DESCRIPTION Field of the invention

The present invention relates to a method and an apparatus for detection of imperfections in hot transparent objects, such as glass products which objects are inspected after having been formed and placed on a transport device.

Background of the invention

In the production process of glass objects, such as bottles, pots, optical components, and table ware - the molten glass gob are led, through a feeder unit, to a forming machine. There, the desired glass object is formed out of a molten glass gob, by means of pressing and/or blowing. The forming machine can be a so-called IS-machine. An IS-machine contains a row of individual sections where one or more glass objects are fonned.

When the forming machine has formed the glass objects, these objects will be placed on a transport device, such as a conveyor belt, for further treatment. On their way on the transport device, the still hot glass objects are inspected for imperfections, for example whether these are deformed, contain inclusions or bubbles, deviate (excessively) in certain parameters or certain properties do not meet set standards. The detected imperfect objects are then removed.

For inspecting of these hot transparent objects, observing meaas, for instance cameras, are used which take images of the passing objects on the transport device.

These images are then processed and analysed by an image-processing unit On the images taken, certain parts, the so-called inspection zones, are inspected for imperfections. If an imperfection is detected in an inspection zone of an image, the associated object is regarded as imperfect.

An example of conventional methods for detecting imperfections in hot glass objects can be found in US 6049379, where two cameras at the side of the transport device, with two different viewing directions, can take images of the passing objects. These images are then compared with each other. If the difference between the two images is too large, the object will be considered as imperfect The inspection of the hot transparent objects to detect imperfections is, however, not without drawbacks, due to the assumption of one single position as well as one specific orientation of the object on the transport device. In practice, however, the objects coming out of the forming machine are not placed on the transport device in the same position and/or with the same orientation. The objects can be placed laterally (slightly) more or less far and/or slightly rotated on the transport device. The latter is particularly important when objects are not entirely rotation-symmetric (rotation-asyinmetric), such as a rectangular bottle. When the hot glass objects have just been formed, the glass is still slightly deformable and touching of these hot objects can therefore lead to undesired surface defects (imperfections). For this reason, the still hot objects cannot be mechanically placed at a desired position and in a desired orientation on the transport device.

When an object which is not entirely rotation-symmetric, such as a rectangular bottle, stands slightly rotated on the transport device, an edge of a wall of the bottle may fall within a fixed inspection zone and the bottle will be detected as imperfect. As a result the rectangular (or the rectangular parts of) bottles are, in practice, often not inspected for imperfections when these have just left the forming machine.

If the objects are placed sideways more or less far on the transport device, the maximum inspection zone may be either too small in case the object is closer to, or too large when the object is farther away from the camera. The inspection will then not be reliable enough to detect an imperfection. Although this problem can be solved by means of cameras with the so-called telecentric lenses, but these lenses will have to have a diameter of at least the height of the bottles. This will render the solution relatively expensive. For this reason, the use of cameras with telecentric lenses is often not the desired solution.

Tt is also possible that both situations, variations in orientation as well as in position, occur simultaneously. Hence, there is a need for a solution whereby the inspection of hot transparent objects, such as a newly formed glass product, on a transport device can be done as well as possible without the orientation and/or the position of the object making the inspection difficult, adversely affected or even impossible. The solution is provided by means of a method according to Claim 1 and a device according to Claim 9.

Summary of the invention An object of the present invention is to provide a method for detecting imperfections in hot transparent objects, such as glass products, which objects are inspected after having been formed and placed on a transport device.

To this end, the method is characterized by the following steps:

a. taking one or more images of a passing object;

b. calculating one or more position parameters for said object, on the basis of one or more images;

c. setting an inspection zone on one or more images of said object, on the basis of said one or more position parameters.

In this way, the inspection zone for the images taken from a passing object, can be optimally adjusted whenever the orientation and/or the position of the object on the transport device so require. The inspection zone can be made smaller, for example, or even split into multiple zones. This method is very effective in case the objects are not entirely rotation-symmetric, such as a rectangular bottle. With this solution the inspection zone will constantly be adapted depending on the orientation and position of the passing objects. This will allow objects that are rotation-asymmetric or that have rotation-asymmetric parts to be inspected as optimally as possible.

One of the position parameters is a distance from the object to a reference line, for example the center line of the transport device. This distance can be used, among other parameters, to more accurately set the inspection zone. Another position parameter is an angle which a wall of the object - facing viewing direction of an observing means - makes with a reference line, for example the centre line of the transport device. A preferred embodiment of the method according to the present invention is characterized in that at least two images, under two different viewing directions, are taken of a passing object. Preferably, these viewing directions are at least substantially perpendicular to one another. In so doing, at least one of the images may be taken from the top of the object and at least one of the other images from the side, along the transport device. Still preferably, one of said two images can be used for calculating the position parameters in order to set the inspection zone for the other image. In this way, the image taken from the top, for instance, can serve to calculate the position parameters in order to set the inspection zone (for the other image) based on those position parameters, while the other image (from the side) is used to inspect the object with that set inspection zone.

In a further advantageous embodiment of the method according to the present invention, more than two images are taken, each with another viewing direction, wherein at least one image is used to calculate the position parameters on the basis of which, for each of the other images, an adapted inspection zone is set, depending on the viewing direction thereof. This allows different images, of the same object, to be taken from multiple angles of sight and a different adapted inspection zone to be set, depending on the position and orientation of that object relative to each viewing direction - and hereby improving the detection of imperfections even further.

Another object of the present invention is to provide an apparatus for detecting imperfections in hot transparent objects, such as glass products, which objects are inspected after having been formed and placed on a transport device. The apparatus comprises:

- at least one observing means, such as a camera, which takes one or more images of a passing object;

- an image-processing unit, which is adapted to process the taken images.

For this purpose, the apparatus is characterized in that said image-processing unit calculates one or more position parameters for said object, on the basis of images taken by the at least one observing means - on the basis of which parameters the image-processing unit sets an inspection zone for the images of said object. Said image-processing unit calculates - as one of the position parameters -- a distance from the object to a reference line, for example the centre line of the transport device. Another position parameter, that the image-processing unit can calculate, is an angle which a wall of the object, facing viewing direction of an observing means, makes with a reference line, for example the centre line of the transport device. An advantageous embodiment of the apparatus according to the present invention is characterized in that the apparatus comprises at lease two observing means, wherein each of the observing means takes images of a passing object with a different viewing direction. Preferably, the at least two observing means are positioned at least substantially perpendicular to one another. Therefore, at least one of the observing means can be positioned on the top and at least one of the other observing means can be positioned at the side of the transport device. The observing means on the top can also be positioned at the bottom of the transport device in case the transport path is transparent

Preferably, the image-processing unit calculates the position parameters, on the basis of the images taken by one of the observing means whereupon the image-processing unit, on the basis of these position parameters, sets the inspection zone for the images taken by at least another observing means than the first-mentioned.

This way, the images taken by the observing means on the top, can be used to determine the position parameters which parameters, in turn, can be used to set the inspection zones for other images.

The apparatus according to the present invention may comprise more than two observing means, wherein each observing means takes images with a different viewing direction, of the passing objects. This allows a passing object to be viewed from multiple angles of sight. The image-processing unit may use the images of at least one of the observing means for example the one on the top to calculate the position parameters and on the basis of these parameters the image-processing unit, for each of the images taken by other observing means, can adjust an inspection zone, depending on the viewing direction. This means that every observing means, since it has its own viewing direction, is assigned its own inspection zone.

This allows more cameras to be used and each camera, depending on the viewing direction, can be given a different inspection zone whereby the detection of imperfections can be further improved. The viewing direction of each camera is then known to the image- processing unit, so that this information can be used to set an inspection zone for images of each camera with a different viewing direction and to adapt this inspection zone when the next passing object has a different orientation and/or position.

Brief description of the drawings

Figure 1 shows the top view of an embodiment of the invention with two cameras perpendicularly positioned.

Figures 2a 2b show an example of two standing bottles, 2a: without being rotated and 2b: slightly rotated.

Figure 3 shows the top view of an embodiment of the invention, such as the one in Figure 1, with two cameras, wherein the bottles are at different distances from the centre line of the transport device.

Figure 4 shows the top view of another embodiment of the invention with four cameras, three of which having the same viewing direction while the other one is positioned at the top, perpendicular to those three, and the bottles are closer to or farther away from the centre line.

Figure 5 shows the top view of another embodiment of the invention with four cameras, each with a different viewing direction, three of which are at the side of the transport device and the other one, on the top, is perpendicularly positioned with reference to the other three.

Detailed description of the drawings

The forming machine (not shown) forms bottles from the molten glass gob and puts these hot bottles (2) on the transport device (1) (conveyor belt), which transports the bottles (along cameras) for further treatments. The bottles (2) are inspected for imperfections, for example deformation, inclusions or gas bubbles. The bottles with detected imperfections are then removed.

A simple embodiment of the invention is shown in Figure 1 , in which two observing means are used, for example two cameras. Of these two cameras, a camera (4) is at the side of the transport device (1), while the other camera (3) is positioned above the transport device (1). These two cameras take images of the passing bottles (2) which have been placed on the transport device (1) by the forming machine. The transport device (1) transports the bottles (2) in the direction of the arrow, from right to left. Here, one can see how the bottles (2) can stand slightly rotated on the transport device (1). Both cameras are connected to an image-processing unit (5), for example a (signal) processor, which can process the images of a bottle, taken by the cameras, in order to detect possible imperfections in the inspection zone on each image of a bottle. The camera (3), which is above the transport device (1), makes images of the passing bottles (2) from the top while the camera (4) takes images from the side of the transport device (1).

Now, since the bottles (2) can be rotated on the transport device (1), an inspection zone (6) on an image, taken by the side camera (4), may catch an edge of the hot bottle (2) too. In that case, the image-processing unit will detect an imperfection anyway, and consequently a good inspection of imperfections will be virtually impossible. Figure 2a clearly shows that the inspection zone ( 6) falls completely inside a wall of the bottle (2) and that a large part of the bottle can be inspected with that inspection zone (6); the bottle (2) in this case stands completely straight (not rotated) on the conveyor belt and thus the side camera (4) can look straight at the bottle (2). This is, however, not the case with bottle (2) in Figure 2b, where the bottle (2) is slightly rotated. The top view shows whether the bottle on the transport device (1) is straight or rotated and the dotted lines show whether the inspection zone catches the edges or not. Figure 2b clearly shows how one or more edges of the bottle can fall within the inspection zone (6) and thus making the (accurate) inspection impossible. In this figure, the right edge of the front wall and the left edge of the rear wall of the bottle, viewed from the side camera (4), fall within the inspection zone (6).

The top camera (3) on the top of the transport device (1) can take images of passing bottles (2) with a substantially perpendicular viewing direction, whereupon these images are processed by the image-processing unit (5) in order to calculate a number of position parameters. For example, an angle can be calculated which the bottle (2) makes with a reference line, for instance the centre line (9) of the transport device (1). When the bottle (2) stands straight (not rotated) on the transport device, the side camera (4), in Figure 1 , will have a clear view of the wall of the bottle (2) facing the camera (4). In that case, the bottle (2) is at an angle of 0° with the centre line (9) of the transport device (1) and as a result the (maximum) inspection zone (6) does not need to be adjusted. In Figure 1, the bottles (2) are, with respect to the centre line (9), either rotated or not. For example, it can be seen that the bottles (2), from left to right, have an angle of (nearly) + 45°, - 45°, 0°, - 60° and + 60° respectively. Here, a rotation of the bottle in a clockwise direction is considered positive, while a counter clockwise rotation is considered negative. In this embodiment, the top camera (3) takes images from the top, which images are then used by the image-processing unit (5) to calculate the angle that a passing bottle (2) makes with the reference line (9). This angle is then used to set the inspection zone (6) on the image of that bottle taken by the camera (4), For example, the inspection zone of a bottle that has a smaller angle (the absolute value) is less reduced than a bottle with a larger angle. The inspection zone is therefore constantly adjusted based on the rotation angle of the bottle. It is self-evident that an angle regardless of its sign (+/-) will have (nearly) the same effect on the inspection zone. The inspection zone (6) of a bottle (2) which is not rotated on the transport device (1) is maximum (angle = 0°), while the inspection zone for a bottle with a larger angle (absolute value) can be relatively much smaller. Thus, the inspection zone (6) becomes smaller and smaller as the angle comes closer to (+/-) 90°.

Figure 3 shows a situation in which the bottles (2) stand either on the centre line (9) of the transport device (1) or at one of the both sides thereof. This means that the bottles (2) can come closer to or farther away from the camera (4). Although in this figure the positions of bottles are somewhat exaggerated, even this may be the case when the bottles are very small in relation to the width of the conveyor belt. In that case, the inspection zone should also be adjusted, namely a larger inspection zone for the bottles closer to the camera and a smaller one for farther standing bottles.

The image-processing unit (5) can calculate the distance from the bottle (2) to a reference line, for example the centre line (9), on the basis of the images taken by, for example, a camera (3) on the top of the transport device (1). Based on this distance, the image- processing unit (5) can set a suitable inspection zone (6) for images taken by camera (4). In the case of multiple reference lines, the image-processing unit (5) for each bottle (2) can set a suitable inspection zone (6) on the basis of a reference line associated with the bottle. This has been shown in the particular embodiment of the invention in Figure 4. In this embodiment, there are four cameras, three (4, 7, and 8) at the side of the transport device (1), all three having the same viewing direction, and a top camera (3). The special feature of this embodiment is that there are three reference lines (9, 10, and 11) and the forming machine puts the bottles in these three positions. The side cameras (4, 7, and 8) are at the same distance from the transport device (1) and have the same viewing direction. Each side camera, in this embodiment, is intended for one of the three positions. The image- processing unit (5) therefore determines the inspection zone (6) for images taken by each of the side cameras.

In Figure 5, similar as in Figure 4, there are four cameras; here however, there are three side cameras (4, 7, and 8) each of which having a different viewing direction, and a camera (3) on the top. In this embodiment, cameras (7 and 8) are, relative to the camera (4) in the middle, each rotated 45° toward a different direction. As such, camera (7) is 45° rotated to the right and camera (8) is 45° rotated to the left. In this way, the images of the passing bottles are taken from three different angles of sight (viewing directions). The viewing direction of each side camera (4, 7, and 8) is already known to the image-processing unit (5), which then takes this into account when setting the inspection zones. The images taken by the top camera (3) are used by the image-processing unit (5) to determine, for example, the angle and/or the distance of each passing bottle (2). On the basis of this angle and/or the distance and by taking into account the viewing direction of each side camera (4, 7, and 8), the image-processing unit (5) sets a suitable inspection zone (6) for each image taken by a side camera. The images of passing bottles, taken by these three cameras, can also be compared with each other. In this way, imperfections can be sought much more accurately. For each bottle (2), there are three images that can be looked at in order to see, for example, whether all three or two of the three show the same imperfections.

It should be clear to a person skilled in the art of the invention that variations of the invention are conceivable without departing from the principle of the invention. For example, a larger number of cameras can be used, the cameras can be on both sides of the transport device, a reference line other than the centre line can be used, several top cameras can be utilized, a top camera can be replaced by a camera under the conveyor belt when the belt is transparent, and more position parameters can be calculated. It is also possible to position the top camera with a different viewing direction than perpendicular to the belt. It is also possible that images are taken first by Die side cameras and then by the top camera, i.e. the bottles pass the side cameras first and then the top camera.