Motor control device and method for detecting out-of-step

1. A motor control device for controlling a stepping motor having at least two coils, through which coil currents having different phases flow respectively, and a rotor configured to rotate by periodically switching a phase of the coil currents flowing through each of the coils, the motor control device comprising:

a controller configured to apply a pulse voltage being subjected to pulse width modulation to each of the coils and to provide a stop period to a target coil being subjected to switching of a direction of the coil current, during which the application of the pulse voltage to the target coil is temporarily stopped;

a back electromotive voltage measuring unit configured to measure a back electromotive voltage induced in the target coil during the stop period; and

a detecting unit configured to detect an out-of-step of the stepping motor when the back electromotive voltage measured by the back electromotive voltage measuring unit satisfies a predetermined out-of-step determination criterion,

wherein the controller performs a control to set on-duty of the pulse voltage applied to all of the coils except the target coil to be either 100% or 0% during the stop period,

by changing a target current of all of the coils except the target coil during the stop period, or

by performing a feed-back control while changing a measured value of the coil current flowing through the all of the coils except the target coil during the stop period.

2. The motor control device according to claim 1 ,

wherein the controller changes the target current of all of the coils except the target coil during the stop period to a level that largely differs compared to the target current set for the coils at a normal period except the stop period.

3. The motor control device according to claim 2 ,

wherein the controller changes the target current of all of the coils except the target coil during the stop period to a level that differs for 1.5 times or more than the target current set for the coils at the normal period except the stop period.

4. The motor control device according to claim 1 further comprising:

a current sensor configured to sense the coil current of the coils and supplies current sensing results; and

a current measuring unit configured to measure the coil current flowing through the coils based on the current sensing results supplied from the current sensor and supplies the measured results to the controller as the measured value.

5. The motor control device according to claim 4 ,

wherein the controller changes the measured value by controlling the current measuring unit to output a signal to the controller indicating that the measured results is zero during the stop period.

6. The motor control device according to claim 1 ,

wherein the controller changes the measured value by setting a variable to zero, the variable indicating the measured value of the coil current flowing through the all of the coils except the target coil during the stop period.

7. The motor control device according to claim 1 ,

wherein the controller changes the measured value to a level half or less than the measured value originally measured during the stop period.

8. The motor control device according to claim 1 ,

wherein the controller changes the measured value by applying sign inversion to the measured value originally measured during the stop period.

9. The motor control device according to claim 1 ,

wherein the controller changes the measured value to a level ten times greater or more than the measured value originally measured during the stop period.

10. A method for detecting out-of-step occurring in a stepping motor having at least two coils, through which coil currents having different phases flow respectively, and a rotor configured to rotate by periodically switching a phase of the coil currents flowing through each of the coils, the method comprising:

applying a pulse voltage being subjected to pulse width modulation to each of the coils;

providing a stop period to a target coil being subjected to switching of a direction of the coil current, during which the application of the pulse voltage to the target coil is temporarily stopped;

setting on-duty of the pulse voltage applied to all of the coils except the target coil to be either 100% or 0% during the stop period,

by changing a target current of all of the coils except the target coil during the stop period, or

by performing a feed-back control while changing a measured value of the coil current flowing through the all of the coils except the target coil during the stop period;

measuring a back electromotive voltage induced in the target coil during the stop period; and

detecting an out-of-step of the stepping motor when the back electromotive voltage satisfies a predetermined out-of-step determination criterion.