DE102015105128B4 - Method and device for measuring the degree of gloss and/or mattness of objects - Google Patents

Abstract

Method for measuring the degree of gloss and/or the dullness of non-transparent objects (1), in which the objects (1) objects (1) are illuminated by a light source (18) and the amount of light reflected from the objects (1) light in a detector (14), or of transparent objects (6), in which the objects (6) are illuminated by a light source (18) and the amount of light reflected and/or transmitted by the object (6) in a detector (14) is detected, the detector (14) being arranged in a defined recording geometry relative to the light source (18) and the object (1, 6), the degree of gloss and/or the dullness of the object (1, 6) can be determined, the light source (18) consisting of a plurality of lighting elements (13, 13a) which can be switched on and off individually and which are switched on and off one after the other, and the detector (14) is designed as a camera (14) with which the brightness profile (15) of the light distribution of the light reflected and/or transmitted by the object (1, 6) is measured in a spatially resolved manner in an image for each lighting element (13, 13a) and represents a curve of different intensities at different locations, the height of the curve, the width of the curve and the steepness of the edge of the curve being included in the determination of the degree of gloss and/or the mattness, characterized in that the object (1, 6) in a transport direction (19) relative to the light source (18) and the detector (14) is moved such that the light source (18) is designed such that the lighting elements (13, 13a) cross the entire width of the object (1, 6). to the transport direction (19), that the detector (14) is designed in such a way that the entire width of the object (1, 6) can be measured simultaneously transversely to the transport direction (19), and that the lighting elements (13 , 13a) are switched on one after the other in such a way that the entire width of the object (1, 6) is measured.

Description

The invention relates to a method and a device for measuring the degree of gloss and/or the dullness of non-transparent or transparent objects according to the preamble of claims 1 and 10, respectively, in which the objects are illuminated by a light source and the quantity of light reflected by the object is measured and/or transmitted light is detected in a detector. Light quantity describes the intensity of the light measured in the detector, which can also be referred to as brightness. This largely depends on the recording geometry, and thus also on the size of the sensor surface of the detector.

In the case of non-transparent objects, light incident on the surface of the object is completely reflected. In the case of transparent objects, which conceptually also include partially transparent objects, light radiated onto the surface of these objects is both reflected on the surface and transmitted through the transparent material of the object. Scattering of part of the light takes place in both reflection and transmission, depending on the material of the object, which determines the reflection and transmission properties.

These reflection and transmission properties of objects or materials are normally described by a so-called bidirectional reflectance distribution function (BRDF), which indicates how much light is reflected or transmitted in each solid angle. The bidirectional reflectance distribution function is dependent on both the wavelength of the light and the angle of incidence of the light on the object's surface. The determination of the bidirectional reflectance distribution function is therefore very complex and is only carried out in practice if there is no other way of determining the degree of gloss and/or the mattness of objects.

In practice, therefore, the parameters “Haze” and “Gloss” are used to describe the optical appearance of surfaces of objects in reflection and/or transmission, as they are easier to determine. Haze determines the dullness of the item's appearance and Gloss determines the gloss level of the item's appearance. The terms “haze” and “mattness” or “gloss” and “degree of sheen” are used synonymously in the context of this disclosure.

Haze and gloss are two quantities with which the reflection properties of a non-transparent, but also of a transparent surface can be characterized in terms of value in a simpler way than with the bidirectional reflectance distribution function. In practice, these two quantities, haze and gloss, are often sufficient because it is not necessary to determine the actual physical light distribution, but only to describe the impression that a human viewer has when looking at the surface.

This is described by how matt or glossy he perceives the surface of the transparent or non-transparent object. Therefore, these quantities are often used to describe the degree of gloss and/or dullness of transparent or non-transparent objects.

Depending on the type of surface, there are different definitions for carrying out a gloss measurement or a haze measurement. These definitions specify which viewing and observation angles are to be used and what the environment of the object (surface sample) must be like. There are also national and/or international standards for certain types of objects or surfaces.

In a gloss measurement in a reflection arrangement, the light that is reflected in the reflection angle is usually measured. In the case of a haze measurement in a reflection arrangement, the light that is not reflected in the reflection angle but is scattered in other directions is measured. In a reflection arrangement, the object, i.e. the surface of the object, is usually illuminated at a defined angle with a point light source and viewed at another defined angle with a detector, which measures the amount of light reflected or scattered at this angle.

Depending on the definition chosen, the distribution of this scattered light is also measured in the haze measurement or is at least implicitly included in the measured value by the measurement arrangement, e.g. by specifying a specific angular deviation of the detector from the reflection angle of the light. The angle of reflection is the angle at which a light beam striking an ideally reflecting surface at a defined angle of incidence is reflected.

Analogous to the reflection on surfaces, values for the two variables haze and gloss can also be used to describe the appearance of transparent surfaces in transmission. The term “transparency” is also often used here instead of the term “haze” or “mattness”.

In contrast to non-transparent objects or materials, with transparent objects there is light that passes through the transparent object in addition to the light that is reflected and scattered back on the surface. This light is called transmitted light. Part of the incident light is also scattered during transmission.

In the case of transparent materials, the control in a reflection arrangement is generally very low, so that often only the scattering in the transmission arrangement is of interest. This arrangement is also primarily about the impression of a human viewer, which can be well described by values for the variables Haze and Gloss and in appearance characterize the transparency of the surface for the human viewer. Here, too, there are various definitions and standards for the measurement conditions. Commonly used here are e.g. ASTM D523 (for a gloss measurement), ASTM D-1003 (for a haze measurement) and ASTM D4039 as well as other measurement conditions.

The physical effects for reflected and transmitted light are shown below schematically using the 1 and 2 describe. It is pointed out that the illustrations are purely schematic sketches that do not allow any conclusions to be drawn about the actual physical size and intensity ratios.

the 1a until 1c show the situation for a reflection arrangement on non-transparent objects 1 with different mattness (haze) or different degrees of gloss (gloss). In this situation, therefore, no transmission occurs.

The non-transparent object 1 or its surface is illuminated by a point light source 2, which emits a light beam 3 focused on the surface. The light incident through the light beam 3 on the surface of the object 1 is reflected. A proportion 4 of the light is reflected directly in the direction of the reflection angle. Another portion 5 of the light is diffusely scattered, i.e. emitted in directions different from the angle of reflection.

This is in the 1a until 1c for materials with different degrees of gloss (Gloss) or different mattness (Haze).

1a shows the light distribution of the reflected light in an object 1 with a high degree of dullness, ie a high haze value (also referred to as haze for short). It turns out that part 4 of the directly reflected light is only slightly more intense than the part of the light scattered in other directions. The light is therefore very diffusely scattered, giving the viewer the impression of great dullness.

In contrast, in 1c an object 1 is shown, the surface of which has a high degree of gloss, ie a high gloss value (also referred to as gloss for short). Accordingly, the surface appears as high-gloss. This is evident from the fact that portion 4 of the directly reflected light is significantly stronger than portion 5 of the diffusely scattered light. The viewer perceives such a surface as a surface with a high degree of gloss.

1b shows a surface with a medium degree of gloss or a medium dullness. In contrast to the in 1a In the case shown, the proportion 4 of the directly reflected light is still clearly recognizable and clearly stands out from the proportion 5 of the diffusely scattered light. However, the proportion 5 of the scattered light is significantly higher than in the in 1c shown example of a very shiny surface. The proportions 4 of the directly reflected light and 5 of the scattered light are in 1b about the same size. The viewer gets the impression of a surface of medium mattness or medium gloss.

2 1 schematically shows a light distribution corresponding to a transparent object 6, which is illuminated by a light beam 3 of a light source 2 in a transmission arrangement focused on the surface of the object 6. The light passes through the transparent object 6 in the transmission arrangement. A proportion 7 of the transmitted light passes through the transparent material of the object 6 essentially unscattered. Another portion 8 of the transmitted light is diffusely scattered.

In 2a a case is shown in which the portion 7 of the unscattered transmitted light, ie that portion 7 which passes through the material directly and without deflection, hardly differs from the portion 8 of the diffusely scattered (transmitted) light. Although the object 6 appears transparent to the user due to the passage of light, it is very dull. This means that a light source can no longer be precisely localized on the side of the object 8 opposite the viewer. Rather, the light distribution is comparatively wide compared to the point light source, with a maximum light intensity in the center. In this case, the object therefore has a high degree of dullness (high haze). Such a case arises, for example, with an optically dense frosted glass.

In contrast, in 2c an example is shown in which the mattness of the object 6 has only a low value and the light beam 3 emitted by the point light source 2 passes through the material of the transparent object 6 clearly and essentially unscattered for the user. Correspondingly, the portion 7 of the unscattered transmitted light is very large. The proportion 8 of the diffusely scattered (transmitted) light is very small and is often not noticed by the user. This case occurs, for example, with high-purity glass.

2 B 12 correspondingly shows a case in which the haze and gloss values are approximately the same, ie the portion 7 of the unscattered transmitted light corresponds approximately to the portion 8 of the diffusely scattered (transmitted) light. Such a case occurs, for example, with glass panes with significant contamination.

With the method according to the invention and the device according to the invention, gloss and haze values should correspond accordingly both for non-transparent objects 1 in a reflection arrangement 1 as well as for transparent objects 6 in a reflection arrangement accordingly 1 and transmission arrangement accordingly 2 be measured. The measurement of the gloss level and/or the dullness of non-transparent or transparent objects thus relates to the characterization of the surface appearance of these objects.

All definitions and standards for determining the appearance of surfaces of transparent or non-transparent objects, i.e. for measuring the degree of gloss (gloss) and/or mattness (haze) of the objects, prescribe fixed measurement arrangements and evaluation steps in order to make the determined values comparable. They differ depending on the material of the object to be measured and the optical impression (haze, gloss or mattness, degree of gloss) to be evaluated. These definitions and standards differ, for example, in the illumination angles, the viewing angles, the recording apertures, the types of light, the reference value used, etc. Ultimately, however, in all measurement arrangements or standards, the light quantity and/or light distribution of the light reflected from the surface and/or transmitted light is measured, which arrives in the detector under the recording conditions described above and is recorded.

What the arrangements have in common is that a point light source is used as the light source. Furthermore, a detector is used, which measures the light of the light source reflected and/or transmitted at a location or point of the object with a defined recording aperture. The light arriving in the area of the recording apertures is therefore integrated accordingly (measurement of the amount of light).

The "point" illuminated by the point light source on the surface of the object to be measured is defined by a small area in the area to the surface of the entire object which, in cooperation with the recording apertures of the detector, provides a defined illumination and recording geometry for the object reflected and /or specifies transmitted light. This applies to arrangements in which the object is illuminated by a point light source and recorded by the detector. Accordingly, photocells are usually used as detectors, which integrate the light incident on the detector in the recording geometry according to their recording aperture and specify a brightness value for the integrated quantity of light.

For a measurement in the in 1 In the reflection geometry shown, in which the light radiated onto the surface of the object is reflected, the detector for measuring the gloss value (gloss) is usually positioned in the reflection angle of the light. On the other hand, for the measurement of dullness (haze), the detector is positioned at one or more positions at an angle different from the angle of reflection. In principle, a similar arrangement can also be used for a transmission measurement, which specifies a detector in the region of the unscattered transmitted light and at least one detector for measuring the diffusely scattered transmitted light in a scattering angle.

In 3 a known arrangement for measuring the mattness of a transparent object 6 is shown in a transmission arrangement. This device has a hollow sphere 9, which is also known as an integrating sphere. The inner surface of the sphere is usually coated in white, or more generally non-absorbent. The hollow sphere 9 has a light entry opening 10a and, relative to the center point of the sphere, a light exit opening 10b opposite this, on which a first detector 11 is arranged. The light entry opening 10a is arranged on the surface of the transparent object 6 in such a way that a light beam 3 generated by the point light source 2, which strikes the surface of the transparent object 6 perpendicularly, enters the hollow sphere 9 through the object 6 and the light entry opening 10a. the inside 2 The illustrated portion 7 of the light transmitted without scatter passes straight through the hollow sphere and reaches the first detector 11 through the light exit opening 10b.

Perpendicular to the axial connecting line between the light entry opening 11a and the light exit opening 11b, starting from the center point of the sphere, a further opening 10c is provided in the hollow sphere 9, behind which a second detector 12 is arranged. This detector 12 detects the diffusely scattered light as it passes through the material of the transparent object 6, which is reflected by the reflections on the non-absorbing or only weakly absorbing inner surface of the hollow sphere 9 and is detected through the further opening 10c in the second detector 12.

Due to the arrangement described, an integrative measurement of the component 8 of the transmitted light that is diffusely scattered in different directions takes place here. In this case, the haze value can be defined as the ratio of the measured quantity of light from the sensor 12 to the measured quantity of light from the sensor 11 .

From the DE 101 49 780 A1 a method and a device for determining the visual properties of bodies is known. An illumination device irradiates a measurement area at a defined angle, while a detector unit detects the reflected light at a defined angle. In this case, the lighting device has a plurality of light-emitting diodes which are arranged in a circle around a central axis of rotation of a carrier disc. For the measurement, the carrier disc is rotated until one of the light-emitting diodes is aligned along the optical axis, with this light-emitting diode illuminating the measuring surface through a gap. By rotating the carrier plate, all light-emitting diodes can be arranged centrally above the gap and used for a measurement.

the DE 10 2014 105 746 A1 describes as post-published prior art an optoelectronic sensor and a method for detecting shiny objects according to the preamble of claims 1 and 10.

The above-described measuring methods and arrangements from the prior art have in common that they require specially manufactured measuring devices because the comparability of the measured values can only be ensured via the special measuring arrangement. All of these arrangements are defined in relation to a point of light radiated onto the surface of the object in order to be able to specify a defined recording geometry. Therefore, the known devices and methods for measuring the degree of gloss and/or mattness of objects are only suitable for measuring these surface properties at exactly one point on the object, because the respectively defined recording conditions are only met for this one special point. In order to measure a complete surface, the measuring device must be guided over the entire surface. This involves a great deal of effort and requires a lot of time, which cannot be used for a fast-running process in which the measurement is to be carried out in-line in a production and/or processing line.

Accordingly, the object of the present invention is to enable a faster measurement of the degree of gloss and/or the dullness of even large-area objects with a desired resolution up to a complete measurement of the surface of the large-area object. In this case, the object is moved in a transport direction relative to the measuring arrangement, as is usual in production and/or processing lines. This is usually done by moving the object. According to the invention, however, this can also be achieved by moving the measuring arrangement in one direction.

This object is achieved by a method having the features of claim 1. It is provided in particular that the light source consists of a plurality of lighting elements which can be switched on and off separately and which are switched on and off one after the other. Furthermore, the detector is designed as a camera, with which the brightness profile of the light distribution of the light reflected and/or transmitted by the object is measured for each lighting element in a spatially resolved manner in an image.

Due to the several separately switchable, i.e. on and off, lighting elements, several different points of the surface relative to the object can be illuminated one after the other with the one light source. The camera results in comparable lighting and recording geometries. In a single relative position of the object, light source and detector, a larger area of the object can therefore be detected and the degree of gloss and/or the dullness of the object in this area can be measured with the desired resolution.

Each lighting element represents a point light source in the sense that it illuminates a point on the surface of the object to be measured, from which the light is then reflected and/or transmitted depending on the type of object. However, if all lighting elements in the light source are switched on at the same time, this no longer represents a punctiform light source, so that defined recording geometries would no longer be achieved.

Since the various lighting elements are switched on separately in succession for measuring the degree of gloss and/or dullness according to the invention, the desired defined recording geometry is available for each measurement (with one lighting element switched on) without overlapping of the reflected or transmitted light from other locations punctiform light source would overlay and falsify the measurement result.

According to the invention, the reflected and/or transmitted light is also recorded by a camera that performs a spatially resolved measurement of the brightness profile of the light distribution of the light reflected and/or transmitted by the object for each lighting element, at least in one spatial direction. A line camera is preferably proposed for a spatially resolved measurement in one spatial direction, in which several light-sensitive elements that can be read separately are arranged in a row. The use of a line camera is a particularly preferred embodiment because the camera can be read out with a high sampling rate.

According to the invention, however, the invention can also be implemented with an area camera in which light-sensitive elements are provided in matrix form. This makes it possible to measure a brightness curve in two spatial directions, i.e. a two-dimensional brightness curve. However, since a significantly larger number of light-sensitive elements have to be read out with an area scan camera, the achievable sampling rate is lower.

According to the invention, it has been shown that it is possible to determine the dullness and/or the gloss of the object, i.e. its To describe the surface impression clearly and quantitatively.

According to the invention, the height of the curve, the width of the curve and the steepness of the edge of the curve are included in the determination. The latter increases the robustness and accuracy compared to measurements that only record the maximum of the curve (e.g. according to a measurement arrangement in the reflection angle of the light for a gloss measurement).

This also applies to measurements that take into account both the height and width of the curve. The width of the curve is an indication of the degree of scatter. The greater the diffuse scattering of the transmitted or reflected light, the broader the curve of the brightness profile of the light distribution. A specific example of a preferred evaluation is the determination of the mean value and the standard deviation of the brightness distribution. In principle, however, all methods are possible that enable conclusions to be drawn about the gradient of the curve, i.e. the steepness of the drop in the signal to the outside.

It has been found that a calibration using comparative measurements for a measurement task, i.e. a specific measurement arrangement and a specific material in accordance with specified definitions or standards, produces a correlation (in the sense of a functional relationship) between the standard measured values and the measured values obtained from the brightness curve according to the invention can be. In principle, such a connection could also be determined theoretically if the optical transmission properties of all objects involved are known exactly. However, since this is often not the case in practice, comparative measurements can be carried out in accordance with the specified definitions and standards, which then lead to a functional relationship with the values determined using the method according to the invention. Thus, even when using the method according to the invention, measured values can be specified which correspond to the normalized measured values and can be used accordingly in production or product control, although these are of course not measured values measured according to the standard.

According to the invention, this aspect of the invention described above can also be used in measuring arrangements that have only one punctiform illumination element as the light source, without the light source consisting of a plurality of individually switchable illumination elements. The invention described also relates to a method and an arrangement with only a single point light-shaped lighting element, the light from which is incident on the object and reflected and/or transmitted is recorded with a camera in order to measure a brightness profile of the light distribution in a spatially resolved manner in an image.

In this case, a lighting element can be formed by a luminous element (for example an LED) or by a plurality of combined luminous elements (for example by a number of LEDs arranged next to one another and connected together).

According to the invention, the light source can have lighting elements on the side of the camera (ie in a reflection arrangement) and/or on the side opposite the camera (ie in a transmission arrangement) in relation to the object point. The light source can also be formed from different partial illuminations that are arranged at different positions of the object in order to be able to measure both a reflection and a transmission arrangement (in the case of transparent objects) in a relative position of light source, object and detector. The method according to the invention and the correspondingly described arrangement can be used to measure the mattness (haze) and/or the gloss (gloss) for transparent and non-transparent objects in one arrangement. The person skilled in the art selects the specific arrangement of the recording geometry according to the task within the scope of his/her professional ability.

A preferred application for the reflection measurement provides for arranging the camera in the angle of reflection (angle of reflection). This is defined by the angle of incidence of the light radiated onto the surface of the object in accordance with the reflection of the light on the surface according to the physical laws of reflection. This means that a light distribution around the angle of reflection of the light is captured by the camera.

For the transmission measurement, the camera preferably records the unscattered light beam passing through the object and the scattered light reflected on both sides thereof in a spatially resolved manner.

Preferably, the entire measurable range is covered, i.e. the light intensity distinguishable from the base level of light (such as that produced by ambient light). In this case, by accessing the spatially resolved measured brightness values, different recording geometries can also be derived from the image and evaluated.

According to a preferred embodiment of the method proposed according to the invention, the camera can be designed in such a way that the brightness curve is detected by each lighting element in a spatially resolved manner until the brightness at the edge of the brightness curve falls to the basic level. The base level corresponds to the intensity measured in the detector, which results when the light source is completely switched off, i. H. when no lighting element of the light source is switched on. In this way it is possible to evaluate the entire measurable course of brightness, which lies above the noise and thus allows conclusions to be drawn about the mattness and gloss of the object.

In this context, it is particularly advantageous if a point light source is used as the lighting element, which generates a point of light on the object. Such a point of light has a small and therefore punctiform extent in comparison to the overall size or surface of the object. In other words, the surface area of the object illuminated by the lighting element is so small that a specific recording geometry is achieved with a defined angle of incidence and angle of reflection of the light generated. In transmission, this also includes an angle of incidence of 90 degrees and an angle of reflection of 90 degrees. Light that is focused on the surface in this way greatly reduces or avoids the influence of light that is reflected onto other surface areas and scattered into the detector.

To generate such a focused light beam to generate a point of light on the surface of the object, a suitable lens focusing the light onto the surface of the object can be provided in front of the lighting element or elements. In the case of a linear light strip made up of lighting elements arranged in a row (line), such a lens can be designed as a rod lens, for example.

According to the invention, the object is moved in a transport direction relative to the light source and the detector. The light source is designed in such a way that the lighting elements cover the entire width of the object transversely to the transport direction, i.e. depending on which lighting element is switched on, they can illuminate the surface in a punctiform manner over the entire width. Furthermore, the detector is designed in such a way that the entire width of the object transverse to the transport direction, which is illuminated by the lighting elements, can be simultaneously measured, for example recorded, in a spatially resolved manner. This means that the entire width is captured in an image from a camera. It is then proposed according to the invention to switch the lighting elements one after the other, i.e. switch them on and off again, in such a way that the entire width of the object is illuminated one after the other. For this purpose, the lighting elements can preferably be or will be arranged perpendicularly or at any angle to the transport direction of the object. It is thus possible to measure the entire width of the object by recording an image for each switched-on lighting element.

The detector is preferably a camera capable of covering the entire width of the object at once. If necessary, several cameras can also be provided, which cover the entire width of the object in addition to one another. This is also understood to mean a camera within the meaning of the disclosure. Multiple cameras can also be transported if necessary offset in direction, as long as they capture the points of light generated by the light source on the surface of the objects and the resulting brightness distribution in a spatially resolved manner.

In particular when measuring transparent objects, illumination elements can be arranged, for example in the form of two or more partial illuminations, on both sides of the object in relation to the camera. In the case of transparent objects, this enables measurement both in a reflection arrangement and in a transmission arrangement in one arrangement during transport of the object. It is also conceivable in principle to arrange several lighting elements in partial lighting, possibly one behind the other in the transport direction, in order to measure different recording geometries if there is sufficient time to carry out the corresponding number of measurements while the object is being transported. This is possible, for example, with clocked transport or with a low transport speed.

A time-optimized measurement can be achieved according to the invention in that the switching frequency at which the lighting elements are switched in succession corresponds to the scanning rate of the camera. The sampling rate is defined by the time required to capture and read out a camera image before the camera is ready to capture the next image. During this time, all lighting elements of the camera are recorded in terms of value. This results in the maximum speed with which the images generated by the individual lighting elements can be recorded and read out. Scanning and switching frequencies of up to around 100 kHz can be achieved with line scan cameras and LED lighting elements. Switching the lighting elements on and off therefore corresponds to a brief flashing of the respective lighting elements.

According to the invention, the image recording is preferably synchronized with the switching on of the lighting, as is known and customary when using flashlights in photography.

According to a preferred further development of the method proposed according to the invention, it can be provided that the switching frequency, the sampling rate and the transport speed are matched to one another in such a way that the entire surface of the object is recorded. Capturing means that the entire surface of the object is illuminated and captured by the camera. For this purpose, the lighting elements can be switched on (flashed) in such a way that the same lighting element is then switched on again when the surface area on the object that was illuminated when it was switched on, due to the transport of the object at the coordinated transport speed, is just different from that illuminated when the same lighting element was subsequently switched on Has moved surface area. The two surface areas preferably directly adjoin one another, so that the entire surface is recorded without gaps or at least with the desired resolution if the areas do not directly adjoin one another.

This corresponds to a synchronization of image recording, switching on the lighting elements and web feed in the sense of transporting the object at the transport speed. Between the successive switching on of the same lighting element, the lighting elements covering the width of the object transversely to the transport direction are switched on one after the other, and an image is recorded in each case.

The method described above also applies to these other lighting elements with regard to the synchronization of image recording, switching on of the lighting elements and web feed. Since the exposure times are usually negligibly short compared to the web advancement of the object that takes place during the exposure time, the measurement can take place while the object is being transported continuously.

A particularly fast detection of the entire surface can be achieved by controlling several lighting elements of the light source at the same time, which are so far apart that the light emanating from this lighting element does not measurably affect the measurement of the brightness distribution of the light emitted simultaneously by another lighting element. Thus, the brightness distributions of several lighting elements are separated from each other in one image. This results in faster coverage of the entire surface.

A preferred variant of the method proposed according to the invention provides that for the measurement of the degree of gloss and mattness in transparent objects, partial lighting in a reflection arrangement and partial lighting in a transmission arrangement are or are provided, which are arranged in such a way that the partial lighting on the surface light emitted by the object and reflected and transmitted by it in the same camera are detected, with the lighting elements of the two partial lights preferably being switched on one after the other.

According to the invention, a measurement of the degree of gloss can preferably take place both in the case of transparent and non-transparent objects in a reflection arrangement. In the case of non-transparent objects, the mattness can also be measured in a reflection arrangement, preferably in such a way that the camera is arranged in the reflection angle of the light.

This is crucial when using a line scan camera and light bar. The mattness values are then derived from the brightness profile of the light distribution recorded by the line scan camera transversely or at an angle to the transport direction.

In contrast, the haze measurement for transparent objects preferably takes place in a transmission arrangement, preferably in such a way that the light falls perpendicularly onto the surface of the object, passes through the object and is captured by the camera on the other side of the object.

In order to capture both the reflected and the transmitted light in one arrangement, the camera has appropriately selected wide-angle optics.

According to the invention, it is also proposed to carry out a zero measurement without the light source being switched on and to correct the measured brightness curve in accordance with the zero measurement. In this preferred application of the method, the accuracy can be improved, particularly when determining the dullness of objects with a high degree of dullness (i.e. with high haze values).

Due to the light source proposed according to the invention, which, in addition to a rapid sequence of switching on and off punctiform lighting elements, also allows area or line lighting by switching on all or a defined selection of the lighting elements of the light source, the measurement of gloss level and dullness can be carried out according to the invention by using other types of lighting can also be used to perform other inspection tasks.

The light source is preferably designed as a light strip with lighting elements arranged in a linear row in an illumination direction or as a light matrix with lighting elements arranged in matrix form, so that different types of area lighting can be implemented. Different illuminations can also be achieved if the light source has a plurality of partial illuminations arranged at different positions. A combination of the measurement of gloss and mattness with other inspection tasks is particularly possible when the switching time of the lighting and the scanning rate of the camera is so high compared to the transport speed of the object that there are pauses when scanning the entire surface or the desired scanning resolution , which can then be used for other measurements or other inspection tasks.

Other inspection tasks can include, for example, a bright field measurement to determine the transmissivity or reflectivity of the object, depending on whether the object is transparent or non-transparent. Such a measurement is also referred to as probe pattern mode illumination.

Furthermore, light/dark field measurements can be used to detect defects, for example surface defects. This type of lighting is also referred to as cross darkfield mode lighting. These other inspection methods are basically known to the person skilled in the art and therefore do not need to be described in more detail at this point.

The invention also relates to a device for measuring the degree of gloss and/or the dullness of non-transparent or transparent objects with the features of claim 10. The device is equipped with a light source for illuminating the surface and a detector for detecting the amount of light reflected by the object and / or equipped with transmitted light. The detector is arranged or can be arranged relative to the light source and the object in a defined recording geometry (for example by means of a controllable manipulator). Correspondingly, the light source can also be adjustable, for example, arrangeable, for example by means of a controllable manipulator.

Furthermore, a control and computing unit is provided, which is set up to control the light source and the detector and to determine the degree of gloss and/or the mattness of the object from the amount of light and/or light distribution detected in the detector. In the context of the proposed device according to the invention, it is provided in particular that the light source consists of several lighting elements that can be switched on and off separately, ie switchable, that can be switched on and off one after the other in terms of time by the control and computing unit, and that the Detector is designed as a camera with which the brightness profile of the light distribution of the light reflected from the object and / or transmitted light for each lighting element is spatially measurable in an image.

According to the invention, the control and computing unit can also be set up to carry out the method described above or parts thereof. The device can also have one or more of the device-related features already described.

In particular, it can be provided that the light source has separately switchable LED elements as lighting elements, which are arranged in at least one row. The light source is then designed as a light strip. In a preferred device for measuring objects moving in a transport device, the at least one row of lighting elements is arranged transversely or at an angle to the transport direction, so that the lighting elements illuminate the object over its entire width (transverse to the movement or transport direction of the object) by switching off individual lighting elements can illuminate each point. In the case of several rows, the light source is designed as an illumination matrix.

The light source can be arranged in a reflection arrangement and/or in a transmission arrangement. In the reflective configuration, the light source and detector are on the same side of the object. In the transmission arrangement, the light source and the detector are on different sides of the object. The transmission arrangement is intended for transparent objects, and in particular for haze measurement. The reflection arrangement can be used for a gloss measurement of both transparent and non-transparent objects. Non-transparent objects can also be measured in the reflection arrangement to determine the haze value.

According to a particularly preferred embodiment of the device, the camera is in the form of a line camera, the design of which permits a high sampling rate. This is arranged in such a way that it measures the light distribution reflected and/or transmitted by the light source (with one or more partial illuminations) on the object. Instead of one camera, several cameras can also be used according to the invention if the entire measurement area cannot be covered in any other way. The images from the multiple cameras then complement each other to cover the width of the object transversely or obliquely to a transport direction, and thus form a logical camera.

Further advantages, features and possible applications of the present invention also result from the following description of exemplary embodiments and the drawings. All the features described and/or illustrated form the subject matter of the present invention on their own and in any combination, also independently of their summary in the claims or their back-references.

• 1 schematisch das physikalische Verhalten von an einem nicht transparenten Gegenstand reflektiertem Licht in der Reflexionsanordnung für Gegenstände verschiedener Mattheit bzw. verschiedenen Glanzgrads;
• 2 schematisch das physikalische Verhalten von durch einen transparenten Gegenstand transmittiertem Licht in der Transmissionsanordnung für Gegenstände verschiedener Mattheit bzw. verschiedenen Glanzgrads;
• 3 eine Vorrichtung zur Messung der Mattheit eines transparenten Gegenstands gemäß dem Stand der Technik;
• 4 eine bevorzugte Ausführungsform einer erfindungsgemäßen Vorrichtung für die Messung der Mattheit eines transparenten Gegenstands in Transmissionsanordnung;
• 5 eine bevorzugte Anwendung der Vorrichtung gemäß 4 zur Messung großflächiger Gegenstände;
• 6 eine bevorzugte Ausführungsform einer erfindungsgemäßen Vorrichtung für die Messung des Glanzgrads und/oder der Mattheit in Reflexion bei einem bewegten, nicht transparenten oder transparenten Gegenstand.

Show it:

• 1 schematically shows the physical behavior of light reflected on a non-transparent object in the reflection arrangement for objects of different mattness or different degrees of gloss;
• 2 schematically shows the physical behavior of light transmitted through a transparent object in the transmission arrangement for objects of different mattness or different degrees of gloss;
• 3 a prior art device for measuring the matteness of a transparent object;
• 4 a preferred embodiment of a device according to the invention for measuring the mattness of a transparent object in transmission arrangement;
• 5 a preferred application of the device according to 4 for measuring large objects;
• 6 a preferred embodiment of a device according to the invention for measuring the degree of gloss and/or mattness in reflection of a moving, non-transparent or transparent object.

The present invention is described below by way of example using two devices which show the application of the method proposed according to the invention in the transmission arrangement (for transparent objects) and in the reflection arrangement (for transparent and/or non-transparent objects). The exemplary embodiments are limited to the description of the features that are essential for the respective arrangement (transmission arrangement or reflection arrangement), without this being intended to have a limiting effect. In particular, as can be seen from the above description, a device is also possible in which the two arrangements are combined.

A preferred application provides that for the measurement of the degree of gloss (gloss measurement) the lighting is always arranged on the same side as the camera for transparent and non-transparent objects. This corresponds to the measurement setup as shown in 6 is shown. In the case of non-transparent objects, this arrangement can also be used for the haze measurement.

In the case of transparent objects, however, the mattness (haze measurement) is preferably measured in the 4 and 5 shown transmission arrangement instead.

In the 4 The device 17 shown is used to measure the dullness of a transparent object 6 in a transmission arrangement. The device is shown in cross section perpendicular to a direction of transport of the object 6 . In other words, the transport direction of the object 6 runs perpendicularly in the image plane shown.

The device 17 has a light source 18 which has a plurality of lighting elements 13 arranged next to one another in a row. The lighting elements 13 can each be controlled separately (individually) in the light source 18 in a switchable manner, it also being possible for a plurality of lighting elements to be switched on and/or off at the same time. A lighting element 13 is preferably switched on in the form of a flash.

In 4 the lighting element 13a is shown switched on, ie during the emission of the flash. As a result, the lighting element 13a emits a light beam 3 focused on the surface of the transparent object 6, with a lens optionally provided for this purpose in front of the lighting element 13a not being shown.

This light beam 3 passes through the transparent medium of the object 6 and is recorded on the side opposite the light source 18 with respect to the object 6 by a camera 14, which in the example shown is designed as a line camera aligned transversely to the transport direction of the object. According to a preferred arrangement of the light source 18 designed as a light bar and the camera 14 designed as a line camera, the alignment of the row of lighting elements of the light bar and the alignment of the line camera run parallel and are aligned transversely or obliquely to the transport direction of the object.

When the light beam 3 passes through the transparent object 6, it becomes, as with reference to FIG 2 already described, divided into a portion 8 of diffusely scattered transmitted light and a portion 7 of unscattered transmitted light. Depending on the dullness of the transparent object 6, the proportions 7, 8 of the divided light are of different sizes.

The two portions 7, 8 of the transmitted light are captured by the camera 14 with spatial resolution in an image whose brightness profile 15 corresponds to the light distribution in 4 is shown above the array 17 centered with the axis of the light beam 3. As expected, the intensity of the brightness curve 15 is highest in the axis of the light beam 3 and drops symmetrically towards the edges. This is because the light beam 3 passes through the transparent object 6 orthogonally.

Even if such an alignment can be evaluated in a particularly simple manner, the invention is fundamentally not limited to an orthogonal passage of the light beam 3 through the transparent object. In the case of a light beam striking the surface of the transparent object at an angle, this also passes through the object at an angle. Depending on the orientation of the camera, this can lead to a distortion of the in 4 , above, lead to the brightness curve 15 shown, which, however, can be evaluated in a comparable manner.

The mattness value (haze value) can be determined from this brightness profile. The area 16 of the brightness curve to be evaluated, also referred to as the haze area, must or should be so wide that the brightness at the edge of the image drops to the intensity that would be recorded without the light source 18 being switched on due to the ambient light. This basic level can be determined, for example, by a reference measurement and subtracted from the measured intensity value, so that the 4 brightness distribution 15 shown, which falls to zero at its edges, even when ambient light is present.

The height of the curve, the width and the steepness of the edge go into determining the haze value. The latter (i.e. the additional evaluation of the slope steepness) leads to a significant increase in robustness and accuracy compared to a measurement that only relies on the height and width of the brightness curve.

The greater the proportion 7 of the unscattered transmitted light compared to the proportion 8 of the diffusely scattered transmitted light, the lower the dullness of the object. The measured brightness curve 15 is correspondingly narrower. In addition to a higher curve, this also leads to a steeper slope, which is particularly sensitive to changes in the matte value. A correlation of the height, width and steepness of the brightness profile therefore leads to a particularly high level of accuracy.

If only one lighting element 13a is switched on in succession, the different areas of the object 6 illuminated by the light beam 3 are measured. Without shifting the light source 18, camera 14 and object 6, the entire width of the object 6 can be measured transversely to the transport direction if the light source 18 and the camera 14 (as is preferred according to the invention) cover the entire width of the object 6, even if this in the schematic representation according to 4 is not visible for the sake of clarity.

When applying the method, care can be taken to measure the entire width of the object by sequentially turning on the lighting elements 13a before the object 6 is shifted in the direction of transport by an amount greater than the area of focussed on the surface in the direction of travel Light beam 3. If this is the case, the entire surface of the object 6 can be scanned by suitably synchronizing the switching on (flashes) of the lighting element 13a, taking an image from the camera 14 and the transport speed of the object 6.

A preferred variant for the measurement is described below with reference to 5 described in more detail. 5 shows the device 17 according to FIG 4 over the entire width of the transparent object 6, the brightness curve 15 recorded by the camera 14 being shown instead of the camera 14.

Three different synchronization times are shown one below the other. In the top image, several lighting elements 13a of the light source 18 are switched on, so that several light beams 3 impinge on the surface of the transparent object 6 at the same time, pass through it and are correspondingly divided into portions 7, 8 of the transmitted light.

Each of these incident light beams 3 leads, in accordance with the division into the portions 7, 8, to the brightness profile 15 of the light distribution shown in each case, which is measured by the camera 14. Since the width of the haze area 16 (i.e. the area to be evaluated) is much smaller than the total width of the transparent object 6, it is possible to simultaneously switch on several lighting elements 13a, which are spaced at least by the haze area 16, and thus several light spots on the transparent object 6 to be measured at the same time.

to the in 5 The switching on of lighting elements 13a that are adjacent compared to the first synchronization time is shown below the second synchronization time shown at the top. Correspondingly, light points adjacent to the first light point are generated and measured on the surface of the transparent object 6 .

This is continued, as indicated by the dots between the middle (second from the top) and the lower representation, until all of the lighting elements 13a have been switched on once.

At the in 5 For example, with four lighting elements 13a switched on at the same time, the measurement of the object across its entire width transverse to the transport direction is four times faster than with just one lighting element switched on at a synchronization time.

Due to the lateral displacement of the in 5 For the illumination pattern shown, the entire width of the surface of the transparent object is measured.

A corresponding application is also in the case of the following with reference to 6 described reflection arrangement possible, in which several lighting elements 13 of the light source 18 can be turned on simultaneously in a corresponding manner.

Also, those in the 4 and 5 as 6 described transmission and reflection arrangements are combined in a device 17. For this reason, for the components in 4 / 5 and 6 also use the same reference numbers.

6 shows the device 17 for measuring the dullness and/or degree of gloss of a transparent object 6 or a non-transparent object 1 in a reflection arrangement, in which the light source 18 and the camera 14 are arranged on the same side of the transparent object 6 or the non-transparent object 1.

As in the transmission arrangement, the light source 18 with the lighting elements 13 arranged in a row as a light strip and the line camera 14 are arranged transversely to the transport and direction of movement 19 of the object 1, 6 aligned. A switched on (flashing) lighting element 13 of the light source 2 produces a light beam 3 focused on the surface of the object 1, 6, which is reflected on the surface both for a transparent object 6 and for a non-transparent object 3.

The proportion 4 of the directly reflected light is distributed as already referred to in FIG 1 described by the exit angle resulting from the angle of incidence of the light beam 3, which is also referred to as the reflection angle. The camera 14 is arranged at this reflection angle, the alignment of the camera 14 , which is preferably designed as a line camera, running transversely to the transport direction 19 .

The proportion 5 of the light 5 that is not reflected, but diffusely scattered from the surface, is not only in that of 6 plane shown, but also in the direction perpendicular to the plane shown, so that the camera 14 records a brightness profile 15 in a direction transverse to the transport direction 19, similar to that in FIG 4 is shown above.

The gloss value can then be determined by evaluating this curve, for example by determining the proportion of the reflected light to the scattered light by integrating the curve. Alternatively, the maximum value of the brightness distribution can be determined and related to the amount of light emitted by the lighting element 13 . This is also a measure of the gloss value or the degree of gloss of the object 1, 6.

If only the degree of gloss (gloss value) is to be determined, it is basically also possible to switch on all the lighting elements 13 of the light source 18 at the same time and to measure the entire width of the object 1, 6 at the same time. In this way, however, only the portion of the directly reflected light is obtained without a reference value. This only makes sense in exceptional cases.

In the case of a non-transparent object 1, the mattness (haze) and the degree of gloss (gloss) can be measured simultaneously with the same measuring arrangement, because the two values can be determined from the same brightness profile. In the case of a transparent material, at least the same camera can be used to alternately switch the two partial illuminations of the light source arranged above and below the material, i.e. in a transmission arrangement and in a reflection arrangement. In the case of a transparent material, the transparency can also be measured by evaluating the total amount of light recorded by the camera.

If a line camera is used as the camera 14, the brightness distribution 15 of the scattered light corresponding to the component 5 can only be seen in the direction of the line camera, ie transversely to the transport direction 19. This is sufficient for fundamentally isotropic materials.

In rare cases, with anisotropic materials, it is interesting to see how the scattering of proportion 5 in the other spatial direction, i. H. in the transport direction 19 behaves. In order to measure this, either an area camera can be used or a second camera can be attached at a different viewing angle in order to obtain a second measuring point in the direction of advance of the object along the transport direction. The use of a second area scan camera is often sufficient.

A particular advantage of the invention also results from today's in-line inspection systems, which generally work with line cameras or area cameras and a light source that illuminates the surface in the image field of the respective camera. These systems can take and process images at very high speeds to look for defects on the surface. Especially with line scan cameras, very high scanning frequencies of well over 100kHz are possible. Due to the high scanning frequencies, these systems can determine the smallest errors even at high transport speeds of the object. In addition, LEDs can be switched as lighting elements with frequencies that are in the same order of magnitude as those of the line scan cameras.

By synchronizing the image recording and illumination, many more images can be recorded in continuous processes, such as the transport of an object in the transport direction, than would actually be necessary for the required resolution in the feed direction. If the image recording is now synchronized with the switchable lighting and the web feed, and if changing lighting patterns are used, the surface inspection can be made significantly more efficient according to the invention by seeing each point on the surface under different lighting situations.

The present invention also makes use of this technology. Switching on the lighting elements arranged next to one another, through which the entire width of the object can be successively illuminated with point light sources, makes it possible to to measure the entire surface. In addition, the lighting and image recording proposed according to the invention can be combined with other lighting work that is suitable for other inspection tasks. In this way, a haze and gloss measurement integrated into an inspection system can be implemented. This saves costs and space, which is very scarce in production lines. The different types of illumination do not necessarily have to be realized by a light source 18 in a housing. Partial illumination of the light source 18 can be used in particular to mix incident and transmitted light methods for transparent objects 6, so that a haze and a gloss measurement can also be carried out simultaneously for these and other different types of illumination can be freely combined.

Due to the flexibility of the arrangement according to the invention, the methods carried out with it for measuring the mattness and degree of gloss of the objects usually cannot comply with the measuring conditions prescribed in the relevant standards, since these are always only defined for one measuring point on the surface and do not allow a planar measurement. However, it has been found that a functional relationship can be established between the standard measured values and the measured values obtained according to the invention from the brightness curves, which can be specified in a reproducible manner in extensive tests. This relationship can be calibrated in particular by comparative measurements. Theoretically, it would also be possible to describe this connection functionally. However, this required optical transmission equipment for all the components involved, which is often not the case in practice.

Since the camera can capture very large solid angles depending on the opening angle of the lens and the brightness distribution is detected with spatial resolution, a corresponding number of values are available to correlate the haze and gloss values determined according to the present invention with the values according to the standards .

Reference List

1

non-transparent object

2

light source

3

beam of light

4

Proportion of directly reflected light

5

Percentage of diffusely scattered light

6

transparent object

7

Portion of light transmitted without scattering

8th

Percentage of diffusely scattered light

9

hollow sphere

10a

light entry opening

10b

light exit opening

10c

further opening

11

first detector

12

second detector

13

lighting element

14

detector designed as a camera

15

brightness gradient

16

Haze range

17

Device for measuring dullness and/or gloss level

18

light source

19

transport direction

Claims (14)

Method for measuring the degree of gloss and/or the dullness of non-transparent objects (1), in which the objects (1) objects (1) are illuminated by a light source (18) and the quantity of light reflected from the objects (1) in a detector (14), or of transparent objects (6), in which the objects (6) are illuminated by a light source (18) and the amount of light reflected and/or transmitted by the object (6) in a detector (14) is detected, the detector (14) being arranged in a defined recording geometry relative to the light source (18) and the object (1, 6), the degree of gloss and/or the amount of light detected in the detector (14) being determined the dullness of the object (1, 6) can be determined, the light source (18) consisting of a plurality of lighting elements (13, 13a) which can be switched on and off individually and which are switched on and off one after the other, and the detector (14) is designed as a camera (14) with which the brightness profile (15) of the light distribution of the light reflected and/or transmitted by the object (1, 6) is measured in a spatially resolved manner in an image for each lighting element (13, 13a) and represents a curve of different intensities at different locations, with the height of the curve, the width of the curve and the steepness of the edge of the curve entering into the determination of the degree of gloss and/or the mattness, characterized in that the object (1, 6) in a transport direction (19) is moved relative to the light source (18) and the detector (14), that the light source (18) is designed so that the lighting elements (13, 13a) the entire Cover the width of the object (1, 6) transversely to the transport direction (19), that the detector (14) is designed in such a way that the entire width of the object (1, 6) transversely to the transport direction (19) can be measured at the same time, and that the lighting elements (13, 13a) are switched on one after the other in such a way that the entire width of the object (1, 6) is measured. procedure after claim 1 , characterized in that the camera (14) is designed in such a way that the brightness profile (15) is detected by a lighting element (13, 13a) in a spatially resolved manner until the brightness at the edge of the brightness profile (15) falls to a basic level. procedure after claim 1 or 2 , characterized in that a point light source is used as the lighting element (13, 13a), which generates a point of light on the object (1, 6). Method according to one of the preceding claims, characterized in that the switching frequency at which the lighting elements (13, 13a) are switched in succession corresponds to the scanning rate of the camera (14). procedure after claim 4 , characterized in that the switching frequency, the sampling rate and the transport speed are coordinated in such a way that the entire surface of the object (1, 6) is detected. Method according to one of the preceding claims, characterized in that several lighting elements (13a) of the light source (18) are controlled simultaneously, which are so far apart that the light emanating from this lighting element (13a) makes it possible to measure the brightness profile (15) of the light source from one other lighting element (13a) simultaneously emitted light not measurably influenced. Method according to one of the preceding claims, characterized in that for the measurement of the degree of gloss and the dullness of transparent objects (6), partial illumination in a reflection arrangement and partial illumination in a transmission arrangement are provided, which are arranged in such a way that the partial illumination on the surface The light emitted by the object (6) and reflected and transmitted by it can be recorded in the same camera (14), the lighting elements (13, 13a) of the two partial lights being switched on one after the other. Method according to one of the preceding claims, characterized in that a zero measurement is carried out without the light source (18) being switched on and the measured brightness curve (15) is corrected in accordance with the zero measurement. Method according to one of the preceding claims, characterized in that the measurement of the degree of gloss and dullness is combined with other types of illumination for carrying out other inspection tasks. Device for measuring the degree of gloss and/or dullness of non-transparent objects (1), comprising a light source (18) for illuminating the surface of the object (1) and a detector (14) for detecting the amount of light reflected by the object (1). light, or of transparent objects (6) with a light source (18) for illuminating the surface of the object (6) and a detector (14) for detecting the amount of light reflected and/or transmitted by the object (6), the Detector (14) is arranged in a defined recording geometry relative to the light source (18) and the object (1, 6), and with a control and computing unit which is used to control the light source (18) and the detector (14) and Determining the degree of gloss and/or the dullness of the object (1, 6) from the amount of light detected in the detector (14), the light source (18) comprising a plurality of lights that can be switched on and off separately elements (13, 13a) that can be switched on and off one after the other by the control and processing unit, and that the detector (14) is designed as a camera (14) with which the brightness profile (15) of the light distribution of the Object (1, 6) reflected and / or transmitted light for each lighting element (13, 13a) is spatially resolved in an image measurable and represents a curve of different intensities at different locations, with the determination of the degree of gloss and / or dullness the height of the curve, the width of the curve and the steepness of the slope of the curve, characterized in that the device (17) has a transport device, that the light source (18) is designed in such a way that the lighting elements (13, 13a) cover the entire width of the object (1, 6) transverse to a transport direction (19) cover that the detector (14) is designed so that the entire width of the object (1, 6) transverse to the transport rich Device (19) can be measured simultaneously, and that the control and computing unit is set up so that the object (1, 6) is moved in the transport direction (19) relative to the light source (18) and the detector (14) and that the lighting elements (13, 13a) are switched on one after the other in such a way that the entire width of the object (1, 6) is measured. device after claim 10 , characterized in that the control and computing unit further to carry out the method according to one of Claims 1 until 9 is set up. device after claim 10 or 11 , characterized in that the light source (18) as lighting elements (13, 13a) has individually switchable LED elements which are arranged in at least one row. device after claim 12 , characterized in that the light source (18) in the case of non-transparent objects (1) is arranged in a reflection arrangement and in the case of transparent objects (6) in a reflection arrangement and/or in a transmission arrangement. Device according to one of Claims 10 until 13 , characterized in that the camera (14) is designed as a line camera.

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