Hydraulic chuck device

A hydraulic chuck device comprising:

• a cylinder portion having a cylinder hole and a piston disposed in the cylinder hole, the piston being operated by pressure oil selectively supplied into either one of two cylinder chambers formed on opposite sides of the piston;
• a chuck having a plurality of jaw portions connected to the piston, the plurality of jaw portions being simultaneously moved in a radial direction by operation of the piston so as to be opened and closed;
• a pressure oil supply switching the cylinder chamber to be supplied with pressure oil to open or close the plurality of jaw portions and controlling pressure of the pressure oil to be supplied;
• and
• a controller controlling the pressure oil supply,
• the controller being configured to,
• when controlling the pressure oil supply to supply pressure oil into the cylinder chamber for clamping for executing a clamping operation of moving the plurality of jaw portions from an unclamping position to a clamping position for clamping a workpiece,
• during movement of the plurality of jaw portions from the unclamping position to a preliminary position situated before the clamping position, control the pressure oil supply based on a first control signal to supply pressure oil set at a first pressure into the cylinder chamber for clamping so as to move the plurality of jaw portions at a constant high speed,
• during movement of the plurality of jaw portions from the preliminary position to the clamping position, control the pressure oil supply based on a second control signal to supply pressure oil set at a second pressure lower than the first pressure into the cylinder chamber for clamping so as to move the plurality of jaw portions to the clamping position at a non-zero low speed, and
• after the plurality of jaw portions arrive at the clamping position, control the pressure oil supply based on a third control signal to supply pressure oil set at a third pressure different from the second pressure and set as a pressure for clamping into the cylinder chamber for clamping, thereby causing the plurality of jaw portions to clamp the workpiece with a clamping force corresponding to the third pressure.