Sheet Feeding Device for an Impact-Type Printer

This application is related to commonly-owned U.S. application Ser. No. 675,327, now abandoned, to Agata filed even date herewith, the entire disclosure thereof being expressly incorporated hereinto by reference as is the underlying priority document herein Japanese Application No. 58-226290 filed Nov. 30, 1983.

The present invention relates to a sheet feeding device for an impact-type printer with a platen. More particularly, the present invention relates to means for causing pressure rollers of the sheet feeding device to be displaced into and out of pressing engagement with the platen of an impact-type printer.

A conventional sheet feeding device in an impact-type printer is shown in FIG. 1. As can be seen, impact-type printers conventionally include a platen 1 and a paper guide 2 for guiding a printing sheet A along the cylindrical exterior surface of the platen 1. A crank arm 3 is positioned below the paper guide 2 in such a manner that it is pivotal about a shaft 4. The crank arm 3 is in slidable contact with a cam roller 6 which is positioned at one end of a lever 5, the latter being pivotal abaout shaft 5a. Therefore, as the lever 5 pivots about shaft 5a (as indicated by the arrow 5b in FIG. 1), the crank arm 3 responsively pivots about shaft 4 as shown by arrow 5c in FIG. 1. In such a manner, a pressure roller 7 which is provided at one end of the crank arm 3 is caused to either press against or be displaced from the sheet A on the platen 1 through an opening 8 formed in the paper guide 2 in dependence upon the direction of pivotal movement of lever 5 about shaft 5a.

The conventional sheet feeding mechanism described above is disadvantageous in several respects. For example, separate mechanisms are required in order to operate the pressure roller 7 via the crank arm 3, the lever 5 and the cam roller 6. As the pressure roller 7 is operated through a plurality of components, the pressure roller operating structure is disadvantageously large in the number of components, intricate in construction and high in manufacturing cost. In general, the lever 5 and the cam roller 6 are laterally provided relative to the platen 1 so that they do not obstruct the operations of the other components comprising the printer. Therefore, when the pressure roller 7 is urged against the platen 1, the pressure may not be uniform over longitudinal length of the platen.

In view of the foregoing, an object of this invention is to provide a sheet feeding device for a printer in which the pressure rollers can be uniformly pressed against the platen, and which reduces the number of components needed for proper sheet-feeding operation which thus leads to a more simplified construction and lower manufacturing cost.

The sheet feeding device for an impact-type printer in accordance with the present invention preferably includes pressure rollers rotatably mounted to a flexible leaf spring member provided below the platen. A cylindrical shaft to movably mount print heads in confronting relationship with the platen defines a planar cut portion which, together with the cylindrical surface of the shaft, establishes a cam surface. One end portion of the leaf spring member is supported by the cut portion so that when the guide shaft rotates, the leaf spring member is flexibly displaced upwardly with respect to the platen thereby causing the pressure rollers to press against the platen due to the transition between the substantially planar surface of the cut portion and the cylindrical outer surface of the shaft.

According to the present invention, one of the guide shafts for supporting the printing mechanism also functions as part of the structure for pressing the pressure rollers against the platen. Accordingly, the number of components of the device is greatly reduced as compared to the number of components needed in conventional sheet-feeding devices. The leaf spring member can be readily formed and assembled into the device of the present invention merely by placing it on the guide shaft below the platen. Therefore, the sheet feeding device of the present invention can be readily assembled thereby lowing manufacturing cost.

In the device of the present invention, the leaf spring member extends longitudinally relative to the platen and thus the pressure rollers mounted on the leaf spring member are uniformly pressed against the platen. Furthermore, the pressure of the pressure rollers is reinforced due to elastic deformation of the leaf spring member which occurs when the pressure rollers are in pressing engagement with the platen. Therefore, the printing sheet is uniformly urged against the platen by the pressure rollers as to achieve positive feed of the paper sheet which avoids skewing of the sheet upon feeding.

Further aspects and advantages of the present invention will become more apparent after careful consideration is given to the following detailed description thereof in conjunction with the accompanying drawings.

Reference will hereinafter be made to the accompanying drawings wherein like reference numerals throughout the various Figures denote like structural elements and wherein:

FIG. 1 is a side view showing a conventional sheet feeding device for an impact-type printer;

FIG. 2 is a perspective view showing essential components of an impact-type printer in which the present invention is utilized;

FIG. 3 is an exploded perspective view of the impact-type printer shown in FIG. 2;

FIG. 4 is a detailed perspective view of a sheet feeding device according to the present invention; and

FIGS. 5 and 6 are side views respectively showing disengagement and engagement of the sheet feeding device shown in FIG. 4 relative to a platen.

As shown in FIGS. 2 and 3, the present invention includes a pair of base frames 11 which are rigidly fixed on a base plate 10 in such a manner that base frames 11 are separated yet in parallel orientation with one another. Parallel adjusting and supporting shafts 12, 13 are provided so as to span the distance between the base frames 11. A planar recessed cut section 14 is defined in the cylindrical outer surface of the adjusting shaft 12 and extends for a predetermined dimension between the base plates 11 in the longitudinal direction of shaft 12. Planar cut section 14 together with the cylindrical outer surface of shaft 12 together define a cam surface, the purpose of which will be described in more detail below.

A head carriage 15 is mounted for reciprocal movement along both of the adjusting shaft 12 and the supporting shaft 13. More specifically, the supporting shaft 13 is inserted into hole 15a defined through the body 15b of the head carriage 15, while the adjusting shaft 12 is inserted through aligned holes 15c formed through a pair of supporting frames 151 which extend from the body 15b of the head carriage 15 towards support wall 26. (Only one frame 151 and its corresponding hole 15c are shown in FIGS. 2 and 3.) A printing mechanism 17 is fixedly provided on the head carriage 15 and includes a plurality of printing heads 16 arranged in side-by-side fashion in the direction of a printing line upon a printing sheet. The supporting frames 151 are positioned between respective lateralmost ones of leaf spring members 25 (to be described below) and base frame 11.

A pair of side frames 18 are provided on the outer surfaces 11a of the base frames 11, respectively. Two end portions 12a of the adjusting shaft 12 protrude outwardly from the outer surfaces 11a of base frames 11 and are fixedly mated with a respective aperture 18a defined substantially at the middle portions of the side frames 18 as shown more clearly in FIG. 2. The side frames 18 define cam grooves 181 which are sized and configured to accept a respective one of the rotatable eccentric cams 19 provided at both ends of the supporting shaft 13. Therefore, as the supporting shaft 13 rotates, the side frames 18 pivot about an axis established by the adjusting shaft 12 through an angle corresponding to the amount of eccentricity of the eccentric cams 19.

A platen 20 is journally supported between the side frames 18 by means of central shaft 21. More specifically, the side frames 18 define receiving grooves 182 respectively formed in the upper edge portions 182a thereof. End portions 21a of the central shaft 21 longitudinally extend from both ends of the platen 20 and define an annular recess 21b registrable with receiving grooves 182 so as to be rotatably supported thereby. Thus, the platen 20 is positioned over the two shafts 12 and 13 by means of the side frames 18 in such a manner that the platen 20 confronts the printing heads 16. As the side frames 18 pivot about the axis established by the adjusting shaft 12 as described above, the platen 20 is responsively moved through an arc so as to be displaced towards or away from the printing heads 16 in dependence upon the direction of pivotal movement of the side frames 18 about shaft 12.

An arcuate paper guide 22 is fixedly held between the base frames 11 and is positioned in such a manner that a gap of predetermined dimension is defined between the platen 20 and the paper guide 22. A printing sheet A (see FIG. 6) is thus insertable into the gap and is arcuately guided along the platen 20 by the paper guide 22. A plurality of slots 23 are formed in the bottom of the paper guide 22 in such a manner that the slots 23 are aligned in the longitudinal direction of the paper guide 22 so as to accept respective ones of a plurality of pressure rollers 24. Thus, a portion of each roller 24 extends through its respective slot 23 so as to press the sheet A against the platen 20. The paper guide 22 may be held between the side frames 18.

As shown in FIGS. 2-4, the pressure rollers 24 are longitudinally arranged, relative to platen 20, on a respective leaf spring member 25. Each pressure roller 24 has a central shaft 241 rotatably engaged with recesses 251 formed in the leaf spring member 25. The leaf spring member 25 is preferably a rectangular flat plate with the pressure rollers 24 extending across rectangular holes 252 formed in the leaf spring member 25. One side portion 25a of the leaf spring member 25 is coupled to the upper edge 26a of mounting wall 26 on the base plate 10. The one side portion 25a of the leaf spring member 25 is preferably secured to the upper edge 26a of the mounting wall 26 by mating engagement between the supporting pieces 261 of wall 26 and mounting holes 253 formed in the one side portion 25a. The other side portion 25b of the leaf spring member 25 rests upon the recessed cut portion 14 of the adjusting shaft 12.

Therefore, as the adjusting shaft 12 rotates, the leaf spring member 25 is flexibly vertically displaced against its own bias force through an angle corresponding to the step between the cylindrical surface of the shaft 12 and the recessed cut portion 14. In such a manner, the recessed cut portion 14 and the cylindrical surface of shaft 12 establish a cam surface which displaces the pressure rollers 24 into and out of pressing engagement relative to the sheet A on the platen 20 in response to rotation of the shaft 12 in opposite rotational directions, respectively.

The sheet A is inserted from above between the platen 20 and the paper guide 22 as shown in FIG. 5 and is held between the platen 20 and the pressure roller 24 as previously described. As the platen 20 rotates about its longitudinal axis established by central shaft 21, the sheet A is respectively moved along the cylindrical surface of the platen 20, guided by the paper guide 22, so that it exits towards the left of platen 20 as viewed in FIGS. 5 and 6. The printing heads 16 of the printing mechanism 17 are then caused to confront printing hammers (not shown), such that the printing heads 16 are selectively hammered to print upon the sheet A on the platen 20.

When the other end portion 25b of the leaf spring member 25 biasingly rests upon the recessed cut portion 14 of the adjusting shaft 12, the pressure rollers 24 are in spaced-apart relationship relative to the platen 20 as shown in FIG. 5. On the other hand, when the sheet A is inserted between the platen 20 and the paper guide 22, the adjusting shaft 12 is then rotated through a predetermined angle to responsively cause engagement of the other end portion 25b of the leaf spring member 25 to be transferred from the recessed cut portion 14 of the shaft 12 to the cylindrical surface of the shaft 12. As a result, the leaf spring member 25 is upwardly displaced through the angle corresponding to the incremental step distance between the recessed cut portion 14 and the cylindrical surface of the adjusting shaft 12 with the one side portion 25a of leaf spring member 25 acting as a fulcrum. As the leaf spring member 25 is upwardly displaced, the pressure rollers 24 are moved as indicated by the arrow 100 in FIG. 6 to press the sheet A against the platen 20 through the openings 23 of the paper guide 22. In this manner, the rotation of the adjusting shaft 12 raises the leaf spring member 25 with uniform pressure and stroke, and therefore the pressure rollers 24 are responsively pressed against the cylindrical surface of the platen 20 under uniform pressure. When the pressure rollers 24 are pushed against the platen 20, the leaf spring members 25 are elastically deformed between end portions 25a and 25b as can be seen in FIG. 6. The reaction force of this elastic deformation is thus exerted through the pressure rollers 24 towards the platen 20. Accordingly, the pressure of the pressure rollers 24 is reinforced and the pressure rollers 24 are positively biased against the platen 20 due to the resultant elastic deformation of leaf spring members 25 and thus the sheet A can be accurately moved with less skew.

When, under the conditions shown in FIG. 6, the adjusting shaft 12 is again rotated through a predetermined angle, the engagement between the other side portion 25b of the leaf spring member 25 and the recessed cut portion 14 of the shaft 12 is reestablished so that the leaf spring member 25 is displaced downwardly under its own bias force to cause the pressure rollers 24 to be moved away from the platen 20 and assume the position as shown in FIG. 5.

In the embodiment described above, the recessed cut portion 14 has been shown as being formed in the cylindrical surface of the adjusting shaft 12 so as to cause displacement of the leaf spring member 25. However, other suitable cam surfaces, such as eccentric or elliptical cams, may be formed on the adjusting shaft 12 to perform similar functions.