WO2021176384A1

WO2021176384A1 - System for locating and treating surface defects on objects, in particular motor vehicle bodies

Info

Publication number: WO2021176384A1
Application number: PCT/IB2021/051795
Authority: WO
Inventors: Daniel RASPONE; Marco Piloni
Original assignee: Geico Spa
Priority date: 2020-03-06
Filing date: 2021-03-04
Publication date: 2021-09-10
Also published as: IT202000004792A1

Abstract

A station for locating and/or treating (10) surface defects on an object (11) (in particular a motor vehicle body) comprises a device (35) for "zeroing" the position of the object (11) in the station. This zeroing device (35) comprises in turn a projector (16) and at least one camera (17). The projector (16) projects a light grid (18) towards the zone of the station intended to receive the object (11) and a processing unit (19) for calculating the "zero position" calculates in the image taken by the camera (17) the position of predetermined points of the object (11) with respect to the grid. This calculation allows the deviation in position of the object with respect to the system of coordinates (20) of the station to be determined. In this way, when the object passes between various stations (10) it is possible to obtain always the real position of the defects detected, despite any differences in positioning of the object inside the stations.

Description

Title

"System for locating and treating surface defects on objects, in particular motor vehicle bodies"

DESCRIPTION

The present invention relates to a system for locating and treating surface defects on objects, in particular motor vehicle bodies. In particular, the defects may be appearance defects on painted surfaces.

The prior art has proposed systems for performing scanning by means of cameras which are able to identify defects on the surfaces of objects, such as motor vehicle bodies. These defects may be, for example, local variations in colour, reliefs, missing material or irregularities on the surface. These defects are referred in the technical jargon as "appearance defects" since the user may visually perceive them. Generally they have dimensions of at least 10-20 microns.

The localization of the defects on a complex surface, such as a motor vehicle body, is a fundamental step of the industrial process since it allows the tracing and optionally the correction of the appearance defects of the product which may be noticed by the end user and which often are regarded as being an indication of the quality of the entire product.

In the prior art, automatic systems have been proposed where the surface to be examined is scanned so as to obtain electronic images of portions of this surface. The images thus obtained are then processed by special computer programs which provide the spatial coordinates of the defect detected. These coordinates are then transmitted to defect treatment stations arranged downstream of the scanning station. The treatment stations may comprise for example both robotic devices which operate on the zone of each defect in order to eliminate it and robotic devices which highlight by means of light indicators the position of the defects so that a human operator may examine them and decide the operation to be carried out on them.

In particular in the case of motor vehicle bodies, a problem of the known systems is that of providing the coordinates of the defects which precisely relate to the object being examined and not simply to the spatial coordinates of the single stations. In fact, the vehicle body transport system may not stop and position the vehicle bodies in a precise manner, such that the coordinates of the defects detected by the scanning system in a station and the subsequent positioning of the robotic systems in the following stations may be subject to errors which may also be of a significant nature. The prior art has attempted to solve the problem by providing suitable precision mechanical stops which stop a vehicle body always exactly in the same position inside each station.

The engagement, with the mechanical positioning system, of the vehicle body (or of the skid locked together with the body for transportation thereof), however, increases the cycle time of the stations, involves the need for additional mechanisms and movements in the station and, in any case, is subject to imprecision due to the mechanical play and the wear of the mechanical stops.

The object of the present invention is to provide a system which does not require precise positioning of the objects inside the stations.

In view of this object, the idea which has occurred is to provide, according to the invention, a method for locating and/or treating surface defects on an object comprising providing at least one station, intended to receive the object, the at least one station comprising an operating head for detection and/or treatment of surface defects, at least one first robotic device for positioning the operating head along paths and/or points above the surfaces of the object, the paths and/or points being identified as a function of coordinates of the paths and/or positioning points of the head with respect to a reference system of the station, characterized by the steps of projecting a light grid onto surfaces of the object; detecting by means of a camera the light grid projected on the object in the station; automatically comparing, by means of an electronic processing unit, the position of the lines of the light grid with respect to the pre-set points of the object; calculating a deviation of these points with respect to the lines of the light grid; correcting, depending on this deviation, the coordinates of the paths and/or positioning points of the head with respect to the reference system of the station.

The idea which has also occurred is to provide, according to the invention, a station operating according to the method of the invention and comprising an operating head for detection and/or treatment of surface defects, at least one first robotic device connected to a control unit for positioning the operating head along paths and/or points above the surface of the object, a device for projection of a light grid on surfaces of the object and a camera for detecting the image of the light grid projected on the object in the station; an electronic processing unit which is connected to the camera so as to receive the image of the light grid and is suitable for calculating the position of lines of the light grid with respect to predetermined points of the object, calculating a deviation of these points with respect to the lines of the light grid and correcting, depending on this deviation, the coordinates of the paths and/or positioning points of the head with respect to the reference system of the station.

In order to illustrate more clearly the innovative principles of the present invention and its advantages compared to the prior art, an example of embodiment applying these principles will be described below with the aid of the accompanying drawings. In the drawings:

- Figure 1 shows a schematic view of a station for detecting or treating defects provided according to the invention;

- Figure 2 shows a schematic view of a system for zeroing the position of a vehicle body in the station according to Figure 1 ;

- Figures 3 and 4 show views similar to that of Figure 1 , but for two variations of embodiment of a system according to the invention.

With reference to the figures, Figure 1 shows a station 10 realized in accordance with the invention for detecting or treating surfaces defects on an object 11 , for example a body of a motor vehicle. The said defects may for example comprise blisters, dents, scratches, areas where paint may be missing, the possible trapping in the paint of foreign bodies (threads, powder, etc.), etc. Flere the term "treatment of defects" will be understood as meaning both a physical treatment of the defect for removal thereof and simply a visual indication of the position of the defect.

Advantageously, the station 10 comprises a known transport system 12 which transports in sequence the objects 11 into the station and removes them from the station at the end of the operations performed in the station. The transport system 12 may be for example a sequential conveyor, such as also a known skid conveyor with the objects (in particular motor vehicle bodies) mounted on known skids.

The station 10 comprises at least one robotic device or positioner 13 for carrying out operations on the surface of the object 11 inside the station. The robotic device 13 will be of a known type designed to position and/or direct suitably an operating head 14 towards and onto the object in the station. For example, the robotic device 13 may advantageously be a suitably programmed robot for automatically moving the operating head 14 along paths above the surfaces 15 of the object 11. The robot may be advantageously a known anthropomorphic robot arm, for example with six axes which can be controlled in an interpolated manner.

The station 10 may be for example a station for detecting defects or a station for treating the previously detected defects.

As will become clear below, several stations 10 according to the invention may be arranged sequentially so that the objects 11 pass in sequence from one station to another. For example, a station 10 for detecting the defects and a following treatment station 10 which is able to operate on the previously detected defects may be provided. The treatment station may comprise both automated treatments and manual treatments or combine the two types of treatment, as will become clear below.

In the case of a defect detection station 10, the operating head 14 may be for example a scanning head for detecting defects, known per se. Usually these heads comprise a vision system, namely they comprise at least one camera and an illumination device for scanning the surface and acquiring images. These images are then sent to a suitable processing unit which, by means of techniques known per se, identifies in them the surface defects and, depending on the position of the head, calculates the coordinates of the spatial position of the defect. These coordinates are then sent to the following stations for treatment of the defect when the object 11 is moved into these following stations.

In a defect treatment station, the operating head 14 may be for example a mechanical processing head known per se for treating the defect, for example for smoothing and/or polishing the surface.

The operating head 14 may also be a head for projecting localized light rays so as to illuminate, for example, with precision the previously detected defects and thus allow a human operator to identify them easily and examine them in order to decide which operations to perform (for example, manual removal of the defect by choosing suitable tools) or the subsequent treatment to be carried out on the object 11 as a result of the defect.

The station 10 according to the invention comprises a device 35 for "zeroing" the position of the object 11 in the station. This zeroing device 35 in turn comprises a projector 16 and at least one camera 17.

The projector 16 projects a light grid 18 towards the zone of the station intended to receive the object 11. The light grid 18 is advantageously projected in a predetermined position with respect to a system of reference coordinates 20 of the station, so as to constitute an absolute reference point within the station. When an object 11 is placed inside the station 10, the camera 17 records the image of the object 11 and the grid 18 which is projected onto it and sends this image to a processing unit 19 for calculating the "zero position", said unit calculating in the image the position of predetermined points of the object 11 with respect to the grid 18 and thus determining the exact position of the object 11 with respect to the grid and, consequently, with respect to the system of coordinates 20 inside the station (or determines the deviation in the position of the object 11 with respect to the system of coordinates 20 of the station).

For example, Figure 2 shows in schematic form the image of the grid 18 projected in a corner zone 21 of an object 11 inside the station. The processing unit 19 obtains from the image significant values of the spatial position of the object with respect to the grid. For example, a distance 22 of a first edge of the object from a line of the grid and a second distance of another edge of the object from a line of the grid perpendicular to the first line are calculated. Moreover, if necessary, the processing unit 19 may also determine an angle 24 of an edge of the object from a line of the grid so as to detect also any slight rotations of the object with respect for example to the direction of transport along the line. Obviously, if this rotation detection is of no interest (for example because it is negligible within the stations) this angle measurement may be omitted. If the positioning problem is only in a precise direction (for example in the transport direction), the system may also calculate only the position of the object with respect to the grid in this direction.

The measurements performed by the processing unit 19 using the grid thus allow a position, so-called "zero position", of the object 11 in the station to be determined. The station may also comprise a unit 25 for controlling the positioner 13 which, depending on the zero position detected by the device 35, may displace the coordinates which the positioner must assume in the station for the various operations of the head 14 on the surface of the object. The control unit 25 and the processing unit 19 may also be combined in a special management unit 26, for example a suitably programmed electronic processing system.

If for example the head 14 is a defect detection head, a known control unit 25 of the station 10 traces the defects in the images taken by the head 14 and determines their spatial location based on the known positioning coordinates of the robotic device 13 (and therefore the head) during scanning of the surface.

The spatial coordinates of the defects with respect to the system of coordinates of the station may be then transferred by the control unit depending on the "zero" position of the object 11 which has been detected by the zeroing device. In other words, the position coordinates of the defects are transferred from the reference system of the station to a reference system of the object 11. In this way, the exact position of the object inside the station is no longer of importance.

The zero position of the object with respect to the grid may serve both to define the zero point of a system of local coordinates and to identify in the same station the deviation in position of an object which has reached the station with respect to a position of an object which has previously reached the station.

For example, the station may be set using a "sample" object (for example a sample motor vehicle body) in order to be able to subsequently carry out an operation (detection of defects, elimination of defects or the like) on the "real" objects which will then be gradually conveyed to the station during the normal operation of the station.

In this way, during setting-up of the station, all the operations will be in relation to the position of the sample object. When the station then carries out these operations on the real objects which gradually arrive at the station, the control unit, via the zero processing unit 19, may correct the coordinates of the operations, which related to the sample object, depending on the deviation in the position of the real object with respect to the position which was detected with the sample object.

Moreover, when during normal operation of the plant, an object passes to a following or new station 10, in the new station the "zeroing" procedure may be carried out in the new station by means of the zeroing device of this new station. Basically, the grid 18 in the new station may fall into a slightly different position on the object 11 owing to the error in positioning of the object 11. The image taken by the camera 17 of the new station may therefore have pre-set reference points on the object 11 which may be in a different position on the grid compared to that detected in the preceding station. The difference between that detected in the first station and that detected in the new station will be the positioning error of the object 11 between the first station and the second station which must be corrected in order to ensure that the spatial reference on the object is identical in both stations and, therefore, that the coordinates of the defects on the object 11 detected in the first station coincide exactly with the real position of the defects on the object detected in the second station. The stations according to the invention may also interchange the data for zeroing of the position of the objects.

For example, if in the first station the measurements 22, 23 and 24 with respect to the grid were detected with a first value, in the new station at the same points of the object, measurements 22', 23' and 24' with a second value will be detected. The differences Difi =22-22’, Dif₂=23-23’ and Dif₃=24-24’ will be the positioning error of the object between the first station 10 and the new station 10.

The processing unit 19 for zeroing of the new station will therefore send the correction parameters to the control unit 25 of the new station so that the control unit 25 may control operation of the robotic device 13 in such a way that the head 14 acts directly on the defects detected by the detection station.

The same procedure may be performed for all the stations 10 through which the object 11 will be transported, thus ensuring that the coordinates of points to be defined on the surface of the object always indicate the same real points on the object, even if the object 11 is positioned differently in the various stations 10.

Figure 3 shows a variant of the invention in which the zeroing device 35 is mounted on a robotic positioner 36 which may also be similar to the positioner 13 of the head 14.

In this way the device 35 may be moved in the space inside the station and, for example, follow with precision paths on the surfaces of the object in order to determine the real position of reference points of the object 11 .

The zeroing device 35 may thus be positioned precisely according to the system of coordinates of the station so as to be able to correct with precision the paths of the system for detection or removal of the defects and provide the coordinates of the defects with precision according to reference points of the object 11 .

By moving the zeroing device 35 with a robotic positioner, the zeroing operation may be performed also only locally, bringing the device 35 into a suitable predetermined position on the object in order to check the position at least of that zone of the object which must then undergo the operation envisaged for the head 14 (for example scanning of the surface with the head 14 in order to search for defects).

This is particularly useful for obtaining the high degree of precision necessary for a system intended to search for (and if necessary eliminate) defects. In fact, a few millimetres of deviation in the reference point of the coordinates of the station or between one station and another one may result in false positives, the failure to scan some regions of the surface or incorrect treatment for removal of the defects.

Moreover in this way the device 35 is prevented from assuming a fixed position which could interfere with the movement of the positioner 13 during the detection or elimination of the defects.

Figure 4 shows a variant of the invention in which the zeroing device 35 is mounted on the same positioner 13 of the head 14. In this way the aforementioned advantages and the further advantage of a lower cost of the system are obtained. Moreover, the correction of the coordinates of the defects is even more precise, since it is performed directly by the same positioning system of the device which detects and/corrects the defects. At this point it is clear how the objects of the invention have been achieved by providing a system which is able to operate suitably on defects present on the surfaces of an object, such as a painted vehicle body, while also displacing it between different stations.

Obviously, the above description of an embodiment applying the innovative principles of the present invention is provided by way of example of these innovative principles and must therefore not be regarded as limiting the scope of the rights claimed herein.

For example, the operating head 14 may have a form, proportions and operation different from those described, it being possible for it to be any type of head for detecting defects, treating surfaces or helping identify defects, also operating remotely from the surfaces of the object. The robotic positioning device may also be different from that shown by way of example. For example, in the case of a head for helping identify defects which projects a light indicator onto the object in order to indicate to the human operators where a defect is present, the robotic device may also be arranged in the station at a distance from the object 11 and simply move so as to orient and direct the light indicator on the surface of the object.

In any case, although only one robotic device has been shown here, in the stations 10 there may be several robotic devices with several heads 14, for example for carrying out operations in parallel on the object and speeding up the cycle times of the station and/or carrying out different operations by means of different heads 14.

In the case of a defect detection head 14 it is also possible to use as camera 17 the same camera situated inside the head 14.

Claims

1. Method for locating and/or treating surface defects on an object (11) comprising providing at least one station (10), intended to receive the object, the at least one station (10) comprising an operating head (14) for detection and/or treatment of surface defects (14), at least one first robotic device (13) for positioning the operating head (14) along paths and/or points above the surfaces (15) of the object (11), the paths and/or points being identified as a function of coordinates of the paths and/or positioning points of the head (14) with respect to a reference system (20) of the station, characterized by the steps of:

- projecting a light grid (18) onto surfaces of the object;

- detecting by means of a camera (17) the light grid (18) projected on the object (11) in the station;

- automatically comparing, by means of an electronic processing unit (19), the position of the lines of the light grid (18) with respect to the pre-set points of the object (11);

- calculating a deviation (22, 23, 24) of these points with respect to the lines of the light grid (18);

- correcting the coordinates of the paths and/or positioning points of the head (14) with respect to the reference system (20) of the station according to said deviation.

2. Method according to claim 1 , characterized in that the projection of the light grid is carried out with a projection device (35) mounted on a second robotic positioning device (36).

3. Method according to claim 1 , characterized in that the projection of the light grid is carried out with a projection device (35) mounted on the same robotic positioning device (13).

4. Method according to claims 2 or 3, characterized in that the projection device (35) comprises both a projector (16) of the light grid and the camera (17).

5. Method according to claim 1 , characterized in that the operating head is designed to comprise a vision system for detecting surface defects on the surfaces of the object.

6. Method according to claim 1 , characterized in that the operating head is designed to comprise a mechanical processing head.

7. Method according to claim 1 , characterized in that the operating head is designed to comprise a head for the projection of localized light rays in order to illuminate previously detected defects.

8. Station (10) operating according to the method of any one of the preceding claims for locating and/or treating surface defects on an object (11), comprising an operating head (14) for detection and/or treatment of surface defects (14), at least one first robotic device (13) connected to a control unit (25) for positioning the operating head (14) along paths and/or points above the surfaces (15) of the object (11), a device (35) for projection of a light grid (18) on surfaces of the object and a camera (17) for detecting the image of the light grid (18) projected on the object (11) in the station; an electronic processing unit (19) which is connected to the camera so as to receive the image of the light grid and is suitable for calculating the position of lines of the light grid (18) with respect to predetermined points of the object (11), calculating a deviation (22, 23, 24) of these points with respect to the lines of the light grid (18) and correcting, depending on said deviation, the coordinates of the paths and/or positioning points of the head (14) with respect to the reference system (20) of the station.

9. Station according to claim 8, characterized in that the projection device (35) is mounted on a second robotic positioning device (36).

10. Station according to claim 8, characterized in that the projection of the light grid is carried out with a projection device (35) mounted on the same robotic positioning device (13).

11. Station according to claims 9 or 10, characterized in that the projection device (35) comprises both a projector (16) of the light grid and the camera (17).

12. Station according to claim 8, characterized in that the operating head comprises a vision system for detecting surface defects on the surfaces of the object.

13. Station according to claim 8, characterized in that the operating head (14) comprises a mechanical processing head.

14. Station according to claim 8, characterized in that the operating head (14) comprises a head for projection of localized light rays in order to illuminate previously detected defects.