Patent ID: 7825653

Claim:
A rotation detecting system which comprises: an encoder provided rotatably and having a plurality of to-be-detected elements arranged equidistantly in a direction circumferentially thereof; a sensor for detecting the to-be-detected elements of the encoder to generate pulses; a multiplying section for multiplying the pulses, generated by the sensor, by a multiplication factor, which is represented by N, to form multiplied pulses; and a speed detecting section for updatingly detecting a period average speed of the encoder during the interval in the past, in which the latest N pieces of the multiplied pulses have been generated, wherein the speed detecting section comprises a pulse generating time storage having a storage area for storing the time of generation of each of the latest N pieces of the multiplied pulses, a timer operable to measure the times of generation of the multiplied pulses, each time the multiplied pulse is generated, and to update the storage contents of the pulse generating time storage to be represented by time of generation of the latest N pieces of the multiplied pulses, and a speed calculating circuit for calculating the difference between the time of generation of the latest multiplied pulse and the time of generation of the past multiplied pulses equal to the number of the multiplication factors stored in the pulse generating time storage and for calculating an average rotational speed, using this calculated difference.