AU696606B2 - Washboard measuring apparatus - Google Patents
Washboard measuring apparatusInfo
- Publication number
- AU696606B2 AU696606B2 AU35569/95A AU3556995A AU696606B2 AU 696606 B2 AU696606 B2 AU 696606B2 AU 35569/95 A AU35569/95 A AU 35569/95A AU 3556995 A AU3556995 A AU 3556995A AU 696606 B2 AU696606 B2 AU 696606B2
- Authority
- AU
- Australia
- Prior art keywords
- light
- washboarding
- image
- distortion
- corrugated board
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Ceased
Links
Landscapes
- Automatic Analysis And Handling Materials Therefor (AREA)
- Vehicle Cleaning, Maintenance, Repair, Refitting, And Outriggers (AREA)
Description
WASHBOARD MEASURING APPARATUS
This invention relates to an apparatus and a method for measurement of the degree of washboarding of corrugated board.
During the production of corrugated board, fluted paper must have a suitable liner attached to both sides. Adhesive is applied to the flute tops and then the liner is attached. As the adhesive dries, the liner may take up, to varying extents, the silhouette of the flutes. This uneven surface on the finished corrugated board product is known as washboarding. The degree of washboarding is dependent upon the stiffness of the individual corrugated board components, the viscosity and solids content of the glue used and the amount of glue applied.
Washboarding is thought to have an effect on the strength of the resultant corrugated board and the likelihood of board warp or curving may be increased as the degree of washboarding increases. Washboarding particularly results in problems in the printing of boxes made from the affected corrugated board. The undulating surface is not optimal for printing and can often result in the image being absent from the "valleys" and over represented on the "hills" of the surface. Washboarding may also cause the valleys to act as channels for the ink causing blurring of the boundaries of the printed image. Wher ^.sing washboard-affected corrugated board, the printer must put more pressure on the printing roll to obtain an acceptable image, thus resulting in the crushing of the corrugated board.
It is therefore necessary to have an apparatus suitable to measure the degree of washboarding of a given sample, not only to determine whether particular samples are suitable for printing, but also to use in the development of corrugated board with minimal washboarding.
No official standard measure of washboarding exists, however, washboard is ~<-.nerally defined by two numbers. The wac oard mean number is the standard deviation of a small number of data points around the zero or reference level. The washboard mean number is therefore a measure of the overall degree of unevenness of the corrugated board sample. The washboard top number is defined as the mean of averaged maximum and minimum
deviations from a reference averaged over a number of washboard mean number determinations. The washboard mean number is used to give an idea about the printability of the corrugated board. However, any parameter which is capable of describing the average topography of the surface of the board may be determined. For example, other distributions of the surface height, rather than standard deviation, may be used.
Current techniques for determining the degree of washboarding involve scanning a small semi conducting laser sensor along the length of each undulation of the corrugated board. Prior to these techniques, a mechanical displacement needle was used. These techniques are slow, and only provide partial area measurements. In addition, they are generally not suitable for conditions on the plant floor or for on-line measurement where the dust, heat and moisture may cause measurement errors.
In a known apparatus, a strip of single flute board is fed into the instrument which measures and records the height of the flute tops. The feeler gauge is a shoe with a small load so that it does not deform even the weakest flutes. The test strip is fed under the feeler and the recorder registers the height of the flutes. This apparatus only allows for the measurement of flute height down one line running perpendicular to the tips of the flutes. It is also difficult to produce a constant reference position, particularly when there is substantial vibration occurring. The test is also time consuming, as the feeler gauge must stop at each point for a sufficient time to take a measurement.
Another known apparatus comprises a laser sensor that is attached to a pneumatic piston. The pneumatic piston is mounted at a cross-bar. The laser sensor can move to the left and to the right whilst the cross-bar moves in a direction perpendicular to the movement of the laser sensor. The sample is attached to a sample locating area by vacuum. The laser sensor scans the surface with a beam measuring distances so that a large number of data points are collected for analysis. This apparatus only allows for the collection of a finite number of data points and thus a complete analysis of the board's surface cannot be obtained. Furthermore, the test results are dependent on the time available. In a short
period of time, only a small number of data points can be obtained. Thus, this apparatus is not suitable for the measurement of washboarding on-line and continuously. It is also difficult to provide a constant reference position for the long length of the test. Vibration must be removed as measurements are made in the micrometer region. A further problem relates to the provision of a level sample.
In order to overcome some of the above-mentioned disadvantages, this invention includes an apparatus for the measurement of surface defects of corrugated board, particularly washboarding, comprising: a source of light; means to project a pattern of straight lines of light and shadow onto the surface of the corrugated board at a predetermined angle; a device for measuring the distortion of the lines of shadow or light produced on the surface of the corrugated board; and means for analysing said distortion to calculate a value or produce an image indicative of the degree of washboarding.
The light beams can take any suitable form. The only requirement is a recognisable and interpretable pattern projected onto the plane to be measured. It is preferred that a laser beam is used, particularly because of the high radiance of its output.
The plane of beams projected onto the board preferably run parallel to the flute tips of the board. It is the distortion of these beams from normal that gives the measure of the washboarding.
The device for measuring the distortion comprises a sensor which captures an image of the distorted lines of light or shadow. Preferably the sensor is a charge couple device (CCD) camera. It is also preferred that the device be connected to a computing means for analysis of the results. It is desirable that the computing means be equipped with a frame grabber facility to digitise the image. This allows for easy storage. Additionally, a microscope objective lens may be placed before the projection slide to provide adequate coverage of the surface of the board.
This apparatus is particularly useful for the continuous, on-line
measurement and analysis of washboarding of corrugated board as it moves through a production line. An operator would be able to control the quality of the corrugated board by monitoring the degree of washboarding and making suitable adjustments if the problem exceeded a predetermined limit. Suitable adjustments include adjusting the glue viscosity, the amount of glue applied or even the drying rate of the glue. These changes need to be made incrementally as the system has considerable lags, with the result being that the effect of the changes are not immediately obvious to the operator.
The invention also provides a method for the measurement of surface defects of corrugated board, particularly of washboarding, comprising: directing a pattern of straight lines of light and shadow onto the surface of the corrugated board at a predetermined angle; measuring the distortion of the light and/or shadow by the board; and analysing said distortion to calculate a value or produce an image indicative of the degree of washboarding.
A preferred embodiment will now be described with reference to the figure. Figure 1 shows a perspective view of the washboard measuring apparatus.
The apparatus comprises a laser (1). The light beams produced are then passed through a projection slide (2) comprising alternating transmitting and opaque regions to produce a plane of alternate straight lines of light and shadow. It is preferred that small spacings between the grid lines of the projection slide are used preferably less than 0.1 mm as this minimises the effect of noise. The lines of shadow and light are projected onto the sample (3) of corrugated board, the washboarding characteristics of which are being analysed. The distance between the projection slide and the board is such that adequate coverage of the surface of the board with the beams is achieved, while maintaining visibility of the projected shadows. These projected beams form an image (4) on the board sample (3) which is a pattern of light and shadow. The degree of distortion apparent in the image produced will depend upon the degree of washboarding of the corrugated board sample (3). Knowing
the angle of projection of the image on the sample, the distortions contain information regarding the absolute values of washboarding present in the sample. Due to the characteristic of washboarding of having a relatively uniform variation in height in one direction across the surface, the pattern of light and shadow produced on the board will roughly appear as lines of light and shadow.
The distance between adjacent lines of light or, equivalently, adjacent lines of shadow on the sample vary depending on the angle that the image is projected. A projection slide that is pre-distorted for a given projection angle may be used to ensure that adjacent lines are the same distance from each other across the illuminated image. Alternatively, and preferably, the analysis software can be used to account for these differences.
Above the sample (3) there is a device for capturing an image of the distortion of the projected lines of light and shadow. It is preferred that this device takes the form of a camera or video (6), in particular, a charge coupled device (CCD) camera. The most preferred CCD camera is manufactured by the Mintron Enterprise Company and has a resolution of 600 TV lines horizontal. However, any optical inspection apparatus employing CCD image acquisition technology may be used. The CCD camera captures the image and passes the information to a computer for storage followed by analysis of phase differences for each digitised row as the image is scanned row by row, over the whole image. A representation of these row by row phase differences is built up and gives information regarding the degree of washboarding.
The distortion of the adjacent lines of light and shadow by the sample results in phase information in the display image which will vary according to the degree of washboarding, where the phase information relates to the relative position of the images of the lines comnared to their expected location when there is no washboarding.
This invention is in part predicated on the discovery that the phase change is directly related to the degree of washboarding. By utilising projected lines as a reference on the surface the degree of emplacement of the reference gives rise to a phase change. For example, the presence of a distortion of 100
microns above the height of the reference surface produces about twice the phase change as a 50 micron distortion does.
To obtain a parameter to describe the variation of the phase of each row, the standard deviation of the variation in phase can be calculated. The standard deviation can be regarded as being indicative of the average degree of washboarding.
In determining the degree of washboarding that has occurred, the phase information may be extracted by computing the Fourier Transform, preferably the Fast Fourier Transform (FFT) of the pattern of the captured image. Changes in phase correlate with changes in displacement of the reference surface. Therefore this will provide a parameter statistically related to the average topography of the surface along a row and which can be regarded as a measure of the root mean square (RMS) roughness of the surface.
Thus, the determination of the surface profile is calculated by the designed software and involves the Fourier analysis of successive cross- sections through the image. It is preferred that this is done perpendicular to the projected lines of light and shadow. This is typically done row by row of the digitised image. The dominant spatial frequency (corresponding to the spacing between the light beams, or equivalently, shadows) is determined for each cross-section and the phase of this spectral component is then calculated for each cross-section. Finally, the phases for each cross-section are connected so that a continuous profile is obtained.
Due to the curvature of the projected shadow arising from some slight convex bowing of the board surface or from curvature of the field of the projected optics, there is a low order quadratic variation superimposed on the phase variation.
The effect of this curvature can be reduced by fitting a low order polynomial to the profile and subsequent subtraction of the polynomial from the profile curve. The image of the distorted light can be viewed on the screen of a personal computer (not shown) or on a television screen (not shown). The computer can also be used to analyse the image providing data such as the
washboard mean number and the washboard top number for given samples. It is preferable that the software used in the computer also has the capability of removing systematic or macro errors due to curl or lack of flatness of the measured sample. The image can be captured or can be viewed continuously, for example, as board passes through the production line. In a preferred embodiment, where the apparatus is used to measure washboarding on-line, a flash light may be used in order to reduce blurring due to image movement during the acquisition of the image.
In another embodiment, a collimator is used to aid in the straightening of the light beams before they enter the projection slide.
In a further embodiment of the invention, an infra-red laser is used as the light source, in conjunction with a CCD camera sensitive to infra-red wavelengths. The CCD camera is then, with the aid of the • ■ecessary software, able to produce an image indicative of the displacement .he infra-red beams when projected on the corrugated board. The image produced has varying intensities, where the low intensities corresponds to shadows and the high intensities to 'light'.
The resolution of the measurements may be altered by changing the angle of the projection of the light beams onto the sample or by changing the field or view on the camera. Alternatively, to increase the resolution of the system, a lens spacer may be utilised. However, a lens-spacer reduces the effective distance of the CCD means from the surface of the board, resulting in a loss of coverage of the board. This would possibly result in multiple scans over different portions of the board being necessary to obtain a representative estimate of the washboarding.
The presence of printing on the corrugated board is not a bar to the use of this technique, however, the p .ting will be a source of noise. Nevertheless, the technique will fail if the surface is printed with a regular pattern of similar spatial frequency as the projected lines of light and shadow of the grid. One proposed method of alleviating this problem is to use an infra-red laser in conjunction with a CCD camera sensitive to infra-red wavelengths as described above, as there should be little difference in reflectance of the colouring used in the board-liner
and the inks used in the printing.
This invention requires no special mountings for the sample as the line pattern is not a Moire or interference pattern. It is therefore entirely suitable for plant floors. As the apparatus does not use interferometry to measure washboard, it is not sensitive to vibration. Additionally, this technique has a significant speed advantage with regard to computational time over Moire techniques, and it can analyse large areas with greater ease and speed than line-scanning profilometry.
The apparatus can be used not only to determine the degree of washboarding in a given sample, but can also be used to determine the presence or absence of peaks and valleys of the fluted board. Furthermore, hi- low measurements (where a flute sits high or low around the average surface height) are obtainable. It is particularly useful for the off-machine determination of washboard severity and for general surface deviation studies regarding print quality, printing pressures, strength affects crushed flutes and mechanisms for washboarding. As the technique is non-contact, it is suitable for on-line continuous measurement and is therefore suitable for on-line quality control of corrugated board.
Claims (20)
1. Apparatus for measuring surface defects of corrugated board comprising: a source of light; means to project a pattern of straight lines of light and shadow onto the surface of the corrugated board at a predetermined angle; a device for measuring the distortion of the lines of shadow and/or light produced on the surface of the corrugated board; and means for analysing said distortion to calculate a value or produce an image indicative of the degree of washboarding.
2. Apparatus of claim 1 wherein the light beams are passed through a projection slide consisting of alternating transmitting and opaque regions before being projected on the corrugated board.
3. Apparatus of claim 1 or 2 wherein the use of a collimator aids in the straightening of the light beams.
4. Apparatus of claim 1 , 2 or 3 with the addition of a microscope objective lens to provide greater coverage of the surface of the board.
5. Apparatus of claim 1 , 2, 3 or 4 wherein the source of the light beams is a laser.
6. Apparatus of claim 5 wherein the laser is an infra-red laser.
7. Apparatus of claim 1, 2, 3, 4, 5 or 6 wherein the device for measuring the distortion includes a camera.
8. Apparatus of claim 7 wherein the camera is a CCD camera.
9. Apparatus of claim 1 , 2, 3, 4, 5 or 6 wherein the device for measuring the distortion includes a video.
10. Apparatus of claim 7, 8 or 9 wherein the device further includes a lens spacer.
11. Apparatus of claim 7, 8, 9 or 10 wherein the device further includes a computer means.
12. Apparatus of claim 11 wherein the computer means includes a frame- grabber facility.
13. Apparatus of claim 11 or 12 wherein the computer converts the digital image using a Fourier transform into a frequency spectrum and calculates the phase of the spectral components.
14. Apparatus of claim 13 wherein the Fourier transform is a Fast Fourier Transform means.
15. A method of measuring washboarding of corrugated board comprising the steps of: directing a pattern of straight lines of light and shadow at a predetermined angle onto the corrugated board; measuring the distortion of the light and/or shadow by the board; and analysing said distortion to calculate a value or produce an image indicative of the degree of washboarding.
16. The method of claim 15 wherein measuring the distortion includes the steps of: capturing an image of the light and shadows reflected on the board; digitising the image; taking a Fourier transform of successive cross-sections of the image; calculating the phase for each cross-section; and representing the phases as a continuous profile.
17. The method of claim 16 wherein the continuous profile of the phases is displayed on a monitor means.
18. The method of claim 16 or 17 wherein a low order polynomial is subtracted from the profile curve.
19. The method of claim 16, 17 or 18 wherein the standard deviation of the variation in phase is calculated and is used to indicate an average degree of washboarding.
20. Apparatus substantially as herein described with reference to figure 1.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AU35569/95A AU696606B2 (en) | 1994-09-19 | 1995-09-18 | Washboard measuring apparatus |
Applications Claiming Priority (4)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| AUPM8219A AUPM821994A0 (en) | 1994-09-19 | 1994-09-19 | Washboard measuring apparatus |
| AUPM8219 | 1994-09-19 | ||
| AU35569/95A AU696606B2 (en) | 1994-09-19 | 1995-09-18 | Washboard measuring apparatus |
| PCT/AU1995/000603 WO1996009518A1 (en) | 1994-09-19 | 1995-09-18 | Washboard measuring apparatus |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| AU3556995A AU3556995A (en) | 1996-04-09 |
| AU696606B2 true AU696606B2 (en) | 1998-09-17 |
Family
ID=25623337
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| AU35569/95A Ceased AU696606B2 (en) | 1994-09-19 | 1995-09-18 | Washboard measuring apparatus |
Country Status (1)
| Country | Link |
|---|---|
| AU (1) | AU696606B2 (en) |
Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5130555A (en) * | 1988-11-28 | 1992-07-14 | Matsushita Electric Industrial Co., Ltd. | Tape crease inspecting method and apparatus having a stripe shaped pattern reflection plate |
-
1995
- 1995-09-18 AU AU35569/95A patent/AU696606B2/en not_active Ceased
Patent Citations (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US5130555A (en) * | 1988-11-28 | 1992-07-14 | Matsushita Electric Industrial Co., Ltd. | Tape crease inspecting method and apparatus having a stripe shaped pattern reflection plate |
Also Published As
| Publication number | Publication date |
|---|---|
| AU3556995A (en) | 1996-04-09 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MK14 | Patent ceased section 143(a) (annual fees not paid) or expired |