Technical Field

This invention relates to a print wire actu- ating device for use in high-speed wire matrix printers, and to a method of manufacturing the same.

Background Art

In the field of wire matrix printers, it has been quite common to provide wire actuators or solenoids arranged to drive the respective print wires a precise distance from a rest or non-printing position to an impact or printing position. The print wires are gen¬ erally secured to the solenoid plunger or armature which is caused to be moved such precise distance when the solenoid coil is energized and wherein the plunger nor¬ mally operates against the action of a return spring.

It has also been quite common to provide a wire matrix print head in which such solenoids are ar¬ ranged or grouped in a circular configuration, the print wires extending from the solenoid to the front tip of the print head near the record media. In such print heads, the actuating ends of the print wires are spaced in accordance with the circular arrangement and the operating or working ends of the print wires are closely spaced in vertically aligned manner adjacent the record media.

Further, it has also been common to provide a plurality of single wire actuators or solenoids which may be equally spaced one from another along a line of printing and wherein the spacing between the solenoids is generally in the range of 12 to 25 millimetres.

The wire actuators or solenoids of these prior art arrangements were generally tubular or cylindrical in shape. Thus, for instance, U.S. Patent No. 4,016,965 discloses a matrix print wire solenoid actuator for a

high speed wire matrix printer in which a small diameter print wire is propelled against printing paper and rib¬ bon by the linear motion of the solenoid plunger to which the print wire is attached. In this arrangement, the housing of the solenoid, the magnetic pole pieces, the bobbin and coil means and the plunger are all cy¬ lindrical elements.

Disclosure of the Invention

While cylindrical units can claim certain ad- vantages as far as efficiency is concerned, their dis¬ advantage is that they occupy a lot of space rendering wire matrix print heads rather bulky, and, since cylin¬ drical elements are normally produced by turning pro¬ cesses, their production is rather costly. It is an object of the present invention to provide a narrow and compact print wire actuator which is simple and cheap to manufacture. hus/ according to the invention, there is provided a print wire actuating device including a pair . of spaced electromagnetic pole pieces, an electromagnetic coil operably associated with said pole pieces, a plunger positioned to be operated upon energization of said electromagnetic coil, a print wire disposed between said pole pieces and abutting said plunger and slidably operated thereby, resilient means for biasing said print wire and said plunger in one direction, and a plate member positioned in relation to said coil and said plunger for providing a path for magnetic flux generated in response to energization of said coil, characterized in that said pole pieces and said plunger are flat members arranged in a substantially planar construction.

According to another aspect of the invention, there is provided a method of making a print wire actu¬ ating device characterized by the steps of: stamping a pair of irregularly shaped, flat, pole pieces, each having a long portion and a short portion in spaced

relationship, providing a bobbin having portions to fit in the space between the long portion and the short portion of each pole piece and to receive a wire coil for wrapping around said short portions, stamping a flat armature member to fit with the short portions of the pole pieces and partly surrounded by said bobbin, pro¬ viding print wire means engageable by said armature member for slidable movement thereby upon energization of the wire coil, stamping a rectangular plate member to fit with one end of said bobbin and surrounding a por¬ tion of said armature member, and providing an end cap abutting said rectangular plate member and formed for receiving the ends of said long portions of the pole pieces, and retaining the rectangular plate member, the armature and the print wire means in an assembly thereof.

An advantage of the print wire actuator ac¬ cording to the invention is that, owing to the narrow¬ ness and compactness thereof, a reduction in distance between print wires of adjacent actuators is possible. Thus, a dot matrix print head comprising a plurality of such actuators may be made smaller and also shorter because the narrow actuators can be placed side-by-side closer to the record medium for a given amount of wire curvature. The availability of narrow actuators permits a narrow print head to be used and thereby reduces the width of the printer because of the reduced clearance at the ends of the printing line.

Another advantage is that narrow actuators disposed along a line of printing effect or enable an increase in throughput or an improvement in print quality.

A further advantage of the print wire actuator according to the invention is that its elements may be made by fine blanking or stamping in a simple manner instead of using costlier turning processes required for the manufacture of cylindrical elements.

While, as is usual in conventional print wire actuators, the print wire may be secured to the plunger

of the solenoid, in the embodiment to be described here¬ after the print wire is free from the plunger and allows ballistic flight of the wire after the plunger is ar¬ rested in its movement by the pole pieces. The ballistic operation permits the use of a smaller, more efficient stroke and provides for more equal impact forces over a large range of print gaps.

Brief Description of the Drawings

An embodiment of the print wire actuating device according to the invention will now be described, with reference to the accompanying drawings, in which:

Fig. 1 is a side view in partial section of a print wire actuator made in accordance with the teaching of the present invention; Fig. 2 is a view taken along the line 2-2 of

Fig. 1;

Fig. 3 is a view taken along the line 3-3 of Fig. 1;

Fig. 4 is a perspective view of the print wire actuator; and

Fig. 5 is a perspective view in diagrammatic form of a print head made by assembling a plurality of ^" the individual print wire actuators.

Best Mode of Carrying Out the Invention Referring to Fig. 1 of the drawing, a matrix print actuator or solenoid 10 is constructed in manner of design thereof in a generally rectangular shape and is made from low-cost parts and fabricated by means involving a low-cost blanking or stamping operation. An armature or plunger 12 of generally blunted-arrow shape is centrally positioned and faces portions of a pair of pole members 14 and 16 which include slanted or angled surfaces 18 and 20. The angle of surfaces 18 and 20 corresponds with the angle of surfaces 22 and 24 on the front of the armature 12 and thereby provides uniform

CV-l

air gaps 26 and 28 between the opposing armature and pole surfaces. The armature 12 has a central, generally U-shaped, rear portion cut out or removed therefrom for the purpose of reducing the mass of the unit. A central member or spring seat 30 of combined rectangular or substantially square and circular configuration is positioned forward of and abutting the armature 12 and includes a counter-sink 32 in the one end thereof abut¬ ting such armature 12 for reception of the flat head 34 of a print wire 36 which extends forward and is slidably contained through a hole or aperture 38 in a wire guide 40, also rectangular or substantially square shaped. The central member 30 and the print wire 36 may, if desired, be integrally molded as a single unit. A coil spring 42 is placed around a reduced diameter or step portion (circular configuration) of the central member 30, which portion serves as a seat for the spring 42 and which spring, in turn, urges the central member 30 against the armature 12. The spring 42 is thus con- tained between and tends to urge the central member or spring seat 30 with its captured print wire 36 against the armature 12 and away from the wire guide 40. The pole members 14 and 16 include step portions adjacent the front of the solenoid for retaining the wire guide 40 which, in turn, has its forward end thereof main¬ tained in engagement with such step-like projections by reason of the force from spring 42.

The pole members 14 and 16 are irregular- shaped, flat pieces and include short end portions or legs 50 and 52 which include the angled surfaces 18 and 20, which lie adjacent the central member 30, the spring 42 and the wire guide 40, and which are _. formed to receive a flanged bobbin or spool 54 around which is wrapped a wire coil 56. The bobbin or spool 54 is rec- tangular shaped and preferably of single piece construc¬ tion in the surrounding of a portion of the armature 12 and the end portions or legs 50 and 52 of the respective

pole pieces 14 and 16. The end portions 50 and 52 extend to approximately the middle of the bobbin 54 and terminate with the angled surfaces 18 and 20 opposite the surfaces 22 and 24 of the armature 12. A rectangular- shaped steel washer 58 is placed at the rear of the bobbin 54 and is apertured to accept the long end por¬ tions or legs 60 and 62 of the pole pieces 14 and 16. Such washer 58 includes a rectangular opening sized to receive the base of the armature 12 and a projecting rectangular portion of the bobbin 54. The steel washer 58 thus serves to carry the flux in its return path around the armature 12. A rectangular-shaped plastic cap 64 is placed over and is in surface contact with the washer 58 and also includes apertures for the tips of the end portions 60 and 62, which tips may be twisted or bent in a crimping manner for retaining the overall assembly of parts.

As understood from Fig. 1, the various parts of the actuator or solenoid 10 are thus captured or contained in the lengthwise direction, left to right, by the tips of the long end portions 60 and 62 of the pole pieces 14 and 16 being bent or deformed over the plastic cap 64. The several parts of the actuator 10 are contained in the depthwise direction, viewed into the plane of Fig. 1, by the rectangular bobbin 54 which surrounds a portion of the armature 12 and the end por¬ tions 50 and 52 enclosing the spring seat 30, the spring 42 and the wire guide 40. A mounting means comprising slotted extensions 66 and 68 of the pole pieces 14 and 16 are provided for convenient attaching of the actuator or solenoid 10 within a carriage aperture (not shown) and retained with a suitable clip (also not shown).

Fig. 2 illustrates an end view of the actuator 10 and includes the rectangular plastic cap 64 receiving the ends 60 and 62 of the pole pieces 14 and 16 for containing the several parts in an assembled condition. The view also shows the rectangular shape of the bobbin 54 in dotted lines.

Fig. 3 illustrates a frontal end view of the actuator 10 and includes the flat-shaped pole pieces 14 and 16 along with the print wire 36 slidably contained in the wire guide 40. The extensions 66 and 68 are also shown as part of the pole pieces 14 and 16.

A perspective view of the print wire actuator 10 is illustrated in Fig. 4 to show the generally flat and rectangular construction thereof but with the bobbin and the wire coil removed to show more clearly the form of the several parts in the assembled arrangement.

Fig. 5 is a perspective view in diagrammatic form of a print head 70 made by assembling a plurality of the rectangular-shaped solenoids 10 with their print wires 36. In the arrangement shown, there are four of the solenoids 10 stacked proximal the observer and three solenoids 10 in distal relationship to form a narrow print head configuration. The rectangular arrangement herein may be contrasted with a representative print head assembly of cylindrical solenoids disclosed in United States Patent No. 4,016,965. While the arrange¬ ment of seven of such solenoids 10 in the instant inven¬ tion may be modified from that shown, the rectangular solenoids which are fabricated from flat stock material provide for a more compact print head and enable a reduction in space required for operation in a matrix type printer.

The flat stock material used in the process of making the solenoid is preferably 1.53 mm thick mild steel. It should be noted that the several parts made by such fine blanking or stamping process include the armature 12, the pole pieces 14 and 16 and the washer 58, and when assembled, as illustrated in Fig. 3, the width of such washer 58 defines an actuator or solenoid that is approximately 6.35 mm wide. The spring seat or central member 30 is made of acetal, the wire guide 40 is Delrin, the bobbin 54 is nylon and the end cap 64 is made from a suitable injection molded plastic. Delrin is a trademark of DuPont Company. The blanking or

stamping process for making the several parts of the rectangular solenoid 10 reduces the cost thereof over the turning process for making cylindrical units.