A failure detecting device of a fault detection system includes a detection time calculator, which calculates a stroke time T3 required for a piston to travel between one end and another end of an actuator based on detection signals from a first sensor and a second sensor, a statistical processor that performs a predetermined statistical calculation with respect to the stroke time T3, and a fault response detector, which detects whether or not a fault of the actuator has occurred based on a processing result of the statistical processor.

In some applications, a piston of a hydraulic actuator may move at high speeds, and large undesired forces may be generated if the piston reaches an end-stop of the hydraulic actuator at a high speed. The undesired forces may, for example, cause mechanical damage in the hydraulic actuator. A controller may receive information indicative of the piston reaching a first position at a first threshold distance from the end-stop, and, in response, may modify a signal to a valve assembly controlling flow of hydraulic fluid to and from the hydraulic actuator. Further, the controller may receive information indicative of the piston reaching a second position at a second threshold distance closer to the end-stop of the hydraulic actuator, and, in response, the controller may further modify the signal to the valve assembly so as to apply a force on the piston in a away from the end-stop.

In some applications, a piston of a hydraulic actuator may move at high speeds, and large undesired forces may be generated if the piston reaches an end-stop of the hydraulic actuator at a high speed. The undesired forces may, for example, cause mechanical damage in the hydraulic actuator. A controller may receive information indicative of the piston reaching a first position at a first threshold distance from the end-stop, and, in response, may modify a signal to a valve assembly controlling flow of hydraulic fluid to and from the hydraulic actuator. Further, the controller may receive information indicative of the piston reaching a second position at a second threshold distance closer to the end-stop of the hydraulic actuator, and, in response, the controller may further modify the signal to the valve assembly so as to apply a force on the piston in a away from the end-stop.

A three-position control device includes a cylinder device, a fluid control unit, and a displacement restriction device. The cylinder device displaces a piston to each of a retracted position, an intermediate position, and an advanced position. The cylinder device has a first fluid chamber for retraction and a second fluid chamber for advance. A fluid control unit switches an advanced/retracted position of the piston. A second working pressure during displacement from an intermediate position to the advanced position is set to be greater than a first working pressure during displacement from the retracted position to the intermediate position. The displacement restriction device has a load receiving portion and a biasing means. A biasing force of the biasing means is set to be greater than a thrust caused by the first working pressure and smaller than a thrust caused by the second working pressure.

A three-position control device includes a cylinder device, a fluid control unit, and a displacement restriction device. The cylinder device displaces a piston to each of a retracted position, an intermediate position, and an advanced position. The cylinder device has a first fluid chamber for retraction and a second fluid chamber for advance. A fluid control unit switches an advanced/retracted position of the piston. A second working pressure during displacement from an intermediate position to the advanced position is set to be greater than a first working pressure during displacement from the retracted position to the intermediate position. The displacement restriction device has a load receiving portion and a biasing means. A biasing force of the biasing means is set to be greater than a thrust caused by the first working pressure and smaller than a thrust caused by the second working pressure.