CA1068100A - Method of measuring the topography of a surface - Google Patents
Method of measuring the topography of a surfaceInfo
- Publication number
- CA1068100A CA1068100A CA232,746A CA232746A CA1068100A CA 1068100 A CA1068100 A CA 1068100A CA 232746 A CA232746 A CA 232746A CA 1068100 A CA1068100 A CA 1068100A
- Authority
- CA
- Canada
- Prior art keywords
- light
- type
- detector
- angle
- incidence
- 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.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01B—MEASURING LENGTH, THICKNESS OR SIMILAR LINEAR DIMENSIONS; MEASURING ANGLES; MEASURING AREAS; MEASURING IRREGULARITIES OF SURFACES OR CONTOURS
- G01B11/00—Measuring arrangements characterised by the use of optical techniques
- G01B11/30—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces
- G01B11/303—Measuring arrangements characterised by the use of optical techniques for measuring roughness or irregularity of surfaces using photoelectric detection means
Landscapes
- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Length Measuring Devices By Optical Means (AREA)
Abstract
ABSTRACT
This invention relates to a method of measuring the topography of a surface. According to this method a light source emits a substantially paral-lel bundle of light beams at a predetermined incident angle to the surface normal. A light of a first type, that is nonanalyzed as to its polarization or, alternately, polarized perpendicularly to the plane of incidence of the bundle of light beams to the surface, reflected from the surface is detected at an angle to said normal, which is substantially as big as the incident an-gle, and a light of a second type, that is polarized substantially parallel to the plane of incidence, reflected from the surface is detected. The quotient between the strength of light of the second type and the strength of light of the first type is formed to be a measure of the topography of the surface.
This invention relates to a method of measuring the topography of a surface. According to this method a light source emits a substantially paral-lel bundle of light beams at a predetermined incident angle to the surface normal. A light of a first type, that is nonanalyzed as to its polarization or, alternately, polarized perpendicularly to the plane of incidence of the bundle of light beams to the surface, reflected from the surface is detected at an angle to said normal, which is substantially as big as the incident an-gle, and a light of a second type, that is polarized substantially parallel to the plane of incidence, reflected from the surface is detected. The quotient between the strength of light of the second type and the strength of light of the first type is formed to be a measure of the topography of the surface.
Description
~06B~00 ~: :
This invention relates to a method of measuring the topography of a surface. ~-With, ~or example, paper intended for printing it is important to ~e able to decide the properties of the paper as a print carrier, which are related to the surface topography of the paper. Earlier it has been tried to characterize this ~ -property of the paper by measuring the air leakage between a measuring head and the paper to be tested and against which ~;
the measuring head is appli~d. Examples of instruments, by means of which such a measuring is carried out, are the Parker-Print-Surf) (PPS-~ instrument and the Bekk, Bendtsen and Sheffield instruments.
With *hese methods the measuring head is applied against the paper under a certain pressure, and therefore the paper must be kept stationary during the measuring operation.
Continuous measuring on e.g. a movable paper web is therefore difficult to carry out.
It is the object of the invention to achieve a non-touching but still reliable measuring of surface topography.
Moreover the measuring should be simple and non-destructive.
According to the invention there is provided a method of measuring the topography of a surface, characterized in that a light source emits a substantially parallel bundle of light beams at a predetermined incident angle (~) to the surface normal and that a light of a first type, which is non-analyzed as to its polarization, is reflected from the surface and detected at an angle to said normal which is substantially equal to said incident angle, and that light of a second type reflected from the surface is detected, which light is polarized substantially parallelly to the plane of incidence, and that ' .~ ' ', ~0681 the quotient between the strength of li~ht of the second type and the strength of light of the first type is formed to be a measure of the topography of the surface. :~
With test measurements by means of the method of the .
invention it has been found that the measuring result has a .
clear relation to the measur~
"'' ' ~ -la-,~
.
106~oo ::
ing result obtained by measuring with the PPS-instrument, in spite of the ~ -fact that the measurements take place according to quite different principles.
With the method of the invention it is essential that the bundle of light beams emitted from the light source be substantially parallel. It can either be non-polarized or polarized. Of course laser light can be used.
Moreover the reflected light of the first type must be detected at an angle to the surface normal, which is substantially equal to the incident angle, and the incident angle of the light emitted from the light source to the surface normal preferably is selected within the range +10 at either side of the Brewster angle.
According to one embodiment of the inventive method the light of the first type and the light of the second type are detected by the same detector in time sequence, e.g. by arranging a filter of a suitable type so that the light of the first type and the light of the second type reach the detector alternately~ the output of the detector being in a definite relation to the strength of the light incident to the detector, and in case the light of the first type is a light polarized perpendicularly to the plane of incidence, a polarization filter can be adapted in the beam path in front of detector, which filter is turned with alternately 90 displacement between said turning operations, the detector signal being registered after each turning.
According to another embodiment of the method of the invention the light reflected from the surface is divided in a polarization prism into light with its polarization direction perpendicular to the plane of incidence which light is fed to a first detector, and into light with its polarization direc-tion parallel to the plane of incidence, which is fed to a second detector, the output from each of the detectors being in a definite relation to the strength of the light incident to the detector in question.
According to an additional embodiment of the inventive method the , ' . ''' ~ . ' ' ', ,, ' .. ' ~ , ~ ' ~068~00 light of the first type and the light of the second type are each detected by an associated detector, the detector of the light of the first type being placed in the light path of the light reflected from the surface at an angle to the surface normal, which is as big as the incident angle, the out- ;
put signal from each of the detectors being in a definite relation to the strength of the light incident to the detector in question. The detector of the light of the second type may be placed outside the plane of incidence of the light.
The invention is described more in detail below with reference to the enclosed drawings, in which:
Figure 1 shows a first embodiment of the invention.
Figure 2 shows a second embodiment of the invention.
Figure 3 shows a third embodiment of the invention.
Figure 4 shows curves of measured, reflected light strength as a function of the detecting angle at a constant incident angle of incidence.
Figure 5 shows curves of the results obtained by the method of the invention as a function of values measured with the PPS-instrument.
Figure 1 shows a first embodiment of a device for carrying out the method of the invention, a beam source 2 emitting substantially parallel light at a definite angle ~ to the surface normal of a surface 1, whose topography is to be measured. The light reflected at the same angle to the surface normal as the plane of incidence passes through a filter 3 changeable in respect of its polarization properties and reaches a detector 4 after passing the filter 3. A control device 5 is connected to the filter 3 as well as to the detector 4, which device controls the filter so that it alternately transfers to the detector 4 the desired light of the first type, which light is non-analyzed as to its polarization or, alternatively, is polarized perpendicular to the plane of incidence of the bundle of rays to the surface, and the desired light of the second type, which light is polar-~ 3 .~ ; . : .
: ~
1~68~(~0 ized substantially parallel to the plane of incidence. The detector 4 issimultaneously controlled by the control device 5 so that light is only detected when the filter is correctly adapted to transfer light of a desired type. If the used light of the first type is non-analyzed as to its polar-ization, the filter can be a polarization filter, which only transfers light polarized parallelly with the plane of incidence of the bundle of rays, which filter is moved forwards and backwards, so that it will be ~lternately in the ~ay of the reflected beam in front of the detector and alternately beside the beam. If instead, the used light of the first type is polarized per-pendicular to the plane of incidence, a rotary polarization filter can beused, the detector 4 being triggered by the control device to émit an output signal each time the filter is in a suitable position to transfer radiation ~-of the first and second type respectively. The outputs from the detector 4 are fed to the utilization device 6, in which the quotient is formed between the signals derived from the light of the second type and the signals derived from the light of the first type, possibly by means of control signals from the control device SO
According to another embodiment of a device for carrying out the method of the invention, which device is shown in Figure 2, the reflected beam hits a polarization prism 7, dividing the beam which lets through light polarized parallelly with the plane of incidence and deflects light polarized perpendicularly to the plane of incidence. The parallelly polarized light and the perpendicularly polarized light are each brought to an associated detector 8 and 9 respectively and the output signals from these are fed to the utilizing device 10 to form the quotient between these output signals.
In Figure 3 an additional device for carrying out the method of the invention is shown. In this device the condition is utilized that only the ~-light polarized perpendicularly to the plane of incidence or the light of the first type non-analyzed with respect to its polarization need be detected in :: :
:
1(~68100 reflected state at an angle to the surface normal which is as big as the in-cident angle. The light of the other type polarized parallelly with the plane of incidence can be detected at an angle, which deviates relatively greatly from the angle of reflection, which is as~-big as the incident angle.
Moreover the light of the second type need not be detected in the plane of incidence, either, but can be detected as displaced from this. It is evident from the figure that the light of the first type is incident to the detector 12 possibly after passing through a polarization filter 11 and that the light of the second type is incident to the detector 14 after passing through the polarization filter 13. The outputs from the two detectors 14 and 12 are fed to the utilization device lS, which forms the quotient between the two signals.
In Figure 4 three curves are shown, which have been drawn for the same strength of incident light and with a constant incident angle of 60 but at different detecting angles for paper. The curve I indicates measured, reflected light non-polarized with respect to its polarization, the curve II
indicates measured, reflected perpendicularly polarized light and the curve III measured, reflected, parallelly polarized light.
It is evident from the diagram that the detecting angle of the light of the first type should be selected so that that part of the curve is reached where the curve has its maximum, as the highest sensitivity of the result is then achieved. It is also apparent from the figure that this maximum occurs for a detecting angle similar to the incident angle. With selection of another incident angle the curves I and II are laterally dis-placed so that their maximum always will be at a detecting angle similar to the incident angle. The consequence of this is that the detecSing angle of the light of the first type should be substantially equal to the incident angle. The setting of the detecting angle of the light of the first type is relatively critical, as the measuring result can be heavily distorted by a . . . ~
lQ6~100 .~, . -change of the position of the detector, in case the detecting angle is selected so that the steeply running flan~s of the curves I and II are reached. ~ - -At selection of another incident angle than the Brewster angle a not so marked maximum is obtained, and the curves run more evenly and with -tests it has been found that the best measuring result is obtained i the incident angle is selected equal to the Brewster angle and should preferably not deviate more than +10 from this angle, and therefore it should be aimed at getting as close to this angle as is practically possible.
In Figure 5 an output signal measured by means of the inventive -~
method is shown as a function of a value measured by means of the PPS
instrument for some different sorts of paper having different surface topography. Values measured by means of the PPS instrument have been plotted along the abscissa and values measured by the method of the invention along the ordinate. Each marked point represents a special sort of paper.
As is apparent a clear connection between the results from these two methods is obtained, although the methods are based on completely different principles.
Several different modifications are possible within the scope of the invention.
The invention can also be used for measurement of the surface topography of other materials than paper.
.
.
This invention relates to a method of measuring the topography of a surface. ~-With, ~or example, paper intended for printing it is important to ~e able to decide the properties of the paper as a print carrier, which are related to the surface topography of the paper. Earlier it has been tried to characterize this ~ -property of the paper by measuring the air leakage between a measuring head and the paper to be tested and against which ~;
the measuring head is appli~d. Examples of instruments, by means of which such a measuring is carried out, are the Parker-Print-Surf) (PPS-~ instrument and the Bekk, Bendtsen and Sheffield instruments.
With *hese methods the measuring head is applied against the paper under a certain pressure, and therefore the paper must be kept stationary during the measuring operation.
Continuous measuring on e.g. a movable paper web is therefore difficult to carry out.
It is the object of the invention to achieve a non-touching but still reliable measuring of surface topography.
Moreover the measuring should be simple and non-destructive.
According to the invention there is provided a method of measuring the topography of a surface, characterized in that a light source emits a substantially parallel bundle of light beams at a predetermined incident angle (~) to the surface normal and that a light of a first type, which is non-analyzed as to its polarization, is reflected from the surface and detected at an angle to said normal which is substantially equal to said incident angle, and that light of a second type reflected from the surface is detected, which light is polarized substantially parallelly to the plane of incidence, and that ' .~ ' ', ~0681 the quotient between the strength of li~ht of the second type and the strength of light of the first type is formed to be a measure of the topography of the surface. :~
With test measurements by means of the method of the .
invention it has been found that the measuring result has a .
clear relation to the measur~
"'' ' ~ -la-,~
.
106~oo ::
ing result obtained by measuring with the PPS-instrument, in spite of the ~ -fact that the measurements take place according to quite different principles.
With the method of the invention it is essential that the bundle of light beams emitted from the light source be substantially parallel. It can either be non-polarized or polarized. Of course laser light can be used.
Moreover the reflected light of the first type must be detected at an angle to the surface normal, which is substantially equal to the incident angle, and the incident angle of the light emitted from the light source to the surface normal preferably is selected within the range +10 at either side of the Brewster angle.
According to one embodiment of the inventive method the light of the first type and the light of the second type are detected by the same detector in time sequence, e.g. by arranging a filter of a suitable type so that the light of the first type and the light of the second type reach the detector alternately~ the output of the detector being in a definite relation to the strength of the light incident to the detector, and in case the light of the first type is a light polarized perpendicularly to the plane of incidence, a polarization filter can be adapted in the beam path in front of detector, which filter is turned with alternately 90 displacement between said turning operations, the detector signal being registered after each turning.
According to another embodiment of the method of the invention the light reflected from the surface is divided in a polarization prism into light with its polarization direction perpendicular to the plane of incidence which light is fed to a first detector, and into light with its polarization direc-tion parallel to the plane of incidence, which is fed to a second detector, the output from each of the detectors being in a definite relation to the strength of the light incident to the detector in question.
According to an additional embodiment of the inventive method the , ' . ''' ~ . ' ' ', ,, ' .. ' ~ , ~ ' ~068~00 light of the first type and the light of the second type are each detected by an associated detector, the detector of the light of the first type being placed in the light path of the light reflected from the surface at an angle to the surface normal, which is as big as the incident angle, the out- ;
put signal from each of the detectors being in a definite relation to the strength of the light incident to the detector in question. The detector of the light of the second type may be placed outside the plane of incidence of the light.
The invention is described more in detail below with reference to the enclosed drawings, in which:
Figure 1 shows a first embodiment of the invention.
Figure 2 shows a second embodiment of the invention.
Figure 3 shows a third embodiment of the invention.
Figure 4 shows curves of measured, reflected light strength as a function of the detecting angle at a constant incident angle of incidence.
Figure 5 shows curves of the results obtained by the method of the invention as a function of values measured with the PPS-instrument.
Figure 1 shows a first embodiment of a device for carrying out the method of the invention, a beam source 2 emitting substantially parallel light at a definite angle ~ to the surface normal of a surface 1, whose topography is to be measured. The light reflected at the same angle to the surface normal as the plane of incidence passes through a filter 3 changeable in respect of its polarization properties and reaches a detector 4 after passing the filter 3. A control device 5 is connected to the filter 3 as well as to the detector 4, which device controls the filter so that it alternately transfers to the detector 4 the desired light of the first type, which light is non-analyzed as to its polarization or, alternatively, is polarized perpendicular to the plane of incidence of the bundle of rays to the surface, and the desired light of the second type, which light is polar-~ 3 .~ ; . : .
: ~
1~68~(~0 ized substantially parallel to the plane of incidence. The detector 4 issimultaneously controlled by the control device 5 so that light is only detected when the filter is correctly adapted to transfer light of a desired type. If the used light of the first type is non-analyzed as to its polar-ization, the filter can be a polarization filter, which only transfers light polarized parallelly with the plane of incidence of the bundle of rays, which filter is moved forwards and backwards, so that it will be ~lternately in the ~ay of the reflected beam in front of the detector and alternately beside the beam. If instead, the used light of the first type is polarized per-pendicular to the plane of incidence, a rotary polarization filter can beused, the detector 4 being triggered by the control device to émit an output signal each time the filter is in a suitable position to transfer radiation ~-of the first and second type respectively. The outputs from the detector 4 are fed to the utilization device 6, in which the quotient is formed between the signals derived from the light of the second type and the signals derived from the light of the first type, possibly by means of control signals from the control device SO
According to another embodiment of a device for carrying out the method of the invention, which device is shown in Figure 2, the reflected beam hits a polarization prism 7, dividing the beam which lets through light polarized parallelly with the plane of incidence and deflects light polarized perpendicularly to the plane of incidence. The parallelly polarized light and the perpendicularly polarized light are each brought to an associated detector 8 and 9 respectively and the output signals from these are fed to the utilizing device 10 to form the quotient between these output signals.
In Figure 3 an additional device for carrying out the method of the invention is shown. In this device the condition is utilized that only the ~-light polarized perpendicularly to the plane of incidence or the light of the first type non-analyzed with respect to its polarization need be detected in :: :
:
1(~68100 reflected state at an angle to the surface normal which is as big as the in-cident angle. The light of the other type polarized parallelly with the plane of incidence can be detected at an angle, which deviates relatively greatly from the angle of reflection, which is as~-big as the incident angle.
Moreover the light of the second type need not be detected in the plane of incidence, either, but can be detected as displaced from this. It is evident from the figure that the light of the first type is incident to the detector 12 possibly after passing through a polarization filter 11 and that the light of the second type is incident to the detector 14 after passing through the polarization filter 13. The outputs from the two detectors 14 and 12 are fed to the utilization device lS, which forms the quotient between the two signals.
In Figure 4 three curves are shown, which have been drawn for the same strength of incident light and with a constant incident angle of 60 but at different detecting angles for paper. The curve I indicates measured, reflected light non-polarized with respect to its polarization, the curve II
indicates measured, reflected perpendicularly polarized light and the curve III measured, reflected, parallelly polarized light.
It is evident from the diagram that the detecting angle of the light of the first type should be selected so that that part of the curve is reached where the curve has its maximum, as the highest sensitivity of the result is then achieved. It is also apparent from the figure that this maximum occurs for a detecting angle similar to the incident angle. With selection of another incident angle the curves I and II are laterally dis-placed so that their maximum always will be at a detecting angle similar to the incident angle. The consequence of this is that the detecSing angle of the light of the first type should be substantially equal to the incident angle. The setting of the detecting angle of the light of the first type is relatively critical, as the measuring result can be heavily distorted by a . . . ~
lQ6~100 .~, . -change of the position of the detector, in case the detecting angle is selected so that the steeply running flan~s of the curves I and II are reached. ~ - -At selection of another incident angle than the Brewster angle a not so marked maximum is obtained, and the curves run more evenly and with -tests it has been found that the best measuring result is obtained i the incident angle is selected equal to the Brewster angle and should preferably not deviate more than +10 from this angle, and therefore it should be aimed at getting as close to this angle as is practically possible.
In Figure 5 an output signal measured by means of the inventive -~
method is shown as a function of a value measured by means of the PPS
instrument for some different sorts of paper having different surface topography. Values measured by means of the PPS instrument have been plotted along the abscissa and values measured by the method of the invention along the ordinate. Each marked point represents a special sort of paper.
As is apparent a clear connection between the results from these two methods is obtained, although the methods are based on completely different principles.
Several different modifications are possible within the scope of the invention.
The invention can also be used for measurement of the surface topography of other materials than paper.
.
.
Claims (6)
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:
1. Method of measuring the topography of a surface, characterized in that a light source emits a substantially parallel bundle of light beams at a predetermined incident angle (?) to the surface normal and that a light of a first type, which is non-analyzed as to its polarization, is reflected from the surface and detected at an angle to said normal which is substantially equal to said incident angle, and that light of a second type reflected from the surface is detected, which light is polarized substantially parallelly to the plane of incidence, and that the quotient between the strength of light of the second type and the strength of light of the first type is formed to be a measure of the topography of the surface.
2. The method as claimed in claim 1, characterized in that the light emitted from the light source is laser light.
3. The method as claimed in claim 1, characterized in that the incident angle to the surface normal of the light emitted from the light source is selected within the range ?10° at either side of the Brewster angle.
4. The method as claimed in claim 1, characterized in that the light of the first type and the light of the second type are detected by the same detector in time sequence, by arranging a filter of such a type that the light of the first type and the light of the second type alternately reach the detector, the output signal of the detector being in a definite relation to the strength of the light incident to the detector.
5. The method as claimed in claim 1, characterized in that the light of the first type and the light of the second type are each detected by associated detector, which are placed beside each other in the plane of incidence, the output signal from each of the detectors being in a definite relation to the strength of the light incident on the associated detector.
6. The method as claimed in claim 5, characterized in that the detector of light of the second type is located outside the plane of incidence of the light.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| SE7410027A SE385048B (en) | 1974-08-05 | 1974-08-05 | PROCEDURE FOR SATURATING THE TOPOGRAPHY OF A SURFACE |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1068100A true CA1068100A (en) | 1979-12-18 |
Family
ID=20321835
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA232,746A Expired CA1068100A (en) | 1974-08-05 | 1975-08-01 | Method of measuring the topography of a surface |
Country Status (4)
| Country | Link |
|---|---|
| JP (1) | JPS5191777A (en) |
| CA (1) | CA1068100A (en) |
| GB (1) | GB1523604A (en) |
| SE (1) | SE385048B (en) |
Families Citing this family (7)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FI63835C (en) * | 1981-02-10 | 1983-08-10 | Altim Control Ky | FOERFARANDE FOER IDENTIFIERING AV ETT VIRKES YTEGENSKAPER |
| NO850157L (en) * | 1984-01-16 | 1985-10-23 | Barringer Research Ltd | PROCEDURE AND APPARATUS FOR DETERMINING HYDROCARBONES ON A WATER SURFACE. |
| US4931657A (en) * | 1989-04-13 | 1990-06-05 | Macmillan Bloedel Limited | On-line texture sensing |
| EP0628787A3 (en) * | 1993-06-08 | 1995-06-21 | Omron Tateisi Electronics Co | Optical sensing device. |
| SE525206C2 (en) * | 2003-11-17 | 2004-12-28 | Optonova Ab | Contact free measurement of material surface properties for e.g. panels or cylinders, by reflecting light off surface onto optical device with image sensor and beam splitter |
| FR2897938B1 (en) * | 2006-02-24 | 2008-04-18 | Peugeot Citroen Automobiles Sa | METHOD FOR ESTIMATING THE ADHESION OF A SURFACE |
| CN110631508A (en) * | 2019-09-25 | 2019-12-31 | 武汉虹之彩包装印刷有限公司 | High-precision positioning paper curling degree detection device |
-
1974
- 1974-08-05 SE SE7410027A patent/SE385048B/en unknown
-
1975
- 1975-08-01 CA CA232,746A patent/CA1068100A/en not_active Expired
- 1975-08-05 JP JP50095355A patent/JPS5191777A/en active Pending
- 1975-08-05 GB GB32712/75A patent/GB1523604A/en not_active Expired
Also Published As
| Publication number | Publication date |
|---|---|
| SE7410027L (en) | 1976-02-06 |
| SE385048B (en) | 1976-05-31 |
| JPS5191777A (en) | 1976-08-11 |
| GB1523604A (en) | 1978-09-06 |
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