Patent Abstract:
In one implementation, an encoder assembly for a printer includes: an encoder scale having indicators thereon for determining a printing parameter; an encoder sensor for sensing indicators on the scale; and a mechanism configured to alternately attach an encoder part (either the scale or the sensor) to the substrate and detach the encoder part from the substrate. In another implementation, a method includes: attaching an encoder part to a print substrate, the encoder part being either an encoder scale or an encoder sensor; the sensor sensing indicators on the scale while advancing the substrate with the encoder part attached; and detaching the encoder part from the substrate.

Full Description:
BACKGROUND 
     Large format inkjet printers print on a variety of different substrates. Large format print substrates include, for example, paper, vinyl and textiles that may be supplied as flexible or rigid pre-cut sheets or rolls of flexible web. Currently, flexible web substrates are more common for large format printing. Some printers handle flexible web substrates up to five meters wide. Large flexible substrates may stretch or otherwise deform as they are moved through the printer, and they may shrink and expand in response to varying temperature and humidity. The irregular and sometimes unpredictable nature of these large flexible substrates may result in improper ink drop placement, thus degrading print quality. It is desirable to monitor the actual position of the substrate as it moves through the printer to allow for corrections to the placement of the ink drops on the substrate to help maintain acceptable print quality. 
    
    
     
       DRAWINGS 
         FIG. 1  is a block diagram illustrating one example of an inkjet printer in which implementations of the invention may be used. 
         FIG. 2  is a diagrammatic elevation view illustrating a roll-to-roll web printer that includes an encoder assembly according to one implementation of the invention. 
         FIGS. 3-5  are diagrammatic elevation views illustrating one example configuration of an encoder assembly, such as the one shown in  FIG. 2 , in which the encoder assembly is located in a channel in the platen. 
         FIGS. 6 and 7  are section views taken along lines  6 - 6  in  FIG. 3  and lines  7 - 7  in  FIG. 5 , respectively. 
         FIGS. 8-11  are enlarged diagrammatic elevation views illustrating one example implementation of an encoder assembly such as that shown in  FIGS. 3-7  in which the encoder scale moves with the print substrate and the encoder sensor is stationary. 
         FIGS. 12-15  are enlarged diagrammatic elevation views illustrating one example implementation of an encoder assembly such as that shown in  FIGS. 3-7  in which the encoder sensor moves with the print substrate and the encoder scale is stationary. 
         FIG. 16  is a perspective view illustrating an example implementation in which multiple encoder scales alternate moving with the print substrate. 
         FIGS. 17 and 18  are diagrammatic views illustrating two operating scenarios for the implementation shown in  FIG. 16 . 
         FIGS. 19 and 20  are perspective views illustrating another example implementation in which the encoder scale is attached to the print substrate indirectly through a linkage. 
     
    
    
     The same part numbers are used to designate the same or similar parts throughout the figures. 
     DESCRIPTION 
     Implementations of the new encoder assembly were developed to help accurately monitor the actual position of large format print substrates as they move through the printer, to allow corrections to the placement of the ink drops on the substrate for better print quality. Implementations of the new encoder assembly, however, are not limited to use with large print substrates or large format printers. In one example implementation, one of the encoder parts—either the encoder scale or the encoder sensor—is attached to the substrate. The sensor reads the markings or other indicators on the scale while advancing the substrate with the encoder part attached. The encoder part is then detached from the substrate and returned to a previous position where the process of attaching, sensing and detaching may be repeated to monitor the position of the substrate during printing. The example implementations described below should not be construed to limit the scope of the invention, which is defined in the Claims that follow the Description. 
       FIG. 1  is a block diagram illustrating one example of an inkjet printer  10  in which implementations of the invention may be used. Referring to  FIG. 1 , inkjet printer  10  includes a printhead  12 , an ink supply  14 , a carriage  16 , a print substrate transport mechanism  18  and a controller  20 . Printhead  12  in  FIG. 1  represents generally one or more printheads and the associated mechanical and electrical components for dispensing drops of ink on to a sheet or a continuous web of paper or other print substrate  22 . Printhead  12  may include one or more stationary printheads that span the width of print substrate  22 . Alternatively, printhead  12  may include one or more printheads that scans back and forth on carriage  16  across the width of substrate  22 . Printhead  12  may include, for example, thermal ink dispensing elements or piezoelectric ink dispensing elements. Other printhead configurations and ink dispensing elements are possible. 
     Substrate transport  18  advances print substrate  22  past printhead  12 . For a stationary printhead  12 , substrate transport  18  may advance substrate  22  continuously past printhead  12 . For a scanning printhead  12 , substrate transport  18  may advance substrate  22  incrementally past printhead  12 , stopping as each swath is printed and then advancing substrate  22  for printing the next swath. Ink chamber  24  and printhead  12  are usually housed together in an ink pen  26 , as indicated by the dashed line in  FIG. 1 . Ink supply  14  supplies ink to printhead  12  through ink chamber  24 . Ink supply  14 , chamber  24  and printhead  12  may be housed together in an ink pen. Alternatively, ink supply  14  may be housed separate from ink chamber  24  and printhead  12 , as shown, in which case ink is supplied to chamber  24  through a flexible tube or other suitable conduit. Printer  10  typically will include several ink pens  26 , for example one pen for each of several colors of ink. 
     Controller  20  in  FIG. 1  represents generally the programming, processor(s) and associated memories, and the electronic circuitry and components needed to control the operative elements of printer  10 . In a printing operation, controller  20  receives print data and, if necessary, processes that data into printer control information and image data. Controller  20  controls the movement of carriage  16  and substrate transport  18 . Controller  20  is electrically connected to printhead  12  to energize the ink dispensing elements to dispense ink drops on to substrate  22 . By coordinating the relative position of printhead  12  and substrate  22  with the location of dispensed ink drops, controller  20  produces the desired image on substrate  22  according to the print data. 
       FIG. 2  is a diagrammatic elevation view illustrating a roll-to-roll web printer  10  that includes an encoder assembly  28  according to one implementation of the invention. Referring to  FIG. 2 , printer  10  includes, for example, a group of multiple ink pens  26  for dispensing different color inks. Ink pens  26  are mounted on a carriage  16  over a platen  30 . In the example implementation shown in  FIG. 2 , substrate transport  18  in printer  10  includes a web supply roller  32  and a web take-up roller  34 . A web substrate  22  extends from supply roller  32  over platen  30  between intermediate rollers  36  and  38  to take-up roller  32 . Intermediate rollers  36  and  38 , for example, help control the direction and tension of web  22  through a print zone  40  over platen  30 . Pens  26  are scanned back and forth (into and out of the page in  FIG. 2 ) on carriage  16  across the width of substrate  22  as it passes over platen  30  through print zone  40 . 
       FIGS. 3-5  are enlarged diagrammatic elevation views illustrating one example configuration for encoder assembly  28  in  FIG. 2 .  FIGS. 6 and 7  are section views taken along lines  6 - 6  in  FIG. 3  and lines  7 - 7  in  FIG. 4 , respectively. Referring to  FIGS. 3-7 , encoder assembly  28  includes a movable encoder scale  42  and an encoder sensor  44 . As best seen in  FIGS. 6 and 7 , scale  42  and sensor  44  are located in a channel  46  in platen  30 . Sensor  44  is operatively connected to a printer controller, such as controller  20  in  FIG. 1 . Scale  42  carries markings or other indicators that may be sensed by sensor  44  and used by controller  20  to determine the location, velocity, acceleration or other parameters associated with substrate  22 . In operation, encoder scale  42  is attached to substrate  22  as shown in  FIGS. 3 and 6 . Then, sensor  44  senses the indicators on scale  42  while advancing substrate  22  with scale  42  attached, as best seen by comparing the position of scale  42  in  FIGS. 3 and 4 . Scale  42  is then detached from substrate  22  as shown in  FIGS. 5 and 7  and returned to a previous position, as best seen by comparing the position of scale  42  in  FIGS. 4 and 5 . The figures depict scale  42  moving up to attach to substrate  22  and moving down to detach from substrate  22  for illustrative purposes only. While scale  42  might move when attached to and detached from substrate  22 , such movement is not necessary. In some implementations, such as the implementation described below with reference to  FIGS. 8-11 , neither scale  42  nor substrate  22  move during attachment and detachment. 
     The process of attaching, sensing, and detaching may be repeated as desired throughout a printing operation. For a printer  10  in which ink pens  26  are scanned back and forth across substrate  22 , scale  42  may be attached to substrate  22  while substrate  22  is stopped for printing a swath as ink pens  26  are scanned across substrate  22 . Scale  42  then moves forward with substrate  22  as substrate  22  is positioned for printing the next swath. Scale  42  may be released from substrate  22  and returned to a previous position while substrate  22  is stopped for printing the next swath. Depending on the length and range of travel of scale  42 , scale  42  may remain attached to substrate  22  as substrate  22  is advanced for printing multiple swaths. For a printer  10  in which substrate  22  moves continuously past a stationary printhead  12  during printing, scale  42  may be repeatedly attached to and detached from a moving substrate  22 . 
     Different parts of a large flexible substrate  22  may behave in different ways. For example, one part of a substrate  22  may be shrinking while another part along the same printing path may be expanding. Multiple encoder assemblies  28  may be positioned across the width of substrate  22  or positioned at other locations along the length of substrate  22  to help more accurately characterize different parts of the substrate  22 . While it is expected that scale  42  will usually be returned to the prior starting position, as shown in  FIGS. 3 and 5 , scale  42  might be returned to a different starting position. Any suitable encoder technology may be used in encoder assembly  28  including, for example, an optical encoder or a magnetic encoder. Also, encoder scale  42  may include position indicators in two dimensions—across the width of substrate  22  as well as along the length of substrate  22 . 
     Data gathered by sensor(s)  44  may be used by controller  10  to adjust the placement of ink drops on substrate  22  or other printing parameters to improve print quality, for example by adjusting the position of substrate  22  through substrate transport  18  and/or by adjusting the ejection of ink drops through ink pens  26 . Drop placement may be adjusted for individual parts of substrate  28  using data from one or more encoder assemblies  28  to compensate for local substrate deformation and to increase local drop placement accuracy. 
     One example technique for attaching encoder scale  42  to substrate  22  and detaching encoder scale  42  from substrate  22  will now be described with reference to  FIGS. 8-11 . Referring to  FIGS. 8-11 , encoder assembly  28  includes a carrier  48  that carries encoder scale  42 . In this example implementation, carrier  48  is configured as a vacuum box operatively connected to a pump or other suitable vacuum source  50 . Scale  42  is attached to or integrated into the bottom of carrier vacuum box  48 . For example, scale  42  may be a reflective scale formed in or attached to the outer surface of the bottom of carrier  48 . The top of vacuum box  48  is positioned close to the bottom side of substrate  22 . For example, where encoder assembly  28  is positioned in a channel  46  in platen  30 , the top of vacuum box  48  may be made flush with the top of platen  30 . In the example implementation shown in  FIGS. 8-11 , vacuum box  48  includes a group of openings  52  along a planar top face  54 . Each opening  52  is connected to vacuum source  50  through an interior plenum  56 . 
     Air is evacuated from plenum  56 , and thus from the space between box face  54  and substrate  22 , to suck together box  48  and substrate  22  as indicated by arrows  57  in  FIG. 8  and attach box  48  and scale  42  to substrate  22 . Sufficient suction is applied to create enough friction between substrate  22  and box  48  to allow box  48  to move with substrate  22 . It is not necessary that one or both substrate  22  and box  48  move toward or actually contact one another. All that is required is enough suction to cause box face  54  to effectively “stick” to substrate  22 . 
     Sensor  44  reads scale  42  as substrate  22  is advanced through print zone  40  with carrier box  48  attached, as shown in  FIG. 9 . Carrier box  48  is detached from substrate  22  by releasing the vacuum applied to openings  52 , as indicated by arrows  57  in  FIG. 10 , and returned to a previous position as shown in  FIG. 11 . In some applications it may be desirable to pressurize plenum  56 , and thus the space between box face  54  and substrate  22  to help maintain an air bearing between box face  54  and substrate  22 , for example by reversing a vacuum pump  50 . The air bearing allows vacuum box  48  and substrate  22  to move freely with respect of one another as box  48  is returned to a starting position as shown in  FIG. 11  and as substrate  22  moves over a stationary box  48 . 
     In an alternative implementation shown in  FIGS. 12-15 , encoder sensor  44  moves with print substrate  22  and encoder scale  42  is stationary. Referring to  FIGS. 12-15 , in this implementation vacuum box carrier  48  carries encoder sensor  44 . Air is evacuated from box  48  to suck together box  48  and substrate  22 , thus attaching box  48  and sensor  42  to substrate  22  as described above with reference to  FIGS. 8-11 . Sensor  44  reads scale  42  as it moves with substrate  22  along scale  42 , as shown in  FIG. 13 . Carrier box  48  is detached from substrate  22  by releasing the vacuum applied to opening(s)  52  and returned to a previous position as shown in  FIGS. 14 and 15 . 
       FIG. 16  is a perspective view illustrating an example implementation in which multiple encoder scales  42  alternate moving with print substrate  22 .  FIGS. 17 and 18  are diagrammatic views illustrating two operating scenarios for the implementation shown in  FIG. 16 . Referring first to  FIG. 16 , encoder assembly  28  is positioned between one of the intermediate rollers  36  or  38  and platen  30 . Encoder assembly  28  includes two encoder scales  42 A and  42 B mounted to respective carrier vacuum boxes  48 A and  48 B. Each box  48 A and  48 B is mounted on a track  58  opposite one another in a direction across the width of substrate  22 . 
     Referring to  FIG. 17 , in one operating scenario for encoder assembly  28  in  FIG. 16 , each scale  42 A and  42 B is mounted on an oval track  58  that moves in only one direction around rollers  60 ,  62  to carry each scale  42 A and  42 B over a single sensor  44 . Track  58  includes an advancing part  64  and a returning part  66 . In operation, scale  42 A on the advancing part  64  of track  58  is attached to and advances with substrate  22  (not shown) past encoder sensor  44  and then is released from substrate  22 . While scale  42 A is advancing with substrate  22  on advancing part  64 , scale  42 B is returning along track part  66  toward a starting position on track advancing part  64 , where it will become the advancing scale attached to substrate  22  moving past sensor  44 . Thus, one scale advances while the other scale returns. 
     Referring to  FIG. 18 , in another operating scenario for encoder assembly  28  in  FIG. 16 , each scale  42 A,  42 B is mounted on a corresponding track part  58 A and  58 B, each moving back and forth at the urging of rollers  60 ,  62  to carry each scale  42 A and  42 B alternately over respective sensors  44 A and  44 B. Each track part  58 A,  58 B advances and returns a scale  42 A,  42 B. In operation, with rollers  60  and  62  turning clockwise, scale  42 A on track part  58 A is attached to and advances with substrate  22  (not shown) past encoder sensor  44 A and then is released from substrate  22 . While scale  42 A is advancing with substrate  22  on track part  58 A, scale  42 B is returning detached from substrate  22  along track part  58 B toward a starting position, where it will become the advancing scale attached to substrate  22  moving past sensor  44 B when rollers  60  and  62  are reversed to turn counter-clockwise. Thus, one scale advances while the other scale returns. 
       FIGS. 19 and 20  are perspective views illustrating another example implementation in which encoder scale  42  is attached to print substrate  22  through a linkage  68 . Referring to  FIGS. 19 and 20 , in this implementation, a carrier  48  carrying encoder scale  42  is attached to and detached from substrate  22  through linkage  68 . Linkage  68  includes a vacuum box  70  and a connecting arm  72  connecting carrier  48  to vacuum box  70 . Vacuum box  48  is positioned close to the bottom side of substrate  22  and operatively connected to a vacuum source  50 . In operation, vacuum is applied to box  70  to suck together box  70  and substrate  22  as shown in  FIG. 20 , thus attaching carrier  48  and scale  42  to substrate  22  indirectly through linkage  68 . Vacuum box  70  and scale  42  connected to box  70  moves along with the advancing substrate  22 , as best seen by comparing the position of scale  42  in  FIGS. 19 and 20 , with sensor  46  sensing indicators on the moving scale  42 . Then, vacuum to box  70  may be released to detach box  70  and thus scale  42  from substrate  22 , and scale  42  returned to the previous position ( FIG. 19 ) at the urging of a pneumatic cylinder  74  or another suitable return mechanism. 
     As noted above, the example implementations shown in the Figures and described above do not limit the invention. Other implementations are possible. Accordingly, these and other implementations, configurations and details may be made without departing from the spirit and scope of the invention, which is defined in the following claims.

Technology Classification (CPC): 1