Abstract: In a hydraulic unit (A) including a hydraulic pump configured to be driven by a motor (2) and a hydraulic cylinder (3) for actuating a chuck, a fixed displacement hydraulic pump is combined with an adjustable speed motor (2) for driving the pump. In order to concurrently provide rapid movement of the cylinder (3) and reduction in the surge pressure, upon the cylinder (3) actuating the chuck, after a teaching movement is imparted to the cylinder (3) to determine an operating stroke of the cylinder (3) based on the number of rotations of the motor (2), the motor (2) is rotated at a high rotational speed for movement until a preset deceleration start point short of the end of movement of the cylinder (3) within the determined operating stroke and then rotated at a low rotational speed for deceleration from the deceleration start point to the end of movement of the cylinder (3), thereby allowing the chuck to chuck a work with a soft touch.

Abstract: In a hydraulic unit (A) including a hydraulic pump configured to be driven by a motor (2) and a hydraulic cylinder (3) for actuating a chuck, a fixed displacement hydraulic pump is combined with an adjustable speed motor (2) for driving the pump. In order to concurrently provide rapid movement of the cylinder (3) and reduction in the surge pressure, upon the cylinder (3) actuating the chuck, after a teaching movement is imparted to the cylinder (3) to determine an operating stroke of the cylinder (3) based on the number of rotations of the motor (2), the motor (2) is rotated at a high rotational speed for movement until a preset deceleration start point short of the end of movement of the cylinder (3) within the determined operating stroke and then rotated at a low rotational speed for deceleration from the deceleration start point to the end of movement of the cylinder (3), thereby allowing the chuck to chuck a work with a soft touch.