Electrophotography – Image formation – Transfer
Reexamination Certificate
2000-08-24
2001-09-04
Grainger, Quana M. (Department: 2852)
Electrophotography
Image formation
Transfer
C226S042000
Reexamination Certificate
active
06285850
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a duplex printer and to a method of duplex printing.
BACKGROUND TO THE INVENTION
In a duplex web-fed printer such as described in United States patent U.S. Pat. No. 5,805,967 (De Bock et al. / Xeikon NV), and European patent specification EP 0871082 (Xeikon NV), moving transfer surfaces in the form of transfer belts carry toner particle images to transfer stations at which the images are transferred to opposed faces of a paper web. The paper web passes through nips at the transfer stations.
It is often desirable to ensure registration of the image printed on one face of the web with the image printed on the opposite face of the web. This can be particularly the case when the web is formed of a transparent or semi-transparent material and/or perforations or other physical modifications extending through the web material need to be aligned with specific parts of both images.
It is an objective of the present invention to enable such back-to-back registration to be achieved in a simple manner.
SUMMARY OF THE INVENTION
We have now discovered that this objective, and other useful benefits, can be obtained when a separate drive device is provided for the web, sensors are used to sense the movement of the transfer surfaces and the movements of the transfer surfaces and of the web are controlled in response to signals received from the sensors.
Thus, according to a first aspect of the invention there is provided a duplex printer comprising:
a first transfer surface drive device for driving a first transfer surface carrying a first toner particle image to a first transfer station at which the first toner particle image is transferred to one face of a substrate web; and
a second transfer surface drive device for driving a second transfer surface carrying a second toner particle image on the second transfer surface to a second transfer station at which the second toner particle image is transferred to the opposite face of the substrate web; characterized by
a web drive device for driving the substrate web along a substrate web path through the first and second transfer stations;
a first transfer surface movement sensor for sensing movement of the first transfer surface;
a second transfer surface movement sensor for sensing movement of the second transfer surface;
a control device for controlling the first, second and transfer surface drive devices and said web drive device in response to signals received from the first and second transfer surface movement sensors thereby to ensure desired registration between the first and second images at a desired location on the substrate web.
According to a second aspect of the invention, there is provided a method of duplex printing comprising:
driving a first transfer surface carrying a first toner particle image to a first transfer station at which the first toner particle image is transferred to one face of a substrate web; and
driving a second transfer surface carrying a second toner particle image on the second transfer surface to a second transfer station at which the second toner particle image is transferred to the opposite face of the substrate web; characterized by
driving the substrate web along a substrate web path through the first and second transfer stations;
sensing movement of the first transfer surface;
sensing movement of the second transfer surface; and
controlling the movements of said first and second transfer surfaces and the substrate web in response to signals received from the first and second transfer surface movement sensors thereby to ensure desired registration between the first and second images at a desired location on the substrate web.
In the prior art duplex web-fed printers, such as that described in United States patent U.S. Pat. No. 5,805,967, the paper web passes through nips at the transfer stations so that it is the movement of the transfer members on which the transfer surfaces are located which drives the web. At the start up of the printer, initial movement of the transfer members causes initial movement of the web. As a result, the initial images are printed at some distance from the leading end of the web, i.e. there is a significant waste of web material. Such waste is undesirable.
According to a preferred aspect of the present invention, at start-up of the printer, movement of the substrate web is delayed to ensure the positioning of the first and second images at a predetermined location on the substrate web. For example, at start-up of the printer, initial movement of the transfer surfaces occurs while the substrate web is stationary and separated from the transfer surfaces at the transfer stations.
The first and second transfer members may be positioned in opposition to each other to form a transfer nip therebetween, through which the substrate path passes. Alternatively, the first and second transfer members are spaced from each other, each being provided with a respective counter pressure roller to define a nip or contact region through which the substrate passes. A more consistent output quality can be obtained if the substrate web wraps partially around the pressure roller both in advance of and following the transfer nip and the temperature of the pressure roller is controlled. Preferably, the printer further comprises means for controlling the pressure exerted by the pressure roller at the transfer nip. A suitable pressure is from 0.1 to 1.0 N/mm
2
, depending upon the materials of which the pressure roller, the transfer member and the substrate are formed, and this pressure may be controlled by mounting the pressure roller in a movable manner by way of adjustable springs or by the use of a controllable linear motor.
The substrate path preferably has a wrapping angle about the pressure roller of at least 10° in advance of the transfer nip. With a smaller wrapping angle, the substrate will only be in contact with the surface of the pressure roller over a short distance before reaching the transfer nip, unless a pressure roller with a large diameter is used. The longer the distance over which the substrate is in contact with the pressure roller, the more complete is the transfer of heat from the pressure roller to the substrate. In general, transfer of heat from the pressure roller to the substrate is more complete when the contact time is high, that is when (i) the wrapping angle is high, (ii) the pressure roller diameter is high, and (iii) the speed of the substrate through the transfer nip is low. The transfer of heat is also influenced by the nature of the material of which the substrate is formed and the surface characteristics of the pressure roller.
The wrapping angle of the substrate path about the pressure roller beyond of the transfer nip need only be small, for example at least 1°. This encourages good separation of the substrate carrying the toner image from the transfer member.
There is no theoretical upper limit to the total wrapping angle, other than that imposed by the geometry of the printer. Usually however a total wrapping angle of up to about 180° will suffice.
The temperature of the pressure roller is preferably controlled to a temperature of from 40 to 100° C., most preferably from 60 to 80°C.
When the second transfer station is downstream of the first transfer station it is preferred that each transfer station has an open position in which the substrate web is separated from the transfer surface and a closed position in which the substrate web makes contact with the transfer surface. The control device may be adapted to control the closure and opening of each transfer station.
Each transfer station may comprises a movable counter roller in rolling contact with the substrate web, the counter roller being movable between a position in which the counter roller forms a nip with the transfer surface, through which nip the substrate web passes, and a position spaced from the transfer surface. The counter roller is preferably movable between the open and closed position along such a path that the substrate web length remain
Dons Kris
Van Weverberg Erik Gabriel Geradus
Grainger Quana M.
Larson & Taylor PLC
Xeikon NV
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