Sheet delivery mechanism

A sheet delivery mechanism designed to discharge successive sheets to different delivery positions includes offset rollers, an offset unit, an offsetting force generator and an offset unit swinging mechanism. The offset rollers is rotatably supported by the offset unit to discharge each sheet in a sheet transport direction. The offsetting force generator produces a driving force for shifting the offset unit back and forth along a direction perpendicular to the sheet transport direction between a reference position and offset positions. The offset unit swinging mechanism swings the offset unit about an axis parallel to rotary shafts of the offset rollers in such a manner that a sheet output direction in which the offset rollers eject each sheet varies to a direction pointing away from a sheet delivery tray when the offset unit is shifted along the direction perpendicular to the sheet transport direction by the offsetting force generator.

CROSS REFERENCE

This Nonprovisional application claims priority under 35 U.S.C. § 119(a) on Patent Application No. 2003-027366 filed in Japan on Feb. 4, 2003, the entire contents of which are hereby incorporated by reference.

BACKGROUND OF THE INVENTION

The present invention relates to a sheet delivery mechanism of an image forming apparatus, such as a printer or a copying machine, for discharging sheets of a printing medium carrying printed images to offset delivery positions.

When an image forming-apparatus for producing printed images on sheets of paper outputs multiple copies of printed sheets onto a sheet delivery tray provided outside a housing of the apparatus, for instance, it is usually difficult to discern boundaries between the individual copies and, therefore, a user needs to sort the individual copies upon completion of image forming operation. When producing two copies of a 10-page document by the image forming apparatus, for example, the user has to find out a boundary between the first and second copies, or the boundary between a last page of the first copy and a first page of the second copy, and separate the two copies from each other.

There are several known types of sheet delivery devices applicable to conventional image forming apparatuses for realizing efficient sorting operation. These sheet delivery devices are designed to selectively deliver multiple copies of printed sheets in different ways or at different (offset) locations by varying sheet delivery positions for easy sorting. Four specific approaches employed in these sheet delivery devices are as follows.

A first approach proposed in Japanese Laid-open Patent Publication No. 1999-199124, for example, is to feed printing paper of the same size in different orientations (portrait and landscape) for every other copy of a document and output printed sheets in the same orientations. Specifically, sheets for printing one copy are fed in such a way that a short side of each sheet goes first and sheets for printing next copy are fed in such a way that a long side of each sheet goes first. As the printed sheets are discharged in the same orientations, individual copies can be easily distinguished.

A second approach disclosed in Japanese Laid-open Patent Publication No. 2000-86056, for example, employs an offset tray. Although printed sheets are discharged from a fixed sheet output position, the offset tray is shifted (offset) to different positions so that the printed sheets are delivered to different locations for easy sorting.

A third approach proposed in Japanese Laid-open Patent Publication No. 1993-186121, for example, includes a pair of sheet output rollers individually mounted on two shafts and a differential gear mechanism provided between the two shafts. While the two sheet output rollers nip a printed sheet for discharging it, a difference is produced between rotating loads of the two sheet output rollers. The differential gear mechanism produces a difference in rotating speed between the two sheet output rollers so that multiple copies of printed sheets are output to different sheet delivery positions for easy sorting.

A fourth approach shown in Japanese Laid-open Patent Publication No. 1996-208091, for example, includes a driving roller assembly and pinch roller assemblies for discharging printed sheets. While a printed sheet to be discharged is nipped between the driving roller assembly and the pinch roller assemblies, the driving roller assembly is shifted in its axial direction. As the nipped sheet pulled by the driving roller assembly is also shifted in the axial direction of the driving roller assembly, the sheet delivery position of each sheet is varied to facilitate a sorting job.

An image forming apparatus recently developed is a so-called front access type as shown inFIG. 11, which is intended to achieve compactness in design. Referring toFIG. 11, the front-access-type image forming apparatus includes an image scanning section160located at an upper part, a sheet feed section170located at a lower part for feeding sheets of paper used for image forming, and an image forming section180disposed between the image scanning section160and the sheet feed section170. The image scanning section160, the image forming section180and the sheet feed section170are arranged generally in a U shape in cross section. A sheet delivery section190to which each sheet carrying a printed image is output is provided in a space between the image scanning section160and the sheet feed section170. To meet an increasing demand for advanced features, this type of image forming apparatus incorporates a duplex (double-sided) image-forming function which is realized by a switchback sheet transport method instead of a normally used intermediate tray method. In the switchback sheet transport method, a sheet of paper is reversed by transferring the sheet in a direction opposite to an ordinary sheet transport direction through a sheet transport path S′ by means of a pair of sheet output rollers191immediately after an image has been formed on one side of the sheet.

For the front-access-type image forming apparatus, it is not desirable to employ the aforementioned first approach of Japanese Laid-open Patent Publication No. 1999-199124. This is because it is necessary to provide multiple sheet cassettes for each paper size to feed the printing paper in different orientations and this makes it difficult to achieve compactness of the apparatus. The aforementioned second approach of Japanese Laid-open Patent Publication No. 2000-86056 is not desirable for the front-access-type image forming apparatus either, because it is difficult to accommodate a movable offset tray in the limited space of the sheet delivery section190. Accordingly, the aforementioned third and fourth approaches shown in Japanese Laid-open Patent Publication Nos. 1993-186121 and 1996-208091, respectively, seem to be suited to the front-access-type image forming apparatus, because arrangements of these approaches do not require a large space.

In the arrangements of Japanese Laid-open Patent Publication Nos. 1993-186121 and 1996-208091, however, sheets already discharged to different (offset) delivery positions on a sheet delivery tray, for example, might be displaced when another sheet is discharged onto the sheet delivery tray. This is because the sheet nipped by the output rollers, when discharged without a sheet output direction in which individual sheets are ejected from the output rollers being changed to a direction pointing away from a sheet delivery tray, goes into contact with at least one of the sheets already discharged onto the sheet delivery tray, and the sheet newly discharged could force, or push, one or more previously discharged sheets outward in the sheet transport direction. As a consequence, successively discharged multiple copies of the sheets might not be properly stacked at the intended delivery positions on the sheet delivery tray.

SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the invention to provide a sheet delivery mechanism which can be disposed in a limited space and improve sheet stacking performance by varying sheet output direction in which individual sheets are ejected from the sheet delivery mechanism from a normal output direction to a direction pointing away from a sheet delivery tray.

According to the invention, a sheet delivery mechanism includes offset rollers rotatably supported for discharging a sheet in a sheet transport direction, an offset unit rotatably supporting the offset rollers, an offsetting force generator for shifting the offset unit back and forth along a direction perpendicular to the sheet transport direction between a reference stop position and an offset stop position relative to a housing of an apparatus, and an offset unit swinging mechanism for swinging the offset unit about an axis parallel to rotary shafts of the offset rollers in such a manner that a sheet output direction in which the offset rollers eject the sheet varies to a direction pointing away from a sheet delivery tray when the offset unit is shifted along the direction perpendicular to the sheet transport direction by the offsetting force generator.

In this construction, the offset unit rotatably supporting the offset rollers can be shifted (offset) back and forth along the direction perpendicular to the sheet transport direction, the offset unit being supported swingably about the axis parallel to the rotary shafts of the offset rollers. When shifted from the reference stop position to the offset stop position, the offset unit swings in such a manner that the sheet output direction in which the offset rollers eject the sheet varies to the direction pointing away from the sheet delivery tray.

When the offset unit is shifted from the reference stop position to the offset stop position, the sheet output direction deviates to the direction pointing away from the sheet delivery tray, so that the offset rollers successively eject sheets in varying directions in a vertical plane. This swinging action of the offset unit serves to prevent the successively discharged sheets from going into contact with and exerting a pushing force in the sheet output direction against previously discharged sheets on the sheet delivery tray.

Furthermore, the offset unit swinging mechanism can be configured with a simple construction since the sheet output direction of the offset rollers is varied by swinging the entire offset unit.

Other features and advantages of the present invention will be more readily understood from the following detailed description when read in conjunction with accompanying drawings.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1is a diagram showing the construction of an image forming apparatus100employing a sheet delivery mechanism41according to a preferred embodiment of the invention. The image forming apparatus100allows user choice of multiple image forming modes, that is, copier mode, printer mode and facsimile mode. In any of these image forming modes, the image forming apparatus100forms images on sheets of paper (or any other types of printing media, such as films for an overhead projector).

The image forming apparatus100includes an image scanning section10, a sheet feeding section20, an image forming section30and a sheet delivery section40as well as other elements, such as an operator panel, which are not illustrated.

The image scanning section10located at an upper part of a housing of the image forming apparatus100includes a platen glass11, an original loading tray12and an optical scanning system13. The optical scanning system13incorporates a light source14, multiple reflecting mirrors15a,15b,15c,an optical lens16and a charge-coupled device (CCD)17. The light source14emits light onto an original placed on the platen glass11or an original being transferred from the original loading tray12through an original transport path R. The multiple reflecting mirrors15a,15b,15csuccessively reflect light reflected from the original to guide the reflected light to the optical lens16. The optical lens16converges the reflected light guided by the reflecting mirrors15a,15b,15conto the CCD17which performs a photoelectric conversion process to convert the reflected light into an electric signal.

The sheet feeding section20located at a lower part of the housing of the image forming apparatus100includes a sheet cassette21, a manual feed tray22and pickup rollers23. Sheets are fed from the sheet cassette21or the manual feed tray22during image forming operation. The pickup rollers23individually provided to the sheet cassette21and the manual feed tray22rotate to feed each sheet from the sheet cassette21or the manual feed tray22into a sheet transport path S.

The image forming section30is located beneath the image scanning section10at one side of the housing of the image forming apparatus100where the manual feed tray22is located. The image forming section30includes a laser scanning unit (hereinafter referred to as the LSU), a photosensitive drum31and a fuser unit36. The image forming section30further includes a charging unit32, a developing unit33, an image transfer unit34and a discharging unit35which are disposed in this order around the photosensitive drum31in a rotating direction of the photosensitive drum31shown by an arrow inFIG. 1.

The sheet delivery section40located above the sheet cassette21includes the aforementioned sheet delivery mechanism41and a sheet delivery tray42. The sheet delivery mechanism41discharges sheets carrying printed images from the sheet transport path S to offset positions on the sheet delivery tray42. The sheet delivery tray42receives the individual sheets output by the sheet delivery mechanism41. The operator panel has a plurality of input keys (not shown) which accept various user settings, such as the number of copies and a printing scale factor. The sheet delivery mechanism41will be later described in greater detail.

When copying original images on sheets in the copier mode, the user places an original to be copied on the platen glass11or on the original loading tray12of the image scanning section10. Then, the user sets the number of copies and a printing scale factor, for instance, by pressing appropriate input keys on the operator panel and presses a start key (not shown).

When the start key is pressed, the image forming apparatus100causes the pickup roller23of the sheet cassette21or the manual feed tray22to rotate to feed a sheet therefrom into the sheet transport path S. The sheet is first fed up to registration rollers51disposed on the sheet transport path S. The registration rollers51nip a leading edge of the sheet located at a forwardmost extremity in a sheet transport direction so that the leading edge of the sheet becomes parallel to an axial direction of the registration rollers51and a toner image formed on the photosensitive drum31correctly aligns with the sheet when transferred thereto.

Image data picked up by the image scanning section10is subjected to an image processing process performed under conditions set by user input keys, for instance, and transmitted to the LSU as print data. An outer surface of the photosensitive drum31is uniformly charged to a specific potential by the charging unit32. The LSU forms an electrostatic latent image of the original image on the surface of the photosensitive drum31by projecting laser light based on the image data (print data) by means of a polygon mirror and various lenses which are not illustrated. Subsequently, toner adhering to an outer surface of a toner drum33aprovided in a developing tank (not shown) of the developing unit33with part of the toner drum33adirectly facing the photosensitive drum31is attracted to the surface of the photosensitive drum31according to a distribution of charged and uncharged areas on the surface of the photosensitive drum31. As a result, the latent image is converted into a visual toner image.

Then, the sheet nipped by the registration rollers51is passed through a gap between the photosensitive drum31and the image transfer unit34at correct registration with the toner image. While the sheet is being transported, the toner image is transferred from the surface of the photosensitive drum31onto the sheet by an image transfer roller (not shown) provided in the image transfer unit34. Residual toner left on the surface of the photosensitive drum31is scraped off by a cleaning blade of a drum unit (not shown) and collected by a cleaner unit (not shown). The sheet carrying the transferred toner image is passed between an upper heat roller36aand a lower heat roller36bprovided in the fuser unit36. Heat and pressure applied by the upper and lower heat roller36a,36bfuse and fix the toner image onto the sheet. The sheet is then delivered onto the sheet delivery tray42by the sheet delivery mechanism41.

FIGS. 2 and 3are sectional side views showing the construction of the sheet delivery mechanism41of the present embodiment. The sheet delivery mechanism41includes an enclosure55, an offset unit60, a roller turning force generator65, a driving force transmission mechanism70, an offsetting force generator75, an offsetting force transmission mechanism80, a offset unit swinging mechanism90and sheet squeezers95. The sheet delivery mechanism41thus constructed ejects each sheet carrying a printed image which is being transferred through the sheet transport path S onto the sheet delivery tray42. If the user has entered a setting for activating a sorting function by pressing appropriate input keys on the operator panel, the sheet delivery mechanism41selectively delivers printed sheets to offset delivery positions B and C as well as to a normal (reference) delivery position A on the sheet delivery tray42by successively shifting the individual sheets along the direction of an arrow Y shown inFIG. 4, perpendicularly to the sheet transport direction.

The enclosure55, which is supported by a frame110of the housing of the image forming apparatus100, incorporates the offset unit60and part of the driving force transmission mechanism70in an internal space and is fitted with the offsetting force generator75and the offsetting force transmission mechanism80disposed on the outside. The offset unit60, which includes an internal enclosure61and a pair of upper and lower offset roller assemblies62, shifts along the direction of an arrow Y (FIG. 2) from a position shown inFIG. 2to a position shown inFIG. 3, for instance, to selectively output the printed sheets to the individual delivery positions A, B, C. The internal enclosure61rotatably supports the individual offset roller assemblies62so that the offset roller assemblies62can push out the printed sheets in the sheet transport direction. The offset roller assemblies62carry multiple pairs of upper and lower offset rollers62a,62bas illustrated. These rollers62a,62brotate while nipping each sheet to deliver it onto the sheet delivery tray42.

The roller turning force generator65produces a driving force for turning the offset roller assemblies62. The driving force transmission mechanism70, which includes a driving gear71, a shaft72, connecting gears73a,73b,73cand a sliding sleeve74, transmits the driving force of the roller turning force generator65to the offset roller assemblies62. Mounted directly on the shaft72, the driving gear71connected to the roller turning force generator65turns the shaft72.

The shaft72is rotatably supported in the frame110of the housing in such a manner as to be parallel to the rotary shafts63a,63bsupporting the offset rollers62a,62b.Mounted on the shaft72, the sliding sleeve74is made slidable along the shaft72. Also, the shaft72supports the offset unit60via the sliding sleeve74-and the connecting gears73a,73b,73cmovably along the direction of the arrow Y (FIG. 2) which is perpendicular to the sheet transport direction. To limit a movable range of the offset unit60and the accompanying connecting gears73a,73b,73c,the shaft72has a stopper pin72awhich projects outward through a slotted hole74aformed in the sliding sleeve74, the slotted hole74aextending along an axial direction of the shaft72.

The three connecting gears73a,73b,73cprovided in the offset unit60are meshed together, with the connecting gear73bplaced between the gears73aand73c.The connecting gear73aprotrudes from the internal enclosure61through an opening formed therein on a side of the internal enclosure61facing the shaft72. The connecting gear73athus protruding is fitted on the sliding sleeve74and supported thereby, so that the connecting gear73ais slidable over the shaft72along the direction of the arrow Y together with the sliding sleeve74. When the shaft72rotates, its rotary motion is transmitted to the connecting gear73avia the stopper pin72aof the shaft72. Therefore, the shaft72, the sliding sleeve74and the connecting gear73atogether rotate in the same direction as a single piece, causing the connecting gear73bto rotate in an opposite direction. The connecting gear73bis fitted on one end of a rotary shaft63asupporting the rollers62aof the upper offset roller assembly62, so that the connecting gear73bturns the upper rollers62avia the shaft63a.On the other hand, the connecting gear73cis fitted on one end of a rotary shaft63bsupporting the rollers62bof the lower offset roller assembly62, so that the connecting gear73cturns the lower rollers62bvia the shaft63b.

As the gears73band73cturn in opposite directions, the upper rollers62aand the lower rollers62bturn in such a way that their contact portions (nip areas) correctly push out each sheet in the aforementioned sheet transport direction.

The offsetting force generator75connected to the offsetting force transmission mechanism80produces a driving force for shifting the offset unit60along the direction of the arrow Y (FIG. 2). The offsetting force transmission mechanism80includes a pinion81and a rack82. The pinion81is rotatably supported and connected between the offsetting force generator75and the rack82. When driven by the offsetting force generator75, the pinion81rotates and causes the rack82to move in the direction of the arrow Y. The rack82affixed to an upper rear position of the internal enclosure61as illustrated inFIG. 2causes the internal enclosure61to shift along the direction of the arrow Y when moved by the pinion81. When the internal enclosure61moves along the direction of the arrow Y in this fashion, the connecting gear73aand the sliding sleeve74also move in the same direction as one of edges of the opening formed in the internal enclosure61comes into contact with one of side surfaces of the connecting gear73a.

The offset unit swinging mechanism90includes offsetting enclosure support members91, guide grooves92and projecting pins93.

The offsetting enclosure support members91are shafts installed in the enclosure55parallel to the rotary shafts63a,63bsupporting the offset rollers62a,62b.The offsetting enclosure support members91, individually fitted in holes formed in side walls of the internal enclosure61along the direction of the arrow Y (FIG. 2), support the entire offset unit60slidably along the direction of the arrow Y such that the offset unit60can swing about the offsetting enclosure support members (shafts)91which are parallel to the rotary shafts63a,63b.The guide grooves92are located outside a side wall of the internal enclosure61on an upstream side thereof with respect to the sheet transport direction as shown inFIGS. 5A and 5B. The projecting pins93are provided on an upper inner wall of the enclosure55. As the projecting pins93are individually fitted in the guide grooves92as illustrated, the guide grooves92limits the movable range of the offset unit60along the direction of the arrow Y. Therefore, when the offset unit60moves from a reference stop position shown inFIG. 5Ato a position shown inFIG. 5Balong the direction of the arrow Y, the entire offset unit60vertically swings from a position shown inFIG. 6Ato a position shown inFIG. 7Aabout the offsetting enclosure support members (shafts)91.

In this construction, a sheet output direction in which the offset roller assemblies62ejects each sheet varies from the direction of an arrow P directed obliquely downward toward the sheet delivery tray42as shown inFIG. 6Ato the direction of an arrow Q directed obliquely upward pointing away from the sheet delivery tray42as shown inFIG. 7Awhen the offset unit60vertically swings in the aforementioned manner. This swinging action of the offset unit60helps prevent the earlier-mentioned problem of the prior art that successively discharged sheets come into contact with and exert a pushing force against previously discharged sheets on the sheet delivery tray42in the direction of the arrow P, displacing the sheets already stacked on the sheet delivery tray42. This construction of the offset unit swinging mechanism90serves to improve sheet stacking performance of the sheet delivery mechanism41.

Also, since the sheet output direction of the offset roller assemblies62is varied by swinging the entire offset unit60, it is possible to simplify the construction of the offset unit swinging mechanism90and easily dispose the offset unit swinging mechanism90.

In addition, the offset unit60is automatically swung in a vertical plane guided along the guide grooves92when the offset unit60is horizontally shifted along the direction of the arrow Y. This construction of the embodiment makes it unnecessary to provide a dedicated driving force generator for swinging the offset unit60, contributing thereby to further simplification of the offset unit swinging mechanism90. Furthermore, it is possible to reduce the space required for disposing the offset unit swinging mechanism90and avoid an increase in the number of components and a consequent cost increase with this construction. Moreover, it is possible to swiftly discharge individual sheets since the sheet delivery mechanism41can rotate the upper and lower rollers62a,62bwhile shifting the offset unit60along the direction of the arrow Y and swinging the same in the vertical plane.

While the guide grooves92are located on the offset unit60and the projecting pins93are disposed on the housing of the image forming apparatus100in the present embodiment, the invention is not limited to this construction. The embodiment may be modified such that the guide grooves92are located on the housing of the image forming apparatus100and the projecting pins93are mounted on the offset unit60, for example.

Referring toFIGS. 6A and 7A, an upper end95aof each of the sheet squeezers95is mounted loosely on the rotary shaft63aof the upper offset rollers62awhile a lower end95bof each of the sheet squeezers95extends downward beyond a point of contact between the upper rollers62aand the lower rollers62b.When a sheet is discharged from between the upper and lower offset roller assemblies62, the lower ends95bof the sheet squeezers95lie on the sheet in direct contact therewith as shown inFIGS. 6B and 7Band thereby exert a pushing force against an upper side of the sheet forcing it toward the sheet delivery tray42.

More particularly, as the leading edge of the sheet goes into contact with the lower ends95bof the sheet squeezers95, the sheet squeezers95pushed by the leading edge of the sheet are caused to swing upward in a direction toward the upper offset rollers62a.The lower ends95bof the sheet squeezers95lie on the upper side of the sheet in direct contact therewith forcing the sheet downward from the side of the upper offset rollers62aso that the sheet goes into contact with the sheet delivery tray42.

Generally, the sheet ejected from between the upper and lower offset roller assemblies62in the direction of the arrow Q would receive greater resistance by air when falling onto the sheet delivery tray42as compared to the sheet ejected in the direction of the arrow P. For this reason, the discharged sheets are likely to drop at unintended positions without the provision of the sheet squeezers95. In the aforementioned construction of the embodiment, the sheet squeezers95exert a downward pushing force to force the sheet toward the sheet delivery tray42. It is therefore possible to prevent the individual sheets discharged from being delivered to unintended positions due to the resistance of air. The construction of the embodiment serves to further improve the sheet stacking performance of the sheet delivery mechanism41.

FIG. 8is a flowchart showing a procedure of offset sheet delivery operation performed by the sheet delivery mechanism41for outputting individual sheets to the offset delivery positions. Here, it is intended to produce multiple copies of a multiple-page document and output the individual copies to the offset delivery positions using the sorting function. First, a judgment is made to determine whether a current position of the offset unit60coincides with a next stop position of the offset unit60corresponding to a sheet delivery position where a sheet transferred next should be discharged (step S1). If the current position of the offset unit60coincides with its next stop position, the sheet delivery mechanism41outputs a printed sheet onto the sheet delivery tray42by causing the offset roller assemblies62to rotate (step S8). While the sheet is being discharged, the offset roller assemblies62are kept rotating by causing the roller turning force generator65to continuously to run.

If the judgment result in step S1above is in the negative, that is, the current position of the offset unit60is judged to be differing from the next stop position of the offset unit60corresponding to the sheet delivery position where the sheet transferred next should be discharged, a further judgment is made by using an unillustrated sensor, for example, to determine whether a trailing end of a sheet transferred through the sheet transport path S has passed between transport rollers52located immediately upstream of the offset roller assemblies62along the sheet transport path S (step S2).

Then, a judgment is made to determine whether the offset unit60should be moved in a forward shifting direction or in a reverse shifting direction next based on the current position of the offset unit60and its next stop position (step S3). Here, the “forward shifting direction” refers to a shifting direction from the delivery position A to the delivery position C along the arrow Y inFIG. 4and the “reverse shifting direction” refers to a shifting direction from the delivery position C to the delivery position A.

If the offset unit60is to be shifted in the forward shifting direction according to the judgment result in step S3, the sheet delivery mechanism41causes offsetting force generator75to shift the offset unit60in the forward shifting direction (step S4). If the offset unit60is to be shifted in the reverse shifting direction according to the judgment result in step S3, on the contrary, the sheet delivery mechanism41causes offsetting force generator75to shift the offset unit60in the reverse shifting direction (step S5).

Subsequently, a judgment is made to determine whether the offset unit60has reached the next stop position (step S6). The judgment of step S6is repetitively made until the offset unit60reaches the next stop position. When the offset unit60has reached the next stop position (Yes in step S6), the sheet delivery mechanism41causes the offsetting force generator75to stop (step S7) and discharges the sheet onto the sheet delivery tray42(step S8). After the sheet has been discharged, a judgment is made to determine whether there remains another sheet to be transferred through the sheet transport path S (step S9). If there remains another sheet to be transferred, the sheet delivery mechanism41returns to step S1above to reexecute the offset sheet delivery operation ofFIG. 8. If there is no more sheet to be transferred, the sheet delivery mechanism41stops to perform the offset sheet delivery operation.

While the present embodiment uses a combination of the guide grooves92and the projecting pins93for swinging the offset unit60, the invention is not particularly limited to this arrangement but may employ any alternative arrangement which can swing the offset unit60in a like fashion. Shown inFIG. 9is one of such alternative arrangements, in which a pair of rotatable cams96is disposed on the bottom of the internal enclosure61inside the enclosure55at a downstream end of the sheet transport path S. Driven by a cam driver97, the cams96rotate up to a specific angular position to swing the internal enclosure61about the offsetting enclosure support members (shafts)91as illustrated inFIGS. 7A and 7B.

In the aforementioned alternative arrangement, the timing of turning the cams96for swinging the offset unit60need not necessarily coincide with the timing at which the offset unit60is shifted along the direction of the arrow Y. When outputting individual sheets to the offset delivery positions, the offset unit60may be swung by turning the cams96during a period between a point in time when the trailing end of the sheet passes between the transport rollers52and a point in time when the sheet is nipped between the upper and lower rollers62a,62b.

Although the sheet squeezers95loosely fitted on the rotary shaft63apress against the sheet being ejected from between the upper and lower rollers62a,62bto force the sheet toward the sheet delivery tray42in the foregoing embodiment, the invention is not limited to this construction but may be modified in various ways as long as there is made an arrangement for pressing the sheet being ejected from above toward the sheet delivery tray42. Shown inFIG. 10is one of such alternative arrangements, in which there are provided sheet squeezers98swingably fitted to a side wall of the internal enclosure61on a downstream side thereof with respect to the sheet transport direction just above a sheet outlet formed in the side wall. As the leading edge of a sheet being ejected emerges through the sheet outlet in the downstream side wall of the internal enclosure61, the leading edge goes into contact with the sheet squeezers98, whereby the sheet squeezers98swing up and lie on the sheet so that the sheet is forced downward against the sheet delivery tray42.

As so far discussed, the sheet delivery mechanism41of the foregoing embodiment varies the sheet output direction of the offset roller assemblies62from the direction of the arrow P to the direction of the arrow Q by swinging the entire offset unit60when discharging individual sheets to the offset delivery positions and forces each sheet being ejected from between the upper and lower rollers62a,62bdownward against the sheet delivery tray42from the side of the upper offset rollers62ato produce the aforementioned advantageous effects.

Also, the roller turning force generator65for turning the offset roller assemblies62and the offsetting force generator75for shifting the offset unit60along the direction of the arrow Y are disposed separately from each other, and the roller turning force generator65and the offsetting force generator75are simultaneously operated to eject the sheet from between the upper and lower rollers62a,62bwhile shifting the offset unit60along the direction of the arrow Y. This makes it possible to simplify the construction of and facilitate the placement of the mechanisms for transmitting the respective driving forces and swiftly discharge the individual sheets.

Since there are two stop positions of the offset unit60corresponding to the offset delivery positions B and C in addition to the reference stop position of the offset unit60corresponding to the normal delivery position A used as a reference position for delivery of individual sheets, it is possible to easily sort multiple copies of printed sheets with an increased number of delivery positions. Also, it is possible to discharge the printed sheets to multiple delivery positions located along the direction perpendicular to the sheet transport direction with a minimum increase in space requirements, because only the offset unit60is shifted along the direction of the arrow Y.

Although there is provided a pair of prime movers (the roller turning force generator65and the offsetting force generator75) in the present embodiment, the invention is not limited thereto. The same advantageous effects as offered by the foregoing embodiment will be obtained even with a single prime mover if the offset roller assemblies62can be rotated and the offset unit60can be shifted along the direction of the arrow Y in the same fashion as so far discussed.

Although there are two offset sheet delivery positions B, C in addition to the normal delivery position A used as the reference position for delivery of individual sheets in the foregoing embodiment, the invention is not limited to this arrangement. As many sheet delivery positions as necessary may be provided depending on the configuration and physical size of an image forming apparatus.