Actuator and clamp device using same

An actuator comprising:

• a first piston, for high load, inserted into a housing so as to be movable in a direction of an axis;
• a second piston, for low load, movably inserted into a cylindrical hole extending through the first piston in the direction of the axis, the second piston having, at a leading end portion thereof, an output portion projecting to an outside of the housing;
• a pressure fluid chamber and a spring chamber formed by partitioning an inside of the housing by the first piston and the second piston;
• a first spring, for high load, mounted in the spring chamber so as to urge the first piston toward the pressure fluid chamber side and received by a wall surface of the spring chamber;
• a second spring, for low load, mounted in the spring chamber so as to urge the second piston toward the pressure fluid chamber side and received by the wall surface;
• and
• a switching mechanism disposed in the pressure fluid chamber so as to connect the first piston selectively to the housing or the second piston, wherein
• the switching mechanism is configured to connect the first piston to the second piston and release connection between the first piston and the housing when the second spring advances the second piston toward the pressure fluid chamber side by a predetermined stroke in a state where the first piston is connected to the housing, during an actuator operating period when a pressure fluid in the pressure fluid chamber is discharged.