DE19643611A1 - Method of determining colour uniformity of applied toner for printers and copiers - Google Patents

Abstract

The method involves measuring toner markings (4) applied to a carrier medium using a sensor (s). The film thickness of the marker is measured to determine colour uniformity according to a given equation relating the measurement voltage, the thickness of the photosensitive layer (2), the sensor distance, the toner marker, photosensitive layer and ambient medium dielectric constants. The degree of colour uniformity can be determined by measuring the medium without any toner, measuring a toner marking using the same sensor and then comparing the results of the two measurements.

Description

The invention relates to a method and a device for Determination of a degree of coloration in printing and copying directional, concrete areas.

In non-impact printing and copying machines is used for production of a visible image dye or toner on a support dium applied and optionally fixed on this. Here at is between direct and indirect working, a distinction between printing and copying machines. When working directly tendency printing and copying devices, such as Tin ten-beam printers, the image is recorded directly on a carrier generated. With indirectly working printing and knockout pier devices, such as most electro photographic printing and copying equipment, becomes a toner image first on an imaging medium, such as as a photoconductor, generated, then on a Transfer the drawing medium and fix it on it.

An achievable print quality depends in particular on the one degree of coloration of a print or toner image, and thus of the Amount of color transferred to a recording medium substance or toner. Furthermore, for example at full surface Chen, halftone halftone areas, lines, characters u. the The degree of inking of the printed image is kept within certain limits will. Therefore, the degree of coloring of a print or Toner image measured and then with the help of a rulesy stems the color to be applied according to the measurement result amount of substance or toner can be set. According to the The control process can also meet print quality requirements repeated at certain intervals.  

For determining or measuring the degree of coloring of printing or For example, toner images are surface areas targets colored, referred to as print or toner marks will.

A determination or measurement of the degree of coloring of printing or Toner marks can be placed directly on a recording medium and / or an imaging medium such as one Photoconductor drum.

With electrophotographic printing and copying equipment for example, from a two-component developer, i. H. egg nem developer mixture of carrier and toner, the toner from egg ner developer station from transferred to the photoconductor. Here at will depend on the process used the two-component developer of the toner from exposed or non-exposed areas attracted to the photoconductor. The Amount of toner that is attracted to the photoconductor is here among other things, the mixing ratio of the two components ten of the two-component developer and one on the photo parts depending on the applied bias voltage.

To achieve the required print quality, it must be based on the Amount of toner applied to the photoconductor and thus the coloring of a print or toner image exactly within specified limits can be kept, for example because it is black Surface only appears deep black if there is sufficient toner brought. On the other hand, thin Do not put too much toner in close lines wear, otherwise the lines run into each other.

It is also for economic as well as ecological reasons not useful or represented for a surface to be colored bar, more toner on the photoconductor than is absolutely necessary to apply or in other words, it should only be in the as much toner is applied as for each ge desired degree of coloring is required.  

For measuring the degree of coloration of printed or toner images in the form of toner marks are optoelectrically operating sensors systems known. When using such sensor systems, a Toner mark with test light, for example with a visible or infrared light, irradiated. Due to different refle xions- and absorption properties of toner brands, which depend on the amount of toner on the toner brand, or one Medium carrying toner is by means of an optoelectric Sensor system the intensity of the reflected or transmit measured light and from this the degree of coloration Right.

The reflected or transmitted light is ei Nes photo receiver, such as a photo resistor, egg ner photodiode or a phototransistor into an electrical Signal implemented. With the help of this electrical measurement signal the amount of toner to be transferred to the photoconductor for example, by changing the mixing ratio of the two Components of a developer mix readjusted.

Optoelectrically operating sensor systems that ei nes degree of inking of toner marks are used, white sen in particular on the disadvantage that by the optical egg properties of the medium carrying the toner, the intensity of the right reflected light and thus that of the optoelectric sensor sorsystem generated electrical signal is affected. Becomes for example the degree of coloration directly on a recording measured in the carrier, ver different types of paper. Similar print image mismatches can be caused, for example, by Fluctuations occur in the photoconductor batches.

Another disadvantage is that with increasing emphasis from Full-surface toner marks the reflected or transmitted The amount of light only decreases until all surface elements the toner mark is completely covered with toner once. A  thereafter increasing, multi-layer allocation of the toner mark no longer leads to completely absorbent toner material changes in the amount of light reflected / absorbed and thus the electrical signal and can therefore be used with optoelek trical sensors are not recognized.

With the help of an optoelectrically operating sensor system thus do not determine how many toner layers or -Layers on top of each other on a toner mark. There one black area already with an average of 1.5 to 2 toners layers is achieved, each leads additionally applied Unnecessarily high toner consumption; however, this can be done no longer fixed by means of an optoelectric sensor system put.

Another disadvantage of optoelectric sensor systems be is that different brands of toner or ver different colored toners also different reflection and Have absorption properties. Therefore is an optoelectric Sensor to the toner used or each colored Customize toner, which can be costly. In extreme cases, optoelectric sensor systems at be correct color toners are not used at all.

In electrophotographic printing and copying equipment, in which light is used for image generation, the on set of optoelectrically operating sensor systems for detection from toner marks to undesired interactions of the test light with the light-sensitive imaging lead. Through such interactions, the Print quality deteriorates and on the other hand the lifespan of the photosensitive imaging medium can be shortened.

The object of the invention is therefore to determine a one degree of coloration generated in printing and copying equipment ten areas to be improved so that the Application of toner is regulated so that the degree of coloration  a toner image in a predetermined narrow tolerance range is held to thereby improve the image quality and optimize toner consumption at the same time.

According to the invention, this object is achieved by the features in Claim 1, 2 or 3 solved. Furthermore, this is according to the Erfin with a device for carrying out the method reached according to claim 9. Advantageous further developments are Subject of further claims.

In the method according to the invention for determining an on degree of coloration generated in printing and copying equipment th, concreted areas are turned on by a sensor their embodiments preferably by means of two sensors, against a toner mark applied on a carrier medium as measured against an unconcerned carrier medium. Around to obtain these measured values are according to the invention as Sen sensors preferably use capacitive sensors, the usual are usually referred to as distance sensors.

In the method according to the invention is based on knowledge assumed that the degree of coloration of a uniformly beto neren or evenly screened concrete area in one fixed, predetermined dependency on the middle integral Toner layer thickness stands. The means of an inventive capacitive sensor measured toner layer thickness is therefore a Measure of the degree of coloring of the concrete areas.

Using such distance sensors according to the invention is particularly advantageous since no capacitive sensors Test light is required; thus, on the one hand, no kick Interactions with the photosensitive imaging dium, and on the other hand it is not necessary to send the sen sor different toner colors or paper types sen. Rather, using a capacitive sensor according to the invention, the layer thickness of the toner is independent of Type of toner or color or independent of a toner  supporting medium, such as a photoconductor or egg paper type.

When using a capacitive sensor in the invention processes in electrophotographic printing and copying directions is preferably the conductive background of a Photoconductor under its photosensitive layer as one of the two capacitor plates used.

According to an advantageous first embodiment of the method according to the invention for determining a degree of coloration of areas in concrete that are produced in printing and copying devices, measurement is preferably carried out by means of a capacitive sensor against a toner mark provided on a carrier medium and a layer thickness d _{T in} accordance with the in order to determine the degree of coloration Equation (1) below determines:

U _{T is} a voltage that was measured by means of the sensor against the toner mark, K is a geometry and charge-dependent sensor constant, d _{P is} the thickness of a photoelectric layer, and d is the distance between the sensor and the photosensitive layer ε _T denotes the dielectric constant of the toner mark, ε _M denotes the dielectric constant of the medium in the environment, and ε _P denotes the dielectric constant of the photosensitive layer.

According to advantageous second and third embodiments of the The inventive method is countered by means of the sensor the unstressed carrier medium and by means of the same sensor against a toner mark applied to a carrier medium or the two measuring processes are carried out with the help of two sensors carried out. Then both will be beneficial  are embodiments of the method according to the invention obtained two measured values compared.

According to a modified further development of both the second and the third advantageous embodiment of the method according to the invention, the comparison of the two measured values obtained is specified in such a way that to determine the degree of inking, the layer thickness d _{T of} the toner mark by means of a differential potential U _Diff , which is the difference in voltage U _T when measuring against a toner mark and a voltage U _oT when measuring against an unstressed area of a carrier medium, using the following Eq. (2) is determined:

Here, K is a geometry and charge-dependent sensor constant, ε _{T is} the dielectric constant of the toner mark and ε _{M is} the dielectric constant of the medium.

If the voltages U _T and U _oT are measured in succession with only one sensor, the sensor is placed in positions such that the voltage U _{oT is measured} against the unstressed area of the carrier medium in a first position, while in a second position the voltage U _{T is} measured against the toner mark applied to a carrier medium. If the two voltages U _T and U _oT are measured in succession using the same sensor, the voltage value measured at appropriate intervals against the non-stressed carrier medium is preferably stored in a memory and called up from it to form the differential potential U _Diff .

According to yet another modified form of the third advantageous embodiment of the method according to the invention is first, for example, using the first sensor and on closing both against each other by means of the second sensor  the unstressed carrier medium as well as against that on the carrier toner medium applied. Here are the two sensors in the transport direction of the carrier medium arranged one behind the other and measure the same at different times concrete or non-concrete surface elements of the Trä germ medium.

To determine the degree of coloration from the two measured values obtained, the layer thickness d _T is then determined in accordance with the equation given above, with the difference that the difference potential U _{Diff is} replaced by a potential U ′ _{Diff in} accordance with the following equation:

where, are tensions, each by means of the first Sensors against the toner mark or against the unstressed area be measured and as well as voltages that are each because by means of the second sensor against the toner mark or the area without concrete is measured.

According to yet another modified embodiment of the second or third advantageous embodiment of the invention, who, starting from a (for example with the aid of a light barrier) fixed starting position of an unstressed carrier medium by means of a sensor at a plurality of measuring points, the respective voltages U _oT present there measured the unstressed carrier medium; the voltage values obtained in this way are stored in a memory. Then, with respect to the same starting position with a part of the plurality of measuring points on the unstressed area, the respective voltages against the stressed areas (for example in the form of toner marks) are measured. Finally, analogously to the process steps described above for determining the degree of coloration from the measurement values obtained, a layer thickness d _T according to Eq. (2) or (2 ').

When using the last-described advantageous further developments of the method according to the invention, in which the voltages U _oT and U _{T are} preferably measured with two separate but structurally identical sensors, measurement errors that would occur, for example, in electrophotographic printing and copying devices can be excluded which a photoconductor drum is used, the axis of which does not run properly. At the same time, this also eliminates measurement errors that would occur in a photoconductor drum with a high impact.

If two identical sensors are provided, they are in accordance with another preferred embodiment of the invention connected with each other. Here the two can be firmly with one another other connected, identical sensors perpendicular to the trans port direction of a carrier medium or perpendicular to the direction of rotation processing a photoconductor drum next to each other or in the trans port direction of the carrier medium or the direction of rotation of the photo conductor drum can also be arranged one behind the other.

As soon as two identical sensors are firmly connected disturbances, for example due to Shocks do not affect the measurement results. If at the firmly connected sensors in the transport direction or arranged one behind the other in the direction of rotation of the photoconductor the measurement results were not falsified even if the fictitious axis of a photoconductor drum did not actually The axis of the photoconductor drum coincides.

Furthermore, any combinations of the two are first possible arrangement of the sensors conceivable.

Depending on the print image to be generated, Connection with the implementation of the method according to the invention Ren preferably use full-surface or halftone toner marks det. Furthermore, with the method according to the invention  the maximum, minimum, or integral layer thickness can be determined.

The measurements are thus carried out in the method according to the invention neither by type or color of the toner nor by optical egg properties of the medium carrying the toner influences or ver fakes. Since the layer thickness and from this also roughly the type number of layers can be determined, the layer thickness can be determined at for example for coloring a black area 1.5 to 2- should be layered, be optimized accordingly. This can the toner consumption with simultaneously optimized print quality be reduced to what is both economical and ecological is very advantageous.

When using the method according to the invention, significantly improve the quality of full-color printing because for example, required toner layer thicknesses depending on the color can be adjusted.

Below are preferred embodiments of the invention with reference to the accompanying drawings in detail explained. Show it:

FIG. 1a is a schematic structure of a preferred exporting approximate shape of an inventive device for egg NEN use in the present methods;

Fig. 1b is an equivalent circuit of the construction shown in Fig. 1a;

FIGS. 2a and 2b are graphs of voltage waveforms at Ver contact to a further preferred embodiment of the device according to the invention with a photoconductor drum runout, and specifically, FIG. 2a a clamping voltage extending in measuring against a untoned Be rich and Fig. 2b shows a voltage waveform at fairs ge against a concrete area of the photoconductor drum with a pitch;

Fig. 3 is a schematic representation of a structure of a further preferred embodiment of the inventive device with the provision of two perpendicular to the transport direction of a carrier medium arranged side by side, and

Fig. 4 is a schematic representation of a construction of yet another preferred embodiment of the device according to the invention with the provision of two sensors arranged one behind the other in the transport direction of a recording medium.

Fig. 1a shows a basic structure of a preferred imple mentation form of a device according to the invention, in which a sensor S is firmly connected to a bracket 1 . The sensor S is arranged at a distance d from the surface of a photosensitive layer 2 , which is provided, for example, on a photoconductor drum. Below the photo-conductive layer 2 there is a conductive, preferably as metallic base 3 , for example the photo conductor drum.

As can be seen from FIG. 1a, the photosensitive layer has a thickness d _P. Furthermore 1a is provided opposite to the sensor S on the photosensitive layer 2, a toner mark 4 having a thickness d _T Fig..

The determination of the thickness d _{T of} the toner mark 4 is explained below with reference to FIG. 1 b, which shows an equivalent circuit diagram of the structure shown in FIG. 1 a. The uppermost capacitor in the equivalent circuit picture with a capacitance C _M corresponds to the area between the sensor S and the toner mark 4 in FIG. 1 a. The light gray middle capacitor with a capacitance C _T corresponds to the toner mark 4 and the dark gray capacitor with a capacitance C _P corresponds to the photosensitive layer 2 .

The total capacitance C of the equivalent circuit diagram or the arrangement shown in FIG. 1a can thus be calculated according to equation Eq. Calculate 1a.

By inserting the distances d, d _T and d _P defined above and the corresponding dielectric constants ε _M , ε _t and ε _P , namely ε _{M of} the medium between sensor S and toner mark 4 , ε _{T of} the toner mark 4 and ε _{P of} the photosensitive layer , and by introducing a geometry and charge-dependent sensor constant K, the voltage U _T measured by the sensor against the toner mark 4 by Eq. 1b represent as:

Accordingly, the _voltage measured by the sensor U _oT against a non-concrete surface, ie a surface without toner (oT) by Eq. 1c represent as:

By reshaping Eq. 1b and insertion in Eq. 1c can the layer thickness d _{T of} the toner mark 4 by Eq. Represent (1) as follows:

If, when using the device according to the invention, the voltage _values U _T and U _{oT are} present, the difference potential U _Diff can be used to determine the two voltages U _T and U _oT, ie U _Diff = U _T - U _oT from the equations. 1b and 1c the layer thickness d _{T of} the toner mark 4 according to the considerably simpler Eq. 2 calculate as:

FIGS. 2a and 2b show schematic voltage profiles that are using a capacitive sensor or capacitive sensors Sen with respect to a photoconductor drum runout gemes sen. Here, in the graphs of FIGS. 2a and 2b is applied, the time on the ordinate represents a voltage V and on the abscissa.

The sinusoidal line in FIG. 2a shows a voltage curve U _oT which a sensor measures when the measurement is carried out directly against an unstressed photoconductor drum. In contrast, FIG. 2b additionally shows a voltage curve U _oT which is superimposed on that shown in FIG. 2a. The voltage curve in Fig. 2b is obtained when the measurement is made against a concreted area of the photoconductor drum, preferably against a toner mark 4 (see Fig. 1a).

Since the height of the photoconductor drum causes a cyclical, repetitive change in distance between the sensor and the photoconductor drum, an electronic measurement value storage can be carried out. With the help of the measured voltages U _oT and U _T , the layer thickness d _{T of} the toner mark 4 can then be clearly determined.

Fig. 3 shows a schematic representation of a structure of a further preferred embodiment of the device according to the invention. In Fig. 3, two sensors S ₁ and S _{2 are} preferably firmly connected to one another and arranged side by side perpendicular to the direction of rotation of the photoconductor drum 3 . Here, the direction of rotation 3 runs in the schematic representation of FIG. 3 on the viewer of FIG. To what mel under the Fotoleitertrom is indicated by a provided in a circuit section 3, through which the tip of the direction of rotation indicate the arrow a shown is .

As can be seen in FIG. 3, the sensor S _{1 is arranged} opposite an unstressed area of a carrier medium in the form of the photoconductive layer 2 , while the second sensor S ₂ is arranged opposite a toner mark 4 . The measured by the sensors S ₁ and S ₂ voltage waveforms D ₁ and D _2, che wel the voltage waveforms of FIGS. 2a and 2b correspond who created the to the two inputs of a differential member 5. At the output of the differential element 5 , the temporal course of the voltage U _{Diff is shown} , which according to Eq. ( 2 ) is proportionally proportional to the layer thickness d _T to be determined.

In Fig. 4, a further schematic representation of a construction of a preferred embodiment of the device according to the invention is shown, in which, in contrast to the construction in Fig. 3, the two, preferably also firmly connected sensors S ₁ and S ₂ in the trans port direction a carrier medium or in the direction of rotation of the photoconductor drum 3 are arranged one behind the other. Here, the direction of rotation is indicated by the arrow a, which is entered under the photoconductor drum 3 and points to the right.

The one behind the other by means of the two in Fig. 4 arranged sensors S ₁ and S ₂ received voltage curves D _'1 and D' ₂ ent to the voltage characteristic shown in Fig. 2b, wherein the sinusoidal voltage U _oT speak the measured against the toner mark voltage U _T is superimposed. As is shown by the dashed lines between the two diagrams D ' ₁ and D' ₂ , the two of the sinusoidal voltage U _{oT are superimposed} on one _another over voltage _values U _T.

In the direction indicated by the arrow a in Fig. 4 rotational direction of the photoconductor drum 3, the gemes means of the sensor S ₁ sene voltage U _T is located in front of the measured by the sensor S _2, the same large voltage U _T.

In FIG. 4, however, the distances of the voltage values U _T are shown greatly distorted. How strong the distortion is really Lich can be seen from the fact that, for example, a toner mark 4 applied to the photoconductor drum is a square with a side length of 3 mm, while the scope of a photoconductor drum may well be, for example, 750 mm. In the diagrams D ' ₁ and D' ₂ , the sinusoidal course of a complete sine curve corresponds to a single rotation of a photoconductor drum, for example with the drum circumference of 750 mm specified above.

Analogously to the arrangement in FIG. 3, the voltage profiles D ' ₁ and D' ₂ obtained by the sensors S ₁ and S ₂ are also applied to the differential element 5 in FIG. 4. The voltage curve D ' ₃ corresponds to the difference between the voltage curves D' ₁ and D ' ₂ , the peaks pointing up and down the voltage values

and

 represent.

With the help of two sensors S ₁ and S ₂ , which are arranged in the transport direction of a carrier medium or in the direction of rotation of a photoconductor drum, or which are arranged perpendicular to the transport direction of the carrier medium or perpendicular to the direction of rotation of the drum, can, as explained in detail above, a vertical run of the photoconductor drum be fully compensated. However, vibrations acting on the copying and printing device have no effect on a measurement only if the two sensors S ₁ and S _{2 are} firmly connected to one another, since then the vibrations affect both sensors in the same way and therefore no measurement errors arise.

However, if a fictitious axis of a photoconductor drum encloses an angle with the actual axis course, this non-alignment of the fictitious and the actual axis by means of sensors S ₁ and S _{2 which} are firmly connected to one another only has no effect if the sensors with respect to the direction of rotation of the photoconductor drum are arranged one behind the other.

In addition, temperature fluctuations due to the Ver be compensated by two sensors, since both Senso be influenced equally strongly if they are only slightly Distance from each other or even fixed to each other are connected.

Claims (19)

1. A method for determining a degree of coloration of areas in concrete produced in printing and copying, in which

• a) is measured by means of a sensor (S) against a toner mark ( 4 ) applied to a carrier medium, and
• b) to determine the degree of coloration, a layer thickness d _{T of} the toner mark according to Eq. (1) is determined:
  in which
  U _{T is} a voltage measured against the toner mark ( 4 ) by means of the sensor (S),
  K is a geometry and charge dependent sensor constant,
  d _P the thickness of a photosensitive layer ( 2 ),
  d the distance of the sensor (S) from the photosensitive layer ( 2 ),
  ε _T the dielectric constant of the toner mark ( 4 ),
  ε _M the dielectric constant of the medium in the environment, and
  ε _{P are} the dielectric constant of the photosensitive layer ( 2 ).

2. A method for determining a degree of coloration of areas in concrete, generated in printing and copying equipment, in which

• a ₁ ) is measured by means of a sensor (S) against the non-stressed carrier medium,
• a ₂ ) is measured by means of the same sensor (S) against a toner mark ( 4 ) applied to a medium, and
• b ₁ ) to determine the degree of coloration, the two measured values obtained are compared with one another.

3. A method for determining a degree of coloration of areas in concrete produced in printing and copying, in which

• a ₁ ') is measured by means of a first sensor (S ₁ ) against an unstressed carrier medium,
• a ₂ ') is measured by means of a second sensor (S ₂ ) against a toner mark ( 4 ) applied to the carrier medium, and
• b ₁ ) to determine the degree of coloration, the two measured values obtained are compared with one another.

4. The method according to claim 2 or 3, in which after the steps
a ₁ ) and a ₂ ) or a ₁ ') and a ₂ ')

• b ₂ ) to determine the degree of coloration from the two measured values obtained, a layer thickness d _T according to Eq. (2) is determined:
  withU _Diff = | U _T - U _oT | where
  U _{Diff is} a differential _potential
  U _{T is} a voltage which is measured by means of the sensor (S) or the second sensor (S ₂ ) against the toner mark ( 4 ),
  U _{oT is} a voltage that is measured by means of the sensor (S) or the first sensor (S ₁ ) against an unconcrete surface,
  K is a geometry and charge dependent sensor constant,
  ε _{T is} the dielectric constant of the toner mark ( 4 ), and
  ε _{M is} the dielectric constant of the medium in the environment.

5. The method according to claim 3, in which instead of the steps te ₁ ') and a ₂ ')

• a ₃ ) is measured by means of the first sensor both against the unstressed carrier medium and against the toner mark applied to the carrier medium;
• a ₄ ) is measured by means of a second sensor both against the unstressed carrier medium and against the toner mark applied to the carrier medium, and
• b ₃ ) to determine the degree of coloration from the two measured values obtained, a layer thickness d _T according to Eq. (2 ') is determined:
  With
  in which
  U ' _{Diff is} a differential _potential
  is a voltage which is measured by means of the first sensor (S ₁ ) against the toner mark,
  is a voltage which is measured by means of the first sensor (S ₁ ) against the unstressed area,
  is a voltage which is measured by means of the second sensor (S ₂ ) against the toner mark,
  is a voltage which is measured by means of the second sensor (S ₂ ) against the unstressed area,
  K is a geometry and charge dependent sensor constant,
  ε _{T is} the dielectric constant of the toner mark, and
  ε _{M is} the dielectric constant of the medium in the environment.

6. The method according to any one of claims 2 to 5, characterized in that instead of steps a ₁ ) and a ₂ ) or a ' ₁ ) and a' ₂ )

• a ₄ ) starting from a defined starting position of an unconcreted carrier medium by means of a sensor ( 2 ), the respective voltages U _{oT are} measured at a plurality of measuring points and the voltage values obtained are stored in a memory;
• a ₆ ) then, based on the same starting position of the carrier medium with respect to a part of the plurality of measuring points on the unconcentrated carrier medium, the respective voltages (U _T ) against concreted areas (toner marks) are measured, and
• b ₄ ) to determine the degree of coloring from the measurement values obtained, a layer thickness d _T according to Eq. (2) or (2 ') is determined.

7. The method according to any one of claims 2 to 6, in which steps a ₁ ') and a ₂ ') are carried out simultaneously by means of two sensors. 8. Device for performing the method according to one of the preceding claims, characterized in that ka capacitive sensors and a processing unit are provided as sensors (S) or sensors (S ₁ , S ₂ ). 9. Device according to claim 8, characterized records that a sensor plate of each capacitive Sen sors (S, S1, S2) formed by a conductive background is. 10. Device for performing the method according to one of the Claims 3 or 7, characterized in that that the two sensors are perpendicular to the direction of transport of the carrier medium are arranged side by side and a Ver unit of work is provided. 11. Device for performing the method according to one of the Claims 3 or 7, characterized in that that the two sensors in the transport direction of the Trä Germediums are arranged one behind the other and a processing unit is provided. 12. Device according to one of the preceding claims, there characterized in that the two sensors are firmly connected.   13. Means for performing the method according to one of the An sayings 1 to 7, characterized, that a full-surface toner mark is read as the toner mark hen is. 14. Means for performing the method according to one of the An sayings 1 to 7, characterized, that a raster toner mark is provided as the toner mark is. 15. Means for carrying out the method according to one of the An Proverbs 1 to 7, in which a record as the carrier material Mungträger is provided. 16. Means for performing the method according to one of the An Proverbs 1 to 7, in which an image as the carrier material generating medium is provided. 17. Use of the method according to one of claims 1 to 7, to determine a maximum layer thickness. 18. Use of the method according to one of claims 1 to 7, to determine a minimum layer thickness. 19. Use of the method according to one of claims 1 to 7, for determining an integral layer thickness.