United States Patent r191
`Granger et al.
`
`[54] POSITION-MARKING METHOD FOR A
`MACHINE THAT MEASURES IN THREE
`DIMENSIONS, AND APPARATUS FOR
`IMPLEMENTING THE METHOD
`
`[75]
`
`Inventors: Romain Granger, Montoire, France;
`Homer Eaton, Carlsbad, Calif.
`
`[73] Assignee: Romer, Montoire, France
`
`[21] Appl. No.: 308,304
`
`[22] Filed:
`
`Sep. 19, 1994
`
`[30]
`
`Foreign Application Priority Data
`
`[FR]
`
`France ................................... 93 11157
`
`Sep. 20, 1993
`Int. Cl.6
`............................ G06F 19/00; G05B 19/18
`[51]
`[52] U.S. CI . ................................ 364/474.37; 364/474.28;
`364/167.01; 318/568.16; 395/86
`[58] Field of Search ......................... 364/167.01, 474.03,
`364/474.05, 474.37, 474.28; 318/568.16,
`577; 901/9, 15, 46; 395/80, 86, 93, 94,
`97
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`3,279,079
`3,636,635
`3,774,311
`3,774,312
`3,944,798
`4,453,085
`4,575,802
`4,821,207
`4,894,788
`4,954,762
`5,380,978
`
`10/1966 Schiler ...................................... 33/179
`1/1972 Lemelson .................................. 33/174
`11/1973 Stemple ................................ 33/174 R
`11/1973 Esch ...................................... 33/174 L
`3/1976 Eaton .................................. 33/174 PC
`6/1984 Pryor ................................... 250/203 R
`3/1986 Walsh et al ........................ 364/167.01
`4/1989 Ming et al. ............................. 364/193
`1/1990 Stelzer ............................... 364/474.35
`9/1990 Miyake et al ...................... 318/568.19
`1/1995 Pryor .................................. 219/121.64
`
`FOREIGN PATENT DOCUMENTS
`
`0188623
`
`7/1985 European Pat. Off ..
`
`I 1111111111111111 11111 lllll 111111111111111 1111111111 11111 lll111111111111111
`US005528505A
`[lll Patent Number:
`[45] Date of Patent:
`
`5,528,505
`Jun. 18, 1996
`
`0511396 11/1991 European Pat. Off ..
`2597969 10/1987 France .
`1498009
`1/1987 United Kingdom.
`
`OTHER PUBLICATIONS
`
`Proceedings 1987 IEEE International Conference on Robot(cid:173)
`ics and Automation, vol. 2, Apr. 1987, Raleigh, North
`Carolina, USA pp. 807-815 C. H. Chen, A C. KAK,
`'Modeling and calibration of a structured light scanner for
`3-D robot vision'.
`
`Primary Examiner-Paul P. Gordon
`Attorney, Agent, or Firm-Sixbey, Friedman Leedom &
`Ferguson; Gerald J. Ferguson, Jr.; Tim L. Brackett, Jr.
`
`[57]
`
`ABSTRACT
`
`The contact sensor of the hinged arm of a measurement
`machine for taking measurements in three dimensions is
`replaced by a light sensor secured at the same position. A
`first position-marking axis defined by a light beam emitted
`by an emitter disposed in a first position is used to determine
`a first vector by two measured points. The emitter is moved
`in a plane so as to take up a second position, and a second
`position-marking axis defined by the light beam of said
`emitter is used by measuring a point on the second axis. The
`projection [01] of the second axis point onto the first
`position-marking axis is then used to enable a frame of
`reference (01 X, 0 1 Y, 0 1 Z] to be established. If the machine
`needs to be displaced in order to take measurements in a
`zone that is further away, a new frame of reference is
`determined using the same steps, using the same first axis
`and using a new point on another second axis that is obtained
`by a new displacement of the emitter performed so that it
`remains in the same plane, thereby enabling the origin (02 ]
`of the new frame of reference to be determined, thus making
`it possible to make available a plurality of known frames of
`reference.
`
`11 Claims, 4 Drawing Sheets
`
`EX1076
`Yita v. MacNeil
`IPR2020-01139
`
`

`

`U.S. Patent
`U.S. Patent
`
`Jun. 18, 1996
`Jun. 18, 1996
`
`Sheet 1 of 4
`Sheet 1 of 4
`
`5,528,505
`5,528,505
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`U.S. Patent
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`Jun. 18, 1996
`
`Sheet 2 of 4
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`5,528,505
`
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`U.S. Patent
`U.S. Patent
`
`Jun. 18, 1996
`Jun. 18, 1996
`
`Sheet 3 of 4
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`U.S. Patent
`U.S. Patent
`
`Jun. 18, 1996
`Jun. 18, 1996
`
`Sheet 4 of 4
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`1
`POSITION-MARKING METHOD FOR A
`MACHINE THAT MEASURES IN THREE
`DIMENSIONS, AND APPARATUS FOR
`IMPLEMENTING THE METHOD
`
`The present invention relates to the field of techniques
`for measuring the shape and/or position of an object by
`means of a machine for measuring in three dimensions.
`
`BACKGROUND OF THE INVENTION
`
`5
`
`2
`An object of the invention is thus to design a position(cid:173)
`marking method, and apparatus for implementing it, to
`enable large volumes to be measured using a machine of
`small dimensions, and to enable the three-dimensional mea-
`surement machine to be displaced without losing accuracy,
`while keeping the design simple and the cost reasonable.
`More particularly, the present invention provides a posi(cid:173)
`tion-marking method for a measurement machine that mea(cid:173)
`sures in three dimensions and that is constituted by a support
`10 and a deformable arm in the form of hinged arm segments,
`with a contact sensor mounted at the end of the last hinged
`arm segment to measure the shape and/or the position of an
`object, said method using a computer associated with said
`measurement machine to determine the coordinates of the
`
`Such machines, referred herein as "three-dimensional
`machines", are generally constituted by a support and a
`deformable arm made up of hinged arm segments, with a
`contact mounted at the end of the last hinged arm segment.
`A plurality of points on the object to be measured are then
`touched by means of the sensor which is movable relative to
`a reference coordinate system. The measurement machine is
`also connected to a computer which makes use of the 20
`information provided by the sensor and by position detectors
`associated with the arm.
`The present trend is towards machines that are simulta(cid:173)
`neously compact, lightweight, and accurate. This poses
`problems that are particularly difficult when measuring the 25
`positions of objects inside motor vehicle bodywork.
`The machines that were designed about 20 years ago are
`bulky and expensive (see for example documents U.S. Pat.
`Nos. 3,774,312, 3,774,311, 3,636,635, and 3,279,079). Fur(cid:173)
`thermore, those machines are of limited application since the
`size of the machine determines the size of the objects that
`can be measured, and the cost of the machine increases
`rapidly with size. Because of difficulties in maintaining
`positioning and displacement accuracy for elements that are
`cantilevered out, machines of that type must also be massive
`throughout to ensure that they are of sufficient stiffness, such
`that measuring objects of large dimensions (in length or in
`height) requires the use of machines that are bulky, heavy,
`and expensive.
`Machines that are simpler and easier to handle have been
`proposed, as illustrated in documents U.S. Pat. No. 3,944,
`798 and GB-A-I 498 009, or more recently in document
`FR-A-2 597 969. However those more recent machines are
`de facto more restricted as to accessible length: measurable
`volumes are generally limited to about 1 meter from the
`support of the deformable arm. As a result, if it is absolutely
`essential to perform measurements in a zone that is further
`away, then the support must be moved, and that gives rise to
`a loss of accuracy since the computer determines the coor(cid:173)
`dinates of the contact sensor in a frame of reference based 50
`on the machine.
`It might be tempting to use a guide rail and to mount the
`support so as to be free to move in translation on the rail.
`However, if it is desired to maintain high accuracy ( to within
`two-tenths of a millimeter), then the rail must be of a section
`that is large enough to avoid twisting, and must therefore be
`heavy and bulky.
`
`15 ~i::~~~~~s~i!;ri:~l::~~rii!t!; ~:;se~e~r::dm;rr~~
`out displacing the support of the machine:
`the contact sensor is replaced with a light sensor secured
`at the same position;
`use is made of a first position-marking axis as defined by
`a light beam emitted by an emitter disposed in a first
`position, by measuring two points on said first axis with the
`light sensor thereby defining a first vector;
`the emitter is displaced in a plane so as to take up a second
`position in such a manner that the light beam it emits is
`coplanar and not parallel to the light beam emitted in the first
`position; and
`use is made of a second position-marking axis defined by
`the light beam emitted by the emitter when disposed in said
`30 second position, by measuring a point on said second axis,
`and by determining the projection of said point on the first
`position-marking axis, thereby defining a second vector, said
`projection being selected as the origin of a frame of refer(cid:173)
`ence in which the three leading vectors are constituted by
`35 said first and second vectors and by a third vector which is
`the result of the vector product of the second and first
`vectors;
`and wherein a determined displacement of the support of
`the machine for the purpose of taking measurements in a
`40 zone that is further away requires a new frame of reference
`to be determined using the same steps, using the same first
`axis or another first axis at a known angle to said first axis,
`and using a new point on another second axis obtained by a
`new displacement of the emitter performed to keep it in the
`45 same plllne, so as to determine the origin of the new frame
`of reference, thereby making it possible to make available a
`plurality of known frames of reference.
`When the support of the machine is displaced in or close
`to a fixed plane, it is advantageous for the emitter to be
`displaced by pivoting about a fixed axis which is perpen(cid:173)
`dicular to said fixed plane. In which case, it is possible to use
`a second emitter secured relative to the fixed axis carrying
`the first emitter, and the same steps are performed with said
`second emitter which is therefore displaced in a plane that is
`parallel to the displacement plane of the first emitter.
`In a variant, it is possible to provide for the emitter to be
`displaced by sliding over a fixed support surface belonging
`to a reference block, said surface being parallel to said fixed
`60 plane.
`Also preferably, the magnitude of the displacement of the
`machine support is determined by means of a linear mea(cid:173)
`surement member such as a flat strip or an elongate bar
`having reference marks at known distances, said linear
`65 measurement member extending along a direction that is
`close to the direction of the first position-marking axis. In a
`variant, the magnitude of the displacement of the machine
`
`55
`
`OBJECTS AND SUMMARY OF THE
`INVENTION
`
`The invention seeks specifically to solve that problem by
`means of a position-marking technique that enables the
`volume that is measurable by means of a three-dimensional
`measuring machine to be increased while retaining high
`accuracy.
`
`

`

`5,528,505
`
`4
`FIG. 6 shows a bench for assembling vehicle bodywork,
`with the front panel removed;
`FIG. 7 shows the inside face of the middle panel, with its
`three locations associated with fixing the machine support,
`5 FIGS. Sa, 8b, and Sc showing the machine in said locations;
`FIG. 9 shows how the use of a pivoting emitter makes it
`possible to obtain accurate position-marking in each of the
`volumes associated with the above-mentioned locations; and
`FIG. 10 is a fragmentary view of a reference block
`enabling a sliding emitter to be easily repositioned, in this
`case in another plane that is perpendicular to the plane first
`used.
`
`3
`support is determined by means of pre-established reference
`marks associated with fixing or fastening the support of the
`machine on a fixed unit.
`In some cases, particularly for voluminous objects and
`after a reference frame has been determined, it is advanta(cid:173)
`geous to provide for the emitter to be repositioned in such a
`manner as to enable it to be displaced in another plane that
`is not parallel to the first plane used, and another frame of
`reference is determined using the same steps, optionally
`together with another new frame of reference following 10
`determined displacement of the support of the machine in
`order to take measurements in a zone that is further away in
`the direction of said other plane. In particular, the other plane
`may be perpendicular to the first plane used. It is then
`possible to provide for the emitter to be repositioned by 15
`being pressed against two fixed support surfaces that are
`mutually perpendicular and perpendicular to the first fixed
`support surface used, said surfaces belonging to a reference
`block whose rectified faces are in known orientations.
`The invention also provides apparatus specially designed
`for implementing the above method in which one or more
`pivoting emitters are used, the apparatus comprising at least
`one emitter mounted to pivot about a fixed axis which is
`perpendicular to the plane in which the light beam associ(cid:173)
`ated with each emitter is displaced, together with a light
`sensor replacing the contact sensor of the arm of the mea(cid:173)
`surement machine and secured in the same position as said
`contact sensor. In a variant having a sliding emitter, the
`apparatus comprises a reference block whose rectified faces
`are in known orientations and serve as fixed support surfaces
`for an emitter capable of being displaced by sliding over one
`of said surfaces, together with a light sensor replacing the
`contact sensor of the arm of the measurement machine and
`secured at the same position as the contact sensor.
`
`20
`
`MORE DETAILED DESCRIPTION
`In FIG. 1 there can be seen a three-dimensional measure(cid:173)
`ment machine 10 of known type designed to measure shapes
`and/or positions on an object A symbolized by chain-dotted
`lines. The machine 10 shown herein is constituted by a
`support 1 and a deformable arm 12 made up of hinged arm
`segments 13, 14, 15, and 16, together with a contact sensor
`17 mounted at the end of the last hinged arm segment 16 for
`the purpose of making measurements on the object A. The
`25 shape and/or position of the object A can be measured by
`moving the hinged arm so as to bring the contact sensor 17
`into contact with a determined point of the object A. The
`machine 10 shown herein has six axes of rotation 20, 21, 22,
`23, 24, and 25, which axes are locked against rotation by
`30 progressive abutments that are not shown. A computer 30
`connected to the measurement machine 10 by means of a
`cable 31 is associated with said measurement machine to
`determine the coordinates of the contact sensor 17 (assumed
`to be a point) for any position of the hinged arm segments
`35 making up the deformable. arm 12. The computer 30 shown
`is a portable microcomputer having a keyboard 34 and a
`screen 32 having a portion 33 used for displaying the
`Cartesian coordinates X, Y, and Z of the sensor 17 in the
`frame of reference of the measurement machine 10. Move-
`40 ments of the sensor 17 are controlled by rotating the last two
`encoders of the deformable arm 12 that are associated with
`the axes 24 and 25, and the screen 32 includes a reference
`mark 35 having an abscissa axis which corresponds to
`horizontal movement of the encoder associated with the axis
`45 25, and an ordinate axis which corresponds to vertical
`movement of the encoder associated with the axis 24. The
`operator can use the keyboard 34 of the computer to display
`the Cartesian .. coordinates of the sensor 17 at any moment,
`and in this case a remote control button 40 is also provided
`to make it possible to avoid using the keyboard 34: while
`holding the deformable arm of the three-dimensional mea-
`surement machine 10 in place, the operator can then readily
`simultaneously input the command when the sensor 17 is in
`contact with the object A at the point to be measured. Under
`such circumstances, the operator can monitor proceedings
`on the screen 32 which displays a cursor that moves hori-
`zontally and vertically relative to the reference mark 35.
`When the three-dimensional measurement machine 10 is in
`the position shown in solid lines, it can perform shape and/or
`position measurements within a volume defined by a sphere
`Sl. It should be observed that the contact sensor 17 of the
`machine is replaced in this case by a light beam sensor 10
`secured to occupy the same position as otherwise occupied
`by the contact sensor, said light beam sensor serving to
`implement the position-marking method of the invention,
`which method makes it possible to displace the threes
`dimensional. machine and then perform measurements in a
`
`65
`
`BRIEF DESCRIPTION OF IBE DRAWINGS
`
`Other characteristics and advantages of the invention
`appear more clearly in the light of the following description
`of a particular embodiment given with reference to the
`accompanying drawings, in which:
`FIG. 1 shows a preferred implementation of the method of
`the invention using a light beam emitter a laser beam) that
`is pivotally mounted (in this case in a vertical plane),
`together with a flat strip of distance markers extending in a
`direction close to that of the light beam, the three-dimen(cid:173)
`sional machine being shown in a first position (support
`shown in solid lines) with an associated frame of reference
`referred to the machine, and in a second position (support
`shown in dashed lines) with another associated frame of 50
`reference which is also positioned relative to the initial light
`beam;
`FIG. 2 is a diagram showing the steps in constructing a
`frame of reference marked by the machine and using the 55
`method of the invention;
`FIG. 3 shows a moving support for the three-dimensional
`machine which is displaced past the object concerned (in
`this case a motor vehicle), and FIG. 4 shows the various
`measurement volumes that are obtained for the positions 60
`occupied by the above-mentioned moving support;
`FIG. 5 is a diagrammatic plan view showing the various
`measurement volumes that can be obtained using two emit(cid:173)
`ters referred to a common axis, and disposed on either side
`of the vehicle, the volumes of the middle row (internal
`measurements) being obtained with a rail (not shown) or by
`offsetting from previously measured points;
`
`

`

`5
`
`5,528,505
`
`5
`
`new volume.
`In FIG. 1, the support 11 of the machine is shown by
`means of dashed lines in a new position, thereby enabling
`the measurement machine to use its contact sensor 17 to
`perform measurements in a new volume as defined by a
`sphere S2. This situation arises frequently when the object A
`is bulky, or very long, and insofar as there is a need to make
`measurements in a zone that is further away, lying outside
`the first volume as defined by the sphere Sl.
`There follows an explanation of how the position-marking
`method of the invention is implemented whereby it becomes
`possible to measure large volumes using a machine of small
`dimensions but without thereby losing accuracy. '
`In the method, it is possible to establish known frames of
`reference for different positions of the measurement
`machine support, with each of these frames of reference
`being referred to a fixed position-marking axis.
`The description begins with the way in which a reference
`frame is established for a first position of the measurement
`machine 10 by using a beam sensor 100 mounted in the
`place of and instead of the contact sensor of the three(cid:173)
`dimensional machine, and also using a light beam emitter
`101 (preferably a laser beam emitter), said emitter being
`mounted on a support 102 in such a manner as to enable it
`to be moved so that the light beam can be displaced to some
`other position in which it is coplanar but not parallel to the
`beam as emitted in the first position.
`In FIG. 1, an emitter 101 is provided that is pivotally
`mounted on its support 102 so as to be capable of being
`pivoted about a fixed axis 110 that is perpendicular to the
`fixed plane in which the light beam propagates in the various
`angular positions of the emitter 101. As shown in FIG. 1, the
`support 102 stands on the ground or on a support block
`having a horizontal face, such that the fixed plane in which
`the light beam moves is vertical in this case. As explained
`below, it is possible to provide for other types of displace(cid:173)
`ment for the emitter 101, in particular displacements by
`sliding over a fixed support surface. The beam sensor 100
`replaces the contact sensor of the machine's hinged arm by
`being secured at the same position as the contact sensor, i.e., 40
`when the beam sensor is constituted by a microcamera, its
`light sensitive grid which has a radius of about 3 cm is in the
`form of a circular disk centered on the point previously
`occupied by the contact sensor 17 prior to being substituted
`therefor.
`The method of establishing a frame of reference for the
`position occupied by the support of the machine is described
`below with reference to FIG. 1 and to the construction
`shown diagrammatically in FIG. 2.
`Initially, a first position-marking axis 111 is used as
`defined by the light beam emitted by the emitter 101 while
`it is disposed in a first position, with this being done by
`measuring two points A 11 and A12 on said first axis by means
`of the light sensor 100. The computer 30 uses the resulting
`data to define a first vector Vl.
`Thereafter the emitter 101 is moved in a plane (in this case
`a vertical plane) so as to take up a second position in which
`the light beam is coplanar and not parallel to the beam
`emitted in the first position. Since the emitter is pivotally
`mounted, the second position is obtained in this case by
`rotation through an angle a about the fixed axis 110. A
`second position-marking axis 112 is then used as defined by
`the light beam emitted by the emitter 101 while in its second
`position, with a point B 1 being measured on the second axis.
`This information makes it possible to determine a projection
`0 1 of the point B1 on the first position-marking axis 111, the
`
`6
`projection preferably being orthogonal so as to simplify the
`calculations. The point 0 1 is then selected as the origin of a
`frame of reference whose three leading vectors are consti(cid:173)
`tuted by the first vector Vl, a second vector V2 extending
`from 0 1 to B1, and by a third vector V3 which is the result
`of the vector product of the second and first vectors. This
`provides a frame of reference marked 0 1 X, 0 1 Y, 0 1 Z.
`The support 11 of the machine 10 is then displaced for the
`purpose of taking measurements in a zone that is further
`10 away, thus requiring a new frame of reference to be deter(cid:173)
`mined, with this being done using the same technique. The
`displacement is "determined", i.e. a linear measurement is
`available that represents the displacement of the machine
`support, this measurement being preferably performed in
`15 substantially the same direction as said displacement. In this
`case, a flat or shaped elongate strip 120 is provided that has
`reference marks 121 at known distances, said flat or shaped
`strip extending in a direction that is close to the direction of
`the first position-marking axis 111. The elongate flat or
`20 shaped strip may be constituted, for example, by a conven(cid:173)
`tional type of measurement tape, or by a wire drawn from a
`housing, or if necessary by a solid bar (which nevertheless
`suffers from the drawback of being bulkier). More generally,
`the magnitude of the displacement of the machine support is
`25 determined by means of a linear measurement member, and
`this may be done by any system that enables linear mea(cid:173)
`surements to be taken without making contact, e.g. a laser
`interferometer. The linear measurement member thus makes
`it possible to establish how far the machine support has
`30 moved in translation after being displaced. It should be
`observed that it is not essential in any way for the direction
`established by the linear measurement member to be parallel
`to the plane in which the light beams are displaced, given
`that a small amount of divergence will give rise to a minimal
`35 amount of error that is in any event correctable since the
`relative distances between the reference marks are known
`and the concept of measurement in the machine's frame of
`reference is retained at all times. Thus, a first axis 111' is
`used which may coincide with the first axis 111 as used
`during the preceding determination (as shown), or which
`may be some other first axis at a known angle relative to said
`first axis 111. Two points A21 and A22 on said new first axis
`are then measured using the light sensor 100 so as to
`determine a new first vector. Thereafter, the emitter 101 is
`displaced within its plane (in this case by being rotated about
`the axis 110) so as to move the beam to a second position
`that defines a second axis 112' (which in this case does not
`coincide with the second axis 112 used in the preceding
`determination), thus making it possible, after measuring a
`50 point B2 on this new second axis 112', to determine the
`origin 0 2 of a new frame of reference 0 2X, 0 2 Y, 0 2Z. The
`process can be repeated, thereby providing a plurality of
`known frames of reference.
`FIGS. 3 and 4 show how the above-described position-
`55 marking method is implemented in associated with an object
`that is constituted in this case by a motor vehicle V. In FIG.
`3, there can be seen the various positions of a moving
`support T on which the support 11 of the above-described
`three-dimensional machine can be placed. The moving sup-
`60 port T may run on casters, for example to enable it to be
`moved along the vehicle V. It should be observed that there
`is a strip 120 mounted on the vehicle V, which strip has
`reference marks (not visible in the figure) at known dis(cid:173)
`tances. FIG. 4 is a diagram showing the various frames of
`reference that can then be defined for each measurement
`volume Sl, S2, S3, and S4 within which it is possible to
`measure some of the outside points of the vehicle V. FIG. 4
`
`45
`
`65
`
`

`

`5,528,505
`
`15
`
`25
`
`7
`shows a first position-marking axis 111 and a plurality of
`second position-marking axes 112, 112', 112". In each of the
`zones concerned, the process for determining a frame of
`reference is implemented as described above, thereby malc(cid:173)
`ing it possible in each of the zones concerned, 1, 2, 3, and 5
`4, to determine the following frames of reference with ease
`and with great accuracy (0 1 X, 0 1 Y, 0 1 Z), (02X, 0 2 Y, 0 2Z),
`(03X, 0 3Y, 0 3Z), and (04X, 0 4Y, 0 4Z).
`In the application shown in FIGS. 3 and 4, the mode of
`scanning used by the laser beam is essentially vertical. It 10
`may then be of interest to be able to double up the mea(cid:173)
`surements by performing shape and/or position measure(cid:173)
`ments of the same object V but on the other side of the
`object, and using the same apparatus.
`One way of doing this is shown diagrammatically in FIG.
`5 which is a plan view. This is done by using a second
`emitter 101 secured to the same fixed axis 110 as carries the
`first emitter. The same steps are then performed using the
`second emitter which is thus displaced in a plane P" parallel
`to the displacement plane P' of the first emitter. Naturally, it
`is important to ensure that the initial angular settings of the
`emitters 101 relative to the axis are the same to within good
`accuracy. In the plane view, the first and second position(cid:173)
`marking axes 111 and 112 associated with each emitter 101
`lie in parallel vertical planes P' and P" that extend on either
`side of the vehicle V on which shape and/or position
`.measurements are being performed. By using the technique
`described above, it becomes possible to perform measure(cid:173)
`ments accurately in successive measurement volumes S'l,
`S'2, S'3, S'4 and also S"l, S"2, S"3, and S"4. If it is desired
`to perform measurements inside the vehicle, along a middle
`zone thereof, using measurement volumes S"'l, S"'2, S"'3,
`and S'"4, it would then be possible to use a support rail (not
`shown) or else by offsetting from previously measured
`points.
`FIG. 6 shows a portion of a bench for assembling vehicle
`bodywork, with the front panel of the bench being removed,
`its rear panel 50 including clamps 51 for holding the
`components of the bodywork A that is to be assembled. The
`front panel is shown in FIG. 7 and is provided not only with
`clamps 51, but also with three locations 140 associated with
`fixing the support 11 of the above-described three-dimen(cid:173)
`sional machine, with an appropriate one of these three
`locations being selected to perform measurements in the
`desired volume Sl, S2, or S3, as shown in FIGS. Sa, Sb, and
`Sc. Members 130 mounted on the panel 50 constitute
`reference points for facilitating position-marking. These
`points can be detected by the laser beam of the emitter,
`thereby making it possible to determine the position of the
`beam relative to the object to be measured, and thus to
`include intermediate means in the position-marking method
`of the invention, simplifying the calculations to be per(cid:173)
`formed. FIG. 9 thus shows the use of a pivoting emitter 101
`for application of the method described above, so as to 55
`achieve accurate position-marking in each of the volumes
`associated with
`the above-mentioned positions. For
`example, the various position-marking axes used when
`determining the frames of reference are marked 111, 112',
`112", and 112"'.
`As a variant to using one or more pivotally-mounted
`emitters, it is possible to use at least one emitter that is
`displaced by sliding over a fixed support surface, said
`surface being parallel to the fixed plane in which, or close to
`which, the three-dimensional machine support is displaced.
`It is then possible to use a reference plate that is fitted in
`the vicinity of a comer with support surfaces making it
`
`8
`possible to guarantee that the position of the first position(cid:173)
`marking axis is indeed constant, with the second axis being
`obtained merely by sliding over the support surface to a
`second position in which the light beam.is coplanar and not
`parallel to the beam as emitted in the first position.
`FIG. 10 shows a support block having additional facilities
`insofar as it malces it possible to reposition the emitter in
`such a manner as to enable it to be displaced in another plane
`that is not parallel to the first plane used (in this case the
`other plane is perpendicular to the first plane used), and
`another reference frame can be determined using the same
`steps, optionally together with another new reference frame
`following determined displacement of the machine support
`for taking measurements in a zone that is further away in the
`direction of said other plane. The reference block 60 thus
`includes rectified faces 61, 62, and 63 having known orien(cid:173)
`tations and preferably defining a base frame of reference
`defined by three right angles.
`In this case, the emitter 101 which is the form of a housing
`constituting a rectangular parallelepiped is initially pressed
`20 against all three reference faces to define the first position(cid:173)
`marking axis 111, and is then displaced by sliding over a
`lateral face 62 to determine the second position-marking
`axis 112. Thereafter, the emitter 101 is repositioned to
`another position shown in chain-dotted lines to define a new
`first axis 111, after which it is moved to define a new second
`position-marking axis 112 by being slid over side support
`face 63. By construction, the light beam plane is then exactly
`perpendicular to the preceding plane, thereby making it
`possible to go very quickly to a new measurement plane
`30 perpendicular to the first. Thus, by using such a reference
`block having rectified faces it is possible to work progres(cid:173)
`sively around the object. Naturally, there are various ways in
`which such a reference block can be made, and in a variant
`it would be possible to use a cube