Patent Application
20110064499
This invention relates to a paper-handling system useful in an electrostatic marking process and, more specifically, to a novel sheet registration device.
This invention includes use in any paper-handling system and the changing or correcting the orientation of the sheets traveling in a sheet transport path. In a marking system, sheets being fed to be marked or printed, sheets being fed for duplex printing, sheets being sent to a stacker and sheets outputted to a finishing station or other modules are all included within the scope of this invention. For clarity and understanding, the sheet registration system of this invention will be described herein in reference to pre-imaging paper feeding in an electrostatic marking systems both color and monochrome.
There have been related sheet registration systems used in the prior art, however, none of them combine effectiveness with acceptable associated costs. In U.S. Pat. No. 7,422,211 B2 (Dejong), a closed loop registration method is disclosed which improves on lateral registration and deskew systems such as that disclosed in U.S. Pat. No. 6,173,952. While effective, both processes involve relatively expensive components especially in high speed marking systems. Dejong's registration system does not use a stalled roll concept whereas use of a stalled roll is an essential part of the present invention.
U.S. Pat. Nos. 7,300,054; 7,303,191 and 7,319,842 issued to Canon disclose various sheet registration systems.
The registration device in color-marking systems has to be able to meet the requirements of Low, Mid and High Entry Production Color (EPC) market. In the Low and Mid EPC market, the machines typically use low cost stalled roll registration devices with front to back registration of 1 to 1.5 mm. The High EPC market requires front to back registration of 0.5 mm with slightly higher Unit Manufacturing Cost (UMC). This invention solves this problem by applying closed loop control of skew and cross process registration to a stalled roll device.
This invention builds on the Xerox color printer's registration module by adding closed loop control for skew correction in addition to the cross process correction. The Xerox registration device uses a stalled roll with a manual skew setup adjustment. Cross process correction is done with a Contact Image Sensor (CIS) and translating the stalled roll registration nip inboard to outboard. This invention closes the loop by adding a second CIS before the stalled roll nip to enable skew measurement and adding a stepper motor to the manual skew adjustment. Also, important to this invention is the combination of closed loop control with a stalled roll registration device. Both of these expedients are essential to the present invention. Proportional feedback from the two CIS devices is used to simultaneously translate and rotate the registration nip to correct cross process registration and skew. A significant advantage of this invention is skew correction done off of the same edge for side 1 and side 2. A stalled roll device deskews side 1 and side 2 with opposite edges of the sheet that can cause a mean skew shift between side 1 and side 2.
As noted earlier, this invention applies the closed loop concept similar to that described in U.S. Pat. No. 7,422,211 but with use of a stalled roll registration device. The stalled roll registration is important to the present invention. The Canon patents do not use stalled roll registration but use the translating and pivoting nip to correct skew and cross process registration. Also, the Canon patents describe open loop corrections without feedback to close the loop as is necessary in the present disclosure.
Stalled roll registration devices have not been known for meeting tight registration targets. The lowest cost stalled roll devices consist of a registration nip that is stopped while a sheet is driven into the nip. An open area upstream of the stalled roll nip allows the paper to buckle, driving the lead edge of the sheet evenly into the nip, deskewing it. The lead edge of the sheet is registered to the image by timing the start of the nip or executing a velocity profile based on the timing from a downstream sensor. Lowest cost stalled roll devices do not have cross process or skew adjustment. In a Xerox method, a motor is used to translate the nip in the cross process direction with a Contact Image Sensor (CIS) to measure the sheet location which is added to provide cross process adjustment. Skew is not adjusted on a sheet by sheet basis. In order to meet a registration target of 0.5 mm front to back, the skew for both sides has to be adjusted on a sheet by sheet basis and off the same edge. Skew is adjusted on opposite edges between the sides allowing the possibility of a mean skew shift. This shift of the skew mean can make it impossible to meet the tight registration specification. This invention builds on the Xerox registration device by adding a second CIS sensor to enable skew measurement and a stepper motor to pivot the registration device for skew adjustment. Closed loop control can be done with a simple proportional control algorithm. The cross process and skew error are measured by the CIS devices and multiplied by a constant to calculate a velocity target for the respective actuators. Logic is used to limit the acceleration of the stepper motors and control their velocities within their operating ranges. When the error falls below an error limit, the actuators are turned off. The error continues to be monitored and the actuators are turned on if the error rises back above the limit until the error returns back below the limit. This is important because skew is removed by tilting the nip which causes the sheet to translate as the sheet moves forward. Continuing the closed loop control until transfer compensates for this situation. The amount of translation is small because the stalled roll nip function reduces the incoming skew to small amounts, limiting the amount of registration nip angle. When the sheet is in transfer, the registration nip is opened eliminating transfer defects and allows the nip to return home for the next sheet.
An advantage of this invention is skew correction which is done off of the same edge for side 1 and side 2. A normal stalled roll device deskews side 1 and side 2 with opposite edges of the sheet that can cause a mean skew shift between side 1 and side 2. Other advantages are performing lateral skew and top edge stall-roll registration correction simultaneously, adding only one additional sensor and motor to the existing hardware configuration and no need for additional system processors. The system of this invention is easily retrofitted into existing marking apparatuses with a minimum cost involved.
Various sheet registration systems used in the prior art vary in price, some as high as about $4,000. It is estimated that the disclosed registration system of this invention will cost approximately up to $200. Thus, besides being an improved and easily retrofitted registration system, the present invention provides a cost effective improvement over the prior art systems. Various optical lead edge optical sensors used in this invention are well known in the prior art such as those disclosed in U.S. Pat. Nos. 5,678,159 and 5,697,608.
The present registration system provides skew correction of the sheet in the process direction, in the cross-process direction and in the sheet skew angle, all at substantially the same time. Stepper motors are used to effectuate each of the above corrections. Prior registration systems that used a stalled roll also used a manual skew setup adjustment. The present invention closes the loop by adding a second contact image sensor (CIS) before the stalled roll nip to enable skew measurement and adding a stepper motor to the previous manual skew adjustment. Also important to this invention is the combination of closed loop control with a stalled roll registration device. All of the sensors and motors used in the present invention are controlled by an appropriate controller. As noted earlier, a normal prior art stalled roll device deskews side 1 and side 2 with opposite edges of the sheet that can cause a mean skew shift between side 1 and side 2. A significant advantage of this invention is skew correction which is done off the same edge for side 1 and side 2. Final skew correction using an upstream CIS sensor and a downstream CIS sensor and a stepper motor to replace manual registration are essential elements of the present invention. Using a CIS sensor between the pre-registration nip and the buckle control sensor is also important to this invention. An important advantage to the present invention is that it takes out the major skew in a first step and the stalled roll actuators need not adjust or correct the major skew.
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By “closed loop” is meant throughout this disclosure and claims a process that continuously measures and adjusts the lateral and skew position of sheets during transport in a marking apparatus and as “closed loop” is defined in U.S. Pat. No. 7,422,211 B2; which patent is incorporated by reference into the present disclosure. By “stalled roll” nip is meant a stationary nip that a sheet is driven against to square the lead edge of the sheet. By “cross process” correction is meant correcting the sheet position in the direction perpendicular to the paper travel direction, by “process direction is meant correcting the sheet position in the direction of sheet travel, by “skew” is meant correcting the angle of the sheet. As noted earlier, it is important to the present invention that simultaneous skew and cross process correction occur simultaneously because as the stalled roll nip is rotated to straighten the sheet angle the sheet will travel in the cross process direction and this requires continuous correction by controller 36 using stepper motor 35.
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All references cited in this disclosure and their references are incorporated by reference herein when appropriate for teachings of or details and features of the present invention.
In summary, the present invention provides a novel electrostatic marking apparatus and a novel paper registration device. The electrophotographic marking apparatus comprises a paper sheet feeding station and a closed loop paper registration device. This closed loop paper registration device comprises a controller, closed loop control and a stalled roll registration nip and a paper sheet transport with a beginning positioned pre-registration nip. This stalled roll registration nip is positioned on the paper sheet transport.
A first upstream contact image sensor (CIS) is positioned on the paper transport between the stalled roll registration nip and the pre-registration nip. A second downstream contact image sensor is positioned on the paper transport at a location after the stalled roll registration nip. The controller and a motor are in contact with both the first upstream and the second downstream CIS. The first upstream and the second downstream CIS are configured to continuously provide proportional feedback information on a skew of the paper sheet.
The controller which is in contact with the first upstream and the second downstream CIS sensors is configured to simultaneously translate and rotate a paper registration nip to correct cross process and skew registration and configured to thereby deskew at least one side of the paper sheet.
A buckle chamber and a buckle control sensor is positioned between the pre-registration nip and the stalled roll registration nip. The paper leading edge sensor is positioned between the stalled roll registration nip and the second downstream CIS. The stalled roll registration nip is configured to provide a buckle in the paper sheet as a leading edge of the paper sheet enters the stalled roll registration nip.
The first upstream CIS and the second downstream CIS are configured to measure two points on the paper sheet to determine paper skew. The paper registration device of this invention is configured to begin skew adjustment by energizing a skew adjustment cam motor after a lead edge of the paper sheet is past the second downstream CIS.
The paper registration device is configured to substantially simultaneously correct sheet skew in a process direction, in a cross-process direction and correct skew angle.
The first upstream CIS is positioned between the pre-registration nip and a buckle control sensor. The first upstream CIS and the second downstream CIS are both configured to measure a paper skew from a same side edge of the paper sheet.
The paper registration device of this invention comprises a paper sheet transport with a beginning positioned pre-registration nip, a closed loop control and a stalled roll. The stalled roll registration nip is positioned on the paper sheet transport. Also on the transport is a first upstream contact image sensor (CIS) positioned on the paper transport at a point before the stalled roll registration nip. A second downstream contact image sensor (CIS) is positioned on the paper transport at a location after the stalled roll registration nip. The first upstream CIS and the second downstream CIS are positioned in substantial horizontal alignment with each other and are configured to provide proportional feedback information on a skew of the paper sheet. The controller is in contact with the CIS sensors and is configured to substantially simultaneously translate and rotate a paper registration nip to correct cross process skew adjustment and configured to thereby deskew at least one side of the paper sheet.
It will be appreciated that variations of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. Various presently unforeseen or unanticipated alternatives, modifications, variations, or improvements therein may be subsequently made by those skilled in the art which are also intended to be encompassed by the following claims.
