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 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;
• a decelerating-motion control section configured to execute a velocity control for making the spindle axis perform a decelerated rotation so as to reach a predetermined intermediate speed, based on the residual rotation amount and the current speed, after the accelerated rotation at maximum capacity;
• a positioning-motion control section configured to execute a position control for making the spindle axis perform a decelerated rotation at a maximum deceleration corresponding to the maximum acceleration so as to reach the target position, based on the residual rotation amount and the current speed, after the spindle axis reaches the intermediate speed;
• and
• a torque-command limiting section configured to limit a fluctuation of a torque command of the position control, instructed from the positioning-motion control section to the spindle axis, to a predetermined range over a time period from a point when the spindle axis reaches the intermediate speed to a point when a predetermined elapse condition is satisfied.