Index phase output characteristics of magnetic rotary encoder using a magneto-resistive element

The purpose of this paper is to develop a magnetic rotary encoder with a resolution more than 4000 pulses per revolution in a magnetic drum with a diameter of 35 mm. The required resolution is more than 2000 pulses per revolution. 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 into account the width of the magneto-resistive element and the magnetization current wave form. As a result, the index pulse has been extremely steady in the magneto-resistive element with a width of 20 μm. It is pointed out that a pulse width of less than 6.9 μm is 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