GB2040817A - Coil for hammer in dot matrix print head - Google Patents

Abstract

A print head includes a number of hammer assemblies, each composed of a plurality of extremely thin, substantially planar hammers 50 suspended from shaft 60 in closely packed side-by- side relationship, all of which are situated between a single pair of "U"- shaped primary magnets. Each hammer consists of an aluminium frame 68 carrying a flat coil 80 and print wire 90. To maximize the number of coil windings within the very limited width each coil is wound with one section thinner than the remainder of the coil by an amount equal to the diameter of the wire lead 84. The lead 84 is caused to extend radially along the flat side surface of the thinner section 99 toward the corner at the periphery of the thinner section which has been outwardly extended to a small degree to compensate for the reduction of the width of the section. The lead 84 is then bent over the edge of the coil and the outermost turn of the coil is wound on top of the lead 84 to maintain it in the position. <IMAGE>

Description

SPECIFICATION Coil for hammer in dot matrix print head The present invention relates to a print head for a dot matrix printer and, more particularly, to a print head wherein coils on the hammers are wound in a manner which permits a plurality of hammer assemblies to be situated in side-by-side relationship between a single pair of primary magnets so as to reduce the size, complexity and cost of the head.

The dot matrix printer is an apparatus which causes a plurality of closely spaced dots to be printed at high speed in seiected locations on a paper strip to form letters, numerals or other intelligible symbols thereon. The dots are formed by causing contact between the paper and the ink impregnated surface at the desired locations by selectively electromagnetically displacing elongated print wires mounted within the print head.

In order to imprint dots in the desired locations on the paper, a plurality of selectively displaceable print wires are required. To provide the necessary print quality, the dots must be imprinted on the paper in close proximity to each other. To achieve this, the ends of the print wires must be situated on a very closely packed matrix array.

In most conventional dot matrix printers, the print wires located in the head are displaced by selectively electrically energizing solenoids, from which the print wires extend, by momentarily connecting the solenoid to a power source. The impact ends of the print wires are retained in position with respect to the paper, and each other, by a wire bearing having a plurality of openings therein arranged in a matrix array. The impact end of each wire is received in one of the openings in the wire bearing and is movable through the opening to cause the end thereof to protrude beyond the surface of the bearing when the solenoid is actuated to cause contact between the paper and an ink impregnated surface.

It is desirable to have the print wires extend between the solenoid and the opening in the wire bearing through which the impact end of same passes in a direction co-linear with the axis of movement of the solenoid, such that all of the forces developed by the actuation of the solenoid are utilized effectively. Thus, it is an important design consideration to provide print wires which extend along lines which are as straight as possible throughout the lengths of the wires.

Both linear and "clapper" type solenoids have been utilized as actuators. However, such solenoids are large and bulky and, therefore, require a great deal more space than the distance permitted between the impact ends of the print wires, if characters of the required quality are to be obtained. In order to design a print head having the required number of actuators and still have print wires extend in a direction co-linear with solenoid movement as much as possible, the lengths of the print wires have been extended and the solenoid actuators have been staggered in different planes and/or arranged in a variety of different arcuate, circular, or flared configurations.However, even with such configurations, it is impossible to situate all the solenoid actuators in positions which are co-linear with the direction of movement of the print wires connected thereto, because of the size of the solenoids. At least some of the wires, therefore, must be situated along a curved path between the solenoids and the wire bearing. In one method used to guide the print wires through the curved path,-each of the print wires is sur rounded by a tubular sheeth composed of plastic or berylbum-copper alloy, which extends along the length thereof, and acts to retain the wire in the proper position, when the solenoid is actuated, and to direct the displacement forces in a plane perpen diculartothe paper.Other methods inciude guiding the wires through guide holes in parallelly situated discs or through guide grooves around a conical centerpiece.

Regardless of the guide method utilized, substan tidal friction is created between the print wires and the guide, as the print wires are displaced along the curved path. This friction significantly reduces the speed and efficiency of the printing operation, creates unwanted heat, and causes the wearing out of the parts, reducing the life of the print head. In addition, a print head comprising a large number of solenoids arranged in a flared, staggered or circular configuration is heavy, bulky and expensive to produce, repair and maintain.

In order to covercomethese problems, actuators of different configurations have been investigated.

Instead of the conventional linear or "clapper" type solenoid, an actuator, commonly referred to as a hammer or flag, has been proposed. Such a hammer is formed of a thin planar frame having an opening into which a flat coil is mounted. The hammer is suspended from a support between a pair of primary magnets. Each hammerframe has a print wire extending outwardly from one side thereof. When a selected coil is energized by connecting the leads thereof to a power source, the coil, and thus the frame and print wire mounted thereon, are abruptly displaced relative to the primary magnets due to the electromagnetic forces created. This movement causes the print wire to cause contact between the paper and an ink impregnated surface so as to imprint the dot.

Such hammers constitute a significant advance over the conventional linear or "clapper" solenoid actuators, because same significantly reduce the weight, bulk and cost of the print head. Further, it is possible, by appropriately staggering the hammers and by utilizing extremely thin primary magnets at either side thereof, to reduce (but not eliminate) the curvature of print wires and, therefore, to reduce the problem of friction created by the movement of the wire through a curved path.However, since a pair of primary magnets is required for each hammer in the assembly, it is still not possible with conventional hammers of this type to locate the hammers suffi ciently close together to permit all of the hammers to be co-linear with the movement of the print wire ends. thus, since a pair of magnets is still required between each of the hammers, this configuration still did not completely solve the friction problems or reduce the bulk of the head to a minimum.

In order to completely eliminate the friction problem caused by curved print wires and to reduce the bulk of the head to a minimum, a new method of winding the coil on the hammer has been devised which permits the hammers to be sufficiently thin such that all of the hammers may be situated between a single pair of primary magnets. Thus, the magnets normally required to be situated between the hammers are eliminated such that all of the hammers and the attached print wires move in substantially the same plane, In order to achieve an apparatus which can operate efficiently at high speeds, the hammers must be quite thin, substantially planar, and be mounted in closely packed, side-by-side relationship, and the magnetic flux density developed by the magnet assembly must be relatively high and uniform across the space within which the hammers are mounted.These results are achieved, in part, through a unique method of winding the coil on the hammer.

Normally, a coil is wound starting with one lead of the wire adjacent to the bobbin such that the other lead of the wire extends from the coil in the plane of the outermost turn. With this winding configuration, in order to connect the inner lead of the wire of the coil to an external source, it is necessary that this inner lead be brought out of the innermost turn of the coil in a plane substantially perpendicular to the plane of the coil and thereafter extend along the flat side surface of the coil until it reaches the periphery of the coil, where it may again be situated within the plane of the coil. Thus, the inner lead of the coil requires as much space as an entire radially extending set of turns.

This addition in the width of the coil is usually not serious when the dimensions of the coil are not critical. However, in a situation where the hammer assembly must be extremely thin and the coil have as many turns thereon as is possible, winding in the conventional manner, with the inner lead extending along the flat side surface of the coil, reduces the maximum number of turns of the coil by the number of turns in an entire radially extending set of turns. In this case, where only five radially extending, multilayer, side-by-side sets of turns are possible because of the size restrictions, the elimination of a single radially extending set of turns reduces the number of turns by one-fifth, substantially reducing the efficiency of the hammer.

In order to overcome this problem, and in accordance with the present invention, each hammer comprises a very thin substantially planar frame member. A recess, defined within the frame, is adapted to at least partially receive a flat wire coil.

Preferably, the coil is wound on a bobbin. The coil is wound to permit the maximum number of turns possible without extending beyond the plane of the frame. The coil has first and second leads adapted to be operably connected to the energizing means. The coil is wound with one section thereof thinner than the remainder of the coil by an amount equal to the diameter of the wire lead. The lead from the innermost turn is caused to extend radially along the flat side surface of the thinner section towards the corner at the periphery of the thinner section, which is extended outwardly to compensate for the reduction of the width of the thinner section. The inner lead is then bent over the edge of the coil and the outermost turn of the coil is wound on top of the inner lead to maintain the position of the inner lead.

In the accompanying drawings, like numerals refer to like parts and in which: Figure 1 is a plan view of the dot matrix printer, of which a preferred embodiment of the present invention forms a part; Figure 2 is a side view of the head of the dot matrix printer of Figure 1; Figure 3 is a rear view of the head of the dot matrix printer of Figure 1; Figure 4 is a view of the head of the dot matrix printer, of which a preferred embodiment of the present invention forms a part, taken along line 4-4 of Figure 3; Figure 5 is an enlarged cross-sectional view of a hammer of the dot matrix printer; Figure 6 is a bottom view of the wire bearing of the dot matrix printer; Figures 7A and 7B are schematic views, respectively, of the side and end of a coil in accordance with the present invention; and Figure 8 is an isometric view of the coil and the mandrel upon which same is wound.

Certain aspects of a dot matrix printer of which the head described herein forms a part are described in detail in co-pending application No. 79 26563 (Serial No 2035220) filed 31st July 1979 entitled "Print Head for Dot Matrix Printer", and copending application No.7926562 (Serial No 2035219) filed 31st July1979 entitled "Method of Coil Winding And Magnet Arrangement for Dot Matrix Print Head". The reader is referred to those applications for a complete description thereof. However, the printer is described herein in general to enhance the reader's understanding of the present invention.

As seen in Figure 1, the dot matrix printer of the present invention includes a paper tray 10 comprises ing a circular bottom portion 12 having an upstanding cylindrical peripheral wall 14 and a center dereeler mechanism 16 of known configuration.

Paper tray 10 is rotatable about a point 18 at the center thereof. A roll of paper to be imprinted (not shown) is situated within tray 10 between the dereeler 16 and outer peripheral wall 14 such that the bottom thereof rests on surface 12. Tray 10 revolves about pivot point 18, such that a paper strip is continuously removed from the inside thereof and fed through a print head, generally designated 20.

The paper strip, as it is removed from the roll, passes from a point beneath head 20 vertically through head 20 towards the viewer, as seen in Figure 1. As the paper strip travels through head 20 it passes between an ink impregnated surface in the form of roller 22 freely rotatably mounted within an opening in the head housing 24 or a ribbon situated in a cassette, and a wire bearing 26. Located behind wire bearing 26 are situated a plurality of hammers or flags. Preferably, twenty-eight hammers are provided. The hammers are situated in a magnetic field created by a magnet assembly, generally designated 28, which is mounted between a top magnet bracket 29 and a bottom magnet bracket 31.Each of the hammers are selectively actuatable by a conventional energization circuit in order to cause a print wire connected thereto to be displaced towards the ink impregnated surface, so as to cause contact between a section of the paper and the ink roller to imprint a dot on the paper. A plurality of dots in closely spaced relationship are imprinted on the paper so as to form letters, numerals, or other ingelligible symbols as the paper passes between the ink roller and the wire bearing.

Also located near the rear of the head is a pair of linear solenoids 30 mounted on brackets 32 connected to head housing 24. Solenoids 30 are of conventional design and, when actuated, serve to imprint a bar code on either side of the space on the paper where the dots imprinted. The imprinted bar code contains machine readable information or the like.

The details of print head 20 can best be observed from Figure 2. The paper strip 34 after it is unwound from a paper reel (not shown) passes around a dancer roller arm (not shown) to a spool guide 36, in the form of a roller rotatably mounted on bracket 37 which forms a portion of head housing 24, and a paper guide 38. The paper strip 34 then passes between a corborundum roller 40 and a powered pinch roller 42, both of which are rotatably mounted on head housing 24. Thereafter, the paper strip 34 passes between ink roller 22 and wire bearing 26 at which point the dots and bars are imprinted thereon.

After passing wire bearing 26, the paper strip is directed between a pair of knife blades 44 and 46 which are actuatable by a conventional solenoid mechanism (not shown) to cut the paper at the desired point, so as to form a ticket or the like.

Located behind the wire bearing 26 is a hammer housing 48 in which a plurality of hammers 50 are mounted. As can best be seen in Figure 3, the hammers 50 are preferably situated in four groups or banks of hammers 52, 54, 56 and 58, each comprised of seven hammers. Each of the hammers is suspended from a pivot shaft 60 situated behind hammer housing 48. Between each of the hammer assemblies 52, 54, 56 and 58 is a spacer member 62 also mounted on pivot shaft 60. The leads from the coils of the hammers (not shown in this figure) are connected to a printed circuit board 64, of conventional design, which contains the circuitry required for the high speed actuation of the individual hammers 50 and the bar code solenoids 30.Also visible in this figure is the stepping motor housing 66 which rotates pinch roller 42 in order to advance the paper strip 34 through head 20.

As is best seen from Figure 4, each of the hammers 50 comprises a substantially planar frame 68, preferably manufactured by stamping an aluminum sheet. Frame 68 includes an elongated flexible support member 70 having a groove or recess 72 along its length. Near the rear of suspension member 70 is a bifurcated part 74 having an opening therein which is adapted to be received over pivot shaft 60. Bifurcated part 74 extends downwardly towards the bottom of hammer housing 48 and the parts thereof are located between a pair of protrusions 76 extending parallel to pivot shaft 60. In this manner, flag 50 is supported in cantilever fashion from hammer housing 48.

Within the body of frame 68, which is generally rectangular in configuration, is situated a coil 80. Coil 80 is preferably wound about a bobbin 78. The periphery of the coil adheres to the inside of the body of frame 68 by a potting compound 81 situated therebetween. Coil 80 has a pair of leads 82, 84, one or both of which extend along groove 72 in suspension member 70 in order to connect coil 80 with printed circuit board 64.

Each of the coils 80 are situated within a magnetic field supplied by magnet assembly 28. By passing an electrical current through leads 82,84 and, thus, coil 80, a force is developed such that the hammer assembly 50 abruptly moves a short distance towards paper strip 34, in a slight arc about the axis of pivot shaft 60. When the current ceases to flow through coil 80, the force developed by the magnetic field terminates and the hammer 50 returns to its original position through the flexing of support member 70 and from energy returned by impace force.

Located on the forward end of hammer 50 near the top corner thereof is a wire guide 86 which passes through an opening 88 in the top surface of hammer housing 24 so as to guide the movement of hammer 50. Located on the forward portion of hammer 50 near the bottom corner thereof is a print wire 90, preferably formed of tungsten, in order to reduce variations in the length thereof due to wear.

Extending from the bottom of head housing 24 towards hammers 50 is a movement limiting member 92 which serves to limit the rebound movement ofthe hammer afterthe current through the coil therein has been terminated. Print wire 90 extends along a channel 94 formed in the bottom portion of the hammer assembly 48 and terminates in wire bearing 26 situated at the lower end thereof. Wire bearing 26, as can best be seen from Figure 6, has a plurality of groups of openings 26a, 26b, 26c, 26d, 27a and 27b therein. The openings are grouped in four groups 26a, 26b, 26c, 26d of seven round openings each, each group being spaced from the adjacent groups, and a pair of bar openings 27a, 27b, located at each end of the wire bearing to accommodate the impact ends of the bar code solenoids 30.

Each of the round openings in each group of openings is designed to accommodate a single print wire 90.

One of the unique features of this construction is that it permits all of the hammer assemblies, 52,54, 56, 58, comprising seven hammers each, to be situated in the magnetic field formed between a single pair of primary magnets, in contradistinction to prior art configurations wherein a pair of magnets is required for each of the hammers. Thus, the size, bulk and complexity of the head is greatly reduced.

In order to achieve this unique result, each hammer must be extremely thin and retain its substantially planar configuration relative to adjacent hammers.

Figure 5 is a greatly enlarged cross-sectional view taken through hammer 50 along line 5-5 of Figure 4.

At the top of the figure is shown in cross section aluminum frame 68 which is stamped from an aluminum sheet and is approximately .016 inch in width. Aluminum is chosen for this component because it will retain its substantially planar shape and because of its strength, lightness and flexibility.

Bobbin 78, one wall of which is shown in the figure, is hollow, made of anodized aluminum and has a width of approximately .020 inch. Bobbin 78 is purposely designed to be wider than the width of frame 68 such that it extends outwardly on either side of the plane of the bobbin so as to form bearing surfaces 78a and 78b on its peripheral edges.

The hammers 50 within each group of hammers are mounted in side-by-side relationship in close proximity such that a minimum of space is required between the two primary magnets, thereby enhancing the magnetic flux density therebetween. Therefore, even the slightest misalignment of one of the hammers 50 will cause same to rub against the adjacent hammers. Such rubbing between adjacent hammers could prevent the free displacement thereof or result in the wearing of parts, eventually destroying the hammers. In order to avoid this, each of the bobbins 78 is made slightly wider than frame 68 such that it is the bobbins of adjacent hammers, and particularly the peripheral anodized bearing surfaces 78a and 78b thereof, which rub together during displacement of the hammers.Thus, any wear on the hammers is confined to the anodized bearing surfaces, which are situated in face-to-face relationship, such that the planar configuration of each of the hammers is maintained and any wearing of the hammer is confined to an area wherein it is not detrimental to the operation of the hammer.

It is therefore clear that the entire coil 80 must be confined within the plane of the frame such that adjacent coils will not rub against each other during displacement. This limitation must be offset against the fact that coil 80 must have an many turns as possible thereon such that sufficient ampere turns will be present to provide the necessary displacement force. In order to achieve this result, the coil 80 must be wound in a unique manner.

Conventional coils are wound such that one lead of the wire is situated at the central coil opening (on the surface of a bobbin, if same is present). A winding arm holding the wire is rotated about the mandrel support (or bobbin, if present) and moved axially such that the wire may be wound to form a first layer of side-by-side turns. Successive axially extending layers of turns are built up over the first layer. The coil can thus be viewed as having a plurality of side-by-side radially extending sets of multiple turns. With this structure, one lead of the wire extends from a turn on the outermost layer and, therefore, can be used to form a lead without requiring any additional widthwise space.

However, the lead from the inner end of the wire, which extends from one of the innermost turns adjacent the central opening of the coil, must also form a lead such that a complete circuit is achieved.

This lead extends from the inside turn of the coil for a short distance in a direction parallel to the axis of the coil and, therefore, perpendicular to the direction of the turns. This lead may be then bent in a direction parallel to the plane of the turns; immediately adjacent to the place where it extends from the inside of the coil and then caused to extend along the side surface of the coil to the periphery thereof.

Thus, this lead will require a space alongside the coil at least equal to the diameter of the wire.

In most situations, this additional amount of space is available and, therefore, the conventional winding configuration creates no problems. In the present situation, however, the width of the coil must be confined to an area less than the width of the frame, to wit, .016 of an inch and, preferably, to an area of .015 of an inch. For practical purposes, the wire utilized to wind a coil must be a minimum of .003 inch in diameter. Thus, if all of the space permitted forthe coil is used effectively, five side-by-side radially extending sets of multiple turns can be placed within the permissible .015 inch maximum width.

If the coil is wound in the conventional manner, starting with one end adjacent the central opening and winding outwardly to form radially extending side-by-side sets of multiple turns, the lead extending from the inner turn will require a space of .003 inch (the diameter of the wire) such that it can pass along the side surface of the coil to the periphery thereof. Thus, the space which could be used for an entire radially extending set of multiple turns is eliminated, if the coil is to be placed within a confined area.Since the wire of .003 inch diameter would permit, at best, five side-by-side radially extending sets of multiple turns within a .015 inch area, if the coil is wound in the conventional manner, such that a lead from the inner turn had to run along the side surface of the coil, only four side-by-side radially extending sets of multiple turns could be possible, the space where the other radially extending set of multiple turns normally would be situated being taken up by the wire lead.

In orderto eliminate this problem and, therefore, permit as many turns as possible, the coil is wound such that one section thereof is thinner than the remainder of the coil and the corner of the thinner coil section is radially extended to compensate for the reduction of width of the coil section. More specifically, the end of the wire which will form inner lead 84 is first caused to extend radially along the interior of one of the mandrel sections 108 and 110 when same are assembled such that the supports 100, 102, 104 and 106 extending from section 108 are received in corresponding openings in mandrel section 110. This differs from the conventional winding procedure wherein the inner end of the wire would, at this point, extend out of the central opening in one of the mandrel sections and, thus, not affect the coil winding. In the conventional coil, the width of the coil would be uniform at all points and the inner lead would, after the coil is wound and removed from the mandrel, be bent alongside of the coil.

In the coil made in accordance with the present invention, after the placement of lead 84, the wire is held by a conventional revolving wire arm and revolved around the mandrel such that the wire is wound about supports 100,102,104, 106, to form the first turn. The arm is moved axially as it revolves such that successive layers of side-by-side turns are formed. However, before the last outermost turn is formed, the inner lead 84 is brought across the periphery of the coil such that it extends in a direction parallel to the axis of the coil. The last turn is then completed such that the portion of lead 84 which extends along the side surface of section 112 of the coil is permanently affixed in the position illustrated. The end of lead 84 thus extends in the plane of the coil when same is complete.

It should be appreciated that the presence of lead 84 will cause the coil section 112, in the vicinity of lead 84, to be thinner than the remainder of the coil by a distance equal to the diameter ofthe wire.

However, the number of turns of the coil must be equal at all points. Therefore, the corner of the coil which forms a part of section 112 must be radially extended with respect to the remaining corners of the coil in order to compensate for the reduction in width of section 112. Thus, by forming section 112 to be thinner than the remainder of the coil and by radially extending the corner which forms a part of section 112 to compensate for same, the number of turns in the coil is maximized because the presence of inner lead 84 does not reduce the number of coil windings.

It is to be understood that the coil may be removed from the support after it is wound and, thereafter, mounted within the recess in the hammer such that the hammer contains a bobbinless coil. However, it is preferable to use a bobbin as a support and to mount the entire assembly, including the coil and bobbin, to the hammer.

In this manner, the maximum number of turns, preferably 175 in total, may be situated within the permitted widthwise space, because this winding configuration results in the maximum number of turns within the limited widthwise space. Thereby, an increase in the number of turns by 20% over conventional configurations is permitted. This results in a substantial increase in the field created by the current flowing through the coil and, thus, contributes substantially to the amount of force developed for displacement.

Another method of winding the coil to accomplish this result is disclosed in copending application No.

7926562 (Serial No 2035219) filed 31st July 1979 entitled "Method of Coil Winding And Magnet Arrangement For Dot Matrix Print Head", and assigned to the assignee hereof.

It should be noted that the width permitted for the support member 70 of the hammers 50 is also limited. However, leads 82,84 from coil 80 must be connected to printed circuit board 68 such that the coil can be energized. Normally, if leads 82,84 were placed alongside member 70, they would take up a minimum of .003 inch space (diameter of the wire lead) in addition to the .016 inch width of member 70 and, thus, create the possibility of rubbing against adjacent suspension members, eventually resulting in damage to the wires. In order to prevent this situation, member 70 is provided with a slot or groove 72 along its length intd which one or both of the leads 82,84 are received. In this manner, the running of leads from coil 80 to the printed circuit board 64 requires no additional widthwise space.

It is necessary to have the magnetic flux density created by the two primary magnets located on either side of the hammer assemblies be as high and as uniform as possible along the space within which the hammers are situated. In order to achieve this result, field shaping magnets, in addition to the primary magnets, are preferably utilized, as is described in detail in copending application No. 79 26562 (Serial No 2035219) filed31 st July 1979 entitled "Method Of Coil Winding And Magnet Arrangement For Dot Matrix Print Head".

it will now be appreciated that the coil for the hammers of a dot matrix printer permits a plurality of hammers to be situated in closely spaced side-byside relationship between a single pair of primary magnets. This configuration is possible because of the novel method of forming the coil mounted on the hammers which permits the maximum practical number of ampere turns on the coil in the minimum space.

Claims (25)

1. A print head for use in a dot matrix printer or the like, said head comprising a support a pair of magnets mounted in spaced relationship on said support and being characterized by at least two hammers mounted in side-by-side relationship on said support between said magnets for displacement relative to said support in substantially parallel planes, each of said hammers comprising a substantially planar frame having a recess therein, a coil mounted within said recess, said coil having a body portion having a section with a side surface, said body portion comprising a plurality of wire turns with first and second leads extending therefrom, and a central opening, said first lead extending from an inner turn of said body portion radially outwardly from said central opening along said side surface of said section and wherein said section is narrower, by a distance at least equal to the diameter of said wire, than the width of the remainder of said body portion a print wire mounted on and extending from said frame a power source and means for energizing said coil to displace said hammer by operably connecting said coil to said power source.

2. The head of Claim 1, characterized in that said section extends radially outwardly of said central opening a distance greater than the periphery of the remainder of said body portion.

3. The head of Claim 1, characterized in that said coil is situated entirely within the plane of said frame.

4. The head of Claim 1, characterized by means for securing a portion of said first lead to the periphery of said body portion.

5. The head of Claim 4, characterized in that said securing means comprises a turn of said wire.

6. The head of Claim 2, characterized in that said coil is situated entirely within the plane of said frame.

7. The head of Claim 6, characterized by means for securing a portion of said first lead to the periphery of said body portion.

8. The head of Claim 7, characterized in that said plane of said frame is approximately .016 inch in width.

9. The head of Claim 8, characterized in that said coil is formed of wire approximately .003 inch in diameter.

10. The head of Claim 2, characterized by means for securing a portion of said first lead to the periphery of said body portion.

11. The head of Claim 8, characterized in that said securing means comprises a turn of said wire.

12. The head of Claim 3, characterized by means for securing a portion of said first lead to the periphery of said body portion.

13. The head of Claim 10, characterized in that said securing means comprises a turn of said wire.

14. The head of Claim 11, characterized in that said plane of said frame is approximately .016 inch in width.

15. The head of Claim 12, characterized in that said coil is formed of wire approximately .003 inch in diameter.

16. A coil for use on the hammer of a print head or the like comprising a body portion having a section with a side surface, said body portion comprising a plurality of wire turns with first and second leads extending therefrom and a central opening, said first lead extending from an inner turn of said portion radially outwardly from said central opening along said side surface of said section and characterized in that said section is narrower, by a distance at least equal to the diameter of the wire, than the width of the remainder of said body portion.

17. The coil of Claim 16, characterized in that said section extends radially outwardly of said central opening a distance greater than the periphery of the remainder of said body portion.

18. The coil of Claim 16, characterized in that said coil is situated entirely within the plane of said frame.

19. The coil of Claim 16, characterized by means for securing a portion of said first lead to the periphery of said body portion.

20. The coil of Claim 19, characterized in that said securing means comprises a turn of said wire.

21. The coil of Claim 17, characterized in that said coil is situated entirely within the plane of said frame.

22. The coil of Claim 21, characterized by means for securing a portion of said first lead to the periphery of said body portion.

23. The coil of claim 22, characterized in that said securing means comprises a turn of said wire.

24. The coil of Claim 22, characterized in that said plane of said frame is approximately .016 inch in width.

25. The coil of Claim 22, characterized in that said coil is formed of wire approximately .003 inch in diameter.