Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Patent
1978-10-23
1980-08-19
Nelms, David C.
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
250237G, 356373, 356375, 356395, G01D 534
Patent
active
042186153
ABSTRACT:
An optical incremental shaft encoder in accordance with this invention involves an illumination source arranged to direct light through an optical slit, with the light then falling upon a series of very closely spaced lines forming a first grating. I have discovered that close by this grating a series of image planes are formed, with each plane containing multiple images of the slit. Generally, these images are distinct for distances of only 1/10th of an inch or less with respect to the grating or mask, and for the purpose of this invention, I do not use image planes further away from the mask or grating than this distance. I have found a way to utilize this diffraction phenomenon to great advantage by providing another grating-like member, placed at a selected one of the image planes, whose line spacing is identical to the image line spacing. This second grating-like member may be linear, or curved in an arcuate-like manner, but in any event, it is arranged to move to reflect the motion of a device whose velocity or position is desired to be sensed accurately. In a first embodiment of my invention, a rotor containing this second grating member is arcuately shaped and is arranged to sense the rotary velocity of a shaft. Whereas a single light source and a single detector are utilized in that embodiment, if a pair of closely spaced light sources and a pair of detectors aligned therewith are utilized, the invention can be used for measuring displacement, such as of a gimbal or the like. As the rotor of my invention is moved by the device, its lines ordinarily mask and unmask the image lines of the selected plane, thus causing a modulation of the transmitted light. This light intensity variation is sensed by a photo detector placed next to the rotor, and by means of well-known processing methods, I interpret the electrical signals from the sensors in order to determine the velocity or displacement of the device.
REFERENCES:
patent: 3812352 (1974-05-01), MacGovern
patent: 4051367 (1977-09-01), Sayce et al.
Chin Gay
Martin Marietta Corporation
Nelms David C.
Renfro Julian C.
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