Electrophotography – Image formation – Transfer
Reexamination Certificate
2001-08-29
2003-04-22
Ngo, Hoang (Department: 2852)
Electrophotography
Image formation
Transfer
C399S066000, C399S167000
Reexamination Certificate
active
06553203
ABSTRACT:
FIELD OF THE INVENTION
The present invention is related to an image reproduction system wherein a developed image is transferred from an image-forming member to a receptor material via at least one intermediate transfer member with control of image distortion.
BACKGROUND OF THE INVENTION
In a typical image reproduction system such as a printing or a copying system, a latent image is formed on an image-forming member by image-wise exposure using a known graphical process. The image-forming member can be an endless member such as a drum or a belt. Typical graphical processes include amongst others magnetography, ionography, elcography and electrography, particularly electrophotography. At present electrophotography is the most widespread. In the latter process, a charged latent image is formed on a pre-charged photosensitive member by image-wise exposure to light. The latent image is subsequently made visible on the image-forming member with charged toner at a development zone. After the development of the latent image, the developed toner image is transferred directly to a receptor material. The receptor material can be in the form of a web or in sheet form. In the latter case, the receptor material is preferably on a conveyor. An example of such an image reproduction system is disclosed in European patent EP629924 (Xeikon N.V.). A disadvantage of these direct transfer type of image reproduction systems are the stringent requirements which the recording media have to meet. It is widely known that for instance the electrical and thermal properties of the receptor material and particularly the accurate control of these properties determine to a large extent the quality and reproducibility of the images which are transferred and potentially fixed to the receptor material. The control of these properties, i.e. the conditioning of the medium, can be implemented in various ways, such as e.g. demonstrated in EP629925 (Xeikon N.V.). In general however, to enable the ability to print on a wide range of recording media one has to go first through an elaborate medium qualification procedure and thereafter through a demanding medium condition procedure.
Amongst others, in order to overcome or at least facilitate these procedures, reproduction systems of the new generation are provided with at least one intermediate transfer member between the image-forming member and the receptor material. In such systems the developed image is transferred from the image-forming member to the receptor material via one or more intermediate transfer members, usually in the form of endless belts or drums. A typical example of such a system is disclosed in U.S. Pat. No. 6,047,156 (De Bock et al., Xeikon N.V.). It is a clear benefit that the use of intermediate transfer members obviates the need for the conditioning of the receptor material or at least makes the conditioning less demanding. The use of intermediate transfer members introduces extra image transfer zones, i.e. regions where a first moving image carrying member and a second moving image carrying member contact each other in order to transfer a developed image from the first moving image carrying member to the second moving image carrying member. For instance, the reproduction system as disclosed in U.S. Pat. No. 6,047,156 uses two intermediate transfer members per side and by consequence each developed image has to pass through three transfer zones, being the transfer zones between the image forming member and the first intermediate transfer member (i.e. the primary belt), between the first and the second intermediate transfer member, and between the second intermediate transfer member and the receptor material. One of the problems which may appear at each transfer zone is image distortion and particularly image stretching or shrinking. The term “image distortion” as used herein is intended to include both image size reduction as well as image size magnification. There are a number of parameters which may affect image magnification such as the contact pressure, the temperature and the properties of the respective image-carrying members, such as for instance surface roughness, thickness, elasticity, stiffness and surface energy. But even when all these parameters are properly controlled, the mutual forces in the contact zones exerted by the respective moving image-carrying members on each image carrying member will significantly influence image magnification. These forces are to a large extent determined by the drive and coupling strategy of the image carrying members in the image reproduction system.
OBJECTS OF THE INVENTION
It is an object of the invention to provide an image reproduction system having in operation at least one intermediate image carrying member contacting at least one other image carrying member, wherein these respective image carrying members are driven in a smooth and slipless way in order to control image distortion and particularly image stretching and shrinkage in the transfer contact zone.
It is a further object of the invention to provide an image reproduction system having at least one intermediate image carrying member, wherein during start-up the respective image carrying members are driven and coupled in a smooth and slipless way to control and limit the overall image distortion and particularly image stretching and shrinkage.
SUMMARY OF THE INVENTION
In an aspect of the invention a method is disclosed for controlling image distortion in the transfer contact zone between a first and a second moving image-carrying member, being part of an image reproduction system, by driving said first image-carrying member with a first drive device, capable of speed and torque control, and driving said second image-carrying member with a second drive device, capable of speed and torque control, such that the force exerted by the first moving image-carrying member on the second moving image-carrying member is countered by the force exerted by the second moving image-carrying member on the first moving image-carrying member.
The countering of the force exerted by the first moving image-carrying member on the second moving image-carrying member by the force exerted by the second moving image-carrying member on the first moving image-carrying member is preferably such as to result in a substantially balanced condition. This balancing is preferably achieved by substantially equally dividing the additional load created in the transfer contact zone by engaging said first moving image-carrying member against said second moving image carrying member over said first and said second motor. At start-up, the first and second image-carrying members are disengaged. The first image-carrying member is driven in speed control mode by a first drive device, capable of speed and torque control. The second image-carrying member is driven in speed control mode by a second drive device, capable of speed and torque control. Both image-carrying members are ramped up to about the same predetermined linear speed. As, when coupled, the first image-carrying member will be the “slave” and the second image carrying member will be the “master”, it may be advantageous to drive the first image-carrying member at a slightly higher speed, typically up to 5% higher, compared to the speed of the second image-carrying member. The de-coupled current and voltage values of the drive devices are stored. Then the maximum current of the first drive device is set to a value slightly higher than its de-coupled value. Next, the two moving image-carrying members are coupled thereby creating a transfer contact zone. In a preferred construction, the first and the second image-carrying member pass over respective guide rollers so positioned, in the coupled position of the first image-carrying belt with the second image-carrying belt, to form a transfer contact zone therebetween. At least one of these guide rollers is movable to enable the first and the second image-carrying belt to be de-coupled from each other.
Due to the coupling action, the first drive device goes into a torque cont
Knobbe Martens Olson & Bear LLP
Ngo Hoang
Xeikon International N.V.
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