METHOD OF RESTORING COMMANDED POSITION

This invention relates to a commanded position restoration method in a numerical control system comprising an NC unit (11) having a path control function and machine position correction function, a motor (15) rotated on the basis of a command from the NC unit for driving a movable machine element, a pulse coder (16a) which rotates in synchronization with rotation of the motor and which generates a pulse whenever it rotates through a prescribed angle, and a counter (16b) which counts the pulses in dependence upon the direction of rotation for storing the machine position, which counter stores the machine position even if power is cut off. In the commanded position restoration method, a counted value C.sub.RA in the counter (16b) at the time of reference point return is set beforehand in a memory (11c) backed up by a battery. Whenever power is introduced to the system, a counted value C.sub.A in the counter (11c) is read, the reference point is hypothetically taken as the present machine position, and the machine position at introduction of power is taken as a target position. An interpolation operation is performed internally in a machine-locked state to update present machine position data C.sub.RA, the movable machine element is moved hypothetically from the reference point to the present machine position which prevailed at introduction of power (i.e. until C.sub.RA =C.sub.A holds), and a commanded position which prevailed at introduction of power is restored by using command data necesary for achieving the abovementioned movement.