To detect the disconnection without using a rotating angle sensor by providing a disconnection detecting means for detecting the disconnection state of a feedback loop line for current measurement value, and starting a motor by the disconnection detecting means.
The absolute value of the difference between the inputted present current measurement value Ia1' and the stored previous current measurement value Ia0 is calculated as time change quantity δIa of current measurement value (S320). It is judged whether the time change quantity δIa is smaller than a constant B determined by experience or not to judge the possibility of disconnection (S330). When δIa is smaller than B, no possibility of disconnection is judged, and the procedure is advanced to the following step (S340). When it is not so, the processing is transferred to the other (S350), and an abnormality processing routine is executed (S370). The abnormality processing routine is performed in order to stop the rotation or control of a motor or the feed to the motor, or change the control method of the motor.
OONISHI KAZUHIRO
SAKAI ATSUO
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