Control device and control method for machine tool

A control device for a machine tool, configured to control synchronous operation for a main shaft and a feed shaft, the control device comprising:

• a numerical control unit configured to, based on a tapping program, create a main shaft command and a feed shaft command;
• a main shaft control unit configured to control a rotation operation by the main shaft in accordance with the main shaft command;
• a rotation detection unit configured to detect a rotation position of the main shaft;
• and
• a feed shaft control unit configured to, based on the rotation position, control a feeding operation by the feed shaft in accordance with the feed shaft command,
• wherein the numerical control unit has
• a main shaft command output unit configured to, when performing two or more times of cutting operations and one or more times of pulling-out operations from a machining start position until a target position, obtain, from the tapping program, a rotation amount and a maximum rotation speed for the main shaft in each operation of the cutting operations and the pulling-out operations, and send the rotation amount and the maximum rotation speed for the main shaft to the main shaft control unit as the main shaft command, and
• the main shaft control unit has
• an initial operation control unit configured to cause the main shaft to undergo accelerating rotation, at a maximum capability in which an allowable current for a drive source is maximally used, from the machining start position toward the target position, with the maximum rotation speed as a target value,
• a maximum acceleration detection unit configured to, based on the rotation position during the accelerating rotation at the maximum capability, detect a maximum acceleration,
• a remaining rotation amount detection unit configured to, based on the rotation amount and the rotation position, detect a remaining rotation amount for the main shaft from a current position until the target position is reached,
• a current speed detection unit configured to, based on the rotation position, detect a current speed for the main shaft, and
• a positioning operation control unit configured to, after the accelerating rotation at the maximum capability and based on the maximum acceleration, the remaining rotation amount, and the current speed, cause the main shaft to undergo decelerating rotation at a maximum deceleration corresponding to the maximum acceleration and cause the main shaft to reach the target position.