System for aligning sheets in printers.

BACKGROUND OF THE INVENTION

Field of the Invention

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0001The present invention generally relates to systems for aligning sheets in printing machines and, more particularly, to systems for aligning sheets in inkjet printers and similar devices used in conjunction with microprocessor-based computers.

State of the Art

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0002In printers such as inkjet printers and similar devices used in conjunction with microprocessor-based computers, sheets must be quickly and uniformly manipulated so that one of their edges is in alignment with a linear guide surface. Such alignment is important, for example, in providing consistent printing margins from one sheet to the next. Alignment is also of value in reducing paper jams during printing.

0003United States Patent No. 4,384,298 discloses an X-Y plotter for plotting on a paper web without registration holes or similar means for maintaining web alignment. In particular, FIGURES 3a and 3b of the patent show idler rollers for feeding a paper web against stop members as the paper traverses a paper holding/driving assembly of a plotter. The patent states that, by allowing free play of the forward ends of the shafts for the idler rollers while not permitting free play on the rearward end of the same shafts, the edges of sheets can be continuously forced against stop members as the sheets are driven in either direction.

SUMMARY OF THE INVENTION

0004Generally speaking, the present invention provides a system for aligning individual sheets in parallel, abutting relation to a linear guide rail as the sheets travel on a generally planar surface toward a printing station. In the preferred embodiment, the alignment system includes a drive roller for driving individual sheets back and forth on the planar surface and a wobble roller mounted in opposition to the drive roller for pivoting in the direction of sheet travel so that the roller pulls the lateral edges of the sheets into parallel, abutting contact with the guide rail. Both the drive roller and the wobble roller are rubber covered, and the rubber coating on the drive roller has a durometer value less than the rubber coating on the wobble roller to provide a degree of compliance. In practice, the durometer of the rubber coating on the wobble roller is less than about seventy, while the durometer of the rubber coating on drive roller is less than about fifty-five.

BRIEF DESCRIPTION OF THE DRAWINGS

0005The present invention can be further understood by reference to the following description and attached drawings which illustrate the preferred embodiment of the invention. For purposes of clarity, identical parts are given the same reference numbers in the various drawing figures. In the drawings: <ul id="ul0001" list-style="none"><li>FIGURE 1 is a perspective view of a sheet alignment system according to the present invention; and</li><li>FIGURE 2 is a cross-sectional detail view, taken along line 2-2 in FIGURE 1 for viewing in the direction of the arrows.</li></ul>

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

0006FIGURE 1 shows one embodiment of an alignment system for manipulating sheets during their travel along a planar surface 5 toward a printing station (not shown). For purposes of simplicity of illustration, only a fragment of a single sheet is shown in the drawing. Typically, sheets are paper, but the other printable materials can be used.

0007Generally speaking, the alignment system in FIGURE 1 includes a rail-like linear guide member 9 and a tow-in means, generally indicated by the number 13, for aligning the sheets with respect to the linear guide member. In the illustrated embodiment, linear guide member 9 is depicted as a rail which extends in the intended direction of sheet travel and which is oriented to provide a guide surface 10 that extends perpendicular to planar surface 5. The tow-in means 13 is located close to the linear guide member 9 for manipulating sheets for printing such that the right-hand lateral edges of the sheets are brought into parallel, abutting alignment with guide surface 10.

0008Further, the system in FIGURE 1 includes a drive means, generally indicated by the number 11, for driving sheets for printing in a direction parallel to linear guide member 9. In the illustrated embodiment, drive means 11 includes a first drive roller 20 and a pinch roller 21 that is mounted in opposition to the drive roller. It should be noted that first drive roller 20 extends upward through an opening in planar surface 5 for engaging the undersurface of individual sheets as they travel along the planar surface; in the illustrated embodiment, however, the opening for drive roller 20 is not specifically shown.

0009In practice, the surface of first drive roller 20 is coated with a gritty material that enhances engagement between the drive roller and the driven sheets. Preferably, the surface of pinch roller 21 is formed from a material such as silicon rubber that is relatively hard (i.e., has high durometer). By way of contrast, the surface of first drive roller 20 is formed of a material which has a higher coefficient of friction, like rubber, and is relatively softer (i.e., has a low durometer) with respect to pinch roller 21. Accordingly, first drive roller 20 and associated pinch roller 21 permit only limited compliance with driven sheets.

0010Further in the embodiment illustrated in FIGURE 1, tow-in means 13 includes a "wobble" roller 27 which is positioned for engaging the top surfaces of sheets travelling on planar surface 5. In practice, wobble roller 27 is rotatable on an axle 29. As will be explained further below, axle 29 allows wobble roller 27 to pivot back and forth in the horizontal plane (i.e., to wobble).

0011Further, tow-in means 13 in FIGURE 1 includes a second drive roller 31 mounted for rotation in opposition to wobble roller 27. Like first drive roller 20, second drive roller 31 is mounted below planar member 5 and extends upward though an opening in the planar member for engaging the undersurface of sheets that travel on planar member 5; again, however, the opening for second drive roller 31 is not specifically shown. Preferably, both the first and second drive rollers are mounted on a common drive shaft 32 to be driven by a drive motor 34.

0012In practice, wobble roller 27 and second drive roller 31 have thin rubber coverings as shown. In practice, the rubber coverings are about 1/16 inch thick. Preferably, the rubber covering on wobble roller 27 is harder than the rubber covering on the second drive roller 31. For example, the rubber covering on wobble roller 27 may have a durometer value of about seventy, while the rubber covering on second drive roller 31 has a durometer value of about fifty-five or less. It should be noted that at such durometer, the rubber covering on second drive roller 31 is somewhat compliant; this could be accomplished, for example, by making the second drive roller thicker.

0013FIGURE 2 shows one embodiment of structure for mounting wobble roller 27 on axle 29. In the illustrated embodiment, axle 29 extends between the legs 41 and 43 of a bifurcated member 45. It should be noted that leg 43 is located nearest linear guide member 9 and leg 41 is located further from the linear guide member. A generally circular aperture 47 is formed in leg 43 for receiving one end of axle 29. In practice, the internal diameter of circular aperture 47 is sufficiently larger than the external diameter of axle 29 that the axle can rotate freely while pivoting to a limited extent.

0014Further in FIGURE 2, it should be noted that a slot-shaped aperture 49 is formed in the leg 41 of bifurcated member 45. The slot-shaped aperture receives the end of axle 29 while allows the axle to pivot horizontally in a limited arc. In practice, slot-shaped aperture 49 has dimensions such that pivotal movement of axle 29 is limited to only a few degrees.

0015Referring again to FIGURE 1, the sheet alignment system includes biasing systems 61 and 63 (e.g. springs and solenoids) for selectively engaging wobble roller 27 and pinch roller 21, respectively. In practice, the biasing systems 61 and 63 are operated in accordance with a selected operational sequence such that wobble roller 27 is disengaged whenever pinch roller 21 engages a sheet, and vice versa. In both circumstances, however, the first and second drive rollers 20 and 31 remain in contact with the bottom surface of sheets that are supported on planar surface 5. It will be understood, however, that first drive roller 20 cannot effectively drive a sheet until pinch roller 21 is biased downward against the sheet and, likewise, second drive roller 31 cannot drive a sheet until wobble roller 27 is biased downward.

0016The operation of the system of FIGURE 1 will now be described. Initially, it should be understood that sheets to be printed are fed individually onto planar surface 5 in the direction of the arrow. As each sheet travels along planar surface 5 for printing, the leading transverse edge of the sheet enters the nip area between wobble roller 27 and second drive roller 31 or, equivalently, the nip area between first drive roller 20 and pinch roller 21. Thereafter, the sheet can be driven by either the first or second drive roller alone.

0017When sheet alignment is desired, pinch roller 21 is disengaged and wobble roller 27 is moved into engagement with a sheet. Then, as the sheet is driven in the forward direction by second drive roller 31, axle 29 begins to pivot in the forward direction. As the pivoting motion continues, wobble roller 27 applies force by frictional engagement with the sheet. One component of the force is parallel to guide surface 10 in the direction of sheet travel and, therefore, tends to drive the sheet forward. The other component is the tow-in force that tends to pull the sheet generally toward guide rail 9. It is important to note that the effectiveness of the tow-in force in urging a sheet toward the guide rail depends upon the compliance of the coverings of wobble roller 27 and second drive roller 31.

0018After wobble roller 27 has pivoted axle 29 to its fullest extent in the forward direction within slot-shaped aperture 49, the direction of rotation of second drive roller 31 is reversed to drive the sheet to travel in the opposite direction. Under such circumstances, axle 29 pivots toward the rearward end of slot-shaped aperture 49 and wobble roller 27 again applies a tow-in force that tends to pull the sheet generally toward guide rail 12. In practice, the lateral edge of a sheet can be brought into parallel, abutting contact with the linear guide member by driving wobble roller 27 back and forth two or three times; typically, such action requires about one-quarter of a second.

0019In practice, for a given displacement of a sheet in the forward or reverse direction on planar surface 5, the sheet will travel a generally constant distance toward guide surface 10. For example, the alignment system of FIGURE 1 could be constructed such that one inch of sheet movement in the forward or reverse direction results in movement of the lateral edge of the sheet by about one-eighth inch toward the guide member.

0020Although the principles, preferred embodiments, and modes of operation of the present invention have been described in the foregoing specification, the invention which is intended to be protected is not to be construed as limited to the particular embodiments disclosed. That is, it should be understood that the embodiment described herein are to be regarded as illustrative rather than restrictive and that variations and changes may be made in the illustrated embodiments without departing from the spirit of the present invention as defined in the following claims.