Tilt device for machine tool

A tilt device for a machine tool, comprising:

• a tilt member on which a workpiece or a tool is disposed;
• a support member that swingably supports the tilt member and that has a swing axis at a position that is different from a position of a center of gravity of the tilt member;
• a drive motor that is provided to the support member and that provides a drive force for swinging the tilt member with respect to the support member;
• an auxiliary cylinder that is coupled to the tilt member and that provides a cylinder pressure to assist swing of the tilt member by the drive motor;
• and
• a control device that performs drive control of the drive motor and the auxiliary cylinder, wherein
• the center of gravity of the tilt member is offset to one side relative to the swing axis from a vertical position by an inclination angle to balance the tilt member at a balanced position,
• a moment about the swing axis generated in the tilt member by a gravitational force at the center of gravity of the tilt member is always directed to only the one side in a rotational direction in a movable range of the tilt member, the moment urging the tilt member back to the balanced position using the gravitational force,
• an assistive moment about the swing axis provided to the tilt member by the cylinder pressure is always directed to only the other side in the rotational direction in the movable range of the tilt member,
• the control device fluctuates the cylinder pressure based on the inclination angle of the tilt member such that the assistive moment is less than the moment generated in the tilt member by the gravitational force, the cylinder pressure being higher when the inclination angle of the tilt member is greater than a predetermined inclination angle than when the inclination angle of the tilt member is less than the predetermined inclination angle, and
• the cylinder pressure is equal to a first value when the inclination angle of the tilt member is greater than the predetermined inclination angle, and the cylinder pressure is equal to a second value when the inclination angle of the tilt member is less than the predetermined inclination angle, the first value being greater than the second value.