Device and method of controlling machine tool, to control synchronized operation of spindle axis and feed axis

A controller of a machine tool, configured to control a synchronized operation of a spindle axis and a feed axis, the controller comprising:

• a numerical control section configured to prepare a spindle-axis command and a feed-axis command based on a tapping program;
• a spindle-axis control section configured to control a rotational motion of the spindle axis in accordance with the spindle-axis command;
• a rotation detecting section configured to detect a rotational position of the spindle axis;
• and
• a feed-axis control section configured to control a feed motion of the feed axis in accordance with the feed-axis command, based on the rotational position;
• the numerical control section comprising:
• a spindle-axis command outputting section configured to obtain, from the tapping program, a total rotation amount and a maximum rotation speed of the spindle axis during a period when the spindle axis operates from a starting position to a target position, and to send the total rotation amount and the maximum rotation speed as the spindle-axis command to the spindle-axis control section;
• the spindle-axis control section comprising:
• an initial-motion control section configured to make the spindle axis perform an accelerated rotation at maximum capacity using a maximum permissible current of a drive source from the starting position, by a velocity control in which the maximum rotation speed is set as a target value;
• a maximum-acceleration detecting section configured to detect a maximum acceleration of the spindle axis during the accelerated rotation at maximum capacity, based on the rotational position;
• a residual rotation-amount detecting section configured to detect a residual rotation amount of the spindle axis during a period when the spindle axis operates from a current position to the target position, based on the total rotation amount and the rotational position;
• a current-speed detecting section configured to detect a current speed of the spindle axis based on the rotational position;
• and
• a positioning-motion control section configured to execute a position control for making the spindle axis perform a decelerated rotation so as to reach the target position, based on the maximum acceleration, the residual rotation amount and the current speed, after the accelerated rotation at maximum capacity,
• wherein the positioning-motion control section is configured to make the spindle axis perform the decelerated rotation at a positioning deceleration higher than a deceleration corresponding to the maximum acceleration and equal to a maximum deceleration capable of compensating for a mechanical loss in the drive source during the decelerated rotation of the spindle axis.