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Publication numberUS2457502 A
Publication typeGrant
Publication dateDec 28, 1948
Filing dateAug 9, 1944
Priority dateAug 9, 1944
Publication numberUS 2457502 A, US 2457502A, US-A-2457502, US2457502 A, US2457502A
InventorsShepherd Judson O'd
Original AssigneeShepherd Judson O'd
Export CitationBiBTeX, EndNote, RefMan
External Links: USPTO, USPTO Assignment, Espacenet
Signal system employing polarized light
US 2457502 A
Abstract  available in
Images(1)
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Claims  available in
Description  (OCR text may contain errors)

' 455-603 nu 233 E a JQERHQL'jE 1 2E5 XR 2,457,502

D 28. 1948. J. 0 0. SHEPHERD 2,451 502 SIGNAL SYSTEM EHPLOYING POLARIZED LIGHT Filed Aug. 9, 1944 I AMPLIFlER I i 7/1 72) OSCiL. QSCIL. AND AND DEMQD. DEM AMP AND DEMOD.

6/ a a. J/ i .52 H r 9 TRAFFIC l CONTROLLER 511 J INVENTOR.

m "n vv UNITED STATES PATENT OFFICE 2,457,502 SIGNAL SYSTEM IiIgIPLOYING POLARIZED Judson OD. Shepherd, Atlanta, Ga.

Application August 9, 1944, Serial No. 548,691

This invention relates in general to signaling systems, and in particular to such systems for effecting remote control operations and transmission of information by telegraphic, telephonic or the like process by modulated radiated or directed energy of a wave length within the visible portion of the spectrum or bordering thereon and to which has been imparted particular polarization.

One objective of the invention is to selectively efiect remote control operations by means of light, or similar energy which will be generally referred to as light, but it will be understood that such reference will include both ultra-violet and infra-red rays -of wave lengths within the range practically employable by means of the class to beset out. An illustrative example of the use of the invention is that disclosed by my pending application Serial No. 325,721, filed March 25, 1940, now Patent No. 2,355,607, dated August 15, 1944, of which this is a continuationin-part, which is directed to remote control of street traffic signals from an authorized vehicle such as a fire truck. Such a vehicle, in accordance with the present invention, is provided with a'projector of suitably polarized light having predetermined modulation. Signal equipped street intersections are provided with detectors for such polarized light and means operatively responsive to such light having said predetermined modulation to actuate the traffic signals to afford the vehicle a protected crossing of the intersections. It is further contemplated that the signals may be selectively controlled from the vehicle.

The employment of light appropriately polarized provides, in the various embodiments of the invention, a primary differentiation between such light and ordinary or normal light. The addition of modulation further distinguishes such light from other light having the same polarization. These two characteristics, therefore, completely difierentiate in a detectable manner the signal energy from other of the same genus which may reasonably be excepted to be present and makes it diificult of mischievous or culpable production by the unauthorized.

The employment of rotative modulations imparted to vibratory polarized light as set out herein has. the further advantage of secrecy'due to difficulty of interpretively intercepting it, particularly where it is employed forvoice or other communication signals. J

A further objective is the transmission'of intelligence by modulated polarized light signals. A first station is provided with means to project 16 Claims. (01. 177-337) a beam of polarized light to which is imparted either controlled predetermined modulation or variable modulation as in response to voice frequencies. Controlled frequencies may comprise make and break signals to provide telegraph signals or, by employing two modulating frequencies, separate marking and spacing signals may be provided. Telegraph printers may be actuated by signals of these types. Multiplex telegraphy and plural channel telephony may be employed by assignment of different frequencies to the several channels.

Modulated polarized light provides, as a feature of the invention, a type of energy which may readily be detected from other energy of similar genus and upon detection readily amplified to a level appropriate for its desired use. Modulated or alternating energy as contemplated herein is more readily amplified than similar energy without modulation or alternation. The polarized light may be modulated, as set out below, either by varying the intensity of a suitable light source by any appropriate means or with a constant source, by a Kerr cell, a light valve or other available means responsive to signals which, in some applications of the invention, may be voice frequency signals. With a periodic light source, signal modulations may be imparted to the beam by varying the angle of polarization. The light source may be supplied from a comparatively high frequency oscillator or generator to which is imparted signal frequencies, or such a source may otherwise be modulated by signal frequencies, to provide what is generally similar to a modulated carrier wave.

Where telegraph signals are employed for audible detection, the frequency of the source may be in the voice frequency range with appropriate keying or the like means to impart information signals to the beam.

A further feature of this invention is the employment of a novel type of energy receiver or detector in a signal system which will be effectively responsive to light having a predetermined characteristic, such as particular polarization, but will be substantially unresponsive to light without such characteristic. This results in a relatively high signal-to-noise ratio. While particular polarization is contemplated as the aforesaid predetermined characteristic, this characteristic may in some employments of the invention be light of a particular wave length such as may be provided by a color filter, or both polarization and wave length characteristics may be jointly employed: a

CROSS mm Other features and-advantages of the invention will be understood from the eight figures of the drawing comprising conventional circuit diagrams as follows:

Figure 1 shows one form of energy transmitter.

Figure 2 indicates alternative means for modulating a beam of polarized light.

Figure 3 discloses arrangements for variab w rotating polarized light.

Figure 4 shows arrangements for modulating polarized light by means of a light valve or the like.

Figure 5 is a detector for modulated polarized!- light.

Figure 6 indicates means for translating received signals into sound.

Figure '7 indicates arrangements for multiplex transmission of signals over a single beam.

Figure 8 is a receiver for use with multiplex signals such as may be produced by arrangements disclosed by Figure '7.

with reference to Figure I, a reflector t, indi'eated in cross-section, 'has a suitable light source I, which may be ot any appropriate type adapted to produce modulated light under control of signals, of which a neon lamp or other eiectronic type is illustrative. It may be of such type that its intensity is a function of signal potentials on a controi grid. A polarizing medium 3, may be a film of light polarizing material such as is marketed under the trade name of Polaroid, intersects the light beam from source 2 and imparts desired polarization thereto. Plane polarization is primarily contemplated but other types may beemployed; A signal' generator 4- is connected tothe primary t transformer through switch key or contacts i. The light source I is connected in a circuit ineluding a two-position switch I. The lightsource provides a varying light intensity under control of generator l. The latter may, in some embodiments of the invention, bean alternating cmrent" generator inwhich case the light beam will have a frequency imparted to it corresponding tothat of the generator. Well known frequency multipliers may be employed to provide a higher frequency than that of generator 4. Telegraphic or control signals may be trans.- mitted by actuation of key 6 0v the like contacts, which may be a portion or a suitable mechanical telegraph transmitter.

If switch I ismovedto terminal 3, potential 9, indicated conventionally as a battery, iscon-- nected in the circuit including light source 2. This potential isof such magnitude as to energize the light source tosuch level that it will provide variably modulated light in accordance withsignal source l. The latter source may, in this case, be suitable means for converting sound into varying current, such as: a microphone with conventional' associatedelements including a battery. The connection to the primary circuit maybe from a communications circuit: or from 81'. plurality 0! frequency sources selectively corrnectibl'e thereto by contacts to provide. marking. and; spacing telegraph signals: for one or more telegraph: channels. By proper selection of the. potential of. battery 9. and thecharacteristics of other circuit elements, the intensity oi the lightham may be made to follow with necessary accuracy the frequency and magnitude of signals; which may be-,. as stated. voice currents.

Element this acolor filter medium which maybe employed to intersect the beam and make it substantially monochromatic, or to filter out certain undesired light wave lengths.

Modulation of a polarized light beam is provided in accordance with Figure 2 by means of a chopper. A preferably parabolic reflector I carries at its focal point a light source 2|, which may be a conventional incandescent lamps A polarizing medium 3 intersects the beam produced by the lamp and reflector. A bladed'member 22 is driven at asuitable speed by a motor, or the like, not shown. This results in modulation of the beam depending on the speed of the motor in View. oi the number of blades provided. The lamp circuit may be keyed or other appropriate means may be employed to impart signals to this beam. Included among the latter may be manually actuatable shutters as used with heliographs or conventional light telegraphy.

The blades of member 22 may be shaped to provide such a wave form to the transmitted bmm as may be desired; The speed of the memlzr may be varied as bygearing or changing the speed of the drivingmctor to provide distinguishing and frequencies to the beam.

angle of polarization may be changed to impart signals to a light beam in accordance with Figure 3.. Areflector l carries alight source 2 of such type as to provide a periodic or modulatedlight beam. A circular frame 3 lcarries a polariz-- ing. medium 32. It is mounted by rollers 33 for rotationin its own plane by handle 34. Movement of the handle to position 34 provides rotation of polarization by 90%, although a smaller angle may beemployed. Rotation of the medium through an anglemay be effected by a solenoid or other electro-mechanical or mechanical means. Chopping or other suitable means may be provided to modulate the beam as an alternative to employing a periodic or modulating light source. I

A. Kerr cell may be advantageously employed to provide rotative modulations to the polarized light beam.

The embodiment set out by Figure 4 provides a 5 reflector carrying a light source 2 powered by a 1 is indicated; as 42. The signals to be transmitted.

are provided by source 43. They may be telegraphic or telephonic signals and will result in the transmitted beambeing modulated in accordance therewith. The beam is appropriately polarized by medium 3. The latter medium may be away from the light valve rather than between it and the reflector.

A. Kerr cell will. as previously mentioned, pro-- vide rotative modulation to a vibratory or to a constant (non-vibratory) polarized beam in response to signals.

A form: of detector which I' may use with this. invention is shown by Figure 5. A suitable housing; 5 L, indicated inpart, is provided with an opening! 52 properly directed for admission of the beam of light from a transmitter such as described above. Reflecting means 53 is mounted at a. suitable angle, say This reflecting means may comprise narrow strips of mirror-like material, so that a portion of the light which reaches the assembly is reflected downward and part is allowed to pass through. That which is reflected downward is. focused by reflector 54 and/or a lens... not shown, on a photo-responsive device 55. indicated as a photoelectric cell. That portion-oi DKAMINER the beam which passes through the interstices of the mirror passes through a suitable polarizing medium 50, said medium being oriented or designed with respect to that of the transmitter so that polarized light therefrom will be substantially extinguished. Light passing through this latter medium is focused as by reflector 51 on photo-responsive device 58.

A suitable source of electric energy 59 is provided. The two cells are connected through resistances 50l and 502, respectively. An electronic tube 503 is connected across these two resistances, and has a proper grid biasing potential 504 and filament power supply 505. The plate circuit of the tube, including an appropriate power source 505, extends to an amplifier 50'! with the output circuit extending to relay 508 through band pass filter 509.

Let is be assumed that unpolarized light reaches the detector. It will actuate photo-cells 55 and 58 equally, so that current will flow through each of them. This will result in equal potential drops through resistances 50l and 502, inasmuch as the light reaching the two cells will be the same. In order to assure the equal actuation of the two cells from unpolarized light I may insert in the portion of the beam reaching cell 55 a translucent medium which will quantitatively pass the same amount of light as medium 56, or use other suitable means to adjust the response of the two cells. While the potential drops through resistances 50! and 502 will be the same, it is to be noted that they will be in opposite directions. As a result of this, the potential drop through both resistances in series will be unchanged from the standpoint of the tube 503 connected across it. In consequence of this, the tube, which is appropriately biased, will not be effective under this condition of equal light reaching both photo-cells,

Now let it be assumed that a beam of suitably polarized light is directed into the detector. Due

- to the medium-56, practically none or the light of the beam reaches cell 58. That reaching cell 55 will cause a potential drop through resistance 50l, to result in the potential on the grid of tube 503 being changed to cause current to flow in the plate circuit. The filter 509 passes only the predetermined frequency for operation of relay 508. Consequently this relay will be actuated in response solely to light so polarized as to be largely or wholly extinguished by medium 56 and having the modulating frequency required to pass filter 509. Should the light not be so polarized but bear the proper frequency -of modulation or be so polarized but not bear the proper modulating frequency, relay 508 will not be operated. Relay 508 may be of such known type as to be responsive solely to one frequency, in which case the band pass filter may be eliminated. A rectifier in series with this relay with a filter will permit the latter to be of the direct current type.

One of the many applications of this invention is to the actuation of street trafiicsignals under control of an authorized vehicle, as was mentioned above. With this arrangement, a suitable projector of particularly polarized light having predetermined modulation is carried by the vehicle in such manner that it is, or may be, directed to receivers such as shown by Figure suitably mounted at intersections. A conventional trafflc signal controller 5|0 actuates trafiic signal lamps of which two are indicated by 5| 1. The operationof relay 508 in response to receipt of the aforesaid characterized light from the vehicle disconnects the lamps from the controller and 6 connects them to power terminal 5|2. Lamps 5| I may be the red or stop signals to halt tramc to protect passage of the vehicle through the intersection.

Relay 508 corresponds to relay 205 of my aforesaid parent application and it will be understood that various of the signal operations described in connection therewith, including difierential signal control, may be effected with polarized light control.

By proper choice of the type of relay 508 and associated circuits, a wide variety of control and signal operations may be effected under control of suitably modulated polarized light. It may be connected to a telegraph sounder or buzzer circuit for providing audible telegraph signals. It may be employed as the line relay of a telegraph printer. A multitude of other applications are apparent.

It was pointed out with respect to Figures 1 and 4 that telephonic signals may be transmitted over a beam of modulated polarized light. Figure 6 shows a modification of Figure 5 for this purpose. The output of tube 503 is extended to amplifier and demodulator 6|. The output of the latter is connected to loud speaker 62 or to a communication circuit, a sound recorder, a telephone receiver or other means for employing frequencies in the voice frequency range. The amplifier and demodulator 6| may also be provided with suitable tuning and/or filter arrangements whereby only the modulations imposed on a higher, or carrier, frequency will actuate reproducer 62, or alternative means. Figures 1 and 4 show means for transmitting such a modulated frequency over a particularly polarized light beam. Another is set out below.

Where rotative signal modulations, such as imparted to a polarized beam by a Kerr cell or other suitable means are employed, they result in an amount of light passing through polarizing medium 56 which corresponds to the signals to result in said signals being reproduced by a suitable receiver.

The arrangement shown by Figure 7 provides for multiplex signalling or communication. A projector similar to that of Figure 1 is indicated. Source 2 is energized by amplifier 10. This amplifier is adapted to combine and amplify fre quencies from a plurality of oscillators and modulators such as H and 12. Each of these is adapted to produce a carrier frenquency individual to itself which is modulated by its connected signal source 13 or 14, which may be a microphone or other signal supply. As a result of this, the polarized light beam will be modulated by the plurality of carrier frequencies each of which is, in turn, modulated by signals.

A receiver for such multiplex signals may be similar to Figure 5 with the output of tube 503 connected to circuit elements in accordance with Figure 8. Band pass filters such as 8| and 82 are provided corresponding to the carrier frequencies produced by transmitter oscillators such as H and 12. These frequencies are transmitted to associated demodulators such as 83 and 84 and the demodulated outputs thereof are connected to suitable receivers such as 85 and 88. While it is contemplated that the receivers 85 and 86 will be for telephonic or telegraphic communications signals, it will be understood that they may be relays to effect separate control operations or jointly controllable arrangements to effect complex selections and operations. a

A light filter I0 is indicated with Figure 1.

This. is repraentative of. means to provide sub-- stantiallymonochromatic light. A similar filter may be employed in connection with other of the: transmitters and with receivers to provide an additional diflerentiating characteristic to the transmitting beam and for its reception.

Where modulations in the form of var able rotation of the polarization of the beam under con trol of signals is provided, an appropriately ori ented polarizing medium, such as that designated 56 in Figure intercepting the beamwill be efiective to convert the rotative modulations into in-' tensity modulations for detectionby a conventional photo-cell, or the like.- I

It will be: understood th t in some practices of this invention a differential detector such as' shown by Figure 5 need not be used and a single photo-cell such as 58 with a polarizing medium 56 may be employed to energize an; amplifying. tube such as 503 to perform functions described above. I

Amplifier tube 503 and other elements are indicated as being powered by batteries. It is to be understood that arrangements well known to this general art may be used for the employment of alternating current power of commercial or-other available frequency.

This invention may be used for. transmission. and reproduction of control and communication: signals of anyfrequency within the frequency range of the elements appropriate for the practice of the invention. This may include signals for facsimile reproduction, for telephotography and for television. This may further include multiplex telegraphy of the voice frequency or high frequency types. It is also contemplated that secrecy equipment may be employed withtelephonic signals with the invention, of which the arrangement disclosed in the Webb Patent No. 2,315,56'7 granted April 13, 1943 is illustrative. The invention provides, in short, a signal channel for practically any use whatever.

It will be understood that arrangements disclosed to accomplish a particular end in connection: with one of the figures may be used as appropriate toaccomplish that end with other of the figures. It is to bestill further understood that various other applications and embodiments of the invention may be made by those skilled in this art without departing from the spirit of the invention as defined within the scope of the appended claims.

What is claimed is:

1. A signaling system including a source of light, means to impart fixed polarization to said light, means to impart signal modulations to said light, a receiver for said light which is functionally responsive solely to light having said polarization, and means controlled by said receiver to produce signals corresponding to those imparted to said light.

2. A signaling system including means to produce light having predetermined polarization and a signal modulated frequency, a receiver for said light which is operatively responsive solely to light having said polarization and means connected to said receiver for demodulating said frequency to produce signals.

3. A signal system including a light source,

means to actuate said source to produce light 70- having a; predetermined frequency modulated by a signal frequency, means to impart to said light; predetermined polarization, a receiver for said light adapted to differentiate between light hav-- ing said polarization and light lacking: it to transnew,

8. late said polarized light intofrequencies in: am electrical circuit and to neutralize thev efiect of light lacking said polarization, and means to demodulate latter said frequencies to produce Sig-- nals.

4. A signal. system including means to producelight having a predetermined frequency, means. to impart signals to said light, a polarizing. medium to impart predetermined polarization to said light, a receiver for said light including photoresponsive elements, a. second polarizing medium. and means including said photo-responsive. elements, said second polarizing medium and demodulating means for producing signals corre-- sponding to those impartedv to said light, and means to neutralize the effect of light lacking said: predetermined polarization.

5. A signal system including means to produce light having a predetermined frequency, means to impart to said light variable polarization hr response to signals and means solely responsive: to light so polarized for translating said variably polarized light into signals.

6. A signal system including means to produce light having a predetermined frequency, means to impart to said light variable polarization in response to signals and means solely responsive to light so polarized including polarizing means and frequency responsive means for translating said light into signals.

7. A. multiplex signal'system including means. to produce a beam of light bearing a plurality of. channel carrier frequencies each of which is modulated by signals, means to impart predetermined polarization to said light, a receiver adapted to discriminate against light without said polarization to neutralize the effect thereof and to be re"- sp'onsive to light having said polarization, means responsive to said receiver receiving light having said polarization and said modulated carrier frequencies to reproduce in an electrical circult said modulated carrier frequencies, means to* separate said frequencies into separate channels and means to demodulate the frequency of each channel to reproduce the signals of that channel.

8. A traffic control system including in combination, a trafilc signaling device, means connected to said device to operate said device toproduce trafiic controlling signals, means to control last said means, means to produce light polar-- ized in a predetermined manner, and a receiver connected to said control means responsive to light so polarized to cause said control means tofunction to result in the production of a prede termined trafilc controlling signal under control of said producer.

9. A tramc control system comprising, in combination, traflic signaling devices, means connectto said devices to operate said' devices to produce trafilc controlling signals, means to control last said means, means to produce light polarized in a predetermined manner and modulated in a particular manner, and means connected to said signal control means responsive to light so polarized and so modulated to cause said control means to function to result in the production of a predetermined traillc controlling signal under control of said light producer.

10. A receiver for light having predetermined polarization including two photo-responsive elements arranged to receive separate portions of said light, an oriented analyzer intersecting the light received by one of said elements, and an output circuit in which said photo-responsive elementsare differentially connected.

11. A receiver for light having a signal frequency and predetermined polarization including two photo-responsive elements arranged to receive separate portions of said light, an output circuit in which said elements are differentially connected to substantially neutralize the eflect of light reaching both of said elements in substantially equal quantity, an analyzer intersecting the light to a first one of said elements, with said analyzer so oriented as to substantially extinguish said light having said predetermined polarization so that the portion of said polarized light which reaches the second of said elements causes said signal frequency to be reproduced in said output circuit, and means connected to said output circuit responsive to said signal frequency.

12. In a traflic control system, trafiic signalling devices, means connected to said devices to operate them to produce traific controlling signals, a receiver for light having predetermined polarization including two photo-responsive elements arranged to receive separate portions of said light, an oriented analyzer intersecting the light received by one of said elements, an output circuit in which said photo-responsive elements are differentially connected, and means connected to said output circuit to cause a predetermined traflic controlling signal in response to receipt by said receiver of light having said polarization.

13. In a traflic control system, traffic signalling devices, means connected to said devices to operate them to produce trafflc controlling signals, a receiver for light having predetermined polarization and predetermined frequency including two photo-responsive elements arranged to receive separate portions of said light, an oriented analyzer intersecting the light received by one of said elements, an output circuit in which said photoresponsive elements are differentially connected, means connected to said output circuit and said devices operating means to cause said device operating means to produce a predetermined traflic controlling signal in response to receipt by said receiver of light having said predetermined polarization and predetermined frequency.

14. A receiver for polarized light including two photo-responsive elements, a normally balanced bridge circuit in which said elements are so connected that the bridge remains effectively in bal- 40 Number ance with substantially equal illumination of the two elements, and an analyzer through which the light to one of said elements passes to result in said bridge being unbalanced upon polarized light having predetermined orientation with respect to said analyzer being directed toward both of said elements.

15. A receiver for light having a predetermined distinguishing characteristic including two photoelectric cells arranged to receive separate portions of said light, a medium arranged to intersect the light received by one of said cells, said medium havin the characteristic of transmitting a substantial portion of light without said distinguishing characteristic and substantially extinguishing light which has said distinguishing characteristic, and an output circuit in which said cells are differentially connected.

16. A device for reproducing signals from a signal modulated beam of light having a predetermined distinguishing characteristic including two photo-electric cells arranged to receive separate portions of said beam, an electrical circuit in which said cells are diiferentially connected, a medium having a light transmitting characteristic complementary to that of said beam, with said medium arranged to intersect the portion of the beam received by one of said cells to effectively reduce the intensity of the portion of the beam reaching latter said cell, and means connected to said circuit to reproduce signals corresponding to those of said beam.

JUDSON OD. SHEPHERD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Name Date Hirt June 23, 1908 Hawkins June 1, 1909 Howard Nov. 21, 1911 Chubb Sept. 13, 1927 Schroeter et al Feb. 10, 1931 Hanna Mar. 15, 1932 Nicolson Nov. 30, 1937 Halstead Sept. 2'7, 1938

Patent Citations
Cited PatentFiling datePublication dateApplicantTitle
US891339 *Dec 11, 1907Jun 23, 1908Gen ElectricRailway-signal.
US923170 *Nov 2, 1908Jun 1, 1909Gen ElectricSignal system.
US1009309 *Sep 8, 1909Nov 21, 1911Union Switch & Signal CoRailway signaling.
US1642011 *Jun 15, 1921Sep 13, 1927Westinghouse Electric & Mfg CoLight telephony
US1791938 *Nov 16, 1929Feb 10, 1931Telefunken GmbhSafety device for railroad operation
US1849488 *Mar 27, 1928Mar 15, 1932Westinghouse Electric & Mfg CoMultiplex transmission
US2100348 *Apr 13, 1934Nov 30, 1937Communications Patents IncLight beam transmission system
US2131042 *Sep 28, 1935Sep 27, 1938Halstead William SRadio traffic control system
Referenced by
Citing PatentFiling datePublication dateApplicantTitle
US2591837 *Mar 27, 1946Apr 8, 1952NasaMethod and apparatus for signaling employing polarized lights
US2631273 *Jun 29, 1948Mar 10, 1953Alertronic Protective Corp OfApparatus for photoelectric detection
US3475092 *Oct 23, 1967Oct 28, 1969Eastman Kodak CoWireless remote control slide changer
US4734575 *Apr 28, 1986Mar 29, 1988Cerberus AgLight barrier utilizing two radiation branches each having differently polarized filters
US4754133 *Apr 25, 1986Jun 28, 1988Williams Electronics Games, Inc.Transceiver circuit for modulated infrared signals
US4972185 *Apr 28, 1989Nov 20, 1990Minnesota Mining And Manufacturing CompanyRadiant energy signal transmitter
US5495243 *Jul 27, 1994Feb 27, 1996Mckenna; LouCollision avoidance system
US6252519Aug 6, 1999Jun 26, 2001Mckenna LouEmergency vehicle signaling system
US20100054744 *Aug 25, 2009Mar 4, 2010Maxson Brian DSystems and methods for detecting orientation of an optical emitter with respect to detector using oppositely polarized beams for reference
DE2855761A1 *Dec 22, 1978Jun 28, 1979Fmc CorpVerfahren zum korrigieren bzw. bestimmen des schlagfehlers von fahrzeug raedern fuer pruefinstrumente und vorrichtung hierfuer
DE2923346A1 *Jun 8, 1979Dec 13, 1979Fmc CorpVorrichtung zum messen der einstellung von raedern eines kraftfahrzeugs und verfahren zum einjustieren der vorrichtung auf das fahrzeug
EP0032823A1 *Jan 16, 1981Jul 29, 1981Fmc CorporationWheel clamp
EP0200186A2 *Apr 26, 1986Nov 5, 1986Cerberus AgLight barrier
Classifications
U.S. Classification340/906, 398/152, 398/184, 340/902, 398/140
International ClassificationG08G1/087, H04B10/10
Cooperative ClassificationH04B10/11, G08G1/087
European ClassificationH04B10/11, G08G1/087