Abstract: An optical detection system for detecting a displacement amount of a movement device with an optical encoder movable in accordance with a movement of the movable device has on a light-reflecting layer a plurality of pits successively strung in a predetermined direction. An optical pickup optically picks up the pit information by irradiating the optical encoder with light beams and receiving reflected light beams from the optical encoder. The optical pickup comprises a light-division device for dividing the light beam from a light-emitting device into three light beams so that the divided three light beams are directed to the pit string to apply three light spots to the pit string. The light-division device is adapted to be rotatable with respect to the optical encoder so that a light passing through the three light spots intersects the pit string at a predetermined angle.

Abstract: A commutatorless electrical motor comprises a cylindrical magnetic rotor having main magnetic poles where N and S poles are alternately arranged in the circumferential direction, and an axis of N and S poles of each magnet extends radially, and a sub magnetic poles at one end of the cylindrical rotor. The sub magnetic poles are arranged such that N and S poles of each magnetized area extends axially. The magnetized area providing each sub magnetic pole has an arcuate extent of .pi./2 or less in an electrical angle. Each of the magnetized area providing each sub magnetic pole makes a given change in the magnetic flux density distribution in the vicinity of rotational position detecting elements so that the rotational position of the rotor can be accurately detected.