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WO1988002845A1 - Sonde optique - Google Patents

Sonde optique Download PDF

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Publication number
WO1988002845A1
WO1988002845A1 PCT/GB1987/000748 GB8700748W WO8802845A1 WO 1988002845 A1 WO1988002845 A1 WO 1988002845A1 GB 8700748 W GB8700748 W GB 8700748W WO 8802845 A1 WO8802845 A1 WO 8802845A1
Authority
WO
WIPO (PCT)
Prior art keywords
light
optical probe
probe according
path
focus
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.)
Ceased
Application number
PCT/GB1987/000748
Other languages
English (en)
Inventor
David Roberts Mcmurtry
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.)
Renishaw PLC
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 WO1988002845A1 publication Critical patent/WO1988002845A1/fr
Anticipated expiration legal-status Critical
Ceased legal-status Critical Current

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
    • G01B11/002—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates
    • G01B11/005—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates coordinate measuring machines
    • G01B11/007—Measuring arrangements characterised by the use of optical techniques for measuring two or more coordinates coordinate measuring machines feeler heads therefor
    • 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
    • G01B11/26—Measuring arrangements characterised by the use of optical techniques for measuring angles or tapers; for testing the alignment of axes

Definitions

  • This invention relates to optical probes.
  • Optical probes are known for use on position determining apparatus such as co-ordinate measuring machines (CMMs) and machine tools. Such probes are used to sense the position of a surface of a workpiece along a measurement axis of the probe, in order to measure or inspect it for dimensional accuracy. Examples are shown in patent specifications GB 2,183,418, WO 87/01886 (both published after the priority date of the present application) and WO 83/00216.
  • the present invention provides an optical probe comprising: a light source; means for focussing light from the light source in the vicinity of a first point on a workpiece surface; ⁇ eans for deflecting the path of the light whereby to focus it in the vicinity of a second point on the workpiece surface, adjacent the first; and means for detecting the light reflected from the surface and for determining therefrom the positions of the first and second points.
  • Fig. 1 is a diagrammatic vertical elevation of an optical probe
  • Fig. 2 is a plan view of a mounting arrangement for such a probe
  • Figs. 3 and 4 are sections on the lines III-III and IV-IV in Fig. 2,
  • Fig. 5 is a plan view of another mounting arrangement
  • Figs.6,7 and 8 are diagrammatic elevations of parts of three further probes.
  • Fig. 9 is a plan view of a modification of Fig. 8.
  • an optical probe 10 comprising a light source 12 such as a laser diode, a lens 14 for producing a parallel beam of light, and a lens 16 for focussing the light as a spot 18 on a workpiece surface 20.
  • the light source 12 and lenses 14,16 are arranged within a housing 42 along an optical axis 22 of the probe, which will be referred to as its Z axis.
  • the image of the spot of light 18 passes back through the lens 16 and is reflected by a beam splitter 24 to a detection system comprising a lens 26 and a beam dividing 'V prism 27 which focuses the image onto a pair of position-sensitive detectors 28A.28B.
  • Each detector 28A.28B gives an indication of the degree to which the spot 18 is in or out of focus, in a manner well understood from compact disc technology (e.g. see European Patent Application EP-0, 177, 108-A) .
  • the detector outputs are combined differentially in a differential amplifier 80.
  • either the whol assembly 12, 14, 16, 24, 26, 27, 28A, 28B, or just the lens 16 may be translatable in the Z direction, e.g. by a probe mounted servo motor 29.
  • a probe mounted servo motor 29 Preferably just the len 16 is thus translatable, since this reduces the inerti of the system and therefore increases its frequency response.
  • the lens 16 may be replaced by a holographic film reproduction of such a lens.
  • the detectors 28A.28B act on the servo motor 29 in a closed loop via the amplifier 80 for Z-axis movement, tending to keep the spot 18 focussed on the surface 20.
  • Such a system is described in more detail in patent specification GB 2,183,418.
  • the amount of Z-axis movement required to keep the spot in focus is sensed by a sensor 82, from which a position determination circuit 84 calculates the Z-axis positio of the surface 20 from the probe. Readings of this quantity are taken when required by a computer 86 whic controls the operation of a CMM or machine tool in which the probe is mounted, in a conventional manner.
  • the circuit 84 may determine the Z-axis position from the servo signal supplied to the servo motor 29 in order to keep the spot 18 in ocus.
  • a parallel-sided plate 30 of a refractive medium e.g. glass.
  • the plate 30 When the plate 30 is in the position shown in full lines in Fig. 1, it has no effect on the light, which passes straight through it undeflected. However, it can be tilted about a Y axis 36 to a position as shown (greatly exaggerated) in dashed lines, in which the light beam, both on the outward and return parts of its path, is deflected to follow a path 32, parallel to th Z-axis 24, to focus at an adjacent spot 18' .
  • Tilting the plate 30 in the opposite direction caused the beam to be deflected along a path 34 to focus at a spot 18".
  • the tilting i performed by a motor system 88 under the control of th computer 86.
  • the system 88 includes a feedback to the computer representing the degree of tilting, and thus the amount of X-axis deflection of the light beam. As this tilting occurs, the detectors 28A,28B and motor 2 keep the spot in focus, and readings are taken by the computer 86 of the Z-axis motion needed for this.
  • Calculation of the local slope of the surface is then straightforward.
  • the calculation is performed by the computer 86, and can include compensation for the change in path length caused by the tilting of the plate 30. It will be appreciated that very little tilting of the plate 30 is needed to produce a measurable effect from which the slope can be determined.
  • the plate 30, as well as being tiltable about the Y-axis 36 may if desired also be tiltable in a similar manner about an X-axis 38, giving full information about the slope in both X and Y directions at point 18.
  • Figs. 2,3 and 4 show a gi bal mounting arrangement for the plate 30 to enable the tilting motion.
  • a gimbal ring 40 is pivotably mounted to the housing 42 of the probe by pivot pins 44, and can be tilted about those pins by motors 46 (as shown by the arrows through the motors 46 in Fig. 4).
  • the plate 30 is provided insid the gimbal ring, pivotably mounted to it (at a location 90° removed from the pins 44) by pivot pins 48, and c be tilted about those pins by motors 50 (as indicated by the arrows in Fig. 3).
  • the motors 46,50 may be bi orph piezo motors, or they may operate magneticall in the manner of a solenoid.
  • Fig. 5 shows an alternative mounting arrangement for the plate 30.
  • a leaf spring 52 is mounted to the housing 42, and has three limbs 54 extending in a partly circumferential direction. Three corners of a triangular version of the plate 30 are attached to th free ends of the limbs 54. These three corners can each independently be driven in the direction of the Z-axis 22 by a respective motor 56, secured between t housing and the plate 30.
  • the motors 56 may be solenoid motors.
  • the limbs 54 may be the form of biomorph piezo motors, with no separate motors 56.
  • Fig. 6 shows an alternative to the glass plate 30.
  • T oblique parallel mirrors 58 are mounted in a ring 60. Tilting of the ring in the sense shown by the arrows causes the axis of the beam of the light to shift as shown by dotted lines 62.
  • one of the mirrors 58 may be moved independently (e.g. in a horizontal direction away from or towards the other) t achieve the same effect.
  • this arrangement requires further mirrors or a more complicated mountin arrangement to achieve tilting in both X and Y directions, and if only one mirror is moved, the probe reading must be adjusted to compensate for the increased or decreased path length of the light thereb caused .
  • Fig. 7 shows an arrangement which can be used to inspect relatively inaccessible surfaces, e.g. inside bore.
  • the light beam is internally reflected through 90° by a prism 64.
  • the prism may be rotated about the Z-axis 22 to take measurements at points circumferentially at either side of the point 18, to inspect for deviations of concentricity of the bore. It may also be tilted about a horizontal axis, or translated horizontally or vertically, to cause this spot 18 to move vertically (i.e. parallel to the Z-axis) to inspect the slope of the surface 20 in that sense.
  • the probe output should be compensated for such motion where it would alter the path length o the light.
  • Fig. 8 shows an arrangement similar to Figs. 2 to 4.
  • the plate 30 is fixedly mounted at a swash angle in a horizontal ring 66.
  • the ring 66 is rotatable on the housing 42 about the Z-axis 22, by means of bearings 70, driven by a conventional servo or stepping motor 68.
  • this rotation is carried ou under the control of the computer 86, with feedback of angular position to the computer.
  • the swashed plate 30 causes the spot 18 to describe an orbit on the surface of the workpiece, the centre of the orbit being the true axis 22 of the probe.
  • the drive may be continuous, or it may be stepped to particular points at which measurements are required. In either case, measurement can be take at various points around the orbit, and the measuremen position of the true centre of the orbit determined by interpolation in the Z direction. The slope can be determined as a vector normal to an elemental plane which is a best fit to the points measured. Travellin in an orbit in this manner is an efficient way of taking the required readings in a short time, and can also be done by the probes of the previous embodiments
  • the motors 46,50 of Figs. 2 to 4 can each be driven by a sinusoidal current, at 90° to those of its nearest neighbours.
  • the motors 56 of Fig. 5 can b driven by sinusoidal currents at 120° . Either three o four readings around the circle will generally be sufficient. In any of these cases, for continuous rotation, the frequency response of the servo system 28A,28B,80,29 should be faster than the speed of rotation, to ensure that the spot 18 remains in focus.
  • the bearings 70 may be air bearings. As shown in
  • th ring 66 in place of the servo or stepping motor 68, th ring 66 may be driven around by a tangential air blast from a nozzle 94 onto suitable projecting blades 90.
  • a marker on the ring by means of which its angular position may be determined, so that the computer is able to work out the orientation of the calculated slope about the Z-axis.
  • a suitable marker would be a white stripe, detected by a photo detector on the housing; or a magnetic marker may be used; or a detector 92 may detect the passing blades 90 and feed a count back to the computer (one of the blades being thicker than the others to provide a reference).

Landscapes

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

Abstract

La sonde optique décrite comprend une source lumineuse (12) et un système de lentilles (14, 16) servant à focaliser un point lumineux (18) sur une surface (20) d'une pièce à usiner. Un système détecteur (26, 27, 28A, 28B) détermine si le point est focalisé et un servo-moteur (29) entraîne la lentille (16) dans un sens axial afin de le maintenir dans un état focalisé. Le mouvement axial nécessaire à cette opération est détecté par un capteur (82) qui fournit une mesure de la position axiale de la surface (20). Afin de mesurer la déclivité de la surface (20), on peut incliner une plaque réfractive (30) qui déviera le faisceau lumineux pour le focaliser en des points adjacents (18', 18'').
PCT/GB1987/000748 1986-10-20 1987-10-20 Sonde optique Ceased WO1988002845A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
GB868625053A GB8625053D0 (en) 1986-10-20 1986-10-20 Optical probe
GB8625053 1986-10-20

Publications (1)

Publication Number Publication Date
WO1988002845A1 true WO1988002845A1 (fr) 1988-04-21

Family

ID=10606009

Family Applications (1)

Application Number Title Priority Date Filing Date
PCT/GB1987/000748 Ceased WO1988002845A1 (fr) 1986-10-20 1987-10-20 Sonde optique

Country Status (2)

Country Link
GB (1) GB8625053D0 (fr)
WO (1) WO1988002845A1 (fr)

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4212438A1 (de) * 1992-04-14 1993-10-21 Dirk Prof Dr Ing Jansen Anordnung zur Erzeugung eines lateralen Strahlversatzes bei Vorrichtungen zur trigonometrischen Distanzmessung
NL1003175C2 (nl) * 1996-05-21 1997-11-25 Wilhelmus Petrus Van Vliet Mechanisch tastsysteem voorzien van een contactloos meetsysteem dat 6 vrijheidsgraden kan meten voor gebruik in coördinaten meetmachines, gereedschapsmachines en robots, geschikt om met hoge snelheid geometrische eigenschappen van werkstukken te bepalen.
US5880465A (en) * 1996-05-31 1999-03-09 Kovex Corporation Scanning confocal microscope with oscillating objective lens
US6674058B1 (en) 2000-09-20 2004-01-06 Compucyte Corporation Apparatus and method for focusing a laser scanning cytometer
US10545019B2 (en) 2015-04-14 2020-01-28 Hexagon Metrology, Inc. CMM probe path controller and method

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3520607A (en) * 1967-10-17 1970-07-14 Hughes Aircraft Co Phase sensing laser contour mapper
GB1591462A (en) * 1978-05-30 1981-06-24 Plessey Co Ltd Grain slope measuring apparatus
US4325639A (en) * 1980-02-04 1982-04-20 H. A. Schlatter Ag Method for measuring distances and apparatus for performing the method

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3520607A (en) * 1967-10-17 1970-07-14 Hughes Aircraft Co Phase sensing laser contour mapper
GB1591462A (en) * 1978-05-30 1981-06-24 Plessey Co Ltd Grain slope measuring apparatus
US4325639A (en) * 1980-02-04 1982-04-20 H. A. Schlatter Ag Method for measuring distances and apparatus for performing the method

Cited By (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE4212438A1 (de) * 1992-04-14 1993-10-21 Dirk Prof Dr Ing Jansen Anordnung zur Erzeugung eines lateralen Strahlversatzes bei Vorrichtungen zur trigonometrischen Distanzmessung
NL1003175C2 (nl) * 1996-05-21 1997-11-25 Wilhelmus Petrus Van Vliet Mechanisch tastsysteem voorzien van een contactloos meetsysteem dat 6 vrijheidsgraden kan meten voor gebruik in coördinaten meetmachines, gereedschapsmachines en robots, geschikt om met hoge snelheid geometrische eigenschappen van werkstukken te bepalen.
US5880465A (en) * 1996-05-31 1999-03-09 Kovex Corporation Scanning confocal microscope with oscillating objective lens
US6674058B1 (en) 2000-09-20 2004-01-06 Compucyte Corporation Apparatus and method for focusing a laser scanning cytometer
US10545019B2 (en) 2015-04-14 2020-01-28 Hexagon Metrology, Inc. CMM probe path controller and method

Also Published As

Publication number Publication date
GB8625053D0 (en) 1986-11-26

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