Patent ID: 7688432

Claim:
A rotary position detector comprising: a housing having an inner space defined by an inner wall, wherein at least a portion of the inner wall is reflective; a light source positioned to emit light rays into the housing inner space; a base positioned within the housing inner space beneath the light source; a light detector assembly positioned within the housing inner space and comprising a first number of substantially toroidal-sector-shaped light sensors positioned on the base and disposed in pairs about an axis of a motor shaft, each pair comprising one “A” detector element and one “B” detector element, the pairs disposed so that each “A” detector is circumferentially positioned between two “B” detectors and each “B” detector is positioned between two “A” detectors; a light blocker affixed within the housing inner space for rotation with the motor shaft between the light detector assembly and the light source, the light blocker comprising a second number of opaque, substantially pie-shaped, substantially equal-surface-area elements arrayed about the motor shaft axis, the second number equal to one-half of the first number, an angular subtense of each of the light blocker elements greater than an angular subtense of a detector element, a radial extent of each of the light blocker elements greater than a radial extent of each of the detector elements, wherein at least a portion of a surface of the light blocker facing the light source is reflective so as to reflect light impinging thereon toward the reflective portion of the inner wall thus increasing an amount of light available for reaching the light detector elements, the inner wall reflecting light impinging thereon toward the light blocker and the light detector elements, and wherein at least some of the light rays are emitted directly toward the light detector assembly from the light source and at least some of the light rays are emitted away from the light blocker; and a signal connection between the light detector elements and a circuit for measuring a signal from the “A” detectors and the “B” detectors relating to an amount of light falling thereon, a difference between the “A” detector signal and the “B” detector signal related to an angular position of the motor shaft.