Patent Application
20080112716
The preferred embodiment concerns a method for regulation of the optical density in an electrographic printing method as well as a toner layer thickness measurement system in an electrographic printer or copier.
In electrographic printing methods (which, for example, comprise electrophotographic, magnetographic or also ionographic printing methods), to achieve a desired optical density it is necessary to effect a specific layer thickness of the toner accumulated on the recording carrier material in the developing process.
Given printing with only one color, in particular given printing with black toner, a desired optical density can be achieved in a relatively trouble-free manner due to the strongly opaque character of black. However, given multicolor printing it is very important for a correct color reproduction that the individual colors correspond exactly to a predetermined optical density.
Density measurement sensors can be provided for measurement and regulation of the optical density in an electrographic printing apparatus. For example, measurement arrangements based on a capacitive principle with which the toner layer thickness of electrographically developed toner images or toner layers can be measured for this purpose are known from DE 101 51 702 A1 and from US 2003/0091355 A1.
An electrographic printing or copying apparatus in which a developer station is supplied with fluidized toner via a negative pressure system is known from WO 03/100520.
A printing apparatus in which a temperature and moisture sensor is provided and in which image recording parameters are corrected when the measured values lie outside of predetermined values is known from U.S. Pat. No. 6,463,226 B2.
Further printing apparatuses with a moisture sensor are known from U.S. Pat. No. 6,353,716 and US 2006/0152775 A1. An electrophotographic printing system with a device for estimation of the toner density in a developer mixture is known from US 2006/0018674 A1.
An electrographic printing apparatus in which the latent image is developed with fluid toner is known from US 2003/0175048 A1.
The aforementioned publications are herewith incorporated by reference into the present specification.
It is an object to specify measures for precise measurement of optical density of an electrographically developed image.
In a method or system for regulation of optical density in an electrographic printing method, a toner layer thickness of a toner image developed with a developer station is scanned with a sensor. The resulting toner layer thickness signal is used for regulation of inking in the developer station. A humidity is measured with a moisture sensor and the resulting humidity signal is used for at least one of compensation of moisture-dependent deviations of the toner layer thickness signal and regulation of the inking in the developer station.
For the purposes of promoting an understanding of the principles of the invention, reference will now be made to the preferred embodiment/best mode illustrated in the drawings and specific language will be used to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended, and such alterations and further modifications in the illustrated device and such further applications of the principles of the invention as illustrated as would normally occur to one skilled in the art to which the invention relates are included.
According to the preferred embodiment, the toner layer thickness of a toner image developed with a developer station is scanned with a capacitive sensor. The humidity is additionally measured with a moisture sensor and the humidity signal is used for compensation of moisture-dependent deviations of the toner layer thickness signal and/or for regulation of the inking in the developer station.
The preferred embodiment is based on the realization that the measurement signal of a capacitive toner layer thickness sensor is dependent not only on the toner layer thickness but rather also significantly on the quantity of water molecules accumulated on the surface of the layer thickness. The water molecules have a significantly higher dielectricity constant than the toner and therefore lead to a significantly altered measurement signal.
The preferred embodiment is furthermore based on the realization that, for the accumulation of water molecules in the toner in an electrographic printing method or electrographic printing apparatus, it is advantageously examined in which regions in which toner is transported or otherwise mechanically processed (in particular is stirred) the toner can absorb water molecules. Via the provision of a humidity sensor in such a region it can be determined what water quantity has accumulated in the toner, and with this the later, capacitively measured toner layer thickness signal or, respectively, the corresponding value can be corrected in an analog or digital manner. This in particular applies when there are one or more regions in which the toner can absorb a particularly large amount of water, for example in particularly damp or particularly warm regions of a printing system.
According to an advantageous exemplary embodiment it is provided to implement the moisture measurement at a point in time of the printing process and/or in a region of the printing apparatus in which the toner absorbs moisture particularly well or absorbs a particularly large amount of moisture. It has thereby turned out that this region is not necessarily identical with the region in which the density sensor is located, meaning that (contrary to initial assumptions) the moisture measurement is not reasonable in the region of the density sensor but rather in another region of the printing apparatus remote from the density sensor. It has in particular been shown that the moisture measurement advantageously occurs in a region in which toner is stirred with surrounding air, i.e. in a toner reservoir region, a toner transport region or a toner mixing region.
It has in particular been shown that the toner absorbs a particularly large amount of moisture in a printing system in which toner is fluidized with air and is transported into a developer station via an air pressure system. The humidity is then advantageously measured in a region representative of the toner transport or in a region in which the air is streamed in or admixed with the toner; it was then detected that the moisture accumulating in the toner in such a system significantly accumulates in the toner during the fluidization.
The moisture measurement in particular occurs at a point in time before the toner passes through the development process while the capacitive toner density measurement only occurs after the development process.
The preferred embodiment advantageously enables electrographic printing or copying apparatuses to be operated without climate control, in particular without interior climate control and without climate control in the space surrounding the printer. With the preferred embodiment this can be achieved without having to accept a print quality loss or severe fluctuations in the optical density of the print image. Without climate control such printing processes (in particular in high-capacity printing) can be implemented in a more cost-effective manner.
The scanning of the toner image can occur on an intermediate image carrier (such as a photoconductor drum, a photoconductor belt) or on a transfer element (in particular a transfer belt) momentarily accommodating the toner image, which transfer element is arranged between a photoconductor and a recording medium ultimately carrying the image. The scanning of the toner image or of the toner layer in particular occurs before a process fixing the toner image, in particular before a thermo-printing fixing process, a cold fixing process based on a flash exposure, or another fixing process. The toner image can comprise productively used images or test images (in particular toner markings) that are specifically generated for regulation of the development process.
In a preferred exemplary embodiment, the measured humidity is already used in the sensor arrangement for compensation of climate influences of the capacitive sensor signal. Alternatively or additionally, the humidity signal can be used for regulation of the inking in a regulation unit of the developer station or of the printing apparatus.
In a further preferred exemplary embodiment, a temperature sensor is additionally provided with which the temperature is measured in the same region of the printing process as the moisture, and the temperature signal is likewise used for regulation of the inking in the developer station. Temperature measurement and/or humidity measurement can occur at points of the printing process or printing apparatus that, depending on the printing apparatus, are representative of the moisture absorption of the toner. For example, this could be the region of a toner transport or the development process in the developer station itself or also a reservoir chamber in the developer station in which the toner is stirred for its triboelectric charging.
The temperature sensor and the moisture sensor can be designed as a common, combined climate sensor. A signal for the relative humidity can be emitted as a moisture signal and the absolute humidity at the measurement location can be determined from this signal and the temperature signal. The subsequent corrections to the toner layer thickness signal and/or to the inking regulation can then occur using the absolute humidity.
A correction value for the toner layer thickness signal can be formed on the basis of the moisture signal and the corrected toner layer thickness signal can be used for regulation of the inking. The correction value K can be determined according to the following formula:
K=a×e
b×H
+c,
whereby a, b and c are empirical values dependent on the employed toner, e is the Euler number and H is the absolute humidity.
In a further advantageous exemplary embodiment of the invention, the moisture signal and/or the temperature signal are used for activation or regulation of further method components of the printing process. For example, such components can be the developer station or its corotron voltages, corotron currents, concentration sensors or concentration regulations or also the fixing station.
Temperature measurement and moisture measurement can occur with known methods and sensors. An averaging can be provided to improve the measurement values.
According to the preferred embodiment, a corresponding measurement system and a corresponding printer or copier are also provided.
A toner transport system 10 of a printer or copier is shown in
The sealing device 20 comprises a hopper or funnel 22 into which the toner material 12 slides from the reservoir container 16. The hopper 22 has a hopper outlet 24 that is connected in an air- and toner-tight manner with a tube system 26. The tube system 26 connects the hopper outlet 24 with a buffer 28 that is arranged in proximity to the developer station 14 and in which toner material 12 is buffered or cached for further transport in the developer station 14. The buffer 28 comprises a stirring hoop 30, a fill level sensor 32 and a dosing device 34 that comprises a bucket wheel. A toner transport tube 36 with a toner transport spiral 38 connects the buffer 28 with the developer station 14 and transports toner material 12 from the buffer 28 to the developer station 14 as needed. The quantity of toner material 12 conveyed into the developer station 14 is adjusted and dosed with the aid of the dosing device 34 and/or the transport tube 36, which are respectively connected with a drive device (not shown).
The stirring hoop 30 stirs the toner material 12 in the buffer 28 to maintain the triboelectric charge of the toner mixture. The buffer 28 is air-tight, whereby the space of the buffer 28 (which space is sealed air-tight) is connected with a central negative pressure line 44 via a tube system 40 that comprises a control valve 42. A negative pressure in the central negative pressure line 44 is generated via a negative pressure blower 46. The tube system 40 is connected with an upper segment of the buffer 28. A filter 50 is arranged below connection point 48 towards the sealed chamber. Below this filter 50 the buffer 28 is connected with the tube system 26. The control valve 42 regulates the negative pressure in the tube system 40 as well as in the buffer 28 connected therewith and in the tube system 26. This negative pressure ensures that toner material 12 is transported from the hopper outlet 24 of the sealing device 20 into the chamber of the buffer 28 via the tube system 26.
The quantity of the conveyed toner material 12 can be adjusted in an analog manner with the aid of the control valve 42 in many positions. However, in other exemplary embodiments the control valve 42 can also be operated in a two-point operation, whereby the conveyed quantity of toner material 12 then depends on the negative pressure in the tube system 44 and the opening time of the control valve 42. Hopper 22 has porous, air-permeable hopper walls. Air is sucked out from the sealing device 20 into the hopper 22 via the negative pressure at the hopper outlet 24. A toner-air mixture which has a fluid-like state (what are known as fluid properties) is thereby generated in the hopper 22. This air that, as described, is drawn into the hopper 22 with the aid of the negative pressure is fed into the sealing device 20 via an opening 52. The air fed through the opening 52 can be controlled via a valve (not shown). The hopper outlet 24 is also connected with a tube system 54 with a control valve 56 via which environment air can be fed to the tube system 26. Furthermore, a return valve (not shown) that prevents an escape of toner material even given disadvantageous pressure ratios in the tube systems 44, 26, 54 is furthermore contained in the control valve 56. The quantity of toner material 12 that is conveyed from the container 16 into the buffer 28 can be regulated via the control valve 56.
The control valves 42 and 56 are electrically actuated valves. The negative pressure ratios in the buffer 28 and in the tube system 26 can be exactly adjusted with the aid of the control valve 42. The toner transport from the reservoir container 16 into the buffer 28 is regulated corresponding to the signal of the fill level sensor 32. As already mentioned, the control valve 42 and the control valve 56 serve as control elements of the regulation. The vacuum air required for toner transport is adjusted via these control valves 42, 56. The toner material 12 escaping from the hopper outlet 24 is carried away by the air current in the tube system 26, 54 and is transported to the buffer 28. The filter 50 in the buffer 28 prevents the further transport of the toner material 12 in the tube system 40.
After the closing of the valve 42 the clean air side of the filter 50 is aerated at environment pressure. A negative pressure relative to the environment pressure in the tube system 40 is thereby at least temporarily in the buffer 28. Given the following pressure compensation between the tube system 40 and the buffer, air flows from the tube system 40 through the filter 50 into the buffer 28. The air flow given this pressure compensation is directed counter to the air flow upon intake of the toner material. Toner material 12 settled on the filter 50 is detached from the filter 50 via the air flow upon pressure compensation and falls into the buffer 28. A potentially possible escape of toner material 12 via the tube system 54 is prevented by the return valve 56. As already mentioned, the toner material 12 is transported from the buffer 28 into the developer station 15 with the aid of a transport tube 36. The transport tube 36 protrudes with one end into the developer station 14 and has wide openings on an underside 57 at this end, through which wide openings the toner material 12 falls from the transport tube 36 into the developer station 14.
The transport spiral 38 contained in the transport tube 36 has an incline such that the toner material 12 in the transport tube 36 is transported from the buffer 28 towards the developer station 14, similar to as in a screw conveyer tube. As already mentioned, the transport spiral 38 is driven with the aid of a drive unit. The dosing device 34 comprises a bucket wheel-like roller that is arranged between the buffer 28 and the transport tube. Such a dosing device 34 is also designated as a cell wheel sluice. The bucket wheel-like roller seals the buffer 28 nearly airtight from the transport tube 36, such that air is sucked from the tube system 26 with the aid of the negative pressure blower 46 upon generation of a negative pressure. The bucket wheel-like roller is advantageously driven synchronously with the transport spiral 38, whereby given a rotation of the bucket wheel-like roller (which is also designated as a cell wheel) toner material falls from the buffer 28 into the bucket chambers or cells and is transported downward to the transport tube 36 via the rotation.
Below the dosing device 34, the transport tube 36 has an opening at the top to the dosing device 34 so that the toner material 12 falls downward from the cells into the transport tube 36. The stirring hoop 30 inside the buffer 28 is driven with the aid of a drive unit (not shown) and, via a rotation, prevents a void formation or cornice formation in the toner material 12 of the buffer 28.
Moisture sensor 107 and temperature sensor 108 can in particular be designed as a combined climate measurement apparatus in a common housing, and their measurement values can, for example, also be transferred digitally and/or via a common data connection. The development controller 109 processes the signals of the sensors 106, 107 and 108 and from these forms a compensated toner layer thickness signal that is used for the control variables for inking in the developer station 14. The compensated signal can be determined computationally or by means of look-up tables (LUTs). The control variables for the developer station can thereby also directly arise from corresponding signal values of the sensors and other development parameters using combined formulae and/or look-up tables. As an alternative to the formation of a compensated signal in the sensor controller, the compensated signal can also be formed in a sensor circuit 110 that is connected between the sensor 106 and the development controller 109 and receives and processes the data or signals of the moisture sensor 107 and of the temperature sensor 108 as additional input data.
The water content in the toner is dependent on the absolute water content of the air. For correction of the sensor signals of the capacitive sensor it is thereby advantageous to detect and use for correction not only the relative humidity but rather also the air temperature. The absolute humidity can then be determined from these two values and the compensation of the toner layer thickness signals of the capacitive sensor can occur with higher precision.
In particular sensors as they are described in the aforementioned DE 101 51 702 A1 or, respectively, US 2003/0091355 can be used as capacitive sensors. For this purpose these publications are again explicitly incorporated at this point of the present specification.
Presented in
The step S6 can implement (computationally or via corresponding look-up tables) the following adaptation or compensation function for the correction value K:
K=a×e
b×H
+c, whereby
a, b, c are empirical values dependent on the employed toner, e is the Euler number and H is the absolute humidity.
For example, the following values have proven to be suitable for a black test toner: a=−213, b=−0.24 and c=32.
The parameters for other toners can easily be empirically determined from the correlations shown in
An exemplary embodiment for measurement value compensation that can be applied in addition to or as an alternative to the embodiment presented in
The invention was described using exemplary embodiments. It is thereby clear that the average man skilled in the art can specify suggested developments and modifications. For example, it can be provided to provide moisture sensors in various regions in one and the same printing process or printing device and to empirically or calculationally determine the total water quantity comprised in the toner from the measurement values of the various sensors.
For example, the invention can be used in a printing device that, as described in
While a preferred embodiment has been illustrated and described in detail in the drawings and foregoing description, the same is to be considered as illustrative and not restrictive in character, it being understood that only the preferred embodiment has been shown and described and that all changes and modifications that come within the spirit of the invention both now or in the future are desired to be protected.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2006 053 843.9 | Nov 2006 | DE | national |
