DE4229349C2 - Method and arrangement for measuring the optical surface quality of reflective materials and the optical quality of transparent materials - Google Patents

Description

The invention relates to a method and an arrangement for measuring the optical surface quality of reflective Materials and more transparent to the optical quality Materials.

The optical surface quality of reflective materials is disturbed for example by scratches, dirt, Bumps, pigment agglomerates and defects.

Reflective materials are e.g. B. all glossy coatings of paints, coating colors and plastic melts, Laminate coatings, ceramic materials such as tiles, earthenware, porcelain, metals with shiny Surface, opaque films and thermosets.

The optical quality of transparent materials is disturbed due to inclusions, scratches, inhomogeneities, Soiling and fingerprints.

Transparent materials are e.g. B. foils, plastic sheets, Glasses and films.

Both the optical qualities of transparent materials, as well as the optical surface qualities of reflective Materials can also be used without those listed as examples  Disorders have different qualities, each by manufacturing, production or manufacturer. This gradual Differences of "flawless" products must also how the disturbances can be measured.

Transparent materials are often only visual judged in grazing light or on light tables. While In production, errors are counted in transmitted light and used as a criterion of quality. These methods do not form an objective yardstick for optical quality of materials.

A method and an apparatus for the detection of Structures of a surface of a flat good is out known from DE 38 14 606 C2. A coherent beam of light is focused on a reflective little spot, which is on a transmitting substrate, and imaged on the surface via an imaging lens. The small spot is in the area facing away from the surface Focal point of the imaging lens. That by beam scattering on the section of the surface subject to abrasion Portions created on the surface become opaque small stain passing through the translucent Substrate and the optics on a detection and evaluation arrangement mapped. The evaluation in terms of abrasion, differences occur Shares versus corresponding in the investigation shares obtained from a standard sample.

The disadvantage is that only an assessment of an abrasion damaged surface of translucent materials is possible to draw conclusions about the strength of the material. The fact that only a comparison with a standard sample can be made can only be determined whether the material assessed committee represents or suitable for further processing is. A fast, precisely differentiating and reproducible  Measurement is not possible.

DE 29 22 163 A1 describes an optical device known for determining the quality of a surface. Of a laser beam generator is a laser beam on the Surface directed. A photoelectric converter measures the light energy arriving in a light spot and provides a representative signal for this. An alongside the light spot arranged further photoelectric Transducer measures part of the outside of the light spot light energy striking the focal plane and there also a representative signal. A Evaluation circuit to which the two signals are fed only calculates their ratio from this, then for the Surface quality of the measurement object to be characteristic should. So only a measure for the middle one is delivered Goodness of surface.

A surface photoelectric scanner is described in DE-OS 20 51 908. Between one Laser and a rotating mirror is one against the axis a laser inclined mirror and lens optics with holes for a passage of the laser radiation arranged. An image of the laser on the surface generated light spot is with a cylindrical lens, a parabolic mirror, the rotating mirror, the lens optics and the tilted mirror to a photoelectronic Throwing device thrown. However, by one downstream circuit only output one output signal, that shows whether the surface is an impermissible Has errors.

DE-AS 15 48 263 describes a method and a device to determine the size of geometric changes or deviations of a reflective surface known from a target surface by means of optical means, where an extensive range of reflective  Surface is illuminated with light rays that are directed almost perpendicular to the surface. The on the target surface and reflected at the defects Radiations are fed to a receiver. With Help of the signals output by the receiver can be made accordingly the proportions of impeccable and of the target deviating output signals only rough conclusions be drawn to the quality of the surface.

It is also known for reflective materials that which strikes the specimen and that which is reflected by it To measure light with a Lange reflectometer different light incidence angles can be selected. Other Devices (e.g. KL measuring device) measure the intensity of the reflected light instead of with a detector Linear camera, so that in addition to the reflection value an indication of the distribution function of the reflected Light is available.

The disadvantage is that the values due to their dispersion do not provide precise information about the surface quality. This makes it impossible to take targeted corrective action in the manufacture of the reflective surface of the Material.

It is also known for measuring homogeneity a reflecting surface mechanical measuring devices, which is actually used to measure surface roughness serve to use, using an analyzer and an external computer with accordingly adapted Software roughness values are measured, the one for Enable gloss or correlation to flatness. This is done with a vertically movable A tip of a sample of the sample to be measured is scanned. The movements of the probe tip are on one electrical transducer transmitted, this in electrical Converts measured values that represent the palpated profile.  In order to get really meaningful values, the material sample must be measured three-dimensionally, d. H. several individual lines must be scanned in parallel (Surfcorders SE-30K, SE-30AK, company brochure Kosaka Laboratory Ltd., pages 1 to 6).

The disadvantage is that for the measurement of a single sample for example a glossy coated one photographic support material for 16 individual measurements parallel to each other and computer evaluation with the surfcorder 25 minutes are needed. Another disadvantage This time-consuming measurement is the high expenditure on equipment. In addition, with soft materials, such as B. in polyethylene layers to scratches on the surface and thus to material destruction come. This creates the existing surface structure not exactly measured, but the one that follows the deformation caused by the probe tips.

The invention has for its object a method and an arrangement for measuring the optical surface quality of reflective materials and optical quality specify transparent materials through which one fast, exact, differentiating, reproducible and non-destructive measurement of the optical quality of these materials is easy and safe.

According to the invention, the object is in an arrangement for Measurement of the optical surface quality of reflective materials and the optical quality of transparent materials solved by the features of claim 1.

The advantages achieved with the invention are in particular in the fact that it was brought into the beam path  Material can be clearly measured immediately. The measured values are reproducible and provide information about the optical quality of the reflective or transparent materials. The measurement results are so accurate that it is is immediately possible, directly in the production process access in order to quickly resolve any errors that occur term. In addition, the materials when measuring in no way damaged, so this particularly designed arrangement especially for a Suitable for use during ongoing production.

It is advantageous

• - that this on the material to be measured scattered light in an out unit of value via an imaging lens and a hole aperture with detector or a CCD camera with image ver work, is supplied, whereby the first reflection or through beam is measurable, and
• - That, if necessary, between the imaging lens and the aperture is a beam splitter, so that about 90 ° to the direction of the first a second reflection or through beam from a second detector with a pre ordered polarizer is measurable.

By dividing into two reflection and through gangs beam paths it is possible to take the finest measurements perform. This also makes it possible high-precision the optical quality of the reflective materia lien to determine.

The second generated by using the beam splitter Beam path is the second detector (photo element) also feedable by z. B. a fiber optic light guide or through a separate opening in the bezel that extends located in the first beam path.  

Are expected material defects not high or none A high level of measurement accuracy is required of the reflection or through beam path is not necessary. In this case, it is sufficient to use the the first reflection or through beam path determined values as the assessment basis for the based on optical quality.

With reflective surfaces, e.g. B. with glossy Fotopa can penetrate at an angle of incidence of the spot beam les from = 0 to 85 ° (measured to the perpendicular) can be measured; however, it has proven advantageous to use the angle α to be set at around 45 ° ± 15 ° because this is the best Measurement results can be achieved.

With transparent materials, e.g. B. a vitreous body, can in principle also at an angle of incidence the spot beam can be measured from 0 ° to 85 °; it has proven advantageous, however, the angle α from 0 ° to 20 °, in particular from 0 °. Here it is possible to use the evaluation unit essentially chen on the same level as the lighting unit to arrange. The values determined in this way for the optical Quality transparent materials are simple and safe determinable and exactly announce the material condition.

It is advantageous if the lighting unit is off a light source with a condenser. As a light source white light (visible light) is used. Of course, other light sources can also be used are used (with adapted measuring arrangement), their Emission spectrum outside the visible range of 400-800 nm.  

It is advantageous that the glossy photo paper as a running web or as a sample, which in a sample holder is held as a measurement object is trained. This makes it possible to Measuring arrangement both during production and for the measurement of individual samples. Straight this different application gives the Users immediately have the opportunity, depending on their pro production conditions occurring as soon as possible Correct error rates.

It is advantageous if z. B. for glossy photo paper

• - several above the surface at regular intervals Lighting units with associated Evaluation units and / or
• - At least one illumination transverse to the surface processing unit with an associated evaluation unit are arranged.

When arranging several lighting units with the associated evaluation unit, it is possible to just the to scan the running material web exactly. This will according to the selected distance of each Lighting units and the associated evaluations units the condition of the glossy surface accurate most analyzed. Based on the available measurement results then it is possible to have errors on a part  to be able to correct the area of the running web immediately. In order to minimize the amount of equipment, it is also possible to the beam path across the surface to let go. This also gives exact measured values received, which is used for further decision-making can be.

The method according to the invention to achieve the object for measuring the optical surface quality of reflective Materials and optical quality more transparent Materials are characterized by the following steps:

• a) emitting one from a lighting unit and with a subsequent transparent body an opaque stain Spot beam with the intensity I₀,
• b) reflection or passage of the spot beam on one or by a calibration material that is essentially a ideally reflective material or an essentially ideally represents transparent material,
• c) Adjusting a pinhole or software screen such that the image of the opaque spot with the hole of the pinhole or the software screen is fully covered,
• d) introduction of a material to be measured,
• e) division of the reflected or permeated Spot beam into a first and a second reflection or through beam,
• f) measurement of the intensity I₁ of the total reflected or scattered light of the first reflection or Through beam,
• g) measurement of the intensity I₂ through the pinhole reached or captured by the software aperture Second reflection or light Through beam,
• h) formation of the final measured value according to the relationship With:
  c₁, c₂ = constants which are caused by the optical structure and are adapted by a rotatable polarizer or electronically,
  as a yardstick for evaluating the reflection on the reflecting material to be measured or the passage through the translucent material.

When using the method according to the invention achieved advantages are in particular that after a calibration of the measuring arrangement in compliance with the individual steps quickly and safely both reflective as well as a transparent material can be measured. Which in deviation from one give values that are essentially the ideal body Information about the state of the respective test sample. Is it an ideal transparent Body or an ideal, plan mirror is

I ₁ (max) × c ₁ = I ₀ (da (I ₂ × c ₂ = 0)).

In this case M = 1 and for an idealized one Condition in which the disturbances of the beam path are so are great that the opaque stain is not at all is shown more

I ₂ (max) × c ₂ = I ₁ × c ₁ (counter becomes = 0).

In this case, M = 0. All measured values lie therefore between 0 and 1 or can be as% numbers can be specified.

It is advantageous if the material in the essentially moved continuously or in the form of Puncture is inserted. This makes it possible adapt to the respective conditions of use and to choose the measurement sample as it is for the respective Is optimal.

The invention is shown in the drawing and will  described in more detail below. Show it:

Fig. 1a shows an arrangement for measuring the optical upper surface quality of a reflecting material having a shared reflection beam path,

FIG. 1b shows an arrangement for measuring the optical quality surface of a reflecting material with an undivided reflection beam path,

Fig. 2a shows an arrangement for measuring the optical quality of a transparent material having a shared passage ge-beam path,

FIG. 2b shows an arrangement for measuring the optical quality of a transparent material having a shared unge passage-beam path,

Fig. 3a shows a measured value series of a gloss measurement, taken up with an arrangement according to Fig. 1a and

Fig. 3b is a series of measurements of a gloss measurement, taken up with a Lange reflectometer.

A measuring arrangement for the gloss measurement of, for example, high-gloss photo paper 2.1 consists, according to FIG. 1 a, of an illumination unit 1 . In the simplest form, the lighting unit 1 is composed of a light source 1.1 and a condenser 1.2 . A lamp that emits white light (visible light) is preferably used as the light source 1.1 . Of course, other light sources can also be used whose emission spectrum lies outside the visible range of 400-800 nm.

A transparent body 4 with an opaque spot 4.1 is arranged between the lighting unit 1 and the high-gloss photo paper 2.1 . An evaluation unit 3.1 is installed behind the high-gloss photo paper. In the evaluation unit there is an imaging lens 31 , which is followed by a pinhole with detector 32 or CCD camera with image processing (software screen) 32 . A beam splitter 34 is located behind the imaging lens 31 . This beam splitter 34 is formed as a partially transparent mirror. A polarizer is arranged next to the beam splitter 34 , behind which there is a second detector 36 .

It is also possible, as can be seen from FIG. 1b, to install a measured value unit 3.2 after the high-gloss photo paper 2.1 . This evaluation unit 3.2 corresponds essentially to the evaluation unit 3.1 without beam divider.

If a transparent material is evaluated, a measuring arrangement according to FIG. 2a is used. Here is a transparent material, for example, a glass body 2.2 parallel to the lighting unit, which also consists of a light source 1.1 and a downstream condenser 1.2 . Thereafter, the transparent body 4 with the opaque spot 4.1 is also arranged. The subsequent evaluation unit 3.1 corresponds to that already described for FIG. 1a.

Here, too, it is possible to arrange the evaluation unit 3.2 in the form described after the vitreous body 2.2 .

The measuring arrangement has the following function:

In the measuring arrangement according to FIG. 1a, an ideal mirror is illuminated at an angle of incidence α. A spot beam with the intensity I _{0 is} emitted from the lighting unit 1 via a transparent body with an opaque spot. The spot beam is deflected according to the law of reflection and fed to the imaging lens 31 . The hole of the pinhole or the software screen 32 is adjusted so that the image of the opaque spot which arises in the plane of the pinhole is optically fully aligned with the hole of the pinhole. No light gets into the detector. The direct illumination beam path is therefore darkened.

A fault occurs due to a sample introduced into the beam path for the purpose of measurement, for example of the glossy photo paper 2.1 . The reflection beam deflected by this disturbance partly passes through the aperture or software aperture 32 and thus contributes with an intensity 12 to the measurement value acquisition. The sample to be measured of the high-gloss photo paper 2.1 to be measured is introduced between the opaque spot 4.1 and the imaging lens 31 into the spot beam with the intensity I ₀ .

The more light that passes through the pinhole or the software aperture 32 , the greater the interference in the beam path, ie the lower the optical quality or optical surface quality of the measured sample high-gloss photo paper 2.1 . The arrangement of the beam splitter 34 divides the incoming light into two reflection or through beam paths. One reflection beam leads via the polarizer 35 with the intensity I ₁ into the detector 36 , the other reflection beam leads via the pinhole into the detector or into the CCD camera with the intensity I ₂ .

The entire reflected and / or scattered or deflected light behind the sample 2.1 is now measured in the detector 36 , and only the light that has passed through the pinhole or is detected by the software aperture in the detector or the CCD camera with image processing 32 .

The final measured value M is then formed by the difference between the light intensities I, measured in the two detectors or image processing 33 , 36 . The measured value M is calculated according to the relationship

where c ₁ and c ₂ are constants due to the optical structure, which can be adjusted by the rotatable polarizer or electronically.

Thereafter applies to an ideal transparent or one ideal, plan mirror:

I ₁ (max) × c ₁ = I ₀ (since I ₂ × c ₂ = 0).

In this case M = 1. For an idealized one Condition in which the disturbances of the beam path are so are great that the opaque stain is not at all more is shown

I ₂ (max) × c ₂ × I ₁ × c ₁ (counter becomes = 0).

In this case, M = 0. All measured values lie therefore between 0 and 1 and can be expressed as percentages can be specified.

It can be useful for certain materials from which two detector signals as the measured value M the quotient

to build.  

Just as the high-gloss photo paper according to FIG. 1a was measured by way of example, a transparent material can also be measured in a measuring arrangement according to FIG. 2a.

For a measurement, a high-gloss photo paper 2.1 was selected, which consists of 175 g / m ^{2 base} paper, 30 g / m ² back layer made of transparent polyethylene and 30 g / m ² front layer made of polyethylene, filled with 11% by weight titanium dioxide. It was cut into narrow 1.60 m long strips transversely to the web direction and the gloss on each of these strips was measured at 12 measuring points. The angle of incidence of the spot beam was 45 °. The following measured value distribution was determined, as shown in FIG. 3a.

On the same samples, the series of measurements shown in FIG. 3b were measured with a Lange reflectometer at a 20 ° angle of incidence.

The results of the arrangement according to the invention lie closely next to one another, so are largely reproducible and differentiate so clearly that a quality profile can be sketched from them across the paper web. With these measurement results, it is definitely possible to easily control a production machine. The measurement results of the Lange reflectometer, on the other hand, are so scattered that there is a different quality profile across the paper web from each series of measurements. With these measured values, it is extremely difficult to make statements about the quality of the glossy photo paper 2.1 . The measured values which were measured with the Lange reflectometer at 60 ° incidence of light were not shown in FIG. 3b. All of these measured values were 97 ± 1.5% and thus at the same level. A differentiation was not possible.

If measurements are to be made on glossy or transparent materials 2.1 or 2.2 , which either have almost ideal values or for which the result of the measurement is not so important, it is also possible to use measuring arrangements according to FIGS . 1b and 2b . In the case of measurements carried out, it has proven to be advantageous to choose an angle of incidence of the spot beam of 45 ° ± 15 ° for reflective materials and one of 0 ° -20 °, in particular 0 °, for transparent materials, since this is the most precise and best Measurement results were achieved, as can also be seen particularly from FIG. 2a.

Of course, it is also possible to carry out a measurement not only on samples. Here, the measurement is performed on a running web of glossy photo paper 2.1 . A plurality of light sources 1 , e.g. B. up to 20, with associated evaluation units 3.1 or 3.2 . This choice of arrangement makes it possible to check the glossy photo paper while production is running and to make appropriate corrections during production immediately if there are fluctuations. It is also possible to position the lighting unit 1 and the associated evaluation unit 3.1 or 3.2 transversely to the running web of the high-gloss photo paper 2.1 . This form of measurement makes it possible, on the one hand, to sweep the entire surface and, on the other hand, to keep the number of lighting units 1 and the associated evaluation units 3.1 and 3.2 within limits.

When the measurements were carried out, it was determined that the glossy photo paper must be flat for measurement. For flexible materials such as foils and coated A sample holder must therefore be configured for papers be that these samples are fixed in a flat position become. Have proven themselves for transparent films  preferably stenter and for reflective materials preferably chambers that open on the top are provided and to a negative pressure generating System are connected (suction table).

In order to also be able to carry out measurements on non-planar surfaces, a CCD camera with downstream image processing 32 , which can act together as a software aperture, is used in particular. Of course, as already mentioned above, this arrangement can also be used for flat surfaces.

Reference list

1 lighting unit
1.1 light source
1.2 condenser
2.1 Material, glossy photo paper
2.2 Material, vitreous
3.1 Evaluation unit
3.2 Evaluation unit
31 imaging lens
32 pinhole with detector or CCD camera with image processing
34 beam splitters
35 polarizer
36 detector
4.1 Opaque stain
I ₀ intensity of the spot beam
l ₁ intensity of the reflection or transmission beam
I ₂ Intensity of the disturbed reflection or transmission beam
M measured value

Claims (10)

1. Arrangement for measuring the optical surface quality of reflective materials and the optical quality of transparent materials, with the following features,

• - That a lighting unit ( 1 ) with a subsequent transparent body ( 4 ) with an opaque spot ( 4.1 ) is provided so that a spot beam on the material ( 2.1, 2.2 ) can be emitted, and
• - That an evaluation unit ( 3.1, 3.2 ) is installed through which with at least one detector with an upstream pinhole or a CCD camera with a pinhole corresponding software screen and with subsequent image processing ( 32 ) the light scattered by the material ( 2.1, 2.2 ) as Reflection or through beam is measurable, wherein
• - The pinhole or the software screen are adjusted so that the image of the opaque spot ( 4.1 ) for an ideally reflective calibration material with the hole of the pinhole or the software screen is fully covered and where
• - The spot beam falls on the measuring material ( 2.1 ) at an angle of incidence of 0 ° -85 °.

2. Arrangement according to claim 1, characterized in

• - That the light scattered on the material to be measured ( 4.1 ) in the evaluation unit ( 3.1, 3.2 ) via an imaging lens ( 31 ) of the pinhole with detector or CCD camera with image processing ( 32 ) is supplied, whereby the first reflection or through beam can be measured is and
• - That lies behind the imaging lens ( 31 ) and the diaphragm ( 32 ) in the beam splitter ( 34 ), so that about 90 ° to the direction of the first a second reflection or through beam from a second detector ( 36 ) with an upstream polarizer ( 35 ) is measurable.

3. Arrangement according to claim 1 or 2, characterized in that the reflective material is a high-gloss photo paper ( 2.1 ). 4. Arrangement according to claim 1 to 3, characterized in that the reflective material with a Angle of incidence of the spot beam of 45 ° ± 15 °, preferably 45 °. 5. Arrangement according to claim 1 or 2, characterized in that the transparent material with a Angle of incidence of the spot beam from 0 ° -20 °, preferably 0 °, is arranged. 6. Arrangement according to one of claims 1 to 5, characterized in that the lighting unit ( 1 ) consists of a light source ( 1.1 ) with a condenser ( 1.2 ) arranged in front of it. 7. Arrangement according to claim 3, characterized in that the high-gloss photo paper ( 2.1 ) is designed as a running web or as a sample which is held in a sample holder. 8. Arrangement according to claim 7, characterized in that with a running web glossy photo paper ( 2.1 )

• - Several lighting units ( 1 ) with associated evaluation units ( 3.1, 3.2 ) and / or at regular intervals above the surface
• - At least one lighting unit ( 1 ) with an associated evaluation unit ( 3.1, 3.2 ) is arranged transversely to the surface.

9. Method for measuring the optical surface quality of reflective materials and the optical quality of transparent materials with the following steps:

• a) emitting a spot beam with the intensity I₀ generated by an illumination unit ( 1 ) and a subsequent transparent body ( 4 ) with an opaque spot ( 4.1 ),
• b) reflection or passage of the stain beam on or through a calibration material which is an essentially ideally reflecting material ( 2.1 ) or an essentially ideally transparent material ( 2.2 ),
• c) adjusting a pinhole or software screen ( 32 ) in such a way that the image of the opaque spot ( 4.1 ) is fully covered with the hole in the pinhole or software screen ( 32 ),
• d) introduction of the material to be measured ( 2.1, 2.2 ),
• e) division of the reflected or penetrated spot beam into a first and a second reflection or transmission beam,
• f) measurement of the intensity I 1 of the total reflected or scattered light of the first reflection or transmission beam,
• g) measurement of the intensity I₂ of the light of the second reflection or through beam which has passed through the pinhole or has been detected by the software screen ( 32 ),
• h) Formation of the final measured value (M) according to the relationship With:
  c₁, c₂ = constants which are caused by the optical structure and are adapted by a rotatable polarizer ( 35 ) or electronically,
  as a yardstick for evaluating the reflection on the reflecting material to be measured or the passage through the transparent material ( 2.1, 2.2 ).

10. The method according to claim 9, characterized in that the material ( 2.1, 2.2 ) is moved substantially continuously or is inserted in the form of random samples.