GB2376068A

GB2376068A - Method and apparatus of in-process inspection

Info

Publication number: GB2376068A
Application number: GB0113207A
Authority: GB
Inventors: William Clocksin; Charalampos Bakolias
Original assignee: MILLENNIUM VENTURE HOLDINGS LT
Current assignee: MILLENNIUM VENTURE HOLDINGS LT
Priority date: 2001-05-31
Filing date: 2001-05-31
Publication date: 2002-12-04
Also published as: GB0113207D0

Abstract

The invention concerns an inprocess inspection of a workpiece, such as a ceramic tile, after the workpiece has been shaped into its final form. The workpiece is moved past a beam of light 51 which is directed onto the manufactured surfaces of the workpiece. The pattern of light incident upon the workpiece is sensed and then compared with a standard form of light pattern so as to determine any defects in the workpiece. Conveniently, the workpiece is movable on a conveyor belt past illuminating and sensing devices, the latter of which converts the sensed pattern into electrical signals preferably digital signals, which are then compared with digital signals corresponding to a standard form of light pattern.

Description

METHOD AND APPARATUS OF IN-PROCESS INSPECTION Field of Invention The present invention relates to a method and apparatus for performing in-process inspection, particularly of the sides and chamfers of workpieces, such as ceramic tiles.

Background of the Invention It is well known in the manufacture of workpieces such as ceramic tiles to perform the step of"squaring"in which a straight edge, and optionally a chamfer, is ground simultaneously onto each of the four sides of the tile. This is generally achieved, as will hereinafter be described in more detail with reference to Figures 1 and 2, by grinding two opposed sides of the ceramic tiles so that they are parallel one with the other, rotating the tile through 90 and grinding the remaining two opposed sides so that they are parallel one with the other and at right angles to the two previously ground sides.

It is possible for the squaring process to introduce defects into the side and chamfer of the tile. Typical defects are chamfer size and position out of tolerance, periodic ridges along the side due to prior adjustment of the grinding machine, and chips of material removed from the side and chamfer.

Furthermore, the squaring process may expose defects inherent in the ceramic material, such as cracks or fissures that are visible to the naked eye.

Summary of the Invention It is an object of the present invention to provide a method and apparatus in which the above mentioned disadvantages are substantially overcome.

According to one aspect of the present invention there is provided a method of performing an inprocess inspection of a workpiece, comprising locating a workpiece on support means, directing a light beam upon the workpiece, arranging for relative movement between the workpiece and light beam, sensing a light pattern on the workpiece, and comparing the light pattern with a standard form of light pattern for determining defects in the workpiece.

In one preferred embodiment of the present invention the workpiece is movable on the support means past a fixed beam of light, and sensing means are provided for sensing the light pattern incident upon the workpiece. Preferably, electrical signals are generated in the sensing means representative of the light pattern for producing a visible image of the light pattern. The electrical signals are preferably digital signals.

Conveniently, the displayed image is compared to a standard acceptable image for determining whether the display image conforms to the standard.

In another embodiment in accordance with the present invention the workpiece is illuminated with a pair of light beams one from each side, respectively, of the workpiece.

In an alternative embodiment the workpiece is illuminated with two pairs of opposed light beams, each pair being spaced in the direction of motion of the workpiece between the two oppositely located light beams of the first pair of light beams. Conveniently, the workpiece is rotated through 900 prior to the workpiece being illuminated by the second pair of light beams.

According to another aspect of the present invention there is provided an apparatus for performing an inprocess inspection of a workpiece, comprising support means upon which a workpiece is located, illuminating means for illuminating the workpiece with a light beam, the support means and illuminating means being movable one relative to the other so that the light beam passes along the workpiece, sensing means for sensing a light pattern on a surface (s) of the workpiece and comparator means for making a comparison of the light pattern sensed by the sensing means and a light pattern of an acceptable standard of light pattern.

Conveniently, the support means is movable and the illuminating and sensing means are stationary. The sensing means preferably generates electrical signals representative of the light pattern upon the workpiece, and display means are provided to display an image corresponding to the light pattern.

In an alternative embodiment of the present invention the comparator means is arranged to compare the displayed image with an acceptable standard image to determine the standard manufactured workpiece.

In a further embodiment in accordance with the present invention a pair of illumination means are located on each side, respectively, of the support means.

In another embodiment in accordance with the present invention the apparatus comprises two pairs of opposed illumination means spaced one relative to the other in the direction of movement between the illumination means and the support means. Conveniently, rotation means are provided for rotating the workpiece 90 , the rotation means being located between the two spaced pairs of illuminating means.

In an alternative embodiment in accordance with the present invention the illuminating means is mounted on a fixed frame for pivotal movement about an axis. Conveniently, the sensing means is also mounted on the fixed frame for pivotal movement about an axis. The sensing means conveniently is arranged to generate electrical signals representative of the light pattern on the workpiece. Preferably, the electrical signals are digital signals.

In yet another embodiment of the present invention the apparatus comprises control processor means for receiving the electrical signals and to arrange for the display of images representative of the light pattern on the workpiece.

Preferably, the illuminating means comprises a laser, a fluorescent lamp, or an incandescent lamp.

The construction of the apparatus and its method of operation is advantageously simple, readily incorporated into a production line, does not

affect the workpiece production schedule, and is readily adaptable for operation with workpieces of various sizes. Moreover, the structural configuration of the apparatus advantageously makes it suitable for lengthy and continuous automatic operation in various environments and in particular that environment in which there are fine powders in the air resulting from the grinding processes, and which can otherwise impair the operation of the optical process.

Therefore, a method and apparatus is provided that is capable of detecting side and chamfer deviation from a standard ceramic tile product (the "workpiece") quickly, continuously and to a large extent automatically, and providing one or more measurements for the magnitude of deviation.

Brief Description of the Drawings An embodiment of the present invention will now be described by way of example with reference to the accompanying drawings, in which: Figure 1 is a perspective view of a ceramic tile having chamfered side edges; Figure 2 is a schematic perspective view of a known tile squaring apparatus; Figure 3 is a schematic perspective view of an apparatus in accordance with the present invention including an optical sensor for use with the squaring apparatus of Figure 2;

Figure 4 (a) is a perspective view of a tile illustrating the incident path of a light beam from the optical sensor of Figure 3 on a ceramic tile; Figure 4 (b) illustrates an image produced by the optical sensor equivalent to the path of incident light on the tile in Figure 4 (a); Figures 5 (a) through 5 (b) illustrate various images produced by the optical sensor as referred to in Figure 4 (b) in accordance with a sample standard image and images produced from such tiles following grinding of various tiles ; Figure 6 is a partial schematic perspective view illustrating apparatus in accordance with the present invention having two optical sensors; and Figure 7 is a schematic perspective view illustrating apparatus in accordance with the present invention having four optical sensors.

Detailed Description of the Preferred Embodiments Prior to the specific description of the embodiments of the invention reference will first be made to Figures 1 and 2 which illustrate a standard tile 1 of optimum quality having a body 2, a top surface 3, bottom surface 4 and side edges 5,6, 7,8. Each of the side edges in Figure 1 have an optionally formed chamfer 9,10, 11, 12, respectively, only chamfers 9 and 12 being shown in Figure 1.

In this description, like reference numbers will be used for like parts throughout.

Figure 2 illustrates schematically a known squaring apparatus 20 comprising a conveyor belt system 21 having two narrow belts 22,23 arranged to extend parallel to one another and driven at the same speed in the direction of the arrow 24 by means not forming part of this invention and therefore not shown.

The apparatus further comprises a first pair of grinding machines 25,26 and spaced therefrom in the direction of motion of the conveyor belt a second pair of grinding machines 27,28. The grinding machines are readily available and do not in themselves form part of this invention. Therefore, the grinding machines are not described individually, it being sufficient that they can grind ceramic tiles.

In operating the squaring apparatus 20 a generally rectangular tile 1 is fed onto the conveyor belt 21 from a tile manufacturing plant (not shown). Side edges 6,8 are arranged to lie generally in a direction parallel to the direction of motion 24 of the parallel belts 22,23.

The belts 22,23 take the tile 1 into a preset space between the opposed first pair of grinding machines 25,26 where the machines grind the opposed edges 6,8 of the tile until the tile is of the correct width and the sides 6,8 are parallel one with the other. Optionally, and as is illustrated in Figure 1, the tile 1 is provided at the same time with a ground chamfer 10,12 along side edges 6,8, respectively.

When the tile 1 moves away from the first pair of grinding machines 25, 26 into space 29 between the two pairs of grinding machines, the tile

encounters a rotational device not shown in Figure 2 although having a vertical axis and being represented by circle 30 with arrowhead 31. The rotational device is commonly known in the art and may be of the type which will be briefly described below with reference to Figure 7. The rotational device rotates the tile 1 through 90 so that side edges 5,7 lie generally parallel to the direction of motion of the belts 22,23. The tile 1 then enters the preset spacing between the second pair of grinding machines 27,28 to grind the sides 5,7 parallel to each other and at 90 to the other pair of ground sides 6,8. Optional chamfers 9,11 are also provided on sides 6,8, respectively.

The tile is then passed to a known washing station and then dried to remove all particulate refuse.

The finished tile can as mentioned above have various defects which in the main are caused by the above described squaring apparatus. Accordingly, the washed and dried tile is fed to another conveyor belt system 40 shown in Figure 3 also comprising two elongate narrow belts 41,42 extending around drive wheels 43,44 to move in the direction indicated by arrow 45.

As the belts move in the direction of arrow 45 tile 1 is moved passed an optical sensor apparatus 46 which comprises a fixed frame 47 locatable at one side of the conveyor belt, an illumination unit 48 being located precisely on the frame and positionable about at least one axis at various angles relative to the fixed frame, a sensor unit 49 accurately positionable about at least one axis at various angles relative to the fixed frame, and a control processor 50.

The illumination unit and sensor unit mounted on the fixed frame will hereinafter also be referred to as the"sensing head".

The fixed frame 47 is mounted adjacent the belt 41,42 so as to enable adjustment of the illumination unit and the sensor unit to positions relative to median line X-X. This enables the adjustment of the illumination unit and sensing unit to a given standoff distance from the edge of the tile.

In operation the illumination unit 48 projects a sheet of light 51 onto the tile 1. The intersection of light 51 and the surface of tile 1 is illustrated in Figure 4 (a) by black line 51 (2) which shows a pattern that depicts the layout of the side and chamfer of the workpiece. An image of this pattern, illustrated in Figure 4 (b), is formed by sensor unit 49, and the image is processed using an algorithm executed by the control processor 50.

The algorithm operates on the principle of active triangulation ranging, a technique well known to practitioners versed in the art for obtaining information about the three dimensional layout of surface in a scene.

According to this principle, variations in the imaged pattern provide information about the geometrical layout of the portions of the tile 1 covered by the pattern of illumination. For the purposes of the present invention, it is not necessary to arrive at a solution for absolute measurements. Instead, it is an advantage of the present invention that the positions of the pattern stripes (or in another embodiment one or more dots) within the image can be used directly when taken from a"perfect"tile as a standard optimum measurement.

This system enables the inspection of the sides and chamfers of the tile by performing the following two phases not always as specific separate actions: firstly, the system is taught by placing a tile, known to be free of defects, on the conveyor belt 40 so that it may be inspected in a training mode. As the tile 1 is transported past the sensing head, a sequence of images is acquired that provides the system with a standard measurement of the sides and chamfers of the defect-free tile against which production tiles may be compared. Standard measurements may be recorded by the control processor to be used at any later time. Such measurements include the position of the imaged pattern and its range of variation over the length of the tile's side and chamfer. Secondly, production tiles on the conveyor belt 41,42 are inspected by the optical sensor apparatus and resulting measurements are compared with the recorded standard. Figure 5 illustrates the comparison of standard measurements with the measurements of the production tiles. Depending on the precise way that comparisons are performed, the control processor will report the tile 1 as falling into one of the following categories: (a) normal; (b) re-workable; (c) badly out of tolerance; (d) reject. This result can be displayed to the operator and/or sent to ancillary apparatus for further processing.

A further embodiment is illustrated in Figure 6 and this is substantially the same as described above for Figure 3. However, two sensing heads 34 and 36 are located on either side of conveyor belt 41,42 and connected to

control processor 50. This embodiment permits two opposite sides 6,8 and chamfers 10,12 of the tile 1 to be inspected at the same time.

A further embodiment is exhibited in Figure 7 which has the structure of both Figures 3 and 6 but in addition utilises four sensing heads 46 which are located in first and second pairs on opposite sides of the conveyor belt 40.

Each pair of sensing heads is separated by a tile rotational device 60 well known in the art and not within the scope of the present invention. The tile rotation apparatus comprises two belts 61,62 smaller than the belts 41,42 which rotate as well known in opposite directions to achieve rotation of the tile 1 about a vertical axis by 900 degrees. This embodiment permits all four sides and chamfers of the tile to be inspected as the tile is transported automatically by the conveyor belt 41,43 through the first pair of sensor units 46, rotated 90 by the rotation device 61,62, and then the second pair of sensor units 46..

Conveniently, the light emitted by the sensing heads 46 can be emitted from a laser, a fluorescent lamp, or an incandescent lamp.

Furthermore, the present invention extends to embodiments in which the illumination source projects one or more dots, or one or more stripes onto the tile.

The present invention also extends to embodiments in which the control processor is connected directly to the sensing head, or is connected via a data network to the sensing head.

Although particularly, sued to the inspection of the sides and chamfers of ceramic tiles after they have been ground by a squaring machine, the method of the present invention can be applied to the inspection of the region of the tile encompassing the sides and upper surface of the tile in close proximity to the side, wherein a grinding machine is not used in the tile manufacturing process.

Although particularly suited to the inspection of sides and chamfers of ceramic tiles, the method of the present invention can be applied to the inspection of the sides and chamfers of other workpieces, such as flat laminar rectangular workpieces consistent of materials such as wood, metal, plastics, composites and glasses, wherein the workpiece is transported past the apparatus by a conveyor belt.

The invention has been shown and described with respect to exemplary embodiments thereof. However, various other changes, omissions and additions in the form and detail thereof may be made therein without departing from the scope of the present invention.

Claims

CLAIMS:

1. A method of performing an inprocess inspection of a workpiece, comprising locating a workpiece on support means, directing a light beam upon the workpiece, arranging for relative movement between the workpiece and light beam, sensing a light pattern on the workpiece, and comparing the light pattern with a standard form of light pattern for determining defects in the workpiece.

2. A method as claimed in claim 1, wherein the workpiece is movable on the support means past a fixed beam of light, and sensing means are provided for sensing the light pattern incident upon the workpiece.

3. A method as claimed in claims 1 or 2, including generating electrical signals in the sensing means representative of the light pattern for producing a visible image of the light pattern.

4. A method as claimed in claim 3, wherein the electrical signals are digital signals.

5. A method as claimed in claims 3 or 4, wherein the displayed image is compared to a standard acceptable image for determining whether the displayed image conforms to the standard.

6. A method as claimed in any preceding claim, comprising illuminating the workpiece with a pair of light beams one from each side, respectively, of the workpiece.

7. A method as claimed in claim 6, comprising illuminating the workpiece with two pairs of opposed light beams, each pair being spaced in the direction of motion of the workpiece between the two oppositely located light beams of the first pair of light beams.

8. A method as claimed in claim 7, comprising rotating the workpiece through 900 prior to the workpiece being illuminated by the second pair of light beams.

9. An apparatus for performing an inprocess inspection of a workpiece, comprising support means upon which a workpiece is located, illuminating means for illuminating the workpiece with a light beam, the support means and illuminating means being movable one relative to the other so that the light beam passes along the workpiece, sensing means for sensing a light pattern on a surface (s) of the workpiece and comparator means for making a comparison of the light pattern sensed by the sensing means and a light pattern of an acceptable standard of light pattern.

10. An apparatus as claimed in claim 9, wherein the support means is movable and the illuminating and sensing means are stationary.

11. An apparatus as claimed in claims 9 or 10, wherein the sensing means is arranged to generate electrical signals representative of the light pattern upon the workpiece, and display means are provided to display an image corresponding to the light pattern.

12. An apparatus as claimed in claim 11, wherein the comparator means is arranged to compare the displayed image with an acceptable standard image to determine the standard of the manufactured workpiece.

13. An apparatus as claimed in any of claims 9 to 12, comprising a pair of illumination means one located on each side, respectively, of the support means.

14. An apparatus as claimed in claim 13, comprising two pairs of opposed illumination means spaced one relative to the other in the direction of movement between the illuminating means and the support means.

15. An apparatus as claimed in claim 14, comprising rotation means for rotating the workpiece 90 , the rotation means being located between the two spaced pairs of illuminating means.

16. An apparatus as claimed in any of claims 9 to 15, wherein the illuminating means is mounted on a fixed frame for pivotal movement about an axis.

17. An apparatus as claimed in claim 16, wherein the sensing means is mounted on the fixed frame for pivotal movement about an axis.

18. An apparatus as claimed in claim 17, wherein the sensing means is arranged to generate electrical signals representative of the light pattern on the workpiece.

19. An apparatus as claimed in claim 18, wherein the electrical signals are digital signals.

20. An apparatus as claimed in claim 19, comprising control processor means for receiving the electrical signals and to arrange for the display of images representative of the light pattern on the workpiece.

21. An apparatus as claimed in any of claims 9 to 20, wherein the illuminating means comprises a laser, a fluorescent lamp or an incandescent lamp.

22. An apparatus for performing inprocess inspection of a workpiece substantially as hereinbefore described, and as illustrated in, Figure 3; or Figure 6; or Figure 7 of the accompanying drawings.

23. A method of performing an inprocess inspection of a workpiece substantially as hereinbefore described with reference to and as illustrated in Figure 3, or Figures 4 (a), 4 (b); or Figures 5 (a) to 5 (e) ; or Figure 6; or Figure 7 of the accompanying drawings.