Method and system of introducing media into a media path with minimal positional error

Abstract

A system and method of controlling the movement of a media sheet along a media path to correspond to the timing of a toner image on an intermediate transfer mechanism. A controller controls the timing and sends a pick command to move a media sheet from a pick tray into the media pathway at a time that the media can move at a process speed and intercept the toner image. The controller adjusts the speed of individual rollers within the media path to correct the timing of the media sheet to account for any timing inaccuracies. By the time the media sheet exits the media path and enters a media/image alignment region of the media pathway, the amount of positional error is reduced or eliminated.

Description

BACKGROUND OF THE INVENTION

[0001] Many types of image forming apparatus use a double transfer system to form images. A toner image is initially formed on an intermediate transfer member such as a belt or drum. The intermediate transfer member with the toner image is then rotated to a second transfer point where the toner image is transferred to a media sheet. Intricate timing between the intermediate transfer member and the media sheet is required to produce a high-quality image. Poor timing results in the media sheet either reaching the second transfer point before or after the toner image on the intermediate transfer member and the image being transferred to a position either too high or low on the media sheet. In extreme cases, the media sheet is not present at the second transfer point when the toner image arrives and the image is never transferred to the media.

[0002] The media sheet picked from a media tray moves along a media path prior to arriving at the second transfer point. A number of different media trays are positioned along the media path from which the media sheets are picked with each tray potentially containing different media types and sizes. Each tray includes a pick device for moving the media sheet from the tray into the media path. The media path includes rollers to move the media sheet to the second transfer point.

[0003] The picking of a media sheet from a media tray is carefully synchronized with the placement of the toner image on the intermediate transfer member. When the media is accurately picked the media moves along the media path at a predetermined process speed and intercepts the toner image at the proper time. However, problems occur when the timing of the media pick is incorrect. Problems may result from slippage between the pick rollers and the media sheet, pick command latencies, and variable media stack heights in the pick tray leading to faster or slow picks. Therefore, there should be a method and system of correcting the position of the media sheet in the media path relative to the position of the toner image on the intermediate transfer member.

BRIEF SUMMARY OF THE INVENTION

[0004] The pathway of a media sheet may be divided into two separate regions: a media path region and a media/image alignment region. The media path region comprises the pick trays and duplexer, and the media/image alignment region includes the pathway downstream of the duplexer leading to a second transfer point where the media sheet intercepts a toner image. The media/image alignment region is only capable of correcting positional error of the media sheet that is less than a predetermined amount. The present invention is directed to a system and method of correcting positional error of a media sheet within the media path region to be less than the predetermined amount.

[0005] To ensure proper print quality, a media sheet should intercept a toner image at a second transfer point. The timing of toner image on an intermediate transfer mechanism is carefully timed with the movement of the media sheet along the media pathway. A controller controls this process and sends a pick command to move a media sheet from a pick tray into the media pathway at a time that the media can move at a process speed and intercept the toner image. However, the timing of the media pick from the pick tray may result in the media sheet entering the media path region of the pathway either sooner or later than expected. The speed of individual rollers within the media path may be adjusted to correct the time of arrival of the media sheet. By the time the media sheet exits the media path and enters the media/image alignment region of the media pathway, the amount of positional error should be less than the predetermined amount.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006] FIG. 1 is a side view of one embodiment of an image forming apparatus constructed according to the present invention;

[0007] FIG. 2 is a schematic diagram of the media path extending between the pick trays and the second transfer point;

[0008] FIG. 3 is a schematic diagram illustrating a tray controller and main controller which control the timing of the media sheet along the media path and the toner image on the intermediate transfer belt; and

[0009] FIG. 4 is a flowchart diagram illustrating one embodiment of the steps of coordinating the position of the media sheet on the media path relative to the toner image on the intermediate transfer member.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0010] FIG. 1 illustrates the basic elements of an image forming apparatus 100 and is incorporated for an understanding of the overall electrophotographic image forming process. A four cartridge color laser printer is illustrated as 100, however one skilled in the art will understand that the present invention is applicable to other types of image forming devices. The image forming apparatus, generally designated 100, includes a plurality of similar toner cartridges 110, 210, 310, and 410. Each toner cartridge is of a similar construction but is distinguished by the toner color contained therein. In the preferred embodiment, the device includes a black (K) cartridge 110, a magenta (M) cartridge 210, a cyan (C) cartridge 310, and a yellow (Y) cartridge 410. Each different color toner forms an individual image of a single color that is combined in layered fashion to create the final multi-colored image.

[0011] Each of the toner cartridges is substantially identical and includes a photoconductor, a developer device, and a cleaning device. As the cartridges are identical except for the toner color, the cartridge and elements for forming black images will be described, with the other color image forming units being omitted for simplification.

[0012] The photoconductor 114 is generally cylindrically-shaped with at least one end that intermeshes with the image forming device drive gears to provide for a rotational force. The photoconductor 114 has a smooth surface for receiving an electrostatic charge over the surface as the photoconductor rotates past charger 116. The photoconductor 114 uniformly rotates past a scanning laser 120 directed onto a selective portion of the photoconductor surface forming an electrostatically latent image across the width of the photoconductor representative of the outputted image. The drive gears rotate the photoconductor 114 continuously so as to advance the photoconductor about {fraction (1/600)}th or {fraction (1/1200)}th of an inch between laser scans. This process continues as the image pattern is formed on the photoconductor surface.

[0013] After receiving the latent image, the photoconductor 114 rotates to the developer which has a toner bin 122 for housing the toner and a developer roller 124 for uniformly transferring toner to the photoconductor. The toner is transferred from the toner bin 122 to the photoconductor 114 through a doctor blade nip formed between the developer roller 124 and the doctor blade. The toner is a fine powder usually constructed of plastic granules that are attracted and cling to the areas of the photoconductor 114 that have been discharged by the laser scanning assembly 120.

[0014] The photoconductor 114 next rotates past an adjacently-positioned intermediate transfer mechanism belt 800 (hereinafter, ITM belt) to which the toner is transferred from the photoconductor 114. As illustrated in FIG. 1, the ITM belt 800 is endless and extends around a series of rollers adjacent to the photoconductors. The ITM belt 800 and each photoconductor 114, 214, 314, 414 are synchronized providing for the toner from each photoconductor to precisely align on the ITM belt 800 during a single pass. By way of example as viewed in FIG. 1, the yellow toner will be placed on the ITM belt, followed by cyan, magenta, and black.

[0015] After depositing the toner on the ITM belt, the photoconductor 114 rotates through a cleaning area where residual toner is removed from the surface via a brush or scraper 126. In one embodiment, the photoconductor 114 further passes through a discharge area (not shown) having a lamp or other light source for exposing the entire photoconductor surface to light to remove any residual charge and image pattern formed by the laser.

[0016] As the photoconductors are being charged and gathering toner, a media sheet, such as a blank sheet of media, is being routed to intercept the ITM belt 800. The term “media”, “sheet”, or “media sheet” is used throughout to refer to a discrete unit of recording media. This term is not limited to media sheets, and any form of discrete recording media is intended to be encompassed therein, including without limitation, envelopes, transparencies, postcards, and the like. The media may be placed in one of the lower pick trays 510, 512, 514. A pathway is comprised of a series of rollers to transport the media from the pick tray to a second transfer point Z where the sheet contacts the ITM belt 800 and receives the toner image. The sheet may receive an electrostatic charge prior to contact with the ITM belt 800 to assist in attracting the toner from the belt. The sheet and attached toner image next travel through a fuser 830 having a pair of rollers and a heating element that heats and fuses the toner to the sheet. The sheet with fused image is then transported either through duplexer 300 to form an image on the opposite side of the media sheet or out of the printer for receipt by a user. In one embodiment, duplexer 300 is positioned outside the main housing of the image forming apparatus 100. In another embodiment, the duplexer 300 may be positioned within the main housing of the image forming apparatus 100. FIG. 1 discloses one embodiment of an image forming apparatus in which the present invention may be used. One skilled in the art will understand that the present invention may be used in numerous other image forming apparatus in which a media sheet intercepts a toner image.

[0017] FIG. 2 is a schematic illustration of the pathway for moving the media sheet from the pick trays to the second transfer point Z. The pathway may be divided into two separate regions. A first region includes a media path 200 comprising the pick tray rollers 210, 212, 214 and duplex roller 202. A media sheet is within the media path 200 when the speed of the media sheet is being controlled by one or more of these rollers. Additional rollers may be positioned within this region at various points and are considered to be included within the scope of this invention. A media/image alignment region 400 is positioned downstream of the media path 200 and upstream of the second transfer point Z. The region 400 includes a number of rollers 402 whose rotational speed may be finely adjusted to change the speed of the media sheet to ensure proper intersection timing with the toner image. The region 400 can adjust for minor positional error less than a predetermined amount. The predetermined amount may vary depending upon the image forming apparatus. The rollers and timings of the media/image alignment region 400 are disclosed in U.S. patent application Ser. No. 09/545,202 filed Apr. 6, 2000, herein incorporated by reference in its entirety.

[0018] Each pick tray 510, 512, 514 is equipped with a picking device 516, 517, 518 for moving a media sheet from the pick tray into the media path 200. In one embodiment, the picking devices 516, 517, 518 include a roller that rests against the top media sheet that rotates to move the sheet from the pick tray 510, 512, 514 into the media path 200. The roller and/or motor may be clutched such that the roller releases control of the media sheet when introduced into the media path 200 and accepted by the media path rollers 202, 210, 212, 214. The actual embodiment elements and operation of the picking device may vary depending upon the specifics of the image forming apparatus. As picking devices are well known in the art, only the function is described herein and the actual elements of the device will be understood by those skilled in the art.

[0019] The duplexer 300 provides for printing on both sides of the media sheet. A roller 202 may be positioned within this area on the media path 200. The duplexer 300 and duplexer roller 202 may or may not be included within the image forming apparatus 100. In an embodiment without the duplexer 300, the media path 200 extends through the rollers of the pick trays 510, 512, 514.

[0020] Pass through sensors 220, 222, 224 are positioned along the media path 200 to determine the positions of the media sheets. Pass through sensors 220, 222, 224 may be positioned at a variety of locations along the media path 200 and there may be any number of sensors. In one embodiment, the pass through sensors are located adjacent to the pick trays 510, 512, 514 as illustrated in FIGS. 2 and 3. In one embodiment, pass-through sensors 510, 512, 514 direct a light beam across the media path 200 that is broken upon passing of the media sheet to register the position of the media sheet. In another embodiment, the media sheet hits a small arm that extends into the media path. As the arm pivots out of the way of the media sheet, a light beam is interrupted by a portion of the arm, and registers the position of the media sheet. Specific embodiments include pass through sensor model numbers OS-5101, OS-5201, and OS-5301 manufactured by Aleph. Various other types of media sensors may be used within the present invention and the specific aspects of the sensors are well known in the art.

[0021] The rollers 202, 210, 212, 214 may have a variety of shapes and sizes. The term “roller” and “rollers” is used herein to identify a roller set having at least two rollers positioned a distance apart to form a nip point there between through which the media sheets pass. The rollers 202, 210, 212, and 214 may further provide for lateral alignment of the media sheet and may include conical-shaped or skewed rollers that laterally move the media sheets against an alignment edge (not illustrated) that runs along at least a portion of the media path 200. Additionally, some image forming apparatus 100 may use endless belts in place of rollers. As used herein, both rollers and such endless belts fall under the definition of the term transport mechanism.

[0022] Motors 230, 232, 234 (FIG. 3) are operatively connected to the rollers 202, 210, 212, 214 to control the speed of the media sheets through the media path 200. The motors may control the speed of a single roller such as motor 232 and rollers 212, or may control more than a single roller such as motor 230 that controls rollers 202 and 210. Each motor 230, 232, 234 can rotate the rollers 202, 210, 212, 214 at a variety of speeds between a maximum speed RPMmax and a minimum speed RPMmin. RPMmax and RPMmin may be determined by the maximum potential positional error, acoustics, power, and operational speed range of the media path 200.

[0023] Motors 230, 232, 234 may further include an encoder for sending pulses throughout each motor revolution and are monitored by a tray controller 600. Each revolution of the motor results in roller movement of a predetermined amount. It is further known that the movement of the media accurately matches the travel of the rollers 202, 210, 212, 214. Therefore by counting the motor pulses, tray controller 600 determines the position of the media sheet as it moves along the media path 200. One specific embodiment of a suitable motor is Igarashi Model No. N3649.

[0024] FIG. 3 illustrates schematically the tray controller 600 that controls the motion of the media sheets through the media path 200 and the main controller 700 that controls the overall coordination of the toner image and the media sheet. The main controller 700 sends a pick command to the tray controller 600. Upon receipt of the command, the tray controller 600 signals one of the pick device 516, 517, 518 to move a media sheet from the corresponding pick tray into the media path 200. Pass-through sensors 220, 222, and 224 signal the position of the media sheet to the tray controller 600. At this time, tray controller 600 knows the position of the media sheet and can continually track the progress through the media path 200 by signals received from the motors 230, 232, 234. A variety of tray controllers may be used, and one embodiment includes Mitsubishi Model No. M30201F6.

[0025] The main controller 700 controls the timing of the toner image and the media sheet to ensure proper timing of the intersection at the second transfer point Z. Main controller 700 receives a print request and begins the process of creating the toner image on the ITM belt 800. Toner image creation may occur before or after a pick command is sent to the tray controller 600.

[0026] Main controller 700 may track the location of the toner image on the ITM belt 800 in a variety of different manners. In one embodiment as illustrated in FIG. 3, an image sensor 810 senses the toner image on the ITM belt 800 and signals the main controller 700. The image sensor 810 may be located at a number of locations about the ITM belt 800, and more than one image sensor 810 may be positioned along the ITM belt 800. In another embodiment, a motor 821 driving an ITM roller 820 sends pulses throughout each motor revolution in a similar manner as the roller motors 230, 232, 234. Once a print request is received, main controller 700 signals the cartridges 110, 210, 310, 410 to create the toner image. The position of the toner image on the ITM belt 800 is known, the location of the second transfer point Z is known, and the movement of the ITM belt 800 can be determined as a function of the rotation of the roller 820. Therefore, the location of the toner image relative to the second transfer point Z may be tracked. In one embodiment, the main controller 700 is model no. M16C/62 manufactured by Mitsubishi.

[0027] Tray controller 600 operates the media path rollers 202, 210, 212, 224 at a process speed with each roller rotating at substantially the same linear speed along the media path 200. The timing of the pick command is initially a function of the process speed and the known expected time for a media sheet to be picked from each tray and transferred to the second transfer point Z.

[0028] As the media sheet moves along the media path 200, the distance from the second transfer point can be determined and tracked by the tray controller 600. The media sheet distance (Mdistance) can be calculated as:

Mdistance=(distance from pass through sensor to second transfer point)−[(# encoder pulses since media location identification)(distance per encoder pulse)]  (Eq. 1)

[0029] Additionally, an image distance (Idistance) can be determined as the distance between the toner image and the second transfer point Z:

Idistance=(image distance to second transfer point at the time of media pick)−[(# of milliseconds since pick)(travel speed of ITM belt)]  (Eq. 2)

[0030] Media positional error (Merror) is defined as the difference between the image distance and media sheet distance to the second transfer point Z:

Merror=Idistance−Mdistance  (Eq. 3)

[0031] The process speed of the rollers 202, 210, 212, 214 cannot be adjusted as a whole because there may be more than one media sheet within the media path 200 and this would introduce positional error into the these sheets. Merror is corrected by adjusting the speed of an individual rollers within the media path 200. As illustrated in FIG. 2, the rollers 202, 210, 212, 214 are spaced a distance apart such that each roller independently controls the speed of the media sheet for a distance along the media path 200. By way of example, a media sheet picked from tray three 514 is under the exclusive control of rollers 214 for the initial period within the media path 200 until handoff to rollers 212. In one embodiment, there is at least 125 millimeters of sole control for each roller in which the position of the media sheet can be corrected. In another embodiment, one motor may control more than one roller. Specifically, motor 230 may control rollers 202 in duplexer 300 (FIG. 3).

[0032] Merror is determined by the tray controller 600 and the amount of increase or decrease in the roller speed may be determined during each encoder interrupt. A proportional gain constant (K) may be empirically determined and form a permanent part of the software and/or hardware that drives the rollers. K is dependent in part on the expected amount of error, the known process speeds, the distance available with which to correct error and similar factors. The speed of the motor after determining media position is:

RPMcorrection=process speed−[(Image Position−Media Position)(K)]  (Eq. 4)

[0033] K is applied to remove the positional error of the media. Larger Ks result in larger corrections; smaller Ks result in smaller corrections. It should be noted that this is a repeating equation and is performed for every encoder interrupt, thus it could be rewritten as, where j is the index of the encoder:

RPMcorrectionj=process speed−[(Image Positionj−Media Positionj)(K)]  (Eq. 4A)

[0034] By way of example, a media sheet introduced from tray two 512 passes through pass through sensor 222 and the tray controller determines the positional error. The length of the media path under sole control of roller 212 is determined by the tray controller 600. A desired speed is calculated and motor 232 is signaled to change from process speed to RPMcorrection1. On the next encoder interrupt, RPMcorrection2 is calculated based on the new known position (media position2), K, and the current image position2. This process repeats for each encoder interrupt, resulting in new values of RPMcorrection. As the positional error approaches zero, RPMcorrection approaches process speed.

[0035] In one embodiment, the speed of the roller should be returned to process speed before the media sheet is transferred to the next roller, so as to avoid speed discontinuities at hand off between rollers. Therefore, at some point along the media path 200 prior to when the media sheet contacts the next roller, the controlling roller should alter the speed to ensure there is a smooth transition from the RPMcorrection to the process speed. By way of example, a media sheet picked by pick device 518 moves through sensor 224 at which point a positional error is detected. The rollers 214 will be adjusted from process speed to the RPMcorrection1 in accordance with the tray controller 600. Subsequent RPMcorrectionsj may be determined that continue to eliminate positional error. At a point prior to the media sheet leading edge contacting the rollers 212, rollers 214 will transition back to the process speed to ensure the media sheet is moving at process speed at the transition.

[0036] FIG. 4 illustrates one embodiment of the present invention for correcting the positional error Merror. A pick command is sent by the tray controller 600 to one of the pick trays 510, 512, 514 (step 450). A media sheet is picked from one of the trays and enters into the media path 200 where it is controlled by the rollers associated with the pick tray moving at process speed and the leading edge is detected by the pass through sensor (step 452). The tray controller 600 determines the media positional error Merror (step 456). If there is no positional error, the speed of the pick tray roller is maintained at the process speed.

[0037] In the event there is positional error Merror, the new process speed RPMcorrection for the pick tray rollers is determined (step 462). If the new roller speed RPMcorrection is greater than the roller maximum speed RPMmax (step 464), the speed is set at the maximum speed RPMmax (step 466). Likewise, if the new speed is less than the minimum speed of the roller RPMmin (step 470), the speed is set at the minimum speed RPMmin (step 472). Large initial errors may not be completely eliminated before the sheet must be returned to process speed. However, the amount of error should be lessened to below the predetermined amount and the remainder of the error can be removed in the media/image alignment region 400.

[0038] The pick tray roller will operate at RPMcorrectionj until the time that the leading edge of the media sheet approaches the handoff point to the next rollers (step 474). If the media sheet is not approaching the next roller, the controller accepts another encoder interrupt and recalculates Merror at step 456, repeating as needed. At the handoff point, the speed of the pick tray rollers RPMcorrection is returned to the process speed (step 480) such that the transition of the media sheet does not result in positional error, misalignment of the media sheet, a jam within the media path 200, or other like event. The speed of the pick tray roller may be slowly adjusted to conform with the process speed, such as through a slowly decreasing RPMcorrection or may be returned in one adjustment if the positional error was too great to be corrected by one set of rollers.

[0039] The media/image alignment region 400 may operate at a variety of speeds that may be monitored by the tray controller 600, main controller 700, or both. As the media sheet approaches the region 400, the roller speed within the media path 200 will be adjusted to conform to ensure a smooth handoff. In one embodiment, the media/image alignment region 400 operates at the same process speed as the media path 200.

[0040] In most cases, the positional error introduced during the media sheet pick process causes the media sheet to lag behind the toner image on the ITM belt 800. The lag requires that the pick tray rollers operate above process speed to remove the error. However, the media sheet may also lead the toner image at which time the pick tray rollers are slowed. The present invention accounts for both situations.

[0041] An additional consideration occurs when more than two rollers along the media path 200 are controlled by the same motor and operate at the same speed. An example of this is illustrated in FIG. 3 with motor 230 controlling rollers 202 and 210. In one embodiment, the duplex roller 202 was added to prevent poor media alignment when the media sheets were transferred from the upper pick tray roller 210 into the media/image alignment region 400. The duplexer is not the only place that rollers may be doubled onto a single motor. Other rollers throughout the media path 200 may share motors.

[0042] Correction of Merror via adjacent rollers controlled by one motor requires additional logic to ensure other media sheets within the media path 200 do not get inadvertently mis-positioned. After determining the media sheet has positional error Merror (step 456 in FIG. 4), tray controller 600 then determines if the subsequent roller in the media path 200 is controlled by the same motor. If the roller is controlled by the same roller, the tray controller 600 then determines if the previous media sheet that has moved along the media path 200 has exited the control of the downstream roller. If the answer is no, the tray controller cannot adjust the speed as this would affect the position of the previous media sheet. If the media sheet is out of the downstream roller, the speed can be adjusted to RPMcorrection as in the previous situation.

[0043] By way of example using the embodiment illustrated in FIG. 3, rollers 202 and 210 are controlled by the same motor 230 and operate at the same speed. When the leading edge of sheet N passes through sensor 220, the positional error can be determined. Prior to adjusting the speed of roller 210, tray controller 600 determines whether the previous media sheet N−1 has cleared from roller 202. If N−1 is still controlled by roller 202, the speed cannot be changed. If N−1 has cleared, the speed can be changed to RPMcorrection1.

[0044] If two sheets are within the control of the separate roller concurrently, additional logic may be included for the tray controller 600 to determine the position of sheet N at the time that sheet N−1 leaves control of roller 202. Tray controller 600 would calculate the image position, the media sheet position and deduce an initial RPMcorrection1. Subsequent encoder interrupts are used to recalculate RPMcorrectionj until the media sheet is handed off. The amount of error that can be eliminated may be smaller than otherwise might be the case due to the lack of path length available to media sheet N before reaching roller 202.

[0045] The embodiments described above include a single tray controller 600 that controls each of the media path rollers 202, 210, 212, 214, pick rollers 516, 517, 518, motors 230, 232, 234, and receives signals from the pass-through sensors 220, 222, 224. In another embodiment, each pick tray 510, 512, 514 has a separate controller that controls the section of the media path 200 associated with the pick tray. For example, a first controller controls the third pick tray 514 with pick device 518, roller 214, motor 234, and receives signals from sensor 224, and a second controller controls the second pick tray 512 with pick device 517, roller 212, motor 232, and receives signals from sensor 222. In another embodiment, the main controller 700 controls the function of one or more pick trays. One skilled in the art will recognize that a variety of options may be available and are included within the scope of the present invention.

[0046] The positioning of the rollers 202, 210, 212, 214 along the media path may be spaced in a variety of orientations. Therefore, the amount of sole control of media sheet speed by any roller may also vary. In one embodiment, the distance between rollers 210, 212, and 214 is about 125 millimeters and the distance between roller 210 and the top of the duplexer 300 is 125 millimeters. In another embodiment, the distance between rollers within the media path is between about 110 to 140 millimeters. Additionally, the number of rollers within the media path 200 may vary. Embodiments may include one roller for each pick tray, more than one roller for each pick tray, one roller for every two pick trays, etc. One skilled in the art will understand the arrangement and number of rollers may vary.

[0047] The media/image alignment region may be positioned a variety of distances from the last downstream roller within the media path 200. In one embodiment, the media/image alignment region is positioned about 150 millimeters downstream of the duplex roller 202. In another embodiment, the media/image alignment region is positioned between about 135 to 165 millimeters downstream of the duplex roller 202.

[0048] A high capacity pick tray 513 having a larger capacity than pick trays 510, 512, 514 may be positioned along the media path 200. In one embodiment, the high capacity tray 513 is positioned upstream of the third pick tray 514 as illustrated in FIG. 3. A pick device 519 moves a media sheet into the media path and are sensed by pass through sensor 226. In one embodiment, roller 216 controlled by motor 236 adjusts for Merror and operates in the same manner as the other tray. In another embodiment, Merror is corrected by one of the downstream rollers, such has roller 214 positioned directly upstream of the tray 513.

[0049] In the foregoing description, like-reference characters designate like or corresponding parts throughout the several views. Also, it is to be understood that such terms as “forward”, “rearward”, “left”, “right”, “upwardly”, “downwardly”, and the like are words of convenience that are not to be construed as limiting terms. Certain modifications and improvements will occur to those skilled in the art upon a reading of the foregoing description. The present invention may be used for reducing or eliminating media position errors other than those caused by the pick command. It should be understood that all such modifications and improvements have been deleted herein for the sake of conciseness and readability but are properly within the scope of the following claims.

Claims

1. A method of adjusting a speed of a media sheet moving along a media path region of a pathway within an image forming apparatus to intercept a toner image at a transfer point, the method comprising the steps of:

a. determining a positional error of the media sheet moving along the media path region;

b. determining at least one correction speed that is different than a process speed;

c. moving the media sheet along the section of the media path at the correction speed and reducing the positional error; and

d. moving the media sheet at a speed substantially the same as a process speed along a remaining portion of the media path region.

2. The method of claim 1, wherein moving the media sheet along the section of the media path at the correction speed eliminates the positional error.

3. The method of claim 1, wherein the step of determining the positional error of the media sheet moving along the media path region occurs at least when the media sheet is introduced into the media path region from a pick tray.

4. The method of claim 1, wherein the correction speed cannot exceed a maximum speed.

5. The method of claim 1, wherein the correction speed cannot be less than a minimum speed.

6. The method of claim 1, further including the step of moving the media sheet along the media path region at the process speed prior to determining the positional error.

7. The method of claim 1, wherein the section of the media path is about 110 to 140 millimeters.

8. The method of claim 1 further comprising repeatedly determining a positional error and a correction speed based on a current determined position of the media sheet.

9. The method of claim 1 further comprising controlling a pair of rollers with a single motor, said rollers moving the media sheet.

10. A method of adjusting a speed of a media sheet moving along a media path region of a pathway within an image forming apparatus to intercept a toner image at a transfer point, the method comprising the steps of:

a. introducing the media sheet into the media path region;

b. sensing the position of the media sheet along the media path;

c. determining a positional error of the media sheet;

d. contacting the media sheet with a transport mechanism to control the speed of the media sheet along a media path section;

e. rotating the transport mechanism to move the media sheet at at least one correction speed;

f. at a downstream end of the media path section, rotating the transport mechanism to move the media sheet at a process speed that is different than the correction speed; and

g. contacting the media sheet with a downstream transport mechanism that is rotating to move the media sheet at a speed that is substantially the same as the process speed.

11. The method of claim 10, wherein the step of determining a positional error comprises determining a difference between an image distance and a media sheet distance.

12. The method of claim 10, wherein the at least one correction speed is a difference between the process speed and a difference between an image position and a media position multiplied by a proportional gain constant.

13. The method of claim 10, wherein the positional error results from the step of introducing the media sheet into the media path region.

14. The method of claim 10 further comprising repeatedly determining a position of the media sheet and recalculating the at least one correction speed based in part on said repeated determinations.

15. A method of timing a media sheet to intercept a toner image at a transfer point comprising the steps of:

a. receiving a request to print an image;

b. placing a toner image on a transfer mechanism;

c. moving a media sheet from a pick tray into a media path;

d. sensing a media distance of the media sheet relative to the transfer point and an image distance of the toner image relative to the transfer point;

e. determining a positional error of the media sheet based on the media distance and the image distance;

f. determining at least one correction speed based on the difference between the image distance and the media distance multiplied by a proportional gain constant;

g. moving the media sheet along a first section of the media path at the at least one correction speed by contacting the media sheet with a first roller;

h. moving the media sheet along a second section of the media path at a speed substantially the same as a process speed by contacting the media sheet with a second roller, the process speed being different than the correction speed; and

i. moving the media sheet along a media/image alignment region and intercepting the toner image at the transfer point.

16. The method of claim 15, wherein the request to print the image is received by a main controller.

17. The method of claim 16, wherein the step of determining the positional error of the media sheet is performed by a tray controller.

18. The method of claim 17, wherein the step of moving the media sheet along a first section of the media path is performed by the tray controller.

19. The method of claim 15 further comprising periodically recalculating the correction speed based on concurrently determined media sheet position and image position.

20. A method of synchronizing the arrival of a media sheet and a toner image at a transfer point comprising the steps of:

a. moving the toner image along a transfer belt at a speed to arrive at the transfer point at a predetermined time;

b. moving a plurality of rollers positioned along a media path at a process speed;

c. placing a media sheet within the media path a distance away from the transfer point to arrive at the transfer point at the predetermined time when moving at the process speed;

d. determining a positional error of the media sheet at a point along the media path;

e. changing the speed of one of the plurality of rollers from the process speed to at least one correction speed and moving the media sheet through a section of the media path controlled by the one roller;

f. after the sheet has moved through the section of the media path controlled by the one roller, moving the sheet at a speed substantially the same as the process speed; and

g. transferring the sheet to a media/image alignment region.

21. The method of claim 20, wherein moving the media sheet at the at least one correction speed through the section of the media path controlled by the one roller reduces the positional error.

22. The method of claim 20, wherein the correction speed is limited to a maximum speed at which the one of the plurality of rollers can operate.

23. The method of claim 20, wherein the correction speed is limited to a maximum speed at which the one of the plurality of rollers can operate.

24. The method of claim 20 further comprising recalculating said correction speed based on a later determined positional error of said media sheet.

25. A method of moving a media sheet through a media path of an image forming apparatus comprising the steps of:

a. controlling movement of the media sheet along a first section of the media path with a first roller;

b. controlling the movement of the media sheet along a second section of the media path with a second roller;

c. rotating both the first roller and the second roller at a process speed;

d. detecting a positional error as the media sheet enters the first section of the media path and changing the first roller from the process speed to a correction speed; and

e. after the media sheet has traveled along the first section of the media path, moving the first roller and the second roller at the process speed and moving the media sheet from the first section to the second section.

26. The method of claim 25, prior to the media sheet reaching a downstream end of the first section, changing the speed of the first roller from the correction speed to a speed substantially the same as the process speed.

27. The method of claim 25 further comprising periodically recalculating a positional error of the media sheet and recalculating said correction speed based on the recalculated positional error.

28. A method of controlling an image forming apparatus, comprising:

a. controlling a pair of rollers in a media path with a single motor;

b. correcting positional error of a media sheet with one or more rollers in the media path; and

c. determining if the media sheet has passed a downstream roller of the pair of rollers before correcting for positional error in a subsequent media sheet.