ABSOLUTE MAGNETIC ENCODER

PROBLEM TO BE SOLVED: To provide an absolute magnetic encoder of high resolution without increasing the number of magnetic poles. SOLUTION: An encoder rotor 23 of this absolute magnetic encoder 20 attached to a rotary shaft 5 of a servo motor 1 has the first drum 21 comprising two-pole magnet, and the second drum 22 provided with a multipolar track 31 of Q bits and a reference track 32. An absolute signal is generated in a signal processing part 27, based on detection signals different by 90° in phases of one rotation and one period from X-phase and Y-phase magnetic sensors 24X, 24Y arranged opposedly to the first drum 21, based on A-phase and B-phase signals different by 90° in phases obtained from A-phase, B-phase and Z-phase magnetic sensors 33-35 arranged opposedly to the second drum 22, and based on a reference signal. The high resolution is realized thereby without lengthening a shaft length, since the number of magnetic tracks is not required to be increased even when increasing the number Q of bits in the multipolar track 31 to enhance the resolution. COPYRIGHT: (C)2005,JPO&NCIPI