Abstract:
A sheet cutter cuts a portion of a continuous sheet, discharged through a gap between a pair of moving and stationary knives respectively having arc-shaped and straight knife edges. A motor rotates a pair of rotatable, identical gear wheels engaged with each other and opposed to the moving knife and having a pair of respective link arms thereon. Each link arm has a first end connected to a peripheral position of the respective gear wheel by a pivot thereon and a second end connected to the moving knife by a pin inserted into a respective one of a pair of horizontally extending slits in the moving knife. Rotating motion of the gear wheels is transformed into a reciprocating motion of the moving knife against, and relatively to, the stationary knife, in which the second end of each link arm assumes one of two opposing positions, depending respectively upon a current one of opposite rotating directions of the respective gear wheel, such that one or the other rotating direction of the motor results in the reciprocating motion of the moving knife with a stroke either to cut the sheet completely or incompletely.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to a sheet cutter for cutting a sheet, particularly to one having a motor driven push cutter for cutting a portion of a continuous sheet discharged from a printer such as for hand held electric appliances. 
     2. Description of the Related Art 
     A role of paper used in a printer of some hand held electric appliances, such as a terminal register used in restaurants, is required to be cut bilaterally, namely, sometimes a printed part of the paper is cut off completely as a receipt for a customer and at other times a plurality of printed parts are cut incompletely between the successive printed parts as a series of receipts for a group of respective customers, the plurality of printed parts remaining connected by a central uncut part of narrow width. Each of the printed parts can be easily separated from each other by hand later on if every customer wants to have his. The former is often call full cut and the latter, half cut. 
     FIG. 1 is an exploded view of a main part of a prior art sheet cutter, and FIG. 2 is a front view of the main part of the prior art sheet cutter, which is looked at along an arrow indicated by a letter A. The sheet cutter 1 comprises a driving unit, or member, 11 mounted on a side wall of a chassis 1a, a rotating disc 12 assembled in the driving unit 11, a moving knife unit 13 making a moving knife 131 moved upwardly and downwardly by mounting both on the side wall of the chassis 1a and the rotating disc 12, and a stationary cutter unit 14 having a stationary knife 141 on it opposed to the moving knife 131. The driving unit 11 further includes a gear wheel 111 freely rotatable around a pivot P (i.e., an axle, or a shaft) mounted on a side wall of the chassis 1a, a worm gear 115 engaging with the gear wheel 111, and a driving motor 114 mounted on the side wall of the chassis 1a, a drive shaft of which is directly connected with an axle (i.e., a shaft) of the worm gear 115. Both a rotation pivot (i.e., shaft) 112, for the rotating disc 12, and a first sliding pin 113, restricting an angle of rotation of the rotating disc 12, are formed on respective peripheral positions of the gear wheel 111, projecting from an exposed side of the gear wheel 111. The rotating disc 12, having nearly the same diameter as that of the gear wheel 111, has a pivot bore 12a penetrated by the pivot 112 and an arcuate slit 12b for receiving therein and allowing the first sliding pin 113 to move therein, and which limits the angle of rotation of the rotating disc 12, and a second sliding pin 12c projecting from the exposed side of the gear wheel 111 into an elongated slot, or base, 123b of link arm 132 and which propagates driving forces to the moving knife unit 13. Thus, the rotating disc 12 is rotatable within the limited angle defined by the arcuate slit 12b, relatively to the gear wheel 111, when the rotating disc 12 is mounted on the gear wheel 111 by engaging the pivot 112 with the pivot bore 12a and the first sliding pin 113 with the slit 12b. The moving knife unit 13 comprises a moving knife 131 and the above-noted link arm 132, jointed with each other. The moving knife 131 has a vertical arm 131d on the upper side, an angle knife 131b with a setback area of a square notch 131a at the central region S on the lower side, and a pair of legs 131c. The link arm 132 has a pivot bore 132a on a first end engaged with a pivot 1a&#39; protruding from the side wall of the chassis 1a and a long bore 132b engaged with the second sliding pin 12c of the rotating disc 12 on a second end. The link arm 132 is jointed with the moving knife 131 by a pin 132c (FIG. 2) at the upper end of the vertical arm 131d such that the link arm 132 is rotated around the pin 132c in a plane. 
     The stationary knife unit 14 comprises a knife stage 142 and a stationary knife 141 mounted on the knife stage 142, in which the stationary knife 141 is arranged in the foreground relative to the moving knife 131 in FIG. 1. The knife stage 142 has a narrow groove 142a into which the moving knife 131 is inserted. The narrow groove 142a has a pair of guiding portions 142b on both ends, which guide the respective legs 131c. A printed portion of continuous paper 15 is discharged through a gap between knife edges of the moving and stationary knives in the foreground direction indicated by a letter B. 
     FIGS. 3 and 4 are front views of the main part of a sheet cutter of a first prior art device, to explain full-cut and half-cut operations, respectively. In FIG. 3, the gear wheel 111 rotates clockwise about its axis, or pivot, P as indicated by a letter B 1  by the normal rotation of the motor 114, which causes a pivotal motion of the rotating disc 12 in the direction of an arrow as indicated by a letter C 1  by reactions from the first sliding pin 113 to the slit 12b and from the long bore 132b to the second sliding pin 12c. The reverse rotation of the motor 114 causes a counter clockwise rotation of the gear wheel 111 as indicated by a letter B 2  and then a pivotal motion of the rotating disc 12 in the direction of an arrow as indicated by a letter C 2  as shown in FIG. 4. Since a clockwise rotating radius R 1  of the rotating disc 12 is larger than a counter clockwise rotating radius R 2 , a down stroke of the moving knife 131 for clockwise rotation of the rotating disc 12 is longer than that for counter clockwise rotation of the rotating disc 12. The longer stroke of the moving knife 131 cuts off the discharged portion of continuous paper completely, while the shorter stroke cuts it incompletely by stopping the moving knife 131 such that the setback area of a square notch 131a at the central region on the lower side of the moving knife 131 shown in FIG. 1 is maintained above the upper surface of the paper. Therefore, the full-cut and half-cut of the paper can be carried out by selecting the normal and reverse rotations of the motor 114, respectively. 
     FIG. 5 is a front view of the main part of a prior art sheet cutter to explain a first drawback. The first drawback of the prior art is the fact that since the link arm 132 jointed with the moving knife 131 by the pin 132c is pivoted at 132a, a total force applied to the pin 132c denoted by a letter F 1  has a horizontal component of force when the moving knife 131 is pushed down. Therefore, the horizontal component of force causes an angular momentum in a plane including the moving knife which eventually often hinders the moving knife from moving down smoothly. 
     FIG. 6 is a front view of the main part of a prior art sheet cutter to explain a second drawback. The second drawback of the prior art is the fact that since the square notch 131a having a width denoted by a letter b at the central region on the lower side of the moving knife 131 has no sharp knife edge, a cross-section of the paper is not as sharply-cut in the fall-cut operation, wherein the cutting portion at the central region is protruded by a length corresponding to thickness of the knife edge denoted by a letter t from the other cutting portions in both sides 15a of the paper 15, and wherein, in the half-cut operation, the uncut portion having width 15b causes an irregular cutting shape when it is torn off by hand, which is not favorable in appearance. 
     SUMMARY OF THE INVENTION 
     An object of the present invention is to provide a sheet cutter including a pair of moving and stationary knives, in which the moving knife can move against a stationary knife smoothly along a pair of parallel cutter guides by pushing downwardly or pulling upwardly at two symmetrical points with the identical forces in parallel to the cutter guides, such that a total angular momentum on the moving knife around a gravitational center thereof vanishes (i.e., is nil). 
     Another object of the present invention is to provide a sheet cutter including a pair of moving and stationary knives, in which the moving knife has a thinner knife edge in the central part compared to the rest thereof, such that a cross-section of cut-off paper is smooth and clear-cut when the paper is cut off completely. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The present invention will be more apparent from the following description, when taken to conjunction with the accompanying drawings, in which: 
     FIG. 1 is an exploded view of the main part of a prior art sheet cutter. 
     FIG. 2 is a front view of the main part of the prior art sheet cutter. 
     FIG. 3 is a front view of the main part of a prior art sheet cutter to explain a full-cut operation. 
     FIG. 4 is a front view of the main part of a prior art sheet cutter to explain a half-cut operation. 
     FIG. 5 is a front view of the main part of a prior art sheet cutter to explain the first drawback. 
     FIG. 6 is a front view of the main part of a prior art sheet cutter to explain the second drawback. 
     FIG. 7 is an exploded, perspective view of a main part of a sheet cutter of a first embodiment according to the present invention. 
     FIG. 8 is a front view of the main part of the sheet cutter shown in FIG. 7 according to the present invention. 
     FIG. 9 is a front view of the main part of the sheet cutter shown in FIG. 7 to explain a full-cut operation. 
     FIG. 10 is a front view of the main part of the sheet cutter shown in FIG. 7 to explain a half-cut operation. 
     FIG. 11 is a perspective view of a main part of a sheet cutter of a second embodiment according to the present invention. 
     FIG. 12 is an enlarged side view of the moving and stationary knives of the sheet cutter shown in FIG. 11. 
     FIG. 13 is a perspective view of the main part of a sheet cutter for the third embodiment according to the present invention. 
     FIG. 14 is an enlarged bottom view of the center part of the moving knife of the sheet cutter shown in FIG. 13. 
     FIG. 15 is an enlarged front view of the center part of the moving knife of the sheet cutter shown in FIG. 13. 
     FIG. 16 is an exploded view of a main part of a sheet cutter of a fourth embodiment according to the present invention. 
     FIG. 17 is a front view of the main part of the sheet cutter shown in FIG. 16 to explain a half-cut operation. 
     FIG. 18 is a schematic top view of a pair of convex moving and flat stationary knives of a fifth embodiment according to the present invention. 
     FIG. 19 is a schematic top view of a pair of V-shaped moving and flat stationary knives of a sixth embodiment according to the present invention. 
     FIGS. 20 and 21 are front view of moving knives having setback areas of various shapes according to the present invention. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Reference will now be made in detail to the preferred illustrated embodiments of the invention, examples of which are illustrated in the accompanying drawings. While the invention will be described in conjunction with the preferred illustrated embodiments, it will be understood that they are not intended to limit the invention to these embodiments. On the contrary, the invention is intended to cover alternatives, modifications and equivalents, which may be included within the spirit and scope of the invention as defined by the appended claims. 
     Common reference numbers and symbols are used throughout figures below whenever mechanical parts or functions are same. 
     FIGS. 7 and 8 are an exploded, perspective view and a front view, respectively, of the main part of a sheet cutter of a first embodiment according to the present invention, in which FIG. 8 is viewed in the direction of an arrow denoted by a letter A shown in FIG. 7. 
     A sheet cutter 2 shown in FIG. 7 comprises a driving unit 21 mounted on a side wall of the chassis 2a, a pair of link arms 22 connected with the respective gear wheels 211, 215 (described later) which are components of the driving unit 21, a moving knife 23 connecting with the link arms 22, and a cutter unit 24. The cutter unit 24 comprises a stage 242 having a pair of parallel guides 242a for guiding the moving knife 23 to slide upwardly or downwardly, a stationary knife 241 opposing to the moving knife 23, and a narrow groove 242b for receiving the pair of legs 131c of the moving knife 23. The driving unit 21 comprises a driving motor 213 secured to the side wall of the chassis 2a with a shaft extending parallel to the side wall having a worm gear 214 on an end portion of, and so as to rotate with, the shaft, a worm gear 211 with a shaft attached to the side wall rotated by engaging with the worm gear 214, and a pair of identical gear wheels 212 and 215 engaged with each other, the first one 212 being fixed to the worm gear 211 with the same axis (i.e., shaft) as that of the worm gear 211 and the second one 215 being rotatable in the same plane as that of the first one 212 with a shaft attached to the side wall. The first and second gear wheels 212, 215 have respective pivots 212a, 215a and respective pairs of stoppers 212b -1 , 212b -2 , and 215b -1 , 215b -2  projecting out of the exposed sides of the gear wheels, respectively. Each of the link arms 22 has a through hole at one end into which the respective one of the pivots 212a, 215a is inserted. The pivots 212a and 215a are located in the neighborhood of the respective periphery of the gear wheels 215 and 215, respectively. Each pair of the stoppers 212b -1 , 212b -2  and 215b -1 , 215b -2  limits the respective rotating angle of the link arms 22, respectively. The stoppers 212b -1 , and 215b -1  are located in the neighborhood of the respective centers of the gear wheels 212 and 215, respectively, while the stoppers 212b -2  and 215b -2  are located in the neighborhood of the respective peripheries of the gear wheels 212 and 215, respectively. Each of the link arms 22 15 is connected at a first end to, and is rotatable around, the respective one of the pivots 212a, 215a, and has a pin 22b projecting out of the exposed side at the second end of each thereof, which is inserted into the respective one of a pair of horizontally extended slits 23a in the moving knife 23. The horizontally extended slits 23a in the moving knife 23 are located symmetrically to each other with respect to the vertical axis passing through the gravitational center of the moving knife 23, below the upper side 23c (FIGS. 7 and 8) of the moving knife 23 by a distance denoted by a letter a (FIG. 7), and having an identical length on both sides, which is long enough to cover the horizontal maximum moving range of the pins corresponding to the overall range of the limited rotating angle. In this configuration, when the motor 213 drives the worm 214, rotation of the worm 214 causes a normal (i.e., forward) rotation of the gear wheel 212 and the reverse rotation of the gear wheel 212 through the worm gear 211. Rotation of both the gear wheels gives rise to sliding both pins 22b along the horizontally extended slits 23a on the moving knife 23, symmetrically to each other with respect to the vertical axis passing through the gravitational center of the moving knife 23. Consequently, the symmetrical horizontal motion of both pins 22b makes the moving knife 23 move upwardly or downwardly, depending upon a rotating direction of the motor 213. It should be noted that since the pins move symmetrically to each other, the moving knife 23 moves upwardly or downwardly smoothly along the pair of parallel guides 242a. This is because the horizontal components of the forces exerted on the slits 23a by the respective pins always cancel out each other, and only the vertical components of the forces are exerted on the slits in parallel to the pair of guides 242a. In other words, there is no net angular momentum around the gravitational center of the moving knife during vertical movements of the moving knife. Thus, this structural feature results in smooth vertical movements of the moving knife. 
     Another structural feature according the present invention are that the moving knife 23 has an asymmetric knife edge 23b which consists of two knife edges, both inclined relatively to the stationary knife edge 241, and that one knife edge is slightly longer than the other. Since this knife edge has a setback area of a triangular shape 231 in the central region (shown in FIG. 8 as a shaded area) and which is inclined relatively to the stationary knife edge 241, the uncut region 15b of the paper for the half-cut can be left with a larger allowable error in the stroke of the moving knife than that of the moving knife having no setback area, such as a simple inverse V-shape knife edge, and that the whole paper can be cut off with a clear-cut cross-section for the full-cut. 
     The inclined knife edge in the setback area gives another favorable effect, in that the uncut region 15b shown in FIG. 6 can be chosen to be any desired width by adjusting the stroke of the moving knife, which can leave a better shape of a rupture pattern by narrowing the width of the uncut region 15b as desired for the half-cut when the uncut region 15b is torn by hand. The setback area 231 according to the present invention generally has an inclined upper side 231a. FIGS. 20 and 21 are some modified cases for the setback area. Either one can pronounce the beneficial effects similar to the moving knife shown in FIG. 8. 
     FIGS. 9 and 10 are front views of the main part of the sheet cutter shown in FIG. 7 to explain full-cut and half-cut operations, respectively. 
     In FIG. 9, the motor 213 rotates the worm gear 214 in the direction of an arrow denoted by a letter C, and then rotates both the worm gear 211 about its axis and the first gear wheel 212 clockwise about its axis, or pivot, P3 as indicated by an arrow denoted by a letter C 1 , which produces an accompanying counter clockwise rotation of the second gear wheel 215 as indicated by an arrow denoted by a letter C 2 . Eventually, both the link arms 22 rotate in mutually opposite directions indicated by arrows C 1  &#39; and C 2  &#39;, to relatively to each other and to the directions of C 1  and C 2  of to the first and second gear wheels 212, 215, respectively. Therefore, the first and second gear wheels 212, 215 rotate under conditions that (i.e., to a limit at which) the link arms 22 come into contact with the respective stoppers 212b -2  and 215b -2 , respectively. 
     On the other hand and as shown in FIG. 10, when the motor 213 rotates the worm gear 214 together in the direction of an arrow denoted by a letter C&#39; (FIG. 10), the first gear wheel 212 with the worm gear 211 rotate counter clockwise, as indicated by an arrow denoted by a letter C 3  and then the second gear wheel 215 rotates clockwise as indicated by an arrow denoted by a letter C 4  as shown in FIG. 10. Consequently, the first and second gear wheels 212, 215 rotate about respective thin respective prints P3 in the respective, relatively opposite C 3  &#39; and C 4  &#39; directions under conditions that (i.e., to a limit at which) the respective link arms 22 contact the respective stoppers 212b -1  and 215b -1 , respectively. The rotating radii R 3 , R 4  of the link arms 22 are defined by distances between the center of the first gear wheel 212 and the pin 22b for the clockwise and counter clockwise rotations of the first gear wheel 212 as shown in FIGS. 9 and 10, respectively, wherein the rotating radius R 3  is larger than the rotating radius R 4 . This is because the stoppers 212b -1  and 215b -1  are located in the neighborhood of the respective rotating centers of the first and second gear wheels 212, 215, respectively, while the stoppers 212b -2  and 215b -2  are located in the neighborhood of the respective peripheries of the first and second gear wheels 212, 215, respectively. The difference in radius results that the vertical stroke of the moving knife in FIG. 9 is longer than that in FIG. 10. Therefore, it is possible that the longer stroke as shown in FIG. 9 is applied to the full-cut of the paper, and the shorter stroke as shown in FIG. 10 is applied to the half-cut by optimizing the position of the stationary knife against the moving knife. In other words, the full-cut and half-cut operations can be determined by selecting a rotating direction of the motor 213. 
     FIGS. 11 and 12 are a perspective view of the main part of a sheet cutter for the second embodiment according to the present invention and an enlarged side view of the moving and stationary knives viewed along the direction denoted by a letter B shown in FIG. 11, respectively. 
     The cutter unit 31 for the second embodiment can be obtained by mounting the stationary knife 241 on the stage 242 with an inclination of the angle θ, which may be smaller than 45 degrees, to the moving knife such that only an edge 241a&#39; of the upper side 241a has contact with the moving knife 23 in the cross-section as shown in FIG. 12. The cutter unit 31 has line contact between the flat moving and stationary knives instead of an area contact in the prior art (in which θ=0°); as a result, a stress on the linear contact area between the flat moving and stationary knives is much less than that on the surface area contact of the prior art, and which improves cutting performance. Needless to say, the flat moving and stationary knives are easy to fabricate and less expensive. When the inclination of an angle θ was chosen about three degree (θ=3°), the cutting performance was improved considerably without an appreciable wear of the knife edges. 
     If further improvement in cutting performance is desired, it can be done by providing a pair of moving and stationary knives one of which is bent against another when it is seen from the top position. For instance, FIG. 18 is a schematic top view of a pair of convex moving knife 232 and a flat stationary knife 242 with contact points Q, Q&#39;, while FIG. 19 is a schematic top view of a pair of V-shaped moving knife 233 and a flat stationary knife 243 with contact points Q, Q&#39;. Curvature and bending angle of both the moving knives are exaggerated for illustration. In either case, the moving knife always keeps contact with the respective flat stationary knife only at symmetrical two points Q, Q&#39; on the knife edges during the whole cutting process. In other words, the stress is always concentrated on the two points Q, Q&#39; just at which the paper is cut. The cutting starts at both sides of a sheet of paper, then cutting points approach to each other, and finally the two points get together (i.e., connect, or join) at the central part when the paper is cut off completely. 
     FIG. 13 is a perspective view of the main part of a sheet cutter of the third embodiment according to the present invention. FIGS. 14 and 15 are enlarged bottom and front views of the center part of the moving knife shown in FIG. 13. 
     The moving knife 41 has a recessed area on the back side 41a in the central region indicated by T. The recessed surface 41b is sunken, or recessed relatively to, from the back side 41a by depth of t--t&#39; where t&#39; and t are respective thicknesses of the central region indicated by T and that of the rest of the moving knife, respectively. The moving knife having the recessed area in the central region improves a cutting cross-section for full-cut case and makes a width of the uncut-region 15b narrower for the half-cut, thereby to leave a better appearance for the torn portion. As an example, when t and t&#39; were chosen to be 0.8 mm and 0.3 mm, respectively, an appearance of the torn portion was remarkably improved without any degradation of mechanical strength in the moving knife. 
     FIGS. 16 and 17 are exploded, perspective and front views, respectively, of the main part of a sheet cutter 5 of a fourth embodiment according to the present invention. 
     The sheet cutters of the fourth embodiment comprises a driving unit 51 and a cutter unit 24. The former is essentially the same as the unit 21 of the first embodiment 2 shown in FIG. 7 except that a pair of the gear wheels 212, 215 with respective stoppers are replaced by a new pair of identical gear wheels 511, 512. Namely, the first gear wheel 511 has a sector-shaped groove 511a into which a link arm 22 is sunken, to undergo a pivotal motion around a pivot 511b, while the gear wheel 512 has a sector-shaped groove 512a into which a link arm 22 is sunken to undergo a pivotal motion around a pivot 512b. Both the link arms 22 are limited their pivotal motion within, the respective sector-shaped grooves. Particularly, each pair of side walls in the sector-shaped grooves acts as a pair of stoppers for the respective link arm 22. The resultant benefits of this embodiment are to save the space between the side wall and the cutter, and to simplify the manufacturing process of the cutter unit such that it is easier to make the gear wheel having a sector-shaped groove than that having a pair of stoppers such as 212b -1 , 212b -2 . These advantages provide a sheet cutter which is smaller and less expensive than that of the prior art.