Patent Publication Number: US-8118302-B2

Title: Passive linear encoder

Description:
RELATED APPLICATIONS 
     This patent application is a divisional application of, and claims priority to, U.S. patent application Ser. No. 10/281,935, titled “Passive Linear Encoder”, filed on Oct. 28, 2002, now U.S. Pat. No. 6,860,665 commonly assigned herewith, and hereby incorporated by reference. 
    
    
     BACKGROUND 
     The movement of print media within a printer may require accuracy as great as 100 (ppm) parts per million; in some cases even greater accuracy may be required. This is equivalent to a margin of error of about 0.2 mils associated with a 2 inch movement of the print media. 
     To achieve 100 ppm accuracy, the effective radius of printer roller shafts could be tightly controlled. For example, for a typical shaft having a 0.3 inch radius, the neutral axis, i.e. the line where the rotary velocity of the shaft and the linear velocity of the print media traveling through the paper path are equal, should be within 30 micro inches (i.e. 0.3*100 ppm), a distance which is approximately 1% of the thickness of a sheet of paper. Thus, a small deviation from the desired diameter may cause a media registration error. 
     Increasing the diameter of the roller is a potential solution to the issue of extremely tight tolerances required of the radius of the metering roller. However, an increased diameter can result in greater inertia during operation, which results in difficulty when printing at higher speeds. 
     A roller with a low contact force against the print media (such as paper) could make use of a highly frictional outer surface. However, with this approach it might be more difficult to tightly control the diameter of the roller, since the diameters of highly frictional surfaces are less easily controlled. 
     Alternatively, using a roller with a higher contact force against the print media may result in media deformation, which induces errors in the registration process. 
     SUMMARY 
     A passive linear encoder includes a loop and a sensor. The loop is configured to engage print media and to move in concert with, and under power of, the print media. The sensor is positioned to scan indicia defined on an inner surface of the loop. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The same reference numbers are used throughout the drawings to reference like features and components. 
         FIG. 1  is a top plan view of a printer having an implementation of a passive linear encoder. 
         FIG. 2  is an enlarged top plan view of the passive loop portion of the implementation of the passive linear encoder, as viewed through the registration window defined in a deck portion of the printer. 
         FIG. 3  is a cross-sectional view of the implementation of the passive linear encoder, taken along the  3 - 3  lines of  FIG. 1 . 
         FIG. 4  is an exemplary view of the inner surface of the passive loop, taken along the  4 - 4  lines of  FIG. 3 . 
         FIG. 5  is a cross-sectional view of the implementation of the passive linear encoder of  FIG. 3 , taken along the  5 - 5  lines of  FIG. 3 . 
         FIG. 6  is a cross-sectional view of a second implementation of the passive linear encoder, taken from a perspective similar to that of  FIG. 3 . 
         FIG. 7  is a thin-section view of the second implementation of the passive linear encoder of  FIG. 6 , taken from a perspective similar to that of  FIG. 5 . 
         FIG. 8  is a flow chart illustrating a further exemplary implementation of print media registration using an implementation of the passive linear encoder. 
         FIG. 9  is a flow chart illustrating a further exemplary implementation of a print media registration using an implementation of the passive linear encoder. 
         FIG. 10  is a flow chart illustrating a further exemplary implementation of print media registration using an implementation of the passive linear encoder. 
         FIG. 11  is a flow chart illustrating a further exemplary implementation of print media registration using an implementation of the passive linear encoder, wherein a compound guide is employed. 
     
    
    
     DETAILED DESCRIPTION 
     A passive linear encoder, which measures print media movement within a printer, copier or other hard copy output device, includes a loop and a sensor. The loop is configured to engage print media and to move in concert with, and under power of, the print media. The sensor is positioned to scan indicia defined on an inner surface of the loop. 
       FIG. 1  shows an exemplary implementation  100  of a printer  102  having an exemplary passive linear encoder. The printer  102  may be based on any type of technology, such as that found in ink jet and laser printers. In the exemplary implementation of  FIG. 1 , the printer is based on ink jet technology. A printhead  104  moves along a carriage rod  106 . A print media advancement mechanism  108  may be based on one or more rollers, which drive print media  110 , such as paper, envelopes or other material, through a media or paper path  112 . The direction of media movement  114  indicates the direction by which print media moves during the course of printing. 
     Print media registration involves maintaining knowledge of the location of the print media (e.g. sheets of paper and envelopes) as the print media moves through the paper path  112  in the direction of media movement  114 . As will be seen in greater detail below, a passive linear encoder  116  and registration decoder electronics  118  obtain and use information on print media location. 
       FIG. 2  is an enlarged view of a portion of the sensor/encoder  116  of the print media registration apparatus, taken from the same perspective as seen in  FIG. 1 . Print media  110 , such as the sheet of paper seen in  FIG. 1 , slides along the upper deck  202  of the printer  102  as it moves through the paper path  112 . A registration window  204  is an opening defined in the upper deck  202 . The registration window  204  may be rectangular, having the elongated direction parallel to the direction of media movement  114  through the paper path  112 . 
     As seen from above, a passive loop  206  is carried by a guide  208 . The passive loop  206  is configured to engage the print media  110  in frictional contact through the registration window  204 . Motion of the print media  110  drives the passive loop  206  to rotate about the guide  208 , as will be seen in greater detail, below. 
     Two guide elements  210  are separated by a space that is incrementally greater than the width of the passive loop  206 . Accordingly, as the passive loop  206  rotates on the guide  208 , the guide elements  210  assist in keeping the passive loop  206  correctly oriented on the guide  208 . 
     Two biasing elements, a star wheel  212  and a shim  214  are configured to provide a slight force against the print media  110 , which increases the coefficient of friction between the print media  110  and the outer surface of the passive loop  206 . In the implementation seen in  FIG. 2 , paper (not shown to avoid obscuring the passive loop) moving over the deck surface  202  and through the paper path  112  would move between the passive loop  206  and the biasing elements. The biasing elements would apply a slight bias to the print media  110 , thereby increasing the frictional force between the print media  110  and the passive loop  206 . As a result, the friction between the print media  110  and the passive loop  206  is static friction, rather than kinetic friction; accordingly, the passive loop  206  moves in concert with the print media  110 , as the print media  110  moves through the paper path  112 . 
       FIG. 3  shows a cross-sectional view of the passive loop  206 . The passive loop  206  is configured to revolve about the guide  208  as paper or other print media  110  moves through the paper path  112  adjacent to a printhead  302 . The movement of the passive loop  206  is a result of a high coefficient of static friction between the media  110  and the passive loop  206  and a low coefficient of kinetic friction between the passive loop  206  and the guide  208 . Accordingly, a first component  304  of the passive loop  206  is configured and oriented for movement in the direction  114  of, and at the speed of, print media movement. The first component  304  is generally framed within the registration window or opening  204  within the upper deck  202  of the printer  102 . A second component  306  is configured and oriented for movement in a direction  328  opposed to the media movement. Upstream and downstream directionally translational components  308 ,  310  allow the passive loop  206  to rotate about the guide  208 . 
     The guide  208  includes an upper deck  312 , which supports the first component  304  of the passive loop  206  within the registration window  204  defined in the printer deck  202 . Upstream and downstream turnarounds  314 ,  316  support portions  308 ,  310  of the passive loop  206 . 
     A sensor  318  is configured to detect the passage of indicia, such as a “jail bar” pattern on the inside surface  320  of the passive loop  206 , typically with an accuracy of better than 100 ppm. The sensor  318  communicates with the decoder electronics  118  (seen in  FIG. 1 ) over wiring  322 . A preferred sensor  318  observes the jail bar pattern  402  having alternating light and dark bars  404 ,  406  (seen in  FIG. 4  from the orientation of the  4 - 4  lines of  FIG. 3 ) and produces an analog signal having voltage which varies as a sine wave or a similar signal. 
     In the implementation of  FIG. 3 , the length  324  of the first component  304  of the passive loop  206  is greater than the distance  326  by which the print media  110  is incrementally advanced, which is typically related to the size of the printhead  302  used in an ink jet application. In an alternative implementation, the relative lengths of distances  234 ,  326  could be reversed or altered. 
     Two biasing elements bias the print media  110  against the passive loop  206 , thereby maintaining contact between them, and maintaining a static (as opposed to a kinetic) frictional condition. The star wheel  212  is used downstream, since it is able to apply bias without degrading print quality. The shim  214  is used upstream, prior to application of the ink, since its design might result in ink smearing. 
       FIG. 5  shows a cross-sectional view of the print media registration apparatus of  FIG. 3 , taken along the  5 - 5  lines of  FIG. 3 . The print media or paper  110  is carried on the deck  202  of the printer  102 . The registration window  204 , defined in the deck  202 , allows a portion of the passive loop  206  to extend through the upper deck  202 , and to contact the media  110 . 
     The printhead  302  is adjacent to the media  110 . The star wheel  212  or similar biasing element is partially obscured by the printhead  302 , and provides a slight bias against the media  110  to maintain a static frictional connection between the media  110  and the outer surface  502  of the passive loop  206  and the lower surface of the media  110 . For purposes of illustration only,  FIG. 5  shows these elements slightly separated, thereby revealing that distinct structures exist. 
     The outer surface  502  of the passive loop  206  is highly frictional, having a high coefficient of friction that is well-suited to maintain a static frictional bond with the lower surface of the media  110  as the media moves through the print path  112 . Accordingly, the media  110  will drive the passive loop  206  to revolve about the guide  208 . 
     The inner surface  320  of the passive loop  206  is very smooth, having a very low coefficient of friction that is well-suited to result in very little drag or energy loss due to kinetic friction as the inside surface  320  contacts the guide  208 . As seen above, the jail bar pattern  402  of  FIG. 4 , or an alternative pattern, is defined on the inner surface  320 . The sensor  318  is positioned to monitor movement of the pattern during operation. 
     Optional gutters  504 , defined in the guide  208 , allow paper fibers or similar foreign material to accumulate without resulting in print quality degradation. 
     The implementation seen in  FIG. 6  differs from that seen in  FIG. 3  in that the guide is compound. The compound guide is associated with a platen, which can result in higher print quality in some circumstances. The compound guide provides an upstream segment  602  and a downstream segment  604 . The platen  606  is carried between the segments. An upstream slot  608  and a downstream slot  610  are defined between the platen  606  and the upstream  602  and downstream  604  segments, respectively. The direction of print media movement  114  determines the orientation of upstream and downstream. The passive loop  206  is configured to pass through the upstream and downstream slots  608 ,  610 , and thereby pass on the far side  612  of the platen  606 , i.e. the side of the platen  606  opposite the printhead  302 . 
     Due to the non-linear configuration of the upper portion of the passive loop  206  in the area of the platen  606 , the sensor  318  may be more accurate in an upstream or a downstream location. A representative upstream location is illustrated by sensor  318 ( 1 ) and a representative downstream location is illustrated by sensor  318 ( 2 ). In some implementations, two sensors may be used, including an upstream sensor  318 ( 1 ) and a downstream sensor  318 ( 2 ). In such an application, data originating from the upstream sensor  318 ( 1 ) may initially be more accurate than data originating from the downstream sensor  318 ( 2 ) as the print media  110  approaches the printhead  302 . Later, as the print media  110  begins to move away from the printhead  302 , data from the downstream sensor  318 ( 2 ) may be more accurate. Accordingly, data from both sensors  318 ( 1 ),  318 ( 2 ) may be evaluated, to obtain greater sensing accuracy. 
     Optionally, the shim  214  and the star wheel  212  may be aligned with rollers  614 ,  616 , respectively. The rollers  614 ,  616  reduce friction between the passive loop  206  and compound guide segments  602 ,  604 , respectively. Accordingly, the shim  214  and star wheel  212  are able to increase friction between the print media  110  and the passive loop  206 , while the rollers  614 ,  616  prevent a similar increase in friction between the passive loop  206  and the compound guide segments  602 ,  604 . 
       FIG. 7  shows a thin-section view of the print media registration apparatus of  FIG. 6 , taken from a perspective similar to that of  FIG. 5 . The platen  606  includes two rails  702  on the side of the platen opposite the printhead  302 , i.e. the side of the platen  606  oriented toward the passive loop  206 . The passive loop  206  includes peripherally defined rims  704  configured to ride on the rails  702 . The peripheral rims  704  have surfaces with very low frictional coefficients, which slide easily on the rails  702 . A frictional surface  706 , defined between the rims  704 , has a high coefficient of friction, and is therefore suited for formation of a static frictional bond with the print media  110 . 
     The flow chart of  FIG. 8  illustrates an implementation of an exemplary method  800  for print media registration using a passive linear encoder  116 . The elements of the method may be performed by any desired means, such as by the movement of mechanical parts initiated and controlled through the execution of processor-readable instructions defined on a processor-readable media, such as a disk, a ROM or other memory device. Also, actions described in any block may be performed in parallel with actions described in other blocks, may occur in an alternate order, or may be distributed in a manner which associates actions with more than one other block. 
     At block  802 , a static frictional connection is established between the passive loop  206  and print media  110 . For example, as seen in  FIG. 3 , a first component  304  of the passive loop  206  is in contact with the media  110 . 
     At block  804 , the static frictional connection is maintained between the passive loop  206  and the print media  110  through a highly frictional outer surface  502  on the passive loop  206 . Because the outside surface  502  of the passive loop  206  has a high coefficient of friction, the bond established with the print media  110  is through static friction, rather than through kinetic friction. 
     At block  806 , the print media  110  drives the passive loop  206 , causing the passive loop  206  to rotate about the guide  208 . The print media  110  is in turn driven by the print media advancement mechanism  108 . 
     At block  808 , the passive loop  206  is restricted to a course of travel defined by a guide  208 . Referring to  FIG. 3 , it can be seen that as the media  110  moves from left to right, according to direction  114 , the passive loop  206  moves about the guide  208  in a clockwise manner. 
     At block  810 , the inner surface  320  of the passive loop  206 , having a low coefficient of friction, slides against the guide  208 . The inner surface  320  maybe covered with a material, such as TEFLON®, which results in a low coefficient of kinetic friction as the inner surface  320  of the passive loop  206  is slid against the guide  208 . 
     At block  812 , print media  110  movement is tracked by tracking movement of the passive loop  206 . Since the passive loop  206  moves in concert with the movement of the print media  110 , movement of the print media  110  can be tracked by tracking movement of the passive loop  206 . 
     At block  814 , a signal is generated by a sensor  318  in response to movement of indicia  402  defined on an inner surface  320  of the passive loop  206 . As seen, for example, in  FIG. 3 , a sensor  318  is configured to generate a signal in response to movement of indicia  402  defined on the inner surface  320  of the passive loop  206 . 
     At block  816 , the signal from the sensor  318  is obtained, wherein the sensor  318  monitors a jail bar pattern  402 , such as that seen in  FIG. 4  comprising alternating light  404  and dark  406  bars that is defined on the inner surface  320  of the passive loop  206 . 
     The flow chart of  FIG. 9  illustrates an implementation of an exemplary method  900  for performing print media registration using a passive linear encoder  116  and thereby tracking print media movement. The elements of the method may be performed by any desired means, such as by the movement of mechanical parts initiated and controlled through the execution of processor-readable instructions defined on a processor-readable media, such as a disk, a ROM or other memory device. Also, actions described in any block may be performed in parallel with actions described in other blocks, may occur in an alternate order, or may be distributed in a manner which associates actions with more than one other block. 
     At block  902 , a portion of a passive loop  206  that extends through a registration window  204  defined in a planar surface  202  within a printer  102  makes frictional contact with print media  110 .  FIGS. 2 and 3  illustrate how the passive loop  206  makes contact with the print media  110  through the registration window  204 . 
     At block  904 , a coefficient of friction is increased between the passive loop  206  and the print media  110  by applying pressure to the print media  110  with a biasing element. The biasing element may be a star wheel  212 , a shim  214  or other element such as a pinch roller, as desired. 
     At block  906 , the print media  110  is advanced through a paper path  112  defined in the printer  102  using a media advancement mechanism  108 . For example, rollers may be used to drive the print media  110 . 
     At block  908 , the passive loop  206  is driven by advancing the print media  110  about a course of travel defined by a guide  208 . Referring particularly to  FIG. 3  or  6 , it can be seen how frictional contact between advancing print media  110  and the passive loop  206  drives the passive loop  206  about the guide  208 . 
     At block  910 , an inner surface  320  of the passive loop  206 , having a low coefficient of kinetic friction, is passed against the guide  208 , thereby reducing friction between the passive loop  206  and the guide  208 . 
     At block  912 , print media registration is measured by measuring movement of the passive loop  206 . 
     At block  914 , a signal is generated by a sensor  318 , which is directed to detect indicia, such as alternating light and dark patterns  402 , on the passive loop  206 . 
     At block  916 , the signal from the sensor  318 , corresponding to the pattern defined on an inner surface of the passive loop  206 , is monitored. 
     The flow chart of  FIG. 10  illustrates an implementation of an exemplary method  1000  for print media registration using a passive linear encoder  116 . The elements of the method may be performed by any desired means, such as by the movement of mechanical parts initiated and controlled through the execution of processor-readable instructions defined on a processor-readable media, such as a disk, a ROM or other memory device. Also, actions described in any block may be performed in parallel with actions described in other blocks, may occur in an alternate order, or may be distributed in a manner which associates actions with more than one other block. 
     At block  1002 , print media  110  contacts an outer surface  502  of a passive loop  206 . The outer surface  520  of the passive loop  206  has a highly frictional coefficient, which results in a static frictional bond between the passive loop  206  and the media  110 . 
     At block  1004 , a static frictional bond is maintained between the passive loop  206  and the print media  110  by biasing the passive loop  206  to the print media  110  using a biasing element. As seen in  FIGS. 3 and 6 , the biasing elements may include a star wheel  212 , a shim  214 , or similar element that can apply a slight bias to the print media  110 , thereby resulting in a greater frictional coefficient between the print media  110  and the passive loop  206 . 
     At block  1006 , the passive loop  206  is driven about a course of travel defined by a guide  208  by advancing the print media  110 . 
     At block  1008 , the print media  110  is advanced by an amount less than a length of contact between the print media and the passive loop. For example, as seen in  FIG. 3 , the distance of print media advancement  326  is less than the distance  324  associated with the contact between the print media  110  and the passive loop  206 . 
     At block  1010 , kinetic friction between the passive loop  206  and the guide  208  is lowered because the inner surface  320  on the passive loop  206  is configured to have a low coefficient of friction. Alternatively, the guide  208  may be constructed of a low-friction material, or both the inner surface  320  and the guide  208  may be made of low-friction material. 
     At block  1012 , print media registration is measured by measuring movement of the passive loop  208  by optically sensing a pattern  402  defined on an inner surface  320  of the passive loop  206 . 
     At block  1014 , a signal, typically analog but alternatively digital, is generated by a sensor  318  directed at the passive loop  206 . In the exemplary implementation of  FIGS. 3-5 , the sensor  318  is optical, and is therefore directed at indicia  402  such as that illustrate in  FIG. 4 . Where indicated or desired, an alternative sensor based on an alternative technology (e.g. a magnetically operated sensor) could be substituted. 
     At block  1016 , the analog signal from the sensor  318  is interpreted as the sensor monitors the pattern  402  defined on the inner surface  320  of the passive loop  206 . The signal may then be interpreted by decoder electronics  118 . 
     The flow chart of  FIG. 11  illustrates an implementation of an exemplary method  1100  for print media registration using a passive linear encoder  116  wherein a compound guide is employed. The elements of the method may be performed by any desired means, such as by the movement of mechanical parts initiated and controlled through the execution of processor-readable instructions defined on a processor-readable media, such as a disk, a ROM or other memory device. Also, actions described in any block may be performed in parallel with actions described in other blocks, may occur in an alternate order, or may be distributed in a manner which associates actions with more than one other block. 
     At block  1102 , print media  110  is advanced through a paper path  112  by operation of a media advancement mechanism  108 . 
     At block  1104 , a passive loop  206  is driven, in response to advancing print media  110 , about a course of travel defined by a compound guide  602 ,  604  and a platen  606 . 
     At block  1106 , the passive loop  206  is supported on the compound guide  602 ,  604  in a location configured to result in contact between the passive loop  206  and the advancing print media  110 . 
     At block  1108 , the passive loop  206  is deflected from a straight course between rounded ends  314 ,  316  of the compound guide  602 ,  604  to pass adjacent to a platen&#39;s far side. Referring particularly to  FIG. 6 , it can be seen that the platen  606  is carried between the upstream and downstream segments  602 ,  604  of the compound guide. Moreover, it can be seen that the passive loop  206  is deflected from the straight course seen in  FIG. 3 , passing through openings  608 ,  610  in a manner which allows the passive loop  206  to pass adjacent to the platen&#39;s far side (i.e. the side opposite the printhead  302 ). 
     At block,  1110 , peripherally defined rims  704  (as seem in  FIG. 7 ), which are defined on an outer surface  502  of the passive loop  206 , slide against rails  702  carried by a far side of a platen  606 . 
     At block  1112 , print media registration is measured by measuring movement of the passive loop  206 . Since the passive loop  206  moves in concert with the print media  110 , measurement of the movement of the passive loop  206  reveals the movement of the print media  110 . 
     At block  1114 , movement of the passive loop  206  is measured by obtaining a signal from a sensor  318 , wherein the sensor  318  monitors a pattern  402  on an inner surface  320  of the passive loop  206 . 
     At block  1116 , the signal, comprising an analog sinusoid generated by a sensor  318  monitoring digital indicia  402 , is interpreted. As seen in  FIG. 4 , the digital indicia  402  may include alternating light  404  and dark  406  bars, defined on the inner surface  320  of the passive loop  206 . Alternatively, other further optical, magnetic or alternate technology patterns or indicia may be employed to result in signal generation and interpretation. Interpretation of the signal results in real-time knowledge of the location of the media, which is essential for performance of the printing process. 
     Although the disclosure has been described in language specific to structural features and/or methodological steps, it is to be understood that the appended claims are not limited to the specific features or steps described. Rather, the specific features and steps are exemplary forms of implementing this disclosure. 
     Additionally, while one or more methods have been disclosed by means of flow charts and text associated with the blocks, it is to be understood that the blocks do not necessarily have to be performed in the order in which they were presented, and that an alternative order may result in similar advantages.