Platen support structure for an impact printer

Abstract

 A platen support structure for supporting the platen (3) of an impact printer. Vibration absorbing members (11, 21, 31) are interposed between side frames (15) provided on the main frame of the impact printer and platen collars (7, 27) mounted on a support shaft (5) supporting the platen (3) to absorb and attenuate the vibration of the platen (3) caused by impact applied thereto by the printing wires of the print head so that the vibration is not transmitted to the side frames (15). The platen support structure reduces the noise of the impact printer.

Description

[0001] The present invention relates to a platen support structure for an impact printer, such as a wire matrix printer.

[0002] Generally, the platen of a printer can easily be removed from the main frame of the printer to facilitate removing a recording medium jammed in the printing mechanism and cleaning or replacing the platen. The platen is supported rotatably on the main frame of the printer with the opposite ends of its support shaft projecting from the opposite ends thereof rotatably fitted in platen collars mounted on the side frame members of the main frame.

[0003] A printing mechanism employing such a platen support structure has the following problems.

[0004] When the impact printer is in printing operation, printing wires provided on the print head are projected from the print head to strike at the platen at a frequency in the range of about 1 to 1.5 kHz. The impact of the printing wires on the platen entails the vibration of the platen. The vibration of the platen is transmitted through the platen collars to the side frame members of the main frame and further through the side frame members to the main frame of the impact printer causing the impact printer to generate noise. Further causes of noise are the spacing vibration of the carriage mounted with the print head induced when the carriage travels for spacing, and the line feed vibration of the gearing for transmitting the driving power of the line feed motor to the platen induced when the platen is driven for line feed. Among these causes, the vibration of the platen caused by the impact applied to the platen by the printing wires is the most significant cause.

[0005] It is an object of the present invention to prevent the propagation of the vibration of the platen of an impact printer caused by impact applied to the platen through the entire impact printer to provide a silent impact printer.

[0006] It is another object of the present invention to provide an inexpensive and simple structure capable of preventing the propagation of the vibration of the platen of an impact printer caused by impact applied to the platen.

[0007] In one aspect of the present invention, a platen support structure comprises platen collars rotatably put respectively on the opposite ends of a platen support shaft projecting from the opposite ends of the platen, a pair of side frames provided on the main frame of an impact printer and provided respectively with recesses for receiving the platen collars, and vibration absorbing members provided on the side frames between the platen collars and the corresponding recesses.

[0008] In an impact printer employing the platen support structure of the present invention, the vibration of the platen caused by impact applied to the platen by the printing wires mounted on the print head and transmitted through the platen support shaft to the platen collars is absorbed by the vibration absorbing members to prevent the propagation of vibrations through the side frames. Consequently, the vibration of the impact printer due to the vibration of the platen caused by impact applied thereto can be prevented, noise attributable to the vibration of the platen caused by impact applied thereto is suppressed, and the impact printer is able to operate on a low noise level.

[0009] The above and other objects, features and advantages of the present invention will become more apparent from the following description taken in conjunction with the accompanying drawings.

Fig. 1 is a perspective view of a platen support structure in a first embodiment according to the present invention;

Fig. 2 is an exploded perspective view of a platen support structure of the present invention;

Fig. 3(I) is a perspective view of a platen collar employed in a platen support structure of the present invention, Fig. 3(II) is a front elevation of a platen collar employed in a platen support structure of the present invention, and Fig. 3(III) is a sectional view taken on line A-A in Fig. 3(II);

Fig. 4(I) is a front elevation of a platen collar employed in a platen support structure of the present invention, combined with a vibration absorbing member, and Fig. 4(II) is a sectional view taken on line B-B in Fig. 4(I);

Fig. 5(I), 5(II) and 5(III) are diagrammatic illustrations of assistance in explaining a procedure of mounting a platen collar assembly on a side frame in assembling a platen support structure of the present invention;

Fig. 6(I) is a perspective view of a vibration absorbing member employed in a platen support structure in a second embodiment according to the present invention, and Fig. 6(II) is a front elevation of a vibration absorbing member employed in the platen support structure in the second embodiment according to the present invention;

Fig. 7(I) is a perspective view of a vibration absorbing member employed in a platen support structure in a third embodiment according to the present invention, Fig. 7(II) is a front elevation of a vibration absorbing member employed in the platen support structure in the third embodiment according to the present invention, and Fig. 7III) is a side elevation of a vibration absorbing member employed in the platen support structure in the third embodiment according to the present invention;

Fig. 8 is a perspective view of a vibration absorbing member employed in the platen support structure in the third embodiment according to the present invention, as attached to a side frame; and

Fig. 9(I) is a perspective view of a platen collar employed in a platen support structure in a fourth embodiment according to the present invention, Fig. 9(II) is an exploded perspective view of a platen collar employed in the platen support structure in the fourth embodiment according to the present invention, Fig. 9(III) is a front elevation of a component 29 of a platen collar employed in the platen support structure in the fourth embodiment according to the present invention, and Fig. (IV) is a rear view of the component 29 of a platen collar employed in the fourth embodiment according to the present invention.

[0010] Referring to Figs. 1 and 2, a platen assembly 1 comprises a cylindrical platen 3, a support shaft 5 fixedly mounted with the platen 3, a pair of platen collars 7, a gear 9 and vibration absorbing members 11 for absorbing the vibration of the platen caused by printing operation. The opposite ends of the support shaft 5 project respectively from the opposite ends of the platen 3. The platen collars 7 and the gear 9 are mounted on the support shaft 5. As shown in Fig. 2, a hole 13 is formed in the support shaft 5 for use in fixedly connecting the gear 9 to the support shaft 5.

[0011] Referring to Fig. 3, each platen collar 7 has a through hole 7a for receiving the support shaft 5 therethrough, a neck portion 7i having opposite rectangular surfaces 7b and 7c for inserting the platen collar 7 in a recess formed in a side frame 15 and opposite circular surfaces 7d and 7e for restraining the platen collar 7 from falling off the side frame 15, flanges 7f and 7g formed at the opposite ends of the neck portion 7i to fix the position of the platen collar 7 relative to the side frame 15, and a knob 7h. The platen collar 7 is supported at the neck portion 7i on the side frame 15.

[0012] The gear 9 is provided with a central through hole 9a for receiving the support shaft 5, and a radial through hole 9c in its boss 9b. The gear 9 is connected fixedly to the support shaft 5 by mounting the gear 9 with the through hole 9c in alignment with the through hole 13 of the support shaft 5 and fitting a stopping member, not shown, through the through hole 9c of the gear 9 and the through hole 13 of the support shaft 5. Rotative force of a line feed motor, not shown, is transmitted through the gear 9 and the support shaft 5 to the platen 3 to drive the platen 3 for stepping rotation at a predetermined pitch.

[0013] The vibration absorbing member 11 is formed of an elastic material, such as a plastic or rubber. As shown in Figs. 4(I) and 4(II), the vibration absorbing member 11 is mounted on the neck portion 7i of the platen collar 7. The vibration absorption member 11 may be formed directly on the neck portion 7i, for example, by applying a material, such as a liquid material which becomes elastic when solidified, in a uniform thickness to the surface of the neck portion 7i.

[0014] A manner of mounting the platen collar 7 on the side frame 15 will be described hereinafter with reference to Figs. 5(I), 5(II) and 5(III). The side frame 15 is provided with an opening consisting of a substantially circular aperture 15b and a slot 15a merging into the round aperture 15b. The width of the slot 15a corresponds to the distance between the rectangular surfaces 7b and 7c, and the diameter of the substantially circular aperture 15b corresponds to the diameter of a circle circumscribing the neck portion 7i coated with the shock absorbing member 11. First, the platen collar 7 is held in a position as shown in Fig. 5(I), in which the rectangular surfaces 7b and 7c extend vertically, and the neck portion 7i is passed through the slot 15a so that the neck portion 7i is seated on the bottom of the substantially circular aperture 15b as shown in Fig. 5(II). Then, the platen collar 7 is turned through an angle of 90PTo′ so that the circular surfaces 7d and 7e fit the substantially circular aperture 15b as shown in Fig. 5(III). In this state, the platen collar 7 cannot be removed from the side frame 15. The platen collar 7 is restrained from axial movement relative to the side frame 15 by the flanges 7f and 7g extending respectively on the opposite sides of the side frame 15.

[0015] In this embodiment, the platen collar 7 mounted on the support shaft 5 on the side of the gear 9 is held between the outer end of the platen 3 and the gear 9 fixed to the support shaft 5 at a predetermined position by the fixing member, not shown, and is restrained from axial movement, which facilitates mounting the platen collar 7 on the side frame 15. The platen collar 7 mounted on the other end of the support shaft 5 may be held at a fixed axial position for the same effect by putting a plastic or rubber ring on the support shaft 5 or by screwing a screw in the shaft 5 after mounting the platen collar 7 on the support shaft 5 to position the platen collar 7. The sizes of the slot 15a and the substantially circular aperture 15b are determined taking into consideration the sizes of the neck portion 7i and the vibration absorbing member 11, and the physical properties, such as extensibility and compressibility, of the vibration absorbing member 11.

[0016] The platen collar 7 need not necessarily be held in place on the side frame 15 in the foregoing means; a platen collar having a round neck portion may be mounted on a side frame provided with a simple slot with the round neck portion received in the slot, and the platen collar may be held in place with fixing means.

[0017] When the platen 3 thus supported on the side frames 15 is caused to vibrate by the impact applied thereto by the printing wire mounted on the print head, the vibration is transmitted through the support shaft 5 and the platen collars 7 to the vibration absorbing members 11. Then, the vibration absorbing members 11 absorb and attenuate the vibration, so that the vibration is not transmitted to the side frames 15. Thus, the noise attributable to the vibration of the platen 3 is eliminated and hence the noise generated by the impact printer can be reduced accordingly.

[0018] A platen support structure in a second embodiment according to the present invention employs a vibration absorbing member 21 shown in Figs. 6(I) and 6(II). The platen support structure is substantially the same in construction as the foregoing platen support structure, except the platen support structure in the second embodiment employs the vibration absorbing member 21 shown in Figs. 6(I) and 6(II). The vibration absorbing member 21 is a separate member having the shape of a substantially oblong ring and provided with a single cut 17. In putting the vibration absorbing member 21 on the platen collar 7, the vibration absorbing member 21 is opened elastically at the cut 17 and is put on the neck portion 7i. The vibration absorbing member 21 put on the neck portion 7i restores its original shape by its own elasticity so that the vibration absorbing member 21 holds itself firmly on the neck portion 7i of the platen collar 7. When abraded, worn or aged, this vibration absorbing member 21 can easily be replaced with a new one. A platen support structure in a third embodiment according to the present invention employs a vibration absorbing member 31 shown Figs. 7(I), 7(II), and 7(III). The platen support structure in the third embodiment according to the present invention is substantially the same in construction as the foregoing platen support structures, except that this platen support structure employs the vibration absorbing member 31 shown in Figs. 7(I) to 7(III). The vibration absorbing member 31 is a barrel-­shaped piece provided with a break 19 and an annular groove 23 of a width substantially the same as the thickness of the side frame 15. The annular groove 23 is formed in the middle of the outer circumference of the vibration absorbing member 31. The vibration absorbing member 31 is inserted into the substantially circular aperture 15b of the side frame 15 as shown in Fig. 8 with the annular groove 23 closely engaging the edge of the substantially circular aperture 15b and with the break 19 in alignment with the slot 15a to allow the neck portion 7i of the platen collar 7 to pass through the slot 15a and the break 19. When abraded, worn, or aged, this vibration absorbing member 31, similarly to the vibration absorbing member 21, can easily be replaced with a new one.

[0019] A platen support structure in a fourth embodiment according to the present invention employs a platen collar 27 shown in Figs. 9(I) to 9(IV). The platen collar 27 comprises two parts, namely, a main member 28, and a holding member 29 provided with a groove of the same shape and size as those of the cross section of the neck portion 28a of the main member 28 in the surface facing the main member 28. A vibration absorbing member having neither a cut nor a break can be put on the neck portion 28a of the platen collar 27. In assembling the platen collar 27 and the vibration absorbing member, first, a vibration absorbing member having a length shorter than that of the neck portion 28a is put on the neck portion 28a of the main member 28, and then a portion of the neck portion 28a projecting from the vibration absorbing member is fitted closely in the groove 29a of the holding member 29.

[0020] This platen collar 27 facilitates replacing an abraded, worn or aged vibration absorbing member with a new one and eliminates an additional process for forming a cut or break in the vibration absorbing member. Having neither a cut nor a break, the vibration absorbing member never fall accidentally off the platen collar 27 in mounting the platen assembly on and in removing the platen assembly from the side frames 15,

[0021] Essentially, the platen support structure of the present invention includes vibration absorbing members of any suitable kind provided between the platen collars and the side frame of the impact printer to absorb and attenuate the vibration of the platen so that the vibration of the platen will not be transmitted to the side frames.

[0022] Although the invention has been described in its preferred form with a certain degree of particularity, it is to be understood that many variations and changes are possible in the invention without depating from the scope thereof.

Claims

1. A platen support structure for an impact printer having a cylindrical platen (3), comprising:
a support shaft (5) coaxially mounted with the platen (3) and having opposite ends projecting respectively from the opposite ends of the platen (3);
a pair of platen collars (7, 27) mounted respectively on the opposite ends of the support shaft (5) so as to allow the support shaft (5) to rotate thereon;
a pair of side frames (15) provided on the main frame of an impact printer and each provided with an opening (15a, 15b) for receiving the platen collar (7, 27); and
a pair of vibration absorbing members (11, 21, 31) interposed between the platen collars (7, 27) and the side frames (15).

2. A platen support structure according to Claim 1, wherein said vibration absorbing members (11, 21, 31) are formed of an elastic material.

3. A platen support structure according to Claim 1, wherein said vibration absorbing members (11,21,31) can be removed and has the shape of a ring.

4. A platen support structure according to Claim 1, wherein said vibration absorbing members (11, 21, 31) are attached respectively to the platen collars (7, 27).

5. A platen support structure according to Claim 1, wherein said vibration absorbing members (11, 21, 31) have each a cut (17) or a break (19).

6. A platen support structure according to Claim 1, wherein said vibration absorbing members (11, 21, 31) have each a break (19), and a circumferential groove (23) in the middle of the outer circumference thereof and each vibration absorbing member (11, 21, 31) is inserted into the opening (15b) of the side frame (15) with the edge of the opening (15a) recived firmly in the circumferential groove (23).

7. A platen support structure according to Claim 1, wherein said platen collar (27) comprises two separate parts (28, 29).

Drawing