Patent ID: 8188699

Claim:
A motor characteristics acquiring apparatus for acquiring motor characteristics, the apparatus comprising: a magnet fixed to a rotating shaft of a motor; at least one magnetic sensor, disposed around a periphery of the rotating shaft, which outputs a signal when the magnet passes nearby with a rotation of the motor; and an arithmetic unit which calculates a rate of change in rotation period in a manner such that edges of the signal outputted from the magnetic sensor are detected, edge interval times each of which is an interval between temporally closest edges successively outputted from the magnetic sensor are calculated successively and stored, and corresponding edge interval times in a plurality of rotation periods of the motor are compared, wherein the arithmetic unit calculates the rotation period of the motor by multiplying a predetermined reference period by the calculated rate of change, wherein the arithmetic unit calculates the rotation period of the motor by multiplying the reference period by a rate of change in edge interval times of the same phase interval over a time period of a plurality of rotation periods, wherein the arithmetic unit calculates a tentative rotation period based on an elapsed time, which is the sum total of edge interval times calculated after a start of rotation of the motor at each edge detection during a predetermined time period from the start of rotation of the motor, and the number of edges detected during the elapsed time, wherein the arithmetic unit calculates the rotation period of the motor in such a manner that a tentative rotation period corresponding to each phase interval detected finally during the predetermined time period is used as a tentative reference period at the time of initial edge detection corresponding to each phase interval after the lapse of the predetermined time period, and wherein at each edge detection after the predetermined time period, the arithmetic unit calculates the rotation period of the motor by using the rotation period previously calculated for the same phase interval as the reference period.