Abstract:
A method for assisting the threading of a media web in a continuous feed printer has been developed. The method includes generating an electrical signal that corresponds to a level of tension applied by a media web to a roller positioned along a media path in a printer as the media web travels over the roller. A controller activates at least one actuator to rotate a roller positioned along the media path in response to identifying that the level of tension exceeds a predetermined threshold to facilitate threading of the media web through the printing device.

Description:
TECHNICAL FIELD 
       [0001]    This disclosure relates generally to methods for threading a media web through a media path in a printing device, and more particularly to methods for activating one or more rollers to advance the web as the web advances along the media path. 
       BACKGROUND 
       [0002]    Various printing devices include printers that accept individual sheets of pre-cut media or web printers that form images on a continuous web of print media. In a web printer, a continuous supply of media, typically provided in a media roller, is entrained onto rollers that are driven by motors. The motors and rollers pull the web from the supply roller through the printer to a take-up roller. As the media web moves along the media path, the imaging device forms images on the media web that may include text and graphics in one or more colors. Common embodiments of web printing systems include offset lithographic printing systems and inkjet web printing systems. 
         [0003]    Installation of a media web in a printer to enable printing on the web requires a threading operation. A threading operation feeds a free end of the web media from the supply roller through the media path to the take-up roller prior to the commencement of printing. A threading operation can occur for various reasons. In some circumstances, a new media web replaces an exhausted media web supply. In other cases, breakage of a media web requires a remaining portion of the web roller that broke or a new web roller to be threaded through the media path. Because some media web printers use different media paths for different print modes, changes in the printing mode for a printer may necessitate a threading operation. 
         [0004]    In a typical threading operation, a human operator pulls a free end of the media web through the media path and attaches the free end to the take up roller. Because the media paths in many web printers are long, the media path may make one or more turns through the printer. Manual manipulation of the media web in such printers can be tedious and time consuming. Some existing web printers include one or more manual switches that enable the operator to activate selectively motorized rollers positioned along the media path to assist in pulling the web through various portions of the media path. The selective activation of the motorized rollers still require the operator to pull the free end along and guide the web through the printer while engaging the switches to activate rollers as the free end approaches a still roller. If a switch is not located close enough to the free end of the web, the operator must travel back and forth between the switch and free end of the web. Thus, threading operations can be slow and require extensive operator interaction. Improvements in threading operations that enable more efficient threading of the media web would be beneficial. 
       SUMMARY 
       [0005]    In one embodiment, a method of threading a media web through a media path in a printer has been developed. The method includes generating an electrical signal with a first sensor that corresponds to a level of tension applied by a media web to a roller positioned along a media path in a printer as the media web travels over the roller, and activating with a controller at least one actuator to rotate a roller positioned along the media path in response to the electrical signal generated by the sensor exceeding a predetermined first threshold to facilitate threading of the media web through the printing device. 
         [0006]    In another embodiment, a web printing system has been developed. The web printing system includes a plurality of rollers positioned along a media path and configured to engage a media web, a sensor operatively connected to one roller in the plurality of rollers and configured to generate an electrical signal corresponding to a tension applied to the one roller by the media web while the media web is threaded through only a portion of the media path past the one roller, at least one actuator operatively configured to rotate at least one roller in the plurality of rollers, and a controller that is operatively connected to the tension sensor and at the at least one actuator. The controller is configured to identify a level of tension applied to the one roller with reference to the electrical signal, compare the identified level of tension to a first predetermined threshold, and operate the at least one actuator to rotate at least one roller in the plurality of rollers at a threading rotational speed, the threading rotational speed being slower than an operating rotational speed, in response to the identified level of tension exceeding the first predetermined threshold to facilitate threading of the media web through the media path. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1  is a schematic view of a web printing system that is configured to operate one or more actuators to move a media web along a media path. 
           [0008]      FIG. 2  is a block flow diagram of a process for operating one or more actuators in a web printing system to assist in threading a media web through the web printing system. 
       
    
    
     DETAILED DESCRIPTION 
       [0009]    For a general understanding of the environment for the system and method disclosed herein as well as the details for the system and method, the drawings are referenced throughout this document. In the drawings, like reference numerals designate like elements. As used herein the term “printer” refers to any device that is configured to form images on a print medium including direct imaging printing systems and offset printing systems. As used herein, the term “process direction” refers to a direction of travel of an image receiving member, such a media web along a media path in the printer. The terms “upstream” and “downstream” refer to locations that are more closely positioned to the beginning and end, respectively, of the media path. The term “cross-process direction” is a direction that is perpendicular to the process direction along the surface of the image receiving member. As used herein, the terms “web,” “media web,” and “continuous media web” refer to an elongated print medium that is longer than the length of a media path that the web traverses through a printer during the printing process. Examples of media webs include rollers of paper or polymeric materials used in package printing. The media web has two sides forming surfaces that may each receive images during printing. 
         [0010]    As used herein, the term “rotational speed” refers to the angular movement of a rotating member for a given time period, sometimes measured in rotations per second or rotations per minute. The term “linear velocity” refers to the velocity of a member, such as a media web, moving in a straight line. When used with reference to a rotating member, the linear velocity represents the tangential velocity at the circumference of the rotating member. The linear velocity ν for circular members may be represented as: ν=2πrω where r is the radius of the member and ω is the rotational speed or angular velocity of the member. 
         [0011]      FIG. 1  depicts a continuous web printer system  100  that includes six print modules  102 ,  104 ,  106 ,  108 ,  110 , and  112 ; a media path P configured to accept a print medium  114 , a controller  128 , tension sensors  160 ,  162 ,  164 , and  166 ; and actuators  170 ,  172 , and  174 . The print modules  102 ,  104 ,  106 ,  108 ,  110 , and  112  are positioned sequentially along a media path P and form a print zone for forming images on a print medium  114  as the print medium  114  moves past the print modules. 
         [0012]    In printing system  100 , each print module  102 ,  104 ,  106 ,  108 ,  110 , and  112  in this embodiment provides an ink of a different color. In all other respects, the print modules  102 ,  104 ,  106 ,  108 ,  110 , and  112  are substantially identical. Print module  102  includes two print sub-modules  140  and  142 . Print sub-module  140  includes two print units  144  and  146 . The print units  144  and  146  each include an array of printheads that may be arranged in a staggered configuration across the width of both the first section of web media and second section of web media. In a typical embodiment, print unit  144  has four printheads and print unit  146  has three printheads. The printheads in print units  144  and  146  are positioned in a staggered arrangement to enable the printheads in both units to emit ink drops in a continuous line across the width of media path P at a predetermined resolution. 
         [0013]    Print sub-module  142  is configured in a substantially identical manner to sub-module  140 , but the printheads in sub-module  142  are offset by one-half the distance between inkjet ejectors in the cross-process direction from the printheads in sub-module  140 . The arrangement of sub-modules  140  and  142  enables a doubling of linear resolution for images formed on the media web  114 . For example, if each of the sub-modules  140  and  142  emits ink drops at a resolution of 300 drops per inch, the combination of sub-modules  140  and  142  emits ink drops at a resolution of 600 drops per inch. 
         [0014]    During a threading operation, a free end of the media web  114  is pulled through the media path P to prepare the printing system to generate images on the media web  114  using the print modules  102 - 112 . The free end of the media web  114  unrolls from a source roller  152  and passes through a brush cleaner  124  and a contact roller  126  prior to entering the print zone. The media web  114  is pulled along the media path P through the print zone guided by a pre-heater roller  118 , backer rollers exemplified by backer roller  116 , an apex roller  119 , and a leveler roller  120 . The media web  114  then passes through a heater  130  and a spreader  132  after passing through the print zone. The media web passes an exit guide roller  134  and then winds onto a take-up roller  154 . As described in more detail below, as printing system  100  is configured to rotate one or more rollers along the media path P to assist the threading operation. Alternative web printing system configurations may include tension sensors operatively connected to different rollers and other printer components that engage the media web  114  during threading operations. 
         [0015]    The media path P depicted in  FIG. 1  is exemplary of one media path configuration in a web printing system, but various different configurations may lead the web past different rollers and other components. Printing system  100  also includes a media path P′ for an optional duplex web printer configuration. In the duplex configuration, the media web  114  passes through the media path P described above for first-side imaging, and then passes through media path P′ and web inverter  180  after passing the spreader roller  132 . The web inverter flips the media web  114 , and the media web  114  then passes through the entire media path P a second time for imaging of the second side of the media web. After the second side of the media web  114  is imaged, the media web passes the exit guide roller  134  and winds onto the take-up roller  154 . 
         [0016]    Some of the rollers positioned along the media path P that guide the media web  114  are operatively coupled to one or more actuators that rotate the rollers. The term “drive roller” refers to a roller is operatively coupled to an actuator to enable the actuator to rotate the drive roller. In  FIG. 1 , actuators  170 ,  172 , and  174  are operatively connected to drive rollers  118 ,  120 , and  132 , respectively. The actuators  170 - 174  may be electrical motors, pneumatic rotary actuators, hydraulic rotary actuators, and the like. In printing system  100 , each actuator is operatively connected to a single roller, but in an alternative configuration a single actuator may rotate multiple rollers. The single actuator may rotate the multiple rollers at a single linear and angular velocities, or may engage each roller through a set of gears or transmission that enables the single actuator to rotate various rollers at selected linear and angular velocities. 
         [0017]    In the configuration of  FIG. 1 , each of the drive rollers  118 ,  120 , and  132  engages the media web  114  at different times as the media web is threaded through media path P. Each actuator rotates a corresponding roller to urge the media web along the media path P. For example, actuator  170  rotates the pre-heater roller  118  as shown to pull the media web  114  into the print zone. The actuators  170 - 174  may rotate the corresponding rollers at different velocities during different operating modes of the printing system  100 . During a threading operation, each actuator may rotate the corresponding roller at a predetermined rotational speed to assist in threading the media web  114 . In the embodiment of  FIG. 1 , the drive rollers  118 ,  120 , and  132  rotate at lower angular velocities during threading operations than during imaging operations. 
         [0018]    In  FIG. 1 , some rollers positioned along the media path are operatively connected to sensors that generate electrical signals corresponding to a level of tension force exerted by the media web  114  on the roller. Examples of suitable sensors include load cells and strain gauges. In  FIG. 1 , sensors  160 ,  162 ,  164 , and  166  are operatively connected to the pre-heater roller  118 , apex roller  119 , leveler roller  120  and exit guide roller  134 , respectively. The sensors  160 - 166  generate electrical signals that correspond to a tension force between the corresponding rollers and the media web  114 . During a threading operation, the sensors  160 - 166  generate signals corresponding to the tension between the media web and the corresponding rollers that indicate that the corresponding rollers are in contact with the media web  114 . 
         [0019]    In the embodiment of  FIG. 1 , the pre-heater roller  118  is operatively connected to sensor  160  and actuator  170 , and the leveler roller  120  is operatively connected to sensor  164  and actuator  172 . Rollers  118  and  120  are examples of a single roller coupled to a sensor for measuring tension between the roller and the media web, and an actuator that rotates the roller. The apex roller  119  and exit guide roller  134  are operatively connected to sensors  162  and  166 , respectively, but are not directly connected to an actuator. Rollers  119  and  134  are examples of rollers contact the media web  114 , but are not directly rotated by an actuator. The spreader roller  132  is operatively connected to actuator  174 , but is not directly connected to a tension sensor. Alternative printing system configurations may include rollers and other moving members along a media path that are connected to a sensor, an actuator, or a combination of both a sensor and actuator. 
         [0020]    Controller  128  is configured to control various subsystems, components and functions of printing system  100 . The controller  128  may be implemented with general or specialized programmable processors that execute programmed instructions. These components may be provided on a printed circuit card or provided as a circuit in an application specific integrated circuit (ASIC). Each of the circuits may be implemented with a separate processor or multiple circuits may be implemented on the same processor. Alternatively, the circuits may be implemented with discrete components or circuits provided in VLSI circuits. Also, the circuits described herein may be implemented with a combination of processors, ASICs, discrete components, or VLSI circuits. 
         [0021]    Controller  128  is operatively coupled to the print modules  102 - 112  and controls the timing of ink drop ejection from the print modules  102 - 112  onto the media web  114 . Controller  128  is also operatively connected to sensors  160 - 166  that enable the controller  128  to identify tension between the media web  114  and rollers  118 ,  119 ,  120 , and  134  from the signals generated by each sensor. Controller  128  is also operatively connected to actuators  170 - 174 . The controller  128  generates signals to selectively activate and deactivate each of the actuators  170 - 174 . The controller  128  may also adjust the speed of each actuator and corresponding rotational speed of one or more rollers that are operatively coupled to each actuator. 
         [0022]    A user interface (UI) module  129  provides an interface for operators of the printing system  100  to set different operating modes for the controller  128 . Various implementations of the UI include mechanical controls such as knobs, switches, dials and the like, as well as graphical user interfaces (GUIs). The UI may be physically incorporated in the printing system  100 , or may be presented to a remote operator via a data network. An operator may enter various commands and parameters using the UI  129  to configure the operation of the controller  128 . In printing system  100 , the UI  129  enables the operator to place the controller  128  in an operating mode for threading the media web  114  through the media path P. The controller  128  may also enter a threading mode automatically in response to exhausting an existing media web or by detecting breakage of the media web. 
         [0023]    In the threading operational mode, the controller  128  receives signals from each of the sensors  160 - 166  to identify tension levels between the media web and the rollers  118 ,  119 ,  120 , and  134 , respectively. The controller  128  compares the identified tension levels to predetermined threshold levels, and rotates one or more of the drive rollers  118 ,  120 , and  132  by operating actuators  170 ,  172 , and  174 , respectively, in response to the identified tension levels exceeding the predetermined thresholds. The drive rollers  118 ,  120 , and  132  rotate to assist in threading the media web  114  through the media path P as the operator pulls the media web through the printing system  100  without requiring the operator to operate separate controls during the threading operation. 
         [0024]      FIG. 2  depicts a block diagram of a process  200  for operating a printing system to assist in threading a media web through the printing system. Process  200  is suitable for use with the printing system  100  of  FIG. 1 , and printing system  100  is described in conjunction with process  200  for illustrative purposes. Process  200  begins by providing a free end of a media web  114  to a media path P (block  204 ). The free end of the media web  114  is unwound from a media web supply roller, such as roller  152 . The operator pulls the media web through the media path and engages the media web with a roller along the media path that is operatively connected to a tension sensor, such as the pre-heater roller  118 . 
         [0025]    As the media web  114  passes the pre-heater roller  118 , the media web applies a tension to the pre-heater roller  118 . Sensor  160  generates an electrical signal corresponding to the level of tension between the media web  114  and pre-heater roller  118 , and the controller  128  receives the signal (block  208 ). Controller  128  identifies the tension on the roller  118  from the generated signal (block  212 ). In some embodiments, the controller  128  may identify the tension with reference to a voltage level of the signal. 
         [0026]    If the identified tension level exceeds a predetermined threshold for roller  118  (block  216 ) the controller  128  operates one or more actuators in the printing system  100  to rotate rollers positioned along the media path P (block  220 ). As the media web  114  engages the pre-heater roller  118  and applies sufficient tension to the pre-heater roller  118 , the controller may operate actuator  170  to rotate the pre-heater roller  118 . The rotation of the pre-heater roller  118  pulls the media web  114  along the media path P and assists the operator in threading the media web  114  into the print zone past the print modules  102 - 106 . 
         [0027]    The controller  128  continues to receive signals from the sensor  160  (block  208 ) and monitors the tension on the pre-heater roller  118  (block  212 ) as actuator  170  rotates the pre-heater roller  118 . If the level of tension on the pre-heater roller  118  drops below the predetermined threshold (block  216 ), the controller  128  may deactivate actuator  170  until the identified tension level exceeds the predetermined threshold (block  224 ). The controller  128  deactivates the actuator  170  when the tension level drops below the predetermined threshold to prevent the pre-heater roller  118  from unwinding the media web  114  too quickly during the threading process. As the media web threads past different rollers positioned on the media path, the controller  128  may deactivate one or more actuators in response to identifying the tension level between the media web  114  and any roller in contact with the media web dropping below the predetermined threshold for each roller. In an alternative configuration, the controller  128  may operate the actuator  170  for a predetermined time period in response to the sensor signal corresponding to a tension level that exceeds the predetermined threshold. 
         [0028]    Process  200  continues as the media web  114  passes each roller positioned on the media path (block  228 ). In printing system  100 , the media web  114  threads through the print zone past print units  102 - 106  and over apex roller  119 . The apex roller  119  is not rotated by an actuator directly, but the controller  128  identifies the level of tension placed on apex roller  119  from the electrical signals generated by sensor  162  (blocks  208  and  212 ). The controller  128  operates actuator  170  to rotate the pre-heater roller  118  in response to the tension on the apex roller  119  exceeding a predetermined threshold (block  216 ). The predetermined threshold tension on the apex roller  119  may be different than the predetermined threshold tension on the pre-heater roller  118 . For example, the predetermined threshold tension level on the pre-heater roller  118  may be five Newtons while the predetermined threshold tension level on the apex roller  119  is six Newtons. 
         [0029]    In one embodiment, the controller  128  is configured to operate the one or more actuators based on the identified tension levels for all the sensors  160 - 166  that indicate non-zero tension values. In another embodiment, the controller  128  operates the actuators only with regard to the level of tension applied to a roller that is farthest along the media path P. The controller  128  operates the actuators to rotate the corresponding rollers at a lower rotational speed during the process  200  than during imaging operations when the media web  114  is fully threaded in the printing system  100 . In some configurations, the controller  128  adjusts the rotational speed of one or more of the drive rollers  118 ,  120 , and  132  in proportion to the tension detected by the tension sensors  160 - 166 . 
         [0030]    In one threading process, a human operator pulls on a free end of the media web  114 , applying tension to the media web. The tension sensors  160 - 166  may record potentially spurious tension signals dues to inconsistencies in the force that the human operator applies to the media web  114 . Additionally, the tension force identified by the tension sensors  160 - 166  changes as human applies greater or lesser forces to the media web  114 . In one embodiment, the controller  128  is configured to identify spurious tension forces applied to rollers in the printing system  100 . For example, an operator may lean against a roller during the threading process, resulting in a spurious tension measurement. The controller  128  is configured to identify a maximum expected tension for each of the tension sensors during the threading operation, and can prevent the activation of a corresponding actuator if the recorded tension exceeds the maximum expected tension. 
         [0031]    In some configurations, the controller  128  activates one or more actuators only in response to a predetermined series of signals generated by one or more of the tension sensors  160 - 166 . In one configuration, the controller  128  activates one or more actuators only when a tension sensor detects two tension pulses above a predetermined threshold within a predetermined time period. For example, if the tension sensor  160  detects two tension pulses that are separated by less than three seconds from an operator who pulls on the free end of the media web  114 , then the controller  128  operates the actuator  170  to advance the media web  114 . 
         [0032]    Referring to printing system  100 , as the media web  114  threads over the apex roller  119 , sensor  162  generates an electrical signal corresponding to the tension between the media web  114  and the apex roller  119 . The media web  114  has not yet reached the leveler roller  120  and exit guide roller  134 , so sensors  164  and  166  indicate zero tension. The controller  128  may be preconfigured to assign precedence to media rollers based on the location of the media rollers along the media path P, with media rollers that are located at more downstream positions receiving a higher precedence. Thus, controller  128  may identify a non-zero tension signal generated by tension sensor  162  coupled to the apex roller  119 , and operate the actuator  170  in response to the tension signal from the sensor  162  exceeding the predetermined tension threshold for apex roller  119 . Additionally, the controller  128  may deactivate one or more actuators if the tension level identified for apex roller  119  drops below the predetermined threshold (block  224 ). In some configurations, the controller  128  continues to operate the actuators for a predetermined time after tension drops below the predetermined threshold. The continued operation of the actuators assists an operator during a threading operation when the operator momentarily reduces the force applied to the media web  114 . 
         [0033]    Process  200  continues as the free end of media web  114  is threaded through print units  108 - 112  and the media web engages the leveler roller  120 . The media web applies tension to the leveler roller  120  and sensor  164  generates a signal corresponding to the tension. The controller  128  receives the signal and identifies the level of tension (blocks  208  and  212 ). If the tension identified for roller  120  exceeds the predetermined tension threshold for roller  120  (block  216 ), the controller  128  activates both actuators  170  and  172  to rotate drive rollers  118  and  120 , respectively (block  220 ). In the example of printing system  100 , the media web  114  contacts both drive rollers  118  and  120  during the threading process, and the controller  128  is configured to operate both actuators  170  and  172  to assist in the threading process. 
         [0034]    Process  200  continues in a similar manner as described above for threading the media web past the spreader roller  132  and exit guide roller  134 . When the media web engages the exit guide roller  134 , sensor  166  generates a signal corresponding to a level of tension between the media web  114  and the exit guide roller  134 , and the controller  128  identifies the tension level (blocks  208  and  212 ). If the identified tension level exceeds the predetermined tension threshold for roller  134  (block  216 ), the controller  128  activates actuators  170 ,  172 , and  174  to assist in guiding the media web  114  through the media path P (block  220 ). The free end of the media web  114  is wound around the take-up roller  154 , and process  200  finishes when the media web  114  is fully threaded through the printing system  100  (block  232 ). 
         [0035]    The foregoing description of process  200  as applied to printing system  100  is merely an illustrative example of a printing system configuration that assists an operator in threading a media web through a media path. The media web  114  may be threaded through the duplex path P′ and then guided through the media path P at a cross-process offset position a second time to enable duplex printing. The controller  128  is configured to operate the actuators  170 - 174  to assist in threading the media web  114  through the duplex configuration as well as the simplex configuration. Process  200  is also suitable for use with printing systems having different numbers and arrangement of rollers, sensors, and actuators positioned along a media path than the examples described herein. 
         [0036]    It will be appreciated that variants of the above-disclosed and other features and functions, or alternatives thereof, may be desirably combined into many other different systems, applications or methods. For example, while the printing system embodiments described above are inkjet printing systems, the foregoing systems and methods are applicable to any printing system where a continuous web is threaded through a media path. Various presently unforeseen or unanticipated alternatives, modifications, variations or improvements may be subsequently made by those skilled in the art that are also intended to be encompassed by the following claims.