Controller and control method

A controller which, in a feed apparatus having a guide unit which guides movement of a movable body in a predetermined movement-axis direction and a drive unit which has a ball screw, a ball nut and a drive motor for rotating the ball screw and moves the movable body in the movement-axis direction, controls operation of the drive motor,

• the controller comprising:
• an NC program analysis unit analyzing an NC program, extracting commands relating to a target movement position and a moving velocity contained in the NC program, and outputting the extracted commands relating to the target movement position and the moving velocity;
• a control unit receiving the commands relating to the target movement position and the moving velocity output from the NC program analysis unit, generating, based on the received commands relating to the target movement position and the moving velocity, a command movement position at time intervals corresponding to the moving velocity, generating a control signal in accordance with the generated command movement position, and controlling the drive motor in accordance with the generated control signal to move the movable body;
• and
• a friction compensation unit receiving the commands relating to the target movement position output from the NC program analysis unit and a signal relating to the command movement position generated by the control unit, recognizing, based on the received commands relating to the target movement position and the received signal relating to the command movement position, a reversing position at which a direction of movement of the movable body is reversed by the control unit, and generating a friction compensation signal corresponding to the position of the movable body and adding the generated friction compensation signal to the control signal in order to compensate for at least a positioning error of the movable body caused by friction in the guide unit, wherein:
• the friction compensation unit is configured to, when the direction of movement of the movable body is reversed by the control unit, generate the friction compensation signal using a friction compensation value uf, the friction compensation value uf used being one of predetermined maximum value and minimum value for a period of time until the movable body reaches a predetermined position before the reversing position before the direction of movement is reversed, being a value calculated in accordance with a function f(α) which represents the friction compensation value uf by a relationship with a variable α, for a period of time during which the movable body reaches the reversing position from the predetermined position before the reversing position and is reversed at the reversing position, and then moves to a predetermined position after reverse, and being the other of the predetermined maximum value and minimum value for a period of time during which the movable body moves further from the predetermined position after reverse;
• and
• the function f(α) asymptotically approaches the maximum value and the minimum value of the friction compensation value uf and has an inflection point between the maximum value and the minimum value.