GB2394283A

GB2394283A - Optical imaging, and monitoring of exposed cut ends of a product

Info

Publication number: GB2394283A
Application number: GB0224310A
Authority: GB
Inventors: Brent Alan Coy
Original assignee: Beta Lasermike Ltd
Current assignee: Beta Lasermike Ltd
Priority date: 2002-10-18
Filing date: 2002-10-18
Publication date: 2004-04-21
Also published as: GB0224310D0

Abstract

The monitoring apparatus comprises an imaging station arranged to receive the product (2) of an extruder unit. At least one camera (7, or 10) is arranged to take at least one image of each product cut end in turn. An image processing unit (6) receives at least one image of the cut end cross section and compares at least one value determined from the image with a known value to establish whether the product is within acceptable limits. There may be two cameras for taking the cut end images from different angles, whereby each image may be taken by different camera. The cameras may be mounted at different angles relative to the cut face or each image may be received by a single camera with the help of a mirror arrangement. Alternatively, each image may be taken by a single camera which moves from one location to a different location, or with camera position fixed, as the position of cut end is allowed to move between successive images. Another camera may monitor surface finish.

Description

APPARATUS AND METHOD FOR CROSS SECTION MONITORING

The present invention relates to monitoring the cross-section of an object and particularly, but not exclusively to monitoring product from a continuous extrusion or 5 similar processes where the product is subsequently cut into lengths. For example the extrusion of uPVC frames for windows or doors, lengths of pipe, automotive rubber seals, conduit or similar products.

Considering an extrusion process, variations in the consistency, pressure and 10 temperature of product to be extruded will influence the dimensions of extruded product.

Although the above variables are monitored, it is still desirable to know the true dimensions of the extruded product, for these may be influenced by prevailing conditions experienced immediately after extrusion, for example ambient temperature and rate at which the product is conveyed away from the extruder. Also given the continuous nature of the extrusion 15 process it is important any error is identified as soon as possible.

There are several known systems for monitoring product on a continuous basis as the product is manufactured, for example by line striping, or by ultrasonic wall linear dimension control or by monitoring external dimensions as the extruded product passes 20 through a number of sensors. However, for certain products, such as profiles for window frames, one or more internal cavities may be present in the extrusion and thus not all dimensions can be measured externally. Furthermore these dimensions may have to be within a specific tolerance as these internal cavities may be designed to receive one or more components to fabricate the extruded material into a finished product.

The object of the present invention is to provide a way of measuring all the dimensions (internal and external) of a cross section of any manufactured object manufactured from a process similar to the extrusion process. The system will measure all the dimensions at every cut-length. The system can be part of the manufacturing process or 30 subsequently used to monitor product produced by such a process.

- 2- According to the present invention there is provided cross section monitoring apparatus comprising: an imaging station arranged to repetitively receive product having an exposed cut S end; at least one camera arranged to take at least one image of each product cut end in turn; and image processing apparatus for receiving at least one image of a cut end and comparing at least one value determined from said image with a known value to establish 10 whether the product is within acceptable limits.

The product of many manufacturing processes, such as an extrusion process, is cut into product lengths almost immediately after the product is extruded. Each product length provides access to the cross section of the manufactured product at the cut face, enabling 1 S this to be imaged to establish whether the product is within acceptable limits. The image processor may subsequently generate an alarm if a selected dimension does not correspond to a predetermined value or, where part of the manufacturing process, may control the process accordingly. A value may be either a specific value or a range.

20 Advantageously, a set of images are received from different angles of the cut end face of the product, which images may be received by one or more respective cameras, from a single moveable camera, from a single camera taking images as the product is moved or a single camera using an arrangement of mirrors. The images may be used to determine whether a dimension fails to comply with a predetermined value, either because 25 of a burr due to the cutting process, or because any dimension does not correspond to the specified value. In this case, the processing apparatus may control either the manufacturing unit or provide an alarm to the operator as appropriate.

Advantageously the processing apparatus applies a mathematical geometric 30 translation to translate the images into flat two dimensional images and then compares those translated images to identify any non conformity which may indicate a burr.

-3 Where multiple images are taken of a cut end of a product length, it is preferable that a first image is taken along the axis of the product length and the next image taken at an angle between 0 and 90 to that axis.

5 According to a second aspect the present invention provides a method of monitoring a product cross section, the method comprising the steps of: a) manufacturing product; b) cutting the product into product lengths; and c) imaging the cut end of product lengths and comparing, via image processing 10 apparatus, at least one value determined from said image with a known value to establish whether the product length is within acceptable limits.

One example of the present invention will now be described by way of example 15 only, with reference to Figures 1 and 2 of accompany drawings, of which: Figure 1 illustrates apparatus in accordance with the present invention; and Figure 2 illustrates a cross section of the profile which may be monitored by the present invention.

20 Referring to Figure 1, an example of cross-section monitoring apparatus in accordance with the present invention includes an extruder 1 from which product 2 is extruded, this product being cut by cutting tool 3 into product lengths 2A and 2B. Product 2 is extruded at a continuous rate and cutting tool cutter 3 cuts the product whilst it is being conveyed to tipping table 4.

The tipping table 4 tips products lengths 2B, 2A to a first side or a second side depending on whether the product is dimensioned within acceptable limits or not. In the later case, the product is tipped by tipping table 4 into a rejection bin.

30 Once the product 2 has been cut into product lengths 2A and 2B it is no longer necessary for the product to be conveyed at a continuous rate equal to that at which product 2 is extruded. Conventional mechanical handling apparatus may be employed to hold the

- 4- product so that when a product length 2B is positioned on the tipping table it may be placed there in a steady state for a short period of time. For clarity, such mechanical handling material has been omitted from Figure 1.

S The position of a product 2B is detected by sensor 5. When product is in the correct position it may be secured in place by any conventional clamping means.

When product 2B is secured in the correct position on tipping table 4 this is signalled by sensor 5 to the image processor and control 6, which actuates cameras 7 to take 10 an image at a start position, relative to the axis of the product length, before moving to a next position, indicated by arrow 8, where the next image is taken directly along the axis of the product length. The process is repeated until it reaches an end position. The cut end of product 2B is illuminated by lights 9 arranged at an oblique angle to the cut face and being of a colour to provide maximum contrast with regard to the product type. The lights 9 also 15 illuminate the outer surface of the extruded product length 2B, which is imaged by a second camera 10 as the product is passed across the tipping table for surface inspection.

As an alternative to the illustrated embodiment, multiple cameras could be used to obtain the images, or a single camera imaging the product 2B at different positions as it is 20 placed on the tipping table, The apparatus further comprises a memory 11, in which permitted values are stored.

These are compared by the image processing and control 6 with values generated from the received images. The processing apparatus first applying a mathematical geometric 25 translation to translate the images into flat two-dimensional images and then comparing those translated images to identify any non conformity which may indicate a burr. An alarm 12 is provided for generating an audible alarm to an operator when an unacceptable condition exists. The image processor and control circuitry 6 is additional connected to a cutting tool 3 and an extruder 1 through which a feedback signal may be provided as 30 described below.

- s - Referring now to Figure 2, there is shown the cut end face 13 of product length 2B, held in position on the cutting table in a predetermined position against predefined axes, X and Y. between the start and the end position. This does not mean though that the product needs to be held fixed in position.

The lighting angle, the intensity and colour of the lighting and focal length of the camera may be selected to ensure that face 13 is brightly illuminated relative to the background and the walls of the extrusion. Using standard image processing techniques

and selection of appropriate grey scales, the image is blanked with the exception of face 13, l O and the cross section is extracted as shown in figure 2. This image is then processed by software within the image processor control 6, whereby distances between any number of points may be measured and compared with values held within the memory 11. For any value outside of the permitted range stored within memory 1 l an error is noted.

15 Two images are taken, a first at an angle of 45 relative to the longitudinal axis of the product length 2B, and the second directly along the longitudinal axis. Corresponding errors should occur on each image.

The memory l l may hold two sets of values, the first being a set corresponding to 20 an acceptable, but not ideal value, with the second set of values relating an unacceptable value. Where an error is detected which falls into the unacceptable category, tipping table tips the product into a recycling bin. All other product is classified as acceptable and passed on for further processing.

25 Where the product is categorised as acceptable but not ideal, the image processor at control 6 sends a signal through either the extruder l or saw cutter 3 to modify the operation thereof, to rectify any error in the product dimensions.

The image processor and control receives a signal from camera l O which monitors 30 the colour and surface finish of the product and if any abnormality is detected, again an alarm is signalled to an operator.

- 6- A combination of measuring the surface finish and the dimensions can be used to monitor/control the process. For example, if the finish is faulty it may not warrant measuring the dimensions, because the product is going to be rejected.

5 The above embodiment of the invention has been given by way of example only and many variations and alternatives will be apparent within the scope of the appended claims.

Claims

- 7- CLAIMS

1. Cross section monitoring apparatus comprising: 5 an imaging station arranged to repetitively receive product having an exposed cut end, at least one camera arranged to take at least one image of each product cut end in turn; and image processing apparatus for receiving at least one image of a cut end and 10 comparing at least one value determined from said image with a known value to establish whether the product is within acceptable limits.

2. Apparatus as claimed in Claim 1, comprising means for receiving at least two

images of each cut end, said images being taken from different angles relative to said 1 5 product.

3. Apparatus as claimed in Claim 2, wherein each image is received by a respective different camera, each camera being mounted at a different angle relative to the cut face.

20 4. Apparatus as claimed in Claim 2, wherein each image is received by a single camera using an arrangement of mirrors.

5. Apparatus as claimed in Claim 2, wherein each image is received by a single camera arranged to move to different locations.

6 Apparatus as claimed in Claim 2, wherein each image is received by a single camera at a fixed location, the position of the cut end moving relative to the position of the camera between successive images.

- 8- 7. Apparatus as claimed in Claim 6, wherein a first image is taken at a first position and further images are taken at subsequent positions before an end position is reached,the first image being taken when the cut is completely visible and the end position occurs 5 before the product is moved off line.

8. Apparatus as claimed in any one of claims 2 to 7 wherein the processing apparatus applies a mathematical geometric translation to translate the images into flat two dimensional images and then compares those translated images to identify any non 1 0 conformity.

9. Apparatus as claimed in any preceding claim, comprising an additional camera for monitoring surface finish of the product.

15 10. Apparatus as claimed in any preceding claim, comprising means responsive to the processing apparatus for physically rejecting any product not within acceptable tolerance limits. 11. Apparatus as claimed in any preceding claim, wherein the processing apparatus 20 receives a set of images of a cut end taken from different angles, wherein the processing apparatus is programmed to identify a burr on the cut end.

12. Apparatus as claimed in any preceding claim, wherein the process apparatus signals an alarm to an operator if one or more dimensions, critical dimensions, surface finish or 25 product length are not within acceptable limits.

14 Apparatus as claimed in any proceeding claim further comprising a light source to illuminate the cut face of the product, the light source being selected in dependence on the type of product to provide a high contrast image.

9_ 15. Apparatus as claimed in any proceeding claim comprising a manufacturing unit for producing product as a continuous length and a cutter for cutting the product into lengths, the cut face of which is imaged.

5 16. Apparatus as claimed in claim 15 where the manufacturing unit is an extruder.

17. Apparatus as claimed in claim 15 or 16, wherein the processing apparatus modifies the operation of the manufacturing unit if product is not within acceptable limits.

10 18. Cross section monitoring apparatus substantially as hereinbefore described, with reference to, and/or as illustrated in, the accompanying drawings.

19 A method of monitoring a product cross section, the method comprising the steps of: 15 a) manufacturing product; b) cutting the product into product lengths; and c) imaging the cut end of product lengths and comparing via image processing apparatus at least one value determined from said image with a known value to establish whether the product length is within acceptable limits.

20. A method as claimed in Claim 19 comprising receiving a set of images of a cut end of a product length taken at different positions andlor from different angles to identify a burr. 25 21. A method substantially as hereinbefore described, with reference to, the accompanying drawings.