ROTATIONAL SPEED DETECTING DEVICE FOR THREE-PHASE BRUSHLESS MOTOR

摘要

PROBLEM TO BE SOLVED: To provide a rotational speed detecting device for brushless motors that obtains accurate rotational speeds free from errors due to the influences of displacement of rotor position detecting means installed. SOLUTION: The rotational speed detector for three-phase brushless motors includes three rotor position detecting means that output rotor position detection signals corresponding to the rotational position of a rotor. The rotational speed detector is further provided with a counter means that counts the intervals between the a rising edge and the next rising edge and between a falling edge and the next falling edge of rotor position detection signals outputted from the rotor position detecting means and outputs the counts in sequence, and a calculating means that receives the counts and calculates the rotor rotational speed, based on the counts in sequence.