WO1988002846A1 - Sonde de mesurage optique - Google Patents

Sonde de mesurage optique Download PDF

Info

Publication number
WO1988002846A1
WO1988002846A1 PCT/GB1987/000746 GB8700746W WO8802846A1 WO 1988002846 A1 WO1988002846 A1 WO 1988002846A1 GB 8700746 W GB8700746 W GB 8700746W WO 8802846 A1 WO8802846 A1 WO 8802846A1
Authority
WO
WIPO (PCT)
Prior art keywords
probe
light beam
lens
focus
focal point
Prior art date
Application number
PCT/GB1987/000746
Other languages
English (en)
Inventor
David Roberts Mcmurtry
Original Assignee
Renishaw Plc
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 Renishaw Plc filed Critical Renishaw Plc
Publication of WO1988002846A1 publication Critical patent/WO1988002846A1/fr

Links

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
    • G01B11/026—Measuring arrangements characterised by the use of optical techniques for measuring length, width or thickness by measuring distance between sensor and object

Definitions

  • the present invention relates to optical probes for use in making measurements of surfaces.
  • An object of the present invention is to provide a simplified laser scanning system with the capability of making limited measurements of the surface, and which avoids the need for a servo-system to measure the lens movement.
  • the focal point of the light beam will oscillate between known points above and below the surface as the surface moves through the beam, by detecting the instants in the cycle of the oscillations when the focussed spot at the focal point of the light beam coincides with the plane of the surface, the height of the surface at the position of such coincidence can be determined relative to any previous position.
  • the advantage of such a system is that only a relatively simple focus detection circuit is required to detect the in-focus condition of the spot, and no high speed servo-system is needed to keep the spot in focus.
  • the light beam is preferably collimated or is a coherent light beam from a laser beam generator.
  • Fig. 1 shows diagrammatically the layout of the components of the optical measuring probe and focus detector module of the present invention
  • Fig. 2 shows the focus error signal produced by the focus detection circuit
  • Fig. 3 is an electric circuit diagram illustrating the electrical components required for converting the detector signals of Fig. 1 into measurement information
  • Figs. 4a to 4c shows the wave form diagrams of some of the electrical components shown in Fig. 3, and
  • Fig. 5 shows diagrammatically the system on the spindle of a co-ordinate measuring machine.
  • Fig. 1 there is shown an optical measuring probe having a housing 2 within which is mounted a laser beam generator 10 of any convenient type e.g. a semi-conductor laser.
  • the laser beam generator includes a lens 14 which produces a coherent beam 12 which is directed to a half-silvered mirror 16. From the mirror the beam 12 passes through a second lens system 18 which focusses it down to a very small spot adjacent to the surface 20 to be measured.
  • Detector module 22 includes a focussing lens 24, a prism 25, a photo-diode detector array 26 and a focus detection circuit 27.
  • the photo-diode detector array 26 produces an output in dependence on the amount of light falling on it from the mirror.
  • the reflected light from the mirror 8 is focussed by the lens 24 onto the plane of the photo-diode array and passes through the prism 25 which splits it into two beams directed towards two specific pairs of photo-diode detctors A,B and C,D within the array.
  • the lens system 18 comprises a lens 19 which is mounted from the housing 2 of the probe by means of a planar spring 32.
  • the spring 32 provides support for the lens against transverse or rotational movement, but allows movement , o take place in a direction axially of the beam 12 within a limited range.
  • Such movement is provided by a drive mechanism of any convenient type, e.g. a piezo electric mechanism, or as shown in the Figure, an electro-magnetic device, consisting of a ring magnet
  • the focus detector module 22 determines when the focal spot is coincident with the surface 20 as will be described below with reference to Fig. 3.
  • the range of vertical movement of the lens, and hence of the focussed spot can be pre-determined by a suitable choice of spring and magnetic drive.
  • the frequency of the oscillator is 50 cycles per second and the range of movement of the focussed spot is +100 microns then the spot will move 200 microns in one fiftieth of a second and will be focussed on the surface 20 twice in that period.
  • the surface does not move, or has no variation in height, and if the probe is initially set up so that the spot is focussed on the surface in the centre of the range of movement of the lens, i.e. in the undeflected state of the spring, the two signals from the detector as the spot focusses twice will occur half-way through and at the end of each cycle of the oscillation respectively. Where a change in height of the surface occurs, the signals will occur either earlier or later in the cycle, and a timing device in a processing part of the probe electrical circuit will enable that position to be determined as will be described hereinafter with reference to Fig 3.
  • the components of the focus detector module 27 are arranged such that when the light beam 12 is focussed onto the surface 20, with the spring 16 in its central, i.e. unstrained position, the reflected light will be focussed towards the spaces between the photo-diodes A,B and C,D in each pair.
  • the light spots formed by the prism in the spaces are arranged, in this focussed condition, to equally overlap the edges of the two detectors A,B and C,D on each side of the respective spaces.
  • the two beams leaving the prism 25 will become more or less divergent, and the spots formed by them on the photo-diode pairs will both move either more towards the outer two detectors A and D, or towards the inner two detectors B and C.
  • the result is that the amount of light received by the outer two detectors A and D will either increase or decrease and at the same time the amount of light received by the inner two detectors B and C will respectively decrease or increase.
  • the outputs of the outer two detectors A and D are connected at a summing junction 40, and the outputs of the inner two detectors B and C are connected at a summing junction 41.
  • the outputs of the two summing junctions 40 and 41 are subtracted at a further junction 42 which pro ' Jerusalem an output 43 in the form shown by the curve 44 of Fig. 2.
  • the distance x, between the two peaks of the curve, gives the working range of the detector as the focal point of the light beam 12 moves up and down, and the amplitude of the peaks y, gives a focus error signal.
  • a zero-crossing detector circuit 45 (known per se) is used to determine the point 0 on curve 44 in the working range of the detectors at which the difference in the outputs of the outer and inner detectors is zero, which indicates that the beam 12 is focussed on the surface 20.
  • the zero-crossing detector circuit produces an output 46 in the f+orm of a pulse every time a zero-crossing is detected.
  • the optical measuring probe in operation will often be outside the working range x of the focus detectors, since this is limited to a few microns of relative movement between the surface 20 and the probe.
  • the reflected light becomes more diffused, and the spots formed by the prism 25 on the detector pairs A,B and C,D become rapidly larger and less intense until they cover both detectors, and the difference signal from junction 42 tends to zero. This would give a false trigger signal from the zero crossing detector at point xi or X2 outside the working range of the detectors.
  • a validating circuit is introduced into the focus detection circuit and which is arranged to determine when the zero-crossing point on curve 44 lies inside the working range of the detectors and outputs a signal accordingly.
  • a validating circuit is described in our co-pending UK application entitled “Focus Detection Circuit for use in Optical Measuring Systems” filed on 20 October 1987.
  • Those parts of the detector array 26 other than the focus detectors A,B C and D will be illuminated by light spilling around the focus detectors when the light spots generated by the prism become enlarged as the surface 20 moves away from focus.
  • the outputs of all of the remaining detectors i.e. except the focus detectors A,B C and D are connected together to form a single output G.
  • the remaining detectors are hereinafter collectively referred to as a guard detector 47.
  • the focus detector module will only operate correctly when the light from the prism forms two defined spots on the focus detector pairs A,B and C,D. If this is not the case, i.e. when the light beam 12 is far from beng focussed on the surface 20, the guard detector 47 and the focus detector pairs will be weakly illuminated by the received light.
  • the ratio of the signals from the guard detector and the sum of the signals from the detector pairs A,B and C,D will be proportional to the areas of the respective detectors.
  • a threshold ratio can be set at the level at which the focus detector pairs A,B and C,D are within their working range and a validation signal generated when this level is reached. Only those zero-crossing signals developed while the validation signal is present will then be sent to the machine as true measurement signals.
  • Fig. 3 the part of the focus detection circuit for providing the validation signal is shown as including a divider 52 which receives the output G from the guard detector as a first input, and the sum of the ouputs of the four focus detectors A,B, C and D via a summing junction 54 as a second input F.
  • the divider provides ' an output VR equal to the ratio of inputs G:F.
  • the output VR of the divider is passed to a comparator 56 which also receives a reference voltage V ref. and outputs the validation signal SV when the ratio G:F falls below the threshold value.
  • signals SV from the validation circuit and 46 from the zero-crossing detector are arranged to be positive and are passed to an AND gate 48 which produces a validated output pulse 49 from the detector module when signals SV and 46 are present at the same time.
  • the profile of the surface can be measured as follows:
  • the validated output pulse 49 of the focus detector module is fed to the scale reading apparatus on the measuring machine in a known manner to initiate reading and storing of the scale measurements.
  • the position of the surface in the x-y horizontal plane may be determined by reading the machine scales every time a validated detector output pulse is received and storing the readings in the machine memory.
  • the position of the probe is known in the vertical axis by reading the machine scale, and the position of the focussed spot in the undeflected state of the spring is determined in the x,y and z axes by an initial calibration of the machine with the probe fitted.
  • readings per second of the vertical position of the surface can be made using the validated output signal and on each occasion the x-y co-ordinates of the surface will be read from the machine scales.
  • the scale reading devices may be read at less frequent intervals, e.g. twenty times a second and the x,y measurement interpolated, if required, in between.
  • the timing of the in-focus signals from the focus detector module relative to the lens movement cycle is determined. That is whether or not the in-focus signals are occurring earlier or later in the cycle than previous signals.
  • Fig. 4a illustrates the movement of the focal spot relative to the surface 20, as the surface travels from right to left of the Fig. While the surface is level the in-focus points are evenly spaced at mid range of the movement of the lens.
  • Fig. 4b shows the frequency of the validated in-focus pulses 49 produced by the focus detection circuit and it can be seen that while the surface remains at a constant distance from the lens the pulses are evenly spaced. When the surface moves closer to the lens however, the pulses generated, during the upward movement of the lens are delayed while the pulses generated during the downward movement of the lens are early compared to the previous pulses.
  • the timing circuit shown in Fig. 3 determines the interval by which the pulses are early or late.
  • the oscillator 38 is arranged to provide a triangular wave form so that the relationship between the movement of the lens and time is linear.
  • the triangular waveform is converted to a square wave form in a convertor 58 and the period of the square wave is identical with the period of the triangular wave.
  • Fig. 4c shows the relationship of the square wave to the validated pulses coming from the focus detector circuit.
  • the rising and falling edges of the square wave are in time with the pulses when there is no relative movement between the surface and the probe.
  • a variation occurs.
  • the timing circuit 60 receives the square wave from converter 58 and a clock pulse 62 froa a clock pulse generator 63 with a frequency in the Mega Hertz range, and compares the relative timing of the rising edge of the square wave with the arrival of the detector pulse 49 and computes the time difference which is proportional to the relative movement.
  • ⁇ ma y De described as positive if the pulse appears before the rising edge and negative if it appears after the rising edge.
  • This value is passed to a micro processor 64 along with the reading of the vertical machine scale and an ouput provided which shows the position of the surface on the vertical Z co-ordinate axis.
  • the invention provides a scanning probe which is capable of measuring the position of a surface within certain limits without the need for a servo-system.
  • the error signal can be the signal ⁇ produced by the timing circuit which will be in digital form, and , where the machine has digital drive, can be passed directly to the machine drives. Otherwise the signal would be passed via an analogue to digital converter referenced 66 in Fig. 4 and an analogue signal sent to the machine.
  • the signal is made proportional to the size of the error / > T so that the greater the error the faster the machine will drive the spindle to restore the surface to the middle of the range of movement of the probe lens.
  • Fig. 5 shows diagra matically a machine spindle 70 on which the probe is mounted and a drive 72 adapted to receive the error signal 49 from the detector to move the spindle up or down as required.
  • a drive 72 adapted to receive the error signal 49 from the detector to move the spindle up or down as required.
  • the embodiment described above uses an oscillator to move the .lens system 18, it is clear that the necessaryy relative movement between the focal point of the light beam 12 and the surface 20 could be achieved by other means.
  • the laser beam generator 10 could be mounted for oscillating movement in which case the collimating lens 14 would need to be mounted on static structure in the probe housing separately from the laser body.
  • the probe housing itself including the detector system may be mounted within an outer housing for oscillating movement. If such a system is used then the probe may also be mounted in such a manner that it has the capability of moving the focal spot in the x and y directions of the co-ordinate measuring machine. To accomplish this the probe may, for example, be mounted on two pairs of parallel leaf springs in series, each pair of which may be driven in like manner to the lens drive system described above to provide a range of movement of say 100 microns in each of the two directions.
  • a mounting system of this type is described in relation to a different probe system in our co-pending patent application of the same date entitled "Position-Determining Apparatus".
  • Such a system would require two more detectors to provide signals depending on the position of the reflected spot in the x and y directions within the range of movement of the two drive systems.
  • Such x and y measurement capability would allow more accurate determination of the position of edge surfaces with very steep slopes which could be missed with a one-axis system described in detail above.
  • the detectors could be arranged to send error signals to the drive mechanisms of the co-ordinate measuring machine to enable the greater movements of the machine slides in the x and y directions to be added to the smaller movements of the electro-magnetic drive system of the probe.
  • the laser beam generator 10 and lens 14 are replaced by a system for producing a collimated light beam.
  • circuitry described in Fig. 4 may be incorporated within the probe housing 2.

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

Abstract

Dans une sonde de mesurage optique, un générateur de faisceau laser (10) produit un faisceau laser (12), qui est dirigé à travers un miroir semi-argenté (16) et un système de lentille de focalisation (18), afin de former un point focal adjacent à une surface (20) à mesurer. La lumière réfléchie par la surface (20) est déviée par le miroir semi-argenté (16) vers un module détecteur de foyer (22) qui détermine le moment où le point focal coïncide avec la surface. Pour permettre des mesures de la position de la surface, le système de lentille (18) comprend une lentille montée sur un ressort plan (32), afin de permettre qu'une oscillation à une fréquence présélectionnée sur une amplitude présélectionnée soit effectuée par un système de bobines électromagnétiques (34, 36) excité par un oscillateur (38), faisant ainsi passer le point focal à travers la surface (20). Le module détecteur de foyer produit un signal chaque fois que le point focal coïncide avec la surface. Les signaux ainsi produits sont envoyés à la machine sur laquelle est montée la sonde et les coordonnées des x, des y et des z des échelles de la machine sont lues et stockées chaque fois qu'un signal est reçu. Dès lors que la position de la sonde par rapport à l'axe de la machine est fixe et que la position de la lentille dans la sonde lorsque le ressort est dans son état non fléchi est également fixe, la position de la surface peut être déterminée avec précision et avec une fréquence élevée à des fins d'analyse par balayage. Afin d'accroître l'étendue d'action de la sonde, la présente invention décrit également un servo-système, qui sert à déplacer la sonde en un seul bloc en fonction des signaux produits à partir du circuit détecteur de foyer, ainsi qu'un circuit détecteur de foyer dont l'étendue d'action est accrue.
PCT/GB1987/000746 1986-10-20 1987-10-20 Sonde de mesurage optique WO1988002846A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB8625054 1986-10-20
GB868625054A GB8625054D0 (en) 1986-10-20 1986-10-20 Optical measuring probe

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WO1988002846A1 true WO1988002846A1 (fr) 1988-04-21

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Cited By (15)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0401909A1 (fr) * 1989-06-07 1990-12-12 Koninklijke Philips Electronics N.V. Procédé et dispositif pour déterminer la position d'une surface
WO1991003988A1 (fr) * 1989-09-22 1991-04-04 Peter Rohleder Dispositif pour la fabrication des protheses dentaires
DE3934744A1 (de) * 1989-10-18 1991-04-25 Krupp Gmbh Verfahren zur beruehrungslosen ermittlung der dicke transparenter werkstoffe und vorrichtung zur durchfuehrung des verfahrens
WO1991014923A1 (fr) * 1990-03-23 1991-10-03 Geotronics Ab Capteur a deplacement analogique
EP0505747A2 (fr) * 1991-03-23 1992-09-30 Parker-Prädifa GmbH Méthode et appareil pour la détermination du degré de vulcanisation d'élastomères
EP0646769A1 (fr) * 1993-10-05 1995-04-05 Sony Magnescale, Inc. Capteur de déplacement
EP0647835A2 (fr) * 1993-10-08 1995-04-12 Sony Magnescale, Inc. Dispositif de détection de déplacements
EP0877225A2 (fr) * 1997-03-12 1998-11-11 Brown & Sharpe Limited Appareil et dispositifs optiques pour la mesure de surfaces
US5880465A (en) * 1996-05-31 1999-03-09 Kovex Corporation Scanning confocal microscope with oscillating objective lens
US6185030B1 (en) 1998-03-20 2001-02-06 James W. Overbeck Wide field of view and high speed scanning microscopy
US6201639B1 (en) 1998-03-20 2001-03-13 James W. Overbeck Wide field of view and high speed scanning microscopy
WO2008109908A1 (fr) * 2007-03-14 2008-09-18 Alicona Imaging Gmbh Procédé et appareil de mesure de la topographie d'un échantillon
WO2012075013A1 (fr) 2010-11-30 2012-06-07 Johnson & Johnson Vision Care, Inc. Système de métrologie à capteur confocal à laser
US8810784B2 (en) 2012-02-10 2014-08-19 Johnson & Johnson Vision Care Inc. Method and apparatus for determining a thickness profile of an ophthalmic lens using a single point thickness and refractive index measurements
CN113433564A (zh) * 2020-03-06 2021-09-24 上海禾赛科技有限公司 激光雷达及使用激光雷达测距的方法

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3589815A (en) * 1968-06-21 1971-06-29 Information Dev Corp Noncontact measuring probe
US4355904A (en) * 1978-09-25 1982-10-26 Balasubramanian N Optical inspection device for measuring depthwise variations from a focal plane
DE3322712A1 (de) * 1983-06-24 1985-01-10 Daimler-Benz Ag, 7000 Stuttgart Optisches abstandsmessverfahren
US4527893A (en) * 1982-10-13 1985-07-09 Taylor Francis M Method and apparatus for optically measuring the distance to a workpiece
EP0198557A1 (fr) * 1985-04-15 1986-10-22 B.V. Optische Industrie "De Oude Delft" Procédé et dispositif de mesure du profil de la rugosité d'une surface

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3589815A (en) * 1968-06-21 1971-06-29 Information Dev Corp Noncontact measuring probe
US4355904A (en) * 1978-09-25 1982-10-26 Balasubramanian N Optical inspection device for measuring depthwise variations from a focal plane
US4527893A (en) * 1982-10-13 1985-07-09 Taylor Francis M Method and apparatus for optically measuring the distance to a workpiece
DE3322712A1 (de) * 1983-06-24 1985-01-10 Daimler-Benz Ag, 7000 Stuttgart Optisches abstandsmessverfahren
EP0198557A1 (fr) * 1985-04-15 1986-10-22 B.V. Optische Industrie "De Oude Delft" Procédé et dispositif de mesure du profil de la rugosité d'une surface

Cited By (27)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
EP0401909A1 (fr) * 1989-06-07 1990-12-12 Koninklijke Philips Electronics N.V. Procédé et dispositif pour déterminer la position d'une surface
WO1991003988A1 (fr) * 1989-09-22 1991-04-04 Peter Rohleder Dispositif pour la fabrication des protheses dentaires
DE3934744A1 (de) * 1989-10-18 1991-04-25 Krupp Gmbh Verfahren zur beruehrungslosen ermittlung der dicke transparenter werkstoffe und vorrichtung zur durchfuehrung des verfahrens
WO1991014923A1 (fr) * 1990-03-23 1991-10-03 Geotronics Ab Capteur a deplacement analogique
US5326982A (en) * 1990-03-23 1994-07-05 Geotronics Ab Analogue displacement sensor
EP0505747A2 (fr) * 1991-03-23 1992-09-30 Parker-Prädifa GmbH Méthode et appareil pour la détermination du degré de vulcanisation d'élastomères
EP0505747A3 (en) * 1991-03-23 1994-11-17 Parker Praedifa Gmbh Method and apparatus for the determination of the state of cure of elastomers
EP0646769A1 (fr) * 1993-10-05 1995-04-05 Sony Magnescale, Inc. Capteur de déplacement
US5475209A (en) * 1993-10-05 1995-12-12 Sony Magnescale Inc. Displacement measurement apparatus having first and second servo control circuits and a zone decision circuit
EP0647835A2 (fr) * 1993-10-08 1995-04-12 Sony Magnescale, Inc. Dispositif de détection de déplacements
EP0647835A3 (fr) * 1993-10-08 1996-11-06 Sony Magnescale Inc Dispositif de détection de déplacements.
US5880465A (en) * 1996-05-31 1999-03-09 Kovex Corporation Scanning confocal microscope with oscillating objective lens
EP0877225A2 (fr) * 1997-03-12 1998-11-11 Brown & Sharpe Limited Appareil et dispositifs optiques pour la mesure de surfaces
EP0877225A3 (fr) * 1997-03-12 2000-10-18 Brown & Sharpe Limited Appareil et dispositifs optiques pour la mesure de surfaces
US6181422B1 (en) 1997-03-12 2001-01-30 Brown & Sharpe Limited Optical surface measurement apparatus and methods
US7312919B2 (en) 1998-03-20 2007-12-25 Affymetrix, Inc. Wide field of view and high speed scanning microscopy
US6201639B1 (en) 1998-03-20 2001-03-13 James W. Overbeck Wide field of view and high speed scanning microscopy
US6335824B1 (en) 1998-03-20 2002-01-01 Genetic Microsystems, Inc. Wide field of view and high speed scanning microscopy
US6185030B1 (en) 1998-03-20 2001-02-06 James W. Overbeck Wide field of view and high speed scanning microscopy
WO2008109908A1 (fr) * 2007-03-14 2008-09-18 Alicona Imaging Gmbh Procédé et appareil de mesure de la topographie d'un échantillon
WO2012075013A1 (fr) 2010-11-30 2012-06-07 Johnson & Johnson Vision Care, Inc. Système de métrologie à capteur confocal à laser
CN103229035A (zh) * 2010-11-30 2013-07-31 庄臣及庄臣视力保护公司 激光共焦传感器计量系统
US8953176B2 (en) 2010-11-30 2015-02-10 Johnson & Johnson Vision Care, Inc. Laser confocal sensor metrology system
CN103229035B (zh) * 2010-11-30 2016-09-07 庄臣及庄臣视力保护公司 激光共焦传感器计量系统
US8810784B2 (en) 2012-02-10 2014-08-19 Johnson & Johnson Vision Care Inc. Method and apparatus for determining a thickness profile of an ophthalmic lens using a single point thickness and refractive index measurements
CN113433564A (zh) * 2020-03-06 2021-09-24 上海禾赛科技有限公司 激光雷达及使用激光雷达测距的方法
CN113433564B (zh) * 2020-03-06 2023-05-23 上海禾赛科技有限公司 激光雷达及使用激光雷达测距的方法

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