Abstract:
A sheet conveyer having a sheet registration device for an image forming apparatus having a sheet path for guiding a sheet having an image recorded on one side thereof back to an image forming unit for recording another image on the other side, comprises a mechanism for switching the sheet having the image recorded on one side thereof back to the sheet path, a mechanism for abutting the switched-back sheet against a lateral registration reference plane, and a preliminary shift function shared by the switch-back mechanism for shifting the sheet oppositely to the reference plane.

Description:
This application is a continuation of application Ser. No. 216,499 filed July 8, 1988, now abandoned. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a sheet conveyer having a sheet aligner or register, and more particularly to a sheet conveyer in an image forming apparatus such as a copying machine or printer. Furthermore, it relates to a sheet conveyer having an aligner for aligning a sheet widthwise before the sheet is guided to an image forming apparatus having a path along which the sheet is reconveyed to an image forming position in a both-surface multiple copy machine. 
     2. Related Background Art 
     A prior art apparatus is explained with reference to FIGS. 1A and 1B. 
     In this apparatus, a sheet is guided along a refeed or reload path in order to form images on front and back surfaces of the sheet. 
     In FIG. 1B, the sheet having an image recorded on a first surface thereof is fed from the right along an arrow 15, the image is fixed by a fixing unit 3, and the sheet is switched back by rollers 4 and 5 of roller unit 6 and fed along the direction of arrow 18. The sheet is reversed by a refeed path and again guided to the image forming unit where an image is recorded on a second surface The sheet is then ejected to a tray by rollers 4 and 4. 
     In this apparatus, since the left edge of the print sheet when the print sheet is fed along the direction of arrow 18 and a reference plane of the lateral registration are on the same line, no problem occurs when the sheet skews rightward with respect to the feed direction. However, if the sheet skews leftward even a bit, it abuts against a front plane 14a of the lateral registration plate and the sheet may be folded or jam. It may be theoretically possible to feed the print sheet without any skew but it is actually very difficult because very high precision parts are required. As shown in FIGS. 1A and 1B, the prior art apparatus is provided with an preliminary shift mechanism 23 to skew the print sheet oppositely to the lateral registration plate so that the print sheet is offset from the lateral registration plate and in parallel therewith. The print sheet is then caused to abut against the lateral registration plate by skew rollers 7 and 8 for alignment. 
     In the prior art apparatus, since the preliminary shift mechanism 23 is separately provided between the switch-back mechanism 6 and the skew mechanism 9, the number of parts is considerably large. The overall apparatus is complex and the size of the apparatus must be large because there must be a sufficient spacing to skew the print sheet between the switch-back mechanism and the preliminary shift mechanism, and between the preliminary shift mechanism and the skew roller mechanism. Accordingly, in the prior art apparatus, there are disadvantages of complexity, large size and resulting high cost. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a preliminary shift mechanism of a simple structure. 
     In order to achieve the above object, in accordance with the present invention, a roller bearing is designed such that a sheet is fed straight when the roller is rotated in one direction, but when the roller is rotated in the other direction, the shaft is skewed so that the sheet is fed obliquely. 
     In accordance with a further feature of the present invention, the preliminary shift mechanism is shared by a switch-back mechanism and the bearing described above is used as a reversible roller of the switch-back mechanism. 
     In accordance with the present invention, the above construction is used for the alignment in a copying machine so that a center reference is aligned to a center reference or the center reference is aligned to a side reference. 
     In the present apparatus, since the switch-back mechanism is provided with the preliminary shift function to eliminate the preliminary shift mechanism, the path length of the apparatus is significantly reduced and the size, complexity and cost of the apparatus are reduced. 
     Skew in a reverse feed mode is easily attained by providing a gap in one of the bearings of a center rotation shaft of a follow roller contacting with a drive roller. Thus, a complex and large size link mechanism and means for controlling and driving the link mechanism can be eliminated and the cost is reduced. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIGS. 1A and 1B show a plan view and a front view of a prior art apparatus, 
     FIG. 2A shows a plan view of the present invention, 
     FIG. 2B shows a front view thereof, 
     FIGS. 3A and 3B show a plan view and a front view of a switch-back mechanism used in the present invention, 
     FIGS. 4A and 4B show a plan view and a front view for illustrating an operation of FIGS. 2A and 2B, 
     FIG. 5 shows a plan view of another embodiment, 
     FIG. 6 shows a front view of a copying machine in accordance with the present invention, 
     FIG. 7 shows a perspective view of other embodiment of a lateral registration unit, 
     FIG. 8 shows a front view of the lateral registration unit of FIG. 7, 
     FIG. 9 shows a cross sectional view of an overall apparatus having the unit shown in FIGS. 7 and 8, 
     FIG. 10 shows a top view of the lateral registration unit of FIG. 7, 
     FIG. 11 shows a flow of a record sheet in a printer, as viewed from the top, when a center reference is aligned to a side reference, 
     FIG. 12 shows a front view of a printer using the apparatus of FIG. 11, and 
     FIG. 13 shows a position of the record sheet when an image is recorded thereon. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIGS. 2A and 2B show an embodiment of the present invention. Numeral 3 denotes a fixing unit comprising a heat roller 1 and a press roller 2, numeral 126 denotes a switch-back mechanism comprising reverse rollers 124 and 125, and numeral 9 denotes a skew roller mechanism comprising skew rollers 7 and 8. In the plan view of FIG. 2A, numeral 14 denotes a lateral registration plate defining a lateral registration reference plane, and numeral 12 denotes a refeed mechanism comprising refeed rollers 10 and 11. 
     A print sheet having an image transferred from a photosensitive body 28 (FIG. 6) onto a first surface thereof is fed in a direction of an arrow 15, and the image is fixed by the fixing unit 3. The reverse roller 125 feeds the print paper in a direction of an arrow 16 until a rear edge of the print sheet reaches a reversal point 13. When the rear edge of the print sheet reaches the reversal point (when a switch SW detects the rear edge), it reverses the feed direction (and a flop F is switched) so that the print sheet is fed in a direction of arrows 17 and 18. The switch SW flopper F together form a directing means. 
     The switch-back mechanism 126 (which also functions as a preliminary shift mechanism) is now explained. As shown in FIGS. 3A, 3B; 4A and 4B, a play or gap 120a is provided in one of bearings of the reverse rollers 124. In a forward mode, axes of the reverse roller 124 (which is a follow roller and sides on the reverse roller 125 by its gravity) and the reverse roller 125 (which is a drive roller rotated by a motor) are orthogonal to the direction of the sheet feed and the print sheet is fed orthogonally to those axes. However, when the reverse roller 125 is in a reverse mode, the reverse roller 124 is skewed by an amount corresponding to the play formed in one bearing, by a friction to the print sheet, as shown in FIGS. 4A and 4B. The play 120a is formed in the bearing of the reverse roller facing the lateral registration plate so that the print sheet is skewed oppositely to the lateral registration plate. In this manner, the function of the preliminary shift mechanism is provided. 
     In the present embodiment, in order to shift a feed mode from a center reference feed to a side reference feed, a guide plate 14 is provided. If the lateral registration is effected in the center reference feed mode, the construction of the lateral registration roller would be complex (because the amount of registration must be changed in accordance with a sheet size). 
     FIG. 5 shows another embodiment of the present invention. A bracket 237 having a bearing for a reverse roller 238 is moved around a support point 234 by a solenoid 236 to skew the roller 238 in order to skew the print sheet. Numeral 235 denotes a link. 
     In the above embodiments, the guide plate is fixed. In FIGS. 7, 8, 9 and 10, the guide plate is movable so that the lateral registration is effected in the center reference feed mode. 
     In both-surface printing, the sheet having an image fixed on one surface thereof by the fixing unit 3 is fed to a tray 415 and then guided to a both-surface feed path 419 by the reverse roller 124 and the flopper F, forming a directing means. FIGS. 7 and 8 show a lateral registration unit in the both-surface feed path 419. Numeral 410 denotes a lateral registration plate defining a lateral registration reference for the sheet. It is of U-shape and a side of the sheet is abutted against a side edge 410c. Numerals 7 and 8 denote skew rollers for skewing the sheet 414 so that it is abutted against the side edge 410c, and numeral 413 denotes a cam for moving the lateral registration plate to a predetermined position. It has a helical cam surface 413a. A sheet size identification member 30a of a cassette 30 is detected by a detector SS so that the lateral registration plate 410 is moved by the cam 413 on a guide plate 430 to a position corresponding to the sheet size. The cam 413 is rotated by an amount corresponding to the sheet size so that the cam surface 413a pushes a cam engagement 410a to slide the cam to the left or right. Accordingly, the sheet 414 is fed to the lateral registration plate in the direction shown in FIG. 10 without being jammed by the side of the lateral registration plate 410. The sheet guided to a groove 410b of the lateral registration plate is abutted against a side 410c of the lateral registration groove by the skew rollers 7 and 8 which tends to feed the sheet at an angle α with respect to the direction of feed of the sheet. In this manner, the lateral registration is effected. 
     As described above, the second run lateral registration of the sheet is attained by using a movable lateral registration plate in an image forming apparatus feeding the sheet in the center reference mode. 
     The center reference feed mode and the side reference feed mode are explained in detail with reference to an other embodiment. 
     FIG. 12 shows a printer which embodies the present invention. FIG. 11 shows a flow of the record sheet in the printer of FIG. 12, as viewed from the top. 
     In the printer 101 of FIG. 12, the construction from the sheet cassette 2 to the reverse roller 10 is the same as that of the printer of FIG. 6 and the description of the movement of the record sheet in that area is omitted. 
     The record sheet 3 switched back by the reverse roller 10 is fed to the skew roller 102, which is a feed roller inclined to the left with respect to the direction of feed of the record sheet 3. The lateral registration plate 103 is fixed on the left of the skew roller 102, and a reference plane 103a of the lateral registration plate 103 is aligned to an edge position 3&#39; of a maximum possible width sheet used in the printer 101, as shown in FIG. 11. When the record sheet 3 is pinched by the skew roller 102, it is obliquely fed toward the lateral registration plate 103 as shown by an arrow A, and a left side edge 3a of the sheet abuts against the reference plane 103a of the lateral registration plate 103. The reference plane 103a is a lateral registration reference used when a second image of the printer 101 is recorded. The record sheet 3 is abutted against the reference plane 103a for the lateral registration. After the record sheet 3 has been laterally registered, it is further fed by the skew roller 102 along the reference plane 103a, fed to the registration roller 5, and the second image is recorded. 
     The difference between the lateral registration references when the first image is recorded and the second image is recorded is explained below in detail. 
     The printer 101 feeds the sheet in the center reference feed mode. The record sheet 3 is fed from the cassette 2 to the reverse roller 10, as shown in FIG. 11, such that a center line (bisection line) C orthogonal to the direction of feed is common to all record sheet sizes. When the first image is recorded, the record sheet 3 receives the image at a position 3-1 of FIG. 13. FIG. 13 shows a positional relationship of the record sheet when the image is recorded on the photoconductor drum 6 of the recording unit 6. The record sheet is at the position 3-1. It is then laterally registered by the lateral registration plate 103 and has the second image recorded thereon. The record sheet 3 is fed to the recording unit 6 while the sheet edge 3a determined by the reference plane 103a is kept at the position of the sheet edge of the maximum width record sheet 3&#39;. Accordingly, the second image is recorded at a position 3-2. 
     The situation is same even if the width of the record sheet changes. When the first image is recorded, the record sheet is positioned such that the center line C (bisection line orthogonal to the direction of feed) of the record sheet is aligned to the center line of the record sheet of different width (at the center reference position). When the second image is recorded, the record sheet is positioned such that the sheet edge on a specified side (left or right side with respect to the feed direction) of the record sheet is aligned to the sheet edge of the record sheet of different width (at a side reference position). In other words, when the first image is recorded, the record sheet is fed in the center reference feed mode, and when the second image is recorded, the record sheet is fed in the side reference feed mode. 
     In the above embodiment, a laser printer having a both-surface printing function is shown. The present invention is applicable not only to the record apparatus having the both-surface printing function, but also to a record apparatus having a multi-print function to record a plurality of images on one surface or a record apparatus having the both functions. 
     The recording system is not limited to an electrophotographic system but various recording systems may be used. 
     The record apparatus may be either a printer or a copying machine. 
     By arranging the lateral registration plate 103 on the same side as the lateral reference plane of the sheet cassette 2, the alignment of the references of the first and second images is improved For example, in FIG. 11, the lateral reference plane of the sheet cassette 2 is preferably on the left side with respect to the feed direction of the record sheet 3. 
     The sheet cassette 2 may be a sheet deck which can stack a number of cassettes. 
     As described hereinabove, in the recording apparatus for recording a plurality of images, when the first image is recorded, the record sheet is fed in the center reference feed mode, and when the second image is recorded, the record sheet is fed in the side reference feed mode Accordingly, the present recording apparatus offers the following advantages. 
     1. The lateral registration prior to the recording of the second image is effected by one lateral registration reference without regard to the size of the record sheet Accordingly, a mechanism to change the lateral registration reference position in accordance with the size of the record sheet is not necessary. 
     2. Since it is not necessary to change the lateral registration reference position, the lateral registration plate may be fixed. Accordingly, an adjustment tolerance due to a variation in the stop position of the reference position, which could not be avoided in the mechanism for changing the lateral registration position, is eliminated and high precision lateral registration is attained. 
     3. When the sheet is fed from the sheet cassette, it is fed in the center reference feed mode as is done in the conventional apparatus. Accordingly, the center reference feed mode which is simpler in the construction of the feed rollers than that of the side reference feed mode may be used as it is.