Importance

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Abstract

A control unit enables tapping onto an end surface of a workpiece while rotating the workpiece. A workpiece rotational speed command (Vc) is applied from an NC unit (90) to first and second speed control circuits (111, 121) of first and second control circuits (110, 120), to operate these control circuits in a speed control mode, so that the workpiece (70) and a tapper (80) respectively mounted on first and second main spindles (10, 20) are caused to rotate at the same speed by first and second main spindle motors (11, 21). When an error pulse amount corresponding to a workpiece rotational speed command is set in an error register (123) of the second control circuit, the second control circuit operates in a tapping mode to execute speed loop processing in accordance with a speed command calculated by position loop processing executed on the basis of a movement command, equal to the sum of the workpiece rotational speed command and a tapping speed command (Uv), and a positional feedback signal (PPC) indicative of an actual tapper rotational position, so that the tapper is rotated relative to the workpiece at a predetermined tapping speed. The tapper is axially moved toward the workpiece, whereby tapping onto the end surface of the workpiece is conducted.

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First Claim