DIRECT DRIVE MOTOR SYSTEM

PURPOSE:To enable the detection signal of a displacement detector to be obtained as a highly accurate signal including no higher harmonic component by making light transmitting slits formed in a code plate at prescribed pitches have a sine wave-shaped configuration and detecting the displacement of the code plate. CONSTITUTION:A plurality of sine wave-shaped light transmitting slits 2 arranged in a circumferential direction are formed in a disk-shaped code plate 1. Light from a light source 3 is converted to a parallel beam by a lens 4 and passing the light transmitting slits 2, the beam is irradiated on an image sensor 5. The sensor 5 is formed by a photo diode array wherein eight photo diodes 51-58 are arranged in an array. A signal processor 6 sequentially takes out the detection signals of the photo diodes 51-58 at constant timings and detects the rotation of the code plate 1. The detections signals of a displacement converter take a sine wave-shaped configuration similar to a fundamental harmonic along the arrangement of the photo diodes 51-58. Therefore, the detection signals are highly accurate signals including no higher harmonic component.