Electrophotography – Control of electrophotography process – Control of transfer
Reexamination Certificate
2001-07-23
2003-01-07
Braun, Fred L. (Department: 2852)
Electrophotography
Control of electrophotography process
Control of transfer
C399S302000
Reexamination Certificate
active
06505015
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention is directed to an electrographic printer device with at least one printing unit having a toner image carrier on whose circumferential surface toner can be applied according to an image-like distribution.
2. Description of the Related Art
Such a printer device is utilized in a printer or copier, whereby a latent image is applied on the toner image carrier with the assistance of an electrographic method. This can ensue, for example, by illuminating a photoconductor or by magnetizing a magnetically sensitive layer. Toner agglomerates to the latent image according to the image-like distribution of the electrical charges or of the magnetic poles. This toner is transferred onto a carrier material, generally paper, at a transfer printing location and is fixed thereon later.
An apparatus with such a printer device should work fast and be flexibly employable. Often, toner images must be printed onto a form that has form windows into which individual characters are to be printed. The characters must thereby be positioned exactly within the form windows. Given multi-color printing, the individual chromatic sub-images must be congruently printed in order to generate a multi-color image. All of this makes high demands of the mechanism.
European Patent Document EP 0523870 discloses a printer device wherein a plurality of sub-images of different colors are generated successively and spaced from one another on a photoconductor band. The sub-images are individually transferred onto a sheet-shaped recording medium at a transfer printing location, whereby the recording medium is repeatedly conducted past the transfer printing location such that the sub-images are transfer-printed as congruently as possible. The spacing of two successive sub-images is equal to the circumference of the rollers on which the photoconductor runs or to a multiple thereof, whereby the individual rollers respectively have the same circumference. A non-uniform rotational motion, for example due to an eccentricity of the roller axes, then has the same effect in all sub-images, so that the congruently transfer-printed sub-images yield a full-color image without color errors.
Given the known printer device, a slippage can occur between the drive rollers and the photoconductor band. For example, the unrolled circumference of the drive roller in a revolution is longer than the distance by which the photoconductor band moves forward. Moreover, the mechanics at the transfer printing locations can change. When printing on a form, for example, it is important that the toner image is printed in predetermined sections of the form. The slippage between the photoconductor band and the drive rollers is not constant but can change due to external influences such as, for example, temperature or atmospheric humidity or as a result of aging. The changes in the mechanism at the transfer printing locations are also dependent on external influences. These changes are difficult to determine. When the toner images can no longer be precisely printed onto the form due to a slippage or a modifications of the mechanics, this is often only noticed later and leads to rejects.
German Patent Document DE 198 21 218 shows a printer device wherein the differently colored sub-images are to be congruently transfer-printed onto a transfer band. For this purpose, a number of marks which are detected when they pass by a sensor are arranged at the transfer band. The detection signal of the marks is kept in a fixed phase relation with a line synchronization signal by controlling the circumferential speed of the transfer band. This requires a substantial circuit outlay.
Another printer device wherein differently colored sub-images are congruently transfer-printed is disclosed by the German Patent Document DE 198 06 551. Given this printer device, one mark for each sub-image is printed onto a paper web as the recording medium. The reflectivity of the marks congruently printed on top of one another is measured for checking the alignment of the individual sub-images relative to one another. The drive of the individual printing units is regulated on the basis of this check result. This printer device, too, requires considerable circuit outlay. A positionally exact printing in a form window cannot be achieved given this known printed device.
Given a printer device disclosed by the German Patent Document DE 38 08 620, the leading edge of a sheet-shaped recording medium is detected with a sensor and the feed of the recording medium is controlled dependent on this detection.
Although a positionally exact printing in a form window can thereby be achieved given a sheet-shaped recording medium, this does not lead to the desired outcome given a band-shaped recording medium.
European Patent Document EP 0 281 055 recites a printer device wherein a position sensor for a drum is provided. This printer device, too, can only be employed for sheet-shaped recording media.
Patent Abstracts of Japan JP-A-06027829 discloses components of a printer device wherein a mark is applied on a transfer band, the mark being moved past a sensor together with the transfer band. The passing of the mark is acquired with the assistance of a controller and the rotational speed of the transfer band is identified. Dependent on the result of the determination of the rotational speed, a drive motor is influenced with the assistance of a further controller in order to correct this rotational speed of the transfer band to a predetermined value. It is assured in this way that the transfer band maintains a predetermined rotational speed.
SUMMARY OF THE INVENTION
An object of the PRESENT invention is to provide a printer device that recognizes a transfer of toner images that is not in proper order.
This object is achieved by an electrographic printer device with at least one printing unit having a toner image carrier on whose circumferential surface toner can be applied according to an image-like distribution, whereby the toner image carrier has a photoconductor, whose outer circumferential surface can be charged with a latent charge image, and a transfer band onto which the toner present on the photoconductor can be transferred at a first transfer printing location, a carrier material is conducted past the transfer band such that the toner arranged thereon can be transferred onto the carrier material at a second transfer printing location, a printing mechanism for generating the toner image and that prints at least one mark onto the photoconductor is arranged along a circumferential section of the photoconductor, at least one sensor that acquires the passing of the mark is arranged at the transfer band, a controller determines the transit time of the mark from the printing time of the printing mechanism up to the acquisition time at the sensor, and whereby the transport of the band-shaped carrier material is influenced in controlling fashion dependent on the transit time.
In the invention, the mark moves with a constant speed from the acquisition time until the transfer printing time in the steady state. The time that the toner image requires until the transfer printing onto the carrier material can therefore be calculated from the transit time. When the printing quality deteriorates as a consequence of a change in the slippage, for example due to a modified ambient temperature, this change in slippage also causes a change in the transit time that is monitored by the controller. A change in the slippage is thus indirectly recognized and the printing event can be correspondingly controlled. For example, the transport of the carrier material can be influenced in a controlling fashion dependent on the transit time, for example by halting the printing operation or by readjusting the transport velocity.
In a development of the invention, the transit time is compared to a predetermined rated value, a signal being generated when the latter is upwardly or downwardly transgressed. Given a deviation from the predetermined rated value, the sli
Kopp Walter
Winter Hans
Braun Fred L.
Oce Printing Systems GmbH
Schiff & Hardin & Waite
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