Abstract: An amount of difference between a commanded position and an actual position resulting from reversing a direction of movement is found before machining and is stored in a memory of a positional difference controller (9). Then, a move command Pc is monitored in the process of machining as to whether or not a sign of the move command is reversed, and the amount of difference is added to the move command to correct a move command value when the reversion of the sign is detected. Then, position/speed/current control (3) is performed on the basis of a difference between the corrected move command value and position feedback Pf from a servo motor (5), that is, a corrected positional deviation Er, and the servo motor (5) is driven.

Abstract: A method of and an apparatus for controlling a plurality of servomotors, in which one driven body is driven by one main servomotor and at least one subordinate servomotor. Synchronous control is performed with good response and high accuracy and repetitive control is performed with simple arrangement preventing interference between axes, and further operation mode of the plurality of servomotors is easily switched between coupled driving and independent driving. A plurality of servomotors comprises one main servomotor and at least one other servomotor subordinate to the main servomotor, and position control is performed on the main servomotor side while velocity control and current control are performed individually for each servomotor. A velocity command for the main servomotor is subjected to a position adjustment based on a position deviation between the main servomotor and subordinate servomotor and the adjusted velocity command is used for the subordinate servomotor.

Abstract: In the tandem control method designed for driving one axis using a main motor and a sub motor, a speed difference between the main motor and the sub motor is calculated, and a value for correction of torque is obtained based on this speed difference. Then, the value for correction of torque is added to respective torque commands of both the main motor and the sub motor, thereby making it possible to suppress vibrations occurring in the transmission mechanism. Furthermore, the sign of the torque command generated from a speed control section is detected, whereby a positive or negative torque command is suppressed in accordance with its sign, and the current control section of each motor is always supplied with a one-directional torque command whose direction differs from that of the other motor. Thus, it becomes possible to suppress the occurrence of backlash even when a large torque is applied. Furthermore, the position control is performed by the motor corresponding to the position command.