While the present invention can be used in any suitable marking system, it will be described herein for clarity as used in electrostatic marking systems such as electrophotography or xerography.
By way of background, in marking systems such as xerography or other electrostatographic processes, a uniform electrostatic charge is placed upon a photoreceptor belt or drum surface. The charged surface is then exposed to a light image of an original to selectively dissipate the charge to form a latent electrostatic image of the original. The latent image is developed by depositing finely divided and charged particles of toner upon the belt or drum photoreceptor surface. The toner may be in dry powder form or suspended in a liquid carrier. The charged toner, being electrostatically attached to the latent electrostatic image areas, creates a visible replica of the original. The developed image is then usually transferred from the photoreceptor surface to an intermediate transfer belt or to a final support material such as a paper sheet. When the paper is fed to the system from a paper stack of a feeder mechanism, some papers could be off the home position by many mm and these fed paper sheets need to be deskewed and laterally registered option (1) into position prior to placement on the transport belt or option (2) into position before contacting the image on the photoconductive surface. This is necessary because as the sheets move to the transfer station and approach the imaged photoconductor surface, they need to be in perfect alignment with the toned image on the photoconductive layer for proper image transfer to the sheet to take place.
Thus in a prior art system, the registration carriage moves cross process to perform the lateral registration. There are two issues with this type of design. First, the nips do not separate so the carriage lateral reset must be postponed until there is no paper present (intercopy gap). This reduces the extensibility of the design since the carriage must move only during the intercopy gap. Second, the prior art as implemented allows for the nip forces to produce a non-beneficial reaction force on the lateral move lead screw. The idler nips are loaded against the drive rollers and the nip force is directed perpendicular to the lateral motion. As the nip forces are increased, the load on the lateral registration mechanism is increased causing higher loads at the motor. These forces limit the headroom of the motor system and limit the accelerations possible.
As the paper sheet continues down the transport path, a number of sensors evaluate the positioning of the sheet and convey this information to a controller that will instruct the structure of the present invention on how and when to laterally register the sheet before it reaches the imaged photoconductive surface for image transfer to the sheet. In high speed marking systems, reaction and action time is important. Some prior art registration systems are too slow to be useful in today's high speed systems. Currently, these prior art systems utilize a nip that does not open. This creates an issue that, after its translation of a sheet in the cross process direction, its return to its home position must wait until the sheet leaves the nip. This return must occur in the inter-document zone between the first sheet and the next.
This invention includes amongst others two significant advantages. One is the separation of nips to allow for a lateral reset while the paper is present in the nip space. By separating the nips, the carriage can move to the reset position for the next sheet while the previous sheet is still present at the carriage. This enables higher throughput to be achieved which is extremely important in today's high speed marking systems. The second advantage is the use of a carriage that includes the idler nips and drive nips in a rigid structure. The nip load is then separated from the mechanism controlling lateral motion. As the nip load is applied, no corresponding reaction force is applied to the carriage lead screw or translating system. The reaction load is eliminated and the force/torque required to move the carriage is minimized. This allows for lower torque requirements and improved acceleration rates.