Abstract
In recent years, sensors have come to require high resolution and accuracy because of the progress of control technology. Magnetic encoders are widely used in servo motors in factory automation, because of their suitability for use in difficult environments. At present, the required resolution is more than 2000 pulses per revolution. The authors of this paper are aiming to create an encoder with a resolution of 4000 pulses per revolution in a drum with a diameter of 35 mm. As the resolution increases, ever greater accuracy is needed in the index phase to detect the original position of the encoder. To stabilize the index pulse, the authors took account of the width of the magneto-resistive element and the magnetization current waveform. As a result, the index pulse has been extremely steady in a magneto-resistive element with a width of 20 μm. It was found that a pulse width of less than 6.9 μm was necessary for 4000 pulses per revolution. Moreover, the usable detection gap could be expanded by magnetizing the drum in a wave form in which both sides of a rectangular wave curved inward.
