WO2009048415A1

WO2009048415A1 - Method and device for computerized inspection of objects

Info

Publication number: WO2009048415A1
Application number: PCT/SE2008/051135
Authority: WO
Inventors: Anders Reyier
Original assignee: Binar Aktiebolag
Priority date: 2007-10-08
Filing date: 2008-10-07
Publication date: 2009-04-16
Also published as: EP2198243A1; CN101815924A; SE0702253L; SE533521C2

Abstract

For computerized inspection for the determination of possible deviations in shape and size of objects (2) as compared to a reference, a scanner (8) with a digital camera (17) taking 2D-photos and a laser triangulation unit (16, 17) giving 3D-scannings are used, and the scanner (8) and the object (2) are moved in relation to each other during the scanning in order to change the position and/or orientation of the object (2) in relation to the scanner (8). A computer (11) is connected to the scanner, in which computer the reference, a predefined virtual object, e.g. from a CAD-drawing, is stored. The computer (11) has a software adapted on basis of the 2D-photo to determine the outlines of the object (2) in the scanned portion and on basis of the 3D-scanning to generate a three-dimensional photo of the surface within the portion. The computer (11) also has a software for the comparison of the scanned outlines of the object (2) and the three- dimensional surface within the portion with outlines and three-dimensional surface within a corresponding portion of the reference. The computer (11) is programmed to accept or reject the scanned object (2) depending whether possibly determined deviations fall within or outside the predefined tolerance limits.

Description

Method and device for computerized inspection of objects

TECHNICALFIELD The present invention relates to a method and a device for computerized inspection, especially of produced objects, for the determination of possible deviations in shape and size of the objects, using a digital camera taking 2D-photos.

In the present context, inspection refers to an examination of an object, wherein it is determined if the object fulfils predetermined requirements or if the object is to be rejected.

PRIOR ART

Methods and devices for computerized inspection of bolts provided with heads are previously known through e.g. WO 2005/063415 Al and DE 38 21 393 Al, and they utilize digital cameras taking 2D-photos for the determination of possible deviations in the shape of the bolts. However, these known methods and devices are not suitable for inspection of objects having a more complicated shape, for instance objects provided with blind holes.

Further, SE 529 377 C2 describes a method to locate and pick up objects placed on a carrier. A scanning operation is performed over the carrier. The scanning is performed with a scanner having a line laser. The result of the scanning is used to generate a virtual surface representing the scanned portion. The virtual surface is compared with a predefined virtual object corresponding to an object to be picked from the carrier. In this way, a portion of the virtual surface is identified which portion matches the predefined virtual object. Then, a robot arm is brought to move to a position corresponding to the identified portion of the virtual surface and to pick an object from the carrier in this position.

DISCLOSURE OF THE INVENTION

The purpose of the present invention is to provide a method and a device which are suitable for the inspection of objects having a complicated shape.

Said purpose is achieved with the initially mentioned method by

I RECORD COPY-TRANSLATION a) scanning at least a portion of the object to be inspected by using a scanner comprising the camera taking 2D-photos and a laser triangulation unit giving 3D- scannings; b) moving the scanner and the object in relation to each other during the scanning; c) using the result of the scanning to generate at least one virtual 3D-photo representing the scanned portion; d) comparing said at least one generated virtual 3D-photo with a corresponding portion of a predefined virtual object; and e) accepting or rejecting the scanned object depending whether deviations possibly found at the comparison fall within or outside the predefined tolerance limits.

In a corresponding manner, said purpose is achieved with the initially mentioned device having a scanner for scanning at least a portion of the object to be inspected and comprising the camera and a laser triangulation unit giving 3D-scannings; means to move the scanner and the object in relation to each other during the scanning; a computer connected to the scanner, in which computer a virtual object is stored, which computer has a software adapted on basis of the 2D-photo to determine the outlines of the object in the scanned portion, and on basis of the 3D-scanning to generate a three- dimensional photo of the surface within the portion, and which computer also has a software for the comparison of the scanned outlines and the three-dimensional surface of the object within the portion with outlines and a three-dimensional surface within a corresponding portion of the virtual object, and which computer is programmed to accept or reject the scanned object depending whether deviations, which have possibly been found, fall within or outside the predefined tolerance limits.

By means of the three-dimensional scanning with a laser triangulation unit it is easier to determine measures in depth to check if the scanned object fulfils the requirements set.

Preferably, the laser triangulation unit comprises a line laser. In that way a rapid determination of the shape and dimensions of the object is obtained.

Suitably, the relative movement comprises translation and/or rotation, preferably both, in order to change the position and/or the orientation of the object in relation to the scanner, and it is recommended that the movement is performed by letting the object pass the stationary scanner. Preferably, said translation and/or rotation are performed by a robot, and the robot turns suitably the object about at least one axis of rotation. As the robot may rotate and turn the object, all blind holes and similar structures in the object may be carefully measured, and their conformance with corresponding structures in the reference formed by the predefined virtual object stored in the computer is checked.

It is also suitable that the object is illuminated during the scanning, preferably alternately from two directions, hi that way, it will be easier to obtain exact data at the photography.

Further, it is suitable that possible deviations are determined at fixed points of the object. In such a way, all points, for which there are data, need not be checked but the inspection may be accelerated.

Further, it is preferred that the scanning is performed discontinuously, i.e. only at certain points of the object, where the requirement is to determine possible deviations, so that different portions of the object may be scanned separately. Also this accelerates the inspection.

BRIEF DESCRIPTION OF THE ENCLOSED DRAWINGS

Below, the invention will be described more in detail with reference to the preferred embodiments and the enclosed drawings.

Fig. 1 is a sketch showing an embodiment of the inspection device of the invention.

Fig. 2 is a side view of the inspection device of Fig. 1.

Fig. 3 is a schematic cross sectional view of a combined laser detector and camera used in the inspection device of Fig. 1.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS Figs. 1 and 2 show a device for computerized inspection, especially of produced objects, for the determination of possible deviations in shape and size of the objects, using a digital camera taking 2D-photos.

According to the invention, at least one portion of the object 2 to be inspected is scanned using a scanner 8 with a laser triangulation unit comprising a laser transmitter 16 giving 3D-scannings and a laser detector 17, which is combined with the camera taking 2D-photos. The scanner 8 and the object 2 are moved in relation to each other during the scanning, and the result of the scanning is used to generate at least one virtual 3D-photo representing the scanned portion. The virtual 3D-photo is compared with a corresponding portion of a predefined virtual object, a reference, and the scanned object 2 is accepted or rejected depending whether possibly detected deviations fall within or outside predefined tolerance limits. Thus, possible deviations are determined at certain fixed points of the object 2.

In Figs. 1 and 2, the object 2 is shown lying on a carrier 1, which may have an arbitrary appearance but in the Figs. 1 and 2 it is a conveyor belt and it moves the object 2 in relation to the scanner 8 during the scanning. The carrier 1 may also be stationary and the object 2 may be pushed or drawn forward on the carrier 1 by a suitable device (not shown), e.g. a hydraulically, pneumatically or electrically operated rod piston. Preferably, the scanner 8 is stationary, but when the carrier 1 is fixed, the scanner 8 is movable in relation to the object 2 and is shown suspended in a wagon 9 which may run along a beam 9'. When the carrier 1 is in principle fixed but still movable, it may in a not shown embodiment consist for instance of some kind of a suitably low container or also of a pallet. The relative movement comprises translation and/or rotation in order to change the position and/or orientation of the object 2 in relation to the scanner 8. As a rule, the object 2 has to be turned around an axis of rotation so that it will be possible to scan and photograph predetermined portions of the object 2.

In order to draw the object 2 forward on a fixed carrier 1 , an industrial robot 4 may be used, for instance. The robot 4 shown comprises an arm 5, which may be projected and rotated in both the horizontal and vertical planes. The arm 5 has a free end provided with a device 6 to grip objects 2. It may for instance be provided with a suction cup or a magnet (not shown) to pick up metal objects 2. However, in the preferred embodiments of the invention, the robot arm 5 is adapted to grip objects by using a gripping device 6 in the form of a head 6' with gripping fingers 7. The head 6' is rotatably fixed to the arm 5, and at least one of the gripping fingers 7 is movable. In Fig. 1 two gripping fingers 7 are shown, but it is easily understood that the gripping device 6 may have more than two gripping fingers 7. For instance, it may have three, four, five, or even more gripping fingers 7. Preferably, at least two of the gripping fingers 7 are movable in relation to each other. Preferably, the gripping device 6 is articulately mounted on the robot arm 5 in such a manner that the gripping device 6 may be pivoted about different axes and hence orientated in relation to the object 2 to be gripped by the gripping device 6. The use of a gripping device 6 with movable fingers 7 involves the advantage that greater precision may be achieved and that the reliability of the grip is high. The gripping device 6 is preferably so arranged that it may be pivoted about axes which are perpendicular to each other. Preferably, it may be pivoted about at least three axes which are perpendicular to each other. In advantageous embodiments of the invention the gripping device 6 may be pivoted about more than three axes. For instance, it may be arranged in such a way that it may be pivoted about six axes. If the robot 4 is so complex, that it easily may perform all necessary movements and rotations of the object 2, the scanner 8 may naturally also be mounted to the robot 4, if desired.

The laser transmitter 16 may be a point laser, but with the embodiment of the invention shown in Figs. 1 and 2 it is preferably a line laser. The use of a line laser 16 involves the advantage that a portion may be scanned with only one relative movement of the scanner 8. In a line laser the light is extended from a lumped laser source towards a line. This may be achieved by using a suitable objective lens of e.g. glass, plexiglass or quartz. As Fig. 1 best shows, the scanner 8 with the laser triangulation unit comprises a laser transmitter 16, from which a linear laser beam 10 may be transmitted, and a laser detector 17, which may detect a laser beam having been transmitted from the transmitter 16 and having been reflected from a surface. The laser transmitter 16 may for instance be a line laser of the kind marketed under the trade name Lasiris™ by Stacker Yale Canada, 275 Kesmark, Montreal, Quebec, Canada. Of course, other laser transmitters are, however, also possible. As mentioned above, the laser detector 17 also functions as a 2D-camera in the scanner 8. With the embodiment shown in Figs. 1 and 2, the laser beam 10 is directed substantially perpendicularly to the object 2 to be inspected, while the laser detector 17 has a sensor 17' (Fig. 3) in common with the camera, which sensor detects light being reflected somewhat obliquely. Of course, the laser beam 18 may also, if desired, be directed somewhat obliquely towards the object 2, and the detector may detect light being reflected substantially perpendicularly upwards.

A computer 11 is connected to the scanner 8 with the laser triangulation unit, via a connection 12 which is shown as a cable but which may also be a wireless connection. The computer 11 has a software adapted to generate a virtual three-dimensional surface based on data received from the scanner 8, i.e. the laser detector 17, during a scanning operation. The computer 11 has also a software for receiving the 2D-photo from the combined camera and laser detector 17 via the connection 12, and a software representing a stored virtual object, being a reference, and a software for comparison of the reference with the photographed and scanned portions of the object 2, and for determining possible deviations as to shape and size between the reference and the scanned object 2. It should be understood that the reference corresponds to the physical object 2 to be inspected. The reference may for instance be based on a CAD-model used to produce a corresponding physical object 2.

Further, the computer 11 is connected to the robot 4 via a connection 4' shown as a cable but which also may be a wireless connection, and it has a software for controlling the movement of the robot arm 5, of the gripping device 6 and of the fingers 7 in the extent necessary for moving the object 2 so it gets the orientation and the position required for the photography and scanning. Finally, the computer 11 has a software to control a separation of objects which possibly do not fall within the predetermined tolerance limits for dimensions and shape. Such a separation of rejected objects may be performed with the robot 4, when such one is implemented in the inspection device, or otherwise for instance with a simple pushing device (not shown) pushing rejected objects aside from the carrier 1 while accepted objects may stay on the carrier 1 for transmission to a following treatment station (not shown). For illustrative purposes the computer 11 is shown as being separated from the robot 4. Fig. 4 shows that the robot 4 may transport the accepted objects 2 to another working station 19, as for instance a machine for further treatment of the objects 2.

Although the computer 11 is shown as a separate unit in the drawings, it should, however, be understood that alternatively it may consist of an integrated part of the robot 4.

In the embodiment of the inspection device shown in the figures, the object 2 to be inspected has a vertical through hole 3 and a horizontal blind hole 3'. The dimensions of the through hole 3 may be scanned when the linear laser beam 10 is moved past the hole 3. In order to be able to scan also the dimensions of the blind hole 3', the orientation of the object 2 must be changed by the robot 4 gripping the object and turning it upwards so that the longitudinal direction of the blind hole 3' substantially coincides with the direction of the linear laser beam 10. When the object 2 has a simple shape, for instance it has only one shallow blind hole facing upwards when the object comes to the scanner 8, no such reorientation of the object 2 is required by means of the robot 4 which is not needed for this purpose. To achieve a desired illumination of the object 2 at the photography there is, as shown in Fig. 3, suitably a first lighting unit 22 surrounding an objective lens 23 in the combined laser detector and the 2D-camera 17. The lighting unit 22 is shown as an annular fluorescent lamp 22 but, of course, other embodiments may be used, if desired, e.g. a ring (not shown) of light emitting diodes. At the photography it is suitable that the optic axis of the objective lens 23 forms a right angle to the object 2, which may be achieved for instance by the robot 4 angling the object 2, if the optic axis forms another angle to the horizontal plane. Preferably, the inspection is thus performed with such an orientation of the object 2 that the laser beam 10 hits the object substantially perpendicularly, and then the object is angled so that the optic axis of the objective lens 23 forms a substantially right angle to the object 2 during the photography.

If desired, a second lighting unit 21 may be arranged at the side of the predetermined transport path of the object 2, so that the object may be illuminated with sweep light. As may be seen from Fig. 2, the unit 21 is suitably mounted at the scanner 8, on the opposite side of the laser transmitter 16 in relation to the combined camera and the laser receiver 17, so that the laser transmitter 16 is substantially midway between the two lighting units 21 and 22. This second lighting unit 21 is usually used alternately with the first lighting unit 22, but they may be used together, if desired. It may be worth pointing out that the vertical distance between the scanner unit 8 and the object 2 is considerably exaggerated for the purpose of better clarity.

INDUSTRIAL APPLICABILITY

The computerized inspection according to the invention may be applied everywhere where inspection of objects, especially produced objects, may be performed by the combination of 3D-scanning and 2D-photography described above with a single disposition of the object for determining possible deviations in shape and size of the object.

Claims

1. A method for computerized inspection, especially of produced objects (2), for the determination of possible deviations in shape and size of the objects (2), using a digital camera (17) taking 2D-photos, wherein a) at least a portion of the object (2) to be inspected is scanned by using a scanner

(8) comprising the camera (17) taking 2D-photos and a laser triangulation unit (16, 17) giving 3D-scannings; b) the scanner (8) and the object (2) are moved relative each other during the scanning; c) the result of the scanning is used to generate at least one virtual 3D-photo representing the scanned portion; d) said at least one generated virtual 3D-photo is compared with a corresponding portion of a predefined virtual object; and e) the scanned object (2) is accepted or rejected depending on whether deviations possibly found at the comparison fall within or outside the predefined tolerance limits, characterised in that f) scanning of the object (2) is performed discontinuously, so that all portions of the object (2) are scanned separately.

2. A method according to claim 1, characterised in that the laser triangulation unit (16, 17) comprises a line laser.

3. A method according to claim 1 or 2, characterised in that the relative movement comprises translation and/or rotation in order to change the position and/or orientation of the object (2) in relation to the scanner (8).

4. A method according to claim 3, characterised in that the object (2) is rotated about at least one axis of rotation.

5. A method according to any of claims 1 to 4, characterised in that the object (2) is moved past the scanner (8), which stands still.

6. A method according to any of claims 1 to 5, characterised in that the object (2) is illuminated (21, 22) during the scanning.

7. A method according to claim 6, characterised in that the object (2) is illuminated (21, 22), preferably alternately, from two directions.

8. A method according to any of the claims 1 to 7, characterised in that possible deviations are determined at fixed points of the object (2).

9. A device for computerized inspection, especially of produced objects (2), for the determination of possible deviations in shape and size of the objects (2), by using a camera (17) taking 2D-photos; a scanner (8) for scanning at least a portion of the object (2) to be inspected and comprising the camera (17) and a laser triangulation unit (16, 17) giving 3D-scannings; means (4) for moving the scanner (8) and the object (2) in relation to each other during the scanning; a computer (11) connected to the scanner (8), which computer (11) has a software adapted on basis of the 2D- photo to determine the outlines of the object (2) in the scanned portion, and on basis of the 3D-scanning to generate a three-dimensional photo of the surface within the portion, and which computer (11) also has a software for the comparison of the scanned outlines and the three-dimensional surface of the object (2) within the portion with outlines and a three-dimensional surface within a corresponding portion of the virtual object, and which computer (11) is programmed to accept or reject the scanned object (2) depending whether deviations, which have possibly been found, fall within or outside the predefined tolerance limits, characterised in that said scanner (8), camera (17) and laser triangular unit (16, 17) are arranged to perform discontinuous scanning of the object (2).

10. A device according to claim 9, characterised in that the laser triangulation unit (16, 17) comprises a line laser.

11. A device according to claim 9 or 10, characterised in that the relative movement comprises translation and/or rotation.

12. A device according to claim 11, characterised in that the object (2) is rotated about at least one axis of rotation.

13. A device according to claim 11 or 12, characterised in that said translation and/or rotation is performed by a robot (4).

14. A device according to any of claims 9 to 13, characterised in that the scanner (8) is fixed and the object (2) is moved.

15. A device according to any of claims 9 to 14, characterised in that at least one lamp (21, 22) is provided to illuminate the object (2) during the scanning.

16. A device according to claim 15, characterised in that lamps (21, 22) are arranged to illuminate the object (2), preferably alternately, from two directions.