallic thermostat in a closed loop control system. The basic principle behind this system is that the bending of the bimetallic strip changes as the temperature change and is used to operate an ON/OFF switch for the temperature control of the AC system. The same system is modified by mechatronics approach. This system uses a micro processor controlled thermocouple as the sensor. Such a system advantages over traditional system. The bimetallic thermostat is less sensitive compared to the thermodiode.

4 13. List out the advantages of mechatronics design over traditional design. (N/D 2008) The advantages of mechatronics design over traditional design are Mechatronics system serves the purpose effectively with high dimensional accuracy requirements It provides increased productivity in the industry It provides higher flexibility by pre-supplied programs which facilitate small volume production cycles 14. What are the factors to be considered while selecting a motor? (A/M 2013) The factors to be considered while selecting a motor are Speed of a motor Starting torque and rotational torque of a motor Size and style of a motor. 15. What is meant by servomotor? (N/D 2012) A servomotor is a rotary actuator that allows for precise control of angular position. It consists of a motor coupled to a sensor for position feedback, through a reduction gearbox. 16. What are the applications of a servomotor in mechatronics systems? (N/D 2010) Servomotor are used in mechatronics systems for position control, velocity control and torque control in various applications such as CNC machine tools, robots etc., 17. What are the applications of stepper motor in mechatronics system? (A/M 2010) The applications of stepper motor in mechatronics system are High accuracy positioning applications in robotics Computer hard disc drives 18. What could be a suitable actuator for robot arm joint? Justify. (N/D 2008) The actuator of a robot arm may be servomotor or pneumatic rotary actuator and hydraulic rotary actuator. The selection of actuator depends on the purpose of use of the robot. However, most of the robots uses servomotor as an actuator because of precise and easy control mechanism.

5 DHANALAKSHMI COLLEGE OF ENGINEERING Department of mechanical engineering ME6702 MECHATRONICS Part B 1. What are the roles of sensors in car engine management system? Explain with a block diagram? (16)(N/D - 16) A modern car s Engine Management System consists of a wide range of electronic and electrical components comprising of engine sensors, relays and actuators which work together to provide the car s Engine Control Unit with vital data parameters essential to govern various engine functions effectively. Generally speaking, Engine sensors are electro-mechanical devices which monitor various engine parameters. An engine uses different types of sensors which primarily consist of Thermo-couple, Resistance Temperature Detectors (RTDs), and Hall Effect sensors. Type of Engine Sensors used: Thermo-couples use two different conductors that contact each other at one or more spots. This produces a voltage which in-turn sends the signal in the form of electric current to the ECU. A thermo-couple sensor is a temperature-measuring device which converts temperature into an electrical charge. Thermo-couples are commonly used as temperature sensors for measurement and control of temperature such as Engine Coolant Temperature Sensor.

6 RTDs or Resistance temperature detectors measure the temperature by corelating the resistance of the RTD element with temperature. RTD element is made of pure metals such as platinum, nickel or copper. An air conditioning evaporator unit uses this type of probe sensor. AC Temperature Sensor A Hall Effect sensor comprise of a transducer which varies its output voltage according to the magnetic field. Hall Effect sensors typically detect speed. They are used in positioning applications in automobiles such as Crankshaft Speed, Position etc. The engine sensors provide the Engine Management System with vital data parameters in real time. These engine sensors continuously monitor the engine parameters and provide the ECU with changes that occur in the data from time to time. Based on these inputs, the ECU calculates the correct air-fuel ratio, ignition timing and the amount of fuel required by the engine under various conditions. A modern day car includes the following engine sensors: SL. Name of the Sensor Purpose 01 Air fuel Ratio Meter Monitors the correct air fuel ratio for an engine 02 Engine Speed Sensor Monitors engine speed 03 Throttle Position Sensor Monitors the position of the throttle in an engine 04 Crank Position Sensor Monitors piston s TDC position in engine 05 Cam Position Sensor MonitorsTo monitor position of valves in engine 06 Knock Sensor Detects engine knocking because of timing advance 07 Engine Coolant Temperature Sensor Measures the engine temperature 08 Manifold Absolute Pressure or MAP Sensor Used to regulate fuel metering 09 Mass Air Flow or MAF Sensor Notifies the mass of air entering the engine to ECU 10 Oxygen / Lambda Sensor Monitors the amount of oxygen in the exhaust 11 Fuel Pressure Sensor Measures Fuel Pressure in the system 12 Vehicle Speed Sensor (VSS) Measures the speed of a vehicle

7 After calculating the fuel quantity, the ECU sends signals to various relays and actuators such as Ignition Circuit & Spark Plugs, Fuel Injectors, Engine Idling Air Control valve, Exhaust Gas Re-circulation (EGR) valve etc. It extracts the best possible engine performance while keeping emissions low. Since all the sensors connect to ECU, it can also monitor them for malfunction. The ECU collects signals from faulty sensors and stores them in the ECU memory. You can diagnose these faults either by reading the ECU memory with the help of fault codes or thru' sophisticated engine diagnostic equipment supplied by the vehicle manufacturers. 2. Design a robot to pick and place the object and comment on the various elements in the system. (16)(N/D - 16) A pick and place robot is the one which is used to pick up an object and place it in the desired location. It can be a cylindrical robot providing movement in horizontal, vertical and rotational axes, a spherical robot providing two rotational and one linear movement, an articulate robot or a SCARA robot (fixed robots with 3 vertical axes rotary arms). Advantages Before moving further, let us see few reasons why pick and place robots are preferred: They are faster and can get the work done in seconds compared to their human counterparts. They are flexible and have the appropriate design. They are accurate. They increase the safety of the working environment and actually never get tired. Parts of a Pick N Place Robot Let us see what the pick and place robot actually consists of: A Rover: It is the main body of the robot consisting of several rigid bodies like a cylinder or a sphere, joints and links. It is also known as a manipulator. End Effector: It is the body connected to the last joint of the rover which is used for the purpose of gripping or handling objects. It can be an analogy to the arm of a human being. Actuators: They are the drivers of the robot. It actually actuates the robot. It can be any motor like servo motor, stepper motor or pneumatic or hydraulic cylinders. Sensors: They are used to sense the internal as well as the external state to make sure the robot functions smoothly as a whole. Sensors involve touch sensors, IR sensor etc. Controller: It is used to control the actuators based on the sensor feedback and thus control the motion of each and every joint and eventually the movement of the end effector. Working of a Basic Pick N Place Robot: The basic function of a pick and place robot is done by its joints. Joints are analogous to human joints and are used to join the two consecutive rigid bodies in the robot. They can be rotary joint or linear joint. To add a joint to any link of a robot, we need to know about the degrees of freedom and degrees of movement for that body part. Degrees of freedom implement the linear and rotational movement of the body and Degrees of movement imply the number of axis the body can move.

8 A Simple Pick N Place Robot A simple pick and place robot consists of two rigid bodies on a moving base, connected together with rotary joint. A rotary joint is a one which provides rotation in 360 degrees around any one of the axes. The bottom or the base is attached with wheels which provide linear movement. The 1 st rigid body is fixed and supports the second rigid body to which the end effector is provided. The 2 nd rigid body is provided with movement in all 3 axes and has 3 degrees of freedom. It is connected to the 1 st body with a rotational joint. The end effector should accommodate all 6 degrees of freedom, in order to reach all sides of the component, to take up position to any height. On a whole, the basic pick and place robot works as follows: The wheels underneath the base help to move the robot to the desired location. The rigid body supporting the end effector bends or straightens up to reach the position where the object is placed. The end effector picks up the object with a strong grip and places it at the desired position. Now that we have got a brief idea of the pick and place robot, the basic question is how it is actually controlled. A simple pick and place robot can be controlled by controlling the movement of its end effector. The motion can be using hydraulic motion, i.e. using hydraulic fluid under pressure to the drive the robot, or using pneumatic motion, i.e. using pressurized air to cause mechanical motion. However the most effective way is using motors to provide the required motion. The motors have to be controlled in order to provide required motion to the robot and the end effector.

9 Working Example of Controlling a Pick N Place Robot How about controlling the robot with a just a few buttons on the keypad? Yes, it is possible! Just pressing the required button, we can transmit command to the robot to make it move in any direction to achieve our task. Moreover this can be achieved using simple wireless communication. Let s see how this actually works: The transmitter part consists of the keypad interfaced to the microcontroller. Any button number in decimal format is converted to 4 digit binary by the microcontroller and the parallel output at one of its port is applied to the encoder. The encoder converts this parallel data to serial data and this is fed to the transmitter, fitted with an antenna to transmit the serial data. The receiver side consists of a decoder interfaced to the microcontroller. The decoder converts the received command in serial format to the parallel form and gives this data to the microcontroller. Based on this command the microcontroller sends the appropriate input signals to the motor drivers to drive the respective motors.

10 Block Diagram Showing Receiver of a Pick N Place Robot The system consists of two motors for providing motion to the whole robot and two other motors to provide the arm motion. The end effector or the gripper needs to be controlled to apply proper pressure on the object to handle it effectively, to give it a soft grip. This is ensured by controlling the arm motors through proper command. The output from the arm motors is connected to a 10Ohms/2W resistor and at the time of motor over load or locked condition, a high voltage is developed across the resistor, which causes a logic high level at the output of the opto-isolator and the interrupt pin of the microcontroller connected to the opto-isolator output through a pnp transistor gets logic low signal, which halts all other operations of the gripper. Thus through simple RF communication, we can actually control a pick and place robot. Practical Applications of Pick and Place Robot: Defense Applications: It can be used for surveillance and also to pick up harmful objects like bombs and diffuse them safely. Industrial Applications: These robots are used in manufacturing, to pick up the required parts and place it in correct position to complete the machinery fixture. It can be also used to place objects on the conveyer belt as well as pick up defective products from the conveyer belt. Medical Applications: These robots can be used in various surgical operations like in joint replacement operations, orthopedic and internal surgery operations. It performs the operations with more precision and accuracy. Other than these applications, these robots can also be used in various other applications suitable to mankind.

11 3. Discuss the various stages involved in the design of mechatronic systems. (8) (A/M-17) STAGES IN DESIGNING MECHATRONIC SYSTEMS The design of mechatronic systems can be divided into a number of stages. The Need: The design process starts with the need of a customer. By adequate market research and knowledge, the potential needs of a customer can be clearly identified. In some cases, company may create a market need but failures are more in this area. Hence, market research technology is necessary. Analysis of the Problem: This is the first stage and also the critical stage in the design process. After knowing the customer need, analysis should be done to know the true nature of the problem. To define the problem accurately, analysis should be done carefully Preparation of a Specification: The second stage of the mechatronic process involves in the preparation of a specification. The specification must be given to understand the requirements and the functions to be met. The specification gives mass dimensions, types, accuracy, power requirements, load, praying environments, velocity, speed, life etc. Conceptualization: The possible solution should be generated for each of the functions required. It is generated by verifying the old problems or some newly developed techniques may be used Optimization: This stage involves in a selection of a best solution for the problem. Optimization is defined as a technique in which a best solution is selected among a group of solutions to solve a problem. The various possible solutions are evaluated and the most suitable solution is selected. Detail Design: Once optimizing a solution is completed, the detail design of that solution is developed. This may require a production of prototype etc. Mechanical layout is to be made whether physically all component can be accommodated. Also whether components are accessible for replacement / maintenance are to be checked. The selected design or solution is then translated into working drawings, circuit diagrams, etc. So that the item can be made. Drawings also include the manufacturing tolerances for each component.

12 4. What are the differences between traditional and mechatronics approach? Give a case study. (8) (A/M-17) Sl.no Traditional approach 1 The cam operated rocker arm mechanism control the valve operation. The rotation of cam is based on the crank rotation 2 The engine speed regulation is based on the governor controlled throttle valve. The governor is actuated by the speed of the crack shaft. The speed control has no effect on the engine temperature and air flow 3 Spark timing of the spark plug is controlled by the ignition coil and distributer at constant pre-set interval Sl.no Mechatronics approach 1 The valve operation is controlled by the signal received from electronic control unit.the timing of valve operation is pre- programmed in the micro controller 2 The engine speed regulation is based on the input signal from speed sensor, temperature sensor and MAF sensor. Based on the sensor information the throttling valve is controlled by micro controller 3 Spark timing of the spark plug is controlled by the ignition coil that receives signals from the micro controller through a timing sequence program 5. With necessary diagrams, explain the automatic car park system. (16) (A/M-17) Automatic Car Park System: Consider the coin-operated car park system with barriers. The main requirement of the system is that, the in-barrier is to be opened to allow the car inside if correct money (coin) is inserted in the collection box. The out barrier is to be opened to allow the car outside, if the car is detected at the car park side of the barrier. The automatic car park barrier along with the mechanism to lift and lower it When the current flows through the solenoid A & the piston in the cylinder extends to move upward and causes the barrier to rotate about its pivot and thus the barrier raises to allow the car inside. When the current flows through the solenoid A ceases, the spring on the solenoid valve makes the contacts to open and thus makes the valve to its original position. When the current flows through solenoid B, the piston in the cylinder moves downward end causes the barrier to get down. Limit switches are used to detect when the barrier is down and also when fully up. This control can be controlled by PLC

13 X400 coin operated switch at entrance to car park X401 switch activated when entrance barrier is out X402 switch activated when entrance barrier is down X403 switch activated when car at exit barrier X404 switch activated when exit barrier is -up X405 switch activated when exit barrier is down Y430 solenoid on valve A for entrance barrier Y43 1 solenoid on valve B for entrance barrier Y432 solenoid on valve A for exit barrier Y433 solenoid on valve B for exit barrier Six inputs (X400 to X405) is required for the PLC to sense the six limit switch position namely coinoperated switch, entrance barrier up switch, down switch, car at exit barrier Switch, exit barrier up switch, Exit barrier down switch Whenever, a switch is operated, 0V signal is provided to the corresponding inputs and otherwise +24vsignal is provided to the inputs. Four outputs (Y430 to Y433) are required to operate the two solenoid valves A and B. Program: LD X400 OR Y430 ANI M100 ANI Y431 OUT Y430 LD X401 OUT T450 K 10 LD T450 OUT M100 LD M100 OR Y431 ANI X402 ANI Y430 OUT Y431 LD X403 OR Y432 ANI M101 ANI Y433 OUT Y432 LD X404 OUT T451 K 10 LD T45 1

14 OUT LD OR ANI ANI OUT M101 M101 Y433 X405 Y432 Y433 END Assume a 10 sec delay for the car is to come inside the barrier and to go outside the barrier. These time delays provided by T450 and T451 energizing their Internal relays respectively. 6. Explain the working principle of stepper motor. (N/D-10), (A/M-10) A stepper Motor is basically a synchronous Motor. In stepper motor there is no brushes. This motor does not rotate continuously; instead it rotates in form of pluses or in discrete steps. That s why it is called stepper motor. There are different types of motors available on the basis of steps per rotation, for example- 12 steps per rotation, 24 steps per rotation etc. We can control or operate Stepper motor with the feedback or without any feedback. Working Principle Of Stepper Motor: The principle of Working of stepper motor is Electro-Magnetism. It constructs of a rotor that is of permanent magnet and a stator that is of electromagnets. The following figure shows the construction of a practical stepper motor: Now when we give supply to stator's winding. There will be a magnetic field developed in the stator. Now rotor of motor that is made up of permanent magnet, will try to move with the revolving magnetic field of stator. This is the basic principle of working of stepper motor.

15 7. Briefly explain traditional and mechatronics designs. (N/D-10) Traditional methodology of machine design A traditional design of machine systems, which seem to be mechatronic, is discussed in this paragraph. Considered systems consist of subsystems of different physical nature (mechanics, electrotechnics, electronic, control including software). The subsystems operate independently with limited interactions. Even for these systems, the internal complexity has to be considered from the beginning of design process. A traditional methodology of design process is as follows: System is partitioned into individual homogenous subsystems according to the disciplines, homogenous subsystems are designed by specialists from a design team, each homogenous subsystem is designed by traditional way, and each product function is from the most part realized by only one homogenous Subsystem, interactions are minimized; emphasis is mainly laid on common interfaces of the subsystems. A common approach is as follows: first the mechanical parts are designed (skeleton) followed by electrical systems (muscles), electronic systems (sensors and nervous system) and finally a control system (brain). A resulting system that appears to be mechatronic is only a result of application of existing solutions and corresponding technologies. Research and development of new technologies and/or solutions is not needed if the traditional methodology is used. Mechatronic methodology of machine design Development of technology leads to a continuous increase in demands on properties of designed products: More functions, Higher efficiency and reliability, Lower demands on energy, Minimal size and weight, Lower cost.

16 The following demands, brought about by development of technology, are increasing productivity of developers and designers. Shortening of development and design time is mainly desirable. These demands cannot be fulfilled by traditional methodology. Main concern is that the development cycle of new product is too long, and the required or optimally achievable quality of the product is not guaranteed. It means that the individual homogenous subsystems form a barrier that does not allow us to increase the quality of system without increasing the price. A mechatronic design is a tool which allows us to accomplish required changes. It can be understood as follows: mechatronic approach accepts usefulness of partitioning of solved problems to individual mechatronic disciplines. 8. With neat sketches explain various types of Stepper motors with the control. (N/D-15) The Stepper Motor is of following types: Permanent Magnet Variable Reluctance. Hybrid Stepper Motor The first type is most important, so first we should discuss it. Permanent Magnet Type Stepper Motor: The Working and Construction of the Permanent Magnet Type Stepper Motor is given below: The permanent magnet type stepper motor has a stator, that is of electromagnets and a rotor that is of Permanent Magnet, therefore this motor is called permanent magnet type stepper motor. Working: When we gives supply to the stator, the winding of stator is energized and hence produces magnetic field. As described above, the rotor is made up of permanent magnet, thats why it tends to follow the revolving field. Thus an stepper motor works. The speed or torque of a permanent magnet type motor is changed by the number of poles used in stator, If we use a large number of poles in stator then the speed of motor will increase and if we use a less number of poles then the speed will decrease. The diagram of Permanent Magnet Type Stepper Motor is given below:

17 Variable Reluctance Motor: In Variable reluctance stepper motor, we uses a non magnetic iron core rotor, which has winding turned on its surface. The stator is same as used in the Permanent Type Stepper Motor. Working: When we apply supply to the stator, a magnetic field is induced in the stator winding which causes an e.m.f. induction in the rotor's winding, thus a magnetic field is also set up in the rotor which tends to follow the magnetic field of stator. The diagram of Variable reluctance stepper motor is given below: The speed control method is almost same as in the permanent magnet type motor. In this motor we can increase the speed by increasing the number of poles of stator as well as by increasing the number of teeth of rotor and vice versa. Hybrid Type Stepper Motor: The Hybrid type motor, as the name suggests is a mixture of both above types. This consists a rotor which is magnetic and as well as teethed. The diagram of the construction of this motor is shown below: The rotor of this type of motor is made up of two rotors joining like a shaft of motor. One of them is for north and other is for South Pole. These poles arrange in alternative manner as they designed in such a manner.

18 9. Explain about construction and working principle of DC motors. (M/J-16) A DC motor in simple words is a device that converts electrical energy (direct current system) into mechanical energy. It is of vital importance for the industry today, and is equally important for engineers to look into the working principle of DC motor in details that has been discussed in this article. In order to understand the operating principle of DC motor we need to first look into its constructional feature. The very basic construction of a DC motor contains a current carrying armature which is connected to the supply end through commutator segments and brushes. The armature is placed in between north south poles of a permanent or an electromagnet as shown in the diagram above. As soon as we supply direct current in the armature, a mechanical force acts on it due to electromagnetic effect of the magnet. Now to go into the details of the operating principle of DC motor its important that we have a clear understanding of Fleming s left hand rule to determine the direction of force acting on the armature conductors of DC motor. If a current carrying conductor is placed in a magnetic field perpendicularly, then the conductor experiences a force in the direction mutually perpendicular to both the direction of field and the current carrying conductor. Fleming s left hand rule says that if we extend the index finger, middle finger and thumb of our left hand perpendicular to each other, in such a way that the middle finger is along the direction of current in the conductor, and index finger is along the direction of magnetic field i.e. north to south pole, then thumb indicates the direction of created mechanical force. 10. Explain in detail about the autonomous mobile robot. Autonomous Mobile Robot: A fully autonomous mobile robot has the ability to: Gain information about the environment Work for an extended period without human intervention Move either all or part of itself throughout its operating environment without human assistance Avoid situations that are harmful to people, property, or itself unless those are part of its design specifications. Elements of Autonomous Mobile Robot: Locomotion Sensor perception

19 Knowledge representation Planning Autonomy Collaboration Locomotion: Locomotion is the act of moving from place to place. Locomotion relies on the physical interaction between the vehicle and its environment. It is concerned with the interaction forces, along with the mechanisms and actuators that generate them. The different types of locomotion are: Legged Locomotion Snake Locomotion Free-Floating Motion Wheeled Locomotion Sensor Perception: The robots have to sense their environment in order to navigate in it, detect hazards, and identify goals. Sensor fusion is an important capability, as no single sensor will be able to identify or classify all aspects of the arenas. The simulated victims are represented by a collection of different sensory signatures. They have shape and colour characteristics. Some simulated victims have motions such as waving, and some emit sounds such as low moans, calls for help, or simple tapping. All of the signals of life should be detected, identified, investigated further, and if confirmed as a victim, the location should be mapped. For obstacle detection, the sensors need to see far and only a logic response is required. Common sensors used in mobile robots for detecting obstacles are the digital infra-red (IR) sensor. Line tracing is normally required to distinguish between a white surface and a black one in order to provide guidance by the demarcation. For direction monitoring the obvious sensor to use is a compass, which echoes the bearing of the mobile robot in real time. Proximity sensors are used to sense the presence of an object close to a mechatronics device. Knowledge Representation: In the mobile robot applications, the robots are expected to communicate to humans the location of victims and hazards. They would be providing a map of the environment they have explored, with the simulated victim and hazard location clearly identified. The environment that the robots operate in is three-dimensions, hence they should be able to map in threedimensions. The area may change dynamically during operation time Planning: The planning or behavior generation elements of the robots build on the knowledge representation and the sensing elements.

20 The robots must be able to navigate around obstacles, make progress in their mission take into account time as a limiting resource, and make time critical decisions. The planner should make use of an internal map generated by the robot and find alternative routes to exit the arenas that may be quicker or avoid arm that have become no longer traversable Autonomy: The robots are designed to operate with humans. The level of interaction may vary significantly, depending on the robot's design and capabilities, or on the circumstances. Robots may communicate back to humans to request decisions, but should provide the human with meaningful communication of the situation. The human should provide the robot with high level commands, such as "go to the room on the left" rather that joystick the robot in that direction. Collaboration: The final element to be evaluated in the robot's overall capabilities is collaboration among teams of robots. Multiple robots, either homogeneous or heterogeneous in design and capabilities, should be able to more quickly explore the area. The issues to be examined are how effectively they maximize coverage given multiple robots, whether redundancy is an advantage, and whether or how they communicate among themselves to assign responsibilities. The human may make the decisions about assignments for each robot a priority, but that would not be as desirable as seeing the robots jointly decide how to attack the problem when confronted in the field. 11. Explain about construction and working principle of AC motors. An AC motor is an electric motor driven by an alternating current (AC). The AC motor commonly consists of two basic parts, an outside stationary stator having coils supplied with alternating current to produce a rotating magnetic field, and an inside rotor attached to the output shaft producing a second rotating magnetic field. The rotor magnetic field may be produced by permanent magnets, reluctance saliency, or DC or AC electrical windings. Less commonly, linear AC motors operate on similar principles as rotating motors but have their stationary and moving parts arranged in a straight line configuration, producing linear motion instead of rotation. Operating principles When an AC motor is in steady-state rotation (motion), the magnetic fields of the rotor and stator rotate (move) with little or no slippage (near synchrony).the magnetic forces (repulsive and attractive) between the rotor and stator poles create average torque, capable of driving a load at rated speed. The speed of the stator rotating magnetic field and the speed of the rotor rotating magnetic field, relative to the speed of the mechanical shaft, must maintain synchronism for average torque production by satisfying the synchronous speed relation (i.e. Otherwise, asynchronously rotating magnetic fields would produce pulsating or non-average torque. The two main types of AC motors are classified as induction and synchronous. The induction motor (or asynchronous motor) always relies on a small difference in speed between the stator rotating magnetic field and the rotor shaft speed called slip to induce rotor current in the rotor AC winding. As a result, the induction motor cannot produce torque near synchronous speed where induction (or slip) is irrelevant or ceases to exist. In contrast, the synchronous motor does not rely on slip-induction for operation

21 and uses either permanent magnets, salient poles (having projecting magnetic poles), or an independently excited rotor winding. The synchronous motor produces its rated torque at exactly synchronous speed. The brushless wound-rotor doubly fed synchronous motor system has an independently excited rotor winding that does not rely on the principles of slip-induction of current. The brushless wound-rotor doubly fed motor is a synchronous motor that can function exactly at the supply frequency or sub to super multiple of the supply frequency. 12. Explain the working principle of servo motor. A servo motor is an electrical device which can push or rotate an object with great precision. If you want to rotate and object at some specific angles or distance, then you use servo motor. It is just made up of simple motor which run through servo mechanism. If motor is used is DC powered then it is called DC servo motor, and if it is AC powered motor then it is called AC servo motor. We can get a very high torque servo motor in a small and light weight packages. Doe to these features they are being used in many applications like toy car, RC helicopters and planes, Robotics, Machine etc. Servo Mechanism It consists of three parts: 1. Controlled device 2. Output sensor 3. Feedback system It is a closed loop system where it uses positive feedback system to control motion and final position of the shaft. Here the device is controlled by a feedback signal generated by comparing output signal and reference input signal. Here reference input signal is compared to reference output signal and the third signal is produces by feedback system. And this third signal acts as input signal to control device. This signal is present as long as feedback signal is generated or there is difference between reference input signal and reference output signal. So the main task of servomechanism is to maintain output of a system at desired value at presence of noises. Working principle of Servo Motors A servo consists of a Motor (DC or AC), a potentiometer, gear assembly and a controlling circuit. First of all we use gear assembly to reduce RPM and to increase torque of motor. Say at initial position of servo motor shaft, the position of the potentiometer knob is such that there is no electrical signal generated at the output port of the potentiometer. Now an electrical signal is given to another input terminal of the error detector amplifier. Now difference between these two signals, one comes from potentiometer and another comes from other source, will be processed in feedback mechanism and output will be provided in term of error signal. This error signal acts as the input for motor and motor starts rotating. Now motor shaft is connected with potentiometer and as motor rotates so the potentiometer and it will generate a signal. So as the potentiometer s angular position changes, its output feedback signal changes. After sometime the position of potentiometer reaches at a position that the output of potentiometer is same as external signal provided. At this condition, there will be no output signal from the amplifier to the motor input as there is no difference between external applied signal and the signal generated at potentiometer, and in this situation motor stops rotating.

22 13. Explain the different types of servo motor. Basically, servo motors are classified into AC and DC servo motors depending upon the nature of supply used for its operation. Brushed permanent magnet DC servo motors are used for simple applications owing to their cost, efficiency and simplicity. These are best suited for smaller applications. With the advancement of microprocessor and power transistor, AC servo motors are used more often due to their high accuracy control. DC Servo Motors A DC servo motor consists of a small DC motor, feedback potentiometer, gearbox, motor drive electronic circuit and electronic feedback control loop. It is more or less similar to the normal DC motor. The stator of the motor consists of a cylindrical frame and the magnet is attached to the inside of the frame. The rotor consists of brush and shaft. A commutator and a rotor metal supporting frame are attached to the outside of the shaft and the armature winding is coiled in the rotor metal supporting frame. A brush is built with an armature coil that supplies the current to the commutator. At the back of the shaft, a detector is built into the rotor in order to detect the rotation speed. With this construction, it is simple to design a controller using simple circuitry because the torque is proportional to the amount of current flow through the armature. And also the instantaneous polarity of the control voltage decides the direction of torque developed by the motor. Types of DC servo motors include series motors, shunt control motor, split series motor, and permanent magnet shunt motor. Working Principle of DC Servo Motor A DC servo motor is an assembly of four major components, namely a DC motor, a position sensing device, a gear assembly, and a control circuit. The below figure shows the parts that consisting in RC servo motors in which small DC motor is employed for driving the loads at precise speed and position. A DC reference voltage is set to the value corresponding to the desired output. This voltage can be applied by using another potentiometer, control pulse width to voltage converter, or through timers depending on the control circuitry. The dial on the potentiometer produces a corresponding voltage which is then applied as one of the inputs to error amplifier. In some circuits, a control pulse is used to produce DC reference voltage corresponding to desired position or speed of the motor and it is applied to a pulse width to voltage converter. In this converter, the capacitor starts charging at a constant rate when the pulse high. Then the charge on the capacitor is fed to the buffer amplifier when the pulse is low and this charge is further applied to the error amplifier. So the length of the pulse decides the voltage applied at the error amplifier as a desired voltage to produce the desired speed or position. In digital control, microprocessor or microcontroller are used for generating the PWM pluses in terms of duty cycles to produce more accurate control signals.

23 The feedback signal corresponding to the present position of the load is obtained by using a position sensor. This sensor is normally a potentiometer that produces the voltage corresponding to the absolute angle of the motor shaft through gear mechanism. Then the feedback voltage value is applied at the input of error amplifier (comparator). The error amplifier is a negative feedback amplifier and it reduces the difference between its inputs. It compares the voltage related to current position of the motor (obtained by potentiometer) with desired voltage related to desired position of the motor (obtained by pulse width to voltage converter), and produces the error either a positive or negative voltage. This error voltage is applied to the armature of the motor. If the error is more, the more output is applied to the motor armature. As long as error exists, the amplifier amplifies the error voltage and correspondingly powers the armature. The motor rotates till the error becomes zero. If the error is negative, the armature voltage reverses and hence the armature rotates in the opposite direction. AC Servo Motors AC servo motors are basically two-phase squirrel cage induction motors and are used for low power applications. Nowadays, three phase squirrel cage induction motors have been modified such that they can be used in high power servo systems. The main difference between a standard split-phase induction motor and AC motor is that the squirrel cage rotor of a servo motor has made with thinner conducting bars, so that the motor resistance is higher. Based on the construction there are two distinct types of AC servo motors, they are synchronous type AC servo motor and induction type AC servo motor. Synchronous-type AC servo motor consist of stator and rotor. The stator consists of a cylindrical frame and stator core. The armature coil wound around the stator core and the coil end is connected to with a lead wire through which current is provided to the motor. The rotor consists of a permanent magnet and hence they do not rely on AC induction type rotor that has current induced into it. And hence these are also called as brushless servo motors because of structural characteristics. When the stator field is excited, the rotor follows the rotating magnetic field of the stator at the synchronous speed. If the stator field stops, the rotor also stops. With this permanent magnet rotor, no rotor current is needed and hence less heat is produced.

24 Also, these motors have high efficiency due to the absence of rotor current. In order to know the position of rotor with respect to stator, an encoder is placed on the rotor and it acts as a feedback to the motor controller. The induction-type AC servo motor structure is identical with that of general motor. In this motor, stator consists of stator core, armature winding and lead wire, while rotor consists of shaft and the rotor core that built with a conductor as similar to squirrel cage rotor. The working principle of this servo motor is similar to the normal induction motor. Again the controller must know the exact position of the rotor using encoder for precise speed and position control. Working Principle of AC Servo Motor The schematic diagram of servo system for AC two-phase induction motor is shown in the figure below. In this, the reference input at which the motor shaft has to maintain at a certain position is given to the rotor of synchro generator as mechanical input theta. This rotor is connected to the electrical input at rated voltage at a fixed frequency. The three stator terminals of a synchro generator are connected correspondingly to the terminals of control transformer. The angular position of the two-phase motor is transmitted to the rotor of control transformer through gear train arrangement and it represents the control condition alpha. Initially, there exist a difference between the synchro generator shaft position and control transformer shaft position. This error is reflected as the voltage across the control transformer. This error voltage is applied to the servo amplifier and then to the control phase of the motor. With the control voltage, the rotor of the motor rotates in required direction till the error becomes zero. This is how the desired shaft position is ensured in AC servo motors. Alternatively, modern AC servo drives are embedded controllers like PLCs, microprocessors and microcontrollers to achieve variable frequency and variable voltage in order to drive the motor.

25 Mostly, pulse width modulation and Proportional-Integral-Derivative (PID) techniques are used to control the desired frequency and voltage. The block diagram of AC servo motor system using programmable logic controllers, position and servo controllers is given below. 14. Distinguish between DC and AC servo motor. It delivers high power output DC SERVO MOTOR It has more stability problems It requires frequent maintenance due to the presence of commutator AC SERVO MOTOR Delivers low output of about 0.5 W to 100 W It has less stable problems It requires less maintenance due to the absence of commutator It provides high efficiency The efficiency of AC servo motor is less and is about 5 to 20% The life of DC servo motor depends on the life on brush life It includes permanent magnet in its construction These motors are used for high power applications The life of AC servo motor depends on bearing life The synchronous type AC servo motor uses permanent magnet while induction type doesn t require it. These motors are used for low power applications