Position control apparatus and position control method

A position control apparatus for positioning a control object connected with a motor via a transmission mechanism so as to track a variable position reference varying with time, having:

• a reference generating means for generating said variable position reference;
• a control deviation generating means for generating control deviation of the control object based on said variable position reference and a detected position of said control object;
• a servo control means for generating a control quantity to make said control object track said variable position reference based on said control deviation and controlling the driving of said motor;
• a tracking error compensating means having first and second compensating means of different modes for correcting a detected rotational position of said motor to be used to generate said control deviation so as to suppress tracking error of said control object from said variable position reference caused by mechanical transmission error of said transmission mechanism;
• and
• a compensation selecting means for selecting a compensating means to be operated from said first and second compensating means based on whether the detected position of said control object changes in a period after said control object stops and before said variable position reference is input again to said control deviation generating means.

A position control method comprising:

• generating a variable position reference varying by time;
• generating a control deviation of a control object connected with a motor via a transmission mechanism from said variable position reference based on said variable position reference and a detected position of said control object;
• driving said motor by generating a control quantity for making said control object track said variable position reference based on said control deviation;
• positioning said control object by making it track said variable position reference;
• detecting whether the detected position of said control object changes or not during a period after said control object stops at a target position and before said variable position reference to a next target position is generated;
• selecting one of a first and a second compensating means in accordance with a detected result of change of the detected position of said control object;
• and
• compensating for said control deviation by the selected compensating means so as to suppress the tracking error of said control object from said variable position reference caused by mechanical transmission error of said transmission mechanism.

A position control method comprising:

• generating a variable position reference varying by time;
• generating a control deviation of a control object connected with a motor via a transmission mechanism from said variable position reference based on said variable position reference, and a detected position of said control object, and a detected rotational position of said motor;
• driving said motor by generating a control quantity for making said control object track said variable position reference based on said control deviation;
• positioning said control object by making it track said variable position reference;
• detecting whether the detected position of said control object changes or not during a period after said control object stops at a target position and before said variable position reference to a next target position is generated;
• selecting one of a first and a second compensating means in accordance with a detected result of change of the detected position of said control object;
• and
• correcting the detected rotational position to be used to generate said control deviation by the selected compensating means so as to suppress the tracking error of said control object from said variable position reference caused by a mechanical transmission error of said transmission mechanism.