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 return-rotation amount and a maximum return-rotation speed of the spindle axis during a period when the spindle axis operates from a target thread depth to a return completion position, and to send the total return-rotation amount and the maximum return-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 inverse rotation at maximum capacity using a maximum permissible current of a drive source from the target thread depth or from an initial return position at which the spindle axis has returned by a predetermined rotation number from the target thread depth, by a velocity control in which the maximum return-rotation speed is set as a target value;
• a maximum-acceleration detecting section configured to detect or obtain a maximum acceleration of inverse rotation of the spindle axis during a period when the spindle axis performs the accelerated inverse rotation from the target thread depth;
• a residual rotation-amount detecting section configured to detect a residual return-rotation amount of the spindle axis during a period when the spindle axis operates from a current position to the return completion position, based on the total return-rotation amount and the rotational position;
• a current-speed detecting section configured to detect a current speed of inverse rotation of the spindle axis based on the rotational position;
• a positioning-motion control section configured to execute a position control for making the spindle axis perform a decelerated inverse rotation and stop at the return completion position, after the accelerated inverse rotation at maximum capacity, based on the maximum acceleration of inverse rotation, the residual return-rotation amount and the current speed of inverse rotation;
• and
• an overshoot detecting section configured to detect an overshoot of the spindle axis relative to the return completion position during the decelerated inverse rotation, based on the residual return-rotation amount.

A method of controlling a machine tool, configured to control a synchronized operation of a spindle axis and a feed axis, the method comprising the steps, executed by a controller, of:

• obtaining, from a 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 process start position to a target thread depth;
• making the spindle axis perform an accelerated rotation at maximum capacity using a maximum permissible current of a drive source from the process start position, by a velocity control in which the maximum rotation speed is set as a target value;
• detecting a maximum acceleration of the spindle axis during the accelerated rotation at maximum capacity, based on a rotational position feedback of the spindle axis;
• detecting a residual rotation amount of the spindle axis during a period when the spindle axis operates from a current position to the target thread depth, based on the total rotation amount and the rotational position feedback;
• detecting a current speed of the spindle axis based on the rotational position feedback;
• executing a position control for making the spindle axis perform a decelerated rotation so as to reach the target thread depth, after the accelerated rotation at maximum capacity, based on the maximum acceleration, the residual rotation amount and the current speed;
• and
• detecting an overshoot of the spindle axis relative to the target thread depth during the decelerated rotation, based on the residual rotation amount.

A method of controlling a machine tool, configured to control a synchronized operation of a spindle axis and a feed axis, the method comprising the steps, executed by a controller, of:

• obtaining, from a tapping program, a total return-rotation amount and a maximum return-rotation speed of the spindle axis during a period when the spindle axis operates from a target thread depth to a return completion position;
• making the spindle axis perform an accelerated inverse rotation at maximum capacity using a maximum permissible current of a drive source from the target thread depth or from an initial return position at which the spindle axis has returned by a predetermined rotation number from the target thread depth, by a velocity control in which the maximum return-rotation speed is set as a target value;
• detecting or obtaining a maximum acceleration of inverse rotation of the spindle axis during a period when the spindle axis performs the accelerated inverse rotation from the target thread depth;
• detecting a residual return-rotation amount of the spindle axis during a period when the spindle axis operates from a current position to the return completion position, based on the total return-rotation amount and a rotational position feedback of the spindle axis;
• detecting a current speed of inverse rotation of the spindle axis based on the rotational position feedback;
• executing a position control for making the spindle axis perform a decelerated inverse rotation and stop at the return completion position, after the accelerated inverse rotation at maximum capacity, based on the maximum acceleration of inverse rotation, the residual return-rotation amount and the current speed of inverse rotation;
• and
• detecting an overshoot of the spindle axis relative to the return completion position during the decelerated inverse rotation, based on the residual return-rotation amount.