Wire dot printing head

Abstract: A wire dot printing head comprises armatures (1) each of which is coupled to a printing wire (12), a felt guide for reducing the friction between the printing wire and the printing wire guide, a residual sheet (10) is disposed over a magnetic core frame (8), a biasing leaf spring (9), and an oil leakage preventing chip (19). The chip (19) is disposed over the armatures (1) to prevent oil oozing from the felt guide. An errorneous dot printing operation due to the stick between the armatures (1) and the residual sheet (10) is prevented.

Description: TECHNICAL FIELD TO WHICH THE INVENTION BELONGS The present invention relates to a wire dot printing head for a serial printer, and more particularly to a wire dot printing head with a dot print missing prevention mechanism. RELATED BACKGROUND ART A conventional wire dot printing head has a mechanism wherein a wire fixing armature is supported operably by a biased leaf spring which is attracted to the core of an electromagnet against the elastic force of the leaf spring by a permanent magnet, and the armature is released by activating the electromagnet in printing operation and by demagnetizing the magnetic flux from the permanent magnet. Generally, the wire dot printing head includes a printing wire guide which is formed of an oil impregnated felt to prevent wear of wires and guiding holes. In an usual printing operation, when the conventional wire dot printing head is operated with a high duty printing operation, a temperature rise of the wire occurs, thus causing oil oozing from the felt due to a decrease in oil viscosity, or causing oil elevating through spaces between the printing wires because of capillary phenomena. The oil will leak into a space between the residual sheet and the biased leaf spring. As a result, sometimes, oil sticks the residual sheet with the biased leaf spring, thus causing a dot-print missing. In DE-A 29 31 219 there is disclosed a wire dot printing head with a component supplying the wires with oil as lubricant and a cut positioned on the back side of the printing head. This cut is provided for the protection of the inner side of the printer against oil and dirt. DISCLOSURE OF THE INVENTION It is an object of the present invention to provide an improved wire dot printing head to overcome the above mentioned disadvantages, which in particular is capable for preventing a missing dot print due to oil sticking of a residual sheet and a biasing leaf spring. This object will be solved by a wire dot printing head, which is characterized in the main claim. Advantageous modifications of the wire dot printing head according to the present invention are characterized in the dependend claims. ADVANTAGEOUS EFFECTS OF THE INVENTION IN THE CONTEXT OF THE BACKGROUND ART The advantages offered by the present invention are mainly that the stick between the armature and the residual sheet does not occur, whereby an errorneous dot printing operation is prevented. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a general perspective view showing a wire dot printing head according to the present invention. Fig. 2 is a sectional view of a wire dot printing head taken along the line II-II shown in Fig. 1. Fig. 3 is an assembling view showing the relationship between armatures and dot printing wires and oil absorbing material. Fig. 4 is a general view of an oil elevation prevention chip according to the present invention. Fig. 5 is a sectional view of another embodiment of a wire dot printing according to the present invention. Fig. 6 is a general view of another embodiment of an oil elevation prevention chip according to the present invention. DESCRIPTION OF SPECIAL EMBODIMENT Referring to Figs. 1 and 2, an embodiment of the present invention will be explained. In Figs. 1 and 2, a wire dot printing head comprises a plurality of armatures 1, a first ring yoke 2, a second ring yoke 3, a first ring magnetic spacer 4, a second ring magnetic spacer 5, a third ring magnetic spacer 6, and a ring permanent magnet 7. A core frame 8 forms a magnetic flux circuit together with the above mentioned components. The leaf spring 9 has a plurality of arms or tongues extending toward the middle portion thereof, and is formed by puching out a sheet of steel in a rising sun. The armatures 1 are welded respectively to the ends of the arms of the leaf spring 9. The armatures 1 may be preferably formed of steel or silicon steel. The leaf spring 9 is supported in a cantilever beam by a third yoke 3, so that the one ends of the armatures 1 warp so as to tilt to one side the armatures 1. The armatures 1 are attracted to the end of the core frame 8 against the erastic force of the biasing leaf spring 9 by a magnetic attracting force which is generated by the magnet flux circuit. A residual sheet 10 prevents the wearing of the biasing leaf spring 9 and the end of a core frame 8. The residual sheet 10 may be preferably formed of a silicon steel. A demagnetizing coil 11 is would on the core frame 8. The coil 11 also generates a magnetic flux in the opposite direction to that of the parmanent magnet to release the attractive force to the armature 1. As shown in Fig. 3, wires 12 are fixedly connected to the ends of the armatures 1. When a selected one of the armatures 1 is released from the end of the core frame 8, the corresponding wire 12 dot-prints by impacting a printing medium by way of an ink ribbon. The wires 12, for example, are formed of a superalloy or a high-speed tool steel. A screw 13 is mounted to the second yoke 3, to adjust an impact force of the wire 12 to a printing medium at a release of the armature 1. The screw 13 is contacted to the biasing leaf spring 9 at its edge, and can control the impact force of the wire 12 by adjusting the depth of the screw 13. A dot printing head also includes a first intermediate guide 14, a second intermediate guide 15, and an edge guide 16. An oil penerated felt guide 17 is disposed between the intermediate guides 14 and 15. The felt guide 17 supplies an oil or a lubricant to the friction sliding portion between the wires 14 and 15 to prevent the wearing of the guided opening and the wire. A head frame 18 supports the edge guide 16. A chip 19 is arranged between the armatures 1 and the first intermediate guide 14 neariest to the armature 1 to prevent oil elevation or guide so as to be supportably surrounded with the armatures 1. The chip 19 may be preferably made of an oil absorbing material such as felt, and has a tapered side wall 20, as shown in Fig. 4. In dot printing operation, when the demagnetizing coil 11 is an unexciting state, the magnetic flux from the permanent magnet 7 passes through the first, second and third yokes 2, 3 and 6, and the first and second magnetic spacers 4 an 5, and the armature 1, and the core frame 8. The magnetic force attracts the armatures 1 to the core frame 8, with the leaf spring 9 biased. On the other hand, when the demagnetizing coil 11 is excited, the magnetic flux out of the coil 11 cancels the magnetic flux out of the permanent magnet 7, so that the leaf spring 9 is released from the biased condition. As a result, a wire 12 corresponding to a selected armature 1 is drived to print a dot print on a printing medium by way of an ink ribbon. In printing operation, an oil contained in the oil soaked felt guide 17 may flow into the back of the armature 1 due to a capillary action between the wires and a lowered oil viscosity caused by a temperature rise of the wires at a high duty printing operation. Since the chip 19 absorbs such an invaded oil, it can prevent on the way the oil from flowing into between the bias leaf spring 9 and the residual sheet 10. Hence the chip 19 is capable of preventing a wrong-dot printing operation due to a stick of the bias leaf spring 9 and the residual sheet 10 by oil. A second embodiment according to the present invention will be explained with reference to Fig. 5 and 6. Fig. 5 is a sectional view of a wire dot printing head showing the second embodiment according to the present invention. In Fig. 5, the same numerals represent the same elements as those shown in Fig 1. Fig. 6 is a perspective view of an oil elevation preventing chip used for the second embodiment of the present invention. In Fig. 5, the chip 21, for example, is in a rectangular form with a tapered opening 23 in a substantial oval form, and is made of an oil absorbing material such as felt. As seen in Fig. 6, the chip 2 is arranged between the first intermediate guide 14 and the armatures 1 and surrounds all the wires 12. The chip 21 also can provide the same advantages as that of the first embodiment. Namely, oil oozing along the wires toward the armature 1 is prevented from entering the space between the leaf spring 9 and the residual sheet 10 because the chip 21 traps the travelling oil on the way. Therefore it is possible to prevent the armature from being unmovable due to the adhesion of the leaf spring and the residual sheet with the oozed oil. INDUSTRIAL APPLICABILLITY As describe above, the wire printing head according to the present invention provides an improved printing operation during a long period of printing time. The wire printing head according to the present invention is applicable to printers for various electronic apparatus such as personal computers, word processors and bank terminals. It should note that the present invention is not be limited to the above embodiments and various modification may be possible on basis of the scope as defined in the claims.

Claims: Wire dot printing head comprising: armatures (1) each of which is securely connected to the tip of a printing wire (12) thereof; a core (8) mounted so as to face to the amatures (1); a biasing leaf spring (9) connected securely to the armatures (1) and supported in a cantilever state; a coil (11) wound on the core for generating a magnetic flux by an electrical activation, whereby a magnetic flux from the permanent magnet is suppressed to release the armature from the permanent magnet, and an oil supplying guide (17), characterized in that a chip (19,21) is placed between the armatures (1) and a wire guide (14) nearest to the armatures for preventing oil elevation; said chip having a side slope which meets substantially a trace of movement of the wire at a printing operation and being of an oil absorbing material; said chip prevents a stick between the armatures (1) and a residual sheet (10) disposed between said leaf spring (9) and said case (8). Wire dot printing head according to claim 1 characterized in that the side slope is provided on the outer side of the chip (19). Wire dot printing head according to claim 1 characterized in that the side slope is provided on the inner side of the chip (21). Wire dot printing head according to claim 2 or claim 3 characterized in that said chip is formed of felt. Wire dot printing head according to one of the claims 1 to 4, characterized in that the oil supplying guide (17) is positioned nearer to the tip side of the head than to the chip (19,21).

Inventors: ANDOU HIROKAZU OKI ELECTRIC IN, KOYAMA TATSUYA OKI ELECTRIC IN, TATSUKAMI MASAHIRO OKI ELECTRI, YAMADA TETSUHIRO OKI ELECTRIC, ANDOU, HIROKAZU OKI ELECTRIC INDUSTRY CO., LTD, KOYAMA, TATSUYA OKI ELECTRIC INDUSTRY CO., LTD, TATSUKAMI, MASAHIRO OKI ELECTRIC INDUSTRY CO., LTD, YAMADA, TETSUHIRO OKI ELECTRIC INDUSTRY CO., LTD.
Applicants: OKI ELECTRIC IND CO LTD, OKI ELECTRIC INDUSTRY COMPANY, LIMITED
Application year: 1989
Main classification: B41J2
IPC codes: B41J2