EP0221127A1 - Velocimetre de diffraction optique - Google Patents

Velocimetre de diffraction optique

Info

Publication number
EP0221127A1
EP0221127A1 EP86902876A EP86902876A EP0221127A1 EP 0221127 A1 EP0221127 A1 EP 0221127A1 EP 86902876 A EP86902876 A EP 86902876A EP 86902876 A EP86902876 A EP 86902876A EP 0221127 A1 EP0221127 A1 EP 0221127A1
Authority
EP
European Patent Office
Prior art keywords
light
signal
frequency
source
electrical signal
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP86902876A
Other languages
German (de)
English (en)
Inventor
Keith Gardner
Philip Adrian Storey
Ralph Edward Ecclestone
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
PA Consulting Services Ltd
Original Assignee
PA Consulting Services Ltd
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by PA Consulting Services Ltd filed Critical PA Consulting Services Ltd
Publication of EP0221127A1 publication Critical patent/EP0221127A1/fr
Withdrawn legal-status Critical Current

Links

Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S17/00—Systems using the reflection or reradiation of electromagnetic waves other than radio waves, e.g. lidar systems
    • G01S17/02—Systems using the reflection of electromagnetic waves other than radio waves
    • G01S17/50—Systems of measurement based on relative movement of target
    • G01S17/58—Velocity or trajectory determination systems; Sense-of-movement determination systems
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/48—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S17/00
    • G01S7/491—Details of non-pulse systems
    • G01S7/4912—Receivers

Definitions

  • This invention concerns measuring instruments and particularly instruments for measuring speed of movement and thereby distance travelled.
  • a speckle pattern is formed by the interference of coherent light scattered from a diffuse object and that the pattern moves with a velocity proportional to the object velocity and can be detected to produce an electrical signal proportional to speed.
  • a laser velocimeter Such a device is commonly referred to as a laser velocimeter.
  • the basic principle of operation and typical construction of such a device is contained in the paper entitled Optical Diffraction Velocimeter by G. Stavis published in Instruments and Control Systems in February 1966 at page 99.
  • a different approach involves the use of two interlaced gratings so that the phase of the speckle signal received by a detector associated with one of the two gratings is out of phase with the signal received by a second detector, associated with the other of the two gratings. Again the difficulty in practice of aligning the two gratings means that this approach has also proved impractical for a general purpose instrument.
  • a laser velocimeter comprises:
  • beam splitting means which receives light reflected from the said surface and directs it into two different channels
  • first light responsive detector means for generating a first electrical signal from the light in one channel
  • the speckle size is proportional to the wavelength of the light producing the speckle pattern and the size of the speckles varies around a mean value on a statistical basis.
  • the line pair spacing in the grating is preferably selected so as to correspond to the mean speckle size expected for the known wavelength of the coherent light source.
  • N is the number of line pairs per cm of the grating
  • the distance signal will be proportional to the length of the elongate member which has passed relative to the source.
  • a device embodying the invention will function whether the surface producing the speckle pattern is moving relative to the coherent light source and detectors, or vice versa.
  • the detectors are each photoelectric devices such as semi-conductor junctions.
  • the output signal from at least one of the detectors is amplified by signal amplifying means having adjustable gain, and the signals from the detectors (via the adjustable gain amplifier(s) ) are supplied to the input of a differential amplifier, and the output of the differential amplifier can be nulled in the absence of signals from the beam splitting device (ie with the laser off or blocked) or in the absence of a reflective surface, by adjusting the gain of the adjustable gain amplifiers.
  • the frequency measuring means is a phase locked detector or similar.
  • a method of determining the velocity of a moving surface from which a speckle pattern image can be obtained by reflection of light from a coherent light source of known wavelength comprises the steps of:
  • a laser velocimeter comprises:
  • a reflecting grating means which receives light reflected from the said surface and splits it into two different channels, the plane of the grating being substantially perpendicular to the direction of the light and with the grating lines transverse to the direction of movement of the speckle pattern,
  • first light responsive detector means for generating a first electrical signal from the light in one channel
  • frequency measuring means for determining the centre frequency of the signal spectrum in the output of the signal processing means to thereby generate an electrical signal indicative of velocity.
  • the output signal relating to frequency may be an analogue signal of which typically the amplitude varies with frequency and an analogue measuring device such as a moving coil meter display or the like may be used to indicate the mean frequency measured.
  • an analogue measuring device such as a moving coil meter display or the like may be used to indicate the mean frequency measured.
  • the instrument can give as a direct reading the velocity of the reflecting surface.
  • Further apparatus and/or a further method step may be provided to convert the signal from an analogue form into a digital form for display in a digital display device such as a liquid crystal display device or the like.
  • a digital display device such as a liquid crystal display device or the like.
  • the digital signal can be in the form of a direct reading of velocity.
  • the beam splitting device may take any convenient form and whilst it is generally desirable that the available light is split approximately 50/50 between the two channels it will be appreciated that since the speckle pattern in each channel is converted into an electrical signal it is possible to compensate for a different split between the light levels in the two channels by appropriate adjustment of the gain of signal amplifying means responsive to the electrical signals generated by the detectors in the two channels.
  • a laser velocimeter comprises:
  • a reflecting grating means which receives light reflected from the said surface and splits it into two different channels, the plane of the grating being substantially perpendicular to the direction of the light and with the grating lines transverse to the direction movement of the speckle pattern,
  • first light responsive detector means for generat a first electrical signal from the light in one channe
  • frequency measuring means for determining the ce frequency of the signal spectrum in the output of the signal processing means to thereby generate an electri signal indicative of velocity.
  • a lase velocimeter comprises:
  • a receiver adapted to receive light reflected by said surface and comprising a linear array of photosensitive elements with the outputs from alterna elements summed to form two electrical output signals, spacing between each adjacent pair of elements being selected so as to correspond to the mean speckle size the given wavelength, c) electrical signal processing means for combining the two electrical signals to obtain a difference signal therefrom, and
  • frequency measuring means for determining the centre frequency of the signal spectrum in the output of the signal processing means to thereby generate an electrical signal indicative of velocity.
  • the frequency of the signal indicative of velocit is the parameter thereof which varies with velocity
  • a measure of length is most simply obtained by integrating the signal indicative of velocity with respect to time.
  • the integrator may simply comprise a pulse counter.
  • a display is preferably provided responsive to the integration signal (or accumulating count value) to indicate the distance or length.
  • the display may be analogue or digital .
  • the differential electrical output signal is filtered by a bandpass filter to restrict the frequency content of the signal to dynamic range of interest.
  • the filtered signal is passed through a so-called tracking filter typically a high pass filter, where bandwidth is determined by subsequent frequency to voltage converter means, whereby the dynamic characteristics are such that the pass band increases if the signal is lost.
  • the tracking-filter output constitutes the input signal for a frequency to voltage converter means whose output is an approximation of the signal frequency for feeding back to the tracking filter and forward to a phase locked loop detector.
  • Figure 1 is a diagrammatic view of a known type of laser velocimeter
  • Figure 2 illustrates graphically the power/frequency distribution in the signal supplied to the frequency analyser
  • Figure 3 illustrates a more acceptable form of power to frequency curve such as can be obtained by using the present invention
  • FIG. 4 illustrates diagrammatically one embodiment of the present invention
  • Figure 5 illustrates another embodiment of the present invention
  • Figure 6 illustrates a further embodiment of the present invention
  • Figure 7 is a circuit diagram of the signal processing means and velocity signal generating circuit.
  • a laser light source 10 of known wavelength is directed towards a moving diffuse surface 12.
  • Light reflected from the surface produces a speckle pattern which is intercepted by an optical grating 14.
  • the lines of the grating are transverse to the direction of movement of the speckle pattern.
  • the latter produces an electrical signal in the output of a photodetector 16, the position of the detector and grating 14 being selected so that the distance of the image of the speckle pattern from the surface 12 is the same as the distance from the source 10 to the surface 12.
  • the output from the photodetector is analysed using a frequency analyser 18 and if displayed on a cathode ray display device such as 20 a frequency/power distribution curve will be obtained such as is shown in Figure 2.
  • N is the number of line pairs per cm in the grating and v is the velocity of the surface in cm per second.
  • An optical grating 24 is interposed between the in-line output of the beam splitting device 22 and a first detector 26 whilst the diverted light is supplied directly to a second photodetector device 28.
  • the outputs from the two detectors are amplified by means of buffer amplifiers 30 and 32 respectively and the outputs from the two amplifiers 30 and 32 are supplied to a differential amplifier 34.
  • the gain of each of the amplifiers may be adjustable for setting up.
  • the output from the differential amplifier 34 is conveniently passed through a wave shaping circuit 36 so as to produce a relatively square wave shape to any pulses released by the differential amplifier 34 and the mean frequency of any such shaped signals is determined using a phase locked detector 38.
  • a voltage is available at a point 40 the value of which and the actual value of this voltage can be displayed using a meter type display or the like as denoted by reference numeral 42.
  • the latter can be calibrated to give a direct reading of velocity v_ since from the formula quoted above it is seen that frequency F is proportion to the velocity /.
  • the grating 24 has been shown in the path of the light which passes straight through the beam splitting device 22, it may of course be located alternatively in the channel containing the diverted light from the beam splitting device 22.
  • The. operation of the circuit shown in Figure 4 is to reduce the lower frequency pedestal from the spectrum of the signals applied to the shaping circuit 36 and phase locked detector 38.
  • the success of the circuit depends on producing a balance between the signal relating to the low frequency end of the spectrum appearing in the output of amplifier 30 and the corresponding low frequency signal from amplifier 32. To this end the outputs from the two amplifiers are adjusted so as to be approximately equal whilst the surface 12 is stationary. Movement of the surface then produces signals centred around the mean frequency F, the actual value of which will be dependent upon the speed of the surface 12. It is a signal centred around this frequency which will appear in the output of the differential amplifier 34.
  • a summing amplifier can be used in place of the differential amplifier 34 if the signal from one of the detectors 26 and 28 is inverted in phase (ie through 180°) relative to the other signal.
  • the laser source 10 and the detector are contained in a single housing, or in two housings which are rigidly secured together, to form a unitary assembly, to avoid the need for accurately setting up the various parts of the system relative to the moving surface 12.
  • the unitary assembly be placed at a correct distance from the surface 12 so as to obtain the desired reflection of the illumination region of the surface to form the speckle pattern.
  • FIG. 7 A block diagram of the signal processing circuits is shown in Figure 7.
  • the signal processing may be considered to start at the differential amplifier 34 in Figures 4, 5 and 6.
  • the electrical difference signal is passed through a bandpass filter 48 to restrict the frequency content to the dynamic range of interest. It then passes through a tracking filter 50 which is a highpass filter whose bandwidth is determined by subsequent frequency-to-voltage converter 52.
  • the dynamics are arranged such that the pass band increasesif the signal is lost.
  • the output of the tracking filter 50 is fed into a frequency- o- y Oltage (F/V) converter, whose output is an approximation of the signal frequency.
  • the output of the frequency-to-voltage converter 52 is fed back to the tracking filter (see above) , and forward to a phase locked loop 54 to guide it to approximately the correct frequency.
  • phase locked loop This is done by summing the F/V output signal into a voltage controlled oscillator (VCO) input of the phase locked loop, along with the phase error signal.
  • the phase error signal is also multiplied by the F/V output signal (prior to the VCO) in order to maintain a constant ratio of tracking and lock range of the loop to centre frequency, over the whole frequency range of the instrument. This tracking and lock range prevents the phase locked loop 54 from locking to odd harmonics or subharmonics of the input signal, allowing for inaccuracies in the F/V ou ⁇ put signal.
  • the output of the phase locked loop 54 is a clean signal whose frequency is proportional to the speed to be measured. It is quite insensitive to the wide dynamic range and occasional drop-outs of the originating signal and can be fed into a display 56 for displaying velocity or to a counter 58 and thence to a display 60, whose output (suitably calibrated) indicates distance (ie length of surface 12 "seen").
  • an analogue to digital converter 66 and digital display 68 may be provided.
  • an analogue to digital converter 70 and digital display 72 may be provided.
  • the signal is monitored by a level detector 62 and when the signal level drops below a pre-determined threshold the level detector causes switches A and B to change state.
  • the input to the tracking filter (at switch A) is now an LF oscillator 64, whose frequency is chosen to be at the bottom of the acceptable dynamic range. This holds the tracking system at the lower end, ready to re-acquire the signal when it reappears.
  • Switch B disables the counter, ensuring that no distance is counted whilst switched A and B are in the changed state.
  • switches A and B revert to their initial state and the system continues to measure speed or distance (ie length).

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • General Physics & Mathematics (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Electromagnetism (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

Vélocimètre à laser destiné à mesurer la vitesse relative d'une surface et d'une source de lumière cohérente dirigée sur ladite surface et comprenant un dispositif électro-optique destiné à produire des signaux électriques, dont l'un correspond au contenu du motif des taches produit par illumination de la surface par le circuit lumineux, afin d'obtenir un signal de différence à partir des deux signaux électriques. Ledit vélocimètre comprend également un dispositif de mesure de la fréquence destiné à déterminer la fréquence centrale du spectre de signaux du signal de différence, afin de produire ainsi un signal électrique indiquant la vitesse relative de la surface et de la source. Ledit vélocimètre peut également mesurer la longueur et la distance parcourues en intégrant le signal de vitesse. Le dispositif élecro-optique comprend un réseau situé sur le parcours d'un ou de deux détecteurs ou un ensemble linéaire de photodétecteurs, dont certains sont regroupés par alternance, afin de produire deux signaux électriques, dont l'un correspond au motif des taches.
EP86902876A 1985-05-10 1986-05-08 Velocimetre de diffraction optique Withdrawn EP0221127A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB858511866A GB8511866D0 (en) 1985-05-10 1985-05-10 Measuring instruments
GB8511866 1985-05-10

Publications (1)

Publication Number Publication Date
EP0221127A1 true EP0221127A1 (fr) 1987-05-13

Family

ID=10578936

Family Applications (1)

Application Number Title Priority Date Filing Date
EP86902876A Withdrawn EP0221127A1 (fr) 1985-05-10 1986-05-08 Velocimetre de diffraction optique

Country Status (5)

Country Link
EP (1) EP0221127A1 (fr)
AU (1) AU5868886A (fr)
GB (1) GB8511866D0 (fr)
PT (1) PT82544A (fr)
WO (1) WO1986006845A1 (fr)

Families Citing this family (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
JPS63317775A (ja) * 1987-06-19 1988-12-26 Omron Tateisi Electronics Co 長さ・速度測定装置
SE9100916L (sv) * 1991-03-27 1992-09-28 Nobeltech Electronics Ab Laservarnare
US5557395A (en) * 1992-10-27 1996-09-17 Omron Corporation Optical device for measuring speed
EP0926631A3 (fr) * 1997-12-21 2000-09-06 Ascom Hasler Mailing Systems AG Mesurage de la vitesse du papier utilisant la détection de la granulation produite par laser
US6409294B1 (en) * 1997-12-21 2002-06-25 Ascom Hasler Mailing Systems Ag Digital postage franking with coherent light velocimetry
US6220686B1 (en) 1998-02-13 2001-04-24 Ascom Hasler Mailing Systems Ag Measurement of paper speed using laser speckle detection
US6424407B1 (en) 1998-03-09 2002-07-23 Otm Technologies Ltd. Optical translation measurement
WO1999046602A1 (fr) 1998-03-09 1999-09-16 Gou Lite Ltd. Mesure de la translation par voie optique
GB0209053D0 (en) 2002-04-22 2002-12-18 Bae Systems Plc Method and apparatus for laser vibrometry
IL174713A0 (en) 2006-04-02 2007-05-15 Abraham Aharoni System and method for optical sensing of surface motions
US8151646B2 (en) * 2008-10-24 2012-04-10 Raytheon Company Differential mode laser detection and ranging device

Family Cites Families (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3432237A (en) * 1964-03-31 1969-03-11 Singer General Precision Velocity measuring device
DE978074C (de) * 1964-06-13 1980-04-17 Messerschmitt-Bölkow-Blohm GmbH, 8000 München Optisches Ortungsgerät mit einer Einrichtung zur Kompensation der Hintergrundstrahlung
FR2044366A5 (fr) * 1969-05-19 1971-02-19 Schnerb Gilbert
GB1330163A (en) * 1971-04-28 1973-09-12 British Aircraft Corp Ltd Measurement of fluid or surface velocities
GB1356430A (en) * 1971-08-09 1974-06-12 Rank Organisation Ltd Optical elements

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
See references of WO8606845A1 *

Also Published As

Publication number Publication date
WO1986006845A1 (fr) 1986-11-20
GB8511866D0 (en) 1985-06-19
PT82544A (pt) 1986-11-28
AU5868886A (en) 1986-12-04

Similar Documents

Publication Publication Date Title
EP0790484B1 (fr) Mécanisme de correction d'erreur de position horizontale pour niveau électronique
EP0352133A2 (fr) Polarimètre optique
GB2178165A (en) Optical monitoring method and apparatus
EP0221127A1 (fr) Velocimetre de diffraction optique
US5526109A (en) Multi-velocity component LDV
US3900264A (en) Electro-optical step marker
US4729654A (en) Laser interferometer
EP0167277B1 (fr) Appareil de mesure de microdéplacements
US4929077A (en) Interferometric range finder
US4678337A (en) Laser based gaging system and method of using same
EP0704685A1 (fr) Appareil pour détecter l'angle d'inclinaison d'un miroir de balayage dans un interféromètre du type Michelson
US4040741A (en) Polarized grating optical odometer
US4679932A (en) Method of and apparatus for measuring moving velocity of linear object moving and vibrating
GB2043387A (en) Optical velocity measurement
JPH0444211B2 (fr)
RU2010236C1 (ru) Устройство для градуировки средств измерений угловых параметров движения
SU1091076A1 (ru) Оптический доплеровский измеритель напр жений Рейнольдса в потоке жидкости или газа
SU785644A1 (ru) Фотоэлектрическое устройство дл измерени геометрических размеров объектов
JPS5939683B2 (ja) 光学式変位検出方式
SU916976A1 (ru) Устройство дл контрол углового положени объекта
SU868496A1 (ru) Способ измерени флуктуаций угла прихода излучени
RU1841278C (ru) Устройство для измерения угловых перемещений
SU930215A1 (ru) Устройство дл измерени посто нной времени фотоприемников
SU739448A1 (ru) Способ измерени волнистости водной поверхности
SU641274A1 (ru) Фотоэлектрическое устройство дл контрол пр молинейности

Legal Events

Date Code Title Description
PUAI Public reference made under article 153(3) epc to a published international application that has entered the european phase

Free format text: ORIGINAL CODE: 0009012

17P Request for examination filed

Effective date: 19870108

AK Designated contracting states

Kind code of ref document: A1

Designated state(s): GB

RIN1 Information on inventor provided before grant (corrected)

Inventor name: ECCLESTONE, RALPH, EDWARD

Inventor name: STOREY, PHILIP ADRIAN

Inventor name: GARDNER, KEITH

STAA Information on the status of an ep patent application or granted ep patent

Free format text: STATUS: THE APPLICATION IS DEEMED TO BE WITHDRAWN

18D Application deemed to be withdrawn

Effective date: 19901201

RIN1 Information on inventor provided before grant (corrected)

Inventor name: ECCLESTONE, RALPH, EDWARD

Inventor name: STOREY, PHILIP ADRIAN

Inventor name: GARDNER, KEITH