Patent ID: 7940380

Claim:
A rotary position detector comprising: a housing having an inner space defined by an inner wall and having an aperture in a top portion thereof for admitting a motor shaft therethrough; a base positioned within the housing inner space; a light source positioned to emit light rays upwardly into the housing inner space from adjacent a bottom thereof; 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 the motor shaft and about the light source, 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 within the housing inner space rotatable with the motor shaft above the light detector assembly and the light source, the light blocker comprising a second number of opaque, substantially equal-surface-area elements arrayed about the motor shaft axis, the second number equal to one-half of the first number, wherein a radial extent of the light blocker elements is substantially less than a radial extent of the light sensors; a reflective surface within the housing inner space above the light blocker, wherein light rays emanating from the light source that reach the reflective surface are reflected downward, so that some of the light rays reach the light detector assembly, and light rays that are blocked by the light blocker from reaching the reflective surface are not received by the light detector assembly; 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 impinging thereon, a difference between the “A” detector signal and the “B” detector signal related to an angular position of the motor shaft.