Abstract:
An impact line printer comprising a print ribbon wound on a pair of spools for traversal in two directions across a plurality of print hammers having tips for impacting the print ribbon to print on a media. A permanent magnet having two pole pieces having pole piece ends in adjacent relationship to the print hammers retains the print hammers until a coil in associated relationship with each pole piece releases the magnetic retention of the hammers. A magnetically permeable extension is longitudinally adjacent each hammer which acts as a magnetic shunt to permit more rapid printing rates and higher impacts. The extensions conduct and shunt magnetic flux from the hammers through the longitudinally adjacent extensions.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The field of this invention lies within the art of impact printing. Impact printing can take place by a hammer having a tip which impacts a ribbon to place a series of dots or a dot matrix format on an underlying media. The invention more specifically is directed toward hammerbanks of line printers having a series of hammers which are retained by a permanent magnet and are released for impact by an electrical coil which overcomes the permanent magnetism. 
     2. Background of the Invention and Prior Art 
     The prior art with respect to impact printers generally incorporates a number of impact printers of various designs and various configurations. One of the preferred types of impact printers are those impact printers referred to as line printers. The configuration of line printers is such where a hammerbank having a number of printing tips impacts a print ribbon overlying a media to be printed upon. The hammers are held and retained by a permanent magnet prior to being released for impact. The permanent magnet provides a certain amount of magnetic flux to the hammer in order to retain it. The flux required is dependent upon the size, form, configuration, and magnetic characteristics of the hammer. 
     In the design of hammerheads and the hammers in general, there are key elements with regard to maintaining sufficient flux to retain or pull down the hammers. At the same time consideration must be given in allowing the hammers to fire on a rapid and high impact basis. 
     The retention and return of the hammers is oftentimes referred to as the pull down force by the permanent magnets. 
     Other characteristics of the hammers must consider the natural frequency of the spring. This is a criteria as to the firing at a particular rate. 
     Another criteria is the pull down force required by the permanent magnets. Generally, as the mass of the hammerspring head increases, a greater stored energy can be maintained. However, as can be appreciated, this can be undesirable inasmuch as a greater mass of the head of the hammer can decrease the operational firing rate. 
     This invention is a significant improvement over the prior art by reason of the fact that it utilizes and replaces part of the hammerhead mass with shunt mass. This causes the hammerhead to be lighter and accelerate faster when released. 
     To the foregoing extent, the shunts or the fingers that are emplaced between the hammers allows the mass of the hammerhead to be reduced. At the same time the shunts help to maintain the pull down force or retention force by the permanent magnets. Therefore, the natural frequency of the spring can be increased allowing the spring to fire at an increased rate with the same impact energy. 
     Another improvement of this invention and an object thereof is to create a greater pull down force or retention force without an increase to the hammer mass. This allows the use of a stiffer spring thereby increasing stored energy in the spring. The net result is to increase the impact energy without a decrease in the firing rate. 
     Both of the foregoing aspects of the impact energy and the operational firing rate can be increased by a trade-off between the two. Thus, one skilled in the art can design the line printers of this invention in a manner to increase impact energy or firing rate. For instance, when multiple forms are being utilized, higher impact is required. On the other hand, when thinner forms are required and a greater speed or firing rate of the hammerbank is required, faster printing can take place. 
     Thus, with this invention, greater impact and faster firing rates can be accomplished as set forth hereinafter. 
     SUMMARY OF THE INVENTION 
     In summation, this invention comprises one or more hammerbank magnetic shunts emplaced between hammers in order to allow a larger magnetic flux to be applied to the bottom of the hammers of the hammerbank through the pole pieces than that flux required to saturate the hammerhead cross section. 
     More specifically, the invention incorporates the aspects of a hammer shunt plate made of a highly permeable magnetic material having fingers that are placed between the hammerheads. The flux leaving the bottom of the pole piece in a dual pole piece arrangement enters the bottom of the hammerhead. The quantity of flux entering the bottom of the hammerhead is beyond the saturation flux of the hammerhead cross section. This saturation causes an increase in the MMF drop along the hammerhead forcing the flux into the shunt fingers. 
     A key element is to cause the entire flux from the pole piece to enter the bottom of the hammerhead. It is this flux that creates a magnetic force pulling the hammer down. The use of the shunt fingers replaces part of the hammerhead mass with the shunt finger mass so that the hammerhead can be lighter and accelerate faster when released. 
     The invention can also allow a reduction of the mass of the hammerheads while maintaining pull down force. This increases the natural frequency of the spring force allowing the hammer to be fired at an increased rate. 
     On the other hand, a greater pull down force or retention can be achieved without an increase to the head mass providing for increased stored energy so that greater impact energy without a decrease in the operational firing rate can be accommodated. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a perspective view of a line printer. 
     FIG. 2 shows a perspective view of the prior art as to a double row hammerbank in a fragmented configuration as seen in the direction of lines  2 — 2  of FIG.  1 . 
     FIG. 3 shows a perspective fragmented portion of the invention utilizing the shunts. 
     FIG. 4 shows a sectional view of a hammer of this invention as sectioned along lines  4 — 4  of FIG.  3 . 
     FIG. 5 shows a sectional view of a shunt as sectioned along lines  5 — 5  of FIG.  3 . 
     FIG. 6 shows a pole piece interacting with the respective flux of a hammer of the hammerbank. 
     FIG. 7 shows an elevation view of the flux interacting with the pole pieces and the shunts of this invention. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Looking more specifically at FIG. 1, a perspective view of a line printer has been shown. The line printer can be mounted on a stand, base, or be incorporated in a cabinet. In this particular showing, a line printer  10  is shown having a base frame  12 . The base frame  12  mounts the various components of the line printer including hubs  14  and  16 . Hubs  14  and  16  are utilized to mount spools  18  and  20 . Spools  18  and  20  are respectively the feed ribbon spool and takeup spool. 
     Wrapped around the spools  18  and  20  is a print ribbon  22  which is utilized to print on a media  24   
     The media  24  is shown overlying a support plate  25 . Such media can be fan fold forms., bar code labels, combinations of plastic and paper labels and formats, paper media for graphics, and other such items. Depending upon the thickness of the media  24 , the high impact of printing that is developed by this invention can improve the multi-form and multi-layered printing by the improved impact. Also, depending upon the speed that is desired for printing on the media  24 , the invention improves the rapidity of movement of the media for increased printing by the ribbon  22 . 
     A well known method of moving the media  24  is by tractors  26  and  28  driven by the media drive shaft  30 . The media drive shaft  30  also incorporates the ability to increment the media  24  by a manual knurled knob  32 . This moves the media  24  on a manual basis for indexing, alignment, or other purposes. 
     A printer controller is utilized to control the various components and cause the printing and firing of the hammers against the ribbon  22 . This includes driving and controlling the hubs  14  and  16  for traversing the hammers to be described hereinafter. 
     Looking more specifically at FIG. 2, it can be seen that a hammerbank of the prior art has been shown, namely hammerbank  36 . The hammerbank  36  is formed with a machined or cast base  38  having an elongated channel or groove  40 . The elongated channel or groove  40  receives a circuit board  42  therein which provides the driving of the respective coils to cause firing of the hammers. 
     The showing of FIG. 2 is of a double row hammerbank having hammers  46  on the top and the bottom rows with respective tips  48  at the ends of the enlarged heads  50  on the hammers. The hammers  46  are formed on frets  54 . These frets  54  are secured by screws  56 . 
     A cover plate  60  is utilized to cover the hammers. The cover plate  60  incorporates a number of openings  62  that are indexed respectively to the tips  48  of the hammers  46 . The cover plate  60  can seat proximate to the frets  54 . It is indexed to the tips  48  which are released through the openings  62  against a print ribbon such as print ribbon  22 . The tips  48  impact against the ribbon  22  and the media  24  which is attendantly masked by a mask. The mask masking the media  24  from the ribbon  22  has openings indexed to openings  62  which receive the impacts by the tips  48 . 
     In order to secure the cover  60  to the base  36 , indexing studs  66  are utilized and various securements through openings such as opening  68  can be utilized or other such securement. 
     Looking more specifically at FIG. 3, it can be seen wherein a hammerbank of this invention has been shown in a fragmented perspective form. The hammerbank replaces the prior art in great measure whether it be a single hammerbank or row of hammers as in the showing of FIG. 3 or a double hammerbank showing as in FIG. 2. A substitution would also be fundamentally with regard to the drives from the printed circuit board and the permanent magnet as set forth hereinafter. 
     Looking more specifically at the invention of FIG. 3, it can be seen that a base or support of the hammerbank  80  has been shown analogous to the base  38 . A group of hammers  82  have been shown that have been formed on a fret  84  analogous to the fret  54  of the prior art. The respective hammers  82  have heads terminating in tips  86 . The fret  84  with the hammers  82  can be secured by screws or other fittings  88  into the base  80  of the hammerbank. 
     Looking more specifically at the upper portion of FIG. 3, it can be seen that a fret  90  has been shown with a plurality of fingers, extensions, appendages, shunts, or shunt extensions  94  that have been formed from the fret  90 . The fret  90  is formed with an upper shunt plate portion  91  to which the extensions  94  are connected. These extensions or shunts have been secured on the base  80  by the plate  91  as to the respective formation of the fret shunts by means of screws or other securement means  96 . 
     Both the extensions  94  and shunt plate portion  91  are formed of a highly permeable magnetic material. In effect, conductance of flux to a significant degree is desired through the extension  94  and the plate  91  which form the entire fret  90 . 
     Here again, a cover  60  can be utilized to cover the hammer  82  and the respective tips  86 . 
     Again, looking at FIG. 3, a cover  102  has been shown analogous to the cover  60  of the prior art. This cover  102  also has openings  104  through which the tips  86  can project for impact printing. Here again, any type of cover or plate can be utilized in order to provide for the cover of the line printer. 
     A sectional view as shown in FIG. 4 shows the hammers  82  with the fret  84  on which they are formed. The hammers  82  have the tips  86  that are shown with an enlarged hammerhead  108 . The enlarged hammerhead  108  is mounted on a relatively narrow spring portion  110 . 
     Adjacent to the hammerhead  108  are the shunts, extensions, or fingers  94  set forth hereinbefore that have been formed and mounted on the shunt fret  90 . Within the hammerbank base and the channel  81  analogous to channel  40  of the prior art, is a printed circuit board  116  analogous to prior art circuit board  42 . The printed circuit board  116  has terminals  118  and  120  that allow the circuit board  116  to be connected to a printer controller. 
     Within a channel is a permanent magnet  122 . The magnet  122  retains the hammers  82  into a position in close proximity to a lower pole piece extension  126  and an upper pole piece extension  128 . 
     The pole piece extensions  126  and  128  are respectively extensions of pole pieces  130  and  134  having coils  136  and  138  wrapped around the pole pieces. The permanent magnetism of magnet  122  pulls the hammerhead  108  into juxtaposition with the pole piece extensions  126  and  128 . The hammers  82  are retained until released by a magnetomotive force through coils  134  and  136  as driven by circuit board  116 . 
     FIG. 4 shows the extensions of the pole pieces  126  and  128 . The pole pieces are relatively flat on their exposed surfaces. The pole pieces  126  and  128  have been shown in the elevation view of FIG.  7 . FIG. 7 shows the pole piece ends of the pole pieces  126  and  128  seated between the fingers, extensions, or shunts  94  as shown previously in FIGS. 3 and 4. 
     Again, looking more specifically at FIG. 5, it can be seen that the cover  102  is shown with the openings  104  through which the tips  86  of the hammers  82  can project. 
     As seen from the cross section of FIG. 5, the hammerhead  108  should be designed such that it is closer to the pole piece than the extensions  94 . This is in order to assure that the hammerhead  108  receives a significant amount of the flux rather than it flowing initially before hammer release from the pole pieces  126  and  128  through the extensions  94 . 
     As will be seen in FIG. 5, a showing of the enlarged hammerhead  108  of the hammer  82  is such wherein it is closer to the pole piece  126  and  128  ends. This is in order to rely upon the lesser amount of magnetic resistance in any air gap so that the pole pieces will function with respect to the hammers  82  rather than flux being imparted to the extensions  94  initially. 
     The showing of FIG. 5 also includes a wall portion  140 . The wall portion  140  is fundamentally the area that separates each respective series of pole pieces  130  and  134 . These also separate the pole pieces  126  and  128  ends so that a finite relatively smooth surface is seen at the ends of pole pieces  126  and  128 . In effect, the pole pieces  126  and  128  ends are substantially flush with the surface of the base  80  of the hammerbank. 
     As previously stated the base  80  can be made from a casting or milled bar. The pole pieces  130  and  134  are inserted therein and then potted with a potting material or other material which provides the separation walls  140  as can be seen in the two respective FIGS. 4 and 5. The potting is filled in around the pole pieces  130  and  134  as well as the coils  136  and  138 . 
     The showings of FIGS. 4,  5 ,  6 , and  7  are such wherein a dynamic released configuration is shown. Normally, when the hammers  82  are retracted or in the pulled back position, they are adjacent to the ends of the pole pieces  126  and  128 . In FIG. 6, the hammer  82  has been released so that it is specifically moving into an impacting position with its tip  86  against the print ribbon  22 . However, after release, the pull back force of the flux at the ends of pole pieces  126  and  128  pulls the hammerhead  108  back into contact therewith. 
     Looking more specifically at FIGS. 6 and 7, it can be seen that the lines of flux flow from the lower pole piece  126  end through the hammerhead  108  and shunts  94  and then back through the upper pole piece  128  end. The division of flux between the hammerhead  108  and shunt pieces  94  depends on the cross sectional area of the hammerhead which relates to the flux required to saturate. 
     The concept and features of this invention are such where the shunts or extensions  94  are formed from the fret  90  which includes the shunt plate  91 . Both the plate  91  or fret  90  and extension  94  are made of a highly permeable magnetic material. 
     The flux as seen in FIGS. 6 and 7 leaves the pole piece  126  end in order to retract the hammerhead  108  into a pull down position. The design is such where the quantity of flux is beyond the saturation flux of the hammerhead  108 . This causes an increase in the MMF drop along the hammerhead  108  forcing the flux into the shunt fingers or extension  94  as can be seen in FIG.  7 . 
     The design and path of the magnetism of the permanent magnet  122  is through the pole pieces  126  and  128 . For improved performance the entire flux of the pole piece should enter the bottom of the hammerhead  108 . It is this flux that creates the magnetic force pulling the hammerhead  108  backwardly after release. The dynamic position of the firing of the hammer  82  with the respective hammerheads  108  are shown released in FIGS. 4,  5 , and  6 . When the hammer  82  is pulled back, the spring portion  110  is slightly bowed, and upper and lower portions of the hammerhead  108  are in close contact or adjacent relationship with the ends of pole pieces  126  and  128 . 
     Inasmuch as the mass of the hammerhead is replaced with the mass of the shunt fingers or extensions  94 , the hammerhead  108  can be lighter and can accelerate faster when released. The foregoing results in the shunt fingers or extensions  94  allowing the mass of the hammerhead  108  to be reduced while at the same time maintaining the pull down force or pull back force through the pole piece  126  and  128  ends. Therefore, the natural frequency of the spring portion  110  can be increased. This allows the hammers  82  to fire at an increased rate with the same energy. 
     A greater pull down force can be achieved without an increase in the mass of the hammerhead  108  or hammer  82 . Thus, the use of a stiffer spring  110  can be utilized which increases the stored energy in the spring. The net effect is that an increase in the hammer  82  impact by the tips  86  increases the impact energy without a decrease in the operational firing rate. 
     The foregoing improvements can be effected depending upon whether a faster firing rate is desired or a greater impact. In the alternative, a degree of both increased firing rates and increased impact force can be effected with a balance between each characteristic. A faster firing rate would be such where greater throughput of the printer is experienced. On the other hand, when multi-forms having 4, 5, 6, or more layers are utilized, a greater impact is desirable. 
     Depending upon the net results desired, either the increased rate or the higher impact can be implemented depending upon the particular design and functions of the printer. The effect is so that both the impact energy and operational firing rate can be increased by a trade-off between one of the foregoing design characteristics. 
     The cover  102  can rest on top of the shunt fingers or extensions  94  to provide a low reluctance path to the cover. This allows the cover mass to act as part of the flux shunting mechanism of the fingers or extensions  94 . It has been found that the shunt path of the fingers or extensions  94  are such where greater flux is carried through them rather than through the cover  102 .