US 5,491,632 AGranted

Rotary encoder with neutral position

AssigneesGeneral Motors Corporation, Delco Electronics Corporation

InventorsAndrzej M. Pawlak, William C. Lin, David W. Graber, Dennis C. Eckhardt, Scott E. Weiss, Maged Radamis, Thomas A. Perry, John R. Bradley

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Abstract

A rotary encoder capable of detecting angular rotation of a rotating shaft, and identifying its neutral position without the need for multiple encoder wheels. A magnetoresistive sensor is positioned adjacent the periphery of a single multipole magnet ring attached to a steering wheel shaft. The magnet ring comprises alternating N-pole and S-pole magnetic regions along its periphery, the surface of one of the regions containing a demagnetized portion. The sensor produces a sinusoidal signal as the shaft is rotated, responsive to the passage of the magnetic regions, with a period equal to the passage of two successive magnetic regions adjacent the sensor. The angular position of the shaft which aligns the demagnetized portion adjacent the sensor corresponds to the shaft's neutral position. Aligning of the demagnetized portion adjacent the sensor causes a voltage irregularity within the sensor's otherwise sinusoidal output signal, which is detected by a signal processing circuit.

Claims3

Dependent claims

An apparatus for detecting angular rotation and a neutral position of a rotary object, the neutral position corresponding to a predetermined angular position of the rotary object, the apparatus comprising:

an encoder wheel attached to the rotary object, the periphery of the encoder wheel having equally-sized alternating regions of N-pole and S-pole magnetization, one of the magnetized regions having a demagnetized portion;
a sensor located adjacent the periphery of the encoder wheel and generating a sinusoidal output signal responsive to passage of the magnetized regions as the encoder wheel is rotated, a period of the sinusoidal output signal corresponding to passage of two successive magnetic regions, passage of the demagnetized portion resulting in a signal irregularity;
means for detecting values of the sinusoidal output signal equal to a predetermined threshold voltage, each detected value corresponding to an incremental angular rotation of the rotary object;
and
means for detecting the signal irregularity, the angular position of the rotary object when the signal irregularity is detected being the neutral position of the rotary object.

2 more elements

Dependencies are inferred from the claim text.