WO1984003142A1 - Procede et appareil pour determiner la position optique d'un faisceau analyseur - Google Patents

Procede et appareil pour determiner la position optique d'un faisceau analyseur Download PDF

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Publication number
WO1984003142A1
WO1984003142A1 PCT/US1983/000185 US8300185W WO8403142A1 WO 1984003142 A1 WO1984003142 A1 WO 1984003142A1 US 8300185 W US8300185 W US 8300185W WO 8403142 A1 WO8403142 A1 WO 8403142A1
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WO
WIPO (PCT)
Prior art keywords
light
receiver
target surface
pattern
image
Prior art date
Application number
PCT/US1983/000185
Other languages
English (en)
Inventor
Donald L Laib
Original Assignee
Coe Mfg Co
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 Coe Mfg Co filed Critical Coe Mfg Co
Priority to PCT/US1983/000185 priority Critical patent/WO1984003142A1/fr
Priority to EP19830901124 priority patent/EP0137772A1/fr
Publication of WO1984003142A1 publication Critical patent/WO1984003142A1/fr

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Classifications

    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/06—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material
    • G01B11/0691—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness for measuring thickness ; e.g. of sheet material of objects while moving
    • G—PHYSICS
    • G01—MEASURING; TESTING
    • G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
    • G01B11/00—Measuring arrangements characterised by the use of optical techniques
    • G01B11/02—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness
    • G01B11/026—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring distance between sensor and object

Definitions

  • This invention relates to apparatus and a method for rapidly determining the amount of separation between a target surface and a predetermined reference position,- and particularly to apparatus for on-line precise monitoring of the thickness of moving material such as sawn lumber, which is subject to thickness var ⁇ iation throughout its lateral cross-section as a result of having been sawn from a waning portion of a log.
  • OMPI roller sensors and similar mechanical and electro ⁇ mechanical devices using physical contact between the thickness sensing device and the moving material.
  • prior art devices because of the frictional wear produced by the continuous contact with the moving material, constantly require readjustment and repair.
  • non-contact optical measuring apparatus utilizing coherent light sources (lasers), such as the instruments described in Kerr U.S. patent No. 3,671,726, and Dawson U.S. patent No. 3,779,647, has also become known, but because of the complexity of laser apparatus, such equipment is unde ⁇ sirably expensive.
  • Optical measuring devices used in applica ⁇ tions other than saw mills and the like where the prod ⁇ ucts whose thickness is to be monitored move contin ⁇ ually past a monitoring station depend on counting optical interference fringes produced as light passes through optical gratings.
  • the aforementioned need for a non-contact measuring device for determining the location of a dif ⁇ fuse target surface relative to a reference position is fulfilled by the optical measuring device of the pres- ent invention.
  • the preferred apparatus of the present invention includes a projector which periodically sweeps or scans beams of collimated light over a target surface, defining a periodically moving pattern of illuminated and non-illuminated areas projected on the target surface.
  • a reference photoelectric sensing de ⁇ vice is arranged to detect portions of the periodically sweeping beams of light at a predetermined position with respect to the projector, either directly or by receiving a reflection of the pattern of light from the target surface, producing a periodic reference electri ⁇ cal signal corresponding to the movement of the pro ⁇ jected beams of light.
  • the path of motion of the light beams of the pattern defines a reference sweep plane, and a receiver, preferably located in the reference sweep plane, collects light reflected in a predetermined direction from the target surface.
  • the receiver is angularly offset from the direction in which the beams of light are projected toward the target surface, and is in a position to receive light reflected from the target surface when the target surface is within a pre ⁇ determined distance from the reference position.
  • An optical lens or reflector establishes a receiver axis and focuses the light reflected from the target surface along the receiver axis toward a receiver photoelectric sensing device.
  • the receiver device is masked to per ⁇ mit a maximum amount of the reflected image of the pro- jected pa-ttern of light to reach it only at a prede ⁇ termined phase of the periodic sweeping motion of the projected light beams.
  • the photoelectric sensing device of the receiver With the scanning pattern of light falling on a target surface at a predetermined distance from the projector, the photoelectric sensing device of the receiver receives the reflected image of the projected pattern of light from the target surface along the receiver axis, through the open portions of the mask, in a predetermined phase relationship with detection of the light beams by the reference photoelectric sensing device.
  • the angular variation bet ⁇ ween the receiver axis and the reference axis, should the target surface be located in a plane at a different distance from the projector, the light beam images reflected from the target surface would fall on the photoelectric sensing device in a different phase rela ⁇ tionship with the detection of the light beams by the reference photoelectric sensing device.
  • the reference and receiver photoelectric sensing devices each generate a periodic elec ⁇ trical signal in response to receiving images of the projected sweeping beams of light.
  • the phase relation ⁇ ship, however, between the reference electrical signal and the receiver electrical signal is related to the distance between the projector and the target surface, so that these signals will have a predetermined phase relationship when the target surface is at a reference position a predetermined distance from the projector, and a different phase relationship will result from any change in the distance between the projector and the target surface.
  • a signal corresponding to the phase angle between the reference electrical signal and the receiver electrical signal is determined automatically by electrical means.
  • the . phase angle signal is then electrically converted into an indication of the separation between the target sur- face and the reference position.
  • a light source such as an incandescent filament is used.
  • a relay lens projects a focused image of the light source into an aperture in an opaque diaphragm.
  • the aperture is located at the focal point of a projection lens, such that light projected from the light source through the relay lens exits from the projection lens as substantially only parallel rays, being collimated by the telecentric combination of the aperture and the projection lens.
  • a chopper disc having a plurality of aper ⁇ tures of uniform size evenly spaced about its peri ⁇ phery, is rotated at a predetermined speed, with the apertures passing through the path of light from the relay lens toward the telecentric aperture, generating the periodically scanning pattern of light.
  • the pro ⁇ jected image of the moving apertures of the chopper disc is kept in focus throughout a substantial depth of field because of the collimation provided by the tele ⁇ centric aperture and the projection lens, so that a bright, sharp image of the scanning pattern of light is projected onto the target surface.
  • the rela ⁇ tively large angle required by location of a separate lens system in a position which does not interfere with the projection lens limits the range of target motion which may be observed without ambiguity.
  • a smaller angle between the direction of the projection pattern of light and the image reflected from the target surface may be obtained by viewing the image on the target sur ⁇ face through the same projection lens.
  • a mask having apertures corresponding in size and shape to the apertures of the chopper disc is interposed in the path of the reflected image, and located at a dis- tance from the telecentric aperture equal to the dis ⁇ tance from the chopper disc to the telecentric aperture.
  • a similar reflector may be located on the opposite side of the telecentric aperture and a similar photoelectric sensing device and mask may be used to produce a refer- ence electric signal.
  • the reflectors establish respec ⁇ tively a reference axis and a receiver axis along which reflected images of the pattern of light are conducted. These axes are preferably symmetrically arranged with respect to the projection axis, converging on the pro- jection axis at a common point and thus establishing a reference position for a target surface.
  • the use of the projection lens both for pro ⁇ jection of the pattern of light and for receiving reference and receiver images of the pattern of light reflected from the target surface has an additional ⁇ benefit of promoting inexpensive production of a plu ⁇ rality of measuring devices according to the invention, all having closely similar optical characteristics with a minimum of lens position adjustment required because of slight dissimilarities of particular lenses.
  • variations of the relay lens become insig ⁇ nificant, since the telecentric aperture collimates the projection of the pattern of light, and slight varia ⁇ tions of the focal length of the relay lens affect merely the intensity of the image of the light source if the location of the light source and relay lens are predetermined with respect to the location of the tele ⁇ centric aperture.
  • the method and apparatus of the invention may be used to unambiguously measure greater or smaller variations of distance between the projector and the target surface area, without exceeding three hundred sixty degrees difference in phase between the reference and receiver signals.
  • the instantaneous phase angle measurements determined by the apparatus may be electronically averaged to eliminate error caused by inconsequential irregularities in the physical dimensions and motion of the chopper disc and the electrical circuitry used.
  • the apparatus of the invention may be used to measure the thickness of a work piece traveling along a path by measuring the distance of the top surface of the workpiece from a reference position when the work- piece rests on a support whose location is known, or pairs of apparatus according to the invention may be used in caliper fashion to directly determine the thickness of a work piece. Variations of the cyclic rate of sweep of the light beam, of the angular rela ⁇ tionship between the light beam projection axis and the receiver axis, and of the dimensions of individual pro- jected beams of light each bear upon the measurable range of position and the accuracy of measurement.
  • FIGS. 1-4 are directed to an illustrative em ⁇ bodiment of the optical system portion of the position- determining apparatus of the present invention.
  • FIG. 1 is a pictorial view of an exemplary array of measuring devices embodying the present inven ⁇ tion as arranged to measure the thickness of a work- piece.
  • FIG. 2 is a pictorial schematic view of an internal optical system for a typical one of the meas- uring device units shown in FIG. 1.
  • FIG. 3 is a simplified schematic diagram of the optical apparatus of FIG. 2 showing the manner in which the receiver detects the image of a projected beam of light reflected from a target surface located at various positions.
  • FIG. 4 is a fragmentary view of the measuring apparatus shown in FIG. 2, showing the optical fiber light conductor used in generating the reference signal.
  • FIG. 5 is a block diagram of the electronic circuitry used to process the electrical signals devel ⁇ oped by the photoelectric detectors included in the measuring apparatus shown in FIGS. 1-4.
  • FIGS. 6-10 are directed to an alternative em ⁇ bodiment of the optical system portion of the position- determining apparatus of the present invention.
  • FIG. 6 is a schematic view of the alternative embodiment of the optical system.
  • FIG. 7 is another schematic view of the alternative embodiment of the optical system taken at right angles to the plane of FIG. 6.
  • FIG. 8 is a pictorial view of the telecentric slit aperture and a fragment of the chopper wheel of the embodiment of FIG. 6, on an enlarged scale.
  • FIG. 9 is a partially cut away view of the receiver mask and the receiver photoelectric sensing device of the embodiment of FIG. 6, on an enlarged scale.
  • FIG. 10 is an elevational view of the projec ⁇ tion lens of the embodiment of FIG. 6, on a reduced scale, taken along line 10-10.
  • FIGS. 11-13 are electrical schematic diagrams of receiver, flutter compensator and phase detector circuits usable with the optical scanner system portion of the position-determining apparatus of the present invention.
  • FIG. 11 is a schematic diagram of an exem- plary electronic receiver circuit.
  • FIGS. 12 A and B when placed together side- by-side, are an exemplary flutter compensation circuit.
  • FIG. 13 is a schematic diagram of a phase detector circuit.
  • three optical position ⁇ ing determining scanners 10 embodying the present invention are shown arranged exemplarily for automati- cally determining the thickness of a workpiece such as a sawn board 12 passing between the scanners 10 and a supporting surface at various locations along its length.
  • the board 12 is supported from below while the
  • OMPI measuring devices 10 measure the location of a target surface 14 on the top of the board 12 as the board is moved in the direction indicated by the arrow 16.
  • an exemplary position- determining scanner 10 comprises a projector 18 and a receiver 20.
  • an incandescent filament light source 22 approximately .015 inch X .35 inch (.38mm X 8.89mm) in size
  • light passes through a con ⁇ denser lens assembly comprising a pair of lenses 24 and 26, then into a collimating projection lens assembly 28.
  • an opaque chopper disc 30 Interposed between the condenser lens assembly and the collimating projection lens assembly 28 is an opaque chopper disc 30, having a plurality of apertures 32 and opaque sectors 33 arranged about its periphery, each aperture being, for example, approximately .047 inch (1.2mm) in width as measured between its radially extending sides.
  • the chopper disc 30 is mounted on a synchronous motor (not shown), and is rotated exem- plarily at 3600 rpm.
  • a scanner 10 having 128 apertures 32 thus interrupts the light emitted from the filament at the rate of 7680 times per second and thus periodi ⁇ cally permits light to pass toward a target surface as 7,680 sweeping beams per second.
  • a diaphragm 34 comprising an object plane aperture 36 is located adjacent to the chopper disc 30.
  • the size of the aperture 36 is equivalent to two com ⁇ plete cycles of the apertures 32 of the chopper disc 30, or approximately about three sixteenths of an inch in width.
  • Interposed in the center of the object plane aperture 36 is an end of an optical light conductor 38 which is used to transmit light received through the apertures 32 and the object plane aperture 36 to a reference photoelectric sensing device 40, producing a reference electrical signal to be compared with a re- DC signal to determine the phase sepa ⁇ ration between the two in a manner to be described more fully below.
  • the collimating projection lens assembly 28 comprises exemplarily a convex focusing lens 46, a dia ⁇ phragm 48 having an aperture 50, a forward diaphragm 52 having a front aperture 5 * 4 which limits transmission of stray light, and a convex projection lens 56.
  • the aperture 50 is centered about the coincident focal points of the focusing lens 46 and the projection lens 56, and is hereinafter referred to as a telecentric aperture.
  • the telecentric aperture 50 is small enough to permit transmission of essentially only parallel light rays from the projection lens 56 toward the target surface 14, while the focusing lens 46 permits sharp images of the light source to be projected through the apertures 32 of the chopper disc as a pattern of scanning light beams.
  • the projected pattern of light After passing through the collimating projec ⁇ tion lens assembly 28 the projected pattern of light is imaged upon the target surface 14, and since substan ⁇ tially only parallel rays are transmitted, the image of the pattern of light is projected sharply on the target surface object throughout the range of target surface positions which is of interest.
  • the reflection of the light beam image on the target surface 14 of the work- piece is then transmitted through the receiver lens assembly 58, which defines a receiver axis 60.
  • the receiver axis 60 converges toward intersection with the projection path 62 of the projection lens system 28 defining an angle ⁇ .
  • the relationship between the angle ( ⁇ (the angle between the optic axis 62 of the projection lens system 28 and the optic axis 60 of the receiver) and the spacing between corresponding parts of the aper ⁇ tures 32 of the chopper disc 30 is preferably such that the tangent of the angle ⁇ is equal to the size of the projected image width 63, as shown in FIG. 2, of a complete aperture 32 together with an opaque sector 33, divided by the total desired unambiguously measurable range of variation of the distance of the target surface
  • the range as indicated by the arrow 64 is about 2-1/8 inches (53.97mm).
  • the angle ⁇ is approximately 11.2 degrees. The angle is not particularly significant except that if the desired measurable range of the location of the target surface is substantially greater, then the angle ⁇ would be decreased correspondingly.
  • Another way of expressing this relationship as a formula is that the unambiguously measurable range equals the projected aperture image spacing divided by the tangent of the angle ⁇ .
  • the receiver lens assembly 58 comprises an objective lens 65, which is preferably an achromatic lens, and a diaphragm 66 including a light-limiting aperture 67 which is used to reduce internal reflec ⁇ tions and stray light in the system.
  • a diaphragm 68 defines a collimating, depth-of-field enhancing aper ⁇ ture 70 which is centered about the focal point of the objective lens 65.
  • the receiver 20 also includes a grating or mask 72 which is located where the projected image of the light beams on the target surface 14, as viewed through the receiver lens assembly 58, is gen ⁇ erally in focus. As shown in FIG.
  • this grating 72 is aligned so as to be both perpendicular to the optic axis 60 of the receiver lens assembly 58 and perpen ⁇ dicular to the plane defined by the optic axes 62 and 60, respectively, of the projector lens assembly 28 and the receiver lens assembly 58.
  • Behind the receiver grating 72 is a photo- electric device 76 which measures the received light and generates a periodic receiver electrical signal whose frequency is the same as the frequency of pro ⁇ jecting individual sweeping beams of light, but whose phase relationship to the reference electrical signal is dependent upon the position of the target surface, as may be more clearly seen with reference to FIG. 3. It is this difference in phase, caused by the position of the target surface 14 (thickness of the workpiece) which is detected and analyzed in the balance of the circuitry.
  • the mask 72 in the receiver 20 is located in the image plane of the receiver lens 62.
  • the light received along the receiver axis 60 from the target surface 14 passes through the receiver lens assembly 58 and the mask 72.
  • the size and spacing of openings 74 of the receiver mask 72 correspond to the size and spacing of the image on the target surface 14 of the beams of light projected through the chopper disc apertures 32, multiplied by the magnification.
  • the magnification of the received image at the mask 72 is equal to the ratio of the object distance to the image distance.
  • the light beam image of the chopper wheel aper ⁇ tures 32 directly and exactly overlies and corresponds with the apertures 74 in the receiver mask 72, and there is an exact correspondence in the overlay of the received image on the receiver mask.
  • This relationship is of course subject to the limitations of the lens systems in that there are certain aberrations as well as imperfect collimation of the light beams.
  • the exact correspondence occurs at only one position in the measurable range of movement of the target surface, but the congruency is sufficiently close over the balance of the range that the system operates satisfactorily.
  • the image of a light beam passing through an aperture 32 aligned with - ⁇ 5- the object plane aperture 36 onto the target surface 14 is reflected along the receiver axis 60 and through the openings 74, producing an electrical output from the receiver photoelectric sensor 76 which is in phase with the reference signal produced by the reference photo ⁇ electric sensing device 40.
  • the target surface 14 is located at position B, which is closer to the pro ⁇ jector 18, the image reflected from the target surface will coincide with the receiver grating 72 before the chopper disc has rotated as far as it had rotated for an image of a beam reflected from the target surface 14 located at the position A to coincide with the grating.
  • phase difference between the reference and receiver electrical signals is proportional to the target displacement.
  • these low level reference and receiver electrical signals are amplified, con- verted to square wave form and then fed via a flutter compensator 79 into a phase detector 80, as shown in FIG. 5.
  • the reference and receiver electrical signals contain a direct current component resulting from ambient light sensed by the photodetectors 40 and 76, and a periodic component corresponding to the scanning beams of light.
  • Resonant alternating current ampli ⁇ bombs 82 and 83 are used to block the unwanted direct current (ambient light) component of the reference and receiver electrical signals and to increase the signal- to-noise ratio to a useful level, by band pass limit ⁇ ing, while amplifying the signals enough to drive sine wave-to-square wave converters 84 and 85.
  • the resonant amplifiers 82 convert small frequency deviations to indications of large phase variations.
  • the flutter compensator 79 adds a correction to each phase angle observed.
  • the compensator is zeroed in an initialization run in which it measures the phase difference between the reference and receiver signals as a function of chopper disc rotation, with a target surface 14 located at a reference position, such as the position A of FIG. 3.
  • a measurement of the phase difference is made for each edge of each aperture 32 by comparing the rising or falling edge of the reference signal with the corres ⁇ ponding rising or falling edge of the receiver signal.
  • phase detector 80 To com ⁇ pensate for this error later on, every time there is a transition of the reference signal to the flutter com ⁇ pensator, caused by a specific optical transition of the chopper disc, (i.e. light-to-dark, and vice versa), the reference electrical signal going to the phase detector 80 is adjusted by precisely the time measured during the initialization cycle. As a result, any such cyclic phase errors present during initialization do not show up at the output of the phase detector. This procedure also zeroes the scanner 10. That is, the position of the target surface 14 during the initiali ⁇ zation of the flutter compensator becomes the position which will cause an indication of zero displacement thereafter.
  • An exemplary phase detector 80 consists of an
  • EX-OR gate i.e., an exclusive OR logic gate whose two inputs are the square wave reference and receiver elec ⁇ tric signals. Its output is a square wave whose duty cycle is proportional to the phase difference. This variable duty cycle square wave may be filtered to produce a direct current voltage proportional to the displacement of the target surface.
  • This output is ambiguous in that it gives the same voltage for two different target positions, since this type of phase detector does not discriminate be ⁇ tween leading and lagging phase differences. Two sets of signals whose phase differences are equal, but of opposite direction, will produce the same voltage indi ⁇ cation of phase angle. Therefore a D-type flip flop may be used as a leading/lagging detector to resolve the ambiguity.
  • While the embodiment described above provides analog measurements of phase and displacement, it is also possible to use exclusively digital information to determine displacement directly from each successive beam of light swept across the target surface.
  • the digital values obtained by direct measurement of the delay between corresponding transitions of the refer ⁇ ence signal and the received signal contain all the phase information.
  • All of the signal processing after the amplifiers 82 and 83 may be digital, and instantan- • eous displacement may be calculated as the target sur ⁇ face displacement which will cause a full cycle phase ifference between corresponding points in reference and receiver electric signals, multiplied by the ratio of the actual signal time difference to the full cycle period.
  • the smoothed or filtered displacement may for example be a running mean for the largest number of samples consistent with the system response time required.
  • FIGS. 6-9 An alternative embodiment 100 of the optical apparatus of the invention, shown in FIGS. 6-9, com- prises a light source 102, such as an incandescent lamp preferably having a filament 104 which is generally linear in shape.
  • a relay lens 106 e.g. an f/l.6 trip ⁇ let lens having a 25.4mm focal length, is positioned two focal lengths, that is, 50.8mm from the filament 104.
  • a projection lens 110 preferably of at least half the speed of the relay lens, e.g., an f/3 achro ⁇ matic convex lens, is aligned with the light source 102, the relay lens 106, and the slit 108, and spaced one focal length of the projection lens 110 from the slit 108, so that the position of the slit 108 relative to the projection lens 110 forms a telecentric system.
  • the projection lens 110 then receives light from the light souce through the slit 108, hereinafter referred to as a telecentric slit, and collimates the diverging rays 111 of light.
  • the projection lens transmits the light received from the telecentric slit 108 in rays 109 which appear parallel as viewed in FIG. 6 toward a target surface 112 whose distance from a predetermined location is to be determined.
  • a telecentric slit 108 (see FIG. 8) having a width 113 of 3mm and a length of 12mm with a 120mm focal length pro ⁇ jection lens 110 has been found effective to provide a usable depth of field of at least 4-1/2 inches (114mm). Outside the limits of that field the signal/noise ratio and linearity of the measuring system are sharply reduced.
  • a relay lens diaphragm 107 Directly adjacent to the relay lens 106, on the side nearer the telecentric slit 108, is a relay lens diaphragm 107 defining an elongated relay lens aperture 109 which extends across the full diameter of the relay lens with an exemplary height 105 of .05 inch (1.27mm) .
  • relay lens diaphragm 107 Between the relay lens diaphragm 107 and the telecentric aperture or slit 108, and preferably lo ⁇ cated as close as possible to the relay lens diaphragm
  • a chopper disc 114 driven exemplarily by a synchronous motor 117 which is essentially an enlarged version of the chopper disc 30 of the previously de- scribed apparatus 10, with 256 apertures 116 extending radially and arranged evenly about its periphery.
  • the chopper disc 114 is rotated, preferably at 1800 rpm, it periodically interrupts the converging rays 115 of light transmitted by the relay lens 106 through the relay lens apertures 109 toward the telecentric aperture
  • the projection lens 110 collimates the light in a plane perpendicular to the length of the telecentric slit 108, as shown in FIG. 6, the same is not true in a plane aligned with the length of the slit
  • OMPI 108 as shown in FIG. 7, where the reason for orienta ⁇ tion of the filament 104 of the light source 102 par ⁇ allel to the telecentric slit 108 becomes more clear.
  • a ray of light 131 from a central portion of the fila- ment 104 is transmitted in a straight line through the relay lens 106, the aperture 116 of the chopper disc 114, the slit 108, and the projection lens 110 to the target surface 112.
  • FIGS. 6 and 7 are schematic views of the optical " system of the position-determining apparatus in two respective orthogonal planes whose intersection coincides with the optic axis of the apparatus and which planes are also mutually orthogonal with the plane of the target surface 112.
  • the plane of FIG. 6 is perpendicular to the slit 108, the filament 104, the receiver reflector 118 and reference reflector 126 and is also parallel to the direction of movement of the projected light pattern generated by the apertures 116 in the moving disc 114.
  • the projection system is tele- centric in the plane of FIG. 6 (but need not be so in the plane of FIG.
  • FIG. 6 the depth-of-field and linearity of the system is increased, though at the expense of light throughput (or luminance) .
  • light throughput or luminance
  • the system for the system to have maxi ⁇ mum useful measurement range and linearity it must be telecentric in this plane.
  • max ⁇ imum light throughput in those applications such as the one referred to previously, in which there is measure ⁇ ment of a moving strip of material, the optical system
  • OMPI must not be telecentric in the plane (shown in FIG. 7) which is perpendicular to the direction of motion of the moving light pattern.
  • the optimum width of the moving light pattern, in the direction perpendicular to its direction of movement, is dependent on the particular application of the system. For example, if area measurement rather than line measurement is desired, then the opening of the aperture 109 is configured to correspond to that of the area desired to be measured. In a particular application where the point of interest is the measure ⁇ ment of the target surface along one axis (i.e., a line measurement as opposed to an area measurement extending in two orthogonal directions) , then the aperture open- ing 109 may be configured to be relatively narrow, in the form of a slit. For example, a particular applica ⁇ tion of the latter would be in using the system to mon ⁇ itor the thickness of moving material.
  • the alternative embodiment 100 as con ⁇ trasted with the previously-described embodiment 10, instead of there being a separate receiver objective lens and apertures the image of the scanning pattern of light as projected onto the target surface 112 is viewed through the projection lens 110 itself, by the use of a receiver reflector 118 located adjacent to the telecentric slit 108.
  • the receiver reflector 118 reflects the image toward a receiver photoelectric sensing device 122 used to produce a receiver electrical signal.
  • a reflector of a different shape could be used, a planar
  • OMPI receiver reflector 118 has the advantage of simplicity of construction, facilitating production of multiple units of the apparatus 100 of the invention having sim ⁇ ilar range measuring characteristics without the neces- sity for complex adjustment of location of the lenses and reflectors, and without requiring extremely close tolerances for the focal lengths of the lenses used.
  • the width 123 of the receiver reflector 118 may pref ⁇ erably be equal to the width 113 of the slit 108 in the focal plane of the projection lens 110, thereby causing the receiver portion of the system to be telecentric in the same manner and to the same degree as the projec ⁇ tion portion of the system.
  • the plane of the receiver reflector 118 is aligned parallel to slit 108 and angled with respect to the path of light received from the target surface 112 in order to reflect the light toward the receiver photoelectric sensing device 122 which is located conveniently with respect to the remainder of the apparatus.
  • a receiver mask 124 interposed between the receiver reflector 118 and the receiver photoelectric sensing device 122 is located in the path of the light reflected on the receiver reflector 118, the distance between the receiver mask 124 and the receiver * reflec- tor 118 being equal to the distance from the chopper wheel 114 to the telecentric slit 108, so that a re ⁇ ceiver mask 124 having apertures 125 of the same size and spacing as the apertures 116 of the chopper disc 114 will permit the complete reflected image of the projected scanning pattern of light to be incident upon the receiver photoelectric sensing device 122 only at a particular phase of the scanning cycle determined by the displacement of the target surface 112 from a reference location.
  • a planar reference reflector 126 which is preferably similar to the receiver reflector 118 is located preferably on the opposite side of the tele ⁇ centric slit 108 from the receiver reflector 118, to
  • OMPI similarly reflect another image of the projected pat ⁇ tern of light to a reference photoelectric sensing device 128.
  • a reference mask 129 is located adjacent to the apertures 130 to produce a reference electric signal for comparison with the receiver electric signal in the manner described in connection with the pre ⁇ viously described scanner 10.
  • Displacement of the target surface 112 from the position shown in FIGS. 6 and 7 in solid line toward the position shown in phantom line generates a change in the phase relationship between the signals developed respectively in the reference and receiver photoelectric sensing devices 122 and 128.
  • a non-reflective strip 134 (FIG. 10) about 0.1 inch (2.54mm) wide, for exam- pie, is located extending across the diameter of the projection lens 110 parallel with the aperture 109.
  • a pair of fiber optic light pipes 136 and 138 are
  • OMPI positioned in front of the non-reflective strip 134 to receive a portion of the projected scanning pattern of light and provide corrective signals 180 degrees out of phase relative to the resultant spurious signal, and of equal amplitude, thus cancelling the effect of the spurious signal on the photoelectric sensing devices 122 and 128.
  • the desired effect is obtained by ad ⁇ justing the position of the receiving end 140 of the light pipe 136, the end near the projection lens 110, to adjust the phase of the feedback, and positioning the other, or transmitting end 192 of the light pipe 136 to limit the amount of light projected from the light pipe onto the photoelectric sensing device 122.
  • the receiving end 144 and transmitting end 146 of the light pipe 138 are positioned to provide a compensating light signal to the photoelectric sensing device 128.
  • the location of the reflectors 118 and 126 adjacent to the telecentric aperture, or slit, permits the angle ⁇ between the receiver axis 132 and the ref ⁇ erence axis 135 to be smaller than is possible using a separate receiver lens and aperture assembly 58 as in the previously-described embodiment 10.
  • a greater range of target surface positions may be measured within a total phase angle shift of less than 360 degrees between the receiver and reference electrical signals, since the tangent of the angle ⁇ is reduced and a greater distance of motion toward or away from the apparatus 100 is required to cause a given shift in the apparent location of the image of the pattern of light as viewed along the receiver axis 132.
  • OMPI angle ⁇ is, then, the angle between the reference axis and the receiver axis.
  • the angle ⁇ is thus twice the angle ⁇ between the receiver axis and the projection axis.
  • the angle ⁇ is smaller in this embodiment than is possible with the apparatus of the first described embodiment of the invention, because the light is both projected and received through a single lens, eliminat- ing the necessity for a large angle g to avoid physical interference between the projection lens assembly and the receiver lens assembly.
  • the problems of adjust ⁇ ment of lens positions in order to achieve a desired level of accuracy are largely eliminated.
  • the accuracy of the focal length of the projection lens is critical, as much as 5% variation of the focal length of the relay lens 106 can be tolerated without requir ⁇ ing relocation of the relay lens 106 or the light source 102 relative to the aperture 108.
  • the positions of the receiver and reference masks and photoelectric sensing devices may likewise be predetermined and manufactured mechani ⁇ cally.
  • Provision, then, of a projection lens 110 whose focal length is determined within less than 1% of error permits production of a plurality of measuring devices embodying the present invention within 1% optical error tolerance. While the image of the incandescent fila ⁇ ment 104 of the light source 102 may not be focused precisely on the telecentric slit 108 if the focal length of the relay lens 106 is not precisely accurate, the major disadvantage of an inaccuracy of the focal length of the relay lens 106 is a reduction in the intensity of the received light signal.
  • FIGS. 11-13 Exemplary electronic circuits usable in con- junction with eithe.r of the scanner embodiments 10 or 100 are shown schematically in FIGS. 11-13 and consist of three main sections: the receiver (FIG. 11), the flutter compensator (FIG. 12) and the phase detector (FIG. 13).
  • the receiver circuit 77 including the photo ⁇ electric sensors 122 and 128, detects the reference and receiver light beams, converts them to electrical sig ⁇ nals which are then filtered, amplified and converted into square wave forms respectively.
  • the flutter com ⁇ pensator 79 then processes the two receiver circuit output signals to remove any flutter (as previously described) therein that would otherwise cause erroneous indications of target surface position values.
  • the phase detector 80 takes the two respective flutter com ⁇ pensated reference and receiver signals, compares them to obtain the net phase difference between them and generates as an output a voltage level which is repre- sentative of the position of the target surface.
  • R41, R42 Resistor 100 ohms

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  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Length Measuring Devices By Optical Means (AREA)

Abstract

Procédé et appareil pour déterminer l'emplacement d'une surface cible (14) en projetant un diagramme de balayage périodique de lumière sur la surface cible (14) et en comparant le temps de projection sur un point prédéterminé du diagramme le long d'un chemin prédéterminé avec le temps d'observation d'une image du point prédéterminé du diagramme réfléchie le long d'un chemin de réception d'intersection. On fait tourner un disque comportant des ouvertures (30) entre une source de lumière (22) et un montage de lentille de projecteur de collimation (28) afin d'obtenir un diagramme de balayage de lumière. Des détecteurs photo-électriques (40, 76) envoient des signaux électriques de référence et de récepteur en réponse à la projection et à la réception du diagramme de lumière et il est possible de déterminer électriquement la distance entre la surface cible et un emplacement de référence comme une fonction définie géométriquement de l'angle de phase entre les signaux électriques. Dans un mode de réalisation, le diagramme de balayage de lumière est à la fois projeté et reçu par une simple lentillede projection (110), rendant possible une petite séparation angulaire entre le chemin de projection et le chemin de réception, ce qui permet de prendre les mesures de toute une série d'emplacements de la surface cible avec une variation d'angle de phase inférieure à 360o.
PCT/US1983/000185 1983-02-14 1983-02-14 Procede et appareil pour determiner la position optique d'un faisceau analyseur WO1984003142A1 (fr)

Priority Applications (2)

Application Number Priority Date Filing Date Title
PCT/US1983/000185 WO1984003142A1 (fr) 1983-02-14 1983-02-14 Procede et appareil pour determiner la position optique d'un faisceau analyseur
EP19830901124 EP0137772A1 (fr) 1983-02-14 1983-02-14 Procede et appareil pour determiner la position optique d'un faisceau analyseur

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Cited By (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1987007008A1 (fr) * 1986-05-10 1987-11-19 Robert Bosch Gmbh Machine-outil, de preference perceuse
DE3831217A1 (de) * 1988-09-14 1990-03-22 Zeiss Carl Fa Verfahren und vorrichtung zur topometrischen erfassung der oberflaechengestalt eines auges
EP0498495A1 (fr) * 1991-02-06 1992-08-12 Koninklijke Philips Electronics N.V. Dispositif pour la mesure optique de la hauteur d'une surface

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Publication number Priority date Publication date Assignee Title
US3671726A (en) * 1969-05-23 1972-06-20 Morvue Inc Electro-optical apparatus for precise on-line measurement of the thickness of moving strip material
US3783270A (en) * 1971-05-19 1974-01-01 Olympus Optical Co Focus indicating devices
US3951548A (en) * 1974-07-22 1976-04-20 Baird-Atomic, Inc. Electro-optical fourier vernier device
US4125025A (en) * 1976-01-21 1978-11-14 Fuji Photo Optical Co., Ltd. Instrument for measuring the amplitude of vibration of a vibrating object
US4158507A (en) * 1977-07-27 1979-06-19 Recognition Equipment Incorporated Laser measuring system for inspection
US4171160A (en) * 1976-11-03 1979-10-16 Dr. Johannes Heidenhain Gmbh Distance measuring instrument
US4212073A (en) * 1978-12-13 1980-07-08 Balasubramanian N Method and system for surface contouring

Patent Citations (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3671726A (en) * 1969-05-23 1972-06-20 Morvue Inc Electro-optical apparatus for precise on-line measurement of the thickness of moving strip material
US3671726B1 (fr) * 1969-05-23 1984-02-21
US3783270A (en) * 1971-05-19 1974-01-01 Olympus Optical Co Focus indicating devices
US3951548A (en) * 1974-07-22 1976-04-20 Baird-Atomic, Inc. Electro-optical fourier vernier device
US4125025A (en) * 1976-01-21 1978-11-14 Fuji Photo Optical Co., Ltd. Instrument for measuring the amplitude of vibration of a vibrating object
US4171160A (en) * 1976-11-03 1979-10-16 Dr. Johannes Heidenhain Gmbh Distance measuring instrument
US4158507A (en) * 1977-07-27 1979-06-19 Recognition Equipment Incorporated Laser measuring system for inspection
US4212073A (en) * 1978-12-13 1980-07-08 Balasubramanian N Method and system for surface contouring

Cited By (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1987007008A1 (fr) * 1986-05-10 1987-11-19 Robert Bosch Gmbh Machine-outil, de preference perceuse
JPH01502411A (ja) * 1986-05-10 1989-08-24 ローベルト ボツシユ ゲゼルシヤフト ミツト ベシユレンクテル ハフツング 手持工具、有利にはドリル
DE3831217A1 (de) * 1988-09-14 1990-03-22 Zeiss Carl Fa Verfahren und vorrichtung zur topometrischen erfassung der oberflaechengestalt eines auges
EP0498495A1 (fr) * 1991-02-06 1992-08-12 Koninklijke Philips Electronics N.V. Dispositif pour la mesure optique de la hauteur d'une surface

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