Optical angular position detection apparatus and method
An annular position detection method provides a plurality of light emitters on a first imaginary circle centered on an axis, the emitters directing individual, well-defined, overlapping light beams to a pair of light detectors positioned on a second imaginary circle centered on that axis. The detectors include pairs of diametrically opposite photosensors producing outputs depending upon the areas thereof exposed to light from the emitters. A light blocker is rotatably mounted on the axis so that the blocker blocks light to different extents of the photosensors depending upon its orientation about the axis. The outputs from all of the photosensors are processed to produce a position signal that varies with the angular position of the blocker and the relative intensities of the emitters are adjusted so that the position signal is substantially linear at all operative angles of the blocker. Apparatus for practicing the method is also disclosed.
1. An angular position detection apparatus comprising
a first light detector disposed on a first imaginary circle centered on an axis, said first light detector including first and second photosensors spaced side-by-side, each photosensor producing an output depending upon the area thereof exposed to light;
at least one pair of light emitters spaced in front of said first light detector on a second imaginary circle centered on said axis, said light emitters being arranged and adapted to direct separate, well-defined, overlapping light beams simultaneously to all the photosensors;
a light blocker rotatably mounted on said axis between the detector and emitters, said light blocker being arranged and adapted to block the light to different extents of said first and second photosensors depending on its orientation about said axis;
a processor responsive to the outputs from all the photosensors for producing a position signal that varies with the angular position of the light blocker; and
a calibration circuit for adjusting, independently, an intensity of each light emitter so that the position signal is substantially linear at all operative angles of the light blocker.
2. The apparatus defined in claim 1 and further including
a second pair of light emitters positioned on said second circle;
a second similar light detector positioned on said first circle and exposed to light from the overlapping light beams, said second light detector including first and second photosensors positioned, respectively, diametrically opposite the first and second photosensors of the first light detector, the photosensors of the second light detector being blocked by the light blocker to substantially the same extents as the corresponding photosensors of the first light detector; and
the processor first sums the outputs of the first photosensors and the second photosensors separately in order to produce said position signal.
3. The apparatus defined in claim 1 wherein the calibration circuit includes a separate control channel for each light emitter pair, each channel containing that pair of light emitters connected in series and further connected in series or in parallel with one or more resistors.
4. The apparatus defined in claim 2 wherein each light emitter is positioned directly opposite a different one of the photosensors.
5. The apparatus defined in claim 2 wherein each light emitter is located directly opposite a space between different adjacent ones of the photosensors.
6. The apparatus defined in claim 2 wherein multiple pairs of light emitters are distributed around said second circle and direct separate, well-defined, overlapping light beams to all of the photosensors whose outputs are processed by the processor to provide said position signal.
7. The apparatus defined in claim 2 wherein each light emitter is a light emitting diode.
8. The apparatus defined in claim 2 wherein the first light detector is a split diode that constitutes the first and second photosensors.
9. The apparatus defined in claim 2 wherein
the detection apparatus is mounted to an end of a scanner including a rotary shaft extending along said axis; and
said light blocker is fixed to an end of said shaft so that said position signal indicates the angular position of the shaft.
10. An annular position detection method comprising:
providing a plurality of light emitters positioned on a first imaginary circle centered on an axis, said emitters directing individual, well-defined, overlapping light beams to a pair of light detectors positioned on a second imaginary circle centered on said axis, said detectors including corresponding pairs of diametrically opposite spaced-apart photosensors which produce outputs depending upon the areas thereof exposed to light from the emitters;
rotatably mounting a light blocker on said axis between the emitters and detectors so that said blocker blocks light to different extents of the photosensors depending upon its orientation about said axis;
processing said outputs from all of the photosensors to produce a position signal that varies with the angular position of the blocker; and
adjusting, independently, an intensity of each emitter so that said position signal is substantially linear at all operative angles of the light blocker.
11. The method defined in claim 10 wherein a plurality of pairs of diametrically opposite emitters are provided on said first circle.
12. The method defined in claim 11 wherein two pairs of emitters are provided.
13. The method defined in claim 12 wherein the emitters are located opposite the photosensors.
14. The method defined in claim 12 wherein the emitters are angularly offset from the photosensors.