Abstract:
There is disclosed a hand-held printer for printing on linerless label webs wherein a thermal print head is maintained in pressure contact with the linerless web and a platen roll throughout successive printing cycles, but wherein the pressure is automatically relieved at or shortly after each printing cycle is completed.

Description:
BACKGROUND OF THE INVENTION  
   1. Field of the Invention 
   This invention relates to method and apparatus for printing on linerless labels. 
   2. Brief Description of the Prior Art 
   The following patent documents are made of record: U.S. Pat. No. 4,477,305; U.S. Pat. No. 5,487,337; U.S. Pat. No. 5,497,701; U.S. Pat. No. 5,868,893; U.S. Pat. No. 6,585,437; U.S. Pat. No. 6,607,318; Japanese 2004-58553, Feb. 26, 2004; Japanese 2004-58554, Feb. 26, 2004. 
   In prior art linerless label printers the linerless web, which can be composed of a web of label material with a release-coated printable side and a tacky adhesive on the other side, is fed between a print head and an adhesive-resistant:platen roll. The adhesive contacts the platen roll. The web passes between a print head and the platen roll. The print head exerts pressure on the paper and the platen roll. Because the platen roll is made adhesive-resistant by use of silicone rubber and/or by special coatings, the adhesive of the linerless web does not adhere aggressively to the platen roll unless the platen roll becomes worn or the print head is in pressure contact with the linerless web for an extended period of time. Should either or both of these conditions occur, the web can adhere excessively to the platen roll and when the web is advanced, the web can tend to follow around with the platen roll as the platen roll rotates during printing of the next label. Various ways have been tried to avoid this type of action, for example, picks or scrapers are used as in patents and U.S. Pat. No. 6,585,437, for example. Another way of dealing with this problem is disclosed in LINERLESS ADDENDUM, ©1998 Monarch Marking Systems, Inc. wherein the printer is manually opened to a position where the print head is spaced from the platen roll if the printer will be unused for extended periods of time. 
   SUMMARY OF THE INVENTION  
   It is a feature of the invention to provide improved method and apparatus for printing on linerless webs which involve relaxing the pressure between the print head and platen roll and on the intervening linerless label web following each printing cycle to prevent the linerless web from adhering excessively to the platen roll. 
   It is a feature of the invention to provide an improved linerless printing method and apparatus wherein the print head exerts pressure against the linerless web and against the platen roll during each printing cycle but wherein the pressure is automatically removed or reduced following printing to prevent excessive adherence of the adhesive on the linerless web to the platen roll. 

   
     BRIEF DESCRIPTION OF THE DIAGRAMMATIC DRAWINGS  
       FIG. 1  is a right side elevational view of a hand-held label printer in accordance with the invention; 
       FIG. 2  is a fragmentary side elevational view showing the manner in which a label web from a supply roll passes through the printer; 
       FIG. 3  is a fragmentary side elevational view showing gearing to drive the platen roll; 
       FIG. 4  is perspective diagrammatic view of a mechanism for moving the print head into printing cooperation with the platen roll; 
       FIG. 5  is a perspective view of an armature assembly; 
       FIG. 6  is a partly sectional view showing one embodiment of a control assembly for the print head, wherein printing pressure is relaxed; 
       FIG. 7  is a view similar to  FIG. 7 , but showing the print head under printing pressure; 
       FIG. 8  is a view similar to the embodiment of  FIGS. 4 and 5  but showing an alternative form of print head control mechanism; 
       FIG. 9  is a sectional view of a fragmentary portion of the print head control mechanism; 
       FIG. 10  is a block diagram; 
       FIG. 11  is a flow chart depicting the control sequence; and 
       FIG. 12  is a prior art depiction of a linerless label web between a print head and a platen roll. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
   With reference to  FIG. 12 , there is shown a prior art arrangement of a driven platen roll  30  cooperable with a print head  31  to print on a linerless web  32  of label material, wherein tacky adhesive  33 , also known as pressure sensitive adhesive, is adhered to the underside of the web  32 . The platen roll  30  includes a drive shaft  34  and a sleeve of resilient elastomeric material such as silicone rubber  35 . The print head  31  prints on the printable surface of the web  32  opposite the adhesive  33  while the platen roll  30  advances the web  32 . If the platen roll  30  is in contact with the adhesive  33  for a long period of time, the adhesive has the propensity to hold to the platen roll  30  tenaciously, and the web  32  may have a tendency to follow the platen roll around as indicated by broken lines  32 ′. To deal with this problem the present invention relieves the printing pressure following each printing cycle. 
   With reference to  FIG. 1 , there is shown a hand-held printer generally indicated at  20  having a housing or frame  21  with a handle  21 ′ with parts broken away to show batteries  22  within the handle  21 . A keyboard  23  is used to input data to the printer and a display  24  can display information entered by the keyboard, prompts and the like. A trigger switch  25  disposed at the handle  21  is used to initiate a printing cycle after data has been entered. An applicator  26  in the form of a roll is used to apply printed labels L to the article to be labeled. 
   With reference to  FIG. 2 , there is shown a roll R of a linerless label web  40  having a coating of tacky or pressure sensitive adhesive  41  on its underside. The top side of the web  40  has a coating of a thermally responsive material (not shown). The web  40  passes from the roll R beneath a roll  42  and from there to a printing position between a thermal print head  43  and a platen roll  44 . From there the web  40  passes into underlying relationship to the applicator  26 . The platen roll  44  is driven by an electric motor  45  which is preferably a stepping motor. The motor  45  drives a worm gear  46  which meshes with a gear  47  keyed to a shaft  48 . A gear  49  also keyed to the shaft  48  meshes with a gear  50  (FIGURE.  3 ) keyed to a shaft  51  for the platen roll  44 . 
   As diagrammatically illustrated in  FIG. 4 , the web  40  has transversely extending lines of weakening  52  which divide the longitudinally extending web  40  onto labels L. The weakening can be provided by perforations which enable the leading label to be torn from the remainder of the web upon application of the leading label L by the applicator  26 . The print head  43  is mounted on a print head carrying plate  53 . An electromagnet or solenoid generally indicated at  54  is mounted to a block  55 ′ secured to frame member  55  ( FIG. 2 ) of the printer  20  and a coil  56  of the electromagnet  54  is mounted to the block  55 ′. An armature  57  includes a flat electromagnetically-responsive disc  58  and a cylindrical shaft  59 . The disc  58  is close to but is spaced from a surface  60  of the coil  56 . The shaft  59  includes an adjusting screw  61  having a rounded end  62 . The rounded end  62  rests against the plate  53 . The block  55 ′ is cored out as indicated at  63  to permit free movement of the shaft  59  and its adjusting screw  61 . The block  55 ′ threadably receives a threaded stud  64  which passes through an elongate enlarged slot  65 . A nut  66  is threaded onto the stud  64 . This arrangement enables the print head carrying plate  53  to pivot relative to the block  55 ′. Energization of the coil  56  via conductors  67  will cause the disc  58  to be drawn toward the coil  56  which in turn will cause the rounded end  62  to bear with greater force against the plate  53  to pivot the plate  53  so that the print head  43  bears with printing pressure against the platen roll  44 . This printing pressure exists until the coil is de-energized, at which time the force exerted by the print head is reduced or eliminated.  FIG. 5  shows the armature  57  in greater detail. 
     FIGS. 6 and 7  illustrate another embodiment wherein an electromagnet  68  includes a coil  69  and an armature  70  having an electromagnetically-responsive disc  71  and a shaft  72 . The coil  69  is secured to a support  73  secured to the frame  55 . The shaft  72  extends through a hole  74  in the support  73 . The shaft  72  has a screw threaded portion  72 ′ which threads adjustably into the remainder of the shaft  72  and its rounded terminal end bears against a plate  75 . The plate  75  is spaced from a plate  76  which mounts the print head  43 . The plate  76  includes brackets  78  with flanges  78 ′ that overlie the plate  75  to limit the travel of the plate  76  and the print head  44 . A pair of compression springs  79  bias the plates  75  and  76  relatively away from each other. In  FIG. 6  the plate  75  is shown in abutment with the flanges  78 ′.  FIG. 6  shows the coil  69  as being de-energized so the springs  79  are only under slight compression.  FIG. 7  shows the coil  69  as being energized, thereby compressing the springs  79  so that the print head exerts printing pressure against the web  40  and the platen roll  44 . 
   The embodiment of  FIGS. 8 and 9  is the same as the embodiment of  FIGS. 1 through 5 , except that the print head  43  is held spaced from the platen roll  44  except when the coil  56  is energized. A threaded stud  75 ′ secured to the plate  53  passes through an enlarged hole  76 ′. A compression spring  77 ′ is positioned between washers  78 ″ and  79 ′ under compression. A nut  80 ′ threaded into the stud  75 ′ enables the force of the spring  77 ′ to be adjusted. When the coil  56  is energized the plate  53  can pivot slightly to bring the print head  43  into printing pressure contact with the web  40  and the platen roll  43 . 
   With reference to  FIG. 10 , there is shown a block diagram of the control system generally indicated at  81 . Block  82  represents a controller or printer control circuitry which includes a microprocessor for controlling the printer  20 . The circuitry  82  controls a motor driver  83  to drive the motor  45  to in turn drive the platen roll  44  during each printing cycle. The circuitry  82  also controls the energization of the coil  56  (or  69 ). The energization of the coil  56  or  69  continues during the printing cycle and preferably also thereafter for a predetermined period of time to allow the user enough time to apply the label using the applicator  26 . The print head  43  acts as a brake while the leading label L is being applied to prevent loss of print registration and excessive unwinding of the roll R. As shown, a time delay circuit  84  is controlled by the circuitry  82 . A driver  85  energizes the coil  56  or  69  from the start of the printing cycle until a predetermined period of time has passes after the end of the printing cycle. Alternatively, a mechanical brake (not shown) can be used and the coil  56  or  69  can be de-energized as soon as the printing cycle is complete. 
   With reference to  FIG. 11 , data is first inputted from the keyboard  23  or a suitable external source as indicated at  86 . Next the data is translated into a bit map format as indicated at  87 . When the trigger switch  25  is operated, the motor  45  is turned on as indicated at  88 . At the same time the coil  56  or  69  is energized as indicated at  91 . After the motor  45  brings the platen roll up to its printing speed, the bit map data is sent to the print head as indicated at  89 . When the printing cycle is complete, the motor  45  is turned off as indicated at  90 . Even though the motor  45  has been turned off the coil  56  or  69  remains energized as indicated at  92  for a finite period of time, for example five seconds, so that the user has time to apply the leading label L at which time current flow to the coil  56  or  69  is terminated as indicated at  93 . While the coil  56  or  69  remains energized, the web  40  is clamped between the print head  43  and platen roll  44  and as the user applies the label L with the applicator  26 , the leading label is torn from the remainder of the web  40  along a line of weakening  52  without causing the web to move out of registration with the print head  43 . 
   The invention is not limited to a portable or hand-held printer but is applicable to a stationary printer that prints or prints and applies linerless labels. 
   Other embodiments and modifications of the invention will suggest themselves to those skilled in the art, and all such of these as come within the spirit of this invention are included within its scope as best defined by the appended claims.