FR2741438A1 - Substrate deposited glue band dimension checking optical device - Google Patents

Abstract

The device includes a halogen lamp (6) directed towards a band of glue (3) being deposited on a substrate (5) by a nozzle (2), and a CCD camera (7). The camera is attached to the nozzle body and monitors continuously the deposition process and the glue band dimensions. Images generated by the camera are processed by a module (8) which comprises an image digitiser and an image analyser. Images which reveal a defect are stored in a memory (11) so that they can analysed later. A screen (9) displays the images generated by the CCD camera.

Description

 The present invention relates to a method of dimensional control of a bead of material deposited on a surface, as well as a device for such dimensional control.

 The deposition of a material joint is a fundamental industrial process used in many technical fields.

The invention will be described by way of nonlimiting example in relation to the deposition of a bead of adhesive on the surface of a sheet, as is practiced in the automotive industry, it being understood that the invention can be generalized and extended to control the deposition of any pasty or pulverulent material on a support of any kind.

 In the example chosen as context for the description of the invention, we are looking for a device which is able to carry out the dimensional control of a bead of adhesive, extruded by a nozzle and placed on a sheet carried by a robot. The nozzle is for example fixed, and the sheet is movable relative to the nozzle along a three-dimensional trajectory. Such a glue bead control device is particularly useful when depositing a bead of glue on a motor vehicle body element.

 Are already known in the prior art, devices for controlling a bead of adhesive. Such a device is described in patent FR-A-2 703 784 by the same applicant. This device is capable of indicating whether the bead of adhesive checked is continuous, but it does not give information on the position of the bead on the support, nor on the diameter of the bead. In addition, the known control device is of limited use, since it is movable around the glue deposit nozzle, and cannot operate in combination with a fixed nozzle which deposits a bead of glue on a movable sheet .

 Therefore, the purpose of the invention is in particular to propose a device and a method for dimensional control of a bead of glue, making it possible to control the position and the diameter of a bead of glue extruded by a fixed nozzle which deposits the cord on a mobile sheet carried by a robot on a three-dimensional trajectory.

 The invention also aims to propose a device and a method capable of acting in real time so as to present to an operator the images of possible quality defects as quickly as possible, and in any case as soon as the deposition cycle ends. of a cord by a robot.

More specifically, the device sought must in particular be able to detect, in decreasing order of severity
- interruptions of the adhesive bead having a length greater than the diameter of the bead
- the lack of glue at the beginning or at the end of glue deposit
- defects in the position of the adhesive relative to the sheet, in particular at the start of deposition, and with respect to a reference deposition
- variations in the diameter of the adhesive bead by a predetermined percentage more or less, for example 5%, relative to the diameter of a reference deposit.

To this end, the invention relates to a device for dimensional control of a bead of material deposited on a support, in particular a bead of glue deposited on a sheet, the bead of material being provided by a nozzle and the support being movable. relative to the nozzle along a three-dimensional trajectory, characterized in that it comprises:
- lighting means capable of lighting an area in the vicinity of the part of the bead of material being deposited
- at least one camera to record the images of the cord during the deposit operation
image processing means for processing the images recorded by the camera, and for deducing therefrom quality control information from the operation of depositing the bead of material.

According to other characteristics of the control device according to the invention:
- It includes memory means for recording the images of deposit defects, and means for digitizing and analyzing the images thus memorized
- Preferably, the memory means comprise a fast memory, of the VRAM video memory type with dual access, and the digitization and analysis means consist of a processor connected to the memory means by a fast video bus
the lighting means comprise lighting in halogen light, and are placed so as to emit a beam directed in a manner substantially parallel to the camera
- the camera and the lighting means are fixed on the nozzle near its end, so as to obtain a large image
- the image scanning and analysis processor operates at a rate greater than or equal to the image acquisition rate, so as to analyze the images in real time.

 advantageously, the device comprises means for viewing the analyzed images, in the form of a screen connected to the means for digitizing and analyzing the images.

The invention also relates to a method for dimensional control of the deposition of a bead of material on a support, in particular a bead of glue on a sheet, the bead of glue being provided by a nozzle and the support being movable relative to the nozzle along a three-dimensional trajectory, characterized in that it comprises steps consisting in
- carry out an automatic learning of the position and the diameter of a reference bead
- determine the current position and diameter of the bead of material being deposited
- automatically compare the current position and diameter with the corresponding reference values, and depending on the result, indicate whether the position and diameter of the current cord are acceptable.

According to other characteristics of the control process:
to determine the position of the current cord relative to the reference cord, the distance between the median of the reference cord and the median of the current cord is determined, in a plurality of successive transverse planes of the cord in the direction of formation of the latter this
- to determine the diameter of the current bead, its transverse limits are determined using gray levels, the passage over the bead corresponding to a rising edge of a signal representative of the gray level, and the passage to leave the bead corresponding to a falling edge of the signal representing the gray level, the current diameter of the cord being constituted by the distance between the rising edge and the falling edge.

The invention will be better understood by referring to the following description given by way of nonlimiting example and to the attached drawings, in which
- Figure 1 shows schematically the elements of the control device according to the invention;
- Figure 2 shows the memory structure used in the device of Figure 1, in correspondence with steps of the control process
- Figure 3 shows the parameters useful during the learning phase of the method according to the invention;
- Figure 4 shows the parameters useful during the automatic control phase of the process according to the invention;
- Figure 5 shows a functional flow diagram of the steps of the control method according to the invention.

 Reference is made to FIG. 1. This diagram shows a block diagram of the control device 1 according to the invention. The device 1 is associated with an extrusion nozzle 2 known per se, allowing the extrusion of a bead of material 3, which is for example a bead of glue to be deposited on a support such as a sheet 5. The control device 1 includes lighting means 6 oriented towards the bead of glue 3 to be checked, a camera 7 also oriented towards the bead 3 being deposited, and intended to continuously record the images of the deposit, means 8 for processing the images of the camera 7, and a display screen 9 intended to represent for an operator an enlarged image of the deposited cord 3.

 The lighting means 6 are preferably constituted by a halogen lamp, the beam of which is directed towards the cord 3, and of sufficient power so that the illuminated area is not disturbed by the ambient lighting in the workshop.

The camera 7 is notably constituted by a camera
CCD black and white filming the bead of glue 3 deposited on the sheet 5 just after extrusion by the nozzle 2. The camera 7 and the lighting means 6 are preferably substantially coaxial and oriented towards the bead 3, and are fixed on the body of the nozzle 2 near the end of the latter, by means of a common support 10. Thus it is possible not only to obtain an accurate and large image of the cord 3, but also an image devoid of parasitic vibrations, since the movements of the camera 7 and of the nozzle 2 are coordinated.

 The image processing device 8 is a device comprising an image acquisition / digitization stage connected to an image analysis stage, these stages being produced by electronic circuits known per se, which will not be detailed in the part of this description.

Preferably, the images supplied by the camera 7 are analyzed at the video rate, which supposes that the image processing time is less than their acquisition time,
The analysis of the images is done in masked time relative to the acquisition time, so that the control device 1 does not lengthen the industrial cycle of glue deposition.

 According to the invention, the analysis means 8 comprise memory means 11 (FIG. 2) for saving the images of the defects of the cord 3 which are located during the deposition, these memory means 11 being organized to allow analysis images without increasing the glue deposition cycle time.

 The stored images are viewed either simultaneously or after the production of the cord 3.

Ultimately, it is the operator who, in view of the faults noted on the screen, decides to validate a cord deposit or to refuse it.

 Reference is made to FIG. 2, where the structure of the memory 11 of the processing means is schematically represented, serving to memorize the digitized images of the cord.

 The processing of images at the video rate is made possible by the use of a VRAM type video memory with dual access. This allows on the one hand the acquisition of the image number n in a memory area M1 and on the other hand, simultaneously, the processing by the processor of the image number nl which is stored in a memory area M2, as shown in Figure 2A. Then the image number n + 1 is digitized in M2 while the processor accesses the image n in M1, as shown in FIG. 2B.

 A high-performance video transfer bus 12 ensures communication from the VRAM memory to the processor. The processing time of a given image is thus limited to a duration less than the image acquisition time, of the order of 40 ms for example. The device 1 therefore makes it possible to control 25 images per second in this case, that is to say that it operates in real time video. When a fault is detected on image n, the acquisition of image number n + 2 is shifted in the memory area M3, as shown in FIG. 2C. At the end of the cycle, it is possible to view image number n again.

 Reference is made to FIGS. 3 and 4 to explain the steps of the method according to the invention.

 The implementation of the device 1 is carried out according to a process in two main stages: a learning phase (FIG. 3) and an automatic control phase (FIG. 4).

 The learning phase requires the operator to validate, on a plurality of images of a sequence of images, the position of the median 13 of the cord. Preferably, the entire glue deposition sequence of the learning phase is stored in memory, so that it can be reviewed at will.

As shown in FIG. 3, the bead 3 extruded by the nozzle 2 moves radially relative to the nozzle 2.
The learning will consist in giving on each image the position of the cord 3 symbolized by the median 13 of the cord.

Consider the processed image number n. We denote by C1 and
C2 the circles centered on the nozzle 2, on which one searches for the presence of the bead of adhesive 3. An and Bn denote the points of intersection of the median segment 13 of the bead with the circles C1 and C2.

 The coordinates An and Bn of the ends of the median of the cord are stored in memory. The system typically processes image number n in a time on the order of at most 40 ms. On the following image, that is to say the image number n + l, the points An + 1 and Bn + 1 will be deduced from the preceding points An and Bn by a tracking mechanism step by step. The learning phase only requires knowledge of the initial position of the cord, symbolized by the points Ao and Bo.

 At the end of this training, the device 1 will calculate the diameters and positions of the cord 3 (FIG. 3) on each image, thus constituting the reference measurements. Thereafter, each new bead analyzed will be compared with these reference measurements.

 The second phase of the process is an automatic control phase during each industrial bead glue deposition cycle 3. It continuously gives the diameters and positions of the bead 3 during each deposition operation.

 Consider the processed image number n (see Figure 4). The points An and Bn are provided by the learning phase as described above, then the successive profiles Pj orthogonal to the segment [An, Bn] are positioned.

 According to the invention, the control algorithm makes it possible to determine the upper edges B2j and lower B2i +, of the bead 3, despite the possible presence of reflections on the sheet and / or the bead.

 In practice, for this phase of the process, the different gray levels corresponding to the absence or the presence of the bead are used. By considering the gray levels on the segment Pj, the edge B2 corresponds to a rising edge and the edge B2i + 1 to a falling edge of a signal representative of the gray levels. On each of the profiles Pj, two rising edges and two falling edges are determined. The detected cord 3 corresponds to the pairing of a rising edge and a falling edge. The bead diameter is then defined as the distance between the two fronts. The position of the bead 3 in the image is given for example by the position of the rising edge relative to the median of the reference bead. Thus, erroneous detections, due to sheet metal edge effects or reflections, are eliminated.

 From the points B2 and B2i + ,, representing the position of the edges of the bead 3, the values obtained are compared with those of the reference bead saved during the learning phase described above. Possible position faults or drifts in the cord 3 are thus characterized.

The image corresponding to the defect is preferably saved in memory during the normal continuation of the processing until the end of the deposit operation.

 FIG. 5 schematically illustrates the unfolding of an algorithm implementing and summarizing the two main phases of the method, namely the learning phase, represented in 14, and the analysis phase, represented in 15. We have represented in 16 and 17 the actions of the operator corresponding to each respective phase 14,15 of the process. It should be noted that the algorithm (block 15) is preferably designed to edit a control report in the event of detection of a fault, in particular to give its dimensional characteristics. The fault detection information is used by the operator to judge whether to validate or reject the part on which the device 1 is working.

 In addition, when adjusting the parameters (block 14), an absolute reference of the position of the bead relative to a mark on the sheet is used to calibrate the entire device 1, both during the learning phase and during each of the adhesive bead deposition cycles.

 The device and method according to the invention make it possible to achieve the goals set, and have many advantages. The control device has great detection robustness, even in the presence of non-uniform lighting for a given image, or variable lighting from one image to another during deposition. It makes it possible to calculate up to ten diameters of adhesive per image and therefore ensures a control of the adhesive diameter every 2 mm during the deposition (by considering for example the parameters of the device described in FIG. 1).

 2. Device (i) according to claim 1, characterized in that the image processing means (8) comprise memory means (11) for recording the images of deposit defects, and means for scanning and analysis of the images thus memorized.

 3. Device (1) according to claim 2, characterized in that the memory means (11) comprise a fast memory, of the VRAM video memory type with dual access, and in that the digitization and analysis means are constituted by a processor connected to the memory means (11) by a fast video bus (12).

 4. Device (i) according to any one of the preceding claims, characterized in that the lighting means (6) comprise lighting with halogen light,

Claims (7)

and are placed so as to emit a beam directed substantially parallel to the camera (7).  5. Device (1) according to one of the preceding claims, characterized in that the camera (7) and the lighting means (6) are fixed on the nozzle (2) near its end, so as to obtain a large image.  6. Device (i) according to one of the preceding claims, characterized in that the image scanning and analysis processor operates at a rate greater than or equal to the image acquisition rate, so as to analyze images in real time.  7. Device (i) according to one of the preceding claims, characterized in that it comprises display means (9) of the analyzed images, in the form of a screen (9) connected to the digitization means and image analysis (8).  8. Method for dimensional control of the deposition of a bead of material (3) on a support (5), in particular a bead of glue on a sheet, the bead of glue being supplied by a nozzle (2) and the support (5) being movable relative to the nozzle (2) along a three-dimensional trajectory, characterized in that it comprises a learning phase (14) and an analysis phase (15), the learning phase (14 ) consisting in carrying out an automatic learning of the position and the diameter of a reference bead, and the analysis phase consisting in  - determine the current position and diameter of the bead of material (3) being deposited  - automatically compare the current position and diameter with the corresponding reference values, and depending on the result, indicate whether the position and diameter of the current cord (3) are acceptable compared to a predefined standard.  9. Method according to claim 8, characterized in that to determine the position of the current cord (3) relative to the reference cord, the distance between the median (13) of the reference cord and the median of the current cord is determined, in a plurality of successive transverse planes (Pj) of the cord in the direction of formation thereof.  10. Method according to claim 8 or claim 9, characterized in that to determine the diameter of the current bead, its transverse limits are determined using gray levels, the passage over the bead (3) corresponding to a front amount of a signal representative of the gray level, and the passage for leaving the bead (3) corresponding to a falling edge of the signal representative of the gray level, the current diameter of the bead being constituted by the distance between the rising edge and the falling edge.  11. Method according to any one of claims 8 to 10, characterized in that the analysis phase of an image is carried out in masked time during the acquisition of a subsequent image.