Patent Publication Number: US-7907290-B2

Title: Printer with variable lead advance

Description:
FIELD OF THE INVENTION 
     The invention relates to the field of printers that use rolled receiver medium. 
     BACKGROUND OF THE INVENTION 
     A wide variety of printers record images on receiver medium such as paper, fabrics, or films that are specially treated at least one side in order to facilitate the formation of images thereon or to provide enhanced stability of an image printer thereon. In some of these printers, such receiver mediums are provided in roll form with the receiver medium being rolled with the treated side facing outward. This arrangement enables the components of a printer that uses such a rolled receiver medium to be arranged in relatively compact form factor. However, this creates a risk that the specially treated side will be brought into contact with the hands of an operator when manipulation of the receiver medium is necessary, such as to load receiver medium or to clear jams. Further, it will be appreciated that during loading of the receiver medium or at various times during the use of such a rolled receiver medium, there exists a risk that contaminants will be released and will contact the specially treated surface of the receiver medium. Such manual or contaminant contact can have deleterious effects on the receiver medium, including but not limited to altering the distribution or concentration of treated materials on the treated surface, introducing contaminates on the treated side or by compressing, reshaping, stretching, creasing, or tearing the receiver medium. 
     Where contact causes such deleterious effects it can be difficult to provide a printed image having an appropriate appearance using the affected receiver medium. Further, where a receiver medium that is torn, stretched, or contaminated as a result of contact, the use of such receiver medium can seriously interrupt the use of the printer by contaminating a series of subsequent printing operations or by ripping, tearing or otherwise failing in a manner that interferes with the flow of receiver medium through the printer or with other operations of the printer. 
     One possible approach to addressing this problem is to use special packaging materials to package rolled medium so that a user can load a rolled medium, without directly touching the medium. For example, U.S. Pat. No. 5,839,839, entitled “INK FILM REFILL FOR HEAT-TRANSFER PRINTER” filed on Jan. 31, 1997 by Brot et al. describes a removable wrapping that is applied around a rolled donor medium at the time of manufacture. This wrapping is shaped and positioned so that it covers areas of the receiver medium that are likely to be contacted during loading. In some instances, the wrapping contains printed instructions that illustrate or describe a loading process that a user is to use that will only require manipulation of the wrapped portion of the receiver medium. After loading, the wrapping is discarded. 
     However, it will be appreciated that this approach merely provides protection for the rolled medium during an initial loading process. However, this does not protect the receiver medium against deleterious effects caused by manual or contaminant contact with the receiver medium at any time after the receiver medium is loaded. For example, the approach of the &#39;839 patent is ineffectual when it may be necessary or desirable for a user to remove and reload rolled medium such as to clear paper jams or to switch from one type of receiver medium to another type receiver medium. Similarly, the approach of the &#39;839 patent does not protect the rolled medium from contamination that contact can occur after loading of the rolled medium. 
     Another approach has been to preprogram printers that use rolled receiver medium to discard a predetermined length of such receiver medium upon loading. One example of a prior art printer  10  of this type is illustrated in  FIG. 1 . As is illustrated in  FIG. 1 , when an unused roll  14   a  of receiver medium  12  is loaded, prior art printer  10  advances receiver medium  12  by a predetermined length. In this illustration, the predetermined length is equivalent to six printable image frames  16   a - 16   f . Typically, this predetermined length is intended to be long enough so that when unused roll  14   a  of receiver medium  12  is loaded into prior art printer  10 , a length equal to an entire circumferential length of unused roll  14   a  of receiver medium  12  is discarded. This approach avoids the use of potentially contacted receiver medium  12  by discarding an outermost layer of receiver medium  12  and allowing use of other layers that were effectively wrapped by the outermost layer at the time of the potential contact. 
     While this approach is useful and simple to implement, it can be wasteful when a used roll  14   b  of receiver medium is reloaded into prior art printer  10  as may occur during printer maintenance or as may occur when a user wishes to use different types of receiver medium. 
       FIG. 2  illustrates an example of how this waste can occur. As illustrated in  FIG. 2 , used roll  14   b  of receiver medium  12  has a circumference  18   b , that is substantially smaller than the circumference  18   a  of the unused roll  14   a  of receiver medium  12 . The length of receiver medium  12  that may be subject to contact during loading or reloading is smaller than the length of receiver medium  12  that may be subject to contact if an unused roll  14   a  of receiver medium  12  had been located in printer  20 . However, the prior art printer  10  discards the same length L of receiver medium  12 , including in this example, six image frames  16   a - 16   f . Thus, such a prior art printer  10  discards excess receiver medium. In printers such as thermal printers where donor ribbon and receiver medium are sold in matched combinations, this can cause user of the prior art printer  10  to have an apparent excess of donor ribbon after receiver medium  12  is exhausted. This can lead such users to assume that they have not been provided with the appropriate amounts of receiver medium  12 , which in turn, can lead to user dissatisfaction. 
     What is needed therefore is a method for operating a printer that minimizes the potential risks imposed by the use of receiver medium that has potentially been compromised through manual or contaminant contacts. 
     SUMMARY OF THE INVENTION 
     In one aspect of the invention, a method for operating a printer that prints using a receiver medium having a rolled portion with layers of rolled receiver medium leading to an outermost layer from which an unrolled portion of the receiver medium extends to a print engine. The method comprises the steps of: sensing a condition indicating the receiver medium may have been contacted by other than a component of the printer or by a donor material applied by the print engine; measuring an aspect of the receiver medium indicative of the circumferential length of the outermost layer; determining a circumferential length of the receiver medium based upon the measured aspect of the rolled portion of the receiver medium; determining an exclusion length of the receiver medium based upon the determined circumferential length and a travel distance that is a representation of a length of the unrolled portion between the rolled portion and the print engine; and automatically advancing the receiver medium by the exclusion length so that a subsequent printed image by the printer will be printed using a portion of the receiver medium that was not directly subject to the possibility of such contact. 
     In another aspect of the invention, a printer is provided. The printer comprises: a medium advance including a roll receiving area for receiving a rolled portion of a receiver medium having a preferred side for use in recording images during printing with the receiver medium being rolled so that the preferred side faces outward of the roll, the medium advance having a motorized system for advancing an unrolled portion of the receiver medium away from the rolled portion of the receiver medium to a print engine that is adapted to use the preferred side for recording images; a sensor system having a receiver medium sensor located at the roll receiving area and adapted to provide signals from which a processor can determine a circumferential length of the rolled portion of the receiver medium; the sensor system further having a condition sensor adapted to detect at least one condition that can be used to determine when a possibility exists that the preferred side of the receiver medium has been in contact with something other than a component of the printer or a donor material applied by the print engine, the condition sensor generating a signal from which the possibility of such contact can be determined. A processor is operatively connected to the medium advance, the print engine, the receiver medium sensor, and the detector system. The processor is adapted to determine from the signal that a possibility exists that the preferred side of the receiver has been in contact with something other than a component of the printer or a donor medium applied by the print engine. When such a condition is detected, the processor further is operable to determine a circumferential length based upon signals received from the receiver medium sensor to select an exclusion length of receiver medium based upon the determined circumferential length and a length representing a length of the unrolled portion; and to cause the medium advance to advance the receiver medium by at least the exclusion length so that portions of the receiver medium that have potentially been contacted, are not used for printing; wherein the selected non-printing length is proportional to the measured aspect of the receiver medium. 
     In still another aspect of the invention, a printer is provided. The printer comprises: a medium advance including a roll receiving area for receiving a rolled portion of a receiver medium having a preferred side for use in recording images during printing and a receiver medium path leading to a print engine, the receiver medium being rolled so that the preferred side faces outward of the spool, the medium advance having a motorized system for advancing an unrolled portion of the receiver medium away from the rolled portion to a print engine that is adapted to use the preferred side for recording images; a sensor system having a receiver medium sensor located at the roll receiving area and adapted to provide signals from which a processor can determine a circumferential length of the rolled portion of the receiver medium currently rolled onto the loaded spool and a condition sensor adapted to detect at least one condition indicating that a possibility exists that the exposed side of the receiver medium has been in contact other than with a component of the printer or print engine applied donor material, the sensor generating a signal from which a processor can determine the existence of such a possibility of contact. A processor is operatively connected to the medium advance, the sensor system, and the print engine. The processor is adapted to determine when a condition exists suggesting that the receiver medium may have been contacted and, when such a condition is detected, the processor further being operable to determine a circumferential length of the rolled portion based upon signals received from the receiver medium sensor to select an exclusion length of receiver medium based upon the assigned circumferential length designation; and to cause the medium advance to advance the receiver medium in a manner that excludes from printing a length of the receiver medium beginning at a start point of the receiver medium to extending at least by the exclusion length of the receiver medium; wherein the selected exclusion length is proportional to the measured aspect of the receiver medium. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  illustrates a prior art printer with an unused roll of receiver medium advanced in accordance with the prior art; 
         FIG. 2  illustrates a prior art printer with a used roll of receiver medium advanced in accordance with the prior art; 
         FIG. 3  shows one embodiment of a printer; 
         FIG. 4  shows one embodiment of a method for operating a printer; 
         FIG. 5  shows an embodiment of a receiver medium storage area; 
         FIGS. 6-10  illustrate the operation of one embodiment of a receiver medium sensor; 
         FIG. 11  illustrates another embodiment of a receiver medium sensor; 
         FIG. 12  illustrates another embodiment of a receiver medium sensor; and 
         FIGS. 13 and 14  illustrate another embodiment of a printer. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 3  shows one embodiment of a printer  20 . In the embodiment of  FIG. 1 , printer  20  comprises a housing  21  having a print engine  22  that applies markings or otherwise forms an image on a receiver medium  24 . Print engine  22  can record images on receiver medium  24  using a variety of known technologies including, but not limited to, conventional four color offset separation printing or other contact printing, silk screening, dry electrophotography such as is used in the NexPress 2100 printer sold by Eastman Kodak Company, Rochester, N.Y., USA, thermal printing technology, drop on demand ink jet technology and continuous inkjet technology. For the purpose of the following discussions, print engine  22  will be described as being of a type that generates color images. However, it will be appreciated that this is not necessary and that the claimed methods and apparatuses herein can be practiced with a print engine  22 , monotone images such as black and white, grayscale or sepia toned images. 
     A medium advance  26  is used to position a receiver medium  24  and/or print engine  22  relative to each other to facilitate recording of an image  64  on receiver medium  24 . Medium advance  26  can comprise any number of well-known systems for moving receiver medium  24  within printer  20 , including motor  28 , driving pinch rollers  30 , a motorized platen roller (not shown) or other well-known systems for the movement of paper or other types of receiver medium  24 . Typically medium advance  26  positions receiver medium  24  and or print engine  22  such that print engine  22  can print an image  64  in an image frame  62   a - 62   g  on receiver medium. Image frame  62   a - 62   g  typically represents a maximum image size that print engine  22  can print on receiver medium  24  without advancing the same. 
     Print engine  22 , medium advance  26  and color sensing system  60  are operated by a processor  34 . Processor  34  can include, but is not limited to, a programmable digital computer, a personal computer system, a programmable microprocessor, a programmable logic processor, a series of electronic circuits, a series of electronic circuits reduced to the form of an integrated circuit, or a series of discrete components. Processor  34  can be a single unit or a combination of separate processing units connected by a communication link. Certain functions of processor  34  described herein may be performed by a portion of a processor  34  that is within housing  21 , while other portions can be performed by a portion of processor  34  that is exterior to housing such as, for example, a personal computer that is connected to printer  20  by way of a wired or wireless connection. Processor  34  operates printer  20  based upon input signals from a user input system  36 , sensors  38 , a memory  40  and a communication system  54 . 
     User input system  36  can comprise any form of transducer or other device capable of receiving an input from a user and converting this input into a form that can be used by processor  34 . For example, user input system  36  can comprise a touch screen input, a keyboard, a keypad, a mouse, a touch pad input, a 4-way switch, a 6-way switch, an 8-way switch, a stylus system, a trackball system, a joystick system, a voice recognition system, a gesture recognition system or other such systems. 
     Sensors  38  are optional and can include light sensors and other sensors known in the art that can be used to detect conditions in the environment surrounding image  32  and to convert this information into a form that can be used by processor  34  in governing operation of print engine  22 , medium advance  26  and/or other systems of printer  20 . Sensors  38  can include audio sensors adapted to capture sounds. Sensors  38  can also include positioning and other sensors used internally to control printer operations. 
     Memory  40  can include conventional memory devices including solid state, magnetic, optical or other data storage devices. Memory  40  can be fixed within printer  20  or it can be removable. In the embodiment of  FIG. 1 , printer  20  is shown having a hard drive  42 , a disk drive  44  for a removable disk such as an optical, magnetic or other disk memory (not shown) and a memory card slot  46  that holds a removable memory  48  such as a removable memory card and has a memory interface  50  for communicating with removable memory  48 . 
     In the embodiment shown in  FIG. 3 , printer  20  has a communication system  54  for communicating with a remote memory system  52 , a remote display  56 , and a remote input  58 , such as a remote keyboard  58   a , a remote mouse  58   b  or a remote control  58   c  and, optionally with a local display  66 , and/or a local input  68 . Communication system  54  can be for example, an optical, radio frequency or transducer circuit or other system that converts image and other data into a form that can be conveyed to a remote device such as remote memory system  52  or remote display  56  by way of an optical signal, radio frequency signal or other form of signal. Communication system  54  can also be used to receive a digital image and other information from a host computer or network (not shown). In this way, data including, but not limited to, control programs, digital images and metadata can also be stored in remote memory system  52  that is external to printer  20  such as a personal computer server, computer network or other digital data storage system. Communication system  54  provides processor  34  with information and instructions from signals received thereby. 
     In the embodiment illustrated, local display  66  communicates with processor  34  without involvement of communication system  54 . Similarly, local input  68  comprising a local keyboard  68   a  and a local mouse  68   b  also communicates with processor  34  without involvement of communication system  54 . However, in other embodiments such communication can be made by way of communication system  54  if desired. 
     Turning now to  FIGS. 3 and 4 , what is shown, respectively, is one embodiment of a printer and a method for operating a printer. In a first step of this method, processor  34  detects a signal from one of sensors  38  from which processor  34  can determine the existence of a condition indicating that a receiver medium  24  in printer  20  may have been contacted by something other than a component of printer  20  or a donor material applied to a print engine (step  100 ). There are a variety of ways in which processor  34  can do this. In one embodiment, the condition indicating that a receiver medium  24  in printer  20  may have been contacted comprises a condition that indicates that a storage area for a receiver medium  24  has been accessed. For example, in the embodiment illustrated in  FIG. 3 , a receiver medium storage area  80  comprises a receiver medium storage area  80  comprising in this embodiment an enclosure with an enclosure area  82 , a door  84 , and a door sensor  86  that is positioned proximate to opening and adapted to detect when the door  84  is opened. In this embodiment, receiver medium storage area  80  is arranged so that access to a rolled portion  72  of receiver medium  24  requires opening door  84  in a manner that can be sensed by door sensor  86 . Such a door sensor  86  can comprise, for example, an optical or mechanical or so-called Hall effect switch that is positioned by door  84  to detect movement thereof and which can generate a signal from which processor  34  can determine that door  84  has been opened. When processor  34  determines that door  84  has been opened, processor  34  can determine that a condition exists that indicates that the receiver medium  24  may have been contacted by something other than a component of the printer or a donor material applied by printer engine  22 . 
     In another embodiment illustrated in  FIG. 5 , receiver medium storage area  80  can comprise a shaft  90  onto which rolled portion  72  of receiver medium  24  is loaded and a shaft switch  92  positioned on shaft  90  so that shaft switch  92  will be actuated either by the act of removing rolled portion  72  of receiver medium  24  from shaft  90  or by the act of loading rolled portion  72  of receiver medium  24  onto shaft  90 . In the example, shaft switch  92  is located at a position shaft  90  in a manner that causes shaft switch  92  to be closed whenever a rolled portion  72  is loaded onto shaft  90 . In this embodiment, a processor  34  determines that there is a possibility that a receiver medium  24  may have been contacted by detecting a pattern of signals from shaft switch  92  indicating that a rolled portion  72  of receiver medium  24  has been loaded. 
     In another embodiment, processor  34  and sensors  38  can cooperate to detect errors that can occur during operation of printer  20  and that suggest that a receiver medium  24  may have been manipulated to correct an error condition. For example, processor  34  and sensors  38  can detect error conditions suggesting that a “jam” has occurred in medium advance  26  preventing receiver medium  24  from freely moving within the medium advance  26 . Where such conditions are detected, processor  34  typically causes a signal to be sent advising a user to contact the receiver medium to clear the “jam”. Accordingly, when processor  34  receives signals from sensors  38  that detect such “jams” that alternately indicate that a “jam” exists and that the “jam” has subsequently been corrected, processor  34  can determine that it is possible that receiver medium  24  may have been contacted. There are of a variety of sensors  38  and control strategies that are known in the art and that can be applied for the purpose of sensing so-called jam conditions, any one of which can be applied for this purpose. 
     It will be appreciated that, depending upon the design of printer  20 , the uses to which printer  20  is put and the type of receiver medium  24  that is used, there may be a variety of additional conditions that can be sensed by sensors  38  that may indicate to processor  34  that there is a possibility that receiver medium  24  has been contacted including, but not limited to, a signal indicating that a roll of receiver medium is fully used or a signal indicating that donor material has been replaced or has escaped contamination. 
     An aspect of receiver medium  24  indicative of the circumferential length of receiver medium is then measured (step  102 ). The measured aspect can be any of a number of characteristics of the rolled portion  72  of receiver medium  24 . A receiver medium sensor  122  is used to measure the aspect of receiver medium  24 . 
       FIGS. 6-10  illustrate one example of a receiver medium sensor  122  that is capable of measuring an aspect of rolled portion  72  of receiver medium  24  that is indicative of the circumferential length of outermost layer  76  of receiver medium  24 . In this embodiment, receiver medium sensor  122  comprises a lever arm  124  biased by a biasing member  134  such as a spring about a pivot  135  so that a first end  126  is held against receiver medium  24 . In this embodiment, a resilient roller  133  provides a low friction engagement surface that allows contact with outermost layer  76  of rolled portion  72 . A second end  128  of lever arm  124  is positioned for movement along an arcurate path  130  beginning at a full position illustrated in  FIG. 6  that the second end  128  is moved into when the first end  126  is biased against an outermost layer  76   a  of a rolled portion  72  of receiver medium  24  that has not yet been used and continuing through a range of positions illustrated, for example, in  FIGS. 7 ,  8  and  9  to exhausted position illustrated in  FIG. 10  that second end  128  is moved into when first end  126  is biased against when receiver medium  24  is exhausted. As is illustrated in  FIG. 10 , an optional stop  137  prevents further biased movement of lever arm  124  when lever arm  124  is at the exhausted position. For comparison, purposes a phantom outline is provided in  FIGS. 7-10  depicting the positions of lever arm  124  and the outermost layer  76   a - 76   e  of rolled portion  72  of receiver medium  24 . 
     As is illustrated in  FIGS. 6-10 , a position sensor system  132  is provided and is capable of generating signals that can be used by processor  34  to determine the position of second end  128  relative to the exhausted position ( FIG. 11 ) or the unused position ( FIG. 7 ). In the embodiment of  FIGS. 6-10 , position sensor system  132  comprises a plurality of individual second end sensors  136   a - 136   f , such as switches or electrical contacts, within arcurate path  130 , each second end sensor  136   a - 136   f  being located at a position that is associated with a different range of circumferential lengths of receiver medium  24  and each being adapted to provide a signal to processor  34  when second end  128  is proximate thereto. Signals from position sensor system  132  are then provided to processor  34 . 
     In still another alternative embodiment illustrated in  FIG. 11 , receiver medium sensor  122  can comprise a weight sensor  96  that is positioned on a shaft  90  on which rolled portion  72  of receiver medium  24  is loaded. Weight sensor  96  is adapted to detect a weight of rolled portion  72  and to provide a signal to processor  34  from which processor  34  can determine a circumferential length thereon and from this can determine a circumferential length of outermost layer  76  of the rolled portion  72  of receiver medium  24 . The receiver medium sensor  122  can be adapted to measure distance from the outermost layer  76  of a rolled portion  72  of receiver medium  24  to a fixed point in the printer  20  proximate to area  80  for receiving rolled portion  72  of receiver medium  24 . It will be appreciated that weight sensor  96  can also perform the function of shaft switch  92 . 
     One example embodiment of this type is illustrated in  FIG. 12 , in which the receiver medium sensor  122  comprised an optical or sonic sensor having an emitter  150  and a sensor  152  positioned in receiver medium storage area  80  and directed from a fixed portion thereof onto the outermost layer  76 . The emitter  150  generates a first optical or sonic signal, while the sensor  152  receives a reflected portion thereof, and provides a signal indicative the magnitude of the reflected portion, the magnitude of the reflected portion being indicative of a distance from the receiver medium sensor  122  to the outermost layer  76 . 
     Processor  34  then determines a circumferential length of the rolled portion  72  of receiver medium  24  (step  104 ). This determination is made based upon the measured aspect of the rolled portion  72  of receiver medium  24 . Typically, this determination can be made based upon a look up table or other preprogrammed logical association between the measured aspect and the circumferential length. However, the circumferential length can also be calculated by processor  34  using geometric equations where the measured aspect of the outermost layer of the rolled portion  72  of receiver medium  24  is amenable for use in such equations. 
     Processor  34  then selects an exclusion length  160  (step  106 ) for the receiver medium  24  based upon the determined circumferential length (step  104 ). Exclusion length  160  can be equal to the circumferential length or it can be longer. 
     It will be appreciated that unrolled portion  74  receiver medium  24  travels along a path of some length from rolled portion  72  and that to advance all of receiver medium  24  past print engine  22 , it is necessary to advance the determined circumferential length plus a distance that represents the distance from the rolled portion  72  to print engine  22 . This is, of course, generally a distance that can be determined based upon the length of the unrolled portion  74  of receiver medium  24 . Accordingly, the exclusion length can be established to include a length that corresponds to the length of unrolled portion  74  plus the determined circumferential length. 
     The exclusion length  160  can be measured in any of a variety of ways. In the embodiment illustrated in  FIGS. 13 and 14 , exclusion length  160  is shown as being measured in units of image frames  62   a - 62   g.    
     Receiver medium  24  is then advanced by the exclusion length (step  108 ) so that any portion of receiver medium  24 , that might have been contacted, is moved past print engine  22  so that such portions will not be used for printing. 
     Accordingly, when an unused roll  14   a  of receiver medium  24  is loaded into printer  20  as illustrated in  FIG. 13 , processor  34  will determine a first exclusion length  162  that extends for five image frames  62   a - 62   e . However, processor  34  will determine a second exclusion length  164  that extends for only 3 image frames when a used roll  14   b  of receiver medium  24  is loaded into printer  20 . In other embodiments, an exclusion length can be determined using other units of receiver medium advance 
     The invention has been described in detail with particular reference to certain preferred embodiments thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. 
     PARTS LIST 
     
         
           10  prior art printer 
           12  receiver medium 
           14   a  unused roll 
           14   b  used roll 
           16   a - 16   f  image frames 
           18   a ,  18   b  circumference 
           20  printer 
           21  housing 
           22  print engine 
           24  receiver medium 
           26  medium advance 
           28  motor 
           30  pinch rollers 
           34  processor 
           36  user input system 
           38  sensors 
           40  memory 
           42  hard drive 
           44  removable disk drive 
           46  memory card slot 
           48  removable memory 
           50  memory interface 
           52  remote memory system 
           54  communication system 
           56  remote display 
           58  remote input 
           58   a  remote keyboard 
           58   b  remote mouse 
           58   c  remote control 
           62   a - 62   e  image frame 
           64  image 
           66  local display 
           68  local user input 
           68   a  local keyboard 
           68   b  local mouse 
           72  rolled portion of receiver medium 
           74  unrolled portion 
           76  outermost layer 
           76   a - 76   e  outermost layer 
           80  receiver medium storage area 
           82  enclosure area 
           84  door 
           86  door sensor 
           90  shaft 
           92  shaft switch 
           96  weight sensor 
           100  detect condition step 
           102  measure aspect step 
           104  determine circumferential step 
           106  determine exclusion length step 
           108  advance receiver medium step 
           122  receiver medium sensor 
           124 ,  124   a  lever arm 
           126  first end 
           128  second end 
           130  arcurate path 
           132  sensor system 
           133  roller 
           134  biasing member 
           135  pivot 
           136   a - 136   f  second end sensor 
           137  stop 
           150  emitter 
           152  sensor 
           160  exclusion length 
           162  first exclusion length 
           164  second exclusion length 
         L prior art fixed exclusion length