Servo circuit for use with air pressure actuator capable of improving speed control performance

A servo circuit for use with an air pressure actuator wherein the air pressure actuator includes a guide shaft extending in one axial direction and a slider movable along the guide shaft, and wherein a partition wall is provided on one of the slider and the guide shaft to form pressure chambers between the outer surface of the guide shaft and the internal surface of the slider, and to define these pressure chambers into two cylinder chambers arranged side by side in the axial direction, said servo circuit comprising:

• intake/exhaust systems connected with the two cylinder chambers for supplying a compressed air into the cylinder chambers or discharging the compressed air from the cylinder chambers;
• a plurality of servo valves provided in each of the intake/exhaust systems and having different maximum opening degrees;
• a position detector for detecting the position of the slider;
• and
• a control device receiving the detection results of the position detector and a position instruction value for performing a selection among a plurality of servo valves in accordance with an acceleration or deceleration zone and a constant speed zone of the slider, and for controlling an opening degree of a selected servo valve.