Patent ID: 7635975

Claim:
An absolute multi-revolution encoder comprising: a rotary disc; a multi-revolution signal generation portion; and a within-one-revolution signal generation portion, wherein the rotary disc includes a magnetic material member which generates a multi-revolution signal, and the multi-revolution signal generation portion includes an A-phase magnetic field detection element and a B-phase magnetic field detection element which detect leakage fluxes of the magnetic material member and output signals of one pulse/revolution having phases different by 90 degrees there between, an A-pulse generation portion including an A-phase detection portion which detects a signal from the A-phase, magnetic field detection element and an A-pulse generation circuit which converts the detected signal into an A pulse of a rectangular wave shape, a B-pulse generation portion including a B-phase detection portion which detects a signal from the B-phase magnetic field detection element and an B-pulse generation circuit which converts the detected signal into a B pulse of a rectangular wave shape, a counter which counts the A pulse and the B pulse to generate the multi-revolution signal, and a power supply means which supplies power from a backup power supply for a determined time period to at least one of the B-phase detection portion and the B-pulse generation circuit based on the A pulse or to at least one of the A-phase detection portion and the A-pulse generation circuit based on the B pulse.