Patent ID: 7884563

Claim:
An electric motor comprising: a movable body with a plurality of permanent magnets continuously disposed thereon, the plurality of permanent magnets being alternately magnetized at opposite polarities; a stator having an array of electromagnetic coils disposed thereon, the array of electromagnetic coils being spaced apart from the movable body so that the array of electromagnetic coils does not come into contact with the movable body; a drive circuit that moves the movable body based on an attraction/repulsion between the movable body and the electromagnetic coils generated by supplying an excitation current to the array of electromagnetic coils to alternatively magnetize the electromagnetic coils at opposite polarities; and a magnetic sensor, disposed at a position fixed with respect to the array of electromagnetic coils, that linearly detects a periodic magnetic field change caused by movement of the permanent magnets and outputs an analog value, wherein the drive circuit inputs an alternative current signal as the analog value output by the sensor and creates a Pulse Wide Modulation pattern for exciting the electromagnetic coils by performing Pulse Wide Modulation control, and directly supplies the electromagnetic coils with the pattern; wherein the drive circuit comprises a frequency-voltage converter, hysteresis level setting part, and window comparator; wherein the frequency-voltage converter converts the frequency of the output value of the magnetic sensor into a voltage value; wherein the hysteresis level setting part sets a hysteresis level based on the voltage value; and wherein the window comparator compares the output of the magnetic sensor and the hysteresis level, and creates the Pulse Wide Modulation pattern for exciting the electromagnetic coils.