US3858043A - Light barrier screen - Google Patents

Light barrier screen Download PDF

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Publication number
US3858043A
US3858043A US00398943A US39894373A US3858043A US 3858043 A US3858043 A US 3858043A US 00398943 A US00398943 A US 00398943A US 39894373 A US39894373 A US 39894373A US 3858043 A US3858043 A US 3858043A
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United States
Prior art keywords
light
evaluation
measurement
photoreceiver
light sources
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Expired - Lifetime
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US00398943A
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English (en)
Inventor
Erwin Sick
Ernst Gass
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Erwin Sick GmbH Optik Elektronik
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Erwin Sick GmbH Optik Elektronik
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Expired - Lifetime legal-status Critical Current

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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F16—ENGINEERING ELEMENTS AND UNITS; GENERAL MEASURES FOR PRODUCING AND MAINTAINING EFFECTIVE FUNCTIONING OF MACHINES OR INSTALLATIONS; THERMAL INSULATION IN GENERAL
    • F16P—SAFETY DEVICES IN GENERAL; SAFETY DEVICES FOR PRESSES
    • F16P3/00—Safety devices acting in conjunction with the control or operation of a machine; Control arrangements requiring the simultaneous use of two or more parts of the body
    • F16P3/12—Safety devices acting in conjunction with the control or operation of a machine; Control arrangements requiring the simultaneous use of two or more parts of the body with means, e.g. feelers, which in case of the presence of a body part of a person in or near the danger zone influence the control or operation of the machine
    • F16P3/14—Safety devices acting in conjunction with the control or operation of a machine; Control arrangements requiring the simultaneous use of two or more parts of the body with means, e.g. feelers, which in case of the presence of a body part of a person in or near the danger zone influence the control or operation of the machine the means being photocells or other devices sensitive without mechanical contact
    • F16P3/144—Safety devices acting in conjunction with the control or operation of a machine; Control arrangements requiring the simultaneous use of two or more parts of the body with means, e.g. feelers, which in case of the presence of a body part of a person in or near the danger zone influence the control or operation of the machine the means being photocells or other devices sensitive without mechanical contact using light grids
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01V—GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS
    • G01V8/00—Prospecting or detecting by optical means
    • G01V8/10—Detecting, e.g. by using light barriers
    • G01V8/20—Detecting, e.g. by using light barriers using multiple transmitters or receivers
    • G01V8/22—Detecting, e.g. by using light barriers using multiple transmitters or receivers using reflectors
    • G—PHYSICS
    • G08—SIGNALLING
    • G08B—SIGNALLING OR CALLING SYSTEMS; ORDER TELEGRAPHS; ALARM SYSTEMS
    • G08B13/00—Burglar, theft or intruder alarms
    • G08B13/18—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength
    • G08B13/181—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems
    • G08B13/183—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier
    • G08B13/184—Actuation by interference with heat, light, or radiation of shorter wavelength; Actuation by intruding sources of heat, light, or radiation of shorter wavelength using active radiation detection systems by interruption of a radiation beam or barrier using radiation reflectors

Definitions

  • Grigsby 5 7 ABSTRACT A light barrier screen having a plurality of sequentially arranged light sources which emit a light beam occupying a given predetermined area, and a photosensitive receiver which registers the intensity of the light beam coming out of the predetermined area and emits an output signal upon a given decrease in intensity of one or more light beams, said individual light sources being introduced through a single energy source in rapid temporal sequence.
  • the present invention concerns a light barrier screen with (l) a plurality of sequentially arranged light sources which emit a light beam occupying a predetermined area, and (2) a photosensitive receiver which registers the intensity of the light beam coming out of the predetermined area and emits an output signal upon a given decrease in intensity of one or more light beams.
  • Light barrier screens of this type are already known (DAS 1,170,286) and are utilized as guards for relatively large surface areas. They are, for example, used as safety light curtains in front of the danger zones of machines such as presses, giving an automatic shutoff signal when a hand or other body part approaches the danger zone.
  • the aim of the present invention is a light barrier screen of the above-named type in which the cost of its practical embodiment is substantially lowered without adversely affecting the high requirements of reliability and safety which are made upon such screens.
  • the present screen is also of compact, neat design and easy to manufacture.
  • the present invention provides that the individual light sources can be introduced through a single energy source in quick temporal succession.
  • a sort of radius vector (guide beam) principle results, but without the necessity of using mechanically moving parts such as mirror wheels or vibrating mirrors. It is an advantage of the present invention that only a single energy source is called for,
  • an electronically operated reverser switch which connects the light sources with the energy source in the temporal sequence mentioned above.
  • a further substantial simplification is achieved in accordance with the present invention in that for the evaluation of the electric signals actuated by the individual light beams leaving the guard area there is only one single evaluationelectronics provided.
  • a reverser switch is placed between the photoreceiver and the evaluation-electronics, and the reverser switch is in the same rhythm on the evaluationelectronics as the photoreceivers on the light source side.
  • each light source is set up with a measuring photoreceiver which receives the light beam out of the guard area and another comparison-photoreceiver which receives light emitted by the light source but not traversing the area, and that the outputs of both measuring and comparison-receivers are hooked up to a comparison circuit inside the evaluation-electronics.
  • the comparison circuit the quotient of the two signals is formed, so that differences of background brightness of the light sources utilized as well as age phenomena, temperature influences, etc., are completely excluded.
  • comparison rays emitted by each light source are united by the same optics as the measurement rays to a single comparison-photoreceiver, which is hooked up to a comparison circuit provided in the evaluationelectronics. In the comparison circuit another quotientformation takes place.
  • the light sources are light-emitting diodes, and Ga-AS-Diodes are used to the best advantage. Diodes of this type are remarkable for their ease of handling. In accordance with the present invention, they are hooked up sequentially to the energy source by means of a shifting register which is available at very reasonable cost on the present-day market.
  • the frequency with which the light sources are sequentially hooked up is so high that in case of the instrusion of a human hand inside the light curtain the shut-off signal occurs before the danger zone is reached by the hand.
  • the optimal frequency is in the order of magnitude of SkI-Iz.
  • FIGS. 1 through 5 A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I A perspective view of a typical vehicle.
  • I BRIEF DESCRIPTION OF THE DRAWING
  • FIG. 1 is a schematic representation of the circuit and of the light beam paths of a first embodiment of the inventive light barrier screen
  • FIG. 2 is a side view of the topmost optical partial arrangement indicated in FIG. 1;
  • FIG. 3 is a schematic view of the optical portion of a particularly advantageous embodiment of a light barrier screen in accordance with the present invention.
  • FIG. 4 is a side view of the object of FIG. 3;
  • FIG. 5 is an example of embodiment of an evaluation-electronics for the inventive light barrier screen.
  • Beams 18-23 thus make up a guard area 24. If an obstacle is introduced into this area, the light stream reaching one of the measurement photoreceivers 26-31 is correspondingly weakened. This decrease in intensity is transmitted for evaluation.
  • all six lightemitting diodes 11-16 are connected to an energy source 17 via a reverser 17a.
  • the reverser guarantees that only one diode at one time is charged with voltage and that in rapid sequence all diodes are cyclically charged, while this operation is constantly repeated. If this operation occurs with a sufficiently high frequency in the order of magnitude of 1 through kHz, a light curtain which is for all practical purposes uninterrupted is generated in guard area 24.
  • Measurement photoreceivers 2631 are hooked up to an evaluation-electronics 25, which delivers a signal at its output 55 as soon as the intensity of the light reaching any of the measurement photoreceivers falls beneath a given predetermined value.
  • each of the diodes l116 is arranged in front of guard area 24 but next to the plane mirrors 42, 43, 44, 45, and 46 which are arranged for the measurement of ray paths, said plane mirrors connecting one portion of the light emitted by the relevant diode to comparisonphotoreceivers 32, 33, 34, 35, 36, and 37 respectively.
  • comparison-photoreceivers 32 through 37 are hooked up to the evaluation electronics 25 in which a comparison circuit is located, in which the quotient from the electric signals of each measurement-comparison-photoreceiver pair is formed.
  • differing background brightnesses of the light sources being used are of as little significance in the evaluation as aging phenomena or temperature influences on the light sources.
  • the light rays escaping from guard area 24 are reflected (instead of through lenses) through a wedge 62 arranged as in the drawing and a concave mirror 40 together upon a single measurement-photoreceiver 38 which is hooked up to the evaluation-electronic 25 shown in FIG. 4.
  • a small plane mirror (4247) is connected (said mirrors having been appropriately arranged relative to the measurement beam path).
  • Each of the said mirrors throws light escaping from the light source arranged relative to it onto a con cave mirror 40, which unifies the light coming from all the mirrors onto a single comparison-photoreceiver 41.
  • plane mirrors 4247 are arranged relative to paired lenses 48-53 in such a way that light is used for comparison-beam 39 which otherwise would not enter the measurement beam path.
  • FIG. 5 shows a circuit for evaluation of the signals emitted by photoreceivers 38 and 41. Theseare first boosted in boosters 56 and 57 and then applied to both entrances of a trigger 58.
  • the output of the trigger is zero as long as the signal transmitted from diode 38 is smaller than the signal from reference diode 41.
  • the output of the trigger is however L, if the signal from diode 38 is greater than the signal coming from diode 41.
  • a differentiation step 59 is connected which emits an output only for the positive side of an impulse reaching 41. Also at the output of trigger 58 a differentiation step 60 is connected, which however emits an output impulse only upon the presence of the negative side of an impulse appearing at trigger 58.
  • the two differentiation steps are applied at the inputs of a settable flip-flop 61.
  • a light barrier screen having a plurality of sequentially arranged light sources which emit a light beam occupying a given predetermined area, said individual light sources being introduced through a single energy source in rapid temporal sequence, the light beams coming out of said area being optically unified upon a single measurement-photoreceiver which registers the intensity of the light beams coming out of said area and emits an output signal upon a given decrease in intensity of one or more light beams, and a single evaluation electronics connected to said measurementphotoreceiver for the evaluation of electrical signals actuated by the individual light beams coming out of said area.

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  • Engineering & Computer Science (AREA)
  • General Physics & Mathematics (AREA)
  • General Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • General Life Sciences & Earth Sciences (AREA)
  • Geophysics (AREA)
  • Life Sciences & Earth Sciences (AREA)
  • Mechanical Engineering (AREA)
  • Photometry And Measurement Of Optical Pulse Characteristics (AREA)
  • Geophysics And Detection Of Objects (AREA)
  • Burglar Alarm Systems (AREA)
  • Length Measuring Devices By Optical Means (AREA)
  • Electronic Switches (AREA)
US00398943A 1972-09-26 1973-09-20 Light barrier screen Expired - Lifetime US3858043A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
DE2247053A DE2247053C3 (de) 1972-09-26 1972-09-26 Lichtschrankengitter

Publications (1)

Publication Number Publication Date
US3858043A true US3858043A (en) 1974-12-31

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Family Applications (1)

Application Number Title Priority Date Filing Date
US00398943A Expired - Lifetime US3858043A (en) 1972-09-26 1973-09-20 Light barrier screen

Country Status (7)

Country Link
US (1) US3858043A (ja)
JP (1) JPS5527315B2 (ja)
CH (1) CH558060A (ja)
DE (1) DE2247053C3 (ja)
GB (1) GB1436953A (ja)
IT (1) IT993021B (ja)
SE (1) SE391249B (ja)

Cited By (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0011744A1 (en) * 1978-11-28 1980-06-11 Erwin Sick GmbH Optik-Elektronik Light grid arrangement
US4219802A (en) * 1975-06-19 1980-08-26 "Autostrade"-Concessioni e Costruzioni Autostrade S.p.A. Scanning barrier for the discrimination and counting of objects and more specifically of vehicles in transit through a laminar barrage of electromagnetic microwaves
US4260882A (en) * 1978-05-17 1981-04-07 Barnes Austen B Light sensitive detection circuit
US4286880A (en) * 1979-07-30 1981-09-01 The Bendix Corporation Scanning light beam lumber defect position system and method of using same
EP0035522A1 (en) * 1979-09-10 1981-09-16 Ambler Kenneth Gordon SECURITY MECHANISM FOR INDUSTRIAL APPLIANCES.
EP0070883A1 (en) * 1981-02-10 1983-02-09 Otis Elevator Co PHOTOELECTRIC OBSTACLE DETECTOR FOR ELEVATOR DOORS.
US4467251A (en) * 1979-05-31 1984-08-21 Besam Ab Object sensing apparatus
US4652205A (en) * 1985-05-02 1987-03-24 Robotic Vision Systems, Inc. Robot cell safety system
US4736097A (en) * 1987-02-02 1988-04-05 Harald Philipp Optical motion sensor
US4752768A (en) * 1984-11-30 1988-06-21 U.S. Philips Corp. Intruder detector with anti-obscuring means
US4760381A (en) * 1984-12-22 1988-07-26 Telenot Electronic Gmbh Intruder-detection system for room security
WO1989007277A1 (en) * 1988-01-27 1989-08-10 Harald Philipp Optical motion sensor
US4864121A (en) * 1987-03-12 1989-09-05 Erwin Sick Gmbh Optik-Elektronik Light curtain with periodic light transmitter arrangement
US4879461A (en) * 1988-04-25 1989-11-07 Harald Philipp Energy field sensor using summing means
US5008530A (en) * 1986-12-09 1991-04-16 Erwin Sick Gmbh Optik-Elektronik Autocollimation light curtain
WO1991006018A1 (en) * 1989-10-13 1991-05-02 John Trett Obstruction detection apparatus
US5311012A (en) * 1990-04-10 1994-05-10 Auto-Sense, Limited Method and apparatus for detecting objects with modifying gain and sensor means
US5572183A (en) * 1995-01-17 1996-11-05 Sweeney; Gary L. Laser light fire evacuation system
US5838238A (en) * 1996-03-13 1998-11-17 The Johns Hopkins University Alarm system for blind and visually impaired individuals
US20030222198A1 (en) * 2002-05-30 2003-12-04 Olszak Artur G. Imaging system with an integrated source and detector array
US6701005B1 (en) 2000-04-29 2004-03-02 Cognex Corporation Method and apparatus for three-dimensional object segmentation
US20060010601A1 (en) * 2002-04-19 2006-01-19 Riley Carl W Hospital bed obstacle detection device and method
US7167575B1 (en) 2000-04-29 2007-01-23 Cognex Corporation Video safety detector with projected pattern
US20120152283A1 (en) * 2010-12-16 2012-06-21 The Boeing Company Automated Cleaning System and Method for an Aircraft Fuselage Interior
US11406548B2 (en) 2018-09-27 2022-08-09 Hill-Rom Services, Inc. Obstacle detection IR beam filter

Families Citing this family (13)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
FR2283494A2 (fr) * 1974-09-02 1976-03-26 Cometa Procede et dispositif de balayage photoelectrique
DE2508366C3 (de) 1975-02-26 1979-05-17 Erwin Sick Gmbh Optik-Elektronik, 7808 Waldkirch Optische Vorrichtung mit einem Lichtvorhang
DE2559947C3 (de) * 1975-02-26 1981-04-23 Erwin Sick Gmbh Optik-Elektronik, 7808 Waldkirch Optische Vorrichtung mit einem Lichtvorhang
DE2941739C2 (de) * 1979-10-16 1982-02-18 Krohne Meßtechnik GmbH & Co KG, 4100 Duisburg Lichtgitter
DE2944588C2 (de) * 1979-11-05 1981-11-12 Krohne Meßtechnik GmbH & Co KG, 4100 Duisburg Lichtgitter
JPS59163093U (ja) * 1983-04-18 1984-10-31 積水ハウス株式会社 窓用面格子
JPH0325220Y2 (ja) * 1985-02-15 1991-05-31
GB2177503A (en) * 1985-06-12 1987-01-21 John Peter Hughes Guard system
GB2207999B (en) * 1987-08-13 1992-04-22 Memco Med Ltd Safety systems
DE3833680A1 (de) * 1988-10-04 1990-04-05 Zeiss Carl Fa Schutzeinrichtung fuer langgestreckte maschinenteile
DE4217696C2 (de) * 1992-05-27 1995-01-12 Mannesmann Ag Optoelektronischer Signalgeber
DE102016121204A1 (de) * 2016-11-07 2018-05-09 Pepperl + Fuchs Gmbh Optischer Sensor
DE102016121913A1 (de) * 2016-11-15 2018-05-17 Sick Ag Mehrstrahllichtschranke

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US2930898A (en) * 1956-09-11 1960-03-29 W D Engineering Co Ltd Cathode ray tube apparatus for the inspection of articles
US3293513A (en) * 1962-08-08 1966-12-20 Texas Instruments Inc Semiconductor radiant diode
US3742222A (en) * 1970-02-20 1973-06-26 Endl Elektronik Gmbh Co Photoelectric sensing system
US3764813A (en) * 1972-04-12 1973-10-09 Bell Telephone Labor Inc Coordinate detection system

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2930898A (en) * 1956-09-11 1960-03-29 W D Engineering Co Ltd Cathode ray tube apparatus for the inspection of articles
US3293513A (en) * 1962-08-08 1966-12-20 Texas Instruments Inc Semiconductor radiant diode
US3742222A (en) * 1970-02-20 1973-06-26 Endl Elektronik Gmbh Co Photoelectric sensing system
US3764813A (en) * 1972-04-12 1973-10-09 Bell Telephone Labor Inc Coordinate detection system

Cited By (42)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US4219802A (en) * 1975-06-19 1980-08-26 "Autostrade"-Concessioni e Costruzioni Autostrade S.p.A. Scanning barrier for the discrimination and counting of objects and more specifically of vehicles in transit through a laminar barrage of electromagnetic microwaves
US4260882A (en) * 1978-05-17 1981-04-07 Barnes Austen B Light sensitive detection circuit
EP0011744A1 (en) * 1978-11-28 1980-06-11 Erwin Sick GmbH Optik-Elektronik Light grid arrangement
US4310756A (en) * 1978-11-28 1982-01-12 Erwin Sick Gmbh Optik-Elektronik Light grid arrangement using cyclically switched semiconductor light sources
US4467251A (en) * 1979-05-31 1984-08-21 Besam Ab Object sensing apparatus
US4590410A (en) * 1979-05-31 1986-05-20 Joensson Bert Ove Object sensing apparatus
US4286880A (en) * 1979-07-30 1981-09-01 The Bendix Corporation Scanning light beam lumber defect position system and method of using same
EP0035522B1 (en) * 1979-09-10 1986-11-26 AMBLER, Kenneth Gordon Safety mechanism for industrial machinery
EP0035522A1 (en) * 1979-09-10 1981-09-16 Ambler Kenneth Gordon SECURITY MECHANISM FOR INDUSTRIAL APPLIANCES.
EP0070883A4 (en) * 1981-02-10 1984-05-29 Otis Elevator Co PHOTOELECTRIC OBSTRUCTION DETECTOR FOR ELEVATOR DOORS.
EP0070883A1 (en) * 1981-02-10 1983-02-09 Otis Elevator Co PHOTOELECTRIC OBSTACLE DETECTOR FOR ELEVATOR DOORS.
US4752768A (en) * 1984-11-30 1988-06-21 U.S. Philips Corp. Intruder detector with anti-obscuring means
US4760381A (en) * 1984-12-22 1988-07-26 Telenot Electronic Gmbh Intruder-detection system for room security
US4652205A (en) * 1985-05-02 1987-03-24 Robotic Vision Systems, Inc. Robot cell safety system
US5008530A (en) * 1986-12-09 1991-04-16 Erwin Sick Gmbh Optik-Elektronik Autocollimation light curtain
US4736097A (en) * 1987-02-02 1988-04-05 Harald Philipp Optical motion sensor
US4864121A (en) * 1987-03-12 1989-09-05 Erwin Sick Gmbh Optik-Elektronik Light curtain with periodic light transmitter arrangement
WO1989007277A1 (en) * 1988-01-27 1989-08-10 Harald Philipp Optical motion sensor
US4879461A (en) * 1988-04-25 1989-11-07 Harald Philipp Energy field sensor using summing means
WO1991006018A1 (en) * 1989-10-13 1991-05-02 John Trett Obstruction detection apparatus
US5311012A (en) * 1990-04-10 1994-05-10 Auto-Sense, Limited Method and apparatus for detecting objects with modifying gain and sensor means
US5418359A (en) * 1990-04-10 1995-05-23 Auto-Sense, Limited Method and apparatus for detecting objects with range-dependent blocking
US5572183A (en) * 1995-01-17 1996-11-05 Sweeney; Gary L. Laser light fire evacuation system
US5838238A (en) * 1996-03-13 1998-11-17 The Johns Hopkins University Alarm system for blind and visually impaired individuals
US7167575B1 (en) 2000-04-29 2007-01-23 Cognex Corporation Video safety detector with projected pattern
US6701005B1 (en) 2000-04-29 2004-03-02 Cognex Corporation Method and apparatus for three-dimensional object segmentation
US7680323B1 (en) 2000-04-29 2010-03-16 Cognex Corporation Method and apparatus for three-dimensional object segmentation
US8502663B2 (en) 2002-04-19 2013-08-06 Hill-Rom Services, Inc. Hospital bed obstacle detection apparatus
US8258944B2 (en) 2002-04-19 2012-09-04 Hill-Rom Services, Inc. Hospital bed obstacle detection device and method
US7472437B2 (en) * 2002-04-19 2009-01-06 Hill-Rom Services, Inc. Hospital bed obstacle detection device and method
US20090109025A1 (en) * 2002-04-19 2009-04-30 Carl William Riley Hospital bed obstacle detection device and method
US20060010601A1 (en) * 2002-04-19 2006-01-19 Riley Carl W Hospital bed obstacle detection device and method
US9655796B2 (en) 2002-04-19 2017-05-23 Hill-Rom Services, Inc. Hospital bed obstacle detection apparatus
US8866610B2 (en) 2002-04-19 2014-10-21 Hill-Rom Services, Inc. Hospital bed obstacle detection apparatus
US6987259B2 (en) * 2002-05-30 2006-01-17 Dmetrix, Inc. Imaging system with an integrated source and detector array
US20030222198A1 (en) * 2002-05-30 2003-12-04 Olszak Artur G. Imaging system with an integrated source and detector array
US8381747B2 (en) * 2010-12-16 2013-02-26 The Boeing Company Automated cleaning system for an aircraft fuselage interior
US8580043B2 (en) 2010-12-16 2013-11-12 The Boeing Company Automated cleaning method for an aircraft fuselage interior
CN102556364A (zh) * 2010-12-16 2012-07-11 波音公司 适用于飞机机身内部的自动化清洁系统和方法
CN102556364B (zh) * 2010-12-16 2016-02-24 波音公司 适用于飞机机身内部的自动化清洁系统和方法
US20120152283A1 (en) * 2010-12-16 2012-06-21 The Boeing Company Automated Cleaning System and Method for an Aircraft Fuselage Interior
US11406548B2 (en) 2018-09-27 2022-08-09 Hill-Rom Services, Inc. Obstacle detection IR beam filter

Also Published As

Publication number Publication date
IT993021B (it) 1975-09-30
SE391249B (sv) 1977-02-07
DE2247053A1 (de) 1974-05-22
JPS5527315B2 (ja) 1980-07-19
DE2247053C3 (de) 1979-08-09
DE2247053B2 (de) 1978-12-07
JPS4971980A (ja) 1974-07-11
GB1436953A (en) 1976-05-26
CH558060A (de) 1975-01-15

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