Ribbon mask for impact dot matrix printer

Abstract: Described is a ribbon mask (1) for use with an impact dot matrix printer. The ribbon mask (1) comprises a head confronting surface (2) and a pair of opposed side plates (3R, 3L) each positioned on an opposite side of the head confronting surface (2). An obtuse angle is formed between said head confronting surface (2) and each of the opposed side plates (3R, 3L). A pair of fitting tabs (4R, 4L) are also provided. Each fitting tab (4R, 4L) is positioned on one of the pair of opposed side plates (3R, 3L). An acute angle is formed between each of the fitting tabs (4R, 4L) and the head confronting surface (2). As a result of this construction, when the ribbon mask (1) comes into contact with a sheet of a recording medium, the ribbon mask (1) is deformed so that a portion of the head confronting surface (2) comes into contact with an end of a recording head (10), which in turn prevents the ribbon mask (1) from interfering with the sheet of the recording medium.

Description: The invention relates generally to ribbon masks and more particularly to ribbon masks used for impact dot matrix printers. The use of ribbon masks in prior art impact dot matrix printers is well known in the art, see for example US-A-4 960 337. A prior art ribbon mask a for use with impact dot matrix printers is shown in FIG. 4, and is designed so that a pair of fitting tabs b , b extend from mask a which are dimensioned to be fitted into corresponding grooves g , g of a ribbon mask holder f . Each of fitting tabs b , b are formed so as to project from each side of ribbon mask a , and to extend parallel with a flat surface e of ribbon mask a . Grooves g , g are recessed within each side of ribbon mask holder f . Ribbon mask a is bent into a trapezoidal shape in plan so that flat surface e thereof can be maintained in contact with a recording medium to be printed upon, while allowing fitting tabs b , b to be fitted into corresponding grooves g , g . Fitting tabs b , b are retained within grooves g , g by dowels i, i extending from mask holder f . Ribbon mask a is further formed with a mask hole d formed therein to allow print wires from the impact dot matrix printer to pass therethrough when a printing operation is being performed. In this way ribbon mask a is mounted on a carriage and is positioned to reciprocate when a printing operation is being performed. Ribbon mask a is formed of an extremely thin steel plate whose thickness ranges from about 0.05 to 0.1 mm. Thus, if the carriage travels in the direction indicated by arrow X in FIG. 4 during use so that recording data will be written on a sheet of, for example, a fanfold comprising at least one perforation or gather j , an internal edge of ribbon mask a which forms mask hole d may catch perforation or gather j . Therefore, the movement of ribbon mask a is impeded, and ribbon mask a is pulled away from mask holder f . A print head confronting surface c of ribbon mask a is forced in the direction opposite to the traveling direction (opposite arrow X in FIG. 4) when ribbon mask a comes into contact with perforation or gather j projecting from the surface of the recording medium. As a result, a portion e of the head confronting surface c on the downstream side of mask hole d as viewed in the traveling direction (the direction of arrow X in FIG. 4) is separated from an end of a print head h . Thus, perforation or gather j can enter further into mask hole d . This in turn may further impede the movement of ribbon mask a , thereby causing ribbon mask a to disconnect from dowels i and move from its correct position. Therefore, printing quality will be effected, and the printing operation must be stopped to reposition ribbon mask a . The present invention intends to overcome the problems of prior art as mentioned before. Thus, the object of the invention is to provide a novel ribbon mask that can smoothly slide along a recording sheet without being caught on perforations or gathers contained on the recording medium during a printing operation. The object is solved by the ribbon mask for use with an impact dot matrix printer according to independent claim 1. Further advantages, features, aspects and details of the invention are evident from the dependent claims, the description and the accompanying drawings. Generally speaking, in accordance with the invention, a ribbon mask for use with an impact dot matrix printer is provided. The ribbon mask comprises a head confronting surface and a pair of opposed side plates each disposed on an opposite side of the head confronting surface to form a trapezoid when viewed in plan. An obtuse angle is formed between the head confronting surface and each of the opposed side plates. A pair of fitting tabs are also provided. Each fitting tab is positioned on one of the pair of opposed side plates. An acute angle is formed between each of the fitting tabs and the head confronting surface. As a result of this construction, when the ribbon mask comes into contact with a sheet of a recording medium during a printing operation, the ribbon mask is deformed obliquely so that the tab on the downstream side of the head confronting surface comes into contact with a wall of the ribbon mask holder. The head confronting surface is maintained in contact with the end of the print head, which in turn allows the print head to smoothly slide along a sheet of a recording medium without causing interference between the mask hole and the recording medium. At the same time, the tab on the upstream side of the ribbon mask is deformed and is forced along the upper surface of the corresponding engaging groove, which in turn contributes to reinforcing the engagement of the dowel with the tab to insure that the ribbon mask will not be separated from the dowel and the ribbon mask holder. For a fuller understanding of the invention, reference is made to the following description taken in connection with the accompanying drawings, in which: FIG. 1 is an exploded perspective view depicting a ribbon mask and carriage assembly constructed in accordance with the invention and an associated printer head; FIG. 2 is a top plan view of the ribbon mask and printer head of FIG. 1; FIG. 3(a) is an enlarged sectional view depicting the ribbon mask and printer head when not in operation; FIG. 3(b) is an enlarged sectional view depicting the ribbon mask and printer head when in operation; and FIG. 4 is an enlarged sectional view depicting the functioning of a prior art ribbon mask. Reference is first made to FIGS. 1 and 2, in which a ribbon mask is indicated generally as 1. Ribbon mask 1 is formed of a metal plate with a thickness of approximately 0.06 mm. Ribbon mask 1 is constructed so as to be roughly trapezoidal when viewed in plan. Ribbon mask 1 including a head confronting surface 2 having a front surface 2a and a back surface 2b is disposed between side plates 3L, 3R arranged on either side of head confronting surface 2. Side plates 3L, 3R are each formed with a front surface 3a and a back surface 3b, and are slightly inclined relative to head confronting surface 2 toward a print head 10. Ribbon mask 1 is further formed with fitting tabs 4L, 4R formed on either side thereof, each having a front surface 4a and a back surface 4b. Fitting tabs 4L, 4R project outward from either end edge of side plates 3L, 3R respectively, so that fitting tab 4L, 4R and a plane parallel to the plane which extends from said head confronting surface 2 form an acute angle . Further, fitting tab 4L is formed so that front surface 3a of side plate 3L and front surface 4a of fitting tab 4L form an obtuse angle αL. Similarly, fitting tab 4R is formed so that front surface 3a of side plate 3R and front surface 4a of side plate 4R form an obtuse angle αR. In an exemplary embodiment  is greater than 12° and thus fitting tabs 4L, 4R project toward a platen and a sheet of a recording medium S (FIG. 3(a)). Fitting tabs 4L, 4R are further formed with engaging holes 5L, 5R. Ribbon mask 1 is further formed with a mask hole 6 than allows print wires to be passed therethrough while a printing operation is being performed. Ribbon mask 1, along with ribbon mask holder 12 and the entire print head, is mounted on a carriage 16 which allows for the reciprocal motion of the components during a print operation. In an exemplary embodiment mask 1 is formed as a unitary piece. A ribbon mask holder 12 is formed on a carriage 16. Fitting grooves 13L, 13R are arranged on either side of the back surface of ribbon mask holder 12. Fitting grooves 13L, 13R extend parallel with the surface of ribbon mask holder 12. A pair of corresponding dowels 14L, 14R are arranged at the entrances of fitting grooves 13L, 13R and engage fitting holes 5L, 5R during use. Dowels 14L, 14R project toward print head 10, so that ribbon mask 1 can be attached to ribbon mask holder 12. Now referring to FIG. 3(a), when the carriage is inoperative and a print operation is not being performed, fitting tabs 4L, 4R, which as noted above project toward a platen (not shown) from each of side plates 3L, 3R and form obtuse angles αL, αR therewith, support ribbon mask 1 so that head confronting surface 2 of ribbon mask 1 is positioned to properly extend along the end of print head 10 disposed on carriage 16. The ends of fitting tabs 4L, 4R are maintained in pressured contact with inner surfaces 13aL, 13aR of fitting grooves 13L, 13R and are maintained within narrow fitting grooves 13L, 13R. The pressured contact between the ends of fitting tabs 4L, 4R, and inner surfaces 13aL, 13aR of narrow fitting grooves 13L, 13R causes and maintains head confronting surface 2 to be properly positioned, and to properly extend along the end of print head 10. When a print operation is being performed, carriage 16 travels in the direction indicated by arrow Y, as shown in FIG. 3(b). During this print operation, data is recorded on a recording medium, and head confronting surface 2 of ribbon mask 1 is displaced slightly in the direction opposite to the traveling direction (opposite to the direction indicated by arrow Y). As a result, fitting tab 4R (the fitting tab positioned in the downstream direction from head confronting surface 2) is forced against an inner wall 13bR of corresponding fitting groove 13R. Side plate 3R (the side plate positioned in the downstream direction from head confronting surface 2) is forced toward print head 10 and the angle αR is decreased. This in turn will cause an angle R formed between a portion 2R of head confronting surface 2 and side plate 3R, on the downstream side of head confronting surface 2 to decrease, thereby drawing side plate 3R toward print head 10 and in turn insuring that head confronting surface 2 will remain in contact with an end 11 of print head 10. Thus, even if a perforation or gather j (see Fig. 4) is caught up by an edge portion 6a of mask hole 6, this perforation or gather is pushed away from edge portion 6a by contact with the surface of the ink ribbon R located immediately below the mask hole 6, between print head 10 and ribbon mask 1, the ink ribbon being further supported by print head 10. Because ribbon mask 1 is maintained against end 11 of print head 10, print head 10 forces any perforation or gather j (Fig. 4) out of mask hole 6. As a result, smooth passage of ribbon mask 1 over a perforated, or other non-smooth surface is not impeded. Also during a printing operation, side plate 3L (the side plate positioned in the upstream direction from head confronting surface 2) is pulled in the direction opposite that indicated by arrow Y in FIG. 3(b). This force causes the end of tab 4L (the fitting tab positioned in the upstream direction from head confronting surface 2) to be pulled away from upper surface 13b of corresponding fitting groove 13 while increasing angle αL and also increasing an angle L formed between confronting surface 2 and side plate 3L. This increasing of these angles increases the engaging force between fitting tab 4L and dowel 14L, and also insures that no leverage will allow ribbon mask 1 to be detached from mask holder 12. Thus, during a printing operation, ribbon mask 1 will be deformed, thereby increasing the angles αL, L on the upstream side of the print head, and decreasing the angles αR, R on the downstream side of the print head, and ribbon mask 1 is properly maintained against end 11 of print head 10. Thus, the present invention is characterized in that tabs are arranged on either side of the main body of a ribbon mask. The main body is formed as a shallow trapezoid with a head confronting surface in the middle thereof, and the tabs are bent and inclined towards a platen. The tabs are designed to be fitted into a ribbon mask holder. As a result of this construction, when the ribbon mask comes into contact with a sheet of a recording medium during a printing operation, the ribbon mask is deformed obliquely so that the tab on the downstream side of the head confronting surface comes into contact with a wall of the ribbon mask holder, and the head confronting surface is maintained in contact with the end of the print head, which in turn allows the print head to smoothly slide along a sheet of a recording medium without causing interference between the mask hole and the recording medium. At the same time, the tab on the upstream side of the ribbon mask is deformed and is forced along the upper surface of the corresponding engaging groove, which in turn contributes to reinforcing the engagement of the dowel with the tab to insure that the ribbon mask will not be separated from the dowel and the ribbon mask holder.

Claims: A ribbon mask for use with an impact dot matrix printer, comprising: a head confronting surface (2) having a front surface (2a) and a back surface (2b); a pair of opposed side plates (3R, 3L), each having a front surface (3a) and a back surface (3b), each positioned on an opposite side of said head confronting surface (2); and a pair of fitting tabs (4R, 4L), each having a front surface (4a) and a back surface (4b), each positioned on a respective one of said pair of opposed side plates (3R, 3L), an acute angle being formed between a respective one of said front surfaces (4a) of said fitting tabs (4R, 4L) and a plane parallel to the plane which extends from said head confronting surface (2). The ribbon mask of claim 1, wherein said ribbon mask (1) substantially forms a trapezoid when viewed in plan. The ribbon mask of claim 1 or 2, wherein each of said fitting tabs (4R, 4L) is dimensioned to be fitted into and engaged with an associated engaging groove (13R, 13L) which are each arranged on either side of a ribbon mask holder (12). The ribbon mask of one of the preceding claims, further comprising engaging holes (5R, 5L) formed in each of said fitting tabs (4R, 4L). The ribbon mask of claim 4, wherein said engaging holes (5R, 5L) are each dimensioned to engage a dowel (14R, 14L) formed in the associated engaging groove (13R, 13L). The ribbon mask of one of the preceding claims, wherein said ribbon mask is formed of a thin metal plate. The ribbon mask of claim 6, wherein said thin metal plate is approximately 0.06 mm thick. The ribbon mask of one of the preceding claims, wherein said ribbon mask (1) is bent into a shallow trapezoidal form so as to cover an end of a recording head (10). The ribbon mask of one of the preceding claims, wherein said acute angle between said plane parallel to the plane which extends from said head confronting surface (2) and said front surfaces (4a) of said associated fitting tabs (4R, 4L) is greater than 12°. The ribbon mask of one of the preceding claims, wherein said acute angle changes during a print operation.

Inventors: ISHIDA HIROSHI, KUMAZAKI MASAYUKI, UCHIYAMA YUKIHIRO, YAMAGUCHI KAZUHIKO, YAMAGUCHI NAOTO, ISHIDA, HIROSHI, KUMAZAKI, MASAYUKI, UCHIYAMA, YUKIHIRO, YAMAGUCHI, KAZUHIKO, YAMAGUCHI, NAOTO, Ishida, Hiroshi, c/o Seiko Epson Corp., Kumazaki, Masayuki, c/o Seiko Epson Corp., Uchiyama, Yukihiro, c/o Seiko Epson Corp., Yamaguchi, Kazuhiko, c/o Seiko Epson Corp., Yamaguchi, Naoto, c/o Seiko Epson Corp.
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1996
Main classification: B41J35
IPC codes: B41J35, B41J11