FR2622968A1 - METHOD AND DEVICE FOR PERFORMING DIMENSIONAL CONTROL OF A PART BY OPTOELECTRONIC ROUTE - Google Patents

Abstract

The method essentially consists in carrying out a three-dimensional reading of predefined points of a part 11 by means of a plurality of measuring heads 15 (each provided for the reading of one or more points of the part), so as to obtain, for each point, the respective coordinates related to the reference system of the corresponding head 15 and to convert these coordinates successively into a single reference system related to the part 11, by means of appropriate transformations by rotation and translation applied to the aforementioned coordinates.

Description

Method and device for performing dimension control

  The present invention relates to a method and a device for performing the dimensional control of a part by

optoelectronic channel.

  As we know, it is of fundamental importance to be able to carry out precise dimensional checks on mechanical parts produced by a line of

  mounting. We think, for example, of the field of construction-

  tion of motor vehicles, more and more automated, in which it is advisable to keep under constant control all the parts which are put in movement, at an unceasingly higher rate-, along a line

mounting.

  In the past, dimensional control of production in the automotive industry was generally carried out using traditional static gauges which, of course, were ill-suited to large-scale controls. Flexible measurement machines have also been developed which are capable of executing measurement programs differentiated by model and by number of points measured on each model. Such machines, although they allow a significant improvement in performance

  compared to previous techniques, are particularly

  costly, require precise and constant handling and are still relatively slow in data acquisition and therefore can only be assigned to statistical tests performed on the

  base of predefined sampling plans.

  Recently, optoelectronic type measurement methods have been developed which can be used to check predefined characteristics of all parts in production. According to these methods, point differences are measured using optoelectronic devices

  of the part to be checked in relation to the corresponding points

  dants of a witness piece commonly called "master

  model ". The results of these measurements depend naturally-

  ment of the position and reproducibility of the control piece, as well as the positioning of the piece to be checked with respect to the reading device at the time when the reading is carried out. In addition, the results are not provided in absolute coordinates (those reported to

  the room itself and indicated on the plan).

  The object of the invention is to propose a method and a device for carrying out the dimensional control of a part by optoelectronic means, making it possible to evaluate all the parts belonging to an entire production during their movement on a production line and providing dimensional data in an absolute reference system (for example the workpiece reference system). In addition, the aforementioned data must not depend, at least between certain tolerance limits, on the orientation and positioning of the

  parts to be checked on the production line.

  This object is achieved according to the invention by a method for performing the dimensional control of a part by optoelectronic means, characterized in that it comprises the following essential operations:

  - a plurality of three-dimensional measuring heads are available -

  nelles of optoelectronic type in a support structure, so as to know the relative positions of the heads with respect to said structure; - the heads are positioned on the part, so that

  predefined reference points and checkpoints

  The predefined parts are framed by the measuring heads; - there are, for each of said points, the first coordinates reported to the reference system of the measuring head; and - the first coordinates are converted into second coordinates reported to a single reference system integral with the part using transformations by

  rotation and translation applied to the first coordinates

  born. The invention also relates to a device for performing the dimensional control of a part by optoelectronic means, characterized in that it comprises

  - a multiplicity of optoelectro type measuring heads

  each assigned to one or more points to be measured in the room and anchored to a support structure;

  first means of memory for calibration parameters.

  of each of the measuring heads with respect to said structure

  ture; and a processing and calculation unit connected to the measurement heads and to the first memory means, said unit being suitable for converting first coordinates recorded by each of the measurement heads and reported to a reference system associated therewith. second coordinates related to a single united reference system

of the room.

  Other characteristics and advantages of the invention

  will emerge from the detailed description below of a

  exemplary embodiment, and attached drawings, in which: - Figure 1 is a perspective view of a part

  of a device according to the invention in an exemplary application

  cation; - Figure 2 is a schematic representation by

  blocks of an essentially electronic part of the dispo-

  sitive of Figure 1; - Figures 3 and 4 are schematic views of elements of a part to be inspected considered in different reference systems; - Figure 5 is a flowchart of a possible form

  for carrying out a main program of an arith-

  processing metrics illustrated in the diagram in FIG. 2; and

  FIG. 6 is an essential relative enlarged flowchart.

  Lement to a block of the flowchart of Figure 5.

  Referring in particular to FIG. 1, in which the reference 10 indicates as a whole a device suitable for carrying out dimensional control in sequence of mechanical parts 11 supported by means of a conveyor belt 12 which is part of a line of mounting

(not shown).

  The device 10 comprises a number of identical measuring heads 15, supported by a structure 16 essentially constituted by a cross member 17 whose opposite ends are supported by uprights 18 rigidly fixed to the ground. The device 10 includes

  furthermore an electronic processing unit 20,

  both of the respective inputs / outputs connected to the measuring heads 15, and provided with an input unit 21 (in the particular case a keyboard) and two output units 22,23 (respectively a video unit and a printer). With particular reference to FIG. 2, each measurement head 15 essentially comprises a television camera 25, a device 26 generating a laser beam 27, the emitted optical power of which is continuously adjustable and an illumination device 28 with infrared rays also provided with a continuous adjustment of the optical power emitted and advantageously carried out

  by means of a plurality of light-emitting diodes (not shown

  scented) arranged for example in a circular crown

  re around the camera lens 25.

  The processing unit 20 essentially consists of a unit 29 which fulfills the dual function of interface and preprocessing (filtering, comparison, etc.) of the signals coming from the camera 25 of each measuring head 15, by a processing and calculation unit 30, and by a plurality of memories 31, 32, 33, 34 which are represented

  separate from each other only for convenience.

  In Figure 3 is illustrated on a larger scale and in perspective a schematic view of a measuring head and the corresponding part of the part 11, in which there has, by way of example, a hole 35 appear which wishes to make the reading by the aforementioned head 15. Xh, Yh, Zh indicate the reference system of the measuring head 15 with respect to which the latter detects the values of the coordinates of the barycenter of the hole 35, values obtained by combining the indications obtained by taking, by means of the camera 25, the image without the laser beam 27 and the image with this laser beam, which has an essentially laminar cross section so as to produce on the surface of

Exhibit 11 a trace 37.

  In FIG. 4 is illustrated a part of the part 11 comprising the hole 35 and three reference points 41, 42 and 43, as well as a set of three reference systems

  Xmeas, Ymeas, Zmeas; Xref, Yref, Zref, and Xmod, Ymod, Zmod.

  The first Xmeas, Ymeas, Zmeas reference system is the one associated with all of the measuring heads 15 and

to the support structure 16.

  The second reference system Xref, Yref, Zref is that

  generated by the three reference points 41,42,43 soli-

part 11.

  The third reference system Xmod, Ymod, Zmod is the one used by the manufacturer of part 11 to

  indicate all the dimensions of the points and / or characteristics

protruding ticks from it.

  As will be explained below, the values of the coordinates

  born from the barycenter of hole 35 are converted by successive steps into respective reported coordinates

  to these systems so as to obtain values of co-

  data reported only in Exhibit 11.

  In short, the method proposed by the present invention for carrying out the dimensional control of the part 11

  optoelectronics requires the execution of the operations-

  following essential tions: - the measuring heads 15 are placed in the support structure 16 so as to know the relative positions of the heads with respect to the structure; - The assembly 10 is positioned on the part 11 so that predefined reference points and predefined check points thereof are framed by the measuring heads 15; - there is, for each of the aforementioned points, first coordinates reported to the reference system Xh, Yh, Zh of the corresponding measurement head 15; and - the first coordinates are converted into second coordinates reported to a single reference system Xmod, Ymod, Zmod integral with the part 11 by means of transformations by applied rotation and translation

at the first coordinates.

  It should also be noted that before recording the first

  coordinates, it is necessary to process, by means of algo-

  appropriate triangulation rhythms, the information obtained from the various cameras 25, with the aim of extracting the intrinsic physical characteristics of the objects to be measured, for example the barycenter of a hole. Such operations are facilitated by the use of infrared ray illumination devices, in order to obtain better characterization of the images and consequently easier and faster recognition thereof, which recognition occurs on

  the camera plane and thus provides a two-dimensional measurement

nelle of the point examines.

  The detailed sequence of operations executed under the control of the processing unit 20 to carry out the dimensional control of the part 11, in particular to take up the coordinates of the barycenter of the hole 35, is described below, with particular reference

in Figures 5 and 6.

  We first arrive at a block 50 which has the function of having each of the cameras 25 record the corresponding image in the presence of the laser beam 27 emitted by the corresponding device 26. At the same time, the same image is taken without a laser beam

thanks to block 51.

  The results of the two above shots are sent to a block 52 which makes the difference so as to obtain as result the only information relating to trace 37 (see FIG. 3). We then arrive at a processing block 53 in which the image obtained is preprocessed in order to better highlight the areas of interest (in the present case the outline of the hole 35). Under these operating conditions, it is necessary for the laser beam generators to be adjusted so as to obtain the maximum optical relief of the light trace 37 on the

surface of the part 11.

  More particularly, block 53 processes the drifting image

  different laser traces 37 consecutive to the projection

  tion of the laser planes on the part 11 in translation au-

  below the measuring heads 15 and provides, for each segment of laser traces 37, the values of the coordinates of the barycenter, the coordinates of the points of the contour, the values of the area and of the moments of first and second

orders.

  Knowing the coordinates of the laser blade segments related to the identified reference mark (in this case, the hole 35), we pass to the calculation block 54, which, taking into account the fact that each point of the laser beam 27 must be located on the plan of its generating device 26, reconstructs the spatial position of the point sought using a triangulation algorithm defined by the following set of equations: Perspective equations of each camera 26: (x-xt) * all + (y-yt ) * a21 + (z-zt) * a31 xi = f * - (1) (x-xt) * al3 + (y-yt) * a23 + (z-zt) * a33 + f (x-xt) * al2 + ( y-yt) * a22 + (z-zt) * a32 yi = f * (2) (x-xt) * al3 + (y-yt) * a23 + (z-zt) * a33 + f Equation of the laser plane: O = A * x + B * y + C * z + D (3) o: xi, yi = coordinates of the image of the points of interest of the laser slide; x, y, z = spatial coordinates unknown in the reference system (Xh, Yh, Zh) of the measuring head; aij = guiding cosine of the rotation matrix of the reference system of the camera with respect to the reference system of the measuring head; xt, yt, zt = camera-to-head translations; f = focal length of the camera; A, B, C, D = coefficients of the light plane of the laser projector defined in the reference system of

the measuring head.

  The values of aij; xt, yt, zt; f; A, B, C, D relate to calibration data of each measuring head and are made available by means of a memory block to which the memory 31 corresponds for example in the

diagram of figure 2.

  The solution of equations (1), (2) and (3) provides the values sought for the x, y, z coordinates of the points

of interest of the laser blade.

  The values thus obtained allow, by means of a

  other processing block 56, the identification of the

  data z of hole 35, linked to the z coordinate of the blade

  by the geometric relations determined by the characters-

details of the framed detail.

  We then arrive at a block 57 which has the function, in case the part 11 is not correctly positioned,

  bring them with the help of an appropriate algorithm

  required for the value of the calculated coordinate, deducting the value of the zpt coordinate used by

a next block 58.

  From block 57, we arrive at a calculation block 58 having a

  first entry where the cali-

  bration of the measuring head contained in block 55.

  A second input of block 58 is connected to the output of a set of blocks 60, 61, 62 arranged in series, which respectively determine the course of the following operations: block 60: acquisition, by means of camera 25, of the image illuminated by the illumination device 28; block 61: image processing obtained with the illumination device 28; block 62: calculation of target coordinates (hole 35)

in the image plane.

  The function of block 58 is to solve the equilibrium system

forward looking statements.

  Prospective equations of each camera 26: (xpt-xt) * all + (ypt-yt) * a21 + (zpt-zt) * a31

xipt = f * <-.

  xpt-xt) * al3 + (ypt-yt) * a23 + (zpt-zt) * a33 + f (xpt-xt) * al2 + (ypt-yt) * a22 + (zpt-zt) * a32

yipt = f * -

  (xpt-xt) * al3 + (ypt-yt) * a23 + (zpt-zt) * a33 + f o xipt, yipt = coordinates of the barycenter image of the hole; xpt, ypt, zpt = spatial coordinates of the hole in the reference system (Xh, Yh, Zh) of the measuring head;

f = focal length of the camera.

  The results of the perspective transformation carried out

  by block 58 appear in a memory block 65.

  Then, taking into account the position of each measuring head 15 relative to the structure 16 (position memorized in a block 66, to which corresponds a memory position indicated by 32 in the diagram of FIG. 2), in a block 67 , we transform the values xpt, ypt, zpt into the values Xmeasp, Ymeasp, Zmeasp relative to the basic reference system Xmeas, Ymeas, Zmeas (figure 4) common to all the measurement heads 15, and we transmit these values to a memory block 68 (Figure 6) which is part of a

processing and calculation block 70.

  Particular reference is made to the organization chart

  of Figure 6 (which constitutes an expansion of the organi-

  gram of figure 5) and in figure 4, we proceed essentially

  for converting Xmeasp, Ymeaspy coordinates

  Zmeasp relating to the barycenter of hole 35 in coordinates

  corresponding arrays related to a reference system (Xmod, Ymod, Zmod) specific to part 11, by following the procedure described below inside a block

processing and calculation 70.

  In particular, we first define a system of

  measurement (Xref, Yref, Zref) integral with part 11 in rel-

  vant on the latter the coordinates of the three reference points 41,42, 43 mentioned above (see Figure 4), by means of a command produced by a block 71. These three points define a plane on which we place for example the Xref, Yref, Zref axes. Zref axis is chosen

  perpendicular to the aforementioned plane and so as to meet

  trer this plane in coincidence with one of these points (for

- example point 42).

  The new reference system being defined, through a geometric transformation of the conventional type carried out by means of a calculation block 72, we arrive at a block 73 in which the coordinates of the hole 35 appear (Xrefp, Yrefp, Zrefp) in the latest referral system

  defined. This system is certainly integral with part 11.

  However, as it does not generally coincide with the reference system (Xmod, Ymod, Zmod) used by the manufacturer or by the designer of part 11 to define the coordinates (Xmodp, Ymodp, Zmodp) of the hole

  , we realize a new geometric transformation.

  The latter is performed in a calculation block 75,

  using theoretical data relating to coordinates

  born from the reference points provided by the manufacturer of the part 11 and stored in a block 76, grouped for example with the theoretical data relating to the coordinates of the points (hole 35, etc.) subject to control

  dimensional. The data contained in block 76 contributes to

  rent to define, in a block 77, the correlation between the reference system (Xref, Yref, Zref) based on the reference points 41,42,43 and the reference system

  theoretical (Xmod, Ymod, Zmod) of Exhibit 11.

  The result of the geometric transformation of the coordinates

  born Xrefp, Yrefp, Zrefp performed by means of block 75 determines as a result the definition of the coordinates

  Xmodp, Ymodp, Zmodp recorded by device 10 and reported

  tees in the measurement system adopted by the designer or by the manufacturer of part 11. These coordinates are made available in a memory block 78 from which they can be taken to display them on the unit

  video 22 or on the printer unit 23. In addition, the coordinates

  data stored in block 78 are compared to the inte

  of a block 79 to the theoretical values memorized

  in block 76, so as to obtain a possible indication

  tion relative to the deviation they present in relation to

  to the corresponding theoretical values.

  The advantages provided by the present invention appear clearly from the description of the method and the device.

  Above all, it being observed that the device 10 can perform

  kill the dimensional control of a part in an extremely limited time and, in any case, lower than the normal rate of advance of the parts along the production line, it immediately appears that this device can be used to assess the point dimensional view of all parts belonging to an entire production

  during their movement along this line.

  In addition, the possibility of obtaining data in the reference system of the manufacturer or the parts designer makes it extremely easy to use this data. Finally, the creation of a reference system based on the reading of predefined reference points arranged on the part makes it possible to execute correct measurements even when the part is moved relative to a preferred position of measurement, which is without any advantageous doubt compared to the device which uses the measurement method providing for comparison with a standard part (master

model) as described above.

  Finally, modifications and variants can be made to the method and the device described without leaving

of the invention.

  For example, the measuring heads could be modified to include the use of several cameras, laser illumination devices and infrared and non-infrared illumination devices. Furthermore, the operations executed in sequence by the processing unit 20 and illustrated in the flowcharts of FIGS. 5 and 6 can be modified while retaining the operating principle described. Finally, the number of reference points on part 11 could be greater

at three.

Claims (14)

Claims   1. - Method for carrying out the dimensional control of a part by optoelectronic means, characterized in that it comprises the following essential operations: - there is a plurality of three-dimensional measuring heads (15) of optoelectronic type in a structure   support (16) so as to know the relative positions   heads tives (15) relative to said structure (16); - The heads are positioned on the part (11) so that predefined reference points (41,42,43) and predefined control points (35) of the part are framed by the measuring heads (15); - there is, for each of said points (41,52,43,35),   of the first coordinates reported to the referral system   of the measuring head (15); and - the first coordinates are converted into second coordinates reported to a single reference system integral with the part (11) using transformations by rotation and translation applied to the first coordinates. 2. Method according to claim 1, characterized in that it comprises an operation of defining the reference system integral with the part by reading said predefined reference points (41,42,43) of the part (11).   3. - Method according to one of claims 1 and 2, character-   in that each measuring head (15) comprises at least one laser light illumination device and at least one television camera, and in that the method - comprises a reading operation subdivided into at least two phases during which the reading of the first coordinates is carried out by the television camera, respectively in the presence and in the absence of the light emitted by the laser light illumination device. 4. - Method according to claim 3, characterized in that, each measurement head comprising at least one auxiliary illumination device, said reading operation provides for a phase during which the reading of the coordinates is carried out by the television camera in the presence of the only radiation emitted by the device auxiliary illumination.   5. - Device for performing the dimensional control of a part by optoelectronic means, characterized in that it comprises:   - a multiplicity of measuring heads (15) of opto type   electronics each assigned to one or more points to be measured of the part (11) and anchored to a support structure (16); - first means for storing calibration parameters of each of the measurement heads (15) with respect to said structure (16); and a processing and calculation unit (20) connected to the measurement heads (15) and to the first memory means,   said unit being suitable for converting first co-   data recorded by each of the measurement heads (15) and reported to a reference system associated with it in second coordinates reported to a measurement system   single reference integral with the part (11).   6. - Device according to claim 5, characterized in that each of the measuring heads (15) comprises at least one television camera and at least one device   (26) generator of a laser light beam (27).   7. - Device according to claim 6, characterized in that the television camera (25) has a proper grip axis which forms a predefined angle with a axis of the laser beam (27).   8. - Device according to one of claims 6 and 7,   characterized in that the laser beam (27) has   an essentially laminar cross section.   9. - Device according to any one of claims   5 to 8, characterized in that each of the measuring heads   (15) comprises at least one additional illumination device tional (28).   10. - Device according to any one of claims   5 to 9, characterized in that said structure (16) comprises   a crosspiece (17) supporting the measuring heads (15).   11. - Device according to any one of claims   to 10, characterized in that the processing unit (20)   includes means for memorizing coordinate data   theoretical born of said points of part (11) reported   to the reference system integral with the part (11).   12. - Device according to claim 11, characterized   in that it includes means for comparing the co-   data recorded at theoretical coordinates and for producing indications relating to the deviation of the former from seconds.   13. - Device according to claim 12, characterized in that it comprises display means (22,23)   coordinates recorded and / or said deviation.   14. - Device according to claim 13, characterized in that the display means comprise at least one video unit (22) and / or at least one im- primante (23).