Abstract:
In one embodiment, a hammer bank for a line printer includes a back plate having a front surface, a back surface and a uniform thickness between the front and back surfaces. At least one hammer is disposed in front of the back plate. The at least one hammer is spring-biased for forward movement and away from the back plate and is releasably retained against such forward movement by a magnetic force acting rearwardly thereon. An elongated pole piece that is associated with the at least one hammer extends forwardly from the front surface of the back plate and is selectively operable to interrupt the magnetic force acting thereon.

Description:
RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. patent application Ser. No. 13/654,095, filed Oct. 17, 2012, now U.S. Pat. No. ______, issued ______. 
     
    
     BACKGROUND 
       [0002]    1. Technical Field 
         [0003]    This invention relates to line printers in general, and more particularly, to hammer banks for line printers that are both easier and lower in cost to manufacture and service. 
         [0004]    2. Related Art 
         [0005]    Line impact matrix printers, or line printers, produce letters and graphics in the form of a matrix of dots by employing a “shuttle” mechanism that runs back and forth in a horizontal direction over a page of a print medium, such as single sheet or continuous form paper, coupled with movement of the page perpendicular to that of the shuttle. An inked “ribbon” is typically interposed between the shuttle and the page. The shuttle comprises a “hammer bank,” i.e., an inline row of cantilevered, magnetically retracted hammer printing tips respectively disposed on the ends of elongated spring fingers, or “hammers,” each of which is selectively “triggered,” i.e., electromagnetically released, and timed so as to impact the page through the ink ribbon and thereby place a dot of ink on the page. As a result of the ability to precisely overlap the ink dots produced thereby, line printers can produce vertical, horizontal and diagonal lines that have a solid appearance, and print that closely resembles that of “solid font” printers, and refined graphics similar to those produced by graphics plotters, at speeds of up to 2000 lines per minute. Additionally, because the printing involves impact or mechanical pressure, these printers can also produce carbon and carbonless copies. 
         [0006]    Examples of hammer banks for line printers can be found in the patent literature, including U.S. Pat. Nos. 6,779,935 and 6,821,035, both to John W. Gemmell, the respective disclosures of which are incorporated herein by reference. While these and other prior art line printer hammer banks can provide satisfactory print quality and speeds, they are not without some drawbacks. 
         [0007]    For example, prior art hammer banks typically comprise a machined or die cast base part that is relatively expensive to make, and which is substantially integrated in the shuttle mechanism, which makes both the shuttle mechanism and the hammer bank more difficult and expensive to manufacture and to remove for servicing or replacement of the hammer bank in the field. Additionally, conventional hammer banks typically incorporate relatively complex, dual-pole-piece magnetics for the control of each hammer, which adds to their complexity and cost of manufacture. 
         [0008]    Accordingly, there is a long felt but as yet unsatisfied need in the relevant industry for hammer bank designs that are both efficient and reliable, yet which are easier and lower in cost to manufacture and service. 
       SUMMARY 
       [0009]    In accordance with embodiments of the present invention, hammer banks for line impact printers are provided that are both efficient and reliable, yet substantially easier and lower in cost to manufacture and service than prior art devices. 
         [0010]    In one embodiment, a novel hammer bank for a line printer comprises a back plate having a front surface, a back surface and a uniform thickness between the front and back surfaces. At least one hammer is disposed in front of the back plate. The at least one hammer is spring-biased for forward movement away from the back plate and is releasably retained against such forward movement by a magnetic force acting rearwardly thereon. An elongated pole piece is associated with the at least one hammer and extends forwardly from the front surface of the back plate. The pole piece is selectively operable to interrupt the magnetic force acting thereon. 
         [0011]    A better understanding of the above and many other features and advantages of the novel line printer hammer banks of the present disclosure and their manufacture and use can be obtained from a consideration of the detailed description of some example embodiments thereof below, particularly if such consideration is made in conjunction with the appended drawings, wherein like reference numerals are used to identify like elements illustrated in one or more of the figures thereof. 
     
    
     
       BRIEF DESCRIPTION OF THE FIGURES OF THE DRAWINGS 
         [0012]      FIG. 1  is a partial, upper, front and right-side perspective view of an example line matrix impact printer within which embodiments of the hammer banks of the present invention can be advantageously employed; 
           [0013]      FIG. 2  is a partial, lower, front and left-side perspective view of a front face of an embodiment of a hammer bank in accordance with the prior art, as seen along the lines of the section  2 - 2  taken in  FIG. 1 ; 
           [0014]      FIG. 3  is a sectional view of a single impact hammer of the prior art hammer bank of  FIG. 2 , as seen along the lines of the section  3 - 3  taken therein; 
           [0015]      FIG. 4  is a partial, upper, front and left-side perspective view of a front face of an example embodiment of a hammer bank in accordance with the present invention; 
           [0016]      FIG. 5  is a sectional view of the example hammer bank of  FIG. 4 , as seen along the lines of the section  5 - 5  taken therein, showing a single impact hammer thereof; 
           [0017]      FIG. 6  is a partial front elevation view of three impact hammers and associated flux shunts of the example hammer banks of  FIGS. 4 and 5 , showing the flow of magnetic flux in the shunts; 
           [0018]      FIG. 7  is a partial upper, front and left-side perspective view of an example embodiment of a back plate of the example hammer bank of  FIG. 4 ; and 
           [0019]      FIG. 8  is a cross-sectional view of an alternative embodiment of a hammer bank and associated control magnetics in accordance with the present invention. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    In accordance with the present disclosure, embodiments of hammer banks for line printers are provided, together with methods for making them, that are both efficient and reliable, yet substantially easier and lower in cost to manufacture and service than prior art devices. 
         [0021]      FIG. 1  is a perspective view of an example line matrix impact printer  10  within which embodiments of the present invention can be advantageously employed. As illustrated in  FIG. 1 , the printer  10  can be mounted on a stand or a base, or incorporated in a cabinet. In the particular embodiment illustrated, the printer  10  is shown supported within a base frame  12 . The base frame  12  supports all of the various components of the printer  10 , including a cartridge ribbon system (not illustrated), which comprises an “endless” or Mobius strip of ink ribbon housed inside a cartridge that is fed across the print medium by a motor that creates tension on the ribbon by use of gears on one side and a tension spring on the opposite side of the cartridge. The cartridge ribbon system feeds ribbon horizontally over a print medium, such as paper, to enable ink transfer from the ribbon to the paper and thereby create printed images as the hammers fire. 
         [0022]    In the example embodiment illustrated in  FIG. 1 , the print medium is arranged to advance vertically over an arcuate support plate  25 . The print medium can comprise, for example, single sheets, fan-fold forms or continuous sheets, bar code labels, combinations of plastic and paper labels and formats, paper media for text and graphics, and other such materials. In the particular embodiment illustrated in  FIG. 1 , the print medium is moved vertically up and over the support plate  25  by sprocket drive “tractors”  26  and  28 , which are conjointly driven by a media drive shaft  30 . Of course, other known media drive mechanisms, such as frictional drive wheels, can also be used. The media drive shaft  30  also incorporates a knurled knob  32  for manually incrementing the vertical position of the print medium. The knob  32  can be utilized to move the print medium manually, e.g., for indexing or initial alignment of the print medium, or for other purposes. 
         [0023]    The example line printer  10  of  FIG. 1  further includes a “shuttle”  34  incorporating a scotch yoke mechanism that causes a “hammer bank”  36  (see  FIG. 2 ) to be driven back and forth over the ink ribbon and the print medium in the horizontal direction. As described in more detail below, the hammer bank  36  includes an inline row of cantilevered, magnetically retracted “hammers,” i.e., printing tips respectively disposed on the ends of elongated spring fingers, each of which is selectively “triggered,” i.e., electromagnetically released, and timed so as to impact the page through the ink ribbon and thereby place a dot of ink on the page. 
         [0024]      FIG. 2  is a partial perspective view of a front face of a prior art hammer bank  36 , as seen along the lines of the section  2 - 2  taken in  FIG. 1 . As illustrated in  FIG. 2 , the prior art hammer bank  36  includes a machined or die cast base part  38  and a plurality of inline hammers  40  that are formed integrally in a comb-like “hammer fret”  42  that is mounted on the front face of the base  38 . Each of the hammers  40  has a “head” or upper end terminating in an elongated printing tip  44 . The hammer fret  42  and the integral hammers  40  can be secured by screws  46  or other types of fastening mechanisms onto the base  38  of the hammer bank  36 . As discussed in more detail below, the rear face of the base part  38  can include an elongated channel  39  within which electrical and electromagnetic components of the hammer bank  36  are disposed. 
         [0025]    As illustrated in  FIG. 3 , the hammer bank  36  further includes a second, “shunt fret”  48  having a plurality of downwardly extending, elongated fingers, or magnetic “shunts”  50 , that are likewise formed integrally in the shunt fret  48 . The shunt fret  48  is formed to include an upper shunt fret plate portion  49  to which the downwardly dependent shunts  50  are connected. Like the hammer fret  42  above, the shunt fret  48  can be secured on the front face of the base part  38  by, e.g., screws  52 , with each of the hammers  40  being interdigitated between a pair of adjacent shunts  50 . 
         [0026]    Both the hammer fret  42  and the shunt fret  48 , including the respective integral hammers and shunts  50 , are formed of a highly permeable magnetic material, which results in a high degree of magnetic flux conductance through the frets  42  and  48  and their respective hammers  40  and shunts  50 . 
         [0027]    As shown in  FIG. 2 , the prior art hammer bank  36  includes a protective cover  52 , shown broken away in the figure, that covers the hammer and shunt frets  42  and  48 , including the shunts  50 , hammers  40  and their respective printing tips  44 . The cover  52  includes a plurality of openings  54 , each corresponding to and through which a respective one of the printing tips  44  of the hammers  40  can project for impact printing on the print medium  24  (see  FIG. 1 ). 
         [0028]      FIG. 3  is a sectional view of the prior art hammer bank  36  of  FIG. 2 , as seen along the lines of the section  3 - 3  taken therein, wherein the cover  52  is omitted and showing a single hammer  40  and the hammer fret  42  within which it is formed. As illustrated in  FIG. 3 , the hammer  40  includes an enlarged hammer head  56  on which the elongated printing tips  44  described above are disposed. The hammer head  56  is mounted on the upper end of a relatively narrow, cantilevered spring portion  58  of the hammer  40 . As described above, a shunt  50  extends downwardly on either side of the hammer head  56 . A printed circuit board  60  is mounted within the channel  39  in the back of the base part  38 . The printed circuit board  60  has terminals  62  that enable the circuit hoard  60  to connect to a printer controller (not illustrated). 
         [0029]    As further illustrated in  FIG. 3 , a permanent magnet  64  is also disposed within the channel  39  of the base part  38 . The magnetic flux of the permanent magnet  64  serves to retain the hammer  40  in close proximity to or in abutment with a lower pole piece extension  68  and an upper pole piece extension  70 . The pole piece extensions  68  and  70  are extensions of lower and upper pole pieces  72  and  74 , respectively. The dual pole pieces  72  and  74  have respective electrical coils  76  and  78  wrapped around them. As discussed above, the magnetic force of the permanent magnet  64  pulls the hammer head  56  toward and into juxtaposition with the pole piece extensions  68  and  70  and against a forward bias imposed on the hammer head  56  by the spring portion  58  of the hammer  40 . The shunts  50  disposed on either side of the hammer head  56  serve to complete a magnetic flux path from the pole pieces  72  and  74  to the hammer head  56 . The hammer head  56  is thus retained until released by a magnetomotive force (MMF) induced in the lower and upper pole pieces  72  and  74  by passing an electrical current through the coils  76  and  78 , which “reverse biases” the magnetic flux of the permanent magnet  64 , thereby releasing the hammer head  56  to spring forwardly from its magnetic hold. 
         [0030]    As illustrated in  FIG. 3 , the lower and upper pole pieces  72  and  74 , together with their corresponding coils  76  and  78  and pole piece extensions  68  and  70 , are typically embedded in a bed  80  of epoxy formed in a front cavity  82  of the base part  38  to form a relatively monolithic structure. 
         [0031]    While conventional hammer banks, such as that illustrated and described above, can provide satisfactory print quality and speeds, they are not without certain drawbacks. For example, as can be seen in, e.g.,  FIGS. 2 and 3 , the prior art hammer bank  36  includes a machined or die cast base part  38  that is integrated into and forms part of the shuttle mechanism  34  of the line printer  10 . This makes both the hammer bank  36  and the shuttle mechanism  34  more difficult and expensive to manufacture, and makes the hammer bank  36  relatively difficult to remove as a separate component for servicing or replacement, especially in the field. Additionally, as can be seen in, e.g.,  FIG. 3 , prior art hammer banks  36  typically incorporate relatively complex, “dual pole piece” magnetic actuators for the control of each hammer  40 , which adds to their complexity and cost of manufacture. 
         [0032]      FIG. 4  is a partial, upper, front and left-side perspective view of a front face of an example embodiment of a hammer bank  100  in accordance with the present invention, which overcomes many of the above and other drawbacks of prior art hammer banks.  FIG. 5  is a sectional view of the example hammer bank of  FIG. 4 , as seen along the lines of the section  5 - 5  taken therein, showing the details of a single impact hammer and associated control magnetics thereof. 
         [0033]    As illustrated in  FIGS. 4 and 5 , which respectively correspond to  FIGS. 2 and 3  of the prior art hammer bank  36  described above, the example hammer bank  100  includes a back plate  102  and a plurality of elongated pole pieces  104  extending forwardly from a front surface  106  thereof. Each pole piece  104  has an electrical coil  108  disposed about a circumfery thereof. The construction of the back plate  102  and pole pieces  104  is described in more detail below in conjunction with  FIG. 7 . 
         [0034]    In the particular example embodiment illustrated in  FIGS. 4 and 5 , and referring to the upper portion thereof, a permanent magnet  110  has a back surface that is magnetically coupled to the front surface  106  of the back plate  102 , and a flux bar  112  has a back surface that is magnetically coupled to a front surface of the permanent magnet  110 . A shunt fret  114  that defines a plurality of elongated, downwardly extending shunts  116  has a back surface that is magnetically coupled to a front surface of the permanent magnet  110 . 
         [0035]    Referring to the lower portions of  FIGS. 4 and 5 , a hammer fret mounting bar  118  has a back surface that is coupled to the front surface  106  of the back plate  102 , and a hammer fret  120  has a back surface that is coupled to a front surface of the hammer fret mounting bar  118 . The hammer fret  120  defines a plurality of elongated, upwardly extending hammers  122 . Each of the hammers  122  is interdigitated between a pair of adjacent shunts  116  and includes an elongated spring portion  124  that has a hammer head  126  disposed at an upper end thereof Each hammer head  126  has a printing tip  128  projecting forwardly therefrom. 
         [0036]    As illustrated in  FIGS. 4 and 5 , the back plate  102 , permanent magnet  110 , flux bar  112 , shunt fret  114 , hammer fret mounting bar  118  and hammer fret  120  can be sandwiched with each other and held together in a rigid assembly by, for example, a plurality of fasteners  130 , such as bolts or screws, that can extend partially or completely through the assembly. Additionally, as can be seen in  FIG. 4 , in some embodiments, the permanent magnet  110 , the shunt fret  114  and the hammer fret  120  can be split into bilaterally symmetrical halves for ease of manufacture and assembly without adversely affecting the function of the hammer bank  100 . 
         [0037]    As those of skill in the art will understand, it is desirable that at least the back plate  102 , the pole pieces  104 , the flux bar  112 , the shunt fret  114  and the hammer fret  124  be constructed of a magnetically permeable material. As illustrated in  FIG. 5 , by so doing, a magnetic flux path, as indicated by the arrows  132 , is established in the hammer bank  100  by the permanent magnet  110 . The flux path  132  extends from the permanent magnet  110 , through the flux bar  112 , the shunt fret  114 , the hammers  122 , the pole piece  104 , the back plate  102 , and thence, back to the permanent magnet  110 . 
         [0038]    As in the prior art hammer bank  36  described above, the magnetic flux acts to pull the head  126  of the hammer  122  back toward and into juxtaposition with the front end of the pole piece  102  and against a forward bias exerted on the hammer head  126  by the spring portion  124  of the hammer  122 . As discussed below in connection with  FIG. 6 , the shunts  116  disposed on either side of the hammer head  126  serve to complete the flux path  132  from the pole piece  102  to the hammer head  126  while enabling the hammer head  126  to move freely when released. The hammer head  126  is thus retained in juxtaposition with the single pole piece  102  until it is released to spring forwardly in response to the forward bias of the spring portion  124  of the hammer  122 . As above, this is effected by passing an electrical current through the coil  108  so as to induce a magnetomotive force (MMF) in the pole piece  104  that interrupts the magnetic flux path  32 , thereby releasing the hammer head  126 , and hence, the associated printing pin  128 , to spring forwardly so as to impact an ink ribbon and print a dot on a print medium. 
         [0039]      FIG. 6  is a partial front elevation view of three impact hammers  122  and associated flux shunts  116  of the example hammer bank of  FIGS. 4 and 5 , showing the direction, as indicated by the arrows  134 , taken by the magnetic flux in flowing from the shunts  116  to the hammers  122 , and thence, to the front ends of their associated pole pieces  104  respectively located behind the hammers  122  (see  FIG. 5 ). As may be seen in  FIG. 6 , the magnetic shunts  116  are separated from the hammers  122  by relatively narrow air gaps  136 . Because the magnetic flux is able to bridge the air gaps  136  relatively easily, this arrangement enables the hammers  122  to move back and forth freely, while maintaining the continuity of the magnetic flux paths  132  respectively controlling the movement of the hammers  122 . 
         [0040]      FIG. 7  is a partial upper, front and left-side perspective view of the back plate  102  of the example hammer bank  100  of  FIGS. 4 and 5 , showing the pole pieces  104  protruding forwardly from the front face  106  thereof. As discussed above, the corresponding structure, i.e., the base part  38  of the prior art hammer bank  36  of  FIGS. 2 and 3 , is typically a machined or die cast part, and a comparison of the two structures reveals that the base plate  102  is considerably simpler in its implementation, and indeed, comprises a generally flat plate that can be, for example, die-stamped from a sheet of an appropriate material. 
         [0041]    Additionally, as shown in  FIG. 7 , in which the respective electrical coils  108  of the pole pieces  104  have been omitted for clarity, the pole pieces  104  themselves can also comprise generally flat, rectangular bars, as opposed to the cylindrical pole pieces  72 ,  74  of the prior art. Thus, the pole pieces  104  can, like the back plate  102 , be produced efficiently by stamping them from bar stock of an appropriate material, making them considerably simpler and less expensive to manufacture. Further, as may be seen in  FIGS. 5 and 7 , the pole pieces  104  can be directly coupled to the front face  106  of the base plate  102 , rather than indirectly through, e.g., “lossy” interveiling components, such as pole piece extensions, thereby further simplifying construction and reducing fabrication costs. The back end of each of the pole pieces can be attached to the front surface  106  of the back plate  102  with any magnetically permeable attachment process, such as, for example, stakes  138 , as illustrated in the example of  FIG. 7 , as well as other attachment mechanisms, including press fitting, riveting; brazing, welding or adhesive bonding. 
         [0042]    The straightforward design of the stamped base plate  102  and pole pieces  104  provides a robust supporting structure for the hammer bank  100  and, when coupled with the enhancement of the magnetic pull-down force for the print hammers  122  provided by the use of the flux shunts  116 , enables the use of a single impact pole piece  104  for retracting a print hammer  122 , rather than the more complex and expensive dual pole piece design of the prior art (see, e.g.,  FIG. 3 ). This, in turn, enables the single-pole-piece hammer bank  100  to exhibit a print energy equal to that of the more complex and costly prior art dual pole piece hammer banks. 
         [0043]      FIG. 8  is a cross-sectional view, similar to that presented in  FIG. 5 , of an alternative embodiment of a hammer bank  200  in accordance with the present invention. As can be seen from a comparison of  FIGS. 5 and 8 , the hammer bank  200  is similar to the first example hammer bank  100  described above, except that additional efficiencies in the design have been achieved by forming the back plate  102  to incorporate lateral bends that define portions which are offset from and parallel to the front surface  106  of the back plate  102 , as well as portions that are substantially perpendicular to the front surface  106  thereof. 
         [0044]    The bends and the offset and perpendicular portions can be formed in the originally flat base plate  102  design of the first embodiment  100  above by, for example, well-known stamping, pressing or forging operations. As those of some skill will appreciate, the bends and offsets in the base plate  102  serve not only to enhance the stiffness of the base plate  102 , and hence, the hammer bank  200 , in the lateral direction, but also to enable the flux bar  112  and hammer fret mounting bar  118  of the first embodiment  100  above to be eliminated, thereby achieving an economy in manufacturing. As in the first hammer bank  100  described above, the components of the hammer bank  200  can be sandwiched together in close magnetic coupling with each other and held together with inexpensive fasteners, such as rivets or bolts. 
         [0045]    As those of skill in the art will appreciate, the respective structures of the example hammer banks  100  and  200  illustrated and described above are such as to impart substantial vertical and lateral rigidity to the respective hammer bank assemblies, without the need for a more robust base part, which is typically substantially integrated with the shuttle mechanism in hammer banks of the prior art. Accordingly, using hammer bank designs of the type disclosed herein enable such prior art base parts to be replaced with a simple hammer bank “carrier frame” that is integral to the shuttle mechanism and to which the new hammer bank designs  100  and  200  are removably attached, e.g., by one or more fasteners, such as screws or bolts. This, in turn, enables the hammer banks to be easily removed from the shuttle mechanism, e.g., in the field, for repair or replacement, and additionally, enables the hammer banks to be fabricated and assembled separately from the shuttle mechanisms, e.g., at different manufacturing facilities. 
         [0046]    Indeed, in light of the foregoing description, it should now be clear that many modifications, substitutions and variations can be made in and to the materials, apparatus, configurations and methods of use of the novel line printer hammer banks of the present disclosure, and in light thereof, that the scope of the present disclosure should not be limited to that of the particular embodiments illustrated and described herein, which are merely by way of some examples thereof, but rather, should be fully commensurate with that of the claims appended hereafter and their functional equivalents.