Patent ID: 7913612

Claim:
An actuator control device that controls an expansion/contraction operation of a hydraulic cylinder, comprising: an actuator port connected to the hydraulic cylinder; a main spool that switches the actuator port between communication with a working fluid supply passage and communication with a working fluid return passage; and an operate check valve interposed between the hydraulic cylinder and the main spool, which allows a working fluid to flow from the supply passage to the actuator port, and allows the working fluid to flow from the actuator port to the return passage in accordance with a pressure of a back pressure chamber, wherein, the actuator port communicates constantly with the back pressure chamber of the operate check valve via a connecting passage, the main spool comprises: a pilot spool housed slidably in the main spool; a pilot chamber delimited on one end side of the pilot spool; a spring chamber delimited on another end side of the pilot spool; a biasing member that is housed in the spring chamber and biases the pilot spool against a pressure of the pilot chamber; and a first port that connects the back pressure chamber to a tank passage downstream of the return passage and a second port that connects the return passage to the pilot chamber when the main spool is switched to a discharge position for discharging the working fluid in the hydraulic cylinder, the pilot spool comprises a control throttle that applies resistance to a flow of working fluid flowing out of the pilot chamber into the tank passage, and when the main spool is switched to the discharge position, the pilot spool is maintained in a balanced position by the pressure of the pilot chamber, which acts in accordance with a front-rear differential pressure of the control throttle, and a biasing force of the biasing member in the spring chamber, whereby an opening area of the first port is controlled to and maintained at a fixed level.