Method and apparatus for control in power failure

An apparatus for controlling, in a power failure, a machine in which a tool and a workpiece are numerically controlled in synchronization with each other, the apparatus comprising:

• a power failure detector for detecting a failure of an AC power source and sending a power failure detection signal;
• a numerical control, coupled to a workpiece drive motor, a tool drive motor, and a tool feed motor, for controlling deceleration of the workpiece drive motor and the tool drive motor, in response to the power failure detection signal sent from said power failure detector, in such a way that regenerative energy produced by the deceleration will be equal to energy required for driving the tool feed motor, and for retracting the tool to an area where the tool is not engaged with the workpiece, by driving the tool feed motor with the regenerative energy produced by the deceleration;
• and
• a power regeneration circuit having functions of converting electricity supplied from the AC power source to a DC voltage, converting the regenerative energy produced by the deceleration, and returning the converted regenerative energy to the AC power source, said function of converting the regenerative energy being stopped when the power failure detection signal arrived from said power failure detector.