Patent ID: 7870817

Claim:
An actuator using a fluid cylinder including two chambers and discharge valve mechanisms for the chambers, wherein the opening of a valve of the discharge valve mechanism is set to be in inverse proportion to a target pressure in the chamber, the discharge valve mechanism includes two or more kinds of open/close valves that are connected in parallel to each other and respectively have a discharge path of a different cross-sectional area, the discharge valve mechanism is configured to select one or more of the open/close valves and to optimally adjust a summation of discharge openings of the selected one or more valves in accordance with the target pressure, and the discharge path of one of the two or more kinds of open/close valves has the smallest cross-sectional area among the open/close valves, and the discharge paths of the remaining open/close valves respectively have a cross-sectional area calculated by multiplying the smallest cross-sectional area by a power of a base number larger than one.