Method of controlling synchronous operation of machine tool

In a machine tool having two spindle motors, each controlled by a control circuit which includes a velocity controller and a position controller, wherein first and second spindles are axially oriented in opposition and are driven independently by the respective spindle motors, an apparatus for controlling synchronous operation of the two spindles, comprising:

• means for detecting the respective positions of the spindle, when it is desired to transfer a workpiece from the first spindle to the second spindle;
• means for supplying a position feedback signal for each spindle to a respective spindle motor control circuit;
• signal input switch means for selecting each spindle position command signal and velocity command signal and supplying these signals to the respective control circuit;
• isolating switch means for isolating the position controller of each control circuit from the velocity controller of the same control circuit;
• and
• synchronous operation mode setting means for controlling the isolating switch means and changing over the velocity command to the position command wherein, when synchronous operation of the spindles is desired, the signal input switch means and the isolating switch means are each moved to a first contact side so that the velocity command enters the control circuits as the spindle position command signal, and, when non-synchronous operation of the spindles is desired, the signal input switch means and the isolating switch means are each moved to a second contact side so that the velocity command enters the control circuits.