Control system for stopping spindle at predetermined rotational position

A control system for stopping a spindle, for holding a tool for performing a boring machining operation on a workpiece at a predetermined rotational position, for driving a spindle in such a manner that a positional deviation between the present rotational position of a specified point on the spindle and a predetermined rotational position at which the specified point is to be stopped, is reduced to zero, so that the specified point on the spindle is stopped at the predetermined rotational position, said control system comprising:

• a first rotational position sensor, mounted on the spindle at a first specified point thereof, for producing a first rotational position deviation signal when the tool is inserted into and withdrawn from the workpiece during the boring machining operation;
• a second rotational position sensor, mounted on the spindle at a second specified point thereof, for producing a second rotational position deviation signal during the tool change operation;
• changeover means, operatively connected to said first and second rotational position sensors, for selectively outputting the first rotational position deviation signal from said first rotational position sensor and the second rotational position deviation signal from said second rotational position sensor;
• and
• an orientation control circuit, operatively connected to said changeover means, for receiving the one of the first and second rotational position deviation signals selected by said changeover means and for controlling the spindle such that the spindle is stopped at the predetermined rotational position.