WO1996039299A1

WO1996039299A1 - Dot matrix print head with bidirectional capability

Info

Publication number: WO1996039299A1
Application number: PCT/US1996/006474
Authority: WO
Inventors: Jeffery Groenke
Original assignee: Dh Tech
Priority date: 1995-06-06
Filing date: 1996-05-07
Publication date: 1996-12-12

Abstract

A print head is disclosed which has a printwire output pattern in which the printing ends of the printwires are in an NxN matrix and no printing end occupies the same vertical position, or normally also the same horizontal position, in the matrix as any other printing end. The printwires may be arrayed in polygonal, diamond, oval or circular output patterns, and the array width and height will be equal or generally similar in extent. This output pattern allows printing in two orthogonal directions and has many known advantages of the diamond pattern. Bi-directional printing can be done in either the vertical or horizontal direction because each printwire is on a separate grid line in both directions. This print head is superior in heat dissipation because the coils are placed near the outside diameter. The coils can be potted directly to the heat sink with no other structure in the heat dissipation path. The outside coil location also gives the most physical space for the coil winding. The armature pivot and the magnetic gap are both located at the outside pole. Measured from the pivot, the ratio of the plunger location to the printwire location gives a long stroke. This head increases the flexibility of printer design by providing a snap-in ribbon guide. This head is designed to be mass produced and to be highly adaptable to different printer applications. A method of dot matrix printing with this print head is also disclosed.

Description

DOT MATRIX PRINT HEAD WITH BIDIRECTIONAL CAPABILITY

BACKGROUND OF THE INVENTION

Field of the Invention:

The invention herein relates to dot matrix printers and print heads. More specifically, it relates to ballistic print heads with armature pivots at the outside pole.

Description of the Prior Art:

Dot matrix printers are widely used for transaction receipts and convenience printing. These applications include cash registers, automatic teller machines, gas pumps, lottery tickets, credit card verification, bar code printing, etc. The dot matrix printer, like other impact printers, can produce multiple carbon (or carbonless) copies. It is important for the print head, to be durable, to operate at high speed and to be as simple as possible in construction. One way of improving the print speed is to do bi-directional printing: forward (left to right) and backward (right to left). This avoids the lost time for the carriage to return to the start of a new line. A printer that prints back and forth requires special logic to reverse the character string and the font, but it requires nothing special from the print head. Another bi-directional printing that does not exist in the market today, allows the head to move in horizontal and vertical (orthogonal) directions. The orthogonal motion of the print head requires a special output pattern of the printwire to be designed into the print head.

Printwires are typically arranged in a vertical column. The spacing of the printwire in the column defines the print resolution in dots per inch in the vertical direction. Horizontal resolution in dots per inch depends on the addressability of dot location as the carriage (and head) move across the line. In all previous print head, horizontal resolution is controlled by time delay in the printer in synchronization with the horizontal movement of the head. The output guide of the printwire contains no spacing requirements for horizontal resolution. In order to do orthogonal printing, both the vertical and horizontal resolution must be embedded into the output pattern of the printwires.

In order to achieve sufficient striking force against the print ribbon to form a clean character on multiple layers of paper, the printwire must be relatively stiff. Since the driving magnets for the printwires are usually arranged in a circle, the printwire must be bent to achieve a vertical column at the output guide. The greater the curvature of the printwire, also related to pullback, the more friction, the more wear and the more driving force is needed. It is the goal of the head design to minimize pullback, lower friction and to reduce wear.

Numerous attempts have been made to alleviate the friction and pullback problems. In most cases, the printwire guides are designed to ease the movement of the printwires through their curves. Such devices have been modestly successful, but problems of friction and wear remain significant. Where the pullbacks are different for different wires, there can be unequal darkness and clarity in the image formation on the paper.

The diamond shape output pattern is used in several print heads by US and Japanese vendors. The diamond shape pattern requires time delay and horizontal movement of the head to print a vertical line. However, there are many advantages: reduction in noise, reduction in peak power, smaller printwire pullbacks and more uniform pullbacks. U.S. Patent No. 4,802,781 (Sheerer) describes a method to design the diamond pattern. By placing the wire output at a uniform column spacing, the time delays in the horizontal direction fall in fixed durations. Sheerer clearly identifies the time delay and the design method to minimize pullback. The Sheerer device, like ail other print heads, can print back and forth but not in two orthogonal directions.

Most of the print heads with the magnetic gap at the outside pole have armature pivots at the inside pole of the magnetic yoke. While this provides the maximum room for the coils, it reduces the stoke of the printwire. Using the pivot point at the inside pole also has two other limitations: (1) the printwire length is much shorter than the length of the head, and (2) the pivot point wears and reduce the life of the head. The shorter printwire increases the curvature, the stress and the wear between the wire and the guides. An alternate design has the armatures pivoted at the outside pole, then the coils and the active gap are located at the inside pole. In this case, the coils are crowded and the cooling of the coils are less efficient. SUMMARY OF THE INVENTION

The print head of the present invention overcomes these various problems. It includes a novel output guide pattern which can print in the vertical and horizontal directions. It also permits the coils to be positioned where there is ample room while enhancing the mechanics, the heat transfer and the stroke of the printwire. Heat sink mounting is readily accomplished with excellent heat transfer from the coils. The head can be connected to a variety of different printers through the changing of just the printed circuit board and a snap-in ribbon guide. The ribbon guide and the printed circuit board (or an equivalent flexible printed circuit) may be customized and changed with minimum impact to the head assembly.

In one embodiment, the invention is a print head for a dot matrix printer having a plurality of N printwires, where N is the number of printwires in the plurality, and wherein each printwire has a printing end for formation of an imprinted dot on a receiving medium, the print head comprising the printing ends of the printwire being disposed in an NxN matrix wherein no printing end occupies the same vertical (and normally and preferably also horizontal) position in the matrix as any other printing end. In another embodiment, the invention is a dot matrix print head for imprinting ink markings on a print receiving medium as one of the head and the medium is traversed relative to the other, each marking formed of at least one imprinted ink dot, the head comprising; a plurality of elongated printwires, each wire having a printing end and a driving end; a wire housing comprising a guide nose for aligning the printwires into a predetermined alignment and guiding the wires in the alignment into a first contact of the print end with an ink-containing member, each guided printwire then moving the contacted member in a second contract with the receiving medium, the second contact causing that portion of the member in contact with the print end of the printwire to imprint the ink dot on the medium: reversible actuating means for selectively actuating each of the pπntwires through the driving end, the activation initially urging the activated printwire and the ink-containing member into the first and second contacts and subsequently urging the printwire and member out of the first and second contacts after the ink dot is imprinted; the alignment comprising the printing ends of the printwires being arrayed in a plane transverse to the central axis of the plurality of the printwires such that no printing end is disposed in a vertical or horizontal position in the plane identical to a vertical or horizontal position of any other printing end in the plane; and the actuating means activating the printwires sequentially to impart a predetermined pattern of the imprinted dots on the receiving medium.

In yet another embodiment, the invention is an improved dot matrix print head for imprinting ink markings on a receiving medium as either the head or the receiving medium moves relative to the other, each marking formed of at least one imprinted ink dot, the head comprising a plurality of elongated printwires, each wire having a printing end and a driving end; a wire housing comprising a guide nose for aligning the printwires into a predetermined alignment and guiding the wires in the alignment into a first contact of the print end with an ink-containing member, each guided printwire then moving the contacted member in a second contract with the receiving medium, the second contact causing that portion of the member in contact with the print end of the printwire to imprint the ink dot on the medium; and reversible actuating means for selectively actuating each of the printwires through the driving end, the activation initially urging the activated printwire and the ink-containing member into the first and second contacts and subsequently urging the printwire and member out of the first and second contacts after the ink dot is imprinted; in which the improvement comprises the alignment comprising the printing ends of the printwires being arrayed in a plane transverse to the central axis of the plurality of the printwires such that no printing end is disposed in a vertical or horizontal position in the plane identical to a vertical or horizontal position of any other printing end in the plane; and the actuating means activating the pπntwires sequentially to impart a predetermined pattern of the imprinted dots on the receiving medium.

The print head of this invention may be used for printing on a wide variety of media, including paper, cloth, cardboard, metal and wood, depending on the nature of the ink impregnated into the ribbon on the specific printer into which the print head is mounted. The print head will find use in many business, industry and home applications, including computer generated printing, such as word processing, desktop publishing, graphics and industrial design and CAD applications; point of sale transaction recording, invoicing and receipting; bar code labelling; and the like. The invention also includes methods of printing using the print head, which in one embodiment comprises a method for imprinting ink markings on a receiving medium with a dot matrix print head which prints the markings as one of the head and the receiving medium moves relative to the other, each the marking formed of at least one imprinted ink dot, the method comprising; providing the print head having a plurality of N pπntwires, wherein N is the number of the printwires in the plurality, and wherein each the printwire has a printing end for formation of an imprinted dot on a receiving medium; disposing the printing ends of the printwires in an NxN matrix wherein no printing end occupies the same vertical (and preferably also horizontal) position in the matrix as any other printing end; and causing the printwires to be activated sequentially to impart a predetermined pattern of the imprinted dots on the receiving medium.

In another embodiment, the invention is a method for imprinting ink markings on a receiving medium with a dot matrix print head which prints the markings as one of the head and the receiving medium moves relative to the other, each the marking formed of at least one imprinted ink dot, the method comprising providing the print head comprising a plurality of elongated printwires, each wire having a printing end and a driving end; a wire housing comprising a guide nose for aligning the printwires into a predetermined alignment and guiding the wires in the alignment into a first contact of the print end with an ink-containing member, each the guided printwire then moving the contacted member in a second contract with the receiving medium, the second contact causing that portion of the member in contact with the print end of the printwire to imprint the ink dot on the medium; reversible actuating means for selectively actuating each of the printwires through the driving end, the activation initially urging the activated printwire and the ink-containing member into the first and second contacts and subsequently urging the printwire and member out of the first and second contacts after the ink dot is imprinted; aligning the printing ends of the printwires in an array in a plane transverse to the central axis of the plurality of the printwires such that no printing end is disposed in a vertical position in the plane identical to a vertical position of any other printing end in the plane; and actuating the printwires sequentially to impart a predetermined pattern of the imprinted dots on the receiving medium. BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of the print head of this invention, viewed from the printing end. Figure 2 is an enlarged cross-sectional view taken on line 2-2 of Figure

1.

Figure 3 is an exploded view of a number of components of the head.

Figure 4 is a graphical illustration of a preferred nine-printwire alignment at the printing end of the head. Figure 5 is a graphical illustration of a typical seven-printwire alignment at the printing end of the head.

Figure 6 is a side elevation view of the print head in a finned heat sink.

Figure 7 is a view similar to that of Figure 6, partially cut away to show the print head with the coil cover removed and a thermally conductive material in place.

Figure 8 is a typical circuit board used to distribute power to each magnet coil to activate the individual printwires.

Figure 9 is a plan view of a portion of the return leaf spring integrated with the armature. Figure 10 is a plan view of the leaf spring used to secure the components in assembled configuration.

Figure 11 is a plan view showing alignment of three adjacent fingers of the armature.

DETAILED DESCRIPTION AND PREFERRED EMBODIMENTS

The invention is best understood by reference to the drawings. Figure 1 shows the print head 2 which is composed of a wire housing or nose portion 4 and a drive portion 6. An electrical power cable provides power to the individual driving magnet for each printwire through connector 8 to a circuit board which can be rigid or flexible. The output guide 10 holds the printing ends 12 of the printwires in the critical alignment of this invention.

Figure 2 illustrates in detail the structure of the print head 2 as assembled. There are a plurality of N pins or printwires 14 (typically N is 7, 9, 18 or 24) which by their impact on an inked print ribbon (not shown) causes the ribbon to be forced against a sheet of paper or another print receiving medium (also not shown) creating 1 to N inked dots per activation, depending on how many of the N printwires are activated simultaneously. Traversing movement of the print head 2 with respect to the medium in conjunction with rapidly repeated and selective activations of the printwires 14 and impact with the medium causes multiple arrays of dots to be formed, and the closely spaced vertically arrays form a row of characters (including alphanumeric characters, lines and symbols) printed on the medium. Normally the print head moves to traverse across the medium to print a line, but in many applications the medium may be moved to traverse past a stationary print head. In either case, at the end of one traverse the medium is indexed to align a fresh portion of its surface with the print head and one or the other is traversed to print a second row of characters, and so forth.

Within the housing or nose 4 is an open channel 16 in which the printwires 14 move. Their alignment within the channel 16 is controlled by one or more guides 18 and the output guide 10. Each printwire guide 18 or output guide 10 has a plurality of N holes 20 through which the printwires 14 pass. The alignment of the holes 20 in each successive printwire guide 18 is such that the printwires 14 are curved from their original circular array to the final printing alignment determined by the hole 20 pattern in the output guide 10.

The housing 4 extends out into a hollow circular base 24 and the channel 16 extends to a protruding end 22. A further, smaller protrusion 26 has internal threads 28 and is used to retain the components of the head in the assembly. The base 24 is pressed against a printed circuit board 30 to which a flex-cable (not shown) is attached through connector 8. The circuitry of printed circuit board 30 is such as to connect each magnet coil 32 individually to the an external timing or sequencing device, such as a microcomputer or microprocessor (not shown). A typical circuit board is shown in Figure 8. insulating spacer 34 insures that only the desired magnetic coils 32 receive current flow at a given activation. Each of the magnet coils or bobbins 32 is mounted on an iron pole 36 which is part of a circular magnet plate 38 which has a central hole 40 to accommodate the end portion 22 of housing 4, and which keeps the magnet plate 38 and housing 4 in alignment. The magnet plate 38 forms the yoke for the magnetic flux path when a bobbin coil 32 is activated by application of an electrical current and is, unlike many of the yokes of the prior art, formed with its principal mass on the inside surrounding the centerline. This causes the magnetic flux lines to circle on the inner portion of the device, through the yoke 38, flux plate 75, plunger 62 and pole 36, when an electric current is applied to the coil of the bobbin 32. Because of this "interior" flux pattern, and with the pivot point 66 of the armature fingers 60 placed at the exterior of the device, a long stroke of each finger 60 is obtained. The printwires 14 are long in relation to the length of the overall print head 2 because the magnet plate 38 is in front of the armature 58.. This long printwire path has more gentle curvature and less stress. With the coils 32 mounted on the outwardly disposed poles 36, there is more space for the coils and they are more quickly and readily cooled. The use of the shim 54 prevents the plungers 62 from actually impacting the top of the poles 36, so that neither the plungers 62 nor the poles 36 suffer wear which would otherwise shorten the life of the head. Shim 54 also prevents the armature fingers 60 from wearing against the flux plate 75.

The driven or proximal ends 42 of the printwires 14 pass though holes 44 in the end 22 of the nose 4. Each end 42 of a printwire 14 is surrounded by a compression coil spring 46 and is potted in a solid plastic button 48. Spring 46 is seated between the button and a recess 50 in the end 22 of housing 4.

The armature 58 is formed of a circular armature spring 67 to which are attached individual armature fingers 60, the tips 61 of which in turn contact the printwire buttons 48. The armature spring 67 and the armature fingers 60 may be welded together or joined by an adhesive, but preferably are joined by riveting of the plungers to the armature assembly 58 as illustrated at 63. The armature spring 67 is biased away from the magnet plate 38 and therefore cooperates with the compression spring 46 to enhance the return of printwires 14 after impact. A portion of armature spring 67 is illustrated in Figure 9. The shape of this spring, which has fingers 55 generally conforming to the armature fingers 60, is unique and critical. The one-piece armature spring 67 is designed to provide the appropriate stiffness and strength to return all of the fingers 60 when application of electrical current is halted to the coils 32. Seated on top of the bobbins 32 is a flux plate 52 and a non- conductive (preferably plastic/rubber) shim 54. Following is the armature assembly 58, to which is attached the magnetically soft plungers 62. The flux plate 52 and the shim 54 have holes 64 to accommodate the plungers 62 and allow each plunger to get very close to its respective magnetic pole 36. In operation the application of a current across the windings of a coil 32 induces magnetic flux at the pole 36 which attracts the plunger 62. As the plunger 62 moves toward the pole 36, it causes the tip 61 of finger 60 to pivot at 66 and push the printwire 14 at the button 48. A prior art ballistic print head usually pivots the armature at the outside pole. Unlike the prior art devices, this armature 58 pivots on the spring at locations 66a and 66b.

The armature spring 67 is chosen for the proper stiffness and long life. The armature fingers 60 are chosen to be non-magnetic and have the proper rigidity, weight and cost. The plunger 62 is required to be magnetic soft and have a very high magnetic permeability. The fingers 60 are preferably made of stainless steel, which is non-magnetic, and therefore will not magnetically influence each other at the tip where the fingers push the printwires. Further, because the spring 67 and the fingers 60 are assembled from separate parts, there is a wide selection of materials and thickness. All this flexibility allows the optimum design for long life of the spring as well as optimum mass and strength of the armature. The mass of the armature is reduced because the poles 36 extend nearly to the top of the bobbins 32 to allow shorter plungers. Generally the pole:plunger length ratio will be on the order of approximately 3-4:1. A shorter plunger has two advantages: (1) less mass means higher speed, and (2) there is less radial movement of the plunger as the magnetic gap is opened and closed.

The head assembly is secured together by retainer 68, screw 72 and star spring 74. Spring 74 is seated in hole 76 in retainer 68 in contact with annular shoulder 78. Screw 72 is threaded into threads 28 in protrusion 22 to lock the components together. One or more shock absorbing dampers 77 are used as needed for proper settling of the printwires 14 after rebound from impact. All of the components are kept in alignment by bobbin pins 69, which pass through alignment holes 71 , and retainer pins 70, which pass through holes 75. The use of star spring 74, which is illustrated in Figure 10, regulates the contact of the retainer and the flux plate and allows the component tolerances to be less critical. This controls the tolerances and simplifies the assembly. The assembly is also insensitive to the thickness of the printed circuit board 30 or even to the substitution of a flexible printed circuit. This feature allows interchanging components with minimum impact to the head. If the print head is not to be mounted in a heat sink, coil cover 80 is included to complete the outer shell or housing of the print head 2. However, if the head is to be mounted in a heat sink 82 (Figures 6 and 7), the coil cover 80 is omitted and the space 88 between the bobbins 32 and the inner surface 86 of the heat sink 82 is filled with a thermally conductive material 84 (preferably a polymeric material).

A critical feature of this invention is the array 90 of the printing ends 12 of the printwires 14 at the output guide 10. Two alternative arrays are illustrated graphically in Figures 4 and 5. In each case there is an NxN grid in which each of the ends 12 of the printwires 14 is located at one of the coordinate junctions of the grid. (It will of course be understood that grid lines do not actually appear on the surface of the output guide 10, but are included in Figures 4 and 5 merely for conceptual description). Most of the prior art print heads have a column output pattern, as illustrated in U.S. Patents Nos. 4,884,905 (Smith), 4,459,051 (Kawai) or 4,493,568 (Estabrooks). A departure was the diamond pattern disclosed in the aforesaid Sheerer patent. In all cases, the vertical span from printwires 1 to 9 is wider than the horizontal span from printwires 5 to 6 (using the designations indicated in Figure 4). In any vertical grid line, the number of printwires present may be zero, one, two or up to nine. In the present invention, however, the vertical and horizontal spans are generally similar, and preferably identical. Further, each vertical grid line has one and only one printwire. This feature allows orthogonal printing: both vertical and horizontal. The novel printwire array also lessens wire pull back, decreases wear and noise of the print head in operation, and, since movement and friction are reduced, also reduces the power consumption of the head as compared to heads of the prior art.

Figure 4 and 5 (especially Figure 4) illustrate the printwire end array as being substantially diamond-shaped. It will be understood, however, that the actual shape is not important as long as the principle of not having any two printwire ends with the same horizontal and vertical grid coordinates is maintained. Thus the NxN grid pattern may be square or may have different spacing of the grid lines in either or both the horizontal and vertical directions, and even within a given direction the spacing between adjacent grid lines may vary. Thus the overall grid may be square, rectangular, rhomboid, trapezoidal, or other shape, and the printwires may be arrayed in polygonal, oval or circular patterns, as long as no two printwire ends are in vertical or horizontal alignment. Of course, the most preferred pattern is a square NxN array with the horizontal and vertical dimensions equal, as illustrated in the Figures, since that will normally optimize the average printwire travel, minimize wear and noise, and maximize the operating speed and capabilities of the print head. The operation of the present head will be controlled by a timing device most commonly a microcomputer or microprocessor, which times the application of current to each bobbin coil 32 and thus controls the moment a* which each printwire 14 is driven to contact the inked ribbon and print- receiving medium. Since the alignment of the medium and print head is constantly changing as one moves relative to the other, driven by traversing means (not shown), the printwire ends will cross the vertical printing line at different times. However, the relative movement is at a constant linear rate and therefore the timing device can apply current to the bobbin coil 32 and activate each printwire precisely when it has moved into alignment with the printing line. Normally this will be done by fixing the time when the lead printwire 14 (for instance, printwire no. 5 or 6 in Figure 4, depending on which way the head is moving) as the starting time for formation of each printed character, and then retarding the activation of the remaining printwires sequentially by a predetermined period of time such that each printwire (if its dot is to be part of the character being printed) is activated only as it passes the print line. This is most conveniently accomplished when the vertical elements of the NxN grid are equally spaced.

The present print head 2 can be used with a wide variety of printers and print mechanisms. The external contacts 92 of the circuit board 34 may be connected to any compatible ribbon cable (not shown). Since the cable is not a part of the head structure itself, changing from one printer's cable to another printer's cable is merely a matter of disconnecting one cable and attaching the other; no changes of the head 2 itself are involved. Most printers are expected to last longer than their print heads. The connector 8 allows the print head 2 to be field replaceable at the end of its life. If two printers are plug compatible to the PCB 8 standard, there is a cost advantage in using the largest volume and the lowest cost print head.

It will be evident that there are numerous embodiments of the present invention which, while not discussed above, are clearly within the scope and spirit of the invention. The above discussion is therefore intended to be exemplary only, and the actual scope of the invention is to be defined solely by the appended claims.

I CLAIM:

Claims

1. A print head for a dot matrix printer having a plurality of N printwires, wherein N is the number of said printwires in said plurality, and wherein each said printwire has a printing end for formation of an imprinted dot on a receiving medium, said print head comprising said printing ends of said printwires being disposed in an NxN matrix wherein no printing end occupies the same vertical position in said matrix as any other printing end.

2. A print head as in Claim 1 further comprising no printing end occupying the same horizontal position in said matrix as any other printing end.

3. A print head as in Claim 1 wherein said positions of said printing ends in said matrix form a generally polygonal configuration.

4. A print head as in Claim 3 wherein said configuration is generally diamond-shaped.

5. A print head as in Claim 1 wherein said positions of said printing ends in said matrix form a generally curved configuration.

6. A print head as in Claim 5 wherein said positions of said printing ends in said matrix form a generally circular or oval configuration.

7. A print head as in Claim 1 wherein in said NxN matrix increments between adjacent horizontal elements or between adjacent vertical elements are substantially equal throughout said matrix.

8. A print head as in Claim 1 wherein the horizontal and vertical dimensions of said NxN matrix are substantially equivalent.

9. A print head as in Claim 8 wherein in said NxN matrix increments between adjacent horizontal elements and between adjacent vertical elements are substantially equal throughout said matrix.

10. A dot matrix print head for imprinting ink markings on a print receiving medium as one of said head and said medium is traversed relative to the other, each said marking formed of at least one imprinted ink dot, said head comprising; a plurality of elongated printwires, each wire having a printing end and a driving end; a wire housing comprising a guide nose for aligning said printwires into a predetermined alignment and guiding said wires in said alignment into a first contact of said print end with an ink-containing member, each said guided printwire then moving said contacted member in a second contract with said receiving medium, said second contact causing that portion c* said member in contact with said print end of said printwire to imprint said ι * ao'. on said medium; reversible actuating means for selectively actuating each o* said printwires through said driving end, said activation initially urging said activated printwire and said ink-containing member into said first and second contacts and subsequently urging said printwire and member out of said first and second contacts after said ink dot is imprinted; said alignment comprising said printing ends of said printwires being arrayed in a plane transverse to the central axis of said plurality of said printwires such that no printing end is disposed in a vertical or horizontal position in said plane identical to a vertical or horizontal position of any other printing end in said plane; and said actuating means activating said printwires sequentially to impart a predetermined pattern of said imprinted dots on said receiving medium.

11. A print head as in Claim 10 wherein one of said receiving medium and said print head is movable with respect to the other bidirectionally and said actuating means is adapted to actuate said printwires sequentially while said one of said print head and said receiving medium is in motion in either direction relative to the other.

12. A print head as in Claim 10 further comprising means for electrical connection to external timing means, said timing means comprises sequencing means responsive to the unique time of alignment of each printwire with said vertical line on said receiving medium for applying electrical current to said activating means.

13. A print head as in Claim 10 wherein said alignment of said printing ends of said printwires forms a generally polygonal configuration.

14. A print head as in Claim 13 wherein said polygonal configuration is generally diamond-shaped.

15. A print head as in Claim 10 wherein said positions of said printing ends in said matrix form a generally curved configuration.

16. A print head as in Claim 15 wherein said positions of said printing ends in said matrix form a generally circular or oval configuration.

17. A print head as in Claim 10 wherein the horizontal and vertical extents of said printwire end alignment are substantially equal.

18. A print head as in Claim 10 further comprising said activation means comprising an armature, said armature comprising a plurality of printwire- contacting fingers equal in number to the number of printwires and a magnetically soft plunger on each said finger, each said finger being cantilevered and having its fulcrum in the outer perimeter area of the armature.

19. A print head as in Claim 18 further comprising a magnetic yoke adjacent said fingers of said armature and having a plurality of activatable electric coils mounted on poles thereon and a flux plate operably associated therewith, each coil in proximity of a respective plunger, such that application of electric current to a coil creates a magnetic field in said yoke, pole and flux plate adjacent said plunger urging said plunger toward said pole and coil and causing deflection in said finger, said deflection urging said printwire into contact with said print receiving medium and imprinting said dot thereon.

20. A print head as in Claim 19 wherein the greater portion of said yoke is disposed toward said central axis and said coils and plungers are disposed outwardly therefrom.

21. A print head as in Claim 20 wherein length of each said pole is substantially greater than length of said respective plunger.

22. A print head as in Claim 21 wherein pole:plunger length ratio is on the order of approximately 3-4:1.

23. A print head as in Claim 20 wherein when magnetic flux lines are induced in said yoke and pole by application of electrical current to said coil, said flux lines form a loop where said coil, pole, plunger and flux plate are disposed in that portion of said loop distal to said center axis.

24. A print head as in Claim 19 further comprising means for electrical connection of said activation means to external timing means, said timing means comprises sequencing means responsive to the unique time of alignment of each printwire with said vertical line on said receiving medium for applying electrical current to said activating means.

25. A print head as in Claim 24 wherein said means for electrical connection comprises a printed circuit board providing separate connection of each said coil to said external timing means.

26. A print head as in Claim 27 wherein tolerances within said assembled print head are not affected by the thickness of said printed circuit board.

27. A print head as in Claim 24 wherein said means for electrical connection comprises a standard plug to which any compatible external timing means can be operably attached.

28. A print head as in Claim 18 further comprising a resilient member incorporated in said armature for biasing said armature fingers away from said printwires when electrical current is not applied to said coils.

29. A print head as in Claim 28 wherein said resilient member comprises a circular ring having a plurality of extensions extending inwardly thereof, said extensions being equal in number and spacing to said fingers of said armature, with said fingers being adhered to said extensions and said resilient member being biased away from said yoke, whereby when electric current is halted to said coil, said resilient member urges all said fingers away from said yoke and enhances retraction of said printwires.

30. A print head as in Claim 29 wherein said fingers pivot at the outer periphery of said circular ring.

31. A print head as in Claim 19 wherein said plurality of coils are surrounded by a cover.

32. A print head as in Claim 19 wherein said print head is enclosed in a heat sink, and space between said plurality of said coils and an inner surface of said heat sink is filled with a thermally conductive material.

33. A print head as in Claim 10 further comprising retaining means for retaining ail components of said print head in alignment, said retaining means comprising an end cap and a resilient member engaged therewith, the initial amount of force with which said resilient member engages said end cap being maintained by said resilient member without further adjustable.

34. A print head as in Claim 33 wherein said resilient member comprises a star spring.

35. In a dot matrix print head for imprinting ink markings on a receiving medium as one of said head and said receiving medium moves relative to the other, each said marking formed of at least one imprinted ink dot, said head comprising; a plurality of elongated printwires, each wire having a printing end and a driving end; a wire housing comprising a guide nose for aligning said printwires into a predetermined alignment and guiding said wires in said alignment into a first contact of said print end with an ink-containing member, each said guided printwire then moving said contacted member in a second contract with said receiving medium, said second contact causing that portion of said member in contact with said print end of said printwire to imprint said ink dot on said medium; and reversible actuating means for selectively actuating each of said printwires through said driving end, said activation initially urging said activated printwire and said ink-containing member into said first and second contacts and subsequently urging said printwire and member out of said first and second contacts after said ink dot is imprinted; the improvement comprising: said alignment comprising said printing ends of said pπntwires being arrayed in a plane transverse to the central axis of said plurality of said printwires such that no printing end is disposed in a vertical position in said plane identical to a vertical position of any other printing end in said plane; and said actuating means activating said printwires sequentially to impart a predetermined pattern of said imprinted dots on said receiving medium.

36. In a print head as in Claim 35 the improvement further comprising no printing end occupying the same horizontal position in said plane as any other printing end.

37. A method for imprinting ink markings on a receiving medium with a dot matrix print head which prints said markings as one of said head and said receiving medium moves relative to the other, each said marking formed of at least one imprinted ink dot, said method comprising; providing said print head having a plurality of N printwires, wherein N is the number of said printwires in said plurality, and wherein each said printwire has a printing end for formation of an imprinted dot on a receiving medium; disposing said printing ends of said printwires in an NxN matrix wherein no printing end occupies the same vertical position in said matrix as any other printing end; and causing said printwires to be activated sequentially to impart a predetermined pattern of said imprinted dots on said receiving medium.

38. A method as in Claim 37 further comprising disposing said printing ends such that no said printing end occupies the same horizontal position in said matrix as any other printing end.

39. A method as in Claim 37 further comprising disposing said printing ends in a generally polygonal configuration.

40. A method as in Claim 39 wherein said configuration is generally diamond-shaped.

41. A method, as in Claim 39 further comprising disposing said printing ends in a generally curved configuration.

42. A method as in Claim 41 wherein said configuration is generally circular or oval.

43. A method for imprinting ink markings on a receiving medium with a dot matrix print head which prints said markings as one of said head and said receiving medium moves relative to the other, each said marking formed of at least one imprinted ink dot, said method comprising; providing said print head comprising a plurality of elongated printwires, each wire having a printing end and a driving end; a wire housing comprising a guide nose for aligning said printwires into a predetermined alignment and guiding said wires in said alignment into a first contact of said print end with an ink-containing member, each said guided printwire then moving said contacted member in a second contract with said receiving medium, said second contact causing that portion of said member in contact with said print end of said printwire to imprint said ink dot on said medium; reversible actuating means for selectively actuating each of said printwires through said driving end, said activation initially urging said activated printwire and said ink-containing member into said first and second contacts and subsequently urging said printwire and member out of said first and second contacts after said ink dot is imprinted; aligning said printing ends of said printwires in an array in a plane transverse to the central axis of said plurality of said printwires such that no printing end is disposed in a vertical or horizontal position in said plane identical to a vertical or horizontal position of any other printing end in said plane: and actuating said printwires sequentially to impart a predetermined pattern of said imprinted dots on said receiving medium.

44. A method as in Claim 43 further comprising aligning said printing ends in a generally polygonal configuration.

45. A method as in Claim 44 wherein said configuration is generally diamond-shaped.

46. A method as in Claim 43 further comprising aligning said printing ends in a generally curved configuration.

47. A method as in Claim 46 wherein said configuration is generally circular or oval.