Control device for machine tool performing oscillation cutting

A control device for controlling a machine tool for cutting an outer peripheral surface or an inner peripheral surface of a workpiece with a tool, the machine tool having a spindle for performing a relative rotation between the workpiece and the tool around a central axis of the workpiece, and at least one feed axis for performing a relative feeding between the tool and the workpiece along a generatrix of the outer peripheral surface or the inner peripheral surface of the workpiece, the control device comprising:

• a position command generation part for generating a position command for the at least one feed axis based on a relative rotation speed of the workpiece and the tool and a relative feed speed of the tool and the workpiece;
• and
• a feed axis control part that controls the at least one feed axis according to the position command,
• the feed axis control part having an oscillation command generation part that generates an oscillation command for the at least one feed axis based on the rotation speed and the position command such that the tool intermittently cuts the workpiece at an oscillation frequency which is a positive non-integral multiple of the rotation speed, and the feed axis control part being configured to control the at least one feed axis based on a resultant command obtained by adding the oscillation command to a position deviation, which is a difference between the position command and an actual position of the at least one feed axis,
• the feed axis control part further comprising:
• a learning controller that obtains a correction amount of the resultant command based on an oscillation phase obtained from the oscillation command and the resultant command and which adds the correction amount to the resultant command;
• and
• a determination part which determines whether or not an oscillation amplitude of the oscillation command is smaller than a predetermined threshold value, and when the oscillation amplitude is smaller than the predetermined threshold value, the determination part turns off the learning controller and sets the oscillation command generated by the oscillation command generating part to zero or only turns off the learning controller.