Research On Digital Proportional Valve’s Control System

Proportional valve is able to control the pressure, flow and other parameters ofhydraulic system according to the proportion of command signal. It is widely used inindustrial production; constituting circuit and system of proportional pressure or flowcontrol and achieving control of parameters such as position, velocity, acceleration, pressureand torque. Electro-hydraulic proportional valve, usually in which proportional solenoid isused as the electro-mechanical converter, has the problems like low precision, easyvibration, hysteresis, and so on. With the development of AC servo, AC servo motor isequipped with fast response, high precision in control and stability. This article is to studyon the control system of proportional valve with proportional solenoid as the electro-mechanical converter and study its feasibility through simulation and experiment.Continuous control of flow in digital proportional valve is realized by control of itsspool position and in this study two control schemes are proposed. In control scheme one,electric coder is adopted to detect the position of motor shaft so as to realize its servocontrol. AC servomotor with position servo controls the spool position by lead screw, in thisstudy it’ll be referred to as “motor shaft position detection control scheme". Lead screw hasproblem of driving error and hysteresis error, which will impact control accuracy. Controlscheme two directly detect spool position to attain full arrangement of controls closed-loopcontrol, this will eradicate the impact that lead screw has on spool position; this scheme willbe referred to as "spool position control scheme".Secondly, control system of digital proportional valve is designed.Control systemincludes pc, plc, servo driver, servomotor, lead screw and proportional valve noumenon.Hardware lectotype of control system is realized; Operate interface design of pc uppercomputer based on VB is carried out; Serial communications of pc and PLC, directingoperation devise of PLC is also done.Based on this, simulation model of digital proportionalvalve in AMEsim environment is established and control system is applied in it. Simulationmodel is composed of AC servo module, proportional valve noumenon and proportionalvalve loop test. Emulation proves that proportional valve achieves the continuous control offlow and possesses better performance in both dynamic and static state; feasibility of control system is verified.Finally, control system composed of PLC from Omron cp1e serial,AC servo from Omron G5, and PC from IBM will be used in experimental prototype andtest the feasibility of control system. Experiments proves above mentioned control systemis not only able to precisely control spool position and attain continuous control of flow,but also in possession of advantages like simplicity in operation, programme control andremote control.