Motor control apparatus equipped with dead-zone processing unit

1. A control apparatus for a motor, which drives and controls a driven body in accordance with a predefined action pattern by repeating a positions command of a specific pattern, comprising:

a position detection unit which detects position of said driven body;

a positional error acquiring unit which acquires for each sampling cycle a positional error representing a deviation between said position command given to said motor and said position of said driven body detected by said position detection unit;

a dead-zone processing unit which replaces said positional error that is located within the dead-zone range with zero and outputs the zero, when (i) said positional error acquired by said positional error acquiring unit lies within a predetermined dead-zone range and when (ii) a speed command to said motor has remained equal to or less than a prescribed value for a predetermined period of time, or the speed detected on said driven body has remained equal to or less than a prescribed value for a predetermined period of time; and

a repetitive control unit which calculates an amount of correction such that said positional error output from said dead-zone processing unit is reduced to zero, and wherein

said motor is controlled based on said positional error acquired by said positional error acquiring unit and said amount of correction calculated by said repetitive control unit, and

wherein said repetitive control unit includes:

a low-pass filtering unit which cuts off high-frequency components,

a memory unit which follows said low-pass filtering unit and which holds said amount of correction for at least a period equal to one sampling cycle, and

an adder which sums together a value obtained by multiplying an output of the memory unit by a gain smaller than 1 and said positional error output from said dead-zone processing unit, and wherein

said sum generated by said adder is fed to the low-pass filtering unit.

2. The motor control apparatus according to claim 1 , wherein when said positional error acquired by said positional error acquiring unit lies within a range outside a boundary of said dead-zone range to lie inside a buffer zone, a boundary of said buffer zone located outside said dead-zone range, said dead-zone processing unit sets a value smaller than said positional error as a new positional error and outputs said new positional error, and

when said positional error acquired by said positional error acquiring unit lies outside said buffer zone, said dead-zone processing unit outputs said positional error directly.

3. The motor control apparatus according to claim 2 , wherein said new positional error that is set when said positional error acquiring unit lies within said range extending from outside said dead-zone range to inside said buffer zone is set in accordance with an increasing function which is zero when said positional error acquired by said positional error acquiring unit is located at the boundary of said dead-zone range and which equals said acquired positional error when said positional error acquired by said positional error acquiring unit is located at the boundary of said buffer zone.