Development and analysis of small-sized quasi-servo valve using on/off valves

Today, the advanced age and less children society is growing up rapidly. The care and welfare equipments to support a nursing care and a self reliance of the senior and the disabled are actively researched and developed by many researchers. However, the power assisted device required many degrees of freedom. The total weight load of the wearable devices increases so that the number of actuator and control valves increases according to degrees of freedom. Therefore, we aim to develop a small and light-weight quasi-servo valve to decrease the burden of the user. In this paper, we proposed and tested a quasi-servo valve by using the small, light-weight and low cost on/off valves driven by the pulse width modulation method. The valve consists of two on/off valves and a microcomputer. Both valves are connected in serial. One valve is used as a switching valve to exhaust or supply, another is used as a PWM control valve that can adjust output flow rate. And we confirmed that the output flow rate of the tested valve could be adjusted in analog way. We also proposed the precise analytical model of the tested valve. By comparing the experimental result with the calculated results using the proposed model and the identified parameters, we could confirm that the model of the valve is valid. In addition, the optimal PWM period 5 ms of the tested valve could be obtained by the calculated result in pressure control simulation of the valve. In addition, the master slave bending control of the pneumatic flexible actuator using the quasi-servo valve was also proposed and tested. As a result, by using the tested valve and PID control method, the control performance of the system could be improved.