Patent ID: 8884571

Claim:
A motor control apparatus for a machine tool that performs cutting by using a spindle motor for rotating a tool or work and a servo motor for contouring control, the motor control apparatus comprising: a converter which converts input AC to DC for output; a spindle motor inverter which converts the DC output of said converter to provide an AC output for driving said spindle motor, and a control part for the same; a servo motor inverter which converts the DC output of said converter to provide an AC output for driving said servo motor, and a control part for the same; and a numerical control part which outputs a motor operation command for commanding the operation of said spindle motor and said servo motor, wherein when AC current or power input to said converter lies outside a predetermined range, in case that said machine tool is not in cutting operation, then said spindle motor inverter control part controls the AC output of said spindle motor inverter so that said spindle motor is operated in accordance with a limited torque command produced by limiting a torque command originally specified in said motor operation command, and in case that said machine tool is in cutting operation, then said servo motor inverter control part controls the AC output of said servo motor inverter so that said servo motor is operated in accordance with a limited rotational speed command produced by limiting a rotational speed command originally specified in said motor operation command, without limiting the torque command originally specified in said motor operation command by said spindle motor inverter control part.