Controller for machine tool including main shafts

A controller for a machine tool including a feed shaft motor driving a feed shaft, a first main shaft motor driving a first main shaft, and a second main shaft motor driving a second main shaft, the controller comprising:

• a converter interconverting AC power on an AC power supply side and DC power on a DC link which is a DC side;
• a feed-shaft-motor inverter connected to the DC link, the feed-shaft-motor inverter interconverting DC power on the DC link and AC power which is drive power or regenerative power of the feed shaft motor;
• a first-main-shaft-motor inverter and a second-main-shaft-motor inverter connected to the DC link, the first-main-shaft-motor inverter and the second-main-shaft-motor inverter interconverting DC power on the DC link and AC power which is drive power or regenerative power for each of the first main shaft motor and the second main shaft motor;
• a power failure detection unit detecting whether or not there is a power failure on the AC power supply side of the converter;
• a voltage detection unit detecting a DC voltage value on the DC link;
• a feed-shaft-motor command unit outputting a command controlling power interconversion of the feed-shaft-motor inverter so as to decelerate the feed shaft motor when the power failure detection unit detects a power failure;
• and
• a main-shaft-motor command unit outputting a first-main-shaft-motor acceleration/deceleration command controlling power interconversion of the first-main-shaft-motor inverter so as to accelerate or decelerate the first main shaft motor in accordance with a DC voltage value detected by the voltage detection unit and a power shutoff command controlling power interconversion of the second-main-shaft-motor inverter so as to shut off drive power to the second main shaft motor, when the power failure detection unit detects a power failure.