Patent Publication Number: US-5893558-A

Title: Sheet guidance channel

Description:
FIELD OF THE INVENTION 
     The invention relates to a sheet guidance channel comprising a pair of opposite surfaces in which are formed elongated raised beads extending in the transport direction and being arranged in pairs opposite to each other, thereby restricting the height of the sheet guidance channel. 
     BACKGROUND OF THE INVENTION 
     Sheet transport in conventional copiers generally takes place in sheet guidance channels closed on both sides and having a constant height. Transport rollers are arranged in pairs in the sheet guidance channel in order to convey the sheet being transported through the sheet guidance channel. In addition, ribs or guide elements are formed over the full length of the sheet guidance channels for guiding the sheet. Since these ribs or guide elements along the transport route contact continually the same part of the sheet being transported, damage or contact marks can occur on the sheet. 
     The patent DE-A-33 13 055 describes a feeder for photographic copiers. Here a cover is shown that is shown on its side facing a sheet stack with full-length guide ribs and additional supporting ribs. The guide ribs project further forward than the supporting ribs, thereby minimizing the contact of the ejected sheet with the guide system. 
     Document JP-A-4-277763 discloses a device for avoiding in an image faults or irregularities that are caused by the guidance of a sheet. The guide surface has two inclined surfaces designed such that only the image-free areas of the copied paper are touched during transportation by the guide surfaces. This prevents the generation of faults or irregularities in an unfixed image. 
     SUMMARY OF THE INVENTION 
     The present invention is to provide a sheet guidance channel designed such that damage or the formation of contact marks on the sheet surface are avoided. This is achieved in accordance with the invention in that, relative to the central axis of the surfaces in the transport direction, the elongated raised beads are inclined by an angle α, and in that the raised beads extend in the transport direction only over limited portions of such surfaces. The advantage of the device in accordance with the invention is that in the sheet guidance channel formed by two opposite surfaces raised beads are provided which are inclined by an angle relative to the central axis of the sheet guidance channel. In addition, the raised beads extend only over limited portions of the surfaces of the sheet guidance channel. By this arrangement of the raised beads, it is possible to achieve a movement of the contact point of the raised beads relative to the sheet surface. 
     Further advantageous embodiments of the invention can be found in the dependent claims. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The subject matter of the invention is described on the basis of a preferred embodiment shown in the drawing. In the drawings: 
     FIG. 1 is a plan view of a surface forming the sheet guidance channel; 
     FIG. 2 is a perspective partial view of the arrangement of the two surfaces forming a sheet guidance channel; 
     FIG. 3 is a diagrammatic side view of the sheet guidance channel with the transport rollers engaging in the sheet guidance channel; 
     FIGS. 4a and 4b are respectively a plan view of an embodiment of the arrangement of the raised beads relative to the transport rollers, and a perspective view of the embodiment shown in FIG. 4a. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A sheet guidance channel is formed from two opposite surfaces. The sheet guidance channel can be designed curved or straight. The description below confines itself to a straight sheet guidance channel. 
     An embodiment of a surface 2 limiting a straight sheet guidance channel either upwards and downwards is shown in FIG. 1. The transport direction of a sheet is reproduced by the arrow A--A. The sheets are conveyed through the channel in such a way that the sheets are centered on a central axis M of the sheet guidance channel that is parallel to the transport direction A--A. In addition, it is conceivable in another embodiment that the sheets are not centered relative to the central axis M, but are alignable on an edge (not shown) or corner (not shown) of the copier. The following description relates to the embodiment in which the sheets are centered relative to the central axis M. 
     On both sides of the central axis M, several rectangular recesses 4 tapering to a point in the transport direction A--A are provided in the surface 2. Through each of the recesses 4 protrudes a roller 6 that interacts with the other rollers 6 arranged in the recesses to move the sheet to be conveyed from an inlet 5a to an outlet 5b. The rollers 6 are arranged in pairs on a shaft 8. In the embodiment shown here, four shafts are provided, each of which is provided at one end with a drive roller 10. 
     Furthermore, several elongated raised beads 12 are provided on the surface 2 and are arranged obliquely to the transport direction A--A. The elongated raised beads can be divided into two groups 12a and 12b. The first group 12a is provided on the left of the central axis M and the second group 12b on the right. All raised beads 12 of the first group 12a are inclined by an angle α relative to a line parallel to the central axis M, and all raised beads 12 of the second group 12b are inclined by an angle -α relative to a line parallel to the central axis. The elongated raised beads 12 extend in the transport direction A--A only over portions of the surface 2. As further shown in FIG. 1, those elongated raised beads the least distant from the central axis M end at the recess 4. The raised beads of the first group 12a and the raised beads of the second group 12b are inclined relative to the central axis such that the contact points move laterally outwards to the lateral sheet edges when a sheet passes through in the transport direction A--A. By this it is achieved that the transported sheet is laterally stretched. 
     FIG. 2 is a perspective partial view of a straight sheet guidance channel formed substantially from an upper surface 2a and a lower surface 2b arranged opposite one another. At the inlet several tabs 14a of the upper surface 2a are bent upwards at an angle. In the same way, several tabs 14b of the lower surface 2b are bent downwards at a certain angle. The funnel-like arrangement achieved in the transport direction facilitates the entry of the sheet into the sheet guidance channel. On the upper surface 2a, side walls 16a projecting vertically upwards are provided to give the upper surface additional stability. In addition, guides, spacers, retaining elements etc. (not shown) can be provided in the side walls. In the same way, downward-projecting side walls 16b are provided on the lower surface 2b. The side walls 16b attached parallel to the transport direction A--A are provided with several holes 18 in which are mounted the shafts 8 for driving the rollers 6 (mountings not shown). The elongated raised beads 12 are arranged on both the upper surface 2a and on the lower surface 2b such that the raised beads 12 are always opposite to one another in pairs. In this way, a local constriction of the sheet guidance channel is achieved in the areas of the raised beads. Furthermore, recesses 4a and 4b are provided in the upper surface 2a and the lower surface 2b through which the rollers 6a arranged above the upper surface 2a protrude in order to interact with the rollers 6b arranged underneath the lower surface 2b. The sheet is transported through the roller nip 20 (see FIG. 3) thus created. 
     The constriction of the sheet guidance channel caused by the raised beads in the area of the roller nip 20 is best shown in FIG. 3. Part of the side wall 16 provided vertical from the upper surface 2a and parallel to the transport direction A--A is shown. Part of the side wall 16b provided vertical from the lower surface 2b is also visible. The roller 6a above the upper surface 2a has a bearing 22 attached inside a holder 24. Opposite the roller 6a a roller 6b is provided that is firmly connected to the rotating shaft 8 passing through one of the holes 18 provided in the side wall 16b. The roller 6a and the roller 6b protrude, as already mentioned, through the recesses and touch at their respective outer circumferences, thereby creating the roller nip 20. 
     In the illustration in FIG. 3, parts of the rollers 6a and 6b can be seen that are provided in the transport direction A--A in front of the rollers 6a and 6b shown here. That part of the sheet guidance channel between two consecutive roller pairs can be subdivided into three areas. A first area 26 of the sheet guidance channel immediately following a roller pair 6a, 6b in the transport direction A--A has a certain width determined by the clearance of the upper surface 2a from the lower surface 2b. The first area 26 is adjacent to a second area 28 and a third area 30 whose extent is determined substantially by the raised bead 12 provided in the upper surface 6a or lower surface 6b. The area 28 is used to keep the sheet to be transported clear of the upper or lower surface respectively and thereby prevent sticking of the sheet due to adhesion in those areas in which no raised beads are provided. The second area 28 has a steeper incline than the third area 30 adjacent to the second area 28. The third area 30, which is substantially longer than the second area 28, extends with a constant incline to the rollers 6a and 6b. The sheet guidance channel therefore narrows from the outlet of one roller pair to the inlet of the next roller pair. 
     FIGS. 4a and 4b show the arrangement of the elongated raised beads 12 in relation to the rollers. The plan view (FIG. 4a) onto the lower surface 2b shows that the elongated raised beads 12 are arranged in pairs in the vicinity of the rollers 6 or recesses 4 for the rollers. The elongated raised bead the least distant from the central axis M of the sheet guidance channel ends at an edge 32 of the recess 4 vertical to the transport direction A--A. The elongated raised bead 12 provided next to it is arranged such that the raised bead 12 in the transport direction A--A later projects from the surface 2b and extends far enough in the transport direction for the end of the raised bead 12 in the transport direction to be in the area of the shaft 8 of the roller 6. 
     The perspective view (FIG. 4b) of the arrangement of the elongated raised beads 12 also shows the form of the raised beads 12. FIG. 4b also shows a plan view onto a partial area of the lower surface 2b. The elongated raised beads 12 have a continuous and rounded outer contour, with the dimensions of the raised beads transverse to the transport direction A--A increasing as they extend further in the transport direction A--A. In the embodiment shown here, the cross-section through the raised beads has the form of an arc. In the embodiment shown in FIG. 4b, the ends of the raised beads 12 have (as already mentioned above) the form of an arc 34. If the raised bead 12 ends at a recess 4 for a roller 6, the arc 34 of the raised bead merges continuously into the edge 32 of the recess 4 arranged vertically to the transport direction A--A. If the raised bead 12 does not end at a recess 4, a penetration 36 in the lower surface 2b can be joined to it for production reasons in the transport direction A--A. Furthermore, a further embodiment is shown in FIG. 4b. Here the end of the raised bead 12 furthest from the central axis M of the sheet guidance channel coincides with the outer circumference of the shaft 8 on which the lower rollers 6b are attached. 
     The present invention has been described with respect to a preferred embodiment, however modifications can also be made that are within the skills of a person skilled in the art without leaving the scope of the claims below. 
     PARTS LIST 
     2 surface 
     2a upper surface 
     2b lower surface 
     4 recess 
     5a inlet 
     5b outlet 
     6 rollers 
     6a rollers above the upper surface 
     6b rollers below the lower surface 
     8 shaft 
     10 drive roller 
     12 elongated raised beads 
     14a tabs of upper surface 
     14b tabs of lower surface 
     16a side walls of upper surface 
     16b side walls of lower surface 
     18 hole 
     20 roller nip 
     22 bearing 
     24 holder 
     26 first area of sheet guidance channel 
     28 second area of sheet guidance channel 
     30 third area of sheet guidance channel 
     32 edge of recess 
     34 arc 
     36 penetration 
     A--A transport direction 
     M central axis of sheet guidance channel 
     α angle