Sheet treating apparatus and image forming apparatus having the same

Abstract: A sheet treating apparatus for avoiding electrostatic charge accumulation discharges the sheet P, bearing an image thereon, onto discharge sheet stacking trays (200,201) provided on the side part of the main body, and receives the trailing end of the sheet by the side part of the main body, and is provided with a grounding member (216) for grounding the sheet by contact with the trailing end of the sheet.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates to a sheet treating apparatus for discharging a sheet, and an image forming apparatus provided with such sheet treating apparatus. Related Background Art There is conventionally known a sheet treating apparatus capable of discharging sheets, on which images are formed in an image forming apparatus, in the shape of a bundle. Such sheet treating apparatus discharges sheets, bearing images thereon, onto discharge sheet stacking means provided on a lateral part of the main body, wherein the trailing ends of the sheets are received by the lateral part of the main body. The image forming apparatus can be a copying machine, a facsimile apparatus, a printer or a composite apparatus thereof. Also the sheet can be a plain paper, a thin resinous sheet used as a substitute for the plain paper, a postcard, a cardboard, an envelope or a thin plastic plate. However, such sheet discharged by the sheet treating apparatus may be electrostatically charged when the sheet is subjected to the image formation in the image forming apparatus or conveyed in the sheet treating apparatus. The sheet tends to bear electrostatic charge particularly when the sheet treating apparatus is used in a dry environment. In the sheet discharging operation under such condition, the electrostatic charge may become resistive against the sheet discharge, eventually leading to defective sheet discharge. Also the electrostatic charge on the sheets causes the sheet to stick mutually, whereby the separation of the sheet becomes difficult. A sheet treating apparatus comprising the features summarized in the pre-characterizing clause of claim 1 is known from document JP-A-57027272. In this known sheet treating apparatus, the stacking means is formed by a discharge tray which comprises a bottom plate and an upright receiving plate at the entrance side of the discharge tray. An inlet part of the bottom plate and the receiving plate are made of a conductive material and are grounded so that they form the grounding member of the known sheet treating apparatus. This grounding member is provided for dissipating, through the grounding member, the electrostatic charges which eventually accumulate on the sheets before they are discharged onto the discharge tray. Document US-A-5 407 188 discloses a sheet treating apparatus which comprises sheet end receiving rollers located at the entrance side of a sheet discharge tray. The sheet end receiving rollers contact the trailing ends of the discharged sheets and are provided for reducing the resistance on the sheets when the sheet discharge tray is moved in a right-to-left direction. Document US-A-4 501 418 discloses a sheet treating apparatus which comprises a grounding member by means of which electrostatic charges formed on the sheets can be eliminated. The grounding member is arranged such that it contacts the sheets before they are discharged onto a stacking means. Document EP-A-0 024 712 discloses a sheet treating apparatus which comprises a discharge means for discharging a sheet, a stacking means for stacking the sheet discharged by the discharge means, and a grounding member for dissipating an electrostatic charge formed on the sheet prior to the discharge. The grounding member is arranged such that it first contacts the leading end of the sheet while this is discharged, and thereafter contacts the lower surface of the sheet. SUMMARY OF THE INVENTION It is an object of the present invention to provide a sheet treating apparatus capable of effectively removing electrostatic charges from the sheets discharged onto the stacking means, thereby avoiding the problems caused by electrostatically charged sheets. Moreover, it is an object of the present invention to provide an image forming apparatus having such a sheet treating apparatus. According to the invention, these objects are achieved by the sheet treating apparatus defined in claim 1 and by the image forming apparatus according to claim 10. The trailing ends of the sheets, discharged onto the discharge sheet stacking means, are received on the lateral part of the main body of the apparatus, and, in such state, the trailing ends of the sheets are received by the grounding member. Therefore, the electrostatic charge eventually present on the sheets is dissipated through the grounding member, whereby the sheets can be made free of the electrostatic charge. The above-mentioned sheets can be discharged in a shape of a bundle onto the discharge sheet stacking means. The electrostatic charge is more easily accumulated in the sheets when the sheets are in the shape of the bundle, but such electrostatic charge can be dissipated by the grounding member. The grounding member may be formed separately from the main body and be mounted on the main body. Further advantageous developments of the invention are defined in the dependent claims. The image forming apparatus of the present invention is provided with image forming means for forming an image on a sheet, and any sheet treating apparatus mentioned above. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic front cross-sectional view showing an entire configuration of a sheet treating apparatus of the present invention; Fig. 2 is a horizontal cross-sectional view of a stacking tray moving mechanism; Fig. 3 is a view showing an arrangement of sensors around the stacking tray; Fig. 4 is a view illustrating an operation of the sheet treating apparatus in a non-sort mode; Figs. 5 to 8 are views illustrating an operation of the sheet treating apparatus in a staple sort mode; and Fig. 9 is an elevation view of an image forming apparatus in which the sheet treating apparatus of the present invention is applicable. DESCRIPTION OF THE PREFERRED EMBODIMENTS Fig. 9 shows an example of an image forming apparatus (copying machine) 310 in which a sheet treating apparatus 1 of the present invention is provided in a main body 300 of the image forming apparatus (main body of the copying machine). The main body 300 of the image forming apparatus (copying machine) is provided with a platen glass 906 serving as an original stocking plate; a light source 907; a lens system 908; a sheet feeding portion 909; an image forming portion (image forming means) 902; an auto original feeder (recycling document feeder (RDF)) 500 for feeding the original to the platen glass 906; and a sheet treating apparatus 1 of the embodiment of the present invention, for stacking the sheet, discharged from the main body 300 and bearing images thereon. The sheet treating apparatus 1 of the embodiment of the present invention may be incorporated not only in the main body of the copying machine but also in that of a facsimile apparatus, a printer or a composite apparatus thereof. Consequently, the image forming apparatus used herein includes not only the main body of the copying machine but also the facsimile apparatus, the printer and the composite apparatus thereof. Also the sheet includes plain paper, thin resinous sheet used as a substitute for the plain paper, postcard, cardboard, envelope, thin plastic sheet etc. The sheet feeding portion 909 is provided with cassettes 910, 911 containing recording sheets P and detachably mounted on the main body 300 of the apparatus, and a deck 913 provided on a pedestal 912. The image forming portion 902 is provided with a cylindrical photosensitive drum 914, and a developing device 915, a transfer charger 916, a separation charger 917, a cleaner 918 and a primary charger 919 provided around the photosensitive drum 914. At the downstream side of the image forming portion 902, there are provided a conveying device 920, a fixing device 904 and a pair of discharge rollers 905. The details of the auto original feeder (RDF) 500 will be omitted. In the following there will be explained the operation of the main body 300 of the image forming apparatus. In response to a sheet feed signal supplied from a controlling device 930 of the main body 300, a sheet P is fed from the cassette 910, 911 or the deck 913. On the other hand, the original D placed on the original stocking plate 906 is illuminated by the light from the light source 907, and the reflected light irradiates the photosensitive drum 914 through the lens system 908. The photosensitive drum 914 is in advance charged by the primary charger 919 and forms an electrostatic latent image thereon by the exposure to light, and the electrostatic latent image is developed by the developing device 915 to form a toner image. The sheet P fed from the sheet feeding portion 909 is subjected to correction of skew feed by the registration rollers 901, and is fed to the image forming portion 902 in a registered timing. In the image forming portion 902, the toner image on the photosensitive drum 914 is transferred onto the fed sheet P by the transfer charger 916, and the sheet P bearing the transferred toner image is charged by the separation charger 917 in a polarity opposite to that of the transfer charger 916 and is thus separated from the photosensitive drum 914. Thus separated sheet P is conveyed by the conveying device 920 to the fixing device 904, in which the transferred image is permanently fixed to the sheet P. The sheet P bearing the fixed image is discharged by the pair of discharge rollers 905 from the main body 300 of the apparatus. In this manner, the sheet P fed from the sheet feeding portion 909 is subjected to image formation and is discharged to the sheet treating apparatus 1 of the present invention. In the following there will be explained the sheet treating apparatus of the embodiment of the present invention. Referring to Fig. 1, the finisher (sheet treating apparatus) 1 is equipped in the main body 300 of the image forming apparatus. In Fig. 1, there are shown paired discharge rollers 905 of the main body 300 of the image forming apparatus; paired entrance rollers 2 of the finisher 1; paired conveying rollers 3; a sheet sensor 31; a punch unit 50 for punching holes in the vicinity of the trailing end of the conveyed sheet; a large conveying roller 5; and depressing rollers 12, 13, 14 adapted to be depressed for conveying the sheet. A change-over flapper 11 executes switching between a non-sort path 21 and a sort path 22. A change-over flapper 10 executes switching between the sort path 22 and a buffer path 23 for temporarily storing the sheets. There are also provided conveying rollers 6. Temporary stacking, alignment and stapling of the sheets can be executed on an intermediate tray (hereinafter referred to as "treating tray") 130 at which a stapler 101 is arranged. Discharge rollers 7 serve to discharge the sheet onto the treating tray 130. A bundle discharge roller 180b is supported by the pivotally movable guide 150, and, when it moves to a closed position, the bundle discharge roller 180b cooperates with a roller 180a provided on the treating tray 130 to discharge the bundle of sheets on the treating tray 130 onto a stacking tray 200. The treating tray 130 is positioned between the conveying portion for conveying the sheet from the main body 300 of the image forming apparatus and the stack tray 200 for receiving and supporting the bundle of sheets handled on the treating tray 130. In the sort path 22 in the vicinity of the paired discharge rollers 7, 7 of the conveying portion, a sensor 183 is provided for detecting the sheet moving in the sort path 22. The sensor 183 is connected to a controlling circuit 301 of the sheet treating apparatus 1. The controlling circuit 301 is connected to the controlling device 930 in the main body of the copying machine, in order to control not only the operation of the sheet treating apparatus but also the smooth cooperative operation with the main body of the copying machine. In the following there will be explained a stack tray 200 and a sample tray 201 with reference to Figs. 2 and 3. These two trays 200, 201 are selected according to the situation. The stack tray 200 in the lower position is selected in case of receiving the copied or printed sheet. The sample tray 201 in the upper position is selected in case of receiving a sample sheet, an interruption processed sheet, a sheet in case of overflow of the stack tray, a sheet by function sorting, or a sheet in job mixed loading. These two trays 200, 201 are respectively provided with motors 202 so as to be independently movable in the vertical direction, and are mounted on a rack 210 which serves also as a roller retainer mounted vertically on a frame 250 of the sheet treating apparatus 1. A regulating member 215 regulates the play of the trays in the front-side direction and the rear-side direction. A tray base plate 211 supports a stepping motor 202, and a pulley force-fitted onto the motor shaft drives a pulley 203 through a timing belt 212. A shaft 213, connected to the pulley 203 with parallel pins, transmits rotary driving force to a ratchet 205 similarly connected to the shaft 213 with parallel pins, thereby biasing an idler gear 204 by a spring 206. The ratchet 205 is connected to the idler gear 204 thereby transmitting driving force thereto. The idler gear 204 is also connected to a gear 207. Another gear 207 is provided on a shaft 208 in order to drive the rack 210 at both front and rear-sides, whereby the rack 210 can be moved through a gear 209. On the tray, two rollers 214 on each side are housed in the roller retainer 210, which also serves as a rack. The trays are mounted on a base plate 211 to constitute a tray unit. On a lateral portion 219a, serving as a position regulating member, of a stacking wall 219 (Fig. 14), a plurality of grounding members 216, 216 extending through the two trays 200, 201 in the vertical direction are mounted from the front-side to the rear-side. The grounding member 216 is mounted on the stacking wall 219 by inserting elastic fingers 216a, 216a in holes 217 formed in the stacking wall 219. The elastic fingers 216a are protruded from plural positions of the grounding member 216 arranged in a longitudinal direction of the grounding member 216. The grounding member 216 is made of a metal plate, a plastic mold on the surface of which a metal plate is incorporated, a plastic mold in which metal powder is mixed or a plastic mold which is plated with a metal, and is provided for receiving the trailing end of the sheets stacked on the trays 200, 201 (Fig. 1) for dissipating the electrostatic charge accumulated on the sheets and is connected to an unrepresented grounding wire connected to the exterior of the sheet treating apparatus 1. In order that the sheet can be discharged onto the trays 200, 201, the grounding members 216 are not provided in the vicinity of the rollers 9, 180a as shown in Fig. 1, thereby not disturbing the sheet discharge. The grounding members 216 serve to dissipate the electrostatic charge accumulated on the sheets, whereby, at the sheet discharge onto the trays, there is reduced the sliding resistance resulting from the mutual sticking of the sheets by the electrostatic charge, thereby resolving the defective sheet discharge. Also the sheets discharged onto the tray 200 or 201 do not mutually stick by the electrostatic charge and can be easily separated. The electrostatic charge tends to accumulate on the sheets particularly when a large number of sheets are stacked on the tray 200 or 201, and in such situation the grounding members 216 exhibit their function of dissipating the electrostatic charge. As the grounding members 216 are mounted by the elastic fingers 216a on the stacking wall 219, it is possible to separately prepare the stacking wall 219 generally by plastic molding and the grounding members 216 requiring high electric conductivity, thereby reducing the manufacturing cost. Also in case the grounding member 216 is damaged, it can be easily detached from the stacking wall 219 and replaced by bending the elastic fingers 216a. Referring again to Fig. 2, the aforementioned ratchet 205 is rendered capable of idle rotation, against the force of the spring 206, only in a direction to lift the tray, in order to prevent damage to the tray driving system by the presence of an obstacle at the descent of the tray. When such idle rotation is carried out, a sensor S201 detects a slit, incorporated in the idler gear, thereby immediately stopping the motor. This sensor is used also for detecting a desynchronization. An area sensor S202 (Fig. 2) detects the flag in an area from an upper limit sensor S203a (Fig. 15) for preventing the excessive elevation of the tray to a treating tray sheet surface sensor S205. A sensor S203b for detecting the 1000 sheet position on the sample tray is provided in a position corresponding to 1000 sheets from the non-sort sheet surface sensor S204, and serves to limit the stacking amount on the sample tray 201 by the height. Also a sensor S203c is provided to limit the stacking amount by the height when the sample tray 201 receives sheets from the treating tray 130, and is provided at a position corresponding to 1000 sheets from the sheet surface sensor S205. A sensor S203d is provided to limit the stacking amount by the height when the stack tray 200 receives sheets from the treating tray 130, and is provided at a position corresponding to 2000 sheets from the sheet surface sensor S205. A lower limit sensor S203e is provided for preventing excessive descent of the stack tray 200. Among the above-mentioned sensors, the sheet surface sensors S204, S205 alone are composed of transmissive sensors between the front and rear sides. Also each tray is provided with a sheet present/absent sensor S206. The sheet surface detection is achieved by at first elevating the tray to a position until the sheet surface sensor is covered, and, after the sheet stacking, lowering the tray until the optical axis of the sheet surface sensor is uncovered and elevating the tray until the optical axis of the sheet surface sensor is again covered. This operation is reiterated. In the following there will be explained the flow of the sheet P. When the user selects the non-sort mode on an operation unit (not shown) of the main body of the image forming apparatus, the paired entrance rollers 2, conveying rollers 3 and large conveying roller 5 are rotated to convey the sheet P, conveyed from the main body 300 of the image forming apparatus and bearing the image thereon, as shown in Fig. 4. The flapper 11 is shifted by a solenoid (not shown) to the illustrated position to convey the sheet P to the non-sort path 21. When the sensor 33 detects the trailing end of the sheet P, the rollers 9 are rotated at a speed suitable for stacking, thereby discharging the sheet P onto the sample tray 201. The discharged sheet P is received, at the trailing end thereof, by the grounding member 216 and is grounded, whereby the electrostatic charge accumulated on the sheet is dissipated. Consequently the sheets P do not stick mutually and can be easily separated one by one. Also the user can be relieved from the electrical shock when grabbing the sheet P. In the following there will be explained the operation when the staple sort mode is selected by the user. As shown in Fig. 5, the paired entrance rollers 2, the conveying rollers 3 and the large conveying roller 5 are rotated to convey the sheet P conveyed from the main body 300 of the image forming apparatus. The flappers 10, 11 are maintained in positions shown in Fig. 5. The sheet P passes the sort path 22 and is discharged by the discharge rollers 7 to the stapler 101. In this state, a retractable tray 170 is in the protruding position, thereby receiving the leading end of the sheet P discharged from the discharge rollers 7 and preventing the sheet P from hanging, thus avoiding insufficient recovery of the sheet P and improving the sheet alignment on the treating tray. The discharged sheet P starts to move, by the self-weight thereof, toward a trailing end stopper (not shown) and a paddle 160 starts to rotate counterclockwise to assist the sheet movement mentioned above. When the trailing end of the sheet P is stopped by securely abutting against the stopper, the rotation of the paddle 160 is stopped and the discharged sheet is aligned. When all the sheets of a first copy are discharged and aligned on the treating tray 130, a pivotally movable guide 150 is lowered as shown in Fig. 6 whereupon the roller 180b rests on the sheet bundle and the stapler 101 staples the bundle of the sheets. On the other hand, a sheet P1 discharged in the meantime from the main body 300 of the image forming apparatus is guided by the flapper 10 and wound around the large conveying roller 5 as shown in Fig. 6 and is stopped at a predetermined distance after a sensor 32. When a next sheet P2 advances by a predetermined distance from the sheet sensor 31, the large conveying roller 5 is rotated as shown in Fig. 7 to superpose the second sheet P2 on the first sheet P1 in such a manner that the second sheet P2 precedes the first sheet P1 by a predetermined distance, and the second sheet P2 is wound around the large conveying roller 5 as shown in Fig. 8 and is stopped after advancement by a predetermined distance. On the other hand, the sheet bundle on the treating tray 130 is discharge onto the stack tray 200 as shown in Fig. 8 and the electrostatic charge eventually accumulated on the sheet bundle is dissipated by the grounding members 216. In this operation, the retractable tray 170 is moved to the home position, before the sheet bundle passes through the discharged sheet bundle rollers, in order to drop the sheet bundle onto the stack tray 200. In the following there will be explained the movement of the stack tray 200 and the sample tray 201 (Figs. 2 and 3). Prior to the start of operation, these trays normally wait in the positions of respective sheet surface sensors. As explained in the foregoing, the stack tray 200 is normally used for stacking the copied or printed sheets. It can receive the sheets treated for example by the stapler 101 or the unstapled sheet bundle discharged with a limited number of sheets, and can support up to 2000 sheets at maximum, which is detected by the sensor 203d. If the printing output still continues, the stack tray 200 is lowered by a height corresponding to 1000 sheets from the position of the sensor S203d (namely to a position S203d'). Then the sample tray 201 is lowered to the position of the sheet surface sensor S205 for the treating tray, and the sheet receiving is started again. The sample tray 201 can support up to 1000 sheets at maximum, which is detected by the sensor 203c. In case of starting a next job without removing the sheets on the stack tray 200 after the completion of the job not exceeding 2000 sheets or executing a job by interrupting the current job, the sample tray 201 may be used for sheet stacking from the non-sort path 21, though the treating operation is not possible. The normal output operation to the sample tray 201 through the non-sort path 21 may be used for the output of a copy only for sample purpose without treating, or in case the output to the sample tray is selected in the function sorting. The sheet treating apparatus of the present invention is capable of dissipating, through the grounding members, the electrostatic charge eventually accumulated on the sheets and thus maintaining the sheets in charge-free state, whereby the sheets discharged onto the tray are not subjected to resistance by the electrostatic charge and are free from defective discharge. Even when the sheets are discharged in a bundled state onto the discharge sheet stacking means are therefore more easily charged, the electrostatic charge can be securely dissipated by the grounding members. Also the sheets do not mutually stick by the electrostatic charge and can be easily separated. Also the grounding member may be provided with an elastic finger capable of engaging with an engaging hole provided in the main body of the apparatus, so that the grounding member can be manufactured separately from the main body and mounted on the main body, and the manufacturing cost of the sheet treating apparatus can therefore be lowered. Furthermore, the grounding member is replaceable. The image forming apparatus of the present invention, being provided with the sheet treating apparatus, can prevent the defective sheet discharge, resulting from the electrostatic charge accumulated on the sheets.

Claims: A sheet treating apparatus, comprising a discharge means (180a, 180b) for discharging a sheet (P), a stacking means (200) for stacking the sheet (P) discharged by said discharge means (180a, 180b), and a grounding member (216) for contacting the sheet (P) stacked on said stacking means (200), characterized in that said grounding member (216) is arranged such that it comes into contact with the trailing end of the sheet (P) stacked on said stacking means (200) and does not come into contact with the lower surface of the sheet (P) stacked on the stacking means (200). A sheet treating apparatus according to claim 1, wherein said grounding member (216) does not come into contact with the sheet (P) while the sheet (P) is discharged. A sheet treating apparatus according to claim 1 or 2, wherein said sheet (P) is discharged in a shape of a bundle onto said stacking means (200). A sheet treating apparatus according to one of claims 1 to 3, wherein said grounding member (216) includes an elastic finger (216a) engageable with and disengageable from an engaging hole (217) formed in a main body (219). A sheet treating apparatus according to one of claims 1 to 4, wherein said grounding member (216) is composed of a metal. A sheet treating apparatus according to one of claims 1 to 4, wherein said grounding member (216) includes a grounded metal plate in a portion receiving the trailing end of said sheet (P). A sheet treating apparatus according to one of claims 1 to 4, wherein said grounding member (216) is composed of a molded plastic member in which metal powder is mixed. A sheet treating apparatus according to one of claim 1 to 4, wherein said grounding member (216) is composed of a molded plastic member which is plated with a metal. An image forming apparatus (310) comprising: image forming means (902) for forming an image on a sheet (P); and a sheet treating apparatus (1) as defined by any one of claims 1 to 8.

Inventors: KAWATA WATARU, KAWATA, WATARU, Kawata, Wataru, c/o Canon Kabushiki Kaisha
Applicants: CANON KK, CANON KABUSHIKI KAISHA
Application year: 1999
Main classification: B65H31
IPC codes: B65H31, B65H33