Patent ID: 6555809
Filing Date: 2003-04-29
Classification: H03M

Abstract:
An incremental rotary encoder having a drum, a first sensor and a second sensor, wherein said first sensor and said second sensor each output two sine wave signals having a phase difference of approximately 90 degrees, wherein one of said drum and said first and second sensors is relatively rotatable with respect to the other of said drum and said first and second sensors, wherein said first sensor and said second sensor are positioned so as to be offset from each other by approximately 180 degrees about said drum, said incremental rotary encoder comprising:an absolute-zero-index detecting device, provided for said first sensor, that outputs a zero index signal each time said first sensor detects an absolute zero index formed on said drum; a binary coding circuit that codes each of said two sine wave signals and said zero index signal into a corresponding binary signal; a holding device that holds level data of said binary signal of each of said two sine wave signals output from said second sensor, at a time period when said absolute-zero-index detecting device outputs said zero index signal; and a controller that determines whether a phase of said two sine wave signals output by said second sensor is one of advanced and delayed with respect to a phase of said two sine wave signals output by said first sensor.