WO1994016290A1

WO1994016290A1 - Web curl measurement system

Info

Publication number: WO1994016290A1
Application number: PCT/US1994/000356
Authority: WO
Inventors: William K. Giguere
Original assignee: Thermo Electron Web Systems Inc.
Priority date: 1993-01-15
Filing date: 1994-01-11
Publication date: 1994-07-21

Abstract

A system for measuring the degree of edge curl present in a web of material includes a light source for illuminating a line extending across a surface portion of the web to an edge thereof, and an optical detection device responsive to reflections from the illuminated line for acquiring an image representative of the profile of the line. A CPU operates to digitize and store the image as discrete profile data points. The process continues by identifying at least one reference profile data point associated with a linear portion of the image at a location inside of the edge, and identifying a second reference profile data point associated with a portion of the image at a location having the greatest linear deviation from the linear portion of the image as represented by the reference profile data point, the linear deviation being representative of the degree of edge curl in the web. According to a further aspect of the invention, a curl removal device is provided which is responsive to the calculated linear deviation for removing the curl from the web.

Description

WEB CURL MEASUREMENT SYSTEM BACKGROUND OF THE INVENTION

The invention relates to a system for measuring the degree of curl present in a web of material.

During the production of web materials, for example paper, a structural defect known as curl often occurs in the web. While webs of paper are often rolled longitudinally for handling purposes, the presence of curl in the web unfortunately tends to make the web roll inward from the edges to the center of the web, thus causing difficulties in further processing of the material. It is therefore desirable to have a reliable and accurate system for detecting the degree of the curl present in an examined web of material. In addition, it is further desirable to utilize the measured curl to implement the use of curl removal devices to remove the curl from the web.

It is therefore an object of the present invention to provide a system for measuring the degree of curl present in a web of material.

It is also an object of the present invention to provide a system which displays quantitative images and data relating to the curl present in the web of material.

It is an additional object of the present invention to provide a system which utilizes the data relating to measured curl present in the web of material for controlling a device which serves to remove the curl from the web of material.

SUMMARY OF THE INVENTION

In accordance with the present invention, there is provided a system and method for measuring any degree of edge curl present in a web of material. The system includes an illuminating means for illuminating a line extending across a surface portion of the web to an edge thereof, and an image acquisition means responsive to reflections from the illuminated line for acquiring an image representative of the profile of the line. A digital storage means digitizes and stores the image as discreet profile data points. A processing means is provided for identifying at least one reference profile data point associated with a linear portion of the image at a location inside of the edge, and for identifying a second reference profile data point associated with a portion of the image at a location having the greatest linear deviation from the linear portion of the image as represented by the reference profile data point, the linear deviation being representative of the degree of edge curl in the web. According to a further aspect of the invention, a curl removal means is provided which is responsive to the calculated linear deviation for removing the curl from the web.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 show a functional block diagram of the curl measurement system in accordance with the present invention; and

Fig. 2 shows an exemplary data output screen associated with a CPU monitor of the present invention.

Figs. 3A-3C show a flow chart describing the operation of the web curl measurement system of the present.

DETAILED DESCRIPTION OF THE ILLUSTRATED EMBODIMENTS

With reference now to Fig. 1, a web curl measurement system 10 is illustrated in functional block diagram form. The system 10 operates to measure the degree of edge curl present in a web 12 of material. The web 12 of material may be stationary or moving along a conveying device (not shown). The system includes a light source 14, preferably a laser, which produces a light beam 15 downward onto the web 12, thus creating an illuminated laser line image 16 across the surface of an edge portion of the web. It will be appreciated that if any degree of curl exists in the web 12, the stresses and tensions applied to the web by conveying rollers or the like will cause the curl to appear at the edges of the web, thus causing the edges to curl in an upward or downward direction. In light of the curl occurring at the edges, only the edge portion of the surface of the web 12 is illuminated by the light source 14. The incident light beam 15 is impinged onto the web surface at an acute angle, preferably in the range of 40-50° and ideally at 45° relative to the horizontal plane of the web 5 12. However, the angle of incidence may fall outside the preferred range depending on the relative positions of the system components and the reflective characteristics of the web surface.

An optical detection device 18, preferably a CCD video 0 camera, is positioned at an opposing acute angle with respect to the horizontal plane of the web 12 for detecting the reflecting laser line image 1 The reciprocal arrangement of the light source 14 and t =? optical detection device 18, preferably 90°, is such thee measuring errors 5 such as parall r. errors are prevented, thus providing greater resolut when the web 12 is moving at a relatively high speed. Ir .dition, arrangement of the light source 14 and the optical detection device 18 wherein each are positioned at an acute angle of approximately 45° with 0 respect to a horizontal plane, the generated laser line image 16 very accurately represents a cross-sectional view of the web 12 with any curl which may be present therein. As shown in Fig. 1, the light source and optical detection device are supported by a support structure 19. Preferably, 5 the light source and optical detection device are positioned within a common housing.

The reflected image 16 is detected by the video camera 18, preferably a CCD video camera having at least 512 X 512 matrix of pixels, and incl iing an interference filter of n the same frequency as the lignt source utilized. The camera is connected to a central processing unit (CPU) 24 for processing the image data. The CPU in turn is connected to both a video monitor 20 and a CPU monitor 26. The video monitor 20 is capable of monitoring the video image from the 5 camera 18, thus providing a real-time video image 22 of the laser line for diagnostic and alignment convenience. The CPU monitor 26 provides a digitized image 28 of the laser line produced by an image capture board in the CPU as well as processed data associated with the amount curl present in the web. The digitized profile image 28 of the laser line 16 and associated data as displayed by the CPU monitor 26 is shown in exemplary form in Fig. 2. The system 10 also includes a curl removal device 30 which is communicatively coupled to the CPU 24. The curl removal device operates in response to receiving data relating to the measured curl in the web 12 for implementing procedures for removing the curl from the web. For example, the curl removal device may be a steam apparatus such as a Steam Foil as manufactured by Thermo Electron Web Systems, Inc. and described in U.S. Patent Nos. 4,765,067 (issued to Taylor) and 5,020,245 (issued to Langevin et al.), both incorporated by reference herein. The aforementioned systems operable for applying steam of selected humidity and temperature to the web in order to remove the curl. Alternatively, the curl removal device may be a conventional roll coater apparatus which utilizes a bath of water at a predetermined temperature for removing curl from the web. With reference now to Figs. 3A-3C, a flow chart describing in more detail the process of measuring the degree of curl present in a web 12 by the system 10 is shown. The system as heretofore described has referred to the light source 14 illuminating a laser line 16 across the surface of an edge portion of the web 12 (step 101). The image of the laser line 16 is reflected from the web such that the camera 18 acquires a video data frame of the laser line (step 102). The camera 18 is connected to the CPU 24 which is capable of digitizing the images received by the use of an image capture board or the like. Therefore, the

CPU converts the video data frame into a digitized data matrix (step 103). For example, the data matrix may be a 512 X 512 pixel matrix wherein each pixel represents eight bits of data. Fig. 4 shows an exemplary version of the data matrix containing the laser line image 16 for further analysis by the CPU 24.

The CPU initially establishes a laser intensity threshold (step 104) in order to distinguish the laser line image from background noise. Portions of the signal corresponding to the low intensity scattered light which equate to a signal voltage lower than the threshold value are ignored by the CPU. The threshold limitation is set to insure that the digitized image has an appearance similar to that of the laser line image 16. One method for establishing the intensity threshold would be to acquire the average value of the first row of data from the data matrix. Once the threshold has been set, the CPU proceeds to do a pixel by pixel examination of sequential rows in the data matrix (step 105). A determination is then made as to whether the data of the presently examined pixel exceeds the predetermined threshold (step 106). If the data does not exceed the threshold, the examination continues to the next pixel in that row. If the threshold is exceeded, a further determination is made as to whether the intensity level is greater than the intensity level of the previously examined pixel (step 107). If the intensity level is not greater than the previous pixel, the routine proceeds with examining the next pixel in the row.

If the intensity level is found to be greater than the previously examined pixel intensity level, the information for that pixel is stored in a two dimensional line position array. The information stored for the row and column position of the pixel is stored as an index and magnitude position data for the line array. Therefore, each position in the two dimensional line array is equivalent to a row of the original data matrix (step 108).

Once the data for a pixel is stored in the line array, a determination is made as to whether any pixels are remaining in the row being examined in the data matrix (step 109). If there are pixels remaining in the presently examined row, the routine proceeds with the next pixel in the row (step 110), and thus returns to step 105 for the pixel by pixel examination of the row. If no pixels remain in the presently examined row, a further determination is made as to whether any rows are remaining in the data matrix (step 111). If there are any rows remaining in the data matrix, the routine proceeds with an examination of the next row of the data matrix (step 112) and returns to step 105 for the pixel by pixel examination of the row.

If the determination is made at step 111 that every pixel of every row in the data matrix has been examined, the process continues by performing averaging techniques on the data now stored in the line array (step 113) in order to minimize the effects of possible scan interlacing and the narrow video band width of the camera 18. One such averaging technique involves the reading of every other row, taking an average and using it as the value for the interlaced row.

Next, the CPU operates to determine the linear slope of the data representing the laser line. This may be done by calculating the angle of the line with respect to a predetermined horizontal plane. If the angle is within a predetermined percentage, eg. 4%, the line will be considered to be linear (step 114). This angular information will be hereinafter utilized in order to compensate for the original laser line 16 deviating from a relatively horizontal plane due to such factors as the light source being misaligned or the machinery causing flutter in the moving web.

A determination is next made as to locating the beginning of the laser line (step 115). This is accomplished by making an examination of the line array and identifying the first non-zero value in the array. Next, a determination is made as to locating the end of the laser line (step 116). This is done by examining the line array for the next occurring zero value following the previously located first non-zero value in the array. For exemplary purposes, the end of the line may typically occur at the very edge of the top surface of the web by a discontinuity of the laser line due to the edge curl of the web. Thereafter, a calculation may be made as to determining the overall length of the laser line (step 117).

The process continues at step 118 wherein the previously calculated slope angle at step 114 is utilized to rotate the linear portion of the line into a relatively horizontal position. The linear portion of the laser line may be identified by those values within the line array which do not deviate from a predetermined average value. At the same time, a predetermined portion, eg. 75 percent of the entire line may be displayed on the CPU monitor 26. The remainder of the line will be displayed following the analysis of the non-linear portions of the laser line which correspond to the edge curl present in the web. The next process step involves an identification of the peak magnitude of the curl present in the non-linear portion of the line (step 119). This identification is done by examining the data in the line array until the peak pixel magnitude is found by comparing each subsequent pixel to previous peaks in the line array. From this magnitude data a determination may be made as to the mechanical height of the curl (step 120). The mechanical height of the curl corresponds directly to the linear deviation of the peak magnitude from the previously identified portion of the laser line. This mechanical height data may be displayed along with the digitized image of the laser line on the CPU monitor 26.

A further analysis of the laser line is carried out by the CPU by determining the radius of the curl present in the web (step 121). The radius of the curl will correspond to the severity of the curl present in the web. This analysis involves identifying a point which is eight pixels greater in magnitude from the linear portion of the line. This point may be referred to as the first point of curl. Next, a point is identified eight pixels inward from the end of the laser line, and is labelled the second point of curl. The difference of the first and second points of curl, which represent index and position data in the two dimensional line array, establish a third point of curl which is positioned in between the first and second points on the non-linear portion of the laser line.

The routine proceeds with calculating a reciprocal value of the determined radius (step 122) to provide a magnitude which will increase with increasing curl and decrease with lesser curl. Thereafter, data relating to the curl including the mechanical height and radius magnitude are displayed on the CPU monitor 26. Upon fully analyzing and determining the presence and degree of curl present in the web 12, the CPU provides feedback control data to a control system (not shown) associated with the curl removal device 30 as previously described. This integrated system therefore is able to determine the degree of curl as well as provide measures for removing the curl from the web.

Claims

1. A system for measuring any degree of edge curl in a web, comprising: illuminating means for illuminating a line on the surface of said web, said line extending inwardly from an edge of said web and having a linear portion; image acquisition means responsive to said illuminated line for acquiring image data representative of the profile of said line; and processing means responsive to said image for determining the maximum of any deviation of said line from said linear portion thereof.

2. The system of claim 1, wherein said processing means comprises digital storage means for digitizing and storing said image data as discrete profile data points.

3. • The system of claim 2, wherein said processing means is operable for identifying at least one first reference profile data point associated with said linear portion of said line, and for identifying a second reference profile data point associated with a portion of said line at a location having the maximum linear deviation from said linear portion of said line as represented by said first reference profile data point, said linear deviation being representative of the degree of edge curl in said web.

4. The system of claim 1, wherein said web comprises paper.

5. The system of claim 1, wherein said illuminating means comprises a laser.

6. The system of claim 1, wherein said illuminating means directs light at an acute angle upon said web surface.

7. The system of claim 6, wherein said acute angle is 45°.

8. The system of claim 1, wherein said image acquisition means comprises a CCD array camera.

9. The system of claim 1, wherein said image acquisition means is positioned at an acute angle with respect to said web surface.

10. The system of claim 9, wherein said acute angle is 45°.

11. The system of claim 1, wherein said processing means is further operable for identifying both linear and non-linear portions of said line.

12. The system of claim 11, wherein said processing means identifies said linear and non^linear portions of said line by determining whether successive profile reference points deviate from a predetermined linear reference plane.

13. The system of claim 1 further comprising compensation means for compensating for said line diverging from a perpendicular path across said web surface.

14. The system of claim 1 further comprising curl removal means responsive to said processing means for removing said curl from said web.

15. The system of claim 14, wherein said curl removal means comprises a steam apparatus.

16. The system of claim 15, wherein said steam apparatus applies steam of a predetermined humidity and temperature to said web surface in accordance with said calculated linear deviation which represents the curl present in said web.

17. The system of claim 14, wherein said curl removal means comprises a roll coater apparatus.

18. The system of claim 1, wherein said processing means further -determines the radius of the curl present in said web.

19. A system for measuring and removing any edge curl in a web, comprising: illuminating means for illuminating a line extending across a surface portion of said web to an edge thereof; detection means responsive to reflections from said illuminated line for detecting the presence of edge curl in said web; processing means responsive to said detected reflections for calculating a curl factor representative of the degree of edge curl present in said web; and curl removal means responsive to said processing means calculating said curl factor for removing the curl present in said web.

20. The system of claim 19, wherein said curl removal means comprises a steam apparatus.

21. The system of claim 20, wherein said steam apparatus applies steam of a predetermined humidity and temperature to said web surface in accordance with said calculated curl factor.

22. The system of claim 19, wherein said curl removal means comprises a roll coater apparatus.

23. The system of claim 19, wherein said detection means comprises image acquisition means responsive to the reflections from said illuminated line for acquiring image data representative of the profile of said line.

24. The system of claim 23, wherein said detection means further comprises digital storage means for digitizing and storing said image data as discrete profile data points.

25. The system of claim 24, wherein said detection means further comprises identifying means for identifying at least one first reference profile data point associated with a linear portion of said line at a location inside of said edge, and a second reference profile data point associated with a portion of said line at a location having the greatest linear deviation from said linear portion of said line as represented by said first reference profile data point, said linear deviation being representative of the degree of edge curl in said web.

26. The system of claim 25, wherein said processing means calculates said curl factor by calculating any linear deviation between said first and second reference profile data points, said linear deviation being representative of the degree of edge curl in said web.

27. The system of claim 19, wherein said web comprises paper.

28. The system of claim 19, wherein said illuminating means comprises a laser.

29. The system of claim 19, wherein said illuminating means directs light an acute angle upon said web surface.

30. The system of claim 29, wherein said acute angle is 45°.

31. The system of claim 19, wherein said detection means comprises a CCD array camera.

32. The system of claim 19, wherein said detection means is positioned at an acute angle with respect to said web surface.

33. The system of claim 32, wherein said acute angle is 45°.

34. The system of claim 25, wherein said identifying means is further operable for identifying both linear and non-linear portions of said line.

35. The system of claim 34, wherein said identifying means identifies said linear and non-linear portions of said line by determining whether successive profile reference points deviate from a predetermined linear reference plane.

36. The system of claim 19, wherein said processing means further comprises compensation means for compensating for said line diverging from a perpendicular path across said web surface.

37. The system of claim 19, wherein said processing means further determines the radius of the curl present in said web.

38. A method for measuring any degree of edge curl present in a web of material, comprising the steps of: illuminating a line on the surface of said web, said line extending inwardly from an edge of said web and having a linear portion; acquiring image data representative of the profile of said line; and determining the maximum of any deviation of said line from said linear portion thereof.

39. A method for measuring and removing edge curl present in a web of material, comprising the steps of: illuminating a line extending across a surface portion of said web to an edge thereof; detecting the presence of edge curl in said web in response to an analysis of reflections from said illuminated line; calculating a curl factor representative of the degree of edge curl present in said web; and removing the curl present in said web in accordance with said curl factor.