Armature Support Device of a Print Head

1. Field of Technology:

This invention relates to a print head in a dot matrix printer and more particularly to a support device for armatures respectively disposed in each of driving means for selectively driving a number of print wires provided in the print head.

2. Prior Art:

U.S. Pat. No. 4,136,978 discloses a support device for armatures with an object of improving the responding speed of the armature for enabling high speed printing of the print head. This device is however far from perfect due to its fundamental structure of supporting the armature by a pair of leaf springs arranged to cross each other almost perpendicularly, so that as the number of print wires increase, the number of parts in the print head increases. The resultant structure is thus more complicated, increased time and labor is needed for assembly thereof. In other words, the pair of leaf springs must be connected or joined at least at four points; that is to say, one end of each leaf spring is joined to the armature and the other end of each leaf spring is connected to the support member. The time and labor required to effect this joining operation in a print head having a large number of armatures is tremendous.

A primary object of this invention is to provide an inexpensive print head provided with an armature support device of simple structure requiring a small number of parts and capable of responding substantially equally to the printing speed in a print head having a support device according to U.S. Pat. No. 4,136,978.

In the armature support device according to the present invention a spring member made of a piece of resilient wire is used in place of the dual leaf-spring structure in the prior art. The spring member is provided with a fixed portion secured to the armature, a pair of coaxial, oppositely directed arm portions extending from the fixed portion and a pair of leg portions extending normal to, and in the same direction from, the arm portions.

This invention exhibits the capability of a high speed printing operation without an attendant random motion of the armature, is simple in structure, has a reduced number of parts, and is low in manufacturing cost because of easy assembly.

FIG. 1 is an elevation in section of a print head including an armature support device according to the present invention;

FIG. 2 is a view showing, in part, the arrangement of armatures in the print head;

FIG. 3 is a plan view of a spring member used in the armature support device;

FIG. 4 is a perspective view of the spring member;

FIG. 5 is a plan view of a spring member used in another embodiment of the invention; and

FIG. 6 is an elevation in section of another embodiment of the invention.

An embodiment of an armature support device of this invention realized in a print head for a dot matrix printer will now be described with reference to the appended drawings. On the external circumferential portion of a print head frame 1 an annular support member 2 is secured. On the front side, i.e., rightward side in FIG. 1, of the support member 2 a number of elongated armatures 4 are respectively rotatably a pivotably retained by way of a spring member 3, preferably comprising a wire spring, with the armatures 4 being arranged so as to extend radially from the support member 2 as shown in FIG. 2. Each of the armatures 4 is composed of a main portion 5 of a magnetic material and a base portion 6 of a synthetic resin material firmly fixed to the root end of the former (located adjacent spring member 3). In the root end of the main portion 5 there is formed a notch 5a and a slot 5b open to the notch 5a. The armature 4 is supported at the base portion 6 thereof by the spring member 3. A print wire 7 is secured in an aperture 8 formed on the free end portion of the armature 4.

The armature 4 is, in this embodiment, usually held in a non-operation posture, being placed at a position shown with a solid line in FIG. 1, due to the spring force of the spring member 3, wherein the print wire 7 is at rest and does not perform a printing operation. When an electromagnet 10, disposed face-to-face with the armature 4, is energized by current flowing through a coil 9 thereof, the armature 4 is forwardly rotated or pivoted about the bight position 11a of spring member 3 (see FIGS. 1 and 2) to the positon shown in phantom lines due to the generated magnetic force, resisting the spring force of the spring member 3, thus permitting printing via the print wire 7 to take place.

Each spring member 3, provided, respectively, for each armature 4, is composed of a hair pin like bent portion 11a made in the middle portion thereof, and forming a fixed portion 11 extending substantially along the longitudinal direction of the armature 4, a pair of coaxial arm portions 12 bent in opposite directions from, and extending normal to, the ends of fixed portion 11 so that the arm portions 12 are substantially perpendicular to the fixed portion 11 and extend away from each other, and a pair of leg portions 13 further bent, from one end of each of the arm portions 12 substantially perpendicularly to the longitudinal direction of the armature 4, toward the support member 2, all of the three portions 11, 12 and 13 being integrally formed.

The fixed portion 11 of hair pin shape is securely imbedded in the base portion 6 of the armature 4, with the bent portion 11a in the middle thereof being inserted into the slot 5b of the main portion 5. The arm portions 12 are wholly disposed in, and relatively rotatably with, the base portion 6 in an imbedded manner except that only the outer end portions project out of the base portion 6. The armature 4 is rotatable or pivotable about the common axis of the arm portions 12. The relative rotation between the arm portions 12 and the base portion 6 is made possible by, when the base portion 6 is formed around the arm portions 12, applying some mold release agent on the external periphery of the arm portions 12. The leg portions 13 are in the greater part thereof firmly inserted respectively into an opening 15 formed in the support member 2 as clearly shown in FIGS. 3 and 5.

The armature 4 is normally held at the solid line position in FIG. 1 due to the spring force of the arm portions 12, but when the electromagnet 10 is energized it is attracted by the electromagnet 10 and forwardly rotated or pivoted about the arm portions 12, with the fixed portion 11 also rotated or pivoted together with the armature 4 causing, in turn, torsion in the arm portions 12. When the armature 4 is rotated or pivoted like this, the leg portions 13 of the spring member 3 firmly inserted into the openings 15 of the support member 2, the arm portions 12 imbedded in the base portion 6 of the armature 4 which are allowed only to be twisted, and the fixed portion 11 engaged at the middle portion thereof with the main portion 5 of the armature 4 and imbedded in the base portion 6, can hardly be bent or buckled. The movement of the armature 4 is consequently limited only to the rotation or pivotal motion about the arm portions 12 so as to perform good printing operation without any random movement. When later the electromagnet 10 is deenergized the armature 4 is restored to the solid line position in FIG. 1 due to a torsional resilient force of the arm portions 12. In this restoring movement the armature 4 has a predetermined regular and accurate motion. With a print head provided with the armatures 4 supported in this way, high quality precise and rapid printing can be expected. Moreover, retaining or supporting of the armature 4 is achieved by the spring member 3 which is nothing but a piece of wire. It makes the structure extremely simple and the manufacturing cost very low.

This invention can further be realized in the mode shown in FIG. 5 wherein, a plurality of spring members 3 may be made as a unit from a single piece of wire, with every two neighboring spring members 3 being linked with each other at the end of the leg portions 13 by a linking portion 20.

In place of a print head provided with an armature 4 which is rotated or pivoted when printing is carried out resisting the spring force of the spring member 3 due to energization of the electromagnet 10, as can be seen in the previous embodiment, this invention can be realized using another print head shown in FIG. 6 wherein magnetic force of a core portion 26 of a magnetic member 27 applied by a permanent magnet 21 is neutralized due to energization of a coil 22 for allowing the armature 23 which has been kept in attraction to the core portion 26 to do the printing operation due to the resilient force of a spring member 24 fixed to a support member 25. The structure of the spring member 24 is similar to that of the said spring member 3, with the exception that the biasing direction of the armature is inverted.

It is to be understood that the present invention is not limited to the above-mentioned embodiments, and that modifications and alterations may occur to those skilled in the art without departing from the scope of the following claims.