Printer head for serial dot printer

• US 4,377,348 A
• Filed: 03/16/1981
• Issued: 03/22/1983
• Est. Priority Date: 03/27/1980
• Status: Expired due to Fees

• Current Assignee: Nippon Telegraph and Telephone Corporation
• Original Assignee: OKI Electric Industry Company Limited
• Inventors: Kikuchi, Hiroshi, Isobe, Minoru, Teshima, Minoru, Kodama, Tadasi
• Primary Examiner(s): Sewell, Paul T.
• Application Number:
  US06/244,077
• Time in Patent Office: 736 Days
• Field of Search: 400/124, 400/691, 400/693, 101/93.05, 335/217, 75/123 R, 75/170
• US Class Current: 400/134
• CPC Class Codes: B41J 2/28 of spring charge type, i.e. with mechanical power under electro-magnetic control
• CPC Class Codes: H01F 7/08 with armatures

Abstract

A serial printer head is provided which comprises a sandwich structure (1,3,5) of a first circular yoke plate (1), a cylindrical magnet (3) and a ring shaped second yoke plate (5); a plurality of electromagnets (2,4) positioned on the first yoke plate (1) at predetermined angle intervals; an armature-print-needle assembly (7,8,9,10) having a circular resilient spring (7), a plurality of armatures (8) and a plurality of print needles (9) placed on the sandwich structure (1,3,5) so that the sandwich structure (1,3,5), electromagnets (2,4) and the armatures (8) provide first a substantially closed magnetic path; and an adjusting yoke (12) attached to the sandwich structure (1,3,5). The adjusting yoke (12) has the magnetic characteristics that the magnetic reluctance increases as the temperature increases. Although the flux generated by the permanent magnet (3) is changed due to the change of the temperature, that flux change is compensated for by the presence of the adjusting yoke (12).

Claims

1. In a printer head for a mosaic printing comprising of a first circular yoke plate;

a cylindrical permanent magnet magnetized in an axial direction positioned on said first yoke plate;

the permanent magnet having the characteristics that the flux generated by the permanent magnet decreases as the temperature increases;

a ring shaped second yoke plate positioned on said permanent magnet;

a plurality of electromagnets each having a column core and a coil wound on the column core, the electromagnets being positioned in a circle on said first yoke plate with predetermined angle intervals therebetween;

an armature-print-needle assembly including a disk shaped circular resilient spring having a plurality of inwardly extending projections, a plurality of armatures each fixed on a corresponding projection of said spring and a plurality of print needles each fixed to a corresponding armature so that the print needle extends perpendicular to the plane of the spring;

a guide frame covering said armature-print-needle assembly said guide frame having a thin linear slit for passing therethrough the tops of said print needles;

wherein a first substantially closed magnetic path is formed from said permanent magnet through said second yoke plate, said armatures, said electromagnets and said first yoke plate to said permanent magnet such that an armature together with the corresponding print needle are attracted to the corresponding electromagnet by the magnetic flux circulating in said first magnetic path and said armature and the corresponding print needle are released by the force of the spring upon application of an electric current to the coil of the corresponding electromagnet to print a dot;

the improvment wherein a cylindrical adjusting yoke means is coupled to said first yoke plate, said permanent magnet and said second yoke plate for forming a second closed magnetic path from said permanent magnet through the second yoke plate, the adjusting yoke means and the first yoke plate to the permanent magnet, said adjusting yoke means having a magnetic characteristic wherein the magnetic reluctance of said adjusting yoke means increases as the temperature of said adjusting yoke means increases.

2. A printer head according to claim 1, wherein said adjusting yoke means surrounds the outer edge of said first yoke plate, said permanent magnet and said second yoke plate.

3. A printer head according to claim 1, wherein said adjusting yoke means is positioned on the first yoke plate and within the inner wall of said permanent magnet and said second yoke plate.

4. A printer head according to claim 1, wherein the the top of said adjusting yoke means is at approximately the same level as that of the column cores of said electromagnets.

5. A printer head according to claim 1, wherein said permanent magnet is made of ferrite material.

6. A printer head according to claim 1, wherein said adjusting yoke means is made of an Fe-Ni-Cr alloy.