Print wheel type printer

Abstract: Described is a print wheel type printer having selection pawls (6), a reset lever (8), shaft holes (1f) for suppor­ ting a selection pawl shaft (7), a reset lever shaft and a reset cam shaft (9), and print wheel positioning pieces (3) constructed as a unit in a trigger unit case (1) in order to make the relative positioning between print wheels (11) and parts of a character selection mechanism easy. For po­ sitioning the unit case (1) on a main housing frame of the printer, guide projections are formed on the sides of the unit case (1) to be engaged with positioning grooves on the main housing frame.

Description: The invention relates to a print wheel type printer in which printing is performed by a selection of corresponding symbols or characters provided on print wheels, by employing a plurality of independently operated selection pawls. A print wheel type printer generally comprises a plurality of print wheels each being united with a respective ratchet wheel, a plurality of selection pawls to stop the print wheels at arbitrary angular positions by engagement with grooves of the ratchet wheels, a plurality of electromagnetic devices operable to rotate the selection pawls into engagement with said grooves, a reset lever for collectively retracting the selection pawls from their stopping or engaging position to a non-stopping or reset position, and a reset cam which is rotatable to drive the reset lever. Since, as disclosed in JP-A-144521/75, positioning members for positioning the print wheels in the direction of a print wheel shaft, selection pawls and the like are separately mounted on a main housing frame of a prior art printer of this kind, many processing steps are necessary for assembling these many parts. Further, since the positioning of these parts is determined indirectly via the main housing frame, relative positional errors caused by uneven precision of the manufacturing process and assembly of many parts involved occur easily, making it necessary to perform fine adjustments after the assembly. Also, since the reset levers are fixed on a trigger unit via a shaft, it is necessary to disengage the trigger unit from the main housing frame each time when the reset lever is put on or off. It is an object of the present invention to provide a print wheel type printer wherein the assembly of a number of parts which function in connection with print wheels is easily performed with high precision. It is another object of the invention to make the positioning of the print wheels with respect to said assembled parts easy and precise. Still another object of the invention is to simplify the putting on/off of a reset lever. These objects are achieved with a print wheel type printer as claimed. In particular, the first object is achieved by that supporting members for supporting the selection pawls and the reset lever are constructed and assembled as one unit in a unit case and this unit case is installed on a main frame. The second object is achieved by constructing positioning members for determining the position of the print wheels in the direction of a print wheel shaft as a unit in said unit case. Putting on/off of the reset lever while the unit case is installed on the main frame is simplified by providing the reset lever with a beam shaped piece which is fixed at one end and formed as a piece at one side of the reset lever and has an engaging portion which becomes engaged with a reset lever supporting portion of the unit case, at the outer side of the free end of the beam shaped piece. Another engaging portion which becomes engaged with another reset lever supporting portion is formed on the other side of the reset lever. On way of carrying out the invention is described in detail below with reference to drawings which illustrate only specific embodiments, and in which: Fig. 1 is an illustration of disassembled key components of a typical print wheel type printer of this invention, Fig. 2 is an illustration of an assembled key structure, Fig. 3 is a side view of the trigger unit case and the main housing frame, Fig. 4 is an illustration of the structure of the printer, Fig. 5 is a front view of the printer, Fig. 6 is an enlarged view of the key part of the reset lever, Figs. 7 and 8 are illustrations of alternative embodiments for installing the reset lever and Figs. 9 to 12 are illustrations for explaining the printing actions of the printer. Fig. 1 is an illustration of disassembled key components of a typical print wheel type printer of this invention. In this Figure, the reference numeral 1 is a trigger unit case. As described later in the text and shown in Fig. 4, trigger unit case 1 comprises trigger magnetic coils 4, permanent magnets 5, a plurality of print wheel position determining pieces 3 protrudingly formed at a print wheel side edge, and at both sides of the upper part of the trigger unit case 1 a long hole 1f for supporting a selection pawl shaft, a hole 1g for supporting a reset lever shaft and a slot 1h for supporting a reset cam shaft. Trigger unit case 1 is positioned on a main housing frame 2 of the printer by means of horizontal positioning grooves 2a as will be explained in detail later. Also, the print wheels 11 are assembled by means of a print wheel shaft 13 shown in Fig. 4, which is supported by shaft holes 2b provided in the main housing frame 2. The position of the trigger unit case 1 and the print wheels 11 is accurately determined via the main housing frame 2. Fig. 3 is an illustration of the structure for positioning the trigger unit case 1 at the main housing frame 2. On the upper part of both sides the trigger unit case 1 has projected guides 1c extending in the horizontal direction on both sides of long hole 1f. In other words the projected guides 1c are elongated in the direction of installation of the trigger unit case 1. The projected guides 1c fit into the horizontal positioning grooves 2a of the main housing frame 2, which are open at one end. The projected guides 1c determine the horizontal and the vertical position of the trigger unit case 1 within the main housing frame 2 due to their abutment against the inner end and the bottom end of the horizontal positioning grooves 2a, respectively. On the upper face of the projected guides 1c there are projections 1d to ensure secure fitting. Figs. 4 and 5 are illustrations of the key structure of the printer. At the print wheel edge side of trigger unit case 1 corresponding to the position of print wheels 11, there is a plurality of upwardly projecting print wheel positioning pieces 3 arrayed at intervals of one unit, which extend in between print wheels 11 and determine their positions. As shown in Fig. 4, selection pawls 6 are rotatably installed on a selection pawl shaft 7. The selection pawl shaft 7 is supported by the long holes 1f provided at the upper portion of both sides of trigger unit case 1 as mentioned before. The selection pawl shaft 7 is forced toward the print wheels 11 by a coil spring 7a. As can be seen in Fig. 1, there is a plurality of rectangular holes 1e in the upper face of trigger unit case 1 for accommodating two downwardly extending legs 6a and 6b of the selection pawls 6. As shown in Fig. 4, a respective trigger coil 4 is positioned below each of these rectangular holes 1e. A permanent magnet 5 is disposed below each of the trigger coils 4 and positioned perpendicular to the print wheel shaft 13. Two pole plates 5N and 5S are fixed on both magnetic poles of each permanent magnet 5. One (6a) of the two legs 6a and 6b of each selection pawl 6 goes through a hollow portion 4a of the respective trigger coil 4 and has its tip located between said two pole plates 5N and 5S so as to be rotatable by these electromagnetic means. The selection pawls 6 each have a nose 6c engagable with one of grooves 12a of a ratchet wheel 12 fixed at one side of each print wheel 11, to position one of characters 11a selected from the periphery of print wheel 11 at a printing position. The selection pawl 6 further has an upwardly extending edge piece 6d engagable with a reset lever 8. Reset lever 8 is driven by a reset cam 10 to retract the selection pawls 6 into an inactive reset position or to release the selection pawls 6 so that they can be selectively operated by the electromagnetic means formed of magnetic coil 4, permanent magnet 5 and pole plates 5N and 5S. At the upper portion of reset lever 8 there is a hitching pawl 8a which is elongated widthwise, so that all selection pawls 6 can be retracted concurrently. At another portion of reset lever 8 a projection 8b is formed which is engaged with the reset cam 10. As shown in Fig. 6, at one side of reset lever 8 along the side of the main housing frame there is a beam shaped piece 8c which is fixed at one end. At the outer side of the free end side of the beam shaped piece 8c and at the opposite side of the reset lever 8 there are shaft portions 8d which become engaged with reset lever shaft support holes 1g provided at the upper part of trigger unit case 1 (see Figs. 1 and 3). Further, there is a wedge 8e on reset lever 8 to be inserted between the beam shaped piece 8c and the main housing frame side face 8f in order to prevent disengagement after the installation of reset lever 8. Figs. 7 and 8 illustrate alternative embodiments concerning the installation of the reset lever 8. In the case of Fig. 7, there are flexible pieces 21 at the reset lever shaft setting portions of a trigger unit case 22. Depressions 28a are formed on both sides of reset lever 28. During installation, while flexible pieces 21 are bent as indicated by arrows in Fig. 7, projections 21a formed on the inner sides of flexible pieces 21 to face each other become engaged with the depressions 28a. In the case of Fig. 8 shaft portions 28b of reset lever 28 become engaged with Ω shaped reset lever shaft support slots 22g of a trigger unit case 22. As mentioned before, the reset lever 8 is driven by the rotation of reset cam 10. A reset cam shaft 9 carrying the reset cam 10 (Fig. 1) is supported by slots 1h located at the top of trigger unit case 1 and, as best shown in Fig. 3, extend upwardly and are open to the top. The slots 1h are located at the vertex of a triangle having formed its base by the long hole 1f and the hole 1g. First, a number of selection pawls 6 corresponding to the number of print wheels 11 are inserted into the rectangular holes 1e located at the top of trigger unit case 1, which is structured as described above. Next, the selection pawls 6 are installed by inserting the selection pawl shaft 7 by inserting it from one side of the trigger unit case 1 through long hole 1f and through the centre hole 6e of each selection pawl 6. Next, the reset cam shaft 9 is positioned in the slots 1h at the top of the trigger unit case 1. Then, projected shaft portions 8d of the reset lever 8, which have been mentioned above, are set into the shaft holes 1g from inside of the trigger unit case 1 while the beam shaped piece 8c is bent inward. The print wheel positioning pieces 3 and all the moving members for selecting characters have now been assembled to the trigger unit case 1 so as to form one unit. Next, the trigger unit case 1 comprising all these members is positioned and accurately fixed both in horizontal and vertical directions by inserting the projected horizontal guides 1c located at both sides of the trigger unit case 1 into the horizontal positioning grooves 2a of the main housing frame 2. Thus, the plurality of print wheel positioning pieces 3 located at the edge of the trigger unit case 1 enter in between respective print wheels 11 to determine their position in the direction of the print wheel shaft 13. Next, the operation of the printer assembled as described above will be explained below. First, as shown in Fig. 9, when reset cam 10 rotates in the direction of arrow A (clockwise) reset lever 8 is turned in the direction of arrow B (counterclockwise) by means of the engagement between the projections 10a and 8b. Due to this movement of reset lever 8 its hitching pawl 8a comes to engage the edge pieces 6d of all selection pawls 6 so that the selection pawls 6 together with the selection pawl shaft are retracted in the direction of arrow C, the noses 6c of the selection pawls 6 becoming disengaged from respective projections 12b of ratchet wheels 12 thereby making a rotation of the print wheels 11 possible. While reset cam 10 further rotates in the direction of arrow A, when projection 8b of reset lever 8 biased by a spring 8f drops into the small diameter portion 10b of reset cam 10, all the selection pawls 6 are released from engagement with hitching pawl 8a and become rotatable. When a voltage is applied to a trigger coil 4 in this state, one (6a) of two legs 6a, 6b of the corresponding selection pawl 6 in magnetized to become a South pole and is repelled by pole plate 5S and attracted by pole plate 5N as shown in Fig. 11. By this action, the selection pawl 6 rotates in the direction of arrow G (clockwise) around selection pawl shaft 7 as the centre of rotation. At this time, the nose 6c of the selection pawl becomes engaged with a corresponding groove 12a of the respective ratchet wheel 12, thereby stopping the print wheel 11 which is united with the ratchet wheel 12. At the same time a print wheel spring 14 comes out of a groove provided in the print wheel shaft 13 allowing print wheel shaft 13 to continue rotation while print wheel 11 is stopped at its present position. When selected characters 11a are thus placed at the printing position a printing roller 17 supported by a printing roller support 16 fixed on a printing shaft 15 presses a recording medium s against the selected characters from behind to perform printing, as shown in Fig. 12. When the printing action is completed, the reset cam 10 which has rotated one cycle, again turns reset lever 8 by step portion 10c counterclockwise in the figure, and all selection pawls 6 are again rotated by the hitching pawl 8a in the direction of arrow C (Fig. 9). Thus the noses 6c of the selection pawls 6 become disengaged from the grooves 12a of the ratchet wheels 12 and engaged with the projections 12b of ratchet wheels 12 to reset the print wheels 11.

Claims: A print wheel type printer comprising a plurality of print wheels (11) each having a ratchet wheel (12) fixed to one side, a plurality of rotatable selection pawls (6) for stopping rotation of said print wheels (11) at specified positions, a rotatable reset lever (8) for returning said selection pawls to reset positions, a unit case (1) having supporting means for supporting said selection pawls (6) and said reset lever (8), and a main housing frame (2) having supporting means for supporting said print wheels (11) and means (2a) for positioning and fixing said unit case (1). A print wheel type printer according to claim 1, wherein said print wheel supporting means includes a print wheel shaft (13) and wherein a plurality of projected positioning members (3) for positioning said print wheels (11) in the shaft direction by going between said print wheels (11) is provided at one part of said unit case (1) corresponding to said print wheels (11). A print wheel type printer according to claim 1 or 2, wherein said positioning means (2a) comprises positioning grooves, which are open at one end, on said main housing frame (2), and wherein longitudinally elongated installation guide projections (1c) are provided on both sides of said unit case (1) for fitting into the positioning grooves. A print wheel type printer according to any of the preceding claims, having supporting means (1f, 1g, 1h) for supporting a selection pawl shaft (7), a reset lever shaft (8d) and a reset cam shaft (9) as one unit on said unit case (1). A print wheel type printer according to any of the preceding claims, wherein a beam shaped piece (8c) fixed at one end is integrally formed at one side of said reset lever (8), and protruded shaft portions (8d) to be fitted in reset lever shaft supporting holes (1g) provided in said unit case (1), are formed at the outer side of the free end of said beam shaped piece (8c) and the other outer side of said reset lever (8). A print wheel type printer according to any of claims 1 to 4, having flexible pieces (21) at reset lever shaft setting portions on said unit case (22) and engaging portions (21a) at the inner sides of the flexible portions so as to be engaged with mating portions (28a) formed on both outer sides of said reset lever (8). A print wheel type printer according to any of claims 1 to 4, having Ω shaped reset lever shaft supporting depressions (22g) on said unit case (1) for supporting shaft portions (28b) formed on both outer sides of said reset lever (8).

Inventors: HAMA SUSUMU C O SEIKO EPSON CO, HARADA YASUHIRO C O SEIKO EPSO, MURATA SADAO C O SEIKO EPSON C, HAMA, SUSUMU, C/O SEIKO EPSON CORPORATION, HARADA, YASUHIRO, C/O SEIKO EPSON CORPORATION, MURATA, SADAO, C/O SEIKO EPSON CORPORATION
Applicants: SEIKO EPSON CORP, SEIKO EPSON CORPORATION
Application year: 1990
Main classification: B41J1
IPC codes: B41J7, B41J1