Liquid crystal closed-loop controlled mirror systems

• US 4,690,508 A
• Filed: 05/17/1985
• Issued: 09/01/1987
• Est. Priority Date: 12/15/1982
• Status: Expired due to Term

• Current Assignee: Gentex Corporation
• Original Assignee: C-D Marketing, Ltd.
• Inventors: Jacob, Keith D.
• Primary Examiner(s): Corbin, John K.
• Assistant Examiner(s): NOT, DEFINED
• Application Number:
  US06/735,419
• Time in Patent Office: 837 Days
• Field of Search: 350/278-283, 350/331 R, 350/338, 350/342, 350/332
• US Class Current: 349/195
• CPC Class Codes: B60R 1/088 using a cell of electrically changeable optical characteristic, e.g. liquid-crystal or electrochromic mirrors
• CPC Class Codes: G02F 1/1313 specially adapted for a particular application

Abstract

A rearview mirror system comprises an electrically controlled optical transmission plate disposed over a reflecting surface. The optical transmission plate is selectively operable to any of a number of different states of opaqueness between a maximum light transmission and a maximum opaqueness. The opaqueness of the optical transmission plate is controlled by an electronic circuit which includes two sensors, one for sensing the brightness of incident light from the field of view and the other for sensing ambient light. The control operates to cause the light which is incident on the reflecting surface to be closed loop regulated to a desired degree of brightness which is also correlated with ambient light conditions. A manually operable adjustment is also provided for the observer to set a desired brightness characteristic.

Claims

1. A variable brightness mirror assembly comprising a reflecting surface for reflecting to an observer a field of view which is incident on the mirror assembly and an electrically controlled optical transmission plate disposed over said reflecting surface, said optical transmission plate being operable to any of a number of different states of light transmission, reference establishing means for establishing any desired level of a reference signal over a range of possible reference signal levels corresponding to a range of different brightnesses for light from the field of view which is incident on said reflecting surface, sensor means disposed to provide a detection signal related to the brightness of the incident field of view on the mirror assembly, and control means coupling said sensor means and said reference establishing means in electrical control of said optical transmission plate for causing the brightness of the light from the field of view which is incident on said reflecting surface to be closed-loop regulated to a particular level established by said desired reference signal for any intensity of brightness of the field of view incident on the mirror assembly within a range of different intensities of incident brightness on the mirror assembly, said control means comprising an amplifier stage for causing said optical transmission plate to operate to a state of light transmission which is correlated with both the level of said desired reference signal and the level of said detection signal so as to render the brightness of the field of view incident on said reflecting surface substantially insensitive to change in the incident brightness on the mirror assembly over said range of different intensities of incident brightness for any given level of said desired reference signal over said range of possible reference signal levels while allowing the brightness which is incident on said reflecting surface to be set to any desired brightness within said range of different brightnesses by operation of said reference establishing means, including observer-settable means settable by the observer to set a desired brightness of light from the field of view which is incident on said reflecting surface and causing said control means to closed-loop regulate the light transmission of said optical transmission plate in correlation with the setting of said observer-settable means, and also including an ambient light sensor means for sensing the prevailing ambient light level and causing said control means to closed-loop regulate the light transmission of said optical transmission plate also in correlation with changes in sensitivity of the observer'"'"'s eyes due to changes in ambient light level, said observer-settable means, said first-mentioned sensor means, and said ambient light sensor means all being in an input circuit relationship to said amplifier stage so as to have an interactive effect on said amplifier stage in performing the closed-loop regulation of said optical transmission plate.

2. A variable brightness mirror assembly as set forth in claim 1 in which said sensor means is disposed behind said optical transmission plate so as to provide said detection signal on the basis of the brightness of the incident field of view as attenuated by the light transmission of said optical transmission plate.

3. A variable brightness mirror assembly as set forth in claim 1 in which said observer-settable means settable by the observer comprises a potentiometer across which a fixed voltage supply is applied, said potentiometer comprising a wiper which is adjustable to supply a desired percentage of said fixed voltage supply as the desired reference signal level.

4. A variable brightness mirror assembly as set forth in claim 1 in which said observer-settable means settable by the observer comprises a potentiometer across which a supply voltage is applied, said potentiometer comprising a wiper which is adjustable to supply a signal which is a percentage of said supply voltage as the desired reference signal level, said supply voltage across said potentiometer being variable.

5. A variable brightness mirror assembly as set forth in claim 4 in which said ambient light sensor means is coupled with said potentiometer to vary the supply voltage across the potentiometer as a function of ambient light.

6. A variable brightness mirror assembly as set forth in claim 1 in which said optical transmission plate and said reflecting surface are so arranged that the reflected field of view also passes through said optical transmission plate.

7. A variable brightness mirror assembly as set forth in claim 1 in which said optical transmission plate and said reflecting surface are disposed in respective planes which are at a small acute angle to each other about a generally horizontal axis and both said optical transmission plate and reflecting surface are below said generally horizontal axis.

8. A variable brightness mirror assembly as set forth in claim 1 in which said mirror assembly includes a housing containing said reflecting surface, said optical transmission plate, said reference establishing means, said sensor means, and said control means.

9. A variable brightness mirror assembly as set forth in claim 8, said housing also containing a battery for supplying all the required power for said control means to control the operation of said optical transmission plate.

10. A variable brightness mirror assembly as set forth in claim 8, said control means comprising an electronic circuit board assembly containing electronic control circuitry, including said amplifier stage, for controlling operation of said optical transmission plate in accordance with said desired reference signal level and said detection signal, said first-mentioned sensor means comprising a photodetector mounted on said circuit board assembly.

11. A variable brightness mirror assembly as set forth in claim 10, said ambient light sensor means comprising a further photodetector mounted on said circuit board assembly.

12. A variable brightness mirror assembly as set forth in claim 11, in which said further photodetector causes said control means to require a certain minimum change in ambient light level before said control means makes a corresponding adjustment of the light transmission of said optical transmission plate.

13. A variable brightness mirror assembly as set forth in claim 11, including a manually operable device on said circuit board assembly having an operator which is accessible to the observer for effecting an adjustment of said manually operable device, said manually operable device having a cooperative association in said mirror assembly for influencing the relative cooperative relationship of said observer-settable means, said first-mentioned sensor means, and said ambient light sensor means in their interactive effect on said amplifier stage.

14. A variable brightness mirror assembly as set forth in claim 10, said amplifier stage comprising a high gain differential amplifier, the output of said high gain differential amplifier being supplied as an input to a diode modulator circuit to modulate the high gain differential amplifier output with a square wave signal from a square wave generator circuit and provide a modulated signal output as an input to a push-pull AC amplifier circuit which drives the optical transmission plate.

15. A variable brightness mirror assembly as set forth in claim 14 including an adjustment device on said circuit board assembly and cooperatively associated with said photodetector for adjusting the contribution of said photodetector in its interactive effect with said observer-settable means and said first-mentioned sensor means on said amplifier stage.

16. A variable brightness mirror assembly as set forth in claim 15, in which said adjustment device comprises an operator which is accessible to the observer for enabling the observer to make a manual adjustment of said device.

17. A variable brightness mirror assembly comprising a reflecting surface for reflecting to an observer a field of view which is incident on the mirror assembly and an electrically controlled optical transmission plate disposed over said reflecting surface, said optical transmission plate being operable to any of a number of different states of light transmission, reference establishing means for establishing any desired level of a reference signal over a range of possible reference signal levels corresponding to a range of different brightnesses for light from the field of view which is incident on said reflecting surface, sensor means disposed to provide a detection signal related to the brightness of the incident field of view on the mirror assembly, and control means coupling said sensor means and said reference establishing means in electrical control of said optical transmission plate for causing the brightness of the light from the field of view which is incident on said reflecting surface to be closed-loop regulated to a particular level established by said desired reference signal for any intensity of brightness of the field of view incident on the mirror assembly within a range of different intensities of incident brightness on the mirror assembly, said control means comprising means for causing said optical transmission plate to operate to a state of light transmission which is correlated with both the level of said desired reference signal and the level of said detection signal so as to render the brightness of the field of view incident on said reflecting surface substantially insensitive to change in the incident brightness on the mirror assembly over said range of different intensities of incident brightness for any given level of said desired reference signal while allowing the brightness which is incident on said reflecting surface to be set to any desired brightness within said range of different brightnesses by operation of said reference establishing means, said control means comprising an electronic control circuit comprising a high gain differential amplifier circuit receiving said reference signal and said detected signal as inputs and providing an output signal which is correlated with the differential of said reference signal and said detected signal.

18. A variable brightness mirror assembly as set forth in claim 17, said electronic control circuit further including a diode modulator circuit receiving the output of said amplifier circuit and modulating same with a square wave signal from a square wave generator circuit to provide a modulated signal output as an input to a push-pull AC amplifier circuit which drives the optical transmission plate.

19. A variable brightness mirror assembly as set forth in claim 17, said reference establishing means comprising ambient light sensor means for sensing prevailing ambient light and providing said desired reference signal in correlation with the level of prevailing ambient light.

20. A variable brightness mirror assembly as set forth in claim 19, including adjustment means for adjusting the gain of said first-mentioned sensor means.

21. A variable brightness mirror assembly as set forth in claim 20, in which said adjustment means comprises an adjustable device having an operator accessible by the observer for adjusting the gain of said adjustable device.

22. A variable brightness mirror assembly as set forth in claim 19 in which said amplifier circuit has a gain G, said ambient light sensor means has a gain K_s /N, L_R is the intensity of the brightness of incident light from the field of view, L_O is the intensity of light incident on the reflecting surface after having passed through the optical transmission plate, L_a is the intensity of ambient light on said ambient light sensor, K_LCP is a characteristic of the optical transmission plate, and said reference establishing means, said first-mentioned sensor means, said amplifier circuit and said optical transmission plate are organized and arranged such that the following relationships exist:

##EQU2##

23. A variable brightness mirror assembly as set forth in claim 22 in which the parameter N is variable by an adjustment cooperatively associated with said first-mentioned sensor means.

24. A variable brightness mirror assembly as set forth in claim 23 in which said adjustment means comprises an adjustment device having an operator accessible to the observer for allowing the observer to manually adjust sensitivity of the control means.

25. A variable brightness rearview mirror system comprising a reflecting surface for reflecting a field of view to an observer, an electrically controlled optical transmission plate disposed in the optical path between the field of view and the observer, said optical transmission plate being operable to any of a number of different states of light transmission, sensor means to provide a detection signal sensitive to change in brightness of the field of view incident on the mirror system, control means coupling said sensor means in electrical control of said optical transmission plate for causing the reflected brightness of the field of view seen by the observer to be closed-loop regulated to compensate for changes in the incident brightness, and adjustable correlation means for adjustably correlating the regulated reflected brightness in a manner correlated with changes in the sensitivity of the observer'"'"'s eyes as a function of ambient light level, said adjustable correlation means comprising ambient light sensor means disposed to sense prevailing ambient light from a direction other than the field of view and provide a signal correlated with prevailing ambient light level over a range of different ambient light levels, and means coupling said ambient light sensor means and said first-mentioned sensor in differential input to a high gain amplifier circuit of said control means so that said amplifier circuit provides an output correlated with the differential between signals provided by the two sensor means, and means coupling the output of said amplifier circuit with said optical transmission plate for causing the latter to be operated to a state determined by the amplifier circuit output.

26. A variable brightness rearview mirror assembly as set forth in claim 25 in which said first-mentioned sensor means is disposed behind said optical transmission plate so as to provide said detection signal on the basis of the brightness of the incident field of view as attenuated by the light transmission of said optical transmission plate.

27. A variable brightness rearview mirror system as set forth in claim 25 in which said adjustable correlation means further includes adjustment means cooperatively associated with said ambient light sensor means to provide for adjustment of the gain of said ambient light sensor means.

28. A variable brightness rearview mirror system as set forth in claim 25 including adjustment means associated with said first-mentioned sensor means to provide for adjustment of the gain of said first-mentioned sensor means.

29. A variable brightness rearview mirror assembly as set forth in claim 25 in which said means coupling the output of said amplifier circuit with said optical transmission plate comprises a diode modulator circuit having one input coupled to the output of said amplifier circuit, a square wave generator circuit providing a square wave signal to another input of said diode modulator circuit, said diode modulator circuit modulating the signal received from said amplifier circuit with the square wave signal provided by said square wave generator circuit to yield a modulated signal, and a push-pull AC amplifier circuit having an input receiving the modulated signal from said diode modulator circuit, and said push-pull AC amplifier circuit having an output which drives the optical transmission plate.

30. A variable brightness rearview mirror system as set forth in claim 25 in which said ambient light sensor means is arranged to sense ambient light from other than the field of view, said control means including means associated with said ambient light sensor means for requiring a certain minimum change in ambient light level before said control means makes a corresponding adjustment of the light transmission of said optical transmission plate.

31. A variable brightness rearview mirror system as set forth in claim 25 in which said amplifier circuit, said ambient light sensor means, and said first-mentioned sensor means are characterized by respective gains and in which said sensor means, said amplifier circuit and said control means are organized and arranged such that a certain change in ambient light level effectuates a substantially proportional change in the brightness which is incident on both the reflecting surface and the first-mentioned sensor means.

32. A variable brightness rearview mirror system as set forth in claim 31 including an adjustment device cooperatively associated with said first-mentioned sensor means for adjusting the gain thereof.

33. A variable brightness rearview mirror system comprising a reflecting surface for reflecting to an observer a field of view and an electrically controlled optical transmission plate disposed in the optical path between the observer and the field of view, said optical transmission plate being operable to any of a number of different states of light transmission between a state of maximum transmission and a state of maximum opaqueness, and control means for controlling the brightness of the reflected field of view seen by the observer comprising means for closed-loop regulating the state of light transmission of said optical transmission plate to compensate for changes in incident brightness over a range of different intensities of incident brightness, and said control means further comprising means for selecting a particular range of different intensities of incident brightness, from a number of possible ranges, over which said control means is effective to closed-loop, regulate the state of light transmission of said optical transmission plate, at least some of said number of possible ranges of different intensities of incident brightness having substantially identical spans, said means for selecting a particular range of different intensities of incident brightness comprising ambient light sensor means for at least in part controlling selection of the particular range.

34. A variable brightness rearview mirror system as set forth in claim 33 in which successive ones of said number of possible ranges of different intensities of incident brightness are partially overlapping.

35. A variable brightness rearview mirror system as set forth in claim 33 in which said control means comprises sensor means for providing a signal sensitive to change in brightness of incident light from the field of view, and an adjustment means for adjusting the gain of said sensor means, and wherein the particular range of different intensities of incident brightness is controlled at least in part by the adjusted gain of said sensor means.

36. A variable brightness rearview mirror system as set forth in claim 33 in which said means for selecting a particular range of different intensities of incident brightness comprises ambient light sensor means for at least in part controlling selection of the particular range, further sensor means for providing a signal sensitive to change in brightness of incident light from the field of view, and means for adjusting the gain of said further sensor means, the selection of the particular range of different intensities of incident light being conjointly determined by said ambient light sensor means and the adjusted gain of said further sensor means, the conjoint selection being such that the selected range is moved lower along a scale of ranges for decreasing intensity of ambient light and for decreasing gain of said further sensor means and the selected range is moved upwardly along a scale of ranges for increasing gain of said further sensor means and for increasing intensity of ambient light.

37. A variable brightness rearview mirror system as set forth in claim 33 in which said means for selecting a particular range of different intensities of incident brightness comprises means for causing the selected range to move from one of said possible ranges having substantially identical spans to another of said possible ranges having substantially identical spans in a downward sense along a scale of ranges for a certain decrease in ambient light intensity.

38. A variable brightness rearview mirror system comprising a reflecting surface for reflecting to an observer a field of view and an electrically controlled optical transmission plate disposed in the optical path between the observer and the field of view, said optical transmission plate being operable to any of a number of different states of light transmission between a state of maximum light transmission and a state of maximum opaqueness, and control means for controlling the brightness of the reflected field of view seen by the observer comprising means for closed-loop regulating the state of light transmission of said optical transmission plate to compensate for changes in incident brightness over a range of different intensities of incident brightness detected by a sensor means, said control means comprising a high gain differential amplifier circuit receiving a differential input signal derived from differential between a signal correlated with the degree of incident brightness of the field of view and a desired reference signal level, said desired reference signal level serving to establish an operating point of nominal incident brightness on the mirror assembly over a range of nominal incident brightnesses about which said sensor means is effective to exercise control of the optical transmission plate over said number of possible states between maximum light transmission and maximum opaqueness.

39. A variable brightness rearview mirror system as set forth in claim 38 in which said control means further includes a diode modulator circuit having an input receiving the output of the high gain amplifier, a square wave generator circuit which supplies a square wave signal to another input of said diode modulator circuit, said diode modulator circuit developing from the amplifier output signal and the square wave signal a modulated signal which is supplied to an input of a push-pull AC amplifier, and said push-pull AC amplifier having an output which drives the optical transmission plate.