1. Technical Field of the Invention
The present invention relates to a method and apparatus of the positioning of a fluid actuator and particularly to improved method and apparatus for rapidly and accurately setting a fluid actuator by supplying pressurized fluid to the right and left actuating chambers thereof through an on-off control valve.
2. Description of the Prior Art
Hydraulic and pneumatic actuators for driving or positioning various types of operating devices are well-known and currently utilized as fluid actuators in various fields of industry. Although these fluid actuators have been utilized mainly in industrial machines, they are recently being used to control robots. There is accordingly required a fluid actuator which can rapidly and accurately be positioned under severer conditions.
In general, the fluid actuator comprises an on-off control valve through which a pressurized fluid is supplied to the right and left actuating chamber of the actuator, the desired position of the actuator being depending on the amount of the supplied fluid. The relatively rough construction of the prior art fluid actuators are disadvantageous in that the positioning operation cannot rapidly be attained within a predetermined range of movement with an accuracy of 100 .mu.m or less only by operating the control valve.
To overcome such a disadvantage in the prior art, some improved fluid actuators have been proposed. For example, Japanese Laid-Open Patent Sho No. 58-174701 discloses a fluid actuator which includes an electromagnetic valve having an expectable delay in response and hydraulic cylinder controlled in accordance with a predetermined result of operation without hunting which would easily be created in such a fluid actuator. However, this proposal also cannot accomplish any high-accuracy positioning.