Method and apparatus for measuring the crepe of a moving sheet

• US 20080013818A1
• Filed: 08/22/2005
• Published: 01/17/2008
• Est. Priority Date: 08/22/2005
• Status: Active Grant

• Current Assignee: Honeywell International Inc.
• Original Assignee: Shakespeare Company LLC (Newell Brands Inc.)
• Inventors: Shakespeare, John F.
• Granted Patent: US 7,545,971 B2
• Time in Patent Office: Days
• US Class Current: 382/141
• CPC Class Codes: G01B 11/306 for measuring evenness
• CPC Class Codes: G01N 2021/8681 Paper fibre orientation
• CPC Class Codes: G01N 21/89 in moving material, e.g. running paper or textiles G01N21/90, G01N21/91, G01N21/94 take precedence
• CPC Class Codes: G01N 33/346 paper sheets
• CPC Class Codes: G06T 2207/30124 Fabrics; Textile; Paper
• CPC Class Codes: G06T 7/001 using an image reference approach

Abstract

An image-based measurement technique that directly measures the crepe pattern on a moving sheet employs a suitable arrangement of illumination, optical elements, and an imaging device to obtain digital images of the sheet surface. The image resolution is sufficient to represent tissue crepe folds at the scale of the crepe. A spectral analysis of some or of all the images reveals the crepe folding pitch. Further analysis of the image optionally reveals other crepe structural parameters, such as the distribution of crepe fold orientation angles and distribution of linear fold lengths. Corrective actions can be implemented in response to changes in the crepe structure. The pitch of creping is the primary parameter for describing the crepe pattern; in addition, analyzing the images with a gradient operator can yield information regarding the orientation of the crepe folds and distribution of angles of the crepe furrows on the hood side or equivalently of the crepe seams on the cylinder side.

Claims

1. A method for measuring the crepe pattern of a moving sheet that comprises the steps of:

(a) illuminating an area on at least one side of the sheet with radiation;

(b) obtaining at least one digital image of the illuminated area; and

(c) calculating the crepe pattern of the sheet by processing at least one digital image.

2. The method of claim 1 wherein step (c) comprises evaluating at least one spectrum on a linear section through the image.

3. The method of claim 2 wherein at least one spectrum is evaluated using a Fourier transform.

4. The method of claim 2 wherein at least one spectrum is evaluated using a wavelet transform.

5. The method of claim 2 wherein at least one spectrum is evaluated using a Wigner-Ville transform.

6. The method of claim 1 wherein each image comprises a plurality of pixels and a pixel in the digital image represents a dimension in the moving sheet that does not exceed one quarter the nominal crepe pitch of the moving sheet.

7. The method of claim 1 wherein the crepe pattern is characterized as an average folding pitch.

8. The method of claim 1 wherein the crepe pattern is characterized as a distribution of folding pitches.

9. The method of claim 1 wherein the crepe pattern is characterized as an average folding length.

10. The method of claim 1 wherein the crepe pattern is characterized as a distribution of folding lengths.

11. The method of claim 1 wherein the crepe pattern is characterized as a distribution of folding angles.

12. The method of claim 1 wherein at least one digital image of the sheet is acquired on an illuminated side of the sheet.

13. The method of claim 1 wherein only one side of the sheet is illuminated and the at least one digital image of the sheet is acquired on the opposite side of the sheet where the sheet is illuminated.

14. The method of claim 1 wherein the crepe patterns are measured for both surfaces of the moving sheet.

15. The method of claim 1 wherein the radiation contains radiation with wavelengths in at least two separate wavelength regions and in step (b) at least two digital images of the illuminated area are acquired substantially simultaneously with the proviso that not all of the images obtained are derived from radiation having the same wavelength and step (c) calculates the crepe pattern of the sheet by processing the at two digital images.

16. The method of claim 14 wherein at least one digital image is obtained from each side of the sheet.

17. The method of claim 1 wherein an image detector is employed in step (b) and step (a) comprises illuminating the area on the sheet with illumination that is directionally symmetric around an optical axis of the image detector.

18. The method of claim 16 wherein the illumination is provided by a plurality of light sources that are arranged in at least one annulus that is substantially concentric around the optical axis of the image detector.

19. The method of claim 1 further comprising the step of supporting the moving sheet with a support structure that is located on one side of the sheet and step (a) comprises illuminating an area on the other side of the sheet.

20. The method of claim 1 wherein the moving sheet is non-opaque with respect to the radiation and step (c) includes compensating for radiation that is transmitted through the sheet and which contains background images.

21. The method of claim 1 wherein the sheet is a multi-ply sheet comprising a plurality of plies of sheet material that are spliced together, wherein the method is further characterized in that the crepe pattern of each of the plurality of plies of sheet material is measured as each ply is in formed as a moving sheet.

22. The method of claim 1 wherein the moving sheet comprises a sheet tissue.

23. The method of claim 1 wherein the moving sheet comprises a sheet of tissue and the illuminated area on the sheet of tissue is located downstream from a Yankee cylinder.

24. The method of claim 23 further comprising comparing the crepe pattern that is calculated in step (c) to a target crepe pattern and, at least one of (i) changing the doctor blade of the Yankee cylinder, (ii) adjusting doctor blade angle, or (iii) adjustment of application of additives to the Yankee cylinder surface.

25. The method of claim 1 wherein step (b) comprises obtaining a plurality of digital images of illuminated areas along a cross direction of the moving sheet.

26. A method for measuring the crepe pattern of a moving sheet that comprises the steps of:

(a) illuminating an area on at least one side of the sheet with radiation;

(b) obtaining at least one digital image of the illuminated area; and

(c) calculating crepe folding of the sheet by processing at least one digital image with a gradient operator.

27. The method of claim 26 wherein for step (c) each image comprises a plurality of pixels and the gradient operator produces a gradient magnitude and direction for at least one of the pixels.

28. The method of claim 26 wherein step (c) employs a gradient operator of a non-integer order.

29. The method of claim 28 wherein the gradient operator has a non-integer order between ¼

and ¾

.

30. A system for measuring the crepe pattern of a moving sheet that comprises:

image obtaining means for obtaining at least one digital image of an illuminated area on the moving sheet; and

control means for calculating the crepe pattern of the sheet by processing the at least one digital image.

31. The system of claim 30 wherein the control means evaluates at least one spectrum on a linear section through the image.

32. The system of claim 31 wherein the spectrum is evaluated using a Fourier transform or using a wavelet transform or using a Wigner-Ville transform.

33. The system of claim 30 wherein each image comprises a plurality of pixels and a pixel in the digital image represents a dimension in the moving sheet that does not exceed one quarter the nominal crepe pitch of the moving sheet.

34. The system of claim 30 wherein the crepe pattern is characterized as at least one of:

(i) an average folding pitch, (ii) a distribution of folding pitches, (iii) an average folding length, (iv) a distribution of folding lengths, and (iv) a distribution of folding angles.

35. The system of claim 30 wherein the image obtaining means comprises a light source that directs radiation to illuminate an area on one side of the sheet and an imaging device that is positioned to obtain at least one digital image of the sheet on the illuminated side of the sheet.

36. The system of claim 30 wherein the image obtaining means includes a light source that directs radiation to illuminate only one side of the sheet and an imaging device that is positioned to acquire at least one digital image of the sheet from the opposite side of the sheet where the sheet is illuminated.

37. The system of claim 30 wherein the image obtaining means includes (i) a light source that provides radiation that contains radiation with wavelengths in at least two separate wavelength regions and (ii) in step (b) image detecting means for acquiring at least two digital images of the illuminated area substantially simultaneously with the proviso that not all of the images obtained are derived from radiation having the same wavelength and the control means processes the at two digital images.

38. The system of claim 30 wherein image obtaining means includes an image detector and a light source that provides radiation that illuminates the area on the sheet with illumination that is directionally symmetric around an optical axis of the image detector.

39. The system of claim 38 wherein the illumination is provided by a plurality of light sources that are arranged in at least one annulus that is substantially concentric around the optical axis of the image detector.

40. The system of claim 30 further comprising control means for calculating the crepe fold orientation of the sheet by processing the at least one digital image with a gradient operator.

41. The system of claim 40 wherein each image comprises a plurality of pixels and the gradient operator produces a gradient magnitude and direction for at least one of the pixels.

42. The system of claim 40 wherein the gradient operator is of a non-integer order.

43. The system of claim 42 wherein the gradient operator has a non-integer order of between ¼

and ¾

.