CA1078489A - Surface sensor - Google Patents
Surface sensorInfo
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- CA1078489A CA1078489A CA251,851A CA251851A CA1078489A CA 1078489 A CA1078489 A CA 1078489A CA 251851 A CA251851 A CA 251851A CA 1078489 A CA1078489 A CA 1078489A
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Abstract
SURFACE SENSOR
ABSTRACT FOR THE DISCLOSURE
A device for continuously indicating the topo-graphical profile of the surface of a travelling paper web is provided by using a light source directed perpendicul-arly to the surface to illuminate areas on the surface no greater than about 1 mm in diameter. Non-specular light reflected from the surface is detected by a pair of detectors arranged around the illuminated-area thereby to generate a pair of signals. These signals are electrically processed by subtracting one from the other to obtain an indication of the slopes of the surface in the instantaneously illuminated areas thereby to obtain continuous indication of the topographical profile of the surface while substantially reducing the effects of local differences in reflectivity of the surface.
ABSTRACT FOR THE DISCLOSURE
A device for continuously indicating the topo-graphical profile of the surface of a travelling paper web is provided by using a light source directed perpendicul-arly to the surface to illuminate areas on the surface no greater than about 1 mm in diameter. Non-specular light reflected from the surface is detected by a pair of detectors arranged around the illuminated-area thereby to generate a pair of signals. These signals are electrically processed by subtracting one from the other to obtain an indication of the slopes of the surface in the instantaneously illuminated areas thereby to obtain continuous indication of the topographical profile of the surface while substantially reducing the effects of local differences in reflectivity of the surface.
Description
~L07848~
--, FIELD OF 'I'llE INVENTION
The present inven-tion relates -to a sensor for- de-termining surface characteris-tics of a travelling surface.
More par-ticularly the present invention relates to a surface sensor for determining small scale surface characteristics of a travelling paper web relating to geometry and reflect-ivity e.g. roughness and dirt.
By roughness (or its opposite smoothness) it is generally understood the geometric proper-ty of -the surface which may be defined as a deviation from (or in -the opposite case closeness to) an ideally flat plane. In the case of paper or board the deviations tha-t are per-ceived as a roughness are on a small scale and occur as topographic features of the surface (peaks or valleys) having dimensions in the order of about 0.1 to 5 mm. in the plane of the paper and about 0.01 to 1 mm in a direction -normal to the p1ane. Deviations of larger dimensions in the plane of the paper are generally attributed to properties other than roughness and may come, e.g. under the designation 0 of waviness, or of variations of thickness, etc.
BACKGROUND OF TE~E PRESENT INVENTION
Sensors for determining the degree of roughness by optical means do not provide generally the amount of information available from the device of the present inven-tion. Also discrimination between a dirt particle and a topographical feature is sometimes difficult. , Devices have been described in the patent litera-ture, for example, Canadian Patent 617,188 issued March 28, 1961 discloses a device for detecting surface conditions on a travelling ~eb. This device is sensitive to longitudinal striations on the sur~ace of the web and operates by direct-ing a light beam obliquely onto the surface in a direc-tion ~ ''" .
.. . ~
.
-~ ~078489 generally perpendicular to -the length of` the striations on the web and sensing the amoun-t of ligh-t reflected.
Canadian Patent 836,242 issued March 10, 1970 to Joyce discloses a device for determining surface character-5 istics of a paper sheet in particular for determining awire mark on a paper sheet. One of the concepts of this invention is to project a light through a web and to use a mask, having a plurality of apertures corresponding at least partially to the pattern of the wire mark, in combination with detecting means which generates signasl and to process the signals to obtain an indication, for example, of web speed. The device does not convey general information of the topographical configuration of the web.
U.S. patent 3,591,291 discloses a device for detecting the roughness of a relatively smooth surface by directing a collimated beam of light against the surface and mounting one light sensitive element at the angle of reflec-tion of said beam from the surface, and further light sen-sitive elements in the same plane as the illuminating and reflected beams but at different angles to the surface. The signal generated by the light sensitive element located at the angle of reflection is compared with signal developed by one of the other light sensitive elements to give an indication of surface roughness. This device is based on the assumption that the amount of ligh-t diffused and diffrac-ted from the peaks on the smoo-th surface is a function of the inclination of the slopes of those peaks and that those inclinations are functions of the height of the peaks and therefore that the amount of diffusion and diffraction of the light by the peaks on a relatively smooth surface is a measure of the height of the peaks. The device is operated by positioning it on the surface and comparing :
~'7~34~39 the light signals with no relative movement between the sur-face being measured and the sensor.
In an earlier device invented by the inventors of the instant application, the roughness of a moving sur-face was sensed by projecting a beam of light at a lowangle of an inclination to sequentially illuminate small areas on the surface, collecting scattered light reflected from the small areas t generating electrical signals in ac-cordance with the amount of light collected and analyzing these signals to provide, for example an index of roughness.
This device is not in general suited for discriminating topography from dirt particles.
SUMM~RY OF PRESENT INVENTION
It is an object of the present invention to pro-vide a surface analyzer capable of extracting informationrelating to the topography of a surface and/or detecting "dirt" spots or blemishes on the surface (spots of signifi-cantly different reflectivity than the average surface).
Broadly the present invention relates to a device for obtaining a continuous indication of the topographical profile of the surface of a travelling paper web comprising, a light source for directing light perpendicularly onto the travelling surface to sequencially illuminate areas-of -said surface no greater than 1 mm in diameter, at least a pair of detectors symetrically positioned relative to the illuminated area to receive non-specular light reflected at substantially the same anyle to the surface fxom said illuminated areas, said angle being between 20-60 to the surface, and the angle sub-tended at the illuminated area between said pai.r of detectors when projected onto the surface being greater than 10, means for generating a signal from each of said detectors in accordance with the amount .
. .
78~
of light sensed and electronic means substantially con-tinuously processing said signals by subtracting one of said signals from the other of said signals from said pair of detectors to indicate the slope of the sur~ace in instantaneously illuminated areas thereby to obtain a con-tinuous indication of the topographical profile of said surface while substantially reducing the effects of local differences in reflectivity of sai.d surface.
Preferably the detectors are in ~airs positioned one on either side of the illuminated area, i.e. 180 apart, and preferably perpendicular to the direction of said relative movement between the surface and the sensor to provide cross-machine direction surface information. When 3 or more detectors are used it i5 preferred to provide at least one detector arranged at 90 to the first pair of detectors whereby at least one detector may be used to determine machine direction surface information.
BRI~F DESCRIPTION OF THE DRAWINGS
Other features, objects and advantages will be evident from the following detailed description of the pre-ferred embodiments of the present invention taken in con-junction with the accompanying drawings in which:
Figure 1 is a schematic illustration of a sensor head of the present invention.
Figures 2 to 5 inclusive illustrate schematically different arran~ements o detectors in the sensor head.
Figures 6a, b, c and d schematically illustrate the effects of different surface configurations on the light detected.
Figures 7a, b, c, d, e, and f schematically illu-strate the scan that would be obtained by the various sensors passing along the scan lines X ro Y of Figures 7a and b.
._b` .,,-~.~4~ ` ' ~.
~78~8~
" ~
Figures 8a, b, c, d, e, f and g schematically illustrate the processing of the signals to provide topo-graphical and dirt indications, and Figure 9 is a schematic illustration of a system 5 for processing signals derived from a pair of detectors positioned on opposite sides of the light source (illum-inated area), i.e. 180 apart.
DESCRIPTION OF THE PR]3F]3RRED EMBODIMENT
Referring to Figure 1 the basic elements of the sensor 10 of the present invention comprise a light source 12 for directing a light beam through a window 14 thereby to illuminate at any instant an area 17 (see fig 1 and 6) of the surface 16 to be scanned. In the illustrated ar-rangement the source 12 projects light through an aperture 7~4~
18 which limits the area of the source 12, and a lens 20 focusses the light through an aperture 22 and the window 14 to illuminate the area 17 on the surface 16. The beam of light from source 12 is projected onto the surface 16 in a direction perpendicular or substantially perpendicular to the surface 16. The area 17 which is illuminated at any given instant is no greater than an area equivalent to a -~ circle of about,d~ mm in diameter and preferably 0.1 to .2 millimeters in diameter.
Detectors such as that schematically illustrated at 24 are suitably positioned about the sensor 10 to detect light reflected from the spot or area 17 illuminated on the sur~ace 16 by the light source 12. A single detector 24 has been shown in Figure 1, however, at least two such detectors will be provided. These detectors are preferably inclined at an angle of about 20 - 60 to the surface 16 with each detector preferably being the same angle to the surface.
It is often more c~nvenient to convey the light to the detectors 24 by a suitable optical means comprising, for example, a fibre light guide 26. The aperture 22 limits the stray light entering the light guides 26 and thus detectors 24.
Figures 2, 3, 4 and 5 illustrate various combina-tions of illuminator beam and detectors. The illuminator beam is schematically illustrated by the arrow 28 while the various reflected beams that are sensed by the detectors 24 are indicated by the designation Ml, M2 and Cl r C2 .
These designations M & C are intended to indicate machine direction and cross machine direction, respectively. The direction of web travel, i.e. the machine direction of the surface is indicated by the arrow 30.
Figure 2, illustrates sensing the two reflected beams Ml and M2 by suitable detectors 24 (not illustrated), figure 3, sensiny the two beams Cl and C2, and Figure 4, the four beams, Ml, M2, Cl, C2 so that topographical character-istics are viewed from two directions, for example, the cross machine and machine directions. Figure 5 illustrates an arrangement wherein three beams, Ml, M2 and Cl are sensed which also views the topography from two directions. Ob-viously the cross machine reflected beams, Cl and C2 and a single machine direction beam could be used to obtain a similar result.
The operation of the various detectors will now be explained with reference to Figures 6a, b, c, and d. It will be seen that when the illuminator beam 28 projects light perpendicular to the average slope of the illuminated area 17 of the surface 16 and when the detectors Dl and D2 are arranyed at the same angle to the surface 16, scattered light reflected to detectors Dl and D2 will be substantially equal (Figure 6a) even if the area 17 is at the top or crest of a hill (fig 6b) or bottom of the valley. It will also be apparent from Figure 6c that if the beam 28 is reflected from a dirt spot the amount of light detected by detectors Dl and D2 will be equal but the intensity of the reflected light and therefore the magnitude of the signal will be considerably reduced. On the other hand if the average inclination of the area 17 is not perpendicular to the beam 28 then the amount of light reflected to and sensed by -the detectors Dl ancl D2 will not be equal and the imbalance will be indicati.ve of the slope of the surface relative to the light beam.
Figure 7 illustrates a pair of scan lines X and Y
crossing a dirty area and a hump as shown in plan and elevation in Figures 7a and 7b respectively. Assuming . ' ,~: ~' '' , .
.
8~9 that the Ml and M2 are from detectors arranged in the machine direction, i.e. direction travel oE the scans and Cl and C2 are in the cross machine it is apparent fr~m Figure 7c, d, e and f that the output of detectors Ml, M2, Cl, C2 are all reduced in the areas 34 where the dirt i5 scanned, i.e. the total reflected light to 1:he detectors Ml and M2, Cl and C2 is reduced by the presence of the dirt particle.
As the sensor moves along scan X (over the center line of a hump) the detector Ml detects a decreasing amount of light and then an increasing amount of light with the intensity increasing to a point higher than the amount of light that is sensed when the inclination of the area 17 i9 perpendicular to the beam 28 and then decreasing back ~o the average, as indicated by the numeral 36. The output M2 as the sensor traverses the hump as indicated at 38 is a mirror image of - the output 36.
It will be noted that the output of Cl and C2 as the sensor head moves relative to the surface along Scan line X traversing the center line of the h~np do not provide any indication that a hump is present since the reflected light received by-the detectors will be the same along the hump. However, on Scan line Y (part way up the hump) as indicated in Figures 7f the output Cl on one side of the Scan line shows an increase in the amount of light detected ~25 along a curve substantially matching with khe shape of the hump (Section 40) whereas the output C2 on the opposite side shows a decxease in the amount of light reflected (Section Cl2 fig 7f). These sections as indicated in Figures 7f and g at 40 and 42 are substantially mirror images.
Figures 8a and b are similar to Figures 7a and b in that they illustrate the scan direction over the dirt and the hump. With the relative movement of the sensor to the ;
_ g _ .
surface along Scan X for example, the output Ml ancl M2 have been repeated in Figures 8c and d and the output M2 has been inverted in Figure 8e. The inverted profile is in-dicated by the numerals 34' corresponds to the oriyinal trace 34 and the inverted trace 38' corresponds with the trace 38. It will be noted in Figure 8f that when the traces 8c and e are added the signal generated by -the dirt com-pletely disappears i.e. 34' cancels 34 whereas the topo-graphical signal is emphasized (sele fig. 8f). On the other 10 ~ hand if the signals or traces illustrated in Figure 8c and ~b are added, without the trace from the siynal M2 being inverted, the topographical signals disappear and the dirt signal is emphasized ~see fig. 8g).
Figure 9 illustrates schematically by simple block diagram how signals Ml and M2 or Cl and C2 may be processed - by electronic means. Signals Ml and M2, as indicated to the left in this drawing, may be added to provide a dirt signal and one of the signals, for example, signal M2 may be in-verted signal added to the signal generated by Ml to give a topographical signal.
When applied for example to a paper machine the sensor may be mounted on a pLatform which travels across the paper web. Specifically the sensor is moved with the platform slowly across the sheet while the paper moves relatively quickly therebeneath. For example, the paper may travel at, say a 1000 ft. per minute and the sensor at a speed of half a foot per second transversely to the direction of web travel. Hence the relative movement between the paper and the scanner is at a very small anyle with respect to the machine direction of the sheet.
It will be apparent that the most e~fective way of handling the signals generated by the sensors is over preset periods of time sufficiently long that the data : - ~ : . : .
: ~ . : . , .. , .: ..
.: :
. . . ' ' ' : " ~ ' :
~,8~8g collected permits meaningful statistical reduetion. ~ox example, at a relative web speed of 1000 per minute suffi-cient data to give an index of roughness is obtained in about one second. (Similar condit:ions apply to the eval-uation of dirt). Hence an index o:E roughness is obtained about every second and sinc~ the p:Latform is simultaneously travelling across the sheet an index of roughness is obtain-ed every half a foot across the sheet (assuming a half a foot per second speed for traverse of the platform across the sheet). This information can be plotted or displayed to give a profile o the variation of roughness across the width of the paper machine.
It will be clear that by the use of conventional equipment to add or invert and add the signals one can obtain a clearer indication of the dirt and of the topo-graphical configuration of the surface being sensed. The signals may be further manipulated or processed such as by appropriate frequency analysis so that other features of the surfacP being scanned may be detected. For example, it may well be possible to detect graininess of a paper sheet due to the pecular effect graininess has on the surface of a sheet, also printability or shrinkage may be detectable by the proper analysis of the topographical features of the web.
The sensed beams Ml, M2, Cl, C2 have been indicated as aligned in either the machine or cross machine direction to simplify obtaining the cross machine and machine direction profiles, however, as above indicated the detectors may be arranged at other angles. Also, the angle between pairs of detectors around the illuminated area may be varied and significant information on the topography and~or brightness be detected and evaluated by proper analysis~ ~owever, the sensitivity is reduced as the detectors approach each other ,,. , ~:
7~8~
and the device tends to be very difficult to use when the angle subtended at the illuminated area by the two detectors projected onto the plane of the paper is reduced to about 10 .
Modifications will be evident to those skilled in the art without departing fr0m the spirit of the invention as defined in the app nded claims.
. -. .. . . . ...
.
--, FIELD OF 'I'llE INVENTION
The present inven-tion relates -to a sensor for- de-termining surface characteris-tics of a travelling surface.
More par-ticularly the present invention relates to a surface sensor for determining small scale surface characteristics of a travelling paper web relating to geometry and reflect-ivity e.g. roughness and dirt.
By roughness (or its opposite smoothness) it is generally understood the geometric proper-ty of -the surface which may be defined as a deviation from (or in -the opposite case closeness to) an ideally flat plane. In the case of paper or board the deviations tha-t are per-ceived as a roughness are on a small scale and occur as topographic features of the surface (peaks or valleys) having dimensions in the order of about 0.1 to 5 mm. in the plane of the paper and about 0.01 to 1 mm in a direction -normal to the p1ane. Deviations of larger dimensions in the plane of the paper are generally attributed to properties other than roughness and may come, e.g. under the designation 0 of waviness, or of variations of thickness, etc.
BACKGROUND OF TE~E PRESENT INVENTION
Sensors for determining the degree of roughness by optical means do not provide generally the amount of information available from the device of the present inven-tion. Also discrimination between a dirt particle and a topographical feature is sometimes difficult. , Devices have been described in the patent litera-ture, for example, Canadian Patent 617,188 issued March 28, 1961 discloses a device for detecting surface conditions on a travelling ~eb. This device is sensitive to longitudinal striations on the sur~ace of the web and operates by direct-ing a light beam obliquely onto the surface in a direc-tion ~ ''" .
.. . ~
.
-~ ~078489 generally perpendicular to -the length of` the striations on the web and sensing the amoun-t of ligh-t reflected.
Canadian Patent 836,242 issued March 10, 1970 to Joyce discloses a device for determining surface character-5 istics of a paper sheet in particular for determining awire mark on a paper sheet. One of the concepts of this invention is to project a light through a web and to use a mask, having a plurality of apertures corresponding at least partially to the pattern of the wire mark, in combination with detecting means which generates signasl and to process the signals to obtain an indication, for example, of web speed. The device does not convey general information of the topographical configuration of the web.
U.S. patent 3,591,291 discloses a device for detecting the roughness of a relatively smooth surface by directing a collimated beam of light against the surface and mounting one light sensitive element at the angle of reflec-tion of said beam from the surface, and further light sen-sitive elements in the same plane as the illuminating and reflected beams but at different angles to the surface. The signal generated by the light sensitive element located at the angle of reflection is compared with signal developed by one of the other light sensitive elements to give an indication of surface roughness. This device is based on the assumption that the amount of ligh-t diffused and diffrac-ted from the peaks on the smoo-th surface is a function of the inclination of the slopes of those peaks and that those inclinations are functions of the height of the peaks and therefore that the amount of diffusion and diffraction of the light by the peaks on a relatively smooth surface is a measure of the height of the peaks. The device is operated by positioning it on the surface and comparing :
~'7~34~39 the light signals with no relative movement between the sur-face being measured and the sensor.
In an earlier device invented by the inventors of the instant application, the roughness of a moving sur-face was sensed by projecting a beam of light at a lowangle of an inclination to sequentially illuminate small areas on the surface, collecting scattered light reflected from the small areas t generating electrical signals in ac-cordance with the amount of light collected and analyzing these signals to provide, for example an index of roughness.
This device is not in general suited for discriminating topography from dirt particles.
SUMM~RY OF PRESENT INVENTION
It is an object of the present invention to pro-vide a surface analyzer capable of extracting informationrelating to the topography of a surface and/or detecting "dirt" spots or blemishes on the surface (spots of signifi-cantly different reflectivity than the average surface).
Broadly the present invention relates to a device for obtaining a continuous indication of the topographical profile of the surface of a travelling paper web comprising, a light source for directing light perpendicularly onto the travelling surface to sequencially illuminate areas-of -said surface no greater than 1 mm in diameter, at least a pair of detectors symetrically positioned relative to the illuminated area to receive non-specular light reflected at substantially the same anyle to the surface fxom said illuminated areas, said angle being between 20-60 to the surface, and the angle sub-tended at the illuminated area between said pai.r of detectors when projected onto the surface being greater than 10, means for generating a signal from each of said detectors in accordance with the amount .
. .
78~
of light sensed and electronic means substantially con-tinuously processing said signals by subtracting one of said signals from the other of said signals from said pair of detectors to indicate the slope of the sur~ace in instantaneously illuminated areas thereby to obtain a con-tinuous indication of the topographical profile of said surface while substantially reducing the effects of local differences in reflectivity of sai.d surface.
Preferably the detectors are in ~airs positioned one on either side of the illuminated area, i.e. 180 apart, and preferably perpendicular to the direction of said relative movement between the surface and the sensor to provide cross-machine direction surface information. When 3 or more detectors are used it i5 preferred to provide at least one detector arranged at 90 to the first pair of detectors whereby at least one detector may be used to determine machine direction surface information.
BRI~F DESCRIPTION OF THE DRAWINGS
Other features, objects and advantages will be evident from the following detailed description of the pre-ferred embodiments of the present invention taken in con-junction with the accompanying drawings in which:
Figure 1 is a schematic illustration of a sensor head of the present invention.
Figures 2 to 5 inclusive illustrate schematically different arran~ements o detectors in the sensor head.
Figures 6a, b, c and d schematically illustrate the effects of different surface configurations on the light detected.
Figures 7a, b, c, d, e, and f schematically illu-strate the scan that would be obtained by the various sensors passing along the scan lines X ro Y of Figures 7a and b.
._b` .,,-~.~4~ ` ' ~.
~78~8~
" ~
Figures 8a, b, c, d, e, f and g schematically illustrate the processing of the signals to provide topo-graphical and dirt indications, and Figure 9 is a schematic illustration of a system 5 for processing signals derived from a pair of detectors positioned on opposite sides of the light source (illum-inated area), i.e. 180 apart.
DESCRIPTION OF THE PR]3F]3RRED EMBODIMENT
Referring to Figure 1 the basic elements of the sensor 10 of the present invention comprise a light source 12 for directing a light beam through a window 14 thereby to illuminate at any instant an area 17 (see fig 1 and 6) of the surface 16 to be scanned. In the illustrated ar-rangement the source 12 projects light through an aperture 7~4~
18 which limits the area of the source 12, and a lens 20 focusses the light through an aperture 22 and the window 14 to illuminate the area 17 on the surface 16. The beam of light from source 12 is projected onto the surface 16 in a direction perpendicular or substantially perpendicular to the surface 16. The area 17 which is illuminated at any given instant is no greater than an area equivalent to a -~ circle of about,d~ mm in diameter and preferably 0.1 to .2 millimeters in diameter.
Detectors such as that schematically illustrated at 24 are suitably positioned about the sensor 10 to detect light reflected from the spot or area 17 illuminated on the sur~ace 16 by the light source 12. A single detector 24 has been shown in Figure 1, however, at least two such detectors will be provided. These detectors are preferably inclined at an angle of about 20 - 60 to the surface 16 with each detector preferably being the same angle to the surface.
It is often more c~nvenient to convey the light to the detectors 24 by a suitable optical means comprising, for example, a fibre light guide 26. The aperture 22 limits the stray light entering the light guides 26 and thus detectors 24.
Figures 2, 3, 4 and 5 illustrate various combina-tions of illuminator beam and detectors. The illuminator beam is schematically illustrated by the arrow 28 while the various reflected beams that are sensed by the detectors 24 are indicated by the designation Ml, M2 and Cl r C2 .
These designations M & C are intended to indicate machine direction and cross machine direction, respectively. The direction of web travel, i.e. the machine direction of the surface is indicated by the arrow 30.
Figure 2, illustrates sensing the two reflected beams Ml and M2 by suitable detectors 24 (not illustrated), figure 3, sensiny the two beams Cl and C2, and Figure 4, the four beams, Ml, M2, Cl, C2 so that topographical character-istics are viewed from two directions, for example, the cross machine and machine directions. Figure 5 illustrates an arrangement wherein three beams, Ml, M2 and Cl are sensed which also views the topography from two directions. Ob-viously the cross machine reflected beams, Cl and C2 and a single machine direction beam could be used to obtain a similar result.
The operation of the various detectors will now be explained with reference to Figures 6a, b, c, and d. It will be seen that when the illuminator beam 28 projects light perpendicular to the average slope of the illuminated area 17 of the surface 16 and when the detectors Dl and D2 are arranyed at the same angle to the surface 16, scattered light reflected to detectors Dl and D2 will be substantially equal (Figure 6a) even if the area 17 is at the top or crest of a hill (fig 6b) or bottom of the valley. It will also be apparent from Figure 6c that if the beam 28 is reflected from a dirt spot the amount of light detected by detectors Dl and D2 will be equal but the intensity of the reflected light and therefore the magnitude of the signal will be considerably reduced. On the other hand if the average inclination of the area 17 is not perpendicular to the beam 28 then the amount of light reflected to and sensed by -the detectors Dl ancl D2 will not be equal and the imbalance will be indicati.ve of the slope of the surface relative to the light beam.
Figure 7 illustrates a pair of scan lines X and Y
crossing a dirty area and a hump as shown in plan and elevation in Figures 7a and 7b respectively. Assuming . ' ,~: ~' '' , .
.
8~9 that the Ml and M2 are from detectors arranged in the machine direction, i.e. direction travel oE the scans and Cl and C2 are in the cross machine it is apparent fr~m Figure 7c, d, e and f that the output of detectors Ml, M2, Cl, C2 are all reduced in the areas 34 where the dirt i5 scanned, i.e. the total reflected light to 1:he detectors Ml and M2, Cl and C2 is reduced by the presence of the dirt particle.
As the sensor moves along scan X (over the center line of a hump) the detector Ml detects a decreasing amount of light and then an increasing amount of light with the intensity increasing to a point higher than the amount of light that is sensed when the inclination of the area 17 i9 perpendicular to the beam 28 and then decreasing back ~o the average, as indicated by the numeral 36. The output M2 as the sensor traverses the hump as indicated at 38 is a mirror image of - the output 36.
It will be noted that the output of Cl and C2 as the sensor head moves relative to the surface along Scan line X traversing the center line of the h~np do not provide any indication that a hump is present since the reflected light received by-the detectors will be the same along the hump. However, on Scan line Y (part way up the hump) as indicated in Figures 7f the output Cl on one side of the Scan line shows an increase in the amount of light detected ~25 along a curve substantially matching with khe shape of the hump (Section 40) whereas the output C2 on the opposite side shows a decxease in the amount of light reflected (Section Cl2 fig 7f). These sections as indicated in Figures 7f and g at 40 and 42 are substantially mirror images.
Figures 8a and b are similar to Figures 7a and b in that they illustrate the scan direction over the dirt and the hump. With the relative movement of the sensor to the ;
_ g _ .
surface along Scan X for example, the output Ml ancl M2 have been repeated in Figures 8c and d and the output M2 has been inverted in Figure 8e. The inverted profile is in-dicated by the numerals 34' corresponds to the oriyinal trace 34 and the inverted trace 38' corresponds with the trace 38. It will be noted in Figure 8f that when the traces 8c and e are added the signal generated by -the dirt com-pletely disappears i.e. 34' cancels 34 whereas the topo-graphical signal is emphasized (sele fig. 8f). On the other 10 ~ hand if the signals or traces illustrated in Figure 8c and ~b are added, without the trace from the siynal M2 being inverted, the topographical signals disappear and the dirt signal is emphasized ~see fig. 8g).
Figure 9 illustrates schematically by simple block diagram how signals Ml and M2 or Cl and C2 may be processed - by electronic means. Signals Ml and M2, as indicated to the left in this drawing, may be added to provide a dirt signal and one of the signals, for example, signal M2 may be in-verted signal added to the signal generated by Ml to give a topographical signal.
When applied for example to a paper machine the sensor may be mounted on a pLatform which travels across the paper web. Specifically the sensor is moved with the platform slowly across the sheet while the paper moves relatively quickly therebeneath. For example, the paper may travel at, say a 1000 ft. per minute and the sensor at a speed of half a foot per second transversely to the direction of web travel. Hence the relative movement between the paper and the scanner is at a very small anyle with respect to the machine direction of the sheet.
It will be apparent that the most e~fective way of handling the signals generated by the sensors is over preset periods of time sufficiently long that the data : - ~ : . : .
: ~ . : . , .. , .: ..
.: :
. . . ' ' ' : " ~ ' :
~,8~8g collected permits meaningful statistical reduetion. ~ox example, at a relative web speed of 1000 per minute suffi-cient data to give an index of roughness is obtained in about one second. (Similar condit:ions apply to the eval-uation of dirt). Hence an index o:E roughness is obtained about every second and sinc~ the p:Latform is simultaneously travelling across the sheet an index of roughness is obtain-ed every half a foot across the sheet (assuming a half a foot per second speed for traverse of the platform across the sheet). This information can be plotted or displayed to give a profile o the variation of roughness across the width of the paper machine.
It will be clear that by the use of conventional equipment to add or invert and add the signals one can obtain a clearer indication of the dirt and of the topo-graphical configuration of the surface being sensed. The signals may be further manipulated or processed such as by appropriate frequency analysis so that other features of the surfacP being scanned may be detected. For example, it may well be possible to detect graininess of a paper sheet due to the pecular effect graininess has on the surface of a sheet, also printability or shrinkage may be detectable by the proper analysis of the topographical features of the web.
The sensed beams Ml, M2, Cl, C2 have been indicated as aligned in either the machine or cross machine direction to simplify obtaining the cross machine and machine direction profiles, however, as above indicated the detectors may be arranged at other angles. Also, the angle between pairs of detectors around the illuminated area may be varied and significant information on the topography and~or brightness be detected and evaluated by proper analysis~ ~owever, the sensitivity is reduced as the detectors approach each other ,,. , ~:
7~8~
and the device tends to be very difficult to use when the angle subtended at the illuminated area by the two detectors projected onto the plane of the paper is reduced to about 10 .
Modifications will be evident to those skilled in the art without departing fr0m the spirit of the invention as defined in the app nded claims.
. -. .. . . . ...
.
Claims (6)
1. A device for obtaining a continuous indication of the topographic profile of a traveling surface of paper comprising, a light source, means for directing light from said source perpendicularly onto said traveling surface to sequencially illuminate areas of said surface no greater than 1 mm in diameter, at least a pair of detectors symetrically positioned relative to said illuminated areas to receive non-specular light reflected at substantially the same angle to said surface from an instantaneously illuminated area, said angle being in the range of 20° to 60° to said surface, the angle subtended at said illuminated area between said pair of detectors when projected onto said surface being greater than 10°, means for generating a signal from each of said detectors in accordance with the amount of light sensed by said detector, electronic means substantially continuously processing said signals by sub-tracting one of said signals from the other of said signals from said pair of detectors, to indicate the slope of said surface in said instantaneiously illuminated area, thereby to obtain a continuous indication of the topographical profile of said surface while substantially reducing the effects of local differences of reflectivity of the surface.
2. A device as defined in claim l wherein said means for processing comprises means adding said signals, and means for inverting one of said signals and adding said inverted signal to another of said signals to obtain an indication of the reflectivity of said surface and said surface topography respectively.
3. A device as defined in claim 1 wherein said pair of detectors are on opposite sides of said illuminated area on a straight line substantially perpendicular to the direction of travel of said surface.
4. A device as defined in claim 1 wherein said pair of detectors are substantially aligned with the direction of movement of said surface.
5. A device as defined in claim 4 further com-prising a further detector angularly spaced midway be-tween said pair of detectors.
6. A device as defined in claim 3 wherein said means for processing comprises means adding said signals and means for inverting one of said signals and adding said inverted signal to another of said signals to obtain an indication of the reflectivity of said surface and said surface profile respectively.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA251,851A CA1078489A (en) | 1976-05-05 | 1976-05-05 | Surface sensor |
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA251,851A CA1078489A (en) | 1976-05-05 | 1976-05-05 | Surface sensor |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1078489A true CA1078489A (en) | 1980-05-27 |
Family
ID=4105877
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA251,851A Expired CA1078489A (en) | 1976-05-05 | 1976-05-05 | Surface sensor |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1078489A (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8155426B2 (en) | 2004-05-27 | 2012-04-10 | Oy Ekspansio Engineering Ltd. | Inspection of wood surface roughness |
-
1976
- 1976-05-05 CA CA251,851A patent/CA1078489A/en not_active Expired
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US8155426B2 (en) | 2004-05-27 | 2012-04-10 | Oy Ekspansio Engineering Ltd. | Inspection of wood surface roughness |
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