Sheet guide device with sheet position adjusting mechanism and image forming apparatus using the same device

Abstract: A sheet guide device to guide a sheet being conveyed in a sheet conveying path of the device includes a device to adjust the widthwise sheet positioning by regulating side edges of the sheet. The adjusting device is provided in a curved part of the sheet conveying path. The sheet guide device further includes a sheet conveying roller to convey the sheet. The adjusting device is positioned on a shaft of the sheet conveying roller and is slidable along the shaft. The sheet conveying roller reverses a conveying direction of the sheet. The adjusting device unitarily includes a guide member to guide the side edges of the sheet.

Description: BACKGROUND OF THE INVENTION Field of the Invention This invention relates to a sheet guide device of an image forming apparatus such as a copying machine, a facsimile, a printer, or the like, and more particularly to a sheet guide device which can guide a sheet with its widthwise position adjusted and convey the sheet without forming wrinkles in the sheet. Discussion of the Background Recently, with widespread uses of digital copying machines and printers, demand for improvement of quality of image is increasing and, for example, a precise positioning of an image on a sheet is more demanded. Additionally, with increasing environmental sensitivity among users, a duplex unit for a two-sided copying has become important. In an image forming apparatus with a duplex unit, the sheet conveying path is longer than in an image forming apparatus for an ordinary one-sided copy, because a sheet carrying an image on one side of the sheet needs to be reversed for receiving another image on the other side of the sheet. Because of the long sheet conveying path, it is relatively difficult to prevent a sheet from being skewed. When a sheet is skewed, image quality on two sides of the sheet becomes uneven. In order to avoid the sheet skew and resulting lateral deviation of sheet positioning in the duplex unit, the duplex unit has been generally configured such that the sheet is temporarily stacked in an intermediate tray and is aligned by being jogged with side fence joggers. Figs. 1(A) and 1(B) illustrate a background duplex unit having a sheet positioning adjustment device. The duplex unit includes a reversible reverse roller 201, an intermediate tray 202, and a pair of side fences 203. The pair of side fences 203 moves in the direction indicated by B via a lengthwise extending groove 202a provided in the intermediate tray 202 such that the sheet is jogged with the side fences 203 to be aligned. When a sheet is fed into the duplex unit from a main body of an image forming apparatus (not shown), the sheet is reversed with the reverse roller 201 in the direction indicated by an arrow A in Fig. 1(A). Then, the sheet is stacked in the intermediate tray 202 between the pair of side fences 203, and the pressure by a pressing roller 204 is once released as illustrated by a dotted line in Fig. 1(B). The pair of side fences 203 moves to jog a sheet in the direction indicated by an arrow B in Fig. 1(A) such that a distance between the opposed side fences 203 in the sheet width direction equals to a predetermined sheet width and thereby, deviation of sheet positioning, e.g., sheet skew and resulting lateral deviation of sheet positioning, are corrected. A mechanism for driving the pair of side fences 203 is not shown. Thereafter, the reverse roller 201 is switched to be driven in a sheet refeed direction indicated by an arrow C in Figs. 1(A) and 1(B) and the pressing roller 204 returns to a position to contact the revere roller 201, so that the sheet is conveyed in the refeed direction by the reversing roller 201 and the pressing roller 204. However, in the above-described duplex unit, if both sides of a sheet 205 are curled upwardly as indicated by an arrow D in Fig. 2(A), the linear dimension L' from one curled edge to another curled edge of the sheet 205 will be shorter than the sheet width L to which the side fences 203 are adjusted, i.e. L'< L, as illustrated in Fig. 2(B). Accordingly, in this condition, i.e. L'< L, the side fences will not contact the edges of the sheet even when the fences are driven to jog the sheet, and as a result the curled sheet 205 cannot be positioned adequately in the sheet width direction. Japanese Laid-Open Patent Publication No.6-51587/1994 describes a sheet skew correcting device in a two-sided image forming apparatus in which a sheet stopper is placed ahead of feeding rollers in the sheet refeed direction, so that skew of a sheet is corrected when the sheet abuts the stopper. In this sheet skew correcting device, however, lateral deviation of sheet positioning is not corrected. Additionally, (1) Japan Patent Publication No. 2692957/1997 describes a background image forming apparatus configured to form an image on two sides of a sheet. In a switchback path of a switch back unit to reverse a sheet, a pair of reversible rollers are disposed for reversing a sheet. The switch back unit allows an entrance of a succeeding sheet into the switchback path when a trailing portion of a preceding sheet, which is switched to a reverse direction to be refed, is situated in the switchback path with the pair of reversible rollers being separated from each other. A lateral registration guide is disposed downstream of the reversible rollers for correcting lateral deviation of the sheet. (2) Japanese Laid-Open Patent Publication No. 8-81105/1996 describes a sheet reverse device in which a sheet is reversed by a pair of reversible rollers in a switchback path. The switchback path is Y-shaped and a separation pick provided at the intersection of the separated paths of the Y-shaped path switches between the separated paths to guide the sheet. (3) Japanese Laid-Open Patent Publication No.7-128921/1995 describes an optional duplex unit in which a sheet is conveyed to a reverse conveying path which is separated from a sheet conveying path in a main body, and then the sheet is reversed by a pair of reversible rollers and adjusted for its sheet position by a sheet position adjusting device. In (1) JP No. 2692957, the switchback path and the lateral registration guide for adjusting sheet positioning are provided at separate positions. Therefore, a space for the switchback path and the lateral registration guide for adjusting sheet positioning is separately necessary, so that the image forming apparatus tends to be a bigger size. Further, because a sheet refeeding path inside the switchback unit is relatively long, a possibility of occurrence of a sheet skew and resulting lateral deviation of the sheet may be increased. Therefore, a precise sheet positioning adjustment may be required. In (2) JP No. 8-81105, because the separation pick switches between the separated paths of the Y-shaped switch back path, a control operation of the separation pick is additionally required. In (3) JP No. 7-128921, the sheet is reversed and adjusted for its sheet position at separate positions like JP No. 2692957. And a space for reversing and sheet positioning adjustment functions is separately necessary. Therefore, the duplex unit tends to be bigger and a manufacturing cost may be increased. EP 0 443 590 A1, on which the preamble of claim 1 is based, discloses a sheet guide device that can only regulate one side edge of a sheet and requires that a movable plate used for regulating the side edge of the sheet is formed integrally with an extension of an adjusting mechanism. The adjusting device is not mounted onto the same shaft as the conveying roller, as the recoil would otherwise disturb a precise functioning of the conveying roller. Accordingly, it is an object of the present invention to provide a sheet guide device for accurately positioning even curled sheets while ensuring a duplex unit of small dimensions and low manufacturing costs. Further, an image forming apparatus comprising such a sheet guide device is to be provided. The above objects are solved by a sheet guide device according to claim 1 and by an image forming apparatus according to claim 9. Further advantageous embodiments are the subject matter of the dependent claims. SUMMARY OF THE INVENTION In order to overcome the above-described and other problems with background apparatus, preferred embodiments of the present invention provide a sheet guide device and an image forming apparatus that can adjust a sheet position accurately in the widthwise direction and correct a sheet skew and resulting lateral deviation of the sheet even if a sheet is curled at its side edges. The preferred embodiments of the present invention also provide a sheet guide device that is capable of adjusting sheet positioning and reversing the sheet as well. By thus configuring the sheet guide device, a space saving can be achieved, and further, the device can be applied to various types of sheet conveying paths. The preferred embodiments of the present invention further provide a sheet guide device and an image forming apparatus that can precisely adjust a sheet position widthwise in a curved sheet conveying path even if a sheet size is different due to a cutting error, and that can convey the sheet in a refeed direction without forming wrinkles in the sheet. According to a preferred embodiment of the present invention, a sheet guide device to guide a sheet being conveyed in a sheet conveying path of the device includes a device to adjust the widthwise sheet positioning by regulating side edges of the sheet. The adjusting device is provided in a curved part of the sheet conveying path. The sheet guide device may further include a sheet conveying roller to convey the sheet. The adjusting device is positioned on a shaft of the sheet conveying roller and is slidable along the shaft. The sheet conveying roller may reverse a conveying direction of the sheet. The adjusting device may unitarily include a guide member to guide the side edges of the sheet. According to another embodiment of the present invention, a sheet guide device to guide a sheet being conveyed in a sheet conveying path of the device includes a first guide member provided in the sheet conveying path to adjust the sheet positioning by regulating a side edge of the sheet. The first guide member is movable widthwise according to a sheet size. A first biasing device to absorb a difference in size of the sheet due to a cutting error of the sheet when the sheet positioning is adjusted, and a second biasing device to bias the side edge of the sheet in accordance with the difference in size of the sheet when the sheet is conveyed. The first biasing device and the second biasing device are provided to the first guide member. The sheet guide device may further include a second guide member being paired with the first guide member to adjust the sheet positioning by regulating the other side edge of the sheet. The second guide member is movable widthwise according to a sheet size. The sheet guide device further includes a third biasing device to bias the other side edge of the sheet in cooperation with the second biasing device when the sheet is conveyed. The third biasing device is provided to the second guide member. A bias force by the first biasing device may be greater than contact resistance between the sheet and the sheet conveying path. The bias force by the first biasing device may be configured not to be applied to the sheet when the sheet is conveyed. The bias force of the second biasing device may be substantially a same as that of the third biasing device. The first and second guide members may be provided in a curved sheet reversing path. Other objects, features, and advantages of the present invention will become apparent from the following detailed description when read in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS A more complete appreciation of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: FIGs. 1(A) and (B) are illustrations of a background duplex unit having a sheet position adjusting device, FIG. 1(A) being a perspective view of the duplex unit, and FIG. 1(B) being a side view of the duplex unit; FIGs. 2(A) and (B) are illustrations showing side curls of a sheet in the background duplex unit illustrated in FIGs. 1(A) and (B), FIG. 2(A) being a perspective view of the curled sheet, FIG. 2(B) being a sectional view of the curled sheet and side fences; FIGs. 3(A) and (B) are illustrations of a sheet guide device of an image forming apparatus according to a first embodiment of the present invention, FIG. 3(A) being a perspective view of the sheet guide device, and FIG. 3(B) being a side view of the sheet guide device; FIG. 4 is a perspective view of the sheet whose side curls are corrected in the sheet guide device in the first embodiment of the present invention; FIG. 5 is a sectional view of a sheet reverse unit having a vertical sheet conveying path to which the sheet guide device in the first embodiment of the present invention is also applied; FIGs. 6(A)-6(C) are illustrations of a background sheet guide device, FIG. 6(A) being a schematic illustration of the sheet guide device, FIG. 6(B) being a schematic side view of the sheet guide device, FIG. 6(C) being a sectional view for explaining a space between sheet side edges and jogger side fences; FIGs. 7(A)-7(D) are illustrations for explaining a operation of sheet position adjustment in another background sheet guide device; FIGs. 8(A) and 8(B) are illustrations for explaining a curved sheet conveying path of a sheet guide device, FIG. 8(A) being a perspective view of the sheet guide device, FIG. 8(B) being a side view of the sheet guide device; FIG. 9 is an illustration for explaining contact resistance of a sheet in a curved sheet conveying path; FIGs. 10(A) and 10(B) are illustrations for explaining operations for sheet positioning adjustment of the background sheet guide device of FIGs. 7(A)-7(D), FIG. 10(A) being an illustration in a case of a horizontal sheet conveying path, FIG. 10(B) being an illustration in a case of a curved sheet conveying path; FIGs. 11(A)-11(D) are illustrations for explaining operations for sheet positioning adjustment of a sheet guide device according to a second embodiment of the present invention; FIGs. 12(A) - 12(C) are illustrations for explaining conditions of the sheet when the sheet is conveyed in the refeed direction in the second embodiment, Fig. 12(A) illustrating a case for a maximum size sheet, Fig. 12(B) illustrating a case for a standard size sheet, Fig. 12(C) illustrating a case for a minimum size sheet; FIG. 13 is an illustration of a duplex unit of an image forming apparatus to which the sheet guide device of the second embodiment is applied; FIG. 14 is a schematic longitudinal sectional view of an image forming apparatus and a duplex unit according to a third embodiment of the present invention; FIG. 15 is a magnified view of a main part of the duplex unit illustrated in FIG. 14; FIGs. 16(A) and 16(B) are illustrations for comparing horizontal and curved switchback conveying paths; FIG. 17 is a perspective view of a configuration of a conveying roller and guide roller used in the sheet guide device according to the third embodiment of this invention; and FIG. 18 is a magnified front view of a guide roller illustrated in FIG. 17. DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views. For the sake of clarity, the elements having the same functions as the ones described in the background example will be designated with the same reference numerals. Figs. 3(A) and 3(B) illustrate a sheet guide device having sheet position adjusting mechanism for an image forming apparatus according to a first embodiment of the present invention. In the first embodiment, a pair of adjusting members 206 are mounted on a shaft 201a for a reverse roller 201 such that the adjusting members 206 can slide smoothly along the shaft 201a in the jogging direction indicated by an arrow B in Fig. 3(A) to adjust the sheet position. A pair of guide portions 206a mounted on the adjusting members 206 is configured to move with the adjusting members 206 and precisely stop at a predetermined sheet position according to the size of a sheet being conveyed to guide the sheet. Further, reverse guide members 207 are mounted unitarily with the adjusting members 206. The reverse guide members 207 guide both corners of a leading edge of a sheet when the leading edge of the sheet is fed into the sheet guide device while the sheet is reversed by the reverse roller 201. Next, operations in the above-described sheet guide device are described. A sheet fed from an image forming apparatus (not shown) is reversed by the reverse roller 201 in the direction indicated by an arrow A, and is stacked in an intermediate tray 202. The sheet is reversed by the reverse roller 201 in the condition that pressure by a pressing roller 204 is not released, and is then fed out in the refeed direction indicated by an arrow C in Figs. 3(A) and (B). As illustrated in Fig. 4, when a sheet 205 passes half, for example, through the reverse roller 201, the sheet 205 is stopped advancing by separating the pressing roller 204 from the reverse roller 201 as illustrated by a dotted line in Fig. 3(B). Then, the adjusting members 206 jog the sheet 205 to adjust its position. Thereafter, the pressing roller 204 abuts on the reverse roller 201 and the sheet 205 is conveyed again in the refeed direction indicated by an arrow C with the both sides of the sheet 205 being guided by the guide portions 206a and the reverse guide members 207. In this configuration, even though the side edges of the sheet 205 are curled upwardly or downwardly relative to the intermediate tray 202, the reverse roller 201, the guide portions 206a, and the reverse guide members 207 correct the curls by bending the sheet 205 in the sheet conveying direction. More specifically, when the sheet 205 is bent in the sheet conveying direction half through the reverse roller 201 as illustrated in Fig. 4, the linear dimension L' from one curled edge to another curled edge of the sheet 205 nearly equals to the actual sheet width L because the curls of the both side edges of the sheet 205 are corrected to be flat. Accordingly, when the adjusting members 206 jog the sheet 205, the sheet 205 can be accurately positioned by being sandwiched by the guide portions 206a, because the guide portions 206a are configured to precisely stop at the predetermined sheet position to guide the sheet. Moreover, the sheet 205 can be conveyed smoothly with the side edges securely guided while the sheet 205 is being reversed. The above-described sheet guide device can be applied not only to the sheet conveying path illustrated in Fig. 3(B) but also to a vertical conveying path illustrated, for example, in Fig. 5. In Fig. 5, a main body of an image forming apparatus 210 and a sheet reversing unit 211 having a vertical conveying path are illustrated. Because the reversing and position adjusting functions are combined in the sheet guide device of the present invention, a space saving can be achieved. Further the sheet guide device in the first embodiment may be applied not only to various sheet reversing paths as described above, but also to any sheet conveying paths in the image forming apparatus. Next, a second embodiment of a sheet guide device having a sheet position adjusting mechanism according to the present invention will be described. Before explaining the second embodiment, a background sheet guide device having side fence joggers will be explained referring to Figs. 6(A), (B), and (C). As illustrated in Fig. 6(A), the sheet guide device includes a conveying roller 101, a base plate 102, and a pair of side fences 103 which moves in the direction indicated by an arrow B via grooves 102a which are provided in the base plate 102. In the above-described sheet guide device, a sheet fed from the direction indicated by an arrow A in Fig. 6(A) temporarily stops advancing when its leading edge passes through the conveying roller 101. The sheet is stopped by separating a pressing roller 104 from the conveying roller 101 as indicated by a dotted line in Fig. 6(B). Thereafter, the side fence pair 103 is driven by a drive mechanism (not shown) to jog the sheet in the direction indicated by an arrow B in Fig. 6(A) to adjust the sheet position in accordance with a predetermined sheet width. Then, the pressing roller 104 presses the sheet again to convey the sheet in the direction indicated by an arrow C in Figs. 6(A) and 6(B). In the above-described configuration, the difference of sheet size due to a cutting error, which is specified as to range "± 2mm of the standard size" for all sheet sizes including B5, A4, A3, etc, in Japanese Industrial Standards, is considered, and a space U is provided as illustrated in Fig. 6(C) between the side edge of the sheet and the side fence 103 such that the space U becomes relatively large when a sheet P having "the standard size - 2mm" is conveyed. As a result, when the sheet P has such smallest size, the sheet P shifts in the space U when the sheet P is conveyed by being pressed by the pressing roller 104 and precise sheet position adjustments cannot be achieved. In Fig. 6(C), a reference character S designates a span between the opposed side edges of the side fence pair 103 specifically set for each sheet size. Figs. 7(A) through 7(D) illustrate another background sheet guide device addressing the above-mentioned problem of shifting of sheet, which is caused by difference in sheet size. In Figs. 7(A) through 7(D), the sheet guide device includes a side fence 106, a side fence 107 disposed opposite the side fence 106 at a predetermined distance, and a belt 112 for driving the side fences 106 and 107. The side fence 106 is set as a standard position side and is configured to move to a predetermined standard position and stay in the standard position while a sheet position is being adjusted with reference to the standard position and while the sheet is being conveyed in the refeed direction. The standard position corresponds to an image writing start position on the photoconductor drum. Integrally provided with the side fence 107 is a frame 113 which includes a slider 109 and a biasing device 108 therein. The slider 109 serves as a coupling device which moves relative to the side fence 107 by being coupled with the belt 112 via a coupling portion 109a. A biasing device 108 such as a spring is provided being supported and sandwiched between the side fence 107 and the slider 109. A side fence 106 is directly coupled with the belt 112 via a coupling portion 106a. The belt 112 is driven by a motor (not shown) via a driven pulley 110 and a drive pulley 111. Assuming that the difference of sheet size due to a cutting error is, for example, ± Z mm of the standard size, a maximum size of a sheet becomes "standard size + Z mm" and a minimum size becomes "standard size - Z mm". In this sheet guide device, a span between the side fences 106 and 107 is preset in accordance with a width of the minimum size sheet (i.e. "standard size - Z mm") and the bias force by the biasing device 108 is preset as 0 relative to the minimum size sheet. Fig. 7(B) illustrates a case when the sheet P has the standard size W0, Fig. 7(C) illustrates a case when the sheet P has a maximum size W1 (the standard size + Z mm), and Fig. 7(D) illustrates a case when the sheet P has a minimum size W2 (the standard size - Z mm). Next, an operation for sheet position adjustment in this sheet guide device is described. As illustrated in Figs. 7(B) through 7(D), when the side fences 106 and 107 move in the direction indicated by an arrow D by being driven by the motor, inner edges 106b and 107a of the side fences 106 and 107 contact a sheet P and adjust its position widthwise in the sheet conveying path. Referring to Fig. 7(C), when the maximum size sheet (W1) is conveyed to between the side fences 106 and 107, the coupling portions 106a and 109a move inwardly by being driven by the motor such that the span between the side fences 106 and 107 becomes substantially equal to a width of the minimum size sheet (W2). Thereby, the inner edge 106b of the side fence 106 and the inner edge 107a of the side fence 107 contact the side edge of the maximum size sheet (W1), thereby the sheet position is adjusted. When the inner edge 107a of the side fence 107 contacts the side edge of the maximum size sheet (W1), the side fence 107 receives a repulsive force of the maximum size sheet (W1) in the left direction in Fig. 7(C). As a result, the biasing device 108 contracts in the left direction due to the repulsive force of the maximum size sheet. At the same time, the biasing device 108 contracts also in the right direction by a pushing force of the slider 109 driven by the motor via the coupling portion 109a. When the biasing device 108 are caused to be contracted by the above described two forces, i.e. the repulsive force of the maximum size sheet and the pushing force of the slider 109, a space X is produced between the frame 113 and the left side edge of the slider 109 by (1) movement of the frame 113 toward left by the repulsive force of the maximum size sheet, and by (2) movement of the slider 109 toward right. Therefore, the width of the space X depends on the amount of the difference of the sheet size due to a cutting error. Accordingly, the space X becomes greatest for the maximum size sheet (W1) as illustrated in Fig. 7(C), becomes smaller for the standard size sheet (W0) as illustrated in Fig. 7(B), and becomes none for the minimum size sheet (W2) as illustrated in Fig. 7(D). Thus, the problem of the difference of the sheet size due to a cutting error in adjusting the sheet positioning in the background sheet guide device is solved. In the above-described background sheet guide device, after a sheet position is adjusted as above, the sheet P is conveyed in the refeed direction in the condition of being biased by the biasing device 108 as illustrated in Figs. 7(B), 7(C) and 7(D), respectively. Therefore, the bias force of the biasing device 108 is desired to be small enough to avoid forming wrinkles in the sheet P when the sheet P is conveyed in the refeed direction. Next, a case in which the sheet guide device having the above-described configuration is used in a curved sheet conveying path is explained. In the curved sheet conveying path illustrated in Figs. 8(A) and 8(B), the sheet P is bent by a conveying roller 101 as illustrated in Fig. 9. When the sheet P is bent in the conveying direction, the sheet P cannot be easily shifted widthwise because contact resistance F between the sheet P and a stack tray (not shown) provided in a stack path becomes greater as a part of the sheet P passed through the conveying roller 101 and a part of the sheet not passed through the conveying roller 101 are being pressed against the stack tray (not shown) provided in the stack path due to a repulsive force of the sheet P, compared to a case in which the sheet guide device is used in a horizontal sheet conveying path. Referring to Figs. 10(A) and 10(B), in the horizontal sheet conveying path, the side fence 107 can easily shift the sheet P in the direction indicated by an arrow E as illustrated in Fig. 10(A), because the sheet P is on the horizontal sheet conveying path and thereby the contact resistance F is small relative to the bias force by the biasing device 108. The reference character H in Fig. 10(B) designates a predetermined standard position of the side fence 106. On the other hand, when the sheet P is bent in the conveying direction as illustrated in Fig. 9, the contact resistance F becomes relatively large as described earlier. In such a case, unless the bias force by the biasing device 108 is greater than the contact resistance F, the side fence 107 cannot shift the sheet P in the direction indicated by an arrow Y in Fig. 10(B), and the position of the sheet P may be deviated from the standard position H, as illustrated in Fig. 10(B). Therefore, when the sheet guide device of the above configuration is used in the curved sheet conveying path, the bias force of the biasing device 108 is desired to be made stronger in order to adjust the sheet P to the standard position. As described above, the bias force of the biasing device 108 is set so as to absorb (1) the pushing force of the slider 109 and (2) the repulsive force of the sheet P corresponding to the space X. However, if the bias force by the biasing device 108 is made stronger, when the maximum size sheet is conveyed in the refeed direction after the position of the sheet P is adjusted with the stronger bias force, wrinkles are produced in the sheet P. The sheet guide device in the second embodiment therefore is configured to be capable of adjusting the bias force of the biasing device to avoid forming wrinkles in the sheet when the sheet is conveyed in the refeed direction regardless of the size of the sheet P and even when the size includes a cutting error. The second embodiment of the present invention is now described referring to Figs. 11(A) through 11(D) as follows. In the second embodiment, a sheet position is adjusted widthwise such that the center of a sheet is aligned with the center of a span between a side fence 6 and a side fence 7, which corresponds to the center of the image writing part on the photoconductor drum. Provided integrally with the side fence 7 is a frame 75 which includes a first biasing device 71, a second biasing device 72, a slider 73 coupled with a belt 12 via a coupling portion 73a, and a relay member 74 therein. The relay member 74 is movable relative to the side fence 7, and the slider 73 is movable relative to the relay member 74. The first biasing device 71 is supported by being sandwiched between the side fence 7 and the relay member 74, and the second biasing device 72 is supported by being sandwiched between the slider 73 and a concave part of a side of the relay member 74. Further, provided integrally with the side fence 6 opposed to the side fence 7 is a frame 63. The frame 63 includes a third biasing device 61, and a slider 62 which is coupled with the belt 12 via a coupling portion 62a and moves relative to the side fence 6. The third biasing device 61 is supported by being sandwiched between the side fence 6 and the slider 62. The belt 12 is driven by a motor (not shown) via a driven pulley 10 and a drive pulley 11. In the sheet guide device of the second embodiment, the bias force by the first biasing device 71 (fm) is set to be strong enough to shift a sheet which is bent in the sheet conveying direction and which thereby has great contact resistance as described above. The bias force of the second biasing device 72 (fs) and the third biasing device 61 (fs) is set to be weak enough to avoid producing wrinkles in the sheet when the sheet is conveyed in the refeed direction with the side edges of the sheet being biased by the biasing devices 72 and 61. Further, the relation of the bias force between the first biasing device 71 (fm) and the second biasing device 72 or the third biasing device 61 (fs) is set to be; fm >> fs. Next, an operation for sheet position adjustment in the sheet guide device of the second embodiment is described. In this sheet guide device, a span between the side fences 6 and 7 is preset in accordance with a width of the minimum size sheet, i.e. "the standard size - Z" for each size (e.g. B5, A4, A3, etc.) of the sheet P as described earlier. In Fig. 11 (A), when a sheet P is conveyed between the side fences 7 and 6, the coupling portions 73a and 62a move inwardly by being driven by the motor via the belt 12 such that the side fences 7 and 6 move inwardly to the predetermined position between the aide fences 7 and 6 which is set corresponding to the minimum size sheet. Thereby, inner edges 7a and 6a of the side fences 7 and 6, respectively, contact the side edges of the sheet P. The second and third biasing devices 72 and 61 are configured so as to be completely contracted as illustrated in Fig. 11(B) when the side fences 7 and 6 move to the predetermined position. More in detail, the sliders 73 and 62 are driven via the coupling portions 73a and 62a to move toward the sheet P, and then abut on projected parts 74a and 63a of the relay member 74 and the frame 63, respectively. Then, the relay member 74 and the frame 63 are moved inwardly and thereby the side fences 7 and 6 are moved inwardly to the predetermined position. Thereby, the position of the sheet P is adjusted such that the center of the sheet P is aligned with the center of the span between the side fences 7 and 6 as illustrated in Fig. 11(B). When the sheet P is bigger than the minimum size sheet, for example, when the sheet P has the maximum size, each of the coupling portions 73a and 62a is driven to move inwardly, and the first biasing device 71 contracts by two forces of opposite directions, i.e. a pushing force of the side fence 6 against the maximum size sheet P in the left direction, and a pushing force of the relay member 74 in the right direction by being driven by the motor via the slider 73. As a result, the maximum size sheet P is shifted in the left direction by the space of X.sub.3 by pushing of the side fence 6 in Fig. 11(C). Assuming that a difference of the sheet width between the maximum size sheet (the standard size + Z) and the minimum size sheet (the standard size - Z) is "2Z", because the side fences 6 and 7 are preset to move such that the span between the side fences 6 and 7 becomes substantially equal to the width of the minimum size sheet (the standard size-Z.), in Fig. 11(C), a space of X.sub.3 equals to a half of the difference of the sheet width between the maximum and minimum size sheets, i.e. 2Z X 1/2 = Z. A space of X.sub.2 is produced between the frame 75 and the left side edge of the relay member 74 by (1) moving of the frame 75 toward left with the first biasing device 71 being contracted in the left direction by the space of X.sub.3, and by (2) moving of the relay member 74 toward right with the first biasing device 71 being contracted in the right direction by the space of X.sub.3. Accordingly, the space of X.sub.2 becomes two times of the space of X.sub.3. In the above described operation in Fig. 11(C), the first biasing device 71 contracts in the left direction by the pushing force of the side fence 6 against the maximum size sheet P in the left direction, because the sheet P bent in the sheet conveying direction as illustrated in Fig. 9 has tension (fz) in the widthwise direction, and the pushing force of the side fence 6 is delivered to the side fence 7 via the maximum size sheet P having the tension (fz). Assuming that the tension of the sheet P is "fz", and the bias force of the first biasing device 71 is "fm", the bias force of the first biasing device 71 (fm) is set to satisfy the relation; fm < fz, in Fig. 11(C). Therefore, even though a relatively strong bias force by the first biasing device 71 is applied to both sides of the sheet P, bulges are not produced on the sheet P. Fig. 11(D) illustrates a state when the maximum size sheet P is conveyed in the refeed direction. Specifically, the maximum size sheet P is shifted by a predetermined distance C (illustrated in Fig. 11(C)) in the right direction by moving the coupling portions 73a and 62a outwardly. The distance C for shifting the sheet P is preset in the sheet guide device. When the distance C is set to be equal, for example, to a half of the difference of the sheet width between the maximum size sheet (the standard size + Z) and the minimum size sheet (the standard size - Z), i.e. "Z", the side edges of the maximum size sheet P return to the position before having been shifted in the left direction by being pushed by the side fence 6 as illustrated in Fig. 11(D). More in detail, while the coupling portions 73a and 62a are moving outwardly by the distance C (Z), the contracted first biasing device 71 expands completely (1) pushing the relay member 74 in the left direction and (2) pushing the maximum size sheet P to the side fence 6 in the right direction. As described earlier, the expanding bias force of the first biasing device 71 is set to be strong enough to shift the sheet P even when the sheet P is bent and thereby has great contact resistance. Therefore the maximum size sheet P is shifted in the right direction by the distance C. Specifically, the expanding bias force of the first biasing device 71 is desired to be greater than contact resistance between the sheet P and the stack tray (not shown) provided in the stack path (illustrated in Fig. 9). After the maximum size sheet P is pushed back to the right by the expanding force of the first biasing device 71, the sheet P is sandwiched securely between the side fences 6 and 7 for being conveyed in the refeed direction. As illustrated in Fig. 11(D), the first biasing device 71 has expanded completely and no bias force acts, even when the sheet P is the maximum size sheet. Therefore, even when the sheet P has the maximum size, the sheet P is conveyed without being wrinkled. In case that the sheet P is a minimum size sheet, the side fences 6 and 7 move to stop at the predetermined position which is preset to be equal to the width of the minimum size sheet in Fig. 11(B). Therefore, the minimum size sheet P is not necessary to be shifted in the left direction like the case of the maximum size sheet P in Fig. 11(C). Thereafter, the coupling portions 73a and 62a move outwardly by the predetermined distance C, and then the minimum size sheet P is conveyed in the refeed direction. Next, referring to Figs. 12(A), 12(B), and 12(C), a condition in which the sheet P is conveyed in the refeed direction (corresponding to Fig. 11(D)) is described. Fig. 12(A) illustrates a case when the sheet P has a maximum size (WB), Fig. 12(B) illustrates a case when the sheet P has a standard size (WJ), and Fig. 12(C) illustrates a case when the sheet P has a minimum size (WS). A space X.sub.4 in Figs. 12(A), 12(B), and 12(C) designate a space between the slider 73 and the projected parts 74a or the slider 62 and the projected parts 63a, which is produced when the coupling portions 73a and 62a move outwardly by the predetermined distance C and the second biasing device 72 and the third biasing device 61 expand in the outward directions in Fig. 11(C) to Fig. 11(D). When the distance C is set to be equal to the space X.sub.3 (i.e., "Z" as described earlier) in Fig. 11(C), even when the sheet P is the maximum size sheet and the space of X.sub.4 becomes none as illustrated in Fig. 12(A), only the second and third biasing devices 72 and 61 act on the sheet P and the first biasing device 71 does not act on the sheet P. Therefore, the sheet P having the maximum size can be conveyed without being wrinkled. The space X.sub.4 becomes "Z/2" for the standard size sheet (WJ) as illustrated in Fig. 12(B), and becomes "Z" for the minimum size sheet (WS) as illustrated in Fig. 12(C). Because the first biasing device 71 does not act on the sheet P either for the standard size and minimum size sheet, the sheet P having the standard or minimum size is also conveyed without being wrinkled. As a variation of the distance C, the distance C may be set to satisfy the relation; C ≥ Z in Fig. 11(C). In such a case, the space of X.sub.4 for the maximum size sheet (WB) becomes; X.sub.4 ≥ 0 in Fig. 12(A), for the standard size sheet (WJ) becomes; X.sub.4 ≥ Z/2 in Fig. 12(B), and for the minimum size sheet (WS) becomes; X.sub.4 ≥ Z in Fig. 12(C). In this case, when the sheet P has the minimum size, a space of X.sub.1, i.e. the distance between the relay member 74 and the left side edge of the slider 73 or between the frame 63 and the right side edge of the slider 62 satisfies the relation; X.sub.1 ≥ 0 in Fig. 12(C). That is, even when the sheet P is the minimum size sheet (WS), the sheet P is biased by the biasing devices 72 and 61 when the sheet P is conveyed in the refeed direction in Fig. 12(C), such that the sheet P is conveyed smoothly by being guided by the sheet guide device. As described above, only the second and third biasing devices 72 and 61 act on the sheet P when the sheet P is conveyed in the refeed direction and extra bias force by the first biasing device 71 does not act on the sheet P. Therefore, occurrence of wrinkles on the sheet P can be obviated. If the bias force by the first biasing device 71 acts on the sheet (as illustrated in Fig. 11(C)) when the sheet is conveyed in the refeed direction, wrinkles may be formed in the sheet, because the above described relation between the tension of the sheet P (fz) and the bias force of the first biasing device 71 (fm) is reversed; fm > fz, after the force by a conveying roller (not shown) in the sheet refeed direction is added to the sheet. In order for the sheet P to keep the adjusted sheet position and advance smoothly when the sheet P is conveyed in the refeed direction, biasing forces of the second and third biasing devices 72 and 61 are desired to be equal in Figs. 11(D), 12(A), 12(B), and 12(C). As a variation of a predetermined span between the side fences 6 and 7, when a span between the side fences 6 and 7 is preset to be "smaller than a width of the minimum size sheet", i.e. the span < "the standard size - Z", the space of X.sub.3 in Fig. 11(C) becomes larger than Z and the distance C in Fig. 11(C) becomes larger than Z in Fig. 11(C). Therefore, even the sheet P has the minimum size, the sheet P is shifted to the right direction to abut on the side fence 6 and thereby the sheet P is positioned more accurately. Thus, in the second embodiment, with the provision of the third biasing device 61 on the side fence 6, an accurate sheet position adjustment is achieved also in the curved sheet conveying path such that the center of a sheet is aligned with the center of a span between the side fence 6 and the side fence 7. Moreover, the sheet guide device is configured such that the first biasing device 71 serves to shift the sheet P in the right direction, so that the sheet P can be adjusted to the precise position, even if the sheet P has great contact resistance in the curved sheet conveying path. Further, in the second embodiment, the side fence 6 in Figs. 11(A) through 11(D) may be fixed as a standard position side to achieve substantially the same effects as in the case where both of the side fences 6 and 7 are moved to align the center of the sheet P with the center of the span between the fences 6 and 7. Furthermore, the sheet guide device of the second embodiment can be applied not only to the curved sheet conveying path illustrated in Fig. 8(A) but also to a reverse sheet conveying path in a duplex unit illustrated in Fig. 13. Fig. 13 illustrates a duplex unit of an image forming apparatus in which the sheet guide device of the second embodiment is utilized. A duplex unit 20 is provided next to a main body of an image forming apparatus 30 and includes a conveying roller 101 and curved side fences 6' and 7'. Still furthermore in the second embodiment, as the first, second and third biasing devices, rubber or a combination of spring and rubber may be used to obtain substantially the same effects as those obtained with the spring. Obviously, numerous additional modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the present invention may be practiced otherwise than as specifically described herein.

Claims: A sheet guide device for guiding a sheet being conveyed in a sheet conveying path of the device, comprising a device (206) to adjust the widthwise sheet positioning by regulating side edges of the sheet, wherein the adjusting device (206) is provided in a curved part of the sheet conveying path, said sheet guide device further comprising a sheet conveying roller (201) to convey the sheet, said sheet conveying roller (201) being adapted to reverse a conveying direction of the sheet, characterized in that said adjusting device (206) is positioned on a shaft (201a) of the sheet conveying roller (201) and is slidable along the shaft (201a). The sheet guide device according to claim 1, wherein a guide member to guide the side edges of the sheet is unitarily provided to the adjusting device. The sheet guide device according to claim 1, wherein said adjusting device is a first guide member (7) provided in the sheet conveying path to adjust the sheet positioning by regulating a side edge of the sheet (P), the first guide member (7) being movable widthwise according to a sheet size; said sheet guide device further comprising: a first biasing device (71) to absorb a difference in size of the sheet (P) due to a cutting error of the sheet when the sheet positioning is adjusted; and a second biasing device (72) to bias the side edge of the sheet (P) in accordance with the variance in size of the sheet when the sheet is conveyed; wherein the first biasing device (71) and the second biasing device (72) are provided to the first guide member (7). The sheet guide device according to claim 3, further comprising: a second guide member (6) being paired with the first guide member (7) to adjust the sheet positioning by regulating the other side edge of the sheet (P), the second guide member (6) being movable widthwise according to a sheet size; and a third biasing device (61) to bias the other side edge of the sheet (P) in cooperation with the second biasing device (72) when the sheet (P) is conveyed; wherein the third biasing device (61) is provided to the second guide member (6). The sheet guide device according to claim 3, wherein a bias force (Fm) by the first biasing device (71) is greater than a contact resistance between the sheet (P) and the sheet conveying path. The sheet guide device according to claim 5, wherein the bias force (Fm) by the first biasing device (71) is configured not to be applied to the sheet (P) when the sheet is conveyed. The sheet guide device according to claim 4, wherein the bias force (Fs) of the second biasing device (72) is substantially the same as that of the third biasing device (61). The sheet guide device according to claim 3, wherein the first and second guide members (6, 7) are provided in a curved sheet reversing path. An image forming apparatus, comprising a sheet guide device according to any of claims 1 to 8.

Inventors: YAMAGISHI MASARU, YAMAGISHI, MASARU
Applicants: RICOH KK, RICOH COMPANY, LTD.
Application year: 1999
Main classification: B65H9
IPC codes: B65H9, B65H5, B65H15