Simultaneous control of vertical position and force of a pneumatic cylinder.

摘要

Recently, pneumatic cylinders and DC servo-motors have be c ome the most favorite actuators utilized as Z axis (vertical axis) actuators of industrial robots. When a robot performs such works as assembly, polishing and deburring, position, together with force of an end-effector or a tool connected to the Z axis must be controlled. Although a linear motion mechanism driven by a DC servo-motor and a ball-screw can provide an excellent positioning accuracy, it is not satisfactory in allowing wide change of force. On the other hand, a pneumatic cylinder has inherently good controllability as to force because of compressibility of air, but it is inadequate for positioning. In order to achieve accurate p ositioning and force c ontrol, together with simultaneous position and force control of a cylinder for the Z axis actuator, a pneumatic servo-system composed of a cylinder installed vertically, double electro-pneumatic proportional control valves, and sensor feedback equipment has been developed. Optimal control methods with and without an integral compensator and micro-computer con trol have been applied to the system. Optimal feedback coefficients derived from Riccati's equation expressed in a digital data system are chosen so as to minimize settling time without overshoot in the step response of position and force of the piston, respectively. Two types of simultaneous position and force control methods are proposed. Experiments show that the integral type optimal control can provide satisfactory results in positioning as well as in force control. Furthermore, one of the simultaneous position and force control methods?a method which gradually diminishes feedback gains in the final stage of the control-gives excellent results.