| 摘要 |
The rotational speed of a motor is detected, and stored in a rotational speed memory. The difference between the present rotational speed output and each of plural past rotational speeds stored in the rotational speed memory is calculated in a plural difference calculator. Whether the difference between the present rotational speed and the most past rotational speed out of the plural differences is larger than a first threshold value is judged. Whether at least one of the differences is larger than a second threshold value is judged. The first and second threshold values are set to values for detecting that the rotational speed of the motor has a decelerating trend through the comparison with the differences concerned, and the first threshold value is set to be smaller than the second threshold value. When both judgments have positive judgment results, it is judged that rotation abnormality of the motor occurs.
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