Impact dot print head and a manufacturing method thereof

Abstract: An impact dot print head and its manufacturing method are disclosed. The impact dot print head consists of: printing wires (9) for forming dot patterns on a printing medium (16); a front end guide (12) having holes for guiding the wire tips; and a nose (13) fixed with the front end guide and having its front end surface confronting with the printing medium. The manufacturing method involves the steps of; holding the nose and the front end guide by a jig so that front end surfaces of the nose and of the front end guide are substantially flush with each other; deforming protrusions thereof; and fixing the nose to the front end guide.

Description: This invention relates to an impact dot print head for an impact printer and its manufacturing method. Impact dot print heads usually have a nose at the (front) side facing a printing medium. Guides are disposed inside the nose for guiding printing wires. In such case when, as illustrated in Fig. 9, a front end guide surface 102a, facing to the printing medium 106, of a front and guide 102 is recessionary from the nose end surface 101a of the nose 101 the following problem may occur. When a printing wire 105 is caught by a stepped portion 106a of the printing medium 106, since the projecting length L of the printing wire 105 from the front end guide surface 102a is large, large stress is applied to the printing wire root 105a, with the result that the printing wire 105 tends to be damaged or broken. On the other hand, with a front end guide surface (102a) projecting from the nose surface 101a and an ink ribbon 107 being sandwiched between the front end guide 102 and a ribbon mask 108, the following further problems arise. The running property of the ink ribbon 107 declines. A deterioration in feeding of the ink ribbon is caused. Abrasion of the front end guide 102 is caused due to friction with the ink ribbon 107. It is therefore desirable that the nose surface 101a be flush with the front end guide surface 102a. Fig. 10 shows one example of a conventional impact dot print head. In this example, the front end guide 202 and middle guides 203 slidably hold the printing wire 201 (only one printing wire is shown for explanation, usually there are plural printing wires). The guides 202, 203 are in turn retained by a nose guide 204. To make a surface 202a, on the side of a printing medium 207, of the front end guide 202 flush with a surface 205b of the nose 205 on the same side, a spacer 206 of a corresponding thickness is interposed between a positioning surface 205a of the nose 205 and a positioning surface 204a of the nose guide 204. Fig. 11 shows another conventional example. After measuring the thickness t of the front end guide 302, the front end guide is bonded to the nose 301 having a recess 301a equivalent to the thickness t of the front end guide, whereby those surfaces are flush with each other. Another thinkable method is that, after bonding the front end guide to the nose, machining-cut is effected to make the surfaces flush with each other. The prior art impact dot print head depicted in Fig. 10, however, presents the following problems. It takes much time to measure the distance D1 from the nose surface 205b to the surface 205a and the distance D2 from the front end guide surface 202a to the nose guide surface 204a, discern the spacer 206, select the suitable spacer 206 and insert this spacer. This renders a mass production difficult and very costly. There are also problems inherent in the method shown in Fig. 11. It requires a good deal of time to measure and select the thickness t of the front end guide 302 and also the depth d of the recess 301a of the nose 301, in which the front and guide 302 is inserted. The mass-production is hard to attain as well as being quite costly. The method of making the nose and the front end guide flush with each other by machining causes the problem that wire guide holes are deformed by machining. A mass-production is not easily attained and highly costly. An impact dot print head according to the prior art portion of claim 1 is disclosed in the document WO84/03255. In this prior art the front end guide is fixed to the nose by means of ears or tabs formed on the front end guide and provided for latching the latter in suitable corresponding insets or grooves in the sides of the front part of the nose. Thus, in this prior art one or both of the parts to be fixed relative to each is elastically deformed. The invention is intended to obviate the foregoing problems inherent in the prior art, and its primary object is to provide an impact dot print head having a nose surface flush with a front end guide surface and capable of being manufactured by mass-production at low cost. This object is achieved with an impact dot print head as claimed in claim 1 and the manufacturing method as claimed in claim 2. In this impact dot print head, the front end guide includes a plurality of protrusions formed at both ends of the front end guide. The protrusions are softened and fixedly charged in a hole or groove formed in the nose. Alternatively or additionally the nose includes a plurality of protrusions. The protrusions are softened and fixedly charged in a hole or groove formed in the end portion of the front end guide. Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawings which illustrate only specific embodiments and in which: Fig. 1 is a sectional view illustrating a whole impact dot print head in a first embodiment of the present invention; Fig. 2 is an exploded perspective view illustrating a nose, a front end guide, a guide holder and middle guides in the first embodiment; Fig. 3 is a diagram depicting the front end guide in the first embodiment; Fig. 4 is a diagram depicting the nose in the first embodiment; Fig. 5 is a diagram showing a manufacturing method in the first embodiment; Fig. 6 is a diagram illustrating charging states before and after fusing a protrusion 12a of the front end guide in the first embodiment; Fig. 7 is a diagram showing states before and after fusing a protrusion 12b of the front end guide in the first embodiment; Fig. 8 is a diagram depicting the nose and the front end guide in another embodiment of the invention; Fig. 9 is a diagram of assistance in explaining a positional relation between the nose and the front end guide; Fig. 10 is a sectional view illustrating a conventional impact dot print head; and Fig. 11 is a sectional view depicting another conventional impact dot print head. Figs. 1 to 7 illustrate a first embodiment of the invention. The entire configuration and operation of the first embodiment will be explained with reference to Figs. 1 and 2. An impact dot print head 19 incorporates a driving unit composed of a front driving subunit 18a and a rear driving subunit 18b both having the same configuration. Therefore, only the front driving subunit 18a will be explained. A core block 3 includes a plurality of cores 2 of a magnetic material (one core is illustrated in the Figure) into each of which a driving coil 1 is inserted. These cores 2 are disposed along the periphery of the print head. To the core block 3 a heat radiation member 4 is bonded with a heat-transferable resin. The core block 3 is potted with a heat-transferable resin 5 as potting compound. Each of plural movable armatures 6 formed of a magnetic material is axially supported on a fulcrum shaft 7 so as to confront with a respective one of the cores 2. The armature 6 is urged into a standby state by a return spring 8. A printing wire 9 is fixed to the tip of the armature 6. The printing wire 9 is slidably retained by a guide hole bored in a guide holder 10, a plurality of middle guides 11 and a front end guide 12. The guide holder 10 is joined to the nose 13 by inserting a bottom protrusion 10d into a positioning hole 13g of the aluminum die casting nose 13 (Fig. 2). The guide holder 10 is also connected to a spring holder 14 formed with a groove for positioning the core block 3 and holding the return springs 8. The plurality of middle guides 11 are held in respective guide grooves 10b of the guide holder 10. A front end protrusion 10c of the guide holder is inserted into a positioning hole 12c of the front end guide 12, thus positioning the front end guide 12. With this arrangement, the guide hole 10a, the middle guide 11 and the front end guide 12 are positioned at a high accuracy. This provides a good sliding property of the printing wires 9. The nose 13 is joined to the heat radiation member 4 and includes a mounting member for mounting to an unillustrated carriage. When the driving coil 1 is energized at a predetermined level, the armature 6 is attracted, while the printing wire 9 is pushed out of the front end guide. The printing wire 9 impinges, through an ink ribbon 15, on a printing medium 16 held against a platen 17, thus forming a dot. After effecting the print and deenergizing the driving coil 1, the printing wire 9 is retracted by the return spring 8 and is thereby returned to the standby position. Next, the configuration of the front end guide 12 will be described referring to Fig. 3. The front end guide 12 is formed of a thermoplastic. The guide 12 includes two kinds of protrusions, i.e., a protrusion 12a extending in an inserting direction A and two protrusions 12b extending in a direction opposite to the inserting direction A. The protrusions 12a and 12b are parallel to the front end surface 12e of the front end guide 12. A surface 12g for abutment of and pushing the guide 12 by a jig during a welding process is formed on the opposite side of the root of the protrusion 12a. The top surface of the guide 12 in the inserting direction A forms a positioning reference surface 12h . A plurality of guide holes 12i for the printing wires are positioned on the basis of the reference surface 12h. A holding member 12j for the protrusions 12b has a hole 12k for reducing the rigidity of the holding member. A spring property is thus given to the holding member 12j. Adjacent to the inner side of each of the protrusions 12b a respective wall 12l is formed on the holding member 12j. The upper and lower portions 12d of the front end surface 12e are tapered. The side surfaces are provided with minute protrusions or ridges 12f. Next, the configuration of the nose 13 will be described with reference to Fig. 4. The front end surface 13d of the nose 13 is formed with a U-shaped groove 13c in which the front end guide 12 is to be inserted. The top end surface 13i of this groove 13c in the direction A is formed substantially complementary to the reference surface 12h of the front end guide 12. In the surface 13i a positioning hole 13a adjoined by a counterbore 13j of a larger diameter than the hole 13a in the inserting direction A is provided in parallel with the front end surface 13d. In its bottom the nose 13 has U-shaped grooves 13b each having a respective larger counterbore 13k towards the bottom, a bottom surface 13l of a respective ridge overlying each of said grooves 13b. The length D from the surface 13i to the inner surface of the bottom surface 13l having the U-shaped grooves 13b is slightly longer than the length D' from the reference surface 12g to the inner surface of the holding member 12j of the front end guide 12. In this embodiment, D is longer than D' by 0-0,5 mm including a tolerance. Receiving members 13e are provided more internally than the fixing position of the front end guide 12. With reference to Fig. 5 the following is an explanation of a manufacturing method for assembling and securing to each other the nose 13 and the front end guide 12 in a manner to make the front end surface 12e of the front end guide 12 flush with the front end surface 13d of the nose 13. The front end guide 12 is inserted into the U-shaped groove 13c of the nose 13 from the bottom to the top, namely in the direction of arrow A. At this moment, the minute protrusions 12f of the front end guide 12 are crushed, and it follows that the guide 12 can be set in the nose with no backlash. The nose 13 is pushed against a positioning plate 21 by use of an unillustrated jig. The front end guide 12 is also pushed against the positioning plate 21 by a presser jig 20. The front end surface 13d of the nose 13 and the front end surface 12e of the front end guide 12 are thus positioned. The presser jig 20 further pushes upward the surface 12g of the front end guide 12, whereby the front end guide reference surface 12h closely contacts the surface 13i of the nose 13 and the bottom surface 12m of the protrusions 12b are brought into contact with the respective bottom surface 13l mentioned earlier. The distance D between the surface 13i of the nose 13 and the bottom surface 13l of the groove 13b is longer than the distance D' between the reference plane 12h of the end guide 12 and the plane 13m of the projection 12b. Therefore, the plane 12m is brought into contact with the bottom 13l first. Further, the jig 20 presses up the end guide 12 so that the reference surface 12h is brought in contact with the plane 13i. The holding member 12j of the end guide 12 is bent thereby to absorb the distance difference between D and D'. In this state, the protrusion 12a of the front end guide 12 now positioned in hole 13a and counterbore 13j undergoes a pressure by a horn 22 for imparting ultrasonic vibrations, with the result that the protrusion 12a is fused. The fused substance is charged in the counterbore 13j of the hole 13a of the nose 13 and then fixed thereto. Figs. 6(a) and 6(b) illustrate charging states before and after fusing the protrusion 12a. At that time, the presser jig 20 exerts the necessary counter pressure on the surface 12g. For this reason, fusing is surely performed, and no deformation is caused in other portions. Next, the two pieces of protrusions 12b of the front end guide 12 are similarly fused while being pressurized by a horn 23 for causing ultrasonic vibrations. The bottom surface 12m is pressed against the bottom surface 13l due to the elastic nature of the holding members 12j so that there is no space and displacement between the bottoms 12m and 13l. The fused substance is charged in the counterbores 13k of the groove 13b of the nose 13 and then fixed thereto. At this time, charging can be surely effected without any outflow from the counterbores 13k because of the existence of the walls 12l of the front end guide 12. Fig. 7 shows charging states before and after fusing the protrusions 12b. Note that the front end guide 12 varies in dimensions when returning to a normal temperature after having undergone a thermal expansion and a thermal deformation during the fusing process. Therefore, a step S is provided between a portion 21a of the positioning plate 21 against which the front end surface 13d of the nose 13 is pressed and a portion 21b against which the front end surface 12e of the guide 12 is pressed. The same plane is obtained after effecting the fixation. In this embodiment, the step S is set in a range from 0 to 0,1 mm. Gaps t are formed between the hole 13a of the nose and the protrusion 12a of the front end guide 12 and between the grooves 13b of the nose 13 and the protrusions 12b of the front end guide 12. With these gaps, the front end guide is able to make a small amount of movement before being fixed. Hence, the front end guide 12 can be positioned without being restricted by the positioning hole 13a or the grooves 13b. The step between the front end surface 13d of the nose 13 and the front end surface 12e of the front end guide 12 can be set to ± 0,03 mm by the method discussed above in this embodiment. A high accuracy is stably attainable. When setting the step to ± 0,03 mm, the rate at which printing wires are broken in the case of being caught by a stepped portion of the printing medium is decreased by a factor of 1/10 compared to the prior art. There is almost no possibility that the wires are broken in the practical use. Even when the front end surface 12e of the front end guide 12 projects from the nose front end surface 13d, the ribbon can be smoothly set and removed owing to the tapered surfaces portions 12d. The fusing time is set from 0,1 s to 2 s in this embodiment. The pressure force is set from 0,5 kgf (5 N) to 10 kgf (100 N), whereby manufacturing can be stably done in a remarkably short time. According to the present invention, the necessity for dimensional measurement and selection is absolutely eliminated. Hence, a good deal of products can be manufactured in a short period of time. An excellent mass-productivity is obtained. The costs can be reduced. Turning to Fig. 8, there is shown another embodiment of the invention. A nose 50 is composed of a thermoplastic. The nose 50 has a hole 50b having a counterbore 50a in an inserting direction A in parallel with a front end surface 50d. The nose 50 has two pieces of protrusions 50c formed opposite thereto. A plastic front end guide 51 has a protrusion 51a in the inserting direction A in parallel with a front end surface 51d. The front end guide 51 also has holes 51b having counterbores 51c formed opposite thereto. The manufacturing method for assembling and securing to each other the nose 50 and the front end guide 51 in a manner to make the front end surface 50d of the nose 50 flush with the front end guide surface 51d is the same as with the first embodiment. The protrusions 50c of the nose 50 are fused and charged in the counterbores 51c of the front end guide 51. The protrusion 51a of the front end guide 51 is fused and charged in the counterbore 50a of the nose 50. The fixation is performed so as to have the said front end surfaces be flush with each other. In this embodiment also, the mass-production is, as in the first embodiment, attainable at low costs to provide the same plane with the high accuracy. Note that a working example based on fusion by means of ultrasonic waves has been given herein, but substantially the same fixation can be effected by a thermocompression bonding method.

Claims: An impact dot print head comprising: a plurality of printing wires (9) for forming desired dot patterns on a printing medium (16); a front end guide (12; 51) formed with holes (12i) for slidably guiding tips of said printing wires; and a nose (13; 50) to which said front end guide is fixed and which has its front end surface (13d; 50d) confronting with said printing medium, wherein said front end guide (12; 51) or said nose (13; 50) is composed of a thermoplastic synthetic resin, and said front end guide and said nose are fixed, by deforming a part of said front end guide or said nose, in such position that the front end surfaces (12e, 13d; 51d, 50d) of said front end guide and of said nose are flush with each other, characterized in that either said front end guide (12) includes a plurality of protrusions (12a, 12b) formed at both ends of said front end guide, or said nose (50) includes a pluraltiy of protrusions (50c), said protrusions are softened and fixedly charged in a hole (13a, 13j; 51b, 51c) or groove (13b, 13k) formed in said nose (13) or the end portion of said front end guide, respectively. A method of manufacturing said impact dot print head as claimed in claim 1, comprising the steps of holding a nose and a front end guide by a jig in such positions that the front end surfaces of said nose and of said front end guide are substantially flush with each other; deforming protrusions of said front end guide or said nose; and fixing said nose to said front end guide.

Inventors: MIMURA HIROMI C O SEIKO EPSON, MIZUNO SHIGEKI C O SEIKO EPSON, YAMAMOTO KAZUHIKO C O SEIKO EP, MIMURA, HIROMI, C/O SEIKO EPSON CORPORATION, MIZUNO, SHIGEKI, C/O SEIKO EPSON CORPORATION, YAMAMOTO, KAZUHIKO, C/O SEIKO EPSON CORPORATION
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1991
Main classification: B41J2
IPC codes: H01R43, B41J2, H01R13