Wire dot print head

Details Wire dot print head Wire dot print head

1990-12-12

1992-11-24

Burr, Edgar S.

Typewriting machines

Typing by other than type-face or type-die

Character formation by impact

101 9305, B41J 2235

Patent

active

051658089

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a wire dot print head for a printer which drives a plurality of printing wires selectively causing the printing wires to impinge through an ink ribbon against a recording sheet for printing.


BACKGROUND ART

A printer incorporating a conventional wire dot print head has been used widely due to its advantages, which include a high option among various recording media and the capability of using it with copying paper as its recording medium. The wire dot print head drives the wires by the magnetic attraction of permanent magnets or electromagnets.
Recently, the so-called spring-charged wire dot print head has been employed in most printers due to its high response speed.
The spring-charged wire dot print head is provided with armatures, each fixedly holding a printing wire and being supported by a biasing flat spring adapted for swinging motion. The armature is attracted against the resilience of the biasing flat spring to a core by the magnetic attraction of a permanent magnet. In printing, a coil wound around the core is energized to release the armature from the permanent magnet by establishing in the coil a magnetic flux of a polarity reverse to that of the permanent magnet.
In the spring-charged wire dot print head, it is possible that leakage flux among a magnetic flux produced by the electromagnet for cancelling the magnetic flux produced by the permanent magnet causes magnetic interference with, the magnetic flux in the adjacent armature and core, thereby causing change in the magnetic flux in the adjacent armature and core. The effect of magnetic interference on the change of magnetic flux increases with the number of printing wires simultaneously driven for printing, and each coil requires an excitation current greater than that necessary for releasing the corresponding armature from the core when the printing wire is driven individually, thereby increasing the power consumption and rate of heat generation for the printing head.
Since variation in the exciting current affects the action of the released armature, the duration of the supply of current to the coil must be controlled according to the number of printing wires to be driven simultaneously for printing.
The power consumption and heat generation of the spring-charged wire dot print head are further increased by magnetic interference particularly when the spring-charged wire dot print head is miniaturized, formed in a compact construction and operated at a high printing speed.
Many, improvements have been developed to solve such problems. Japanese Patent Laid-open Publication No. 58-96568 discloses a wire dot print head which attempt to account for the magnetic interference by magnetizing the adjacent cores respectively in opposite polarities. This known wire dot print head is shown in FIGS. 1 to 3. FIG. 1 is a sectional view of this known wire dot print head, FIG. 2 is a sectional view taken along the line A--A in FIG. 1, and FIG. 3 is a perspective view of an essential portion of the wire dot print head of FIG. 1.
Referring to FIGS. 1 to 3, a circular bottom frame 11 is formed of a nonmagnetic material, such as aluminum. A plurality of cores 12 having a shape substantially resembling the letter L are placed on the bottom frame 11 in a radial arrangement with their upright portions adjacent the center of the print head. Coils 13 are wound around the upright portions of the cores 12 to form electromagnets 14. Permanent magnets 15 are placed respectively on the rear ends of the cores 12, namely, portions of the cores 12 near the circumference of the print head. The respective polarities of the permanent magnets 15 on the adjacent cores 12 are opposite to each other.
Side yokes 16 are placed respectively on the permanent magnets 15. Flat springs 17 are disposed with their free ends positioned opposite to the corresponding electromagnets 14. Armatures 18 are fastened respectively to the free ends of the flat springs 17. Upper yokes 19 are placed on the flat springs 17. A top frame 20 formed of

REFERENCES:
patent: 4995744 (1991-02-01), Goldowsky et al.

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