Abstract: In a machine tool having first and second spindles, which are connected to respective spindle motors and control circuits each control circuit including a velocity controller and a position controller, and which simultaneously grasp the same workpiece, in which state the workpiece is subjected to machining. At such time, a digital velocity command provided by, e.g., a numerical control unit, is supplied to the two spindles simultaneously, switches for isolating the position controller from the velocity controller at each spindle is controlled at the respective spindle, a synchronous operation mode, which changes over the velocity command to a position command, is established, and the digital velocity command value is processed as a position command, whereby the two spindles are subjected to identical positional control. As a result, the rpm's of the spindles are synchronized and the workpiece can be machined and separated into two parts without subjecting it to excessive force.

Abstract: The invention relates to a motor output changeover control apparatus used for the spindle motor of machine tools. Conventionally, since a constant output over a wide range is realized by gears, a spindle motor is constituted by a single winding. The amount of heat produced by the winding is great, and a speed-change mechanism employing the gears is large in size.With the motor output changeover control apparatus of the invention, output characteristics over a wide range from high to low speeds is stabilized by changing over the connection of the power lines of an AC motor.

Abstract: The invention relates to a machine tool having two spindles driven and controlled by servomotors (1), (2) by supplying velocity control circuits (3), (4) with velocity commands (Vcmd.sub.1), (Vcmd.sub.2) for independently controlling the rotational velocities of first and second spindles. The spindles of a machine tool such as a lathe are controlled for synchronous operation so that the two spindles can be controlled in order to machine a workpiece efficiently. According to the invention, synchronous operation is executed efficiently upon achieving coincidence between the rotational angles of the spindles so that a workpiece can be regripped during rotation.

Abstract: A DC motor phase control system is provided in a system having a first controlled rectifier connected to an AC power supply and providing a positive rectified output and a second controlled rectifier providing a negative rectified output. A DC motor is controlled for forward and reverse rotation and is controlled in speed by the firing control of the rectifiers. The pulse indicating the zero point of the AC power supply voltage is delayed according to the actual speed of the motor and the delayed pulse is used as a reference pulse of the controlled firing pulses applied to the controlled rectifiers.