Abstract:
A borderless inkjet printer includes a printhead movable to release ink drops on a print medium, and to release ink drops slightly beyond edges of the print medium in order to ensure edge-to-edge printing on the print medium. A air flow generator generates a constant airstream with direction and force so that ink drops released slightly beyond edges of the print medium are carried away by the constant airstream to prevent the drops from clinging to any edge of the print medium or even migrating to an underside of the print medium. A sump collects inkdrops carried by the constant airstream, to permit them to be reused for printing.

Description:
FIELD OF THE INVENTION  
       [0001]     The invention generally relates to borderless inkjet printing. More particularly, the invention relates to a continuous inkjet printer in which ink drops are released slightly beyond edges of a print medium in order to ensure borderless (edge-to-edge) printing.  
       BACKGROUND OF THE INVENTION  
       [0002]     Typically, in a continuous inkjet printer, a pressurized printing ink is formed into continuous inkjet filaments that project from closely spaced ink discharge nozzles on a printhead. Filament stimulation sources such as ink heaters or piezoelectric transducers operate as ink droplet generators, each time they are activated, by causing filament end-lengths to be broken off to form discrete ink drops. The ink drops are created for every possible pixel location on the print medium since it cannot be known beforehand when and where colored or black pixels will require an ink drop to be deposited on the print medium and when and where white pixels will not require an ink drop to be deposited on the print medium. The many drops not needed because of the white pixels are discarded in some fashion. Often, the discarded drops are electrostatically or otherwise deflected from the continuous stream of ink drops emerging from a nozzle and they are deposited in a gutter. The so-called “gutter drops” are returned to the pressurized ink source in order to be reused as possible “print” drops.  
         [0003]     Historically, image prints were made with a blank border surrounding the printed image. However, today, borderless (edge-to-edge) prints are at least equally in demand. When a continuous inkjet printer is operated in a borderless print mode, it is difficult to cause the printhead to begin to release ink drops exactly at one edge of the print medium and to cease to release ink drops exactly at an opposite edge of the print medium. Instead, the printhead begins to release ink drops shortly before it is aligned with one edge of the print medium, and it continues to release ink drops slightly beyond an opposite edge of the print medium. This is referred to as ink “overspraying” or “overshooting” relative to edges of the print medium, and ensures edge-to-edge printing.  
         [0004]     When ink drops are oversprayed relative to edges of the print medium, the drops can also deposit on the edges. A known problem in this instance is that ink drops can cling to edges of the print medium and even migrate to the underside of the print medium. This results in an unsightly print. Moreover, ink drops falling off edges of the print medium can contaminate components in the printer. Prior art attempts to prevent this problem are disclosed in U.S. Pat. No. 6,168,259 B1 issued Jan. 2, 2001 and U.S. Pat. No. 6,239,817 B1 issued May 29, 2001. In the patents, the printhead begins to release ink drops a predetermined distance, such as 2 mm, before the print head is aligned with one edge of the print medium, and it continues to release ink drops the same distance beyond an opposite edge of the print medium. The oversprayed ink is collected by an ink absorbent material adjacent edges of the print medium. In U.S. Pat. No. 6,168,259 B1, the ink absorbent material is located in open drain bins facing the print head. The drain bins are in communication with suction pumps which suction the collected ink from the drain bins, enabling the ink to gravity flow to a sump.  
       SUMMARY OF THE INVENTION  
       [0005]     According to one aspect of the invention there is provided a borderless inkjet printer, comprising: 
        a printhead movable to release ink drops on a print medium, and to release ink drops slightly beyond edges of the print medium in order to ensure edge-to-edge printing on the print medium; and     a air flow generator that generates a constant airstream with direction and force so that ink drops released slightly beyond edges of the print medium are carried away by the constant airstream to prevent the drops from clinging to any edge of the print medium or even migrating to an underside of the print medium.        
 
         [0008]     According to another aspect of the invention there is provided a borderless inkjet printing method, comprising: 
        moving a printhead to release ink drops on a print medium, and to overspray ink drops relative to edges of the print medium in order to ensure edge-to-edge printing on the print medium; and     generating a constant airstream with direction and force adjacent edges of the print medium so that ink drops oversprayed relative to edges of the print medium are prevented by the constant airstream from clinging to any edge of the print medium or even migrating to an underside of the print medium.       
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0011]      FIG. 1  is a front elevation view, partly in section, of a borderless inkjet printer that is a preferred embodiment of the invention;  
         [0012]      FIG. 2  is a top plan view, partly in section, of the borderless inkjet printer; and  
         [0013]      FIG. 3  is a schematic block diagram of a control system in the borderless inkjet printer. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0014]     The invention is described as embodied in a continuous inkjet printer that can be operated in a borderless print mode. Since the features of such an inkjet printer are generally known, the detailed description which follows is directed in particular to those elements constituting parts of or cooperating directly with the invention. It is to be understood, however, that other elements not described may take various forms known to persons skilled in the printer art.  
         [0015]     Referring now to the drawings,  FIGS. 1-3  show a continuous inkjet printer  10  that is operable to make a borderless (edge-to-edge) print.  
         [0016]     A print medium  12 , e.g. a paper sheet, is supported flat on a medium support such as fixed platen  14 . See  FIG. 1 . The print medium  12  has a front or leading edge  16 , a rear or trailing edge  18 , and a pair of opposite side edges  20  and  22 . See  FIG. 2 .  
         [0017]     A known type continuous inkjet printhead  24  is connected to a reversible motor  26  which in turn is movably mounted on a rod  28 . When the motor  26  is energized, it is moved forward or backward along the rod  28  to translate the print head  24  in opposite x-x directions  30 A and  30 B above the print medium  12 . The printhead  24  can begin to translate forward in the x-direction  30 A in  FIG. 1  before it is aligned with the side edge  20  of the print medium  12 , and it is reversed to be translated backward in the x-direction  30 B only after it is translated to beyond the side edge  22  of the print medium. When the printhead  24  is translated backward in the x-direction  30 B, it always returns to being slightly beyond the side edge  20  of the print medium.  
         [0018]     The rod  28  is suspended at respective ends by parallel equal-length suspension arms  32  and  34 . See  FIG. 1 . The suspension arms  32  and  34  are connected to reversible motors  36  and  38  which in turn are movably mounted on parallel equal-length rods  40  and  42 . When the motors  36  and  38  are simultaneously energized, they are moved forward or backward along the rods  40  and  42  to translate the print head  24  in opposite y-y directions  44 A and  44 B above the print medium  12 . The printhead  24  can begin to translate forward in the y-direction  44 A in  FIG. 2  before it is aligned with the front edge  16  of the print medium  12  (but only when the printhead is returned in the x-direction  30 B to being slightly beyond the side edge  20  of the print medium), and it is reversed to translate backward in the y-direction  44 B only after it is translated to slightly beyond the rear edge  18  of the print medium (and the printhead is returned in the x-direction  30 B to being slightly beyond the side edge  20  of the print medium). When the printhead  24  is translated backward in the y-direction  44 B, it returns to being slightly beyond the front edge  16  of the print medium  12  as shown in  FIG. 2 .  FIG. 2  shows a starting or initial position of the printhead  24 .  
         [0019]     Respective edge sensors  46 ,  48 ,  50  and  52  on the printhead  24  sense when the printhead has moved beyond the front, rear, and side edges  16 ,  18 ,  22 , and  24  of the print medium  12 . The edge sensors  46 ,  48 ,  50  and  52  input sensing signals to a microprocessor control  54  which in turn controls individual energization of the motors  26 ,  38  and  38 . See  FIG. 3 .  
         [0020]     When the printhead  24  is translated forward and backward in the x-x-directions  30 A and  30 B, it releases a succession of ink drops  56  on the print medium  12  in order to make one line of a borderless print. See  FIG. 1 . The printhead  24  is translated forward in the y-direction  44 A each time the printhead is returned to being slightly beyond the side edge  20  of the print medium  12 . This allows the printhead  24  to print the next line of the borderless print. After the printhead  24  has been translated forward in the y-direction  44 A to allow the printhead  24  to print the last (bottom) line of the borderless print, and is then translated forward and backward in the x-x directions  30 A and  34 , the printhead can be translated backward in the y-direction  44 B to the starting position shown in  FIG. 2 . The ink drops  56  and not released when the printhead  24  is translated forward or backward in the y-directions  44 A and  44 B. Thus, the arrangement of the printhead  24 , the edge sensors  46 ,  48 ,  50  and  52 , the reversible motors  26 ,  36  and  38 , and the rods  28 ,  40  and  42  allows the printhead to print one line at a time across the entire width W of the print medium  12 , beginning at a corner  58  of the print medium formed by the front and side edges  16  and  20  of the print medium and ending at a corner  60  of the print medium formed by the rear and edges  18  and  22  of the print medium. See  FIG. 2 .  
         [0021]     The printhead  24  actually begins to release the ink drops  56  shortly before it is aligned with the front and side edges  16  and  20  of the print medium  12 , i.e. when it is initially translated forward in the x-direction  30 A from the starting position shown in  FIG. 2 . The printhead  24  continues to release the ink drops  56  each time it is translated forward or backward in the x-x directions  30 A and  30 B from the side edges  20  and  22  of the print medium  12 . Also, the printhead  24  releases the ink drops  56  when it is slightly beyond the side and rear edges  22  and  18  of the print medium  12 , and is translated backward in the x-direction  30 B to slightly beyond the side edge  20  of the print medium. This is referred to as ink “overspraying” or “overshooting” relative to the front, rear and side edges  16 ,  18 ,  20  and  22  of the print medium  12 , and ensures edge-to-edge printing on the print medium.  
         [0022]     When the ink drops  56  are oversprayed relative to the front, rear and side edges  16 ,  18 ,  20  and  22  of the print medium  12 , the drops can also deposit on the edges. A known problem in this instance is that the ink drops  56  can cling to the edges of the print medium and even migrate to the underside of the print medium. This results in an unsightly print. Moreover, the ink drops falling off the edges of the print medium can contaminate components in the printer.  
         [0023]     To solve this problem, there is generated a constant airstream with suitable direction and force that carries away the ink drops  56  that are oversprayed relative to the front, rear and side edges  16 ,  18 ,  20  and  22  of the print medium  12  so that the ink drops cannot cling to the edges of the print medium and migrate to the underside of the print medium. See  FIG. 1 . To this end, the platen  14  resides within a gravity drain basin  62  that is open facing the print head  12 . A continuous space between the platen  14  and the gravity drain basin  62  defines a rectangular gutter  64  for receiving the oversprayed drops  56  that are carried away by the constant airstream. See  FIGS. 1 and 2 . The gutter  64  empties (drains) into a collection sump  66  which is coupled with the gravity drain basin  62  via an airtight seal  68 .  
         [0024]     A removable cover  70  is fitted onto the gravity drain basin  62  as shown in  FIG. 1 . The cover  70  and the gravity drain basin  62  collectively enclose the printhead  24 , the reversible motors  26 ,  36  and  38 , the rods  28 ,  40  and  42 , and the platen  14 .  
         [0025]     An air intake port  72  including an air filter  74  is centered in a top portion  76  of the cover  70 . An air exhaust port  78  including an air filter  80  and a pump  82  is located in a wall portion  84  of the collection sump  66 . The air intake port  72  and the air exhaust port  78  including the pump  82  serve as an air flow generator for generating the constant airstream that carries away the ink drops  56  that are oversprayed relative to the front, rear and side edges  16 ,  18 ,  20  and  22  of the print medium  12 . As can be appreciated from viewing  FIG. 1 , the constant airstream carries the oversprayed drops  56  into the gutter  64  and thence into the collection sump  66 . The ink drops  56  accumulate in the bottom of the collection sump  66 . When the ink volume accumulated in the collection sump  66  reaches a certain level, a level sensor  86  triggers a warning alarm  88  and inputs a “full” signal to the microprocessor control  54  which then temporarily discontinues operation of the printer  10 . A timer may be employed to delay discontinuing operation of the printer until print-making on the print medium  12  is completed.  
         [0026]     The invention has been described in detail with particular reference to a preferred embodiment thereof, but it will be understood that variations and modifications can be effected within the spirit and scope of the invention. For example, in addition to the air exhaust port  78  including the air filter  80  and the pump  82  located in the wall portion  84  of the collection sump  66 , a second air exhaust port including an air filter and a pump can be located in another wall portion of the collection sump. This change creates a stronger, more forceful, constant airstream. In this instance, the cover  70  can be dispensed with.  
         [0027]     While the medium support is depicted as the fixed platen  14 , a movable belt is a known substitute. In this instance, there is no need for the printhead  24  to be translated forward and backward in the y-y directions  44 A and  44 B since the print medium  12  would be appropriately moved.  
       PARTS LIST  
       [0000]    
       
           10 . borderless inkjet printer  
           12 . print medium  
           14 . medium support  
           16 . front edge  
           18 . rear edge  
           20 . side edge  
           22 . side edge  
           24 . continuous inkjet printhead  
           26 . motor  
           28 . rod  
           30 A. x-direction  
           30 B. x-direction  
           32 . suspension arm  
           34 . suspension arm  
           36 . motor  
           38 . motor  
           40 . rod  
           42 . rod  
           44 A. y-direction  
           44 B. y-direction  
           46 . edge sensor  
           48 . edge sensor  
           50 . edge sensor  
           52 . edge sensor  
           54 . microprocessor control  
           56 . ink drops  
           58 . corner  
           60 . corner  
          W. width  
           62 . gravity drain basin  
           64 . gutter  
           66 . collection sump  
           68 . seal  
           70 . cover  
           72 . air intake port  
           74 . filter  
           76 . top portion  
           78 . air exhaust port  
           80 . filter  
           82 . pump  
           84 . wall portion  
           86 . level sensor  
           88 . warning alarm