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, at least one feed shaft 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, and a position detector for detecting an actual position of the at least one feed shaft, the control device comprising:

• a position command generation part for generating a position command for the at least one feed shaft based on a relative feed speed of the tool and the workpiece;
• a feed shaft control part that controls the at least one feed shaft according to the position command;
• and
• a storage part for storing the rotation speed, the feed speed, machining operation conditions under which oscillation is performed using the feed shaft, and servo control conditions for the control device;
• wherein
• the machining operation conditions include the condition that a maximum oscillation acceleration and a maximum oscillation jerk which are determined from an oscillation frequency and oscillation amplitude of an oscillation command for oscillating the tool and the workpiece relative to each other are less than a maximum acceleration and maximum jerk of an actually-moved moving object;
• the servo control conditions include the condition that a value obtained by dividing a control frequency obtained from a predetermined control cycle when a command is issued to the feed shaft by an oscillation frequency of the oscillation command is not less than a predetermined value;
• the feed shaft control part includes an oscillation command generation part that generates an oscillation command for the at least one feed shaft such that a number of oscillations of the tool per rotation of the spindle becomes a positive non-integral multiple and the tool intermittently cuts the workpiece, and the feed shaft control part is configured to control the at least one feed shaft based on a resultant command obtained by adding the oscillation command to a position deviation, which is a difference between the position command and the actual position of the at least one feed shaft detected by the position detector;
• and
• the oscillation command generation part includes an estimation part for estimating an oscillation amplitude and an oscillation frequency of the oscillation command based on the rotation speed and the position command, and a determination part for determining whether or not the machining operation conditions and the servo control conditions are satisfied, and when the determination part determines that the machining operation conditions and the servo control conditions are satisfied, the oscillation command is generated based on the oscillation frequency and the oscillation amplitude.