Patent Application
20130108334
The presently disclosed technologies are directed to apparatus and methods used to reduce registration errors in a media handling device, such as marking devices, including printing system. The systems and methods described herein use feedforward belt steering control in order to compensate for repeating and measured disturbances to a transfer belt or web in a media handling device.
In media handling assemblies, particularly in printing systems, accurate and reliable registration of an image as it is transferred is desirable. In particular, accurate registration of an image as it is transferred to a target substrate media or an intermediate transfer belt has a direct correlation to image quality.
Contemporary media handling assemblies use controllers, in the forms of automated processing devices, in order to maintain control of the belts and/or sheets they are handling. Often that control is maintained by adjusting a belt velocity which conveys marking material and/or sheets of paper on transfer belts to a transfer station. Also, steering systems are used in order to guide and/or control the position of the belts along a process direction. While controlling the belt speed along the process direction is important, maintaining lateral control and stability can also be a challenge.
Many belt or web transport systems employ an actuator, in the form of a tiltable steering roll, in order to control lateral movement. The rotational axis of the steering roll is tilted in order to encourage the belt supported thereon to laterally shift. After receiving input from sensors measuring the speed and position of a belt, a controller executes a command profile in order to adjust the belt position when it has drifted from its base position. Such systems are particularly common in printing systems, but are also found in other substrate media handling assemblies.
Typically, control systems are employed to manage the operation of the marking device. Additionally, the control systems attempt to manage most disturbances that result in motion errors and thus effect image quality. One example of such control techniques is a closed-loop technique that uses feedback control. Feedback control reacts to disturbances by attempting to correct for them on the next system cycle. Closed-loop feedback control is similar to a trial-and-error based system; making a correction, measuring the results and then further correcting on the next go-around. However, as feedback control is reactionary, it tends to lag in its response and thus may not compensate fully for quick or transient disturbances.
Another known control technique is feedforward control, which uses an open-loop system that accumulates information for future use based on prior calibration and/or preliminary setup of the system. The feedforward control can eliminate the response lag and anticipate known system disturbances. However, belt steering actuators, while useful to reposition a belt, cause an induced disturbance to the belt, which can lead to belt position tracking errors. Such induced disturbances combine with the fact that most endless-loop belt systems have belt edges that are not straight and/or have inherent movement profiles that are not perfectly straight. Accordingly, attempts by feedforward control to manage a combination of inherent movement and steering induced movement errors lead to overcompensation, which translates to position errors of images.
Accordingly, it would be desirable to provide an apparatus and method capable of more accurately reducing registration errors in a media handling assembly, and thereby overcomes the shortcoming of the prior art.
According to aspects described herein, there is disclosed an apparatus to reduce registration errors in a marking device. The apparatus including a transfer belt, edge sensor and belt steering roll. The transfer belt having a lateral edge, where the transfer belt moves in a process direction across a transfer zone. The edge sensor detecting lateral positions of the lateral edge as the lateral edge passes the edge sensor. The belt steering roll controlling lateral movement of the transfer belt. The belt steering roll rotatably mounted maintaining rolling engagement with the transfer belt. The belt steering roll having steering actuator. One example of a steering actuator includes a selectively tiltable axis of rotation. Adjustments by the steering actuator induce a lateral shift profile to the lateral edge of the belt. For example, tilting of the axis of rotation of a tiltable steering roll defines a steering angle with respect to a reference orientation of the axis of rotation. Changes in the steering angle inducing the lateral shift profile to the lateral edge. The lateral shift profile induced by the steering actuator is defined by changes to the lateral positions of the lateral edge during a period in response to the steering actuator adjustment. The adjustments to the steering actuator, such as changes in the steering angle, being based on a differential between a currently detected lateral position of a segment of the lateral edge and a predetermined lateral position for that segment derived from the lateral shift profile.
Additionally, the lateral shift profile can be determined by a calibration procedure, wherein the belt steering roll is tilted to a series of steering angles and the induced lateral shift profile is recorded for each of the series of steering angles. Alternatively, the lateral shift profile can be determined by adaptive tuning of a steering angle gain whereby steering angle is related to induced lateral edge movements. The steering roll can be disposed between the edge sensor and the transfer zone along an extent of the transfer belt. The transfer belt can convey a substrate media sheet thereon. Alternatively, the transfer belt can be an endless loop belt that moves in a recirculating path. Further, the transfer belt can be an image transfer belt conveying a toner image thereon. The apparatus can also include a controller receiving input based on the detected lateral positions, wherein the controller initiates the steering angle being changed. The edge sensor can be a single sensor in one location along the lateral edge, where the segment of the lateral edge is a contiguous unitary section of the transfer belt. Also, the steering angle can be changed based on feedforward control using the currently detected lateral position as an input to signal the tilting of the belt steering roll in order to adjust the lateral position of the segment of the lateral belt edge at least by the time it reaches the transfer zone. The steering actuator can include a selectively tiltable steering roll, wherein tilting of the axis of rotation of the steering roll defines a steering angle with respect to a reference orientation of the axis of rotation, wherein the adjustments to the steering actuator include changes in the steering angle.
According to other aspects described herein, there is discloses a method of reducing registration errors in a media handling system. The method include determining a lateral shift profile induced by steering angles of a belt steering roll. The belt steering roll rotatably mounted and maintaining rolling engagement with a transfer belt. The transfer belt having two opposed lateral edges and moving in a process direction across a transfer zone. The belt steering roll having a selectively tiltable axis of rotation. The steering angles each defined by an angle of tilt of the axis of rotation relative to a reference orientation of the axis of rotation. The lateral shift profile defined by lateral changes in position to one of the two opposed lateral edges in response to the steering roll being tilted to at least one of the steering angles. The method also including determining a corrective steering angle. The corrective steering angle based on a differential between a currently detected lateral position of a segment of the one lateral edge and a predetermined lateral position of the one lateral edge derived from the lateral shift profile. The method also including tilting the belt steering roll to the corrective steering angle.
Additionally, the currently detected lateral position of the method can be measured by an edge sensor detecting lateral positions of the one lateral edge as the one lateral edge passes the edge sensor. Also, the edge sensor can be a single sensor in one location along the one lateral edge, the segment of the lateral edge being a contiguous unitary section of the transfer belt. The belt steering roll tilting can be initiated prior to the segment reaching the transfer zone. Also, the lateral shift profile according to the method can be determined by a calibration procedure, wherein the belt steering roll is tilted to a series of steering angles and the induced lateral shift profile is recorded for each of the series of steering angles. Alternatively, the lateral shift profile according to the method can be determined by adaptive tuning of a steering angle gain whereby steering angle is related to induced lateral edge movements. The transfer belt can convey a substrate media sheet thereon. Also, the transfer belt can be an endless loop belt that moves in a recirculating path. Further, the transfer belt can be an image transfer belt conveying a toner image thereon. The corrective steering angle can be determination uses a feedforward control technique, wherein the feedforward control technique includes the currently detected lateral position and the predetermined lateral position as inputs to a controller, whereby an output is generated that initiates the tilting of the belt steering roll.
These and other aspects, objectives, features, and advantages of the disclosed technologies will become apparent from the following detailed description of illustrative embodiments thereof, which is to be read in connection with the accompanying drawings.
Describing now in further detail exemplary embodiments with reference to the Figures, as briefly described above. The disclosed technologies reduce registration errors using feedforward control that subtracts previously determined belt edge position deviations from instantly measured belt edge position deviations, thereby inducing a more efficient amount of actuator response and stabilizing belt edge movement. The apparatus and methods disclosed herein can be used in a select location or multiple locations of various conventional marking device paths that include an endless loop belt. Thus, only a portion of an exemplary marking device path is illustrated herein.
As used herein, a “marking device,” “printer,” “printing assembly” or “printing system” refers to one or more devices used to generate “printouts” or a print outputting function, which refers to the reproduction of information on “substrate media” for any purpose. A “marking device,” “printer,” “printing assembly” or “printing system” as used herein encompasses any apparatus, such as a digital copier, bookmaking machine, facsimile machine, multi-function machine, and the like, which performs a print outputting function for any purpose.
Particular marking devices include printers, printing assemblies or printing systems, which can use an “electrostatographic process” to generate printouts, which refers to forming an image on a substrate by using electrostatic charged patterns to record and reproduce information, a “xerographic process”, which refers to the use of a resinous powder on an electrically charged plate record and reproduce information, or other suitable processes for generating printouts, such as an ink jet process, a liquid ink process, a solid ink process, and the like. Also, a printing system can print and/or handle either monochrome or color image data.
As used herein, a “media handling assembly” refers to one or more devices used more generally for handling and/or transporting substrate media, including feeding, marking, printing, finishing, registration and transport systems.
As used herein, “substrate media” refers to, for example, paper, transparencies, parchment, film, fabric, plastic, photo-finishing papers or other coated or non-coated substrates on which information can be reproduced, preferably in the form of a sheet or web. While specific reference herein is made to a sheet or paper, it should be understood that any substrate media in the form of a sheet amounts to a reasonable equivalent thereto. Also, the “leading edge” of a substrate media refers to an edge of the sheet that is furthest downstream in the process direction.
As used herein, the term “actuator” refers to a device or assembly of elements that communicate or impart motion to another element, such as a transport handler, or directly regulates the motion of that element. In particular, an actuator is a mechanical device that accepts a data signal and performs an action based on that signal. Actuators include those mechanical devices that can impart motion to a drive wheel, a transfer belt, an imaging drum and other elements of the media handling device. Also, such motion can include tilting an idler roll for steering a belt engaged therewith.
As used herein, the term “belt” or “transfer belt” refers to, for example, an elongated flexible web supported for movement along a process flow direction. Such belts have opposed lateral edges extending generally parallel to one another. For example, an image transfer belt is capable of conveying an image in the form of toner for transfer to a substrate media. Another example includes a media transfer belt, which preferably engages and/or conveys a substrate media within a printing system. The substrate media, in the form of a sheet, may be in intimate contact with the belt through vacuum, electrostatic forces, gripper bars or other methods. Such belts can be endless belts, looping around on themselves within the printing system in order to continuously operate. Accordingly, belts move around a loop in which they circulate, such that a portion of that belt moves in a process direction of the overall assembly. A belt can engage a substrate media and/or carry an image thereon over at least a portion of the loop. Image transfer belts for carrying an image or portions thereof can include non-stretchable electrostatic or photoreceptor belts capable of accumulating toner thereon.
As used herein, the term “roll,” “rollers” or “wheel” interchangeably refer to a revolving element and supporting structure. In the context of an endless loop belt system, rolls are used to support and/or drive the belt in a recirculating cycle. A drive roll is operatively driven by a motor, whereas an idler roll freely rotates. Drive rolls generally drive a belt or substrate media supported thereon. In contrast, idler rolls are driven to rotate about their longitudinal axis by the moving belt or substrate media engaged therewith.
As used herein, the term “image-bearing member” refers to one or more elements that directly engages the substrate media as it moves through at least a portion of the greater media handling assembly. Image-bearing members can carry or manipulate an image directly, such as a latent image on an imaging drum or intermediate transfer belt, or manipulate a substrate media bearing an image or intended to receive an image thereon. Image-bearing members can thus include transfer belts and other elements of the media handling device that convey or carry an image that has been applied to or is going to be applied to a substrate media.
As used herein, “sensor” refers to a device that responds to a physical stimulus and transmits a resulting impulse signal for the measurement and/or operation of controls. Such sensors include those that use pressure, light, motion, heat, sound and magnetism. Also, sensors as referred to herein can include point sensors and/or array sensors for detecting and/or measuring characteristics of a substrate media or a transfer belt, such as speed, orientation, position and disturbances from expected values. An edge sensor is a sensor that can detect or measure the position of a surface edge, such as the lateral edge of a belt or substrate media sheet. Examples of edge sensors include CCD array sensors (edge registered); long range angled Contact Image Sensors (CIS—center registered); point sensors modified to have an analog range (edge registered); moveable point sensors (center registered) or others as are common in the art. It should be appreciated that while a small rectangular shape is illustrated in the figures herein, to represent an edge sensor, almost any edge sensing device can be used to detect edge positions in accordance with the disclosed technologies.
As used herein, the terms “process” and “process direction” refer to a process of moving, transporting and/or handling a transfer belt, an image or substrate media conveyed by a transfer belt. The process direction substantially coincides with a direction of a flow path P along which a portion of the transfer belt moves and/or which the image or substrate media is primarily moved within the media handling assembly. Such a flow path P is said to flow from upstream to downstream. Accordingly, lateral or transverse directions refers to movements or directions perpendicular to the process direction and generally along a common planar extent thereof.
Feedforward control as used herein refers CPU-based automated controls that couple an input signal to a control variable. The control variable adjustment is not simply error-based, but rather is based on knowledge about the process in the form of a mathematical model and knowledge about or measurements of the process disturbances. A feedforward control system includes a means to detect a disturbance or receive an input and process that input through an algorithmic model to determine the required modification to the control action.
In this exemplary embodiment, rolls 30, 35 are both idler rolls rotatably mounted to freely rotate, but roll 30 is additionally a belt steering actuator. In this way, steering actuator 30 is characterized as a soft axis belt steering roll because it is not a drive roll and the longitudinal axis of rotation AS of this roll can be adjusted in order to laterally shift the position of the endless loop belt 20 riding thereon. In this exemplary embodiment, the belt steering roll 30 can be made to tilt. By tilting the axis of rotation AS a certain amount, the belt 20 will react by shifting laterally along the longitudinal extend of the roll. The amount of tilt (measured by an angle α) and consequently the amount of belt shift can be controlled by a motor, such as a step motor (not shown). A step motor would pivot the steering actuator axis AS in predefined increments with respect to the base-line position of that axis AS. Thus, the base-line position provides a fixed line of reference for steering roll axis of rotation and thus the steering actuator. Alternatively, a DC motor, AC Motor, hydrostatic drive or other actuators could be used. Also, the actuator can optionally include gears, belts or other known means of transmission. Further, a power amplifier can be employed that provides actuation power for the actuator through amplification (and sometimes conversion) of a low power control signal. Moreover, a conventional servo controller can be used to control velocity of the transport media by means of outputting a control signal to the power amplifier to drive the respective motor.
While steering actuator 30 is illustrated as a tiltable steering roll, other steering actuators can be used in accordance with the disclosed technologies. For example, the steering actuator can alternatively be a laterally shifting belt steering roll. In this way lateral belt position correction controls can be applied through a gentle lateral force applied to one of the lateral edges of the belt. Such a transverse force is applied to adjust the lateral position of the belt. Such an alternative apparatus and system is disclosed in U.S. Pat. No. 6,594,460 by Lloyd A. Williams et al., which is incorporated herein by reference and which is commonly assigned with the instant disclosure.
Roll 40 is a drive roll that is rotatably driven by a motor assembly (not shown) coupled thereto by gears, belts, pulleys or other known methods (also not shown). The drive roll 40 imparts a velocity to the belt 20 generally in a process direction P. In contrast, the axis of rotation of the lower idler roll 35 and the drive roll 40 are each fixed and thus remain parallel to one another.
The belt edge sensor 50 is shown to be disposed just upstream of the steering actuator 30 with relation to the path of the endless loop belt 20. This position is advantageous so that corrections to the belt edge position can be made by the steering actuator 30 prior to a measured portion of belt reaching the marking device 70 at the transfer station just downstream of the steering actuator. However, the location of the belt edge sensor sometimes is determined or dictated by available space. Nonetheless, for best control performance, a location close to the steering roll is proffered.
For exemplary purposes, the marking device 70 shown in
The marking device 70 can take the form of almost any type of marking device used in printing systems. For example the marking device 70 can be an ink jet assembly or use xerographic imaging with a photoreceptor or intermediate belt. One common marking device forms an image using toner. The toner image is directly transferred on to and fixed on a substrate sheet or temporarily transferred to the endless-loop belt 20 and is thereafter transferred to a substrate. The marking device 70 engages and/or interacts with the belt or sheet in an image transfer zone, also referred to herein as an image transfer station or just transfer station. Transfer of the image to the belt 20 or a sheet should be in precise registration, otherwise it can cause processing interruptions or delays and/or impair the print quality.
Often, marking material is built-up in stages by having the sheet or target section of belt 20 pass through more than one transfer station. For example, in a “highlight color” printing apparatus, where it desired to print black plus one other predetermined color, a typical arrangement is to have a black development unit transfer its portion of the image at one stage and one or more other development units (one for each of a selectable set of highlight colors, only one of which would be used) to transfer its portion of the image at another stage. In the case of a full-color printing apparatus, there are typically four development units; cyan, magenta, yellow, and black (CMYK) and thus four transfers in order to create a full-color image. Other types of architecture include “hexachrome,” where there are two additional color development units beyond CMYK, thus providing an extended color gamut for the printer; and arrangements that include a development unit for applying clear toner, or one applying a toner with special properties such as MICR (magnetic ink character recognition) toner. Accordingly, it should be understood that although
The induced lateral movement of the belt 20 at the location of the belt edge sensor 50 is a function of the steering actuator adjustments. Thus, in the tiltable steering roll embodiment disclosed herein the steering actuator adjustments would mean changes in the angle α of the orientation of the axis of rotation of the belt steering roll. This function is also referred to herein as a “lateral shift profile” and can be calculated, calibrated or found by trial and error. Hence the induced belt edge variation due to the steering angle and other regular system disturbances can be determined ahead of time and used by the system controller 90. Every system has its own peculiar quirks, but preliminary calibration or measurement of repeating disturbances can be used as a natural base line movement profile for the belt 20, and more particularly the measured belt edge 25. What is more, that lateral shift profile can be further correlated to each incremental change in the steering actuator angle α. Thus, any particular point or segment along the belt edge 25, will have a previously determined belt edge position deviation in accordance with the lateral shift profile.
After the initial setup or calibration of the apparatus 10, then the edge sensor 50 continues to be used to detect an current lateral position deviation of a measured portion of the belt edge 25. In accordance with an aspect of the disclosed technologies, the previously determined belt edge position deviation is subtracted from that current lateral position deviation detected by the edge sensor during the current belt loop cycle. The resulting differential is then used to determine the necessary angular correction to induce with the belt steering actuator, rather than simply using the total instant measured belt edge deviation that would result in overcorrection. The result is a greatly reduced amount of variation in the steering roll angle with resulting improvement in tracking and registration. Advantages over other methods is the immediate improvement in performance as compared to have to wait a few belt revolutions and reduced cost.
Hence the methods in accordance with the disclosed technologies include initially determining a preliminary or calibration cycle displacement profile. The preliminary displacement profile representing a repeating belt edge displacement on a steered endless loop belt. The repeating belt edge displacement being correlated to segments along the length of the endless loop belt. That preliminary displacement profile defining a previously determined belt edge displacement. Additionally, a relation can be derived between the steering angle position of a steering actuator and the induced edge variation. This relation can be derived from either a calibration procedure or by developing a profile defining the preliminary value displacement. The calibration procedure can be performed by varying the steering angle of the steering actuator and recording the induced edge variation at the sensor location. Alternatively, this relation can be based on a model that uses roller positions, edge sensor location, belt spans, etc. to calculate the linear relation between steering roll position and induced edge position using simple geometry. As a further alternative, adaptive tuning of a gain that relates induced edge position from steering roll angle can be used to define the preliminary displacement profile. Adaptive tuning is a contemporary control method that generally employs a controller, where the controller adapts to a controlled system with parameters which vary, or are initially uncertain.
The determination of the angular position of the steering roll can be derived from either an angular position measurement sensor or based on a derived model. The model can be derived using many steering systems have a stepper motor driven cam that changes the steering angle. The total step count is proportional to the cam position, which together with the cam profile determines the angular position of the steering roll. In many cases the cam is linear, resulting in a linear relation between step count and angular position of the steering roll. For other steering system configurations, appropriate models can be derived.
Once the preliminary displacement profile is obtained, then instantaneous measurements of the belt edge displacement continue to be taken by a single belt edge sensor. The instantaneous measurements should be correlated to a particular segment of the endless loop belt. Any one particular instantaneous measurement will represent the belt edge displacement of a particular segment of the endless loop belt. In accordance with the disclosed technologies, a previously determined belt edge displacement value is derived from the preliminary displacement profile for the particular measured segment of the belt edge. That previously determined belt edge displacement value is subtracted from the instantaneous measurement in order to determine a differential displacement value. Thereafter, the differential displacement value is used as the error signal for the steering actuator.
Thus, the graphs represented in
It should be understood that the apparatus and method of reducing registration errors as described herein, can be combined with other forms of registration actuators, sensors and control parameter optimization methods to deliver high performance results. Additionally, in accordance with further aspects of the disclosed technologies herein, the belt steering function can be handled by a common controller 90 that works for more than one media handling assembly. Often media handling assemblies, and particularly printing systems, include more than one module or station. Accordingly, more than one registration apparatus as disclosed herein can be included in an overall media handling assembly. Further, it should be understood that in a modular system or a system that includes more than one registration apparatus, the measured disturbance signals can be relayed to a central processor for controlling registration. In this way, particularly in a modular system, one module can learn from the earlier module to further improve the overall media handling. Thus, each sheet passing through a module can be considered a cycle and the number of modules representing that many cycles from which information can be learned regarding the transport handler movements. In this way, the learning system can converge on the ideal signal profile more quickly.
It will be appreciated that various of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems or applications. It will also be appreciated that 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 disclosed embodiments and the following claims.
