Radiant energy – Photocells; circuits and apparatus – Optical or pre-photocell system
Reexamination Certificate
1998-10-26
2001-02-27
Allen, Stephone B. (Department: 2878)
Radiant energy
Photocells; circuits and apparatus
Optical or pre-photocell system
C341S013000
Reexamination Certificate
active
06194709
ABSTRACT:
CROSS-REFERENCE TO RELATED APPLICATIONS
Not Applicable
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
Not Applicable
MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to sensors of the type employed for remotely determining the rotation or angular position of a rotor or shaft by providing an electrical signal indication of the rotational position of the shaft or rotor from a reference datum. The invention relates particularly to providing such a signal on a continuing basis as a transducer.
Rotary angle or position transducers are desired for various control systems; and, in one application is it desired to provide the accumulated angular rotation of a vehicle steering shaft for providing a signal indicative of the steering shaft rotation to a system employed for providing variable effort power assist to the vehicle steering system. Another use for a steering shaft position sensor is to provide a signal from which the turn signal lights may be activated and de-activated.
Angle or rotary position sensors or transducers employing optical sensing of the rotation of a rotor are known and an example of such a device is that shown and described in U.S. Pat. No. 4,947,036 issued to J. D. Pokorski, et al which describes a device utilizing a dual color light source to illuminate a rotating member which includes material providing a gradient of the two colors of the light source disposed thereon for reflection or filtered transmission, the results of which are detected by photodetectors to determine a ratio of the detected output light intensities which is compared with the known arrangement of gradient on the rotating member for determining the position of the rotating member. The aforesaid known techniques employ light beams of different wave length or color chromaticity for detecting the angular or rotary position of a moveable member. Such known devices have used photodetectors to determine the relative intensity of light of a discrete wave length or color chromaticity either transmitted through a filter or reflected from a surface having material of a discrete wave length or color chromaticity. Such known techniques of measuring reflected or transmitted light of a given color chromaticity for determining the rotary position of a member by detecting the relative intensity of the reflected or transmitted light are subject to error and suffer from a relatively low signal-to-noise ratio in the presence of spurious or stray light and to variations in the color chromaticity of the material through which the light is transmitted or reflected.
In such known arrangements, the detector voltage is proportional to the intensity of the detected light, either transmitted or reflected. It is also known to alternately direct the beams of light of a first and second color chromaticity through a filter or on a reflective material of discrete color chromaticity to the photodetector utilizing synchronized time multiplexing to produce a voltage proportional to the intensity of the received light. Typically, a microprocessor is responsive to the photodetector voltage to compute the ratio of the detector voltage arising from the alternate detection of light of the first and second color chromaticity.
In the aforesaid known techniques, proportion of the amount of light detected of one wave length or chromaticity is then correlated with a predetermined relationship between the position of the rotor and the proportion of the colored material of one chromaticity present at a particular station on the rotor. This correlation enables the detection of the rotary position of the rotor.
The known techniques for sensing the position of a rotor using light of two different wave lengths have been proven generally effective; however, where a high degree of accuracy on the order of 1° or less resolution is required, the aforesaid known techniques have been proven inadequate to provide the desired resolution. Known rotary position transducers utilizing color gradient detection have been arranged with the light source and the detectors positioned oppositely with respect to the rotor, and have thus been subject to tolerance accumulation with respect to their placement and this has resulted in variation of the sensed or detected color intensity resulting in error of the measured angle of rotation. Furthermore such known rotary position detectors have been difficult to assemble and calibrate in high volume production and thus costly for automotive steering shift position sensing applications.
In applications for sensing the rotary position of a shaft where a high degree of resolution typically less than 1° angular movement is required, for example in a device for detecting the rotary position of a vehicle steering shaft for purposes of providing a signal useable to control the variable assist in a power steering system it has been desired to provide an accurate, easy to assemble and calibrate and reliable angle sensor which is low in manufacturing cost.
BRIEF SUMMARY OF THE INVENTION
The present invention utilizes a rotor having filter material of opposite angular gradients of two different wave lengths or chromaticities on the rotor to receive and transmit light from a source of illumination alternately of light of one and then the other of the selected wave lengths or chromaticities. The results of which transmission are reflected to a photodetector providing an electrical signal indicative of the amount of light transmitted of the selected wave lengths or chromaticity. The light source preferably comprises light emitting diodes, and the photodetectors are disposed on a circuit board on a common side of the rotor; and, the reflective surface indisposed on an axially opposite side of the rotor enabling complete assembly of all electrical/electronic components on the board prior to final assembly in the housing.
The current in the photodetector is employed to modify the rate of charge of a capacitor; and, the time required for the capacitor to reach a predetermined charge or voltage level is employed to generate a pulse signal having the duration thereof corresponding to the time required to charge the capacitor, thus giving a width modulated signal indicative of the proportion of the resultant light representative of a particular station on the rotor. The proportion of light of the given wave length is then correlated with the predetermined value of the color gradient at the particular location or station on the rotor and the rotor position may thus be electrically determined.
REFERENCES:
patent: 4020912 (1977-05-01), Hino et asl.
patent: 4761551 (1988-08-01), Edwards et al.
patent: 4774494 (1988-09-01), Extance et al.
patent: 4947036 (1990-08-01), Pokorski et al.
patent: 5216245 (1993-06-01), Keegan et al.
patent: EP 0 749 003 (1996-12-01), None
patent: 58055802 (1983-02-01), None
Briggs Roger J.
Corbier Jean-Paul
Ryczek Lawrence J.
Allen Stephone B.
Eaton Corporation
Johnston Roger A.
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