DEVELOPMENT OF ELECTRONICALLY CONTROLLED PROPORTIONING DIRECTIONAL SERVO VALVES COLLEGE BRANCH GUIDE PROJECT REFERENCE NO.: 38S1453 : BAPUJI INSTITUTE OF ENGINEERING AND TECHNOLOGY, DAVANGERE : MECHANICAL ENGINEERING : MR. DR SHARAN A S STUDENTS : MR. ANURAG VERMA KEYWORDS MR. MD MOIN IQUBAL MR. ABHAY SINGH AMAN MR. ASHUTOSH KUMAR SINGH Directional control valve, DC Servo motor, Microcontroller. INTRODUCTION Fluid power is the generation, control and effective transmission of forces and motions using pressurized fluid. The process begins with a prime mover pressurizing a fluid. It ends with an actuator using the energy stored in the pressurized fluid to perform work. Fig. 1 shows the basic hydraulic fluid power system. It is ideal for high speed, high force, and high power applications. Fluid power is ideal for high speed, high force, and high power applications Fig. 1 A basic hydraulic fluid power system Fluid power is ideal for high speed, high force, and high power applications. These systems have a higher bandwidth than electric motors and can be used in applications that require fast starts, stops and reversals, or that require high frequency oscillations. Hydraulic systems are now widely used in
every aspect of our life, such as hydraulic punching, pressing, bending and lifting in machinery manufacture. Research Concept In existing hydraulic systems, pressurized hydraulic fluid is supplied from a pump to the cylinder (actuator) and hydraulic fluid flows out of the actuator to a tank. The flow to the actuator and out of the actuator is controlled by a directional control spool valve. The position of the spool controls the flow of the hydraulic fluid to the actuator. A current is applied to an electromagnetic coil which moves an armature directly acting on the spool to either to completely open or to close the spool position. Thus, solenoid operated valve directs the flow of hydraulic fluid to the actuator. Fig.2 In the present situation it is not possible to regulate the flow in steps to control the speed of the actuator. This arena of flow control opens an innovative way to control the actuator by using intelligent electronics to modify the existing directional control valve. Fig. 2 A Hydraulic Actuator Controlled by a Spool Valve OBJECTIVES 1. To develop an electronically controlled proportioning directional servo valves 2. The pressure gain and flow gain are to be studied in order to further design a more efficient valve with less leakage and higher static pressure recovery 3. Through dynamic modeling, simulation, and time and frequency analysis, component sizing and parameter estimation will be carried out METHODOLOGY
1. The market survey will be made for two major components i.e., direction control valve and DC servo motor unit will be procured. 2. Integration of the direction control valve with the motor system using flexible couplings. 3. Performance test will be conducted for the integrated assembly and the results will be recorded. To improve the performance modification will be suggested. Mathematical Modelling of DC Servo valve Fig. 3 Model of Dc servo valve Fig. 3 shows the mathematical model of the spool used to study the dynamics of the directional control valve. The critical modeling parameters such as Mass, damper and stiffness are effectively employed to represent the spool dynamics. Development of Electronically Controlled Proportioning Directional Servo Valve Fig: 4 driver circuit interfaced of dc servo valve An electronic component is any basic discrete device or physical entity in an electronic system used to affect electrons or their associated fields. Electronic components are mostly industrial
products, available in a singular form and are not to be confused with electrical element, which are conceptual abstractions representing idealized electronic components. Fig: 4 driver circuit interfaced of dc servo valve. The microcontroller is used to drive the dc servo motor. The microcontroller used is having the configuration: 16F877A device on the www.microchip.com web site or as pic16f877.pdf and midrange mcu ref.pdf files in my project directory. The microcontroller clock is generated by an external 4-MHz crystal. This produces a single instruction cycle time of 0.4 microseconds. The program flash memory can be programmed in the circuit through pins 36, 39, and 40 using the CCS ICD-S40 in-circuit programmer. Interface to the RS232 serial line is via a DS14C232 IC, shown in Figure 3, which converts RS232 logic voltage levels to TTL levels accepted by the Results and Discussion Fig. 5.1 Output torque obtained from Dc servo motor model The torque of the armature for a input voltage plotted in Fig 5. It can be seen that the armature has a response time of approximately 0.4s with the magnitude of 3.7, it returns to steady state in three seconds.
Fig. 5.2 Velocity vs time curve The fig. 5.2 shows the velocity response of the spool for the current input. These velocity obtained is 0.23 mm/s and the time taken to reach the position is 0.3s. Fig. 5.3 Force vs current curve The output force exerted by the armature of a DC solenoid depends on the current flowing through it (Fig. 5.3). This fundamental concept can be used in the design of a proportional DC solenoid in which the force exerted by the armature is proportional to the current flowing through it and independent of the armature movement over the working range of the solenoid. The graph showing the relationship between the force and armature current is called a force armature current characteristics.force increases linearly with the armature current.it is seen earlier that armature current is desided by the load.so,as load increases armature current increases increasing the force developed linearly
Fig. 5.4 Torque vs spool displacement curve Fig. 5.4 provides a diagram of torque generated to the current input. Amplification coefficient K a for torque motor enabled the linear dependence from displacement of sliding spool. When the current is made to flow through motor torque coils, armature ends became polarized.a torque is thus produced on the armature and it moves. Fig. 5.5 Spool displacement vs current curve The proportional directional control valves have a spool displacement that is proportional to the input signal. The simplest design uses a proportional solenoid,a spool and a spring the current flowing through the coil induces a force in the armature that pushes the spool against the spring the installed solenoids are degined diffrently that those used in directional controlled valves which are optimised to have two stable operating points. The solenoid in proportional
valves are desgined to induce a force that depends linearly on the current while the influnce of the position of the armature is small. Fig 5.5. shows the variation of the spool displacement with the current input. The position of the spool is proportional to the current.however,the accuracy of this desigin is not high : the linearity between current and spool is slightly poor Fig. 5.6 Flow rate vs spool displacement curve Fig 5.6 shows the change in flow rate due to variation in spool position. This movement opens the orifice which allows the fluid to flow through the actuator. The graph shows the steep increase in the flow rate with increase in the spool position from 1 mm to 3.25 mm. The maximum flow rate is 55 lpm for the spool displacement of 3.25 mm. Fig. 5.7 Pressure vs spool displacement curve
The fig. 5.7 shows the variation in the pressure (at inlet and outlet differential pressure). It is obvious that always the supply pressure is more which is directly given by the pump. The maximum pressure is 42 bars and spool displacement is 2.5 mm. The differential pressure available is 20 bars. The pressure in the outlet drain is almost constant and is around 13 bars. CHARACTERISTICS 1. For set and adjustments 2. Compact and powerful 3. Stays in position when power line fails ( battery operated) 4. Directly driven by a motor with high force level 5. Pressure independent dynamic performance 6. Low current consumption at and near hydraulic null 7. Precise Flow and pressure control CONCLUSIONS In this research work an attempt has been made to develop electronically controlled proportioning directional servo valves. Initially mathematical modelling of servo valves was developed to study the dynamics of the DC servo motor and DCV. Later by applying proper coupling, the motor and DCV are efficiently interfaced. Conclusions are discussed below i. The introduction of electronics has proven beneficial not only in the area of productivity, but also in its performance. This allows manufacturers to deliver intelligent machines to the worksite. ii. A linear relationship has been established between spool displacement and current input. iii. Torque Vs spool displacement relationship has been established to maximise the torque. iv. Flow rate and differential pressure are estimated using hydraulic kit v. The introduction of electronics has proven beneficial not only in the area of productivity, but also in its performance. This allows manufacturers to deliver intelligent machines to the worksite. vi. On board electronics, software allows for the monitoring of variables in a system at once, and automatically makes changes to maximize the efficiency and improve the productivity of the system