Impact dot printer

Abstract: An impact dot printer that includes: a plurality of print wires (15); a front end guide (17) having guide holes (21,23) for guiding the print wires to predetermined print positions; and a guide holding member (16) for holding the front end guide. Such impact dot printers receive lubricant (18) in a portion behind the front end guide (17) and performs the printing operation by biasing an ink ribbon (3) located between the front end guide and a print sheet (4) while projecting the print wires (15) onto the print sheet (4) at appropriate timings. In such an impact dot printer, projections (20) are provided on a surface (17a) of the front end guide (17), the surface being on the print wire projecting side, and these projections form clearances between the surface of the front end guide (17a) and the ink ribbon (3), so that even if the lubricant (18) seeps from the guide holes (21,23), the lubricant does not come in direct contact with the ink ribbon, thus not ruining the ink ribbon to impair printing quality. A means (17b,22; 24,25; 26,27,31; 33-35; 36,37-42; 44) for preventing seepage of the lubricant through clearances between the front end guide and the guide holding member is also provided to further improve printing performance.

Description: The present invention relates to a printer head for an impact dot printer. A known impact dot printer is disclosed in, e.g., Japanese Patent Unexamined Publication No. 7351/1991. Figure 14 illustrates such a print head of an impact dot printer therein disclosed and comprises injecting a lubricant 18 of appropriate viscosity at the back of a front end guide 17 for preventing infiltration of fine particles of ink, ink ribbon scraps, print medium dust, etc., from guide holes 21 in the front end guide 17. The infiltration of such particles impairs slidability of print wires 15 and encourages wear of the print wires 15 with respect to the guide holes 21. As a recent trend in impact dot printers, there is a growing demand for a printing performance capable of achieving neat printing on various types of printing paper such as postcards and labels. Such demand has accelerated the development of horizontally inserted type impact dot printers, which are featured with improved sheet insertion performance because there is no need to bend the paper. Previously a head 6 of a conventional impact dot printer has been mounted so as to be upright, as shown in Figure 15(a). Such demand however has meant that the head 6 is mounted so as to face down enabling the print sheet 4 to be laid horizontally, as shown in Figure 15(b). As shown in Figure 14, in the conventional structure in the vicinity of the tips of wires 15 of the head 6, generally an ink ribbon 3 comes in direct contact with the tips of the wires 15. The ribbon 3 keeps a close distance from a surface 17a of the front end guide 17 with a projecting amount of about 0.01 mm from the surface 17a, which is the distance kept when in a standby position. However, when the head 6 is kept facedown as shown in Figure 15(b) for a long time, the lubricant 18 seeps through the guide holes 21 and through the clearances between the front end guide 17 and a nose 16 by the action of specific gravity. As a result, as shown in Figure 16, the lubricant 18 is transferred onto the ink ribbon 3, and the transferred lubricant 18 causes some ink component to be lost in a lubricant transferred portion 110. Once the ink has been lost, even with the operation of projecting the wires 15 onto the lubricant transferred portion 110, no dot mark can be formed thereon. This results in defective printing such as shown by portions "a" in Figure 17. Also, this defect can occur when the head 6 is mounted upright as shown in Figure 15(a), when the amount or viscosity of the lubricant 18 injected at the back of the front end guide 17 is too large an amount or of insufficient viscosity. This causes the lubricant 18 to leak out through the guide holes 21, causing defective printing similar to the portions "a" in Figure 17. Therefore, the conventional examples have encountered problems of elevated cost, because a strict control over the viscosity and amount of the lubricant 18 which must be effected when injecting the lubricant 18 at the back of the front end guide 17 of the head 6 even if the head 6 is mounted upright. Further, when mounting the head 6 facedown, sometimes lubricant is not injected at the back of the front end guide 17 so as to prevent defective printing. However, there have been noticeable losses in reliability and durability, such as printing quality impairment, due not only to wear of the guide holes 21 of the front end guide 17 but also to an increase in sliding resistance of the wires due to ink, paper dust, and ribbon scraps infiltrating into the guide holes 21, and then picking up of the ribbon by the wires. The present invention has been made to overcome the above problems. Accordingly, an object of the present invention is to provide an impact dot printer which ensures not only stable printing quality but also excellent reliability and durability irrespective of the mounting direction of the head. To achieve the above object, the invention is applied to an impact dot printer according to claim 1. Embodiments of the present invention will now be described with reference to the accompanying drawings, of which: Figure 1 is a schematic front view showing a mechanical portion of an impact dot printer according to a first embodiment of the present invention; Figure 2 is a schematic top view showing the mechanical portion of the impact dot printer of the first embodiment; Figure 3 is a side sectional view showing a print mechanism taken along a line A-A shown in Figure 1; Figure 4 is a partial view of a front end guide 17 as viewed from the direction indicated by an arrow B in Figure 3; Figure 5 is a perspective view of the front end guide of the first embodiment; Figure 6 is a diagram showing a front end guide according to a second embodiment of the present invention; Figure 7(a) is a front view showing a third embodiment of the present invention; Figure 7(b) is a bottom view thereof; Figure 8(a) is an exploded perspective view showing the third embodiment of the present invention; Figure 8(b) is a sectional view taken along a line E-E shown in Figure 7; Figure 9(a) is an unexploded perspective view showing a fourth embodiment of the present invention; Figure 9(b) is a sectional view of the fourth embodiment which is similar to that taken along a line E-E shown in Figure 7; Figure 10(a) is an exploded perspective view showing a fifth embodiment of the present invention; Figure 10(b) is a sectional view of the fifth embodiment which is similar to that taken along the line E-E shown in Figure 7; Figure 11(a) is an exploded perspective view showing a sixth embodiment of the present invention; Figure 11(b) is a sectional view of the sixth embodiment which is similar to that taken along the line E-E shown in Figure 7; Figure 12(a) is a top view of a front end guide of the sixth embodiment of the present invention; Figure 12(b) is a back view thereof; Figure 12(c) is a side view thereof; Figure 13(a) is an exploded perspective view showing a seventh embodiment of the present invention; Figure 13(b) is a sectional view of the seventh embodiment which is similar to that taken along the line E-E shown in Figure 7; Figure 14 is a sectional view of a front end guide according to a conventional example; Figure 15(a) and (b) are side views showing different directions in which a head is mounted; Figure 16 is a diagram of an ink ribbon illustrative of a problem encountered by the conventional example; and Figure 17 is a diagram of a printout illustrative of a problem encountered by the conventional example. Figure 1 is a schematic front view showing mechanical portions of an impact dot printer, and Figure 2 is a schematic top view thereof. This impact dot printer prints dots using a head 6 that is carried on a carriage 1 supported so as to be movable in the direction of right and left. The dots are printed on a print sheet 4 arranged between a platen 2 and an ink ribbon 3 with the head 6 moving on the carriage 1 in the right and left direction, so that the desired characters, graphics, and the like can be printed. A connector 7 is carried on a plate 5 and are connected to each other by a flexible print cable 8 for enabling a head drive circuit and the head 6 to be electrically jointed. A photocoupler 9 provided on the plate 5 has the function of detecting a home position of the carriage 1 by sensing the presence/absence of a fin 10 arranged on the carriage 1. The carriage 1 shuttles horizontally as viewed in Figures 1 and 2 through use of a drive belt 12 and a carriage drive motor 11. An encoder 13 mounted on the carriage drive motor 11 generates a signal for detecting the position of the carriage 1, from which signal a reference print timing signal is generated. Figure 3 is a cross section of a print mechanism according to a first embodiment of the present invention. The cross section being taken along a line A-A shown in Figure 1. The basic print operation of the impact dot head and the basic construction of parts of such head will be described first with reference to Figure 3. Electromagnets 14 are energised at appropriate timings, and the electromagnetic attracting force F thereby generated causes wires 15 to project in the direction indicated by an arrow C. Each wire 15 is supported by one or more guides; particularly, the tip of the wire 15 is supported by a front end guide 17 held by a nose 16 serving as a guide holding member. A lubricant 18 is injected into and stays in a portion behind the front end guide 17. The lubricant 18 may include, e.g., napthene oil, paraffin oil and olefin oil. In the direction of projection of the wires 15, are the ink ribbon 3 and print sheet 4. The print sheet 4 abuts against the platen 2 that serves as a resilient end stopper. Further, between the print sheet 4 and the ink ribbon 3 there is a ribbon mask 19 having an opening larger than an area in which the print wires 15 are arranged. This ribbon mask 19 has the function of preventing the print sheet 4 from being stained due to the ink ribbon 3 coming in direct contact with the print sheet 4. The projected wires 15 strike with a given impact onto the print sheet surface through the ink ribbon 3, thereby forming ink marks on the print sheet surface. The ink ribbon 3 is rewound by a ribbon rewinder (not shown) in a direction indicated by an arrow D in Figure 4 and is in contact with the tips of the print wires 15 of the head 6 under a certain tension. Attention is now directed to the vicinity of the front end guide 17, which will now be described in greater detail. Figure 4 is a partial view mainly showing the front end guide 17 as viewed from a direction indicated by an arrow B in Figure 3, and Figure 5 is a perspective view showing the front end guide 17. The front end guide 17 is secured with the entire parts of side surfaces 17b thereof press-fitted into grooves 22 provided in the nose 16 so as to come in tight contact with one another. In this embodiment projections 20 are provided on a surface 17a on the wire projecting side of the front end guide 17. As a result of these projections 20, a predetermined distance can be provided between the ink ribbon 3 and the surface 17a of the front end guide 17. The lubricant 18 is injected in the portion behind the front end guide 17 but does leak out on the wire projecting side surface 17a of the front end guide 17 through the guide holes 21. However, the lubricant 18 does not flow out through clearances between the side surfaces 17b and the grooves 22 since the front end guide side surfaces 17b and the grooves 22 are in tight contact with each other. The lubricant 18 seeping from the guide holes 21 no longer comes in direct contact with the ink ribbon 3 because of the projections 20. Thus, the lubricant 18 is not transferred onto the ink ribbon 3, thereby not causing defective printing such as shown by portions "a" in Figure 17. In this embodiment the diameter of each print wire 15 is set to 0.2 mm; the distance d o between the two lines of guide holes 21 of the front end guide 17 is set to 0.08467 mm (1/30 inches); and the amount of projection of each print wire 15 from the front guide surface 17a in a standby position is set to 0.01 mm. It has been experimentally verified that if a height H of each projection 20 is set to a value either equal to the amount of projection of the print wire 15 from the front guide surface 17a in the standby position, i.e., 0.01 mm, or more and a distance L between the projection and an edge point of the guide hole 21 is set to 1.5 mm or less, which is 150 times the amount of projection of the print wire 15 from the front end guide surface 17a in the standby position or less, then the lubricant 18 is not likely to be transferred onto the ink ribbon 3: even when the ink ribbon 3 is slackened which sometimes happens under normal printing conditions. Since there is no likelihood that any lubricant 18 leaking from the guide holes 21 will come in direct contact with the ink ribbon 3 in this embodiment, even when mounting the head 6 facedown, less strict control is required over the viscosity and amount of the lubricant 18 without resulting in the lubricant 18 being transferred onto the ink ribbon 3. Figure 6 shows a second embodiment of the present invention in which the projections 20 are formed equidistantly from the guide holes 21. Thus each projection 20 has arcuate recesses on the side confronting the guide holes 21. In this embodiment, the same dimensions of H and L with respect to the print wire projection apply. Thus the second embodiment can attain the same advantages as the first embodiment. A third to a seventh embodiment will hereunder be described with reference to the accompanying drawings. These embodiments attempt to prevent the leakage of the lubricant through clearances between the front end guide and the nose by a means that is different from those employed in the first and second embodiments. Figure 7(a) is a front view in the vicinity of a front end guide according to a third embodiment of the present invention; and Figure 7(b) is a bottom view thereof. Figure 8(a) is an exploded perspective view of the third embodiment, and Figure 8(b) is a diagram showing a section taken along a line E-E shown in Figure 7(a). A plurality of print wires 15 are slidably held by guide holes 21, 23 whose diameters are slightly larger than that of each wire 15. The guide holes 21, 23 are arranged on a front end guide 17 and an intermediate guide 24, respectively. The intermediate guide 24 is held by intermediate guide grooves 25 provided in a nose 16. The front end guide 17 has a mounting groove 26 in a side surface thereof, and a ring-like elastic member 27 is attached to this mounting groove 26. An O ring is used as the elastic member 27 in this embodiment. The front end guide 17 is inserted into front end guide grooves 28 in the nose 16 and firmly secured to the nose 16 by causing pins 29 of the nose 16 to be fitted into fusing holes 30 in the front end guide 17 by fusing. The pins 29 may be fused with the holes 30 by the application of ultrasonic vibration to the pins, so that they melt due to the heat generated by the vibration and then set. Alternatively a soldering iron can be used to generate the heat. Grooves 31 are provided at portions in the nose 16 so that the elastic member 26 can be secured surely, such portions abutting against the elastic member 26. The front end guide 17 has an injection hole 32 that allows a lubricant 18 of appropriate viscosity to be injected therefrom after the front end guide 17, the intermediate guide 24, and the print wires 15 have been assembled. The injected lubricant 18 is kept in a portion surrounded by the front end guide 17, the intermediate guide 24, and the nose 16. Because of this structure, even if a low-viscosity component of the lubricant 18 slowly flows through clearances between the front end guide 17 and the nose 16, such flow can be stemmed by the elastic member 27 at the position where such elastic member 27 is located and, as a result, such lubricant in no way adheres to the ink ribbon 3. Figure 9(a) is an exploded perspective view of a fourth embodiment of the present invention, and Figure 9(b) is a sectional view thereof which is similar to the sectional view taken along the line E-E shown in Figure 7(a). The fourth embodiment has a general construction similar to that of the third embodiment, and so only those points which are different from the third embodiment will be described. The front end guide 17 has grooves 34 in side surfaces thereof, whereas the nose 16 has grooves 35 at positions confronting the grooves 34. After the front end guide 17 has been assembled with the nose 16, a shield member 33 is injected into a space between the grooves 34 and 35. While silicon rubber may be used as the shield member 33 in this embodiment, the material is not limited thereto. An adhesive or the like may be used as long as such adhesive has a shielding property. When the lubricant 18 is injected thereafter, the lubricant 18, is checked by the shield member 33, and will `in no way flow out on the ink ribbon 3. Figure 10(a) is an exploded perspective view of a fifth embodiment of the invention, embodiment of the invention, and Figure 10(b) is a sectional view thereof which is similar to the sectional view taken along the line E-E shown in Figure 7(a). The fifth embodiment has a general construction similar to that of the third embodiment and so only those points which are different from the third embodiment will be described. The front end guide 17 has a plurality of projections 36 on each of front end side surfaces 17c of portions that are inserted into grooves 28 of the nose 16. A length d1 from a surface 17d to the tip of each projection 36 is designed to be slightly larger than a width d2 of the groove 28, the surface 17d coming into contact with the groove 28 and being opposite to the surface 17c having the projections 36. Such dimensional requirements enable the tips of the projections 36 to be crushed when the front end guide 17 has been inserted into the nose 16, thereby causing the opposite surfaces 17d to come in intimate contact with the groove 28. The intimate contact extends along the length of each groove 28. Thus, even if the lubricant 18 is injected, the intimate contact between the grooves 28 and the surfaces 17d along the entire length does not allow the lubricant 18 to leak our into the front end side. As a result, the lubricant 18 cannot reach the ink ribbon 3. While the projections are provided on the front end guide 17 in this embodiment, it goes without saying that the same advantage can be obtained by arranging such projections on the nose 16. Figure 11(a) is an exploded perspective view of a sixth embodiment of the invention, and Figure 11(b) is a sectional view thereof which is similar to the sectional view taken along the line E-E shown in Figure 7(a). Figure 12(a) is a top view of the front end guide 17 of the sixth embodiment; Figure 12(b) is a back view thereof; and Figure 12(c) is a side view thereof. The sixth embodiment has a general construction similar to that of the third embodiment and so only those points which are different from the third embodiment will be described. The front end guide 17 will be described with reference to Figure 12. The front end guide 17 has walls 37 in a direction perpendicular to the front end surface 17a, the walls 37 being tapered toward the back of the front end guide 17. The front end guide 17 is made of resin, and the walls 37 can be elastically deformed horizontally. To reduce the rigidity in the horizontal direction, the walls 37 have cut portions 39 confronting a bottom portion 38. The walls 37 have chamfered portions 43 in a direction G of inserting the front end guide 17. The front end guide 17 has a pin 40 in the insertion direction G, whereas fusing holes 30 and an injection hole 32 are provided in the bottom portion 38 thereof. The construction and operation of the nose 16 will be described next with reference to Figure 11. The nose 16 has a throughhole 41 in the front end guide 17 insertion direction G. The pin 40 of the front end guide 17 is fitted into the throughhole 41 when the front end guide 17 has been inserted into the nose 16. The nose 16 also has pins 29, which are fitted into the fusing holes 30 at the time of inserting the front end guide 17. Continuously extending projected portions 42 are formed on the inside walls of the nose 16 where the front end guide 17 are to be inserted. A distance d3 between the confronting projected portions 42 is designed to be slightly smaller than a distance d4 between the outer surfaces of the walls 37 of the front end guide 17. As a result, the walls 37 elastically deform inwardly at the time of inserting the front end guide 17, causing the walls 37 to come in intimate contact with the continuously extending projected portions 42. At this point, the chamfered portions 43 of the walls 37 allow smooth insertion. The front end guide 17 is held by a tool (not shown) so that the front end surface 17a of the front end guide 17 and a front end surface 16a of the nose 16 stay coplanar, and under this condition the pin 40 and the throughhole 41 as well as the pins 29 and the fusing holes 30 are fused and thereby positioned and fixed. Since the walls 37 are formed in the direction perpendicular to the front end surface 17a, the front end surfaces 17a and 16a can be made coplanar without being restricted by the walls 37. Although clearances are formed by the cut portions 39 between the walls 37 and the bottom portion 38, the surfaces that come in intimate contact cover substantially the same area as an area into which the lubricant 18 is injected. Thus, there is little seepage of the lubricant 18, and there is no likelihood that the lubricant 18 will adhere to the ink ribbon 3. While the elastically deforming walls are provided on the front end guide 17 in this embodiment, it goes without saying that the same advantage can be obtained by arranging such walls on the nose 16. Figure 13(a) is an exploded perspective view of a seventh embodiment of the present invention, and Figure 13(b) is a sectional view thereof which is similar to the sectional view taken along the line E-E shown in Figure 7(a). The seventh embodiment has a general construction similar to that of the third embodiment and so only those points different from the first embodiment will be described. The front end guide 17 has projections 44 continuously extending on both side surfaces 17e thereof. A distance d5 between these projections is designed to be slightly greater than a distance d6 of the front end guide accommodating portion of the nose 16. Thus, the outer surface of each projection 44 gets slightly deformed plastically at the time the front end guide 17 is inserted to thereby come in intimate contact with the nose 16. As result, there is no likelihood that the lubricant 18 will leak out the front end side, nor will the lubricant 18 adhere to the ink ribbon 3. While the continuously extending projections are provided on the front end guide 17, it goes without saying that the same advantage can be obtained by arranging such projections on the nose 16. These embodiments are applied to impact dot printers having a so-called "clapper" type head in which wires are projected by the attraction of electromagnets. However, it goes without saying that the same advantage can be obtained by applying the invention to any impact dot printer in which the print wires are projected from the front end guide, either to one having a so-called "spring charged" type head using permanent magnets or to one having a piezo type impact dot head using piezoelectric elements. As a result of the above constructions, the lubricant seeping from the guide holes is no longer brought into direct contact with the ink ribbon by the projections, which does not allow the lubricant to be transferred onto the ink ribbon, thereby not causing defective printing attributable to the loss of some ink component on the ink ribbon by such transfer of the lubricant onto the ink ribbon. Therefore, the impact dot printer of the invention is free from defective printing in which no dot marks are produced out of the operation of projecting the print wires onto such lubricant transferred portion. Further, the means for preventing seepage of the lubricant through clearances between the front end guide and the guide holding member contributes to preventing outflow of the lubricant from any part except for the guide holes. Therefore, an impact dot printer having stable printing quality and excellent reliability and durability irrespective of the direction in which the head is mounted can be provided inexpensively.

Claims: An impact dot printer comprising: a plurality of print wires (15); a front end guide (17) having guide holes (21, 23) for guiding said print wires to predetermined print positions; a guide holding member (16) for holding said front end guide (17); said impact dot printer arranged for receiving a lubricant (18) injected into a back portion of said front end guide and for performing a printing operation by biasing an ink ribbon (3) located between said front end guide and a print sheet (4) while projecting said print wires at appropriate timings; characterised by projections (20) provided on a surface (17a) of said front end guide (17), said surface being on a side of projecting said print wires (15), and said projections forming a clearance (H) between the surface (17a) of said front end guide and said ink ribbon (3); and means (17b,22; 26,27,31; 33-35; 36,37-42; 44) for preventing seepage of said lubricant (18) through clearances between said front end guide (17) and said guide holding member (16) for holding said front end guide. An impact dot printer according to claim 1, wherein the clearance (H) of each of said projections (20) is set to a value equal to or greater than an amount of projection of each of said print wires (15) from said front end guide surface (17a) in a standby position. An impact dot printer according to claim 1 or 2, wherein a distance (L) between each of said projections and an edge point of each of said guide holes (1) is set to a value 150 times or less the amount of projection of each of said print wires (15) from said front end guide surface (17a) in a standby position. An impact dot printer as claimed in any one of claims 1 to 3, in which said seepage prevention means comprises a first groove (22) in said guide holding means (16) press fit with a side surface (17b) of said front end guide (17). An impact dot printer as claimed in any one of claims 1 to 3, in which said seepage prevention means comprises a second groove (26; 34) in said front end guide (17) and a third groove (31; 35) in said guide holding means (16) and means (27; 33) for sealing between said first and second grooves. An impact dot printer as claimed in claim 5, in which said sealing means comprises an elastic member (27). An impact dot printer as claimed in claim 5, in which said sealing means comprises an injectable member (33). An impact dot printer as claimed in any one of claims 1 to 3, in which said seepage prevention means comprises a fourth groove (28) in said guide holding means (16) which mates with said front end guide (17) and one or more projections (36) provided on said front end guide (17) or on said fourth groove for providing a press fit. An impact dot printer as claimed in any one of claims 1 to 3, in which said seepage prevention means comprises deformable extensions (37) on said front end guide (17) and ridges (42) provided on said guide holding means mating with said deformable extensions for providing a press fit.

Inventors: ASADA TAKASHI C O SEIKO EPSON, YAMAMOTO KAZUHIKO C O SEIKO EP, ASADA, TAKASHI, C/O SEIKO EPSON CORPORATION, YAMAMOTO, KAZUHIKO, C/O SEIKO EPSON CORPORATION
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1992
Main classification: B41J2
IPC codes: B41J2