Patent Publication Number: US-7914099-B2

Title: Media handling system and method

Description:
FIELD OF THE INVENTION 
     The invention relates generally to handling sheets of media through a printing apparatus and more particularly to accurately loading staged media on a moving target. 
     BACKGROUND OF THE INVENTION 
     A media handling subsystem transports a media sheet through a printing apparatus, such as a computer printer, fax machine or copy machine, for imaging. A media sheet is picked from a stack, typically in a tray, then moved along a media path using drive rollers. Along the media path, the media sheet is positioned relative to an imaging mechanism, such as an ink or toner cartridge or printhead, which forms character and/or graphic markings on the media sheet. 
     For drum based printers, for example, a sheet is fed to the rotating drum by a sheet feeder, and a vacuum captures it and rolls it on to the drum. In operation, it is necessary to accurately load the staged media sheets onto the moving drum to effectively obtain media hold down. The media is loaded from the sheet feeder a fixed staged distance from the drum. The time to start moving the staged sheet of media is determined based on the expected motor ability to accelerate and paper velocity to meet the target or drum at the appropriate location. However, a number of variances may result in the operation to become misaligned. Such variances include motor speed mismatch, media thickness, and roller wear, for example. Such misalignment problems may result in increased numbers of media hold down issues, resulting in lower reliability and high numbers of jams and reduced print head lifetimes. A system and method that accurately loads the staged media onto a moving drum is desired. 
     SUMMARY OF THE INVENTION 
     A media handling system for delivering media sheets to be printed from a staging location to a drum along a media path, including: at least one drive roller positioned along the media path between the staging location and the drum; a sensor positioned along the media path between the at least one drive roller and the drum; and, an encoder that provides an output responsive to the sensor; wherein, when the at least one drive roller advances a media sheet from the staging location to engage the drum, the sensor detects a position of the advancing media sheet prior to engaging the drum, and the rate of further advancing of the media sheet to engage the drum by the at least one drive roller is dependent upon the encoder output. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Understanding of the present invention will be facilitated by consideration of the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which like numerals refer to like parts and: 
         FIG. 1  illustrates a schematic view of a media path and printing apparatus according to an embodiment of the present invention; and, 
         FIG. 2  illustrates a flow diagram of a process suitable for use with the path and apparatus of  FIG. 1  and according to an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiments is merely by way of example and is in no way intended to limit the invention, its application, or uses. 
       FIG. 1  shows a schematic view of a media path  5  through a printing apparatus  10  according to an embodiment of this invention. Apparatus  10  may take the form of a printer suitable for use with one or more computing devices, a copier, a facsimile machine or a multi-function printing apparatus that incorporates printing/copying/faxing functionalities, all by way of non-limiting example. 
     Apparatus  10  includes an imaging mechanism  20  for printing images on media sheets while they are supported by drum  30 . The media sheets may take the form of sheets of paper, transparencies or any other substrate suitable for having images printed thereon. Mechanism  20  may take the form of a monochrome and/or color printing mechanism, and incorporate one or more print cartridges (such as cartridges that incorporate ink or toner) and/or one or more print carriages that carry one or more printheads, such as ink-jet pen print bodies, all by way of non-limiting example only. In the illustrated embodiment, drum  30  rotates and transports media sheets past imaging mechanism  20 . 
     Apparatus  10  includes a media handling system that transports media sheets along path  5  to drum  30 , and in the illustrated embodiment, receives media sheets from drum  30 . The media handling system includes a plurality of drive rollers  40 . Each drive roller is akin to an elastomeric “tire”. The driver rollers are typically grouped about a rotating shaft  50 . Each shaft  50  is typically driven by a motor  60  responsively to a media transport controller  70 . 
     Controller  70  may typically take the form of a computing device that includes a processor. A processor generally includes a Central Processing Unit (CPU), such as a microprocessor. A CPU generally includes an arithmetic logic unit (ALU), which performs arithmetic and logical operations, and a control unit, which extracts instructions (e.g., code) from memory and decodes and executes them, calling on the ALU when necessary. “Memory”, as used herein, generally refers to one or more devices capable of storing data, such as in the form of chips, tapes, disks or drives. Memory may take the form of one or more random-access memory (RAM), read-only memory (ROM), programmable read-only memory (PROM), erasable programmable read-only memory (EPROM), or electrically erasable programmable read-only memory (EEPROM) chips, by way of further example only. Memory may take the form of internal or external disc drives, for example. Memory may be internal or external to an integrated unit including a processor. Memory preferably stores a computer program or code, e.g., a sequence of instructions being operable by a processor. Controller  70  may take the form of hardware, such as an Application Specific Integrated Circuit (ASIC) and or firmware, in addition or in lieu of incorporating a processor. 
     The media handling system picks media sheets from stacks of one or more media sheets supported by input trays  82 ,  84 ,  86 . In the illustrated embodiment, tray  86  is a manual feed tray. Media sheets picked from the trays are fed along media path  5  through the print apparatus  10  to receive printed markings by mechanism  20 . 
     In the illustrated embodiment of the present invention there are eight (8) motors that drive shafts coupled to drive rollers, in-turn used to advance media sheets along media path  5 . It may be noted that only two motors  60  are shown in  FIG. 1  for purposes of explanation. In the illustrated embodiment, a first motor operates drive rollers to advance media sheets from trays  82 ,  84 ,  86  to a first position  5   a . A second motor operates drive rollers to advance media sheets from position  5   a  to a position  5   b . A third motor operates drive rollers to advance media sheets from position  5   b  to a position  5   c . A fourth motor operates drive rollers to advance media sheets from position  5   c  to a position  5   d . A fifth motor operates drive rollers to advance media sheets from position  5   d  to a position  5   e  such that the media sheets engage drum  30 . Drum  30  may secure media sheets thereto via a vacuum operation, and be rotated by a drum motor  32 , for example. In the illustrated embodiment drum  30  advances media sheets from position  5   e , past imaging mechanism  20 , to a position  5   f . A sixth motor operates drive rollers to advance media sheets from position  5   f  to a position  5   g.    
     In the illustrated embodiment, print apparatus  10  is configured to print single-sided media sheets in a simplex mode and double-sided media sheets in a duplex mode. In the simplex mode, media sheets travel along simplex path  7 , such that only one side of the media sheet travels past imaging mechanism  20 . In duplex mode, media sheets travel along a duplex path  9 , such that a first side of the media sheets pass by mechanism  20  in a first pass, and a second side of the media sheets pass by mechanism  20  on a second pass. In between the first and second passes, each media sheet is flipped, such that the first printed side of the media sheet abuts drum  30  as the media sheet travels along the second pass. It will be appreciated that printing mechanisms utilizing other simplex and duplex paths may be utilized. 
     In the duplex mode, a seventh motor operates drive rollers to advance media sheets from position  5   g  to a position  5   h . In the illustrated embodiment, the seventh motor also advances the media sheets from the position  5   h  to the position  5   d , so the second side of the media may be printed on by mechanism  20 . 
     After again traversing drum  20  to position  5   g , and in the simplex mode, an eighth motor operates drive rollers to advance media sheets from position  5   g  to a position  5   i , from which printed media sheets are ejected. 
     Apparatus  10  includes a plurality of sensors positioned along media path  5 . The sensors may operate in conjunction with controller  70 . In the illustrated embodiment, apparatus  10  includes flag sensors  90 , a type sensor  100 , a thickness sensor  110  and optical sensors  120 . Each of the sensors may be operatively coupled to controller  70 . In the illustrated embodiment, flag sensors  90  are used in conjunction with controller  70  to determine a media sheet&#39;s progression along path  5  by rollers  40 . In the illustrated embodiment, type sensor  100  is used in conjunction with controller  70  to determine the type of media that is advancing along path  5 . For example, sensor  100  may be used to determine whether a then advancing media sheet is a transparency. In the illustrated embodiment, thickness sensor  110  is used in conjunction with controller  70  to determine a thickness of a then advancing media sheet. Finally, in the illustrated embodiment, optical sensors  120  are used in conjunction with controller  70  to also determine a media sheet&#39;s progression along path  5 . 
     In one embodiment, each flag sensor  90  comprises a lever biased to a first position in which it does not close a light circuit between an optical emitter and optical detector. In one embodiment, the lever is mounted so that gravity biases it to the first position. In another embodiment, the lever is spring-biased to the first position. The biasing force (e.g., gravity, spring tension) is sufficiently minimal, however, so that a media sheet traversing along path  5  past flag sensor  90  tips the lever and pushes it into a tripped, second position in which it closes the light circuit. Each lever may be made of conventional lightweight materials used in print apparatus components. Although a rotatable lever is described to embody a flag sensor, other mechanical structures responding to the media sheet traversing along path  5  may be used. 
     In one embodiment of the present invention, each optical sensor  120  includes a light source and a light detector. Exemplary light sources include a photo-emitter, LED, laser diode, super luminescent diode and fiber optic source. Exemplary light detectors include a photo-detector, charged couple device and photodiode. Each light source is oriented to emit a light beam in a specific direction. Each light detector is aligned to detect light emitted from a corresponding light source, either directly or after being reflected by a media sheet, for example. 
     Together flag and optical sensors  90 ,  120  detect when a media sheet encounters a drive roller and the relative position of one or more edges of media sheets as they advance down path  5 . 
     For one or more reasons, such as constraints imposed by a vacuum system used to hold media pages against drum  30  while they pass mechanism  20 , the leading edge of each media sheet may need to engage a particular location on drum  30  (for example, at one or more loading positions). One such loading position is shown as position  31  in  FIG. 1 . In practice, tolerances for deviation from a loading position may be on the order of a few millimeters. In such a case, media sheets may be held (or staged) at position  5   d  (e.g., a staging position or location) until drum  30  is at an appropriate position. For example, the fifth motor that advances media sheets from position  5   d  to position  5   e , such that they engage drum  30 , may be halted once a media sheet is received. The fifth motor may be activated at a time when drum  30  reaches a position, such that the continued rotation of drum  30  and activation of the fifth motor is expected to result in a leading edge of a staged media sheet to engage drum  30  at a loading position. 
     The leading edge of a media sheet may not always reach drum  30  when expected. If the leading edge of a staged media sheet does not engage drum  30  at a loading position (or within an allowable tolerance thereof), apparatus  10  may indicate a jam condition, and halt operation. 
     Referring still to  FIG. 1 , apparatus  10  may incorporate one or more additional sensors  200  and an encoder  210 . Such an additional sensor and encoder may be used to mitigate the occurrence of jam conditions. In the illustrated embodiment, sensor  200  is positioned between the staging location and drum  30 . In the illustrated embodiment, sensor  200  is positioned between at least one roller activated by the fifth motor and drum  30 . In the illustrated embodiment, sensor  200  is positioned along media path  5  immediately before drum  30 . According to an embodiment of the present invention, sensor  200  may take the form of an optical sensor. Accordingly, sensor  200  may incorporate a light source and a light detector. Exemplary light sources include a photo-emitter, LED, laser diode, super luminescent diode and fiber optic source. Exemplary light detectors include a photo-detector, charged couple device and photodiode. The light source is oriented to emit a light beam into path  5 . The light detector is aligned to detect light emitted from the source, either directly or after being reflected by the media, for example. Other types of detectors, such as one or more flag sensors, may be used as sensor  200 . 
     Encoder  210  may take the form of a motor position encoder. Encoder  210  may be embodied as firmware. Firmware, as used herein, generally refers to a combination of software and hardware. Encoder  210  is coupled to sensor  200 , and responsive thereto to latch (e.g., output and hold) a value indicative of the position of motor  330  when sensor  200  detects the leading edge of a media sheet. The latched value is read by controller  70  and used to adjust the rate at which roller  220  delivers a media sheet to engage drum  30 . In the illustrated embodiment, motor  330  serves as the fifth motor, and operates drive rollers  220  to advance media sheets from the staging location  5   d  to a position  5   e , such that the media sheets engage drum  30 . In the illustrated embodiment, motor  330  is coupled to, and responsive to controller  70 . Controller  70  controls the rate at which roller  220  delivers a media sheet to engage drum  30 . 
     According to an embodiment of the present invention sensor  200  may be positioned along the paper path about 1.5 inches from drum  30 . According to an embodiment of the present invention, when transporting media between staging location  5 D to sensor  200 , encoder  210  is monitored by controller  70  and the control voltage to motor  330  is periodically adjusted in order to maintain a constant roller speed approximately equal to the drum  30  speed. For example, where motor  330  takes the form of a DC motor, a DC operating bias may be applied to motor  330  by or responsively to controller  70 . The operating speed of motor  330  may be substantially proportional to the applied operating bias. The applied operating bias may be indicative of a nominal voltage component in addition to a correction voltage component (e.g., V nominal ±V correction ) where the nominal voltage component is expected to result in a desired motor speed (e.g., 30 inches/sec of media movement), and the correction voltage component alters or corrects the actual motor speed to match the desired motor speed. The correction voltage component may be determined and combined with the nominal voltage component using a motor position encoder coupled to a motor that is periodically checked by a controller, such as controller  70 , to determine its actual speed. 
     When the media edge enters sensor  200 , the encoder  210  value, which is indicative of motor  330  location or angular position, is latched and subsequently received by the controller  70 . Controller  70  then adjusts the operating bias of motor  330  such that motor  330  velocity is adjusted. In other words, when sensor  200  detects a leading edge of an advancing media sheet, the value of encoder  210  is latched. The latched value is indicative of the position of motor  330  when sensor  200  was activated, and hence the distance motor  330  traveled when sensor  200  was activated. Controller  70  compares the latched value to a predetermined value indicative of a distance motor  330  was expected to have traveled when sensor  200  was activated. By way of further, non-limiting example only, when sensor  220  detects a media sheet leading edge, a value x±y is latched, where x is the value expected to be latched and y is a variance of the actual value latched from the expected value. Controller  70  then compares the latched x±y value to the x value, to determine the y value. Controller  70  then modifies or alters the motor  330  operating bias to offset the y value, such as by temporarily ramping the operating bias up or down, to correct for or mitigate the value y. In such a case, the operating bias may be akin to V nominal ±V correction ±V correction-y , where the nominal voltage component is expected to result in a desired motor speed (e.g., 30 inches/sec of media movement), the correction voltage component alters or corrects the actual motor speed to match the desired motor speed, and the y-correction voltage component corresponds to the determine y value. The operating bias of others of motors  60  may analogously be modified to mitigate driving speed mismatch between motors engaging a common media sheet, for example. 
     Referring now to  FIG. 2 , there is shown a flow diagram of a process  300  suitable for use with the system of  FIG. 1  and according to an embodiment of the present invention. Process  300  begins with a media sheet being staged at block  310 . Referring now also to  FIG. 1 , media staging at block  310  may typically involve transporting the media sheet from one of trays  82 ,  84 ,  86  along media path  5  to staging location  5   d.    
     At block  320 , it is determined whether the staged media sheet should be advanced. The leading edge of the media sheet may need to engage drum  30  at a particular location on drum  30  (i.e., at a loading position). In such an embodiment, it may be determined at block  320  when drum  30  is at an appropriate rotating position, such that starting to further advance the staged media sheet is expected to result in the leading edge of the media sheet engaging the drum at a loading position. When it is determined that drum  30  is at an appropriate location to begin further advancing the staged media sheet at block  320 , the sheet is advanced at block  330  by a loading motor (e.g., the fifth motor). 
     The leading edge of the media sheet is detected at block  340  after it begins being advanced from the staging location. Referring again to  FIG. 1 , the leading edge of the staged media sheet advanced at block  330  may be detected at block  340  using sensor  200 . At block  350 , it is determined how far the loading motor has advanced or traveled since being activated at block  330  when the leading edge was sensed at block  340 . According to an embodiment of the present invention, the distance the loading motor has traveled may be measured directly, such as by using encoder  210 . According to an embodiment of the present invention, the distance the loading motor has traveled may be indirectly determined, such as by determining the length of the temporal period that has elapsed between the beginning of advancing a staged media sheet at block  330 , and the time when the sensor positioned relative to the staging location detects the leading edge of the advancing media sheet at block  340 . 
     At block  360 , the distance traveled by the loading motor is compared to a distance the loading motor was expected to travel, to determine a difference. According to an embodiment of the present invention, the distance between the staging location (position  5   d ) and the location of sensor  200  is known. In such an embodiment, the distance the staged media loading motor (e.g., the fifth motor) has traveled between being activated at block  330  and the leading edge detection at block  340  is compared to the expected distance to determine a difference at block  360 . Alternatively, the length of the temporal period between beginning to advance a staged media sheet at block  330  and when the leading edge of the advancing media sheet is detected at block  340  may be compared to an expected value to determine a difference at block  360 . 
     At block  370 , a correction is determined dependently upon the difference determined at block  360 . For example, a correction value may be determined dependently upon the determined difference. The correction value may be applied at block  380  to controller  70 , which in turn adjusts the rate at which the loading motor (e.g., fifth motor) transfers the staged media along media path  5  (e.g., accelerates or decelerates media sheet advancing on a sheet-by-sheet basis). Alternatively, the encoded correction may be applied at block  380  directly to and modulate operation of the loading motor (e.g., fifth motor). 
     By way of further non-limiting example, and according to an embodiment of the present invention, correction is applied by adjusting the motor velocity of the loading motor(s)  330  immediately after the media edge is sensed at sensor  200 . When the media edge is sensed at sensor  200 , the actual distance traveled from staging point  5 D to sensor  200  is computed and compared to a predetermined value stored in the controller. 
     If the actual distance traveled, as sensed at sensor  200 , is larger than the predetermined value, it indicates that the loading motor has traveled “slower” than the expected drum trajectory, and the relative position the media is lagging behind the drum loading location. In this case, the loading motor velocity is temporarily increased (accelerated) for a short period of time, then decreased (decelerated) back down to the original nominal velocity such that the velocity of the loading motor is again nominally matched to the velocity of the drum at the end of the correction move. The correction move follows a predetermined up-ramp and down-ramp table in order to advance the media location relative to the drum, such that the net increase in position (area change under the loading motor velocity curve) will compensate for the distance error detected at sensor  200 . The length of up-ramp and down-ramp used is determined based on the amount of distance correction required. 
     If the actual distance traveled, as sensed at sensor  200 , is smaller that the predetermined value, it indicates that the loading motor has traveled “faster” than the expected drum trajectory, and the relative position of the media ahead of the drum loading location. In this case, the loading motor velocity is temporarily decreased, then increased back up to the same nominal value, such that the media position is retarded relative to the drum position in order to correct for the distance error detected at sensor  200 . Once again, the length of down-ramp and up-ramp used is computed real-time as a function of the correction amount required. 
     In such a manner, variations in media loading (e.g., misalignments between a media sheet leading edge and a loading location) due to a variety of factors may be compensated for in real-time, on a sheet-by-sheet basis. 
     The description of the invention is merely exemplary in nature and, thus, variations that do not depart from the gist of the invention are intended to be within the scope of the invention. Such variations are not to be regarded as a departure from the spirit and scope of the invention.