Printing head for use in a wire impact dot printer

Abstract: A printing head for use in a wire impact dot printer comprising a plurality of printing wires (11); which are movably mounted in a wire guide 27; movement-effecting means (1,2,3,9; 31) for effecting movement of the printing wires (11); a heat-radiating member (4;34) which is in heat-conductive contact with a housing (1;31) of the movement-effecting means (1,2,3,9; 31) for dissipating heat from the latter; and a carriage (20;50) on which the heat-radiating member (4,34) is in heat-conductive contact characterised in that the housing (1;31) is mounted in the heat-radiating member (4;34) and in close contact therewith by way of heat-conductive resin material (12;42); the wire guide (27) being supported by nose frame means (13,14; 43,44,46) which are provided with positioning means (7a,17,37,47) by means of which the nose frame means (13,14; 43,44,46) is positioned with respect to the carriage (20;50).

Description: The present invention relates to a printing head for use in a wire impact dot printer. A printing head for use in wire impact dot printers is known having a heat-radiating member provided with fins. The heat-radiating member is mounted around a core block assembly and is arranged to dissipate into the air heat generated by a coil of the core block assembly. However, such a construction has the disadvantage that if characters in high density are printed continuously and at high speed, the heat generated from the coil may exceed the heat dissipated by the heat-radiating member so that a continuous printing operation may be prevented. In order to overcome such a problem, the Japanese Laid-Open Utility Model Publication No. 63-68436 proposes a printing head which can transmit the heat generated by the coil to a carriage for the printing head and thus to guide shafts on which the carriage is mounted. That is, in the proposed printing head, a nose frame acting as heat-radiating member is mounted directly on the carriage to conduct heat to the carriage. In addition, both the nose frame and the core block are fixed to a reference surface of the nose frame, thus increasing the mountability and the heat-radiating effect due to heat conduction. However, such a construction has the disadvantages that there is an unavoidable gap between the carriage and the core block which does not provide sufficient heat conduction, and that the impact force against the nose frame during printing which acts directly on the nose frame or other structural parts may shift the parts relatively to each other. According to the present invention, there is therefore provided a printing head for use in a wire impact dot printer comprising a plurality of printing wires which are movably mounted in a wire guide; movement-effecting means for effecting movement of the printing wires; a heat-radiating member which is in heat-conductive contact with a housing of the movement-effecting means for dissipating heat from the latter; and a carriage on which the heat-radiating member is in heat-conductive contact characterised in that the housing is mounted in the heat-radiating member and in close contact therewith by way of heat-conductive resin material; the wire guide being supported by nose frame means which are provided with positioning means by means of which the nose frame means is positioned with respect to the carriage. Preferably the nose frame means is positioned vertically by engagement between surfaces of the heat-radiating member and the carriage respectively, the nose frame means being positioned horizontally on the carriage by locating means. Such a construction ensures that the heat from the housing is effectively transmitted to the carriage, and that the wire guide, which is supported by the nose frame means, is positioned accurately in the vertical direction with respect to the printing wires. Preferably, either the nose frame means or the carriage is provided with at least one dowel which is engaged in an opening in the other member. In one embodiment, the heat radiating member has at least one frame mounting portion which extends into a recessed portion of the nose frame means so as to position the latter with respect to the heat-radiating member. In another embodiment, the nose frame means has at least one step portion which is mounted on a frame mounting portion of the heat-radiating member. The heat-radiating member is preferably substantially cylindrical in shape. The heat-conductive resin material preferably comprises a silicone resin. A resin reservoir may be provided for making up a loss of the said heat-conductive resin material. Preferably, the said housing comprises a core block which houses a plurality of cores on each of which is mounted a printing wire drive coil bobbin. Thus in its preferred form, the present invention provides a printing head for use in a wire impact type dot printer wherein the heat from a core block of the printing head as well as an impact force acting against a nose frame of the printing head can be effectively transmitted to a carriage. In the preferred form of the present invention, the heat-radiating member is fixed closely on a mounting reference surface of the carriage and a nose frame is mounted in position with reference to a mounting portion of the heat-radiating member and a positioning portion of the carriage, whereby each of these parts is positioned firmly and accurately. An impact force acting against the nose frame on printing is thus transmitted to the carriage. Furthermore, the heat produced by the coil is dissipated to the heat-radiating member via the heat-conductive resin and also the heat can be effectively transmitted partially or completely to the carriage and the guide shafts on which the carriage is mounted via the mounting portion which closely contacts the mounting reference surface of the carriage. The invention is illustrated, merely by way of example, in the accompanying drawings, in which:- Figure 1 is a side view, partly in cross-section showing a first embodiment of a printing head according to the present invention; Figure 2 is a front view of the said first embodiment; Figure 3 is a side view showing a second embodiment of a printing head according to the present invention; and Figure 4 is a front view of the said second embodiment. In Figures 1 and 2 there is shown a first embodiment of a printing head according to the present invention which comprises a housing having a core block 1 of a movement-effecting means for effecting movement of a plurality of printing wires 11. The core block 1 thus acts as a heat source and is formed in a cup shape. A plurality of cores 2, on each of which is mounted a printing wire drive coil bobbin 3, are arranged on the inside lower surface of the core block 1 and in a circular form. A heat-radiating member 4 is in heat-conductive contact with the core block 1 for dissipating heat from the latter. The heat-radiating member 4 thus acts as a heat sink and has heat radiating fins on the upper surface thereof, the member 4 having a cylindrical form. The core block 1 is inserted hermetically inside the heat-radiating member 4 together with a yoke 8, a plurality of printing levers 9 (only one shown), and a pressure plate 10. The core block 1 is hermetically sealed within the heat-radiating member 4 by way of heat-conductive resin material 12 such as a silicone resin coated around the core block 1. Each printing lever 9 is arranged to move a printing wire 11. Thus outwardly projecting mounting portions 6 are formed on the lower end surfaces of the heat-radiating member 4 and are mounted closely on and in heat-conductive contact with mounting reference portions on surfaces 21 of a carriage 20. Two nose frame mounting portions 7 of the heat-radiating member 4 are integrally formed with the mounting portions 6 so as to extend towards the open end of the heat-radiating member 4. A nose frame 13 supports a wire guide holder 26. The wire guide holder 26 is also supported by a wire guide 27, the latter movably supporting the printing wires 11. The nose frame 13 is mounted in contact with the lower surfaces 7a of the nose frame mounting portions 7, the nose frame 13 having an integral back plate 14. Both the mounting portions 6 and the carriage 20 are subject to an accurate cutting process so that there is close contact between the mounting reference surfaces 21 and the mounting portions 6. The cutting can improve the heat conduction ten to twenty times by comparison with a surface of an un-machined diecast member. The back plate 14 is fixed to the open end of the heat radiating member 4. The back plate 14 has two recessed portions 15 in which are inserted the nose frame mounting portions 7 of the heat-radiating member 4, the recesses 15 being formed at the lower ends of the back plate 14. The back plate 14 has protrusions 16 which protrude downwards into each recessed portion 15 so as to face the lower surface of the latter. Each protrusion 16 is arranged to cause the respective lower surface 7a of the nose frame mounting portion 7 to make close contact with an upwardly facing surface 15a of the respective recessed portion 15. This allows the nose frame 13, 14 to be mounted firmly and accurately to the heat-radiating member 4 with respect to the lower surface 7a which thus acts as a reference. The upwardly facing surfaces 15a are subjected to an accurate machining. The back plate 14 is provided with positioning dowels 17 which are formed so as to protrude from the lower surface of the back plate 14. The nose frame 13 is positioned two-dimensionally by engaging the dowels 17 in positioning openings 23 formed in a surface of the carriage 20. Screws 24 are provided for fastening the heat-radiating member 4 to the mounting reference surfaces 21 of the carriage 20. The carriage 20 is slidably mounted on guide shafts 25. In the construction described above, the core block 1, which is assembled integrally with the yoke 8, the printing levers 9 and the pressure plate 10, is inserted inside the cylindrical heat-radiating member 4 via the heat-conductive resin material 12 coated on the surface of the core block 1. The nose frame 13 is connected to the open end of the heat-radiating member 4 by inserting the nose frame mounting portions 7 protruding from the lower end of the heat-radiating member 4 into the recessed portions 15 formed at the lower ends of the back plate 14 of the nose frame 13. The core block assembly which has been so assembled in the reference inner surface of the heat-radiating member 4 can be mounted in a proper vertical position with respect to the nose frame 13 assembled on the reference lower surfaces 7a of the nose frame mounting portions 7. Furthermore, the heat-radiating member 4 is fastened to the mounting reference surfaces 21 of the carriage 20 with the screws 24 by engaging the positioning dowels 17 at the lower end of the back plate 14 in the positioning openings 23 of the carriage 20. The positioning opening 23 shown on the right hand side of Figure 2 constitutes a track hole to enable the respective dowel 17 to be moved to the right or left of Figure 2. Hence the core block assembly can be properly positioned two-dimensionally with respect to the nose frame 13. In such a construction, heat generated from the coils can be transmitted to the heat-radiating member 4 via the core block 1 and the heat-conductive resin material 12. A part of the heat is dissipated into the air through the heat-radiating member 4 while the remaining part thereof is transmitted effectively from the mounting portions 6 which are in close contact with the mounting reference surfaces 21 of the carriage 20 to the guide shafts 25 by way of the carriage 20, whereby overheating of the printing head can be avoided. In Figures 3 and 4, which show a second embodiment of the present invention, a heat-radiating member 34 is mounted on a mounting reference surface 51 on a carriage 50. A nose frame 43 is integral with or secured to a back plate 44 which is mounted on nose frame mounting step portions 37 of the heat-radiating member 34. The nose frame 43 is positioned by dowels 54 on the carriage 50. The construction can provide accurate positioning and more effective heat-radiation. That is, the heat-radiating member 34, which hermetically houses a core block 31 via heat conductive resin material 42, has mounting portions 36 on the lower end thereof for mounting the heat-radiating member 34 on the carriage 50. Mounting portions 46 which are to be positioned on the carriage 50 are formed at the ends of the nose frame 43 and have positioning openings 47 respectively for receiving the dowels 54. Step portions 45 are formed to face downwards on opposite sides of the back plate 44 and are mounted on the nose frame mounting step portions 37. The nose frame mounting step portions 37 are machined so that the measurement between the portions 37 and the mounting portions 36 is accurate. First, the heat-radiating member 34, which is fastened integrally to the nose frame 43 by screws 48, is mounted by way of the back plate 44 on the nose frame mounting step portions 37. The nose frame mounting step portions 37 are accurately machined with respect to the mounting portions 36. Therefore the nose frame 43 is fixed accurately in the vertical direction with respect to the mounting portions 36. The step portions 45 which are provided on opposite sides of the back plate 44 of the nose frame 43 are brought in contact with the mounting step poertions 37 of the heat-radiating member 34. Therefore the nose frame 43 is accurately positioned with respect to the mounting reference surface 51 in the vertical direction. Next, the dowels 54 on the carriage 50 are inserted into the positioning openings 47 which are formed in the mounting portions 46 of the nose frame 43. The heat-radiating member 34 is in close contact with the mounting reference surface 51 on the carriage 50 at the lower surfaces of the mounting portions 36, the latter being fastened to the carriage 50 by the screws 55. As in the first embodiment, an accurate machining is performed on both the lower surfaces of the mounting portions 36 and on the mounting reference surface 51. Therefore, the nose frame 43 is supported on the carriage 50 accurately through the nose frame mounting step portions 37 in the vertical direction, and supported by the dowels 54 accurately in the horizontal direction. In this embodiment, because an impact produced as a result of a printing operation can be vertically transmitted to and then along the carriage 50, a moment does not occur at the mounting portions 36, so that long term use does not loosen the screws 55. Also, in this embodiment, a resin reservoir 35 in a ring shape is formed at the open end of the heat-radiating member 34. When the core block 31 is inserted into the open end of the heat-radiating member 34, resin from the reservoir 35 makes up for any heat conductive resin material 42 which has overflowed from the said open end. As a result, parallelism between the heat-radiating member 34 and the core block 31 can be effected without difficulty at the time of assembly. In the embodiments of the present invention described above, mounting portions 6, 36 are formed at the lower end of the heat-radiating member 4, 34 and are in close contact with the mounting reference surfaces 21, 51 of the carriage 20, 50. A positioning and fixing portion 17, 47 is formed on the nose frame 13, 14 or 43 and is fixed with respect to the mounting portions 6, 36 of the heat-radiating member 4, 34 and the positioning portions 23, 54 on the carriage 20, 50. The heat-radiating member 4, 34 is fixed closely on the mounting reference surfaces 21, 51 of the carriage 20, 50, and the nose frame 13, 14 or 43 is fixed with reference to the mounting portions 6, 36 of the heat-radiating member 4, 34 and to the positioning portions 23, 54 of the carriage 20, 50. These parts can be positioned and fixed accurately. Both the core block 1, 31 in contact with the heat-radiating member 4, 34 and the nose frame 13, 14 or 43 can be positioned accurately with respect to the mounting reference surfaces 21, 51 of the carriage 20, 50. Furthermore, the impact force against the nose frame 13, 14 or 43 which occurs during a printing operation can be effectively transmitted to the carriage 20, 50, and the heat produced by the coil of the core block 1, 31 can be transmitted effectively to the heat-radiating member 4, 34 via the heat-conductive resin material 12, 42. A part of or the whole of the heat can be transmitted effectively to the carriage 20, 50 and to the guide shafts via the mounting portions 6, 36 which are in close contact with the mounting reference surfaces 21, 51 of the carriage 20, 50. As a result, printing can be performed without overheating the printing head on heavy load.

Claims: A printing head for use in a wire impact dot printer comprising a plurality of printing wires (11) which are movably mounted in a wire guide (27); movement-effecting means (1,2,3,9; 31) for effecting movement of the printing wires (11); a heat-radiating member (4;34) which is in heat-conductive contact with a housing (1;31) of the movement-effecting means (1,2,3,9; 31) for dissipating heat from the latter; and a carriage (20;50) on which the heat-radiating member (4;34) is in heat-conductive contact characterised in that the housing (1;31) is mounted in the heat-radiating member (4;34) and in close contact therewith by way of heat-conductive resin material (12;42); the wire guide (27) being supported by nose frame means (13,14; 43,44,46) which are provided with positioning means (7a,17,37,47) by means of which the nose frame means (13,14; 43,44,46) is positioned with respect to the carriage (20;50). A printing head as claimed in claim 1 characterised in that the nose frame means (13,14; 43,44,46) is positioned vertically by engagement between surfaces (7a,37; 21,51) of the heat-radiating member (4;34) and the carriage (20,50) respectively, the nose frame means (13,14; 43,44,46) being positioned horizontally on the carriage (20,50) by locating means (17,23; 54,47). A printing head as claimed in claim 1 or 2 characterised in that either the nose frame means (13,14; 43,44,46) or the carriage (20;50) is provided with at least one dowel (17;54) which is engaged in an opening (23;47) in the other member. A printing head as claimed in any preceding claim characterised in that the heat-radiating member (4) has at least one frame mounting portion (7) which extends into a recessed portion (15) of the nose frame means (13;14) so as to position the latter with respect to the heat-radiating member (4). A printing head as claimed in any of claims 1-3 characterised in that the nose frame means (43,44,46) has at least one step portion (45) which is mounted on a frame mounting portion (37) of the heat-radiating member (34). A printing head as claimed in any preceding claim characterised in that the heat-radiating member (4;34) is substantially cylindrical in shape. A printing head as claimed in any preceding claim characterised in that the heat-conductive resin material comprises a silicone resin. A printing head as claimed in any preceding claim characterised in that a resin reservoir is provided for making up a loss of the said heat-conductive resin material. A printing head as claimed in any preceding claim characterised in that the said housing (1;31) comprises a core block which houses a plurality of cores (2) on each of which is mounted a printing wire drive coil bobbin (3). A printing head suitable for a wire impact dot printer comprising a heat radiating member; a nose frame; a core block which is inserted closely inside said heat radiating member via a heat conductive resin material; a mounting portion formed at a portion of said heat radiating member and positioned closely and fixedly on a mounting reference surface of a carriage; and a positioning and fixing portion formed on a portion of said nose frame and for positioning in reference with said mounting portion of said heat radiating member and a positioning portion of said carriage.

Inventors: YAMAMOTO KAZUHIKO, YAMAMOTO, KAZUHIKO
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1991
Main classification: B41J29
IPC codes: B41J29