Patent ID: 7696708

Claim:
A ripple detecting device for detecting a ripple from an armature current outputted from a motor by overlapping a low band noise having a frequency of one/n (1/n) of the armature current (wherein “n” is a natural number more than 1), comprising: a feature detecting means for detecting a feature of the ripple from the armature current outputted from the motor; and a ripple detecting means for detecting a ripple while the motor is in a loaded state by comparing a feature of the ripple with the low band noise, occurring during the loaded state, having a frequency of one/n detected by the feature detecting means, at a time point prior to a present time point by a predetermined number of cycles greater than one, with a feature of the ripple in the loaded state detected by the feature detecting means at the present time point, and judging that a ripple is generated when the feature of the time point prior to the present time point and the feature of the present time point satisfy a predetermined relation.