Device and method for measuring optical properties, in particular color measuring device

Abstract

The invention relates to a device for inspecting characteristics of a surface, the device comprising: a housing; first radiation means, arranged within the housing, adapted and intended to emit radiation, in particular light, onto a surface to be inspected; a first radiation detector device arranged within the housing, adapted and intended to receive radiation that has been emitted onto the surface to be inspected and that has been reflected and / or scattered by the surface, where the housing has an opening through which the first radiation device emits radiation onto the surface, where the apparatus comprises a first calibration element, in place of the surface to be inspected, and a second calibration element, in place of the surface to be inspected, adapted and intended to calibrate the radiation on the surface to be inspected. The first calibration element can be arranged such that radiation that has been emitted from the first radiation means onto the first calibration element and has been reflected and / or scattered by the first calibration element reaches the first radiation detector means, characterized in that the apparatus comprises a second calibration element, in place of the surface to be inspected and in place of the first calibration element, the second calibration element can be arranged such that radiation that has been emitted from the first radiation device onto the second calibration element and has been reflected and / or scattered by the second calibration element reaches the first radiation detector device.

Description

Technical Field

[0001] The present invention relates to devices and methods for measuring optical properties, and in particular to devices and methods for determining the optical properties of a surface. In particular, the device is described with reference to a color measurement device, but it should be noted that the present invention is also applicable to other devices for measuring or determining (surface) optical properties such as gloss and the like. Background Art

[0002] Calibration standards, hereinafter referred to as calibration elements, are often used in color measurement devices in order to be able to detect and intercept and / or correct possible aging, such as a decrease in the intensity of light waves. It is well known that such correction is carried out using a calibration factor which ensures that the color measurement values (in a laboratory system, in particular the L value) always remain the same for a consistent sample, regardless of the quality of the illumination.

[0003] However, it has been shown that such measurements are often affected by, for example, a dirty calibration element. For example, a dirty or damaged calibration element can simulate the aging of a light source that does not exist in reality and thus deteriorate measurements such as color measurement via a mis-set calibration factor.

[0004] Therefore, the present invention is based on the task of achieving a more precise calibration of such a device, and in particular on the task of eliminating and / or taking into account various error sources that may affect the calibration. Summary of the Invention

[0005] A device for inspecting the optical properties of a surface according to the present invention has a housing and a first radiation device which is arranged inside the housing and which is adapted and intended to emit radiation, in particular light, in particular light in the visible wavelength range, for example light in the wavelength range from 300 nm to 700 nm, onto the surface to be inspected.

[0006] Furthermore, the device has a first radiation detector device which is arranged inside the housing and which is adapted and intended to receive the radiation irradiated onto the surface to be inspected and the radiation reflected and / or scattered by the surface. Furthermore, the housing has an opening through which the first radiation device emits the radiation onto the surface to be inspected.

[0007] Furthermore, the device has a first calibration element which can be arranged in such a way that the radiation which has been emitted from the first radiation device onto the first calibration element and which has been reflected and / or scattered by the first calibration element reaches the first radiation detector device, instead of the surface to be inspected.

[0008] According to the invention, the device has a second calibration element which, instead of the surface to be inspected and instead of the first calibration element, can be arranged in such a way that radiation which has been emitted from the first radiation device onto the second calibration element and has been reflected and / or scattered by the second calibration element reaches the first radiation detector device.

[0009] Therefore, it is proposed to use two calibration elements or two calibration standards independently of one another in order to perform the calibration as a whole. In this way, certain errors caused by a faulty calibration element can be eliminated or certain errors caused by a faulty calibration element can be made easy to identify.

[0010] Preferably, the first calibration element and / or the second calibration element has a white surface on the surface facing the radiation device. Particularly preferably, this is a predefined white standard which, in addition to the property "white", preferably also has a gloss level suitable for gloss calibration.

[0011] For example, the surface of the calibration element can be made of ceramic. Other materials which are stable and / or color-stable and preferably also aging-resistant can also be used.

[0012] In a preferred embodiment, the calibration element is arranged on a holder. Particularly preferably, the first calibration element and / or the second calibration element is always or permanently arranged in a housing. However, it is also conceivable to arrange the first calibration element and / or the second calibration element outside the housing, for example on a (particularly rotating) support arm.

[0013] Preferably, the first calibration element and / or the second calibration element can be moved and in particular rotated in the beam path, the beam path being between the radiation device and the detector device. Particularly preferably, the calibration element is arranged in a holder. Particularly preferably, the holder is designed to absorb light and / or is made of a material which absorbs light.

[0014] In a preferred embodiment, the first calibration element and / or the second calibration element can be arranged in such a way that the surface exposed to the radiation device coincides with or is parallel to the surface to be inspected. For example, the first calibration element in the housing can be rotated to a position where the surface of the first calibration element is parallel to the surface of the surface used or to be inspected during operation.

[0015] Preferably, in the measurement mode, the second calibration element can be placed on the opening and thus preferably be located at the position where the surface to be analyzed is located.

[0016] In a preferred embodiment, the device has a closing device and, in particular, a baffle cleaning device which is adapted and intended to close the opening during certain time periods, in particular during time periods in which no measurement takes place or the device is switched off. In this way, contaminants can be prevented from entering the device or the housing outside of operation.

[0017] In a further preferred embodiment, the radiation detector device is adapted and intended to record a spatially resolved image of the surface to be inspected.

[0018] In a further embodiment, the radiation detector device is adapted and intended to measure the radiation intensity impinging thereon.

[0019] In a further preferred embodiment, the radiation detector device is adapted and intended to perform wavelength resolution of the radiation impinging thereon. In other words, the radiation detector device allows the analysis of the radiation impinging thereon and / or the output of wavelength-related measurement results with respect to the wavelength of the incident radiation.

[0020] Particularly preferably, the radiation detector device allows a wavelength-related analysis of the radiation impinging thereon, especially in the visible wavelength range.

[0021] The radiation detector device is particularly preferably a spectrometer device.

[0022] Particularly preferably, the device has a holding device or a holding volume for holding one of the calibration elements. Particularly preferably, the device has a holding compartment or a holding volume for two calibration elements. Preferably, the two calibration elements are stored separately from each other.

[0023] In a further preferred embodiment, the two calibration elements are stored in different orientations, in particular in orientations different with respect to the above-mentioned opening through which the surface to be inspected is irradiated in the operating mode. In this way, a space-saving arrangement can be formed.

[0024] Particularly preferably, the second calibration element can be removed from the receiving volume and placed on the opening of the device, for example, in order to perform a calibration measurement.

[0025] In a particularly preferred embodiment, the inner surface of the housing is light-absorbing, for example black.

[0026] In a further advantageous embodiment, the device has a processor device which determines a measured value from the values output by the radiation detector device and in particular determines a calibration value. Particularly preferably, for this purpose, the processor device can use the calibration value. Particularly preferably, the calibration value is stored or can be stored in the memory device of the device. Particularly preferably, the calibration value can be changed and in particular can be changed as a result of a calibration measurement.

[0027] Particularly preferably, one of the calibration elements can be arranged in the housing and preferably can be moved along the beam path within the housing, the beam path being between the first radiation device and the first radiation detector device. Particularly preferably, this one calibration element can be placed against the opening from the inside.

[0028] In a further advantageous embodiment, the device has a processor device which detects a first value which represents the characteristic of a first calibration measurement using a first calibration element, and the processor device detects a second value which represents the characteristic of a second calibration measurement using a second calibration element, and preferably, the device has a comparison device which compares the first value and the second value with each other.

[0029] Particularly preferably, the comparison between the first value and the second value can be used to draw conclusions about a fault condition of the device and / or the calibration element. Particularly preferably, the first value and the second value are comparison values. In a preferred embodiment, this comparison can be used to infer the cause of an error in the context of a calibration measurement.

[0030] In a further preferred embodiment, the device has an output and / or display device which is adapted and intended to output at least one signal which is characteristic of a specific error. For example, the display can indicate that one of the calibration elements is dirty or that the calibration element is not correctly positioned.

[0031] The display device is particularly preferably a display which is particularly preferably integrated into the housing of the device. The display is particularly preferably adapted and intended for the alphanumeric output of information.

[0032] For example, in order to be able to recognize without a doubt that the calibration factor can be correctly changed by a white standard calibration, it is proposed to correlate a number of recorded measurement variables with each other and thus to draw a clear statement about the condition of the device and for example a spectrophotometer and / or the calibration element.

[0033] It is proposed here to use two calibration elements. Preferably, this is an external calibration element and preferably an internal calibration element. The external calibration element is placed on the measurement opening like the sample to be measured, and the internal calibration element is integrated into the sealing cover. When no measurement is being carried out, the sealing cover preferably closes the measurement opening in an electric manner.

[0034] Particularly preferably, at least one calibration element is integrated into a closing device which is intended to close an opening through which the surface to be inspected is irradiated in the operating mode.

[0035] Particularly preferably, the calibration factors of the two calibration elements are determined separately.

[0036] Preferably, the device is selected from a group of devices which includes a color measurement device, a gloss measurement device, an orange peel measurement device, etc. The device is particularly preferably a color measurement device.

[0037] Particularly preferably, the device has a second radiation device which is arranged inside the housing and which is adapted and intended to emit radiation and in particular light onto the surface to be inspected.

[0038] Particularly preferably, the radiation or the reflection and / or scattered radiation generated by the radiation (from the surface to be inspected) is also detected by the detector device described above.

[0039] Particularly preferably, the second radiation device is arranged in such a way that it irradiates the surface with radiation at an angle different from that of the first radiation device mentioned above. The first radiation device can emit radiation at an angle of, for example, 60° or 45° relative to the surface, and the second radiation device emits radiation at an angle of 20° relative to the surface.

[0040] Preferably, at least one radiation device emits radiation onto the surface at an angle between 30° and 60°, preferably between 40° and 50°, relative to the surface. Preferably, at least one radiation device emits radiation onto the surface at an angle between 10° and 30°, preferably between 15° and 25°, relative to the surface.

[0041] Preferably, the radiation can also be irradiated onto or guided to the detector device by means of the calibration element.

[0042] In a further advantageous embodiment, the device also has a second detection device or a second radiation detector device which detects the radiation impinging on it. In particular, the second detector device can be arranged at an angle different from the surface compared to the first radiation detector device described above.

[0043] Particularly preferably, the device has a plurality of radiation devices, each of the plurality of radiation devices being adapted and intended to irradiate light onto the surface to be inspected. For example, these can be a plurality of light sources, which particularly preferably emit white light in part and particularly preferably emit light of different colors and / or wavelengths at least in part.

[0044] The radiation devices can have various radiation characteristics, such as directional illumination, illumination within a predetermined acceptance angle range, or diffuse illumination.

[0045] Particularly preferably, the plurality of radiation devices are arranged along a circular line. Particularly preferably, the circular line is parallel to the surface to be analyzed.

[0046] Particularly preferably, the radiation detector device is arranged such that the radiation detector device is substantially perpendicular above the surface to be inspected, and in particular, the direction in which the radiation detector device collects radiation from the surface is substantially perpendicular to the surface.

[0047] Particularly preferably, the device also has a gloss measurement device (and / or a reflection measurement device). The radiation device of the gloss measurement device and in particular the gloss measurement device preferably emits light onto the surface at a predetermined angle, and the detector device detects the light from the corresponding reflection angle.

[0048] The gloss measurement device can also be used for evaluation calibration. If the device operates in an orientation with the measurement aperture facing upwards, then although the measurement aperture is closed by a baffle, for example, the optics may be contaminated in a very dusty environment. However, a small gloss angle, such as 20°, is more susceptible to this than a large angle such as 60°.

[0049] If only one gloss angle is measured, the gloss value of the first calibration element can be correlated with the gloss value of the second calibration element, and the gloss value of the second calibration element is correlated with a calibration factor. As will be shown in more detail below, different conclusions can be drawn from a suitable combination of observations.

[0050] For example, if the 20° gloss of the internal calibration element deviates significantly more from the calibrated original gloss value, but the 60° gloss remains almost unchanged, this indicates that the optical element is contaminated.

[0051] In a further advantageous embodiment, the device has a gloss measurement device, wherein the gloss measurement device has a further radiation device that irradiates radiation onto the surface at a predetermined angle of incidence, and the gloss measurement device also has a further radiation detector device that detects the radiation irradiated onto the surface by the further radiation device and reflected from the surface at a predetermined angle, wherein the angle of incidence and the further angle are preferably the same.

[0052] The invention also relates to a method for examining the optical properties, and in particular the color properties, of a surface, in which a radiation device arranged in a housing emits radiation and in particular light onto the surface to be examined, and a first radiation detector device arranged in the housing receives the radiation (and / or the radiation hits the radiation detector device) that is irradiated onto the surface to be examined and reflected and / or scattered by the surface, wherein the housing has an opening through which the first radiation device emits the radiation onto the surface, and wherein the device has a first calibration element which, in a calibration mode, is arranged in such a way that, instead of the surface to be examined, the radiation emitted by the first radiation device onto the first calibration element and reflected and / or scattered by the first calibration element reaches the first radiation detector device.

[0053] According to the invention, in the calibration mode, instead of the surface to be examined and instead of the first calibration element, a second calibration element is arranged in such a way that the radiation emitted by the first radiation device onto the second calibration element and reflected and / or scattered by the second calibration element reaches the first radiation detector device.

[0054] It is therefore also proposed to perform different measurements, and in particular at least two measurements using different calibration elements. These different measurements can be used to draw conclusions about different error sources.

[0055] Preferably, a calibration factor is changed based on at least one calibration measurement performed. In particular, if the calibration measurement shows that the deviation in the measurement is caused by a modification of the optical properties of the radiation device, the calibration factor is changed. In particular, the calibration factor is changed in order to take into account and / or compensate for the aging state of at least one radiation device.

[0056] Particularly preferably, a first value and a second value are recorded, the first value representing the characteristics of a first calibration measurement using a first calibration element, and the second value representing the characteristics of a second calibration measurement using a second calibration element.

[0057] Particularly preferably, the first value and the second value are compared with each other, and particularly preferably, based on this comparison, an error instruction or information is sent to the user.

[0058] Preferably, the first value and the second value are set in a mathematical relationship to each other. Thus, a difference can be formed between the first value and the second value. However, a quotient can also be formed between the first value and the second value. Particularly preferably, both a difference between the first value and the second value and a quotient between the first value and the second value are formed. For example, it can be determined which of the two values is larger. This can be used to draw conclusions about the possible error state of the device and / or the calibration element. In addition, the ratio can be used to determine whether the two values are approximately the same or significantly different from each other.

[0059] In a further preferred method, further measured values are also determined, in particular measured gloss values (in particular measured gloss values at a specific angle of incidence). The gloss measurement is preferably carried out in so-called gloss units, as described in detail in current standards (such as ISO 2813 or ASTM D 253). Preferably, the measured gloss value is compared with a predetermined value, such as an initial value.

[0060] It can be determined whether the measured value is approximately equal to the initial value or deviates from the initial value, and in particular is smaller. This gloss value measurement can be used for both the first calibration element and the second calibration element.

[0061] Particularly preferably, several values or analyses determined above are considered in order to draw conclusions about the fault condition of the device or calibration element or optical device. The following table shows the corresponding list of different error sources.

[0062] Particularly preferably, different error sources are distinguished depending on the comparison above.

[0063] Particularly preferably, the calibration value is changed taking into account at least one of the measured values. This can be seen particularly in the table above.

[0064]

[0065]

[0066] The table above shows four examples of errors or states. These are marked with the numbers 1 - 4 in the top row.

[0067] The second row shows the possible measurement results of the calibration factor ca_i of the first calibration element (in particular the calibration element located inside the housing during the calibration measurement). This can be greater than 1 (indicating an error state) or approximately equal to 1 (indicating the target state).

[0068] The third row shows the possible measurement results of the calibration factor ca_a of the second calibration element (in particular the calibration element located outside the housing during the calibration measurement). This can be greater than 1 (indicating an error state) or approximately equal to 1 (indicating the target state).

[0069] The fourth row shows the ratio between the measured calibration factors ca_i and ca_a. If this ratio is approximately 1, i.e., the two calibration factors are approximately equal, then this indicates the target state regarding any contamination of the two calibration elements and in particular the second calibration element. If the ratio ca_i / ca_a is less than 1, then this indicates that the external calibration element is contaminated (see the third column and the second - last row of the table).

[0070] In the fifth row, the measured gloss value gi (and / or the measured reflection value) is determined at an incident angle of 20° and using the first calibration element. In the sixth row, the measured gloss value ga (and / or the measured reflection value) is determined at an incident angle of 20° and using the second calibration element.

[0071] Preferably, these determined gloss measurement values are compared with the corresponding initial measurement values gloss_i0 and gloss_e0. If the two values deviate (second column), this indicates a dirty optical device. If only the value of the second calibration element deviates, this indicates that the optical device is dirty or not properly applied to the opening.

[0072] Optionally, the gloss measurement can also be performed at a second angle such as 60°.

[0073] In another preferred method, in the operating mode, the surface to be inspected is exposed to a number of radiation devices. Preferably, the surface to be inspected is exposed to at least two radiation devices. Particularly preferably, these two radiation devices irradiate the radiation at at least two different angles. Particularly preferably, the irradiation using the first radiation device is temporally offset from the radiation using the second radiation device.

[0074] In a further preferred embodiment, the radiation detector device detects the radiation impinging thereon according to the wavelength.

[0075] The radiation detector device is particularly preferably a spectrometer. Particularly preferably, the radiation detector device outputs a characteristic value representing a specific wavelength. Particularly preferably, this value is output during both the measurement using the surface to be analyzed and during calibration.

[0076] In a further preferred method, at least one calibration (here note that the terms calibration and verification are used synonymously) is used to determine and take into account the aging condition of at least one radiation device.

[0077] In another preferred method, the surface to be analyzed is irradiated with light of different wavelengths and / or with white light.

[0078] In another preferred method, the surface to be analyzed is irradiated from at least two different incident angles.

[0079] In another preferred method, regardless of the quality of the illumination, at least one color measurement value is always substantially constant for a consistent sample. Description of the Drawings

[0080] Further advantages and embodiments are shown in the drawings.

[0081] Shown in the drawings are:

[0082] Figure 1is a view of the device according to the invention;

[0083] Figure 2 is a view of the interior of the device through the measuring opening;

[0084] Figure 3 is an interior view of the device according to the invention;

[0085] Figure 4 is a further interior view of the device according to the invention;

[0086] Figure 5 is a further interior view of the device according to the invention; and

[0087] Figure 6 is a further interior view of the device according to the invention. Detailed Description

[0088] Figure 1 shows an external view of a device 1 according to the invention, which is used for inspecting the optical properties of a surface. The device 1 has a housing 10. In addition, the housing has a receiving opening 38 or a receiving volume for receiving a second calibration element 16 (external calibration element), in particular for storing the second calibration element 16.

[0089] The external calibration element 16 is arranged here on a rotary cover 36. The reference numeral 30 indicates a display device, by means of which, for example, measured values or error states can be displayed. The reference numeral 22 indicates an opening through which the surface to be inspected (not shown) can be inspected with respect to its color and / or with respect to other optical properties such as gloss values. Preferably, light can only enter the interior of the housing 30 via this opening 22.

[0090] In Figure 1 the embodiment shown, the device has a pressure device 35, which here has a rotary arm 32 on which a pressure element 34 is arranged for pressing a sample against the opening 22. The pressure device 35 can be retracted or lowered into a recess 36 of the housing. In one embodiment, a first calibration element can be arranged on the sealing device 35. However, preferably, the second calibration element is arranged inside the housing 10.

[0091] Figure 2 shows a view into the interior of the housing through the opening 22. In particular, this is a vertical view through the measuring opening 22, for example from above. Here, the optical block of the color measuring device can be seen, which preferably also has a dosing fluorescence measuring device and / or a gloss measuring device.

[0092] A large number, or more precisely ten, first radiation devices or light sources 2a, 2b, 2c are provided here. These first radiation devices or light sources 2a, 2b, 2c are each white light LEDs, and the white light LEDs are used for irradiating color measurement. These light sources 2a, 2b, 2c are preferably arranged in such a way that these light sources 2a, 2b, 2c enable irradiation of the surface, i.e., the surface to be analyzed, at 45°.

[0093] Reference numerals 2d, 2e, 2f denote several other light sources, and several other light sources particularly apply colored light to the surface. This can be achieved by using colored light LEDs. However, white light LEDs can also be and are preferably used here, although with narrowband filtering. Monochromatic LEDs can be regarded as an additional lighting option, and monochromatic LEDs are additionally equipped with a narrowband filter, and the bandwidth of the narrowband filter is narrower than the natural bandwidth of the monochromatic LED.

[0094] Particularly preferably, these light sources 2d, 2e, 2f emit light at different wavelengths, especially light in the wavelength range of 300–660 nm.

[0095] Reference numeral 4 indicates a radiation detector device, and particularly indicates a spectrometer. The radiation detector device is adapted and intended to record the light from the irradiation devices 2a - 2f or the light reflected from the surface (not shown).

[0096] Reference numeral 12 indicates a preferably available second radiation device, and the second radiation device is also used for irradiating light onto the surface to be inspected (not shown). The light is reflected by the surface and can thus reach the second radiation detector device 13. Preferably, the second radiation device and the second radiation detector device 13 form a gloss measurement device.

[0097] Figure 3 An internal view of the device described here is shown. An internal first calibration element 6 is shown, and the internal first calibration element 6 is arranged on a holder 62 and can be rotated relative to the rotation axis S to a position where the internal first calibration element 6 is not located in the light beam path (shown in Figure 3 ) and rotated to a position where the internal first calibration element 6 is positioned against the opening 22 from the inside ( Figure 4 ).

[0098] Reference numeral 41 indicates a tubular element through which radiation can be guided onto the radiation detector device (not shown). Reference numeral 45 identifies an optical device, such as a lens, which is used for focusing the radiation hitting the radiation detector device.

[0099] Reference numeral 52 characterizes the housing part adjacent to the opening 22. This housing part is particularly radiation - absorbing, and the color of this housing part is particularly black.

[0100] Reference numeral 32 schematically identifies a processor device which, among other things, is used to control the device 1 and is also used to determine or change a calibration factor. Reference numeral 34 identifies a memory device which is particularly used to store the calibration factor.

[0101] Figure 4 A diagram of a device according to the invention is shown, by means of which a first calibration element 6 here, i.e. an internal standard, is rotated into a position where calibration can be performed.

[0102] Reference numeral 27 indicates an optical block in which the respective radiation devices 2a - 2c and 2d - 2f are arranged.

[0103] Figure 5 A further diagram of a device according to the invention is shown. Here, a radiation detector device 4 and a channel 41 are shown, through which the radiation is guided to the radiation detector device 4. In addition, the opening 22 is shown again, which is closed here and in which the first calibration element 6 points downwards, i.e. in the direction of the radiation detector device 4.

[0104] Figure 6 A bottom view of the device shown in Figure 5 is shown. Here, a further radiation detector device 13 is shown which is particularly used to measure or perform a gloss measurement. The first radiation detector device 4 is also shown again.

[0105] The applicant reserves the right to claim all features which are essential to the invention as disclosed in the application documents, provided that all features are novel compared to the prior art, either individually or in combination. It should also be noted that the individual figures also describe features which may be advantageous per se. A person skilled in the art will immediately recognize that the specific features described in the figures can be advantageous even without adopting additional features from the figures. In addition, a person skilled in the art will recognize that advantages can also result from a combination of several features shown in a single figure or in different figures.

Claims

1. An apparatus (1) for inspecting the optical properties of a surface, having: a housing (10); a first radiation device (2a, 2b, 2c), arranged within the housing (10), adapted and intended to emit radiation and in particular light onto the surface to be inspected; a first radiation detector device (4), arranged within the housing (10), adapted and intended to receive the radiation that has been emitted onto the surface to be inspected and has been reflected and / or scattered by the surface, wherein, the housing (10) has an opening (22) through which the first radiation device (2a) emits radiation onto the surface, and wherein the apparatus includes a first calibration element (6) which, instead of the surface to be inspected, can be arranged such that the radiation that has been emitted from the first radiation device (2a) onto the first calibration element (6) and has been reflected and / or scattered by the first calibration element reaches the first radiation detector device (4), characterized in that, the apparatus includes a second calibration element (16) which, instead of the surface to be inspected and instead of the first calibration element (6), can be arranged such that the radiation that has been emitted from the first radiation device (2a) onto the second calibration element (16) and has been reflected and / or scattered by the second calibration element reaches the first radiation detector device (4).

2. The apparatus (1) according to claim 1, characterized in that, one of the calibration elements (6) can be arranged within the housing (10) and preferably can be moved into the beam path between the first radiation device (2a) and the first radiation detector device (4) within the housing.

3. The apparatus (1) according to at least one of the preceding claims, characterized in that, the apparatus (1) has processor means which detect a first value representing a characteristic of a first calibration measurement using the first calibration element (6), and the processor means detect a second value representing a characteristic of a second calibration measurement using the second calibration element (16), and preferably, a comparison means is provided which compares the first value and the second value.

4. The apparatus (1) according to at least one of the preceding claims, characterized in that, the apparatus (1) is selected from a group of apparatuses (1) including: a color measurement device, a gloss measurement device, an orange peel measurement device, etc.

5. The apparatus (1) according to at least one of the preceding claims, characterized in that, the apparatus (1) has a second radiation device (12) arranged within the housing, the second radiation device being adapted and intended to emit radiation and in particular light onto the surface to be inspected.

6. The apparatus (1) according to at least one of the preceding claims, characterized in that, The device has a gloss measuring device (12, 13), which has an additional radiation device that irradiates radiation onto the surface at a predetermined angle of incidence, and the gloss measuring device also has an additional radiation detector device that detects the radiation irradiated onto the surface by the additional radiation device and reflected from the surface at a predetermined angle, and the angle of incidence and the additional angle are preferably the same.

7. A method for inspecting the optical properties of a surface, wherein, a radiation device (2a) arranged in a housing emits radiation and in particular light onto the surface to be inspected, and a first radiation detector device (4) arranged in the housing (10) receives the radiation irradiated onto the surface to be inspected and reflected and / or scattered by the surface, wherein the housing (20) has an opening through which the first radiation device (2a) emits radiation onto the surface, and wherein the device has a first calibration element (6), and in a calibration mode, instead of the surface to be inspected, the first calibration element is arranged such that the radiation emitted by the first radiation device (2a) onto the first calibration element (6) and reflected and / or scattered by the first calibration element reaches the first radiation detector device (4), characterized in that, in the calibration mode, instead of the surface to be inspected and instead of the first calibration element (6), a second calibration element is arranged such that the radiation emitted from the first radiation device (2a) onto the second calibration element (16) and reflected and / or scattered by the second calibration element reaches the first radiation detector device (4).

8. The method according to the preceding claim, characterized in that, a first value (ca_i) is recorded, which represents the characteristics of a first calibration measurement using the first calibration element (6), and a second value (ca_a) is recorded, which represents the characteristics of a second calibration measurement using the second calibration element (16).

9. The method according to the preceding claim, characterized in that, the first value (ca_i) and the second value (ca_a) are compared with each other, and preferably in consideration of the comparison, an error instruction or information is output to the user.

10. The method according to at least one of the preceding claims, characterized in that, a calibration value is changed in consideration of at least one of the values.

11. The method according to at least one of the preceding claims, characterized in that, in a working mode, the surface to be inspected is exposed to a plurality of radiation devices.

12. The method according to at least one of the preceding claims, characterized in that, the radiation detector device (4) detects the radiation impinging on the radiation detector device according to the wavelength.

13. The method according to at least one of the preceding claims, characterized in that, at least one calibration is used to determine and / or consider the aging condition of at least one radiation device.

14. The method according to at least one of the preceding claims, Characterized in that, the surface to be inspected is irradiated with light of different wavelengths and / or irradiated with white light.

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