Charge and exhaust characteristics of a GAS chamber with an asymmetric pneumatic servovalve

摘要

This paper describes a hardware compensation mehtod for high speed control of the electrode force of a spot welding machine with a new component of an asymmetric electro-pneumatic servovalve. Rise time of 3 ms is needed for the electrode force control system to realize the spatterless spot welding. But there exists big difference between the charge time and the exhaust time of a pneumatic resistance-capacitance circuit. In order to equalize the rise time and step-down time of a pressure feedback force control system at some supply pressure ranges, an asymmetric servovalve is developed whose down-stream port width is twice of the up-stream one. Experimental results of air charge and exhaust characteristics of the open-loop system with a symmetric valve and an asymmetric valve are compared with the simulation results. Experimental results of a closed-loop system shows that when the rise time is fixed to be 5.7 ms, the step-down times are improved from 12 ms for a symmetric valve-controlled cylinder to 7 ms for an asymmetric valve-controlled cylinder.