Sheet Stacking Device and Image Forming Apparatus

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application Nos. 2024-100582, filed on Jun. 21, 2024, and 2024-170270, filed on Sep. 30, 2024, in the Japan Patent Office, the entire disclosure of each of which is hereby incorporated by reference herein.

The present disclosure relates to a sheet stacking device and an image forming apparatus.

An image forming apparatus forms an image on a transfer sheet. After the image is formed on the transfer sheet, a sheet stacking device moves a guide at the same speed as a sheet conveyance speed while a conveyor feeds a trailing end of the transfer sheet into a stacker. The guide conveys the transfer sheet while holding a leading end of the transfer sheet. Thus, the sheet stacking device conveys and stacks the transfer sheets on the stacker.

A marking device cuts a thin sheet marker wound in a roll into a predetermined length and inserts the marker between bundles of the desired number of sheets such that the marker protrudes from the bundles of sheets. The bundles of the desired number of sheets are separated from one another by the marker.

The present disclosure described herein provides an improved sheet stacking device including a stacker, a conveyor, and a marking device. The stacker stacks transfer sheets. The conveyor conveys the transfer sheets toward the stacker in a sheet conveyance direction. The marking device includes a marker storage to store a marker, an ejection port to eject the marker, a marker conveyor to convey and eject the marker from the ejection port, and a guide to prevent the marker ejected from the ejection port from moving in a direction opposite to the sheet conveyance direction. The marking device places the marker on an uppermost sheet of each predetermined number of the transfer sheets on the stacker.

The accompanying drawings are intended to depict embodiments of the present disclosure and should not be interpreted to limit the scope thereof. The accompanying drawings are not to be considered as drawn to scale unless explicitly noted. Also, identical or similar reference numerals designate identical or similar components throughout the several views.

In describing embodiments illustrated in the drawings, specific terminology is employed for the sake of clarity. However, the disclosure of this specification is not intended to be limited to the specific terminology so selected and it is to be understood that each specific element includes all technical equivalents that have a similar function, operate in a similar manner, and achieve a similar result.

Referring now to the drawings, embodiments of the present disclosure are described below. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise.

illustrates an image forming apparatus. In, the image forming apparatusincludes a sheet feeding devicethat stores a transfer sheet S as a recording medium, a sheet position correction devicethat corrects a position of the transfer sheet S, and an image forming devicethat forms an image on the transfer sheet S.

The image forming apparatusfurther includes a sheet drying devicethat dries an image formed on the transfer sheet S, a sheet cooling devicethat cools the transfer sheet S, a sheet reverse devicethat reverses the transfer sheet S, a first sheet stacking deviceand a second sheet stacking devicethat stack the transfer sheet S, and an control panelthat controls the above-described devices based on an instruction of a user.

The sheet feeding deviceand the sheet position correction deviceconvey the transfer sheets S stacked and stored in the sheet feeding deviceone by one. The sheet feeding deviceincludes a sheet size detection sensorthat detects the size of the transfer sheet S to be fed. Specifically, the sheet feeding deviceincludes multiple sheet size detection sensorsthat detect the length and width of the transfer sheet S.

The sheet position correction deviceadjusts the conveyance timing of the transfer sheet S so that the image forming deviceforms an image at a predetermined position of the transfer sheet S based on size data of the transfer sheet S transmitted from the sheet size detection sensor.

The image forming deviceis an inkjet recording device that discharges ink of each color of black (K), cyan (C), magenta (M), and yellow (Y) onto the transfer sheet S to form a full-color image on the transfer sheet S. The image forming deviceincludes liquid discharge devicesK,C,M, andY that discharge the above-described inks of the respective colors. The liquid discharge devicesK,C,M, andY are disposed around a drum rollto form an inkjet image of each color on the transfer sheet S.

The sheet drying deviceand the sheet cooling devicedry and then cool the inkjet image formed on the transfer sheet S. As a result, the inkjet image is held stably on the transfer sheet S.

The sheet reverse devicereverses the transfer sheet S by a switchback manner and conveys the transfer sheet S to the sheet position correction deviceagain, if desired, to switch the image forming surface of the transfer sheet S that faces the drum rollfrom the front side to the back side of the transfer sheet S. The above-described respective devices are appropriately controlled in accordance with a user's operation via the control panelto form an inkjet image on the transfer sheet S.

The inkjet printer that forms an inkjet image has been described as the image forming apparatus, but an image forming apparatus is not limited thereto, and may include an electrophotographic image forming unit as the image forming device. In this case, the image forming apparatus may include a fixing device that fixes a toner image on the transfer sheet S in place of the sheet drying deviceand the sheet cooling device. Such an image forming apparatus may include components having the same or similar configuration as a typical image forming apparatus, and detailed descriptions thereof will be omitted.

The first sheet stacking devicewill be described below. The first sheet stacking deviceand the second sheet stacking deviceare both ejection destinations to which the transfer sheet S is ejected in the image forming apparatus, and may have the same configuration or different configurations. In the following description, the first sheet stacking deviceand the second sheet stacking deviceare not different in configuration, and are different only in the ejection destination of the transfer sheet S.

The first sheet stacking deviceillustrated inincludes a sheet trayas a stacker, a sheet conveyance mechanismas a conveyor that conveys the transfer sheet S to the sheet tray, and a guide mechanismthat grips a leading end of the transfer sheet S conveyed toward the sheet trayand conveys the transfer sheet S to a downstream side in a sheet conveyance direction. The first sheet stacking devicefurther includes a sheet leading end detection sensorthat detects a leading end of the transfer sheet S on an upstream side of the sheet conveyance mechanismin the sheet conveyance direction, and a bypass conveyance paththat conveys the conveyed transfer sheet S to the second sheet stacking devicedisposed on a downstream side of the first sheet stacking devicein the sheet conveyance direction by bypassing the sheet tray.

After image formation, the transfer sheet S is stacked on the sheet tray. An initial position of the sheet trayis located below the transfer sheet S fed by the sheet conveyance mechanism. The sheet traymoves downward as the transfer sheet S is stacked on the sheet tray, and the position of the uppermost surface of a bundle of the transfer sheets S (i.e., a sheet bundle) stacked on the sheet trayis continuously maintained at a height at which the transfer sheet S is ejected from the sheet conveyance mechanismand smoothly stacked onto the uppermost surface of the sheet bundle on the sheet tray. A lift that raises and lowers the sheet traywill be described later. A user pulls out the sheet trayfrom the first sheet stacking deviceto take out the transfer sheets S stacked on the sheet tray.

The sheet conveyance mechanismincludes a typical roller pair including a drive rollerand a driven rollerto convey the transfer sheet S conveyed from the image forming devicetoward the sheet tray. The sheet conveyance mechanismreceives the transfer sheet S ejected by a supply roller pairdisposed at the most upstream position in the sheet conveyance direction in the first sheet stacking device, and conveys the transfer sheet S to the downstream side in the sheet conveyance direction.

The sheet leading end detection sensoris disposed on the upstream side of the sheet conveyance mechanismin the sheet conveyance direction, and detects the leading end of the conveyed transfer sheet S to output a signal.

The guide mechanismis disposed on the downstream side of the sheet conveyance mechanismin the sheet conveyance direction. The guide mechanismconveys the transfer sheet S in the sheet conveyance direction at a speed higher than a sheet conveyance speed of the sheet conveyance mechanismwhile holding the leading end of the transfer sheet S conveyed by the sheet conveyance mechanism. The guide mechanismfunctions as a guide device that holds the leading end of the transfer sheet S and releases the leading end of the transfer sheet S at a release position to guide the conveyed transfer sheet S onto the sheet tray.

The guide mechanismincludes a rotatable endless conveyance beltand a holder. The conveyance beltis looped around a drive rollerand a driven roller. The holderis attached to the conveyance beltand moves along with the rotation of the conveyance belt. The drive rolleris driven by a motor, which is a variable speed stepper motor, to rotate the conveyance beltat a variable rotation speed. The position of the holderon the conveyance beltcan be grasped based on the number of steps of the motor.

As illustrated in, four conveyance belts(i.e., conveyance beltsand) are arranged in parallel to each other in a sheet width direction of the transfer sheet S indicated by arrow B. Two holdersare arranged on each of the conveyance beltsandat positions which are point-symmetrical to each other in the circumferential direction of the conveyance belts. The holderis attached to the outer circumferential surface of the conveyance beltand moves along with the rotation of the conveyance belt. In, the transfer sheet S is conveyed in the sheet conveyance direction indicated by arrow A.

The first sheet stacking devicecauses the holderholding the transfer sheet S to release the transfer sheet S by using a speed difference between the sheet conveyance speed of the sheet conveyance mechanismand the sheet conveyance speed of the guide mechanism. Thus, the released transfer sheet S is stacked on the sheet tray.

A blower fanis disposed at a downstream portion of the guide mechanismin the sheet conveyance direction. The blower fanserves as an air blower that applies (blows) an airflow directed toward the sheet tray, i.e., directed downward, to the conveyed transfer sheet S. The blower fanis constantly operated, and applies the airflow so as to press the transfer sheet S held by the holderagainst the sheet tray.

As illustrated in, the holderhas an openinginto which the leading end of the transfer sheet S is inserted, and a nipping portionthat nips the leading end of the transfer sheet S inserted from the openingThe force of the nipping portionnipping the leading end of the transfer sheet S is set to be smaller than the friction force between the sheet conveyance mechanismand the transfer sheet S. Thus, the nipping portionallows the transfer sheet S to enter the holderstopped at a standby position illustrated inby the rigidity of the transfer sheet S conveyed by the sheet conveyance mechanismand inserted from the openingand elastically holds the transfer sheet S.

The contact face of the holderwith the transfer sheet S is preferably formed of a material having high smoothness such as metal or resin. Such a material enables the holderto smoothly hold the transfer sheet S.

The holderis stopped at the standby position illustrated inwhen receiving the transfer sheet S. The holderstarts conveying the transfer sheet S at a predetermined timing after the leading end of the transfer sheet S is detected by the sheet leading end detection sensorand nipped by the nipping portionAs described above, the holderfunctions as a guide that moves in the sheet conveyance direction after holding the leading end of the transfer sheet S conveyed by the sheet conveyance mechanismat the standby position to guide the conveyance of the transfer sheet S.

In the image forming apparatus, as illustrated in, two holdersare disposed on the outer circumferential surface of the conveyance beltin phases different from each other by 180 degrees. Accordingly, when the conveyance of the transfer sheet S is completed, one of the holdersis rotated by half as the conveyance beltrotates, and the other holderis positioned at the standby position and stopped. Thus, the two holdersare alternately moved to the standby position, so that the time until the holdersreturn to the standby position is shortened to enhance the conveyance cycle of the transfer sheet S.

In the image forming apparatus, as illustrated in, the four conveyance beltsare arranged in the sheet width direction, and the two holdersare disposed on each of the conveyance belts. Accordingly, the holdercan be downsized as compared with one or two conveyance beltseach provided with two holders. As a result, the inertial load of the holderwhen the conveyance beltrotates can be reduced, and the holding posture of the transfer sheet S can be stabilized by increasing the number of the holders.

The four conveyance beltsandare classified into end side conveyance beltsanddisposed at the respective end portions in the sheet width direction and center side conveyance beltsanddisposed between the end side conveyance beltsandThe holdersare arranged so that the attaching positions in the sheet conveyance direction are different from each other between the end side conveyance beltsandand the center side conveyance beltsandSpecifically, the standby positions of the holderson the center side conveyance beltsandare located upstream of the standby positions of the holderson the end side conveyance beltsandin the sheet conveyance direction.

With the above configuration, the timing at which the holderholds the transfer sheet S can be shifted between the end side conveyance beltsandand the center side conveyance beltsandand thus the load when the transfer sheet S enters the holdercan be reduced. Further, the timing at which the holderreleases the transfer sheet S is also shifted, and thus the transfer sheet S can be kept in a stable posture.

As illustrated in, the sheet conveyance mechanismincludes two roller pairs each including the drive rollerand the driven rollerEach roller pair has a narrow width that fits between the end side conveyance beltand the center side conveyance beltIn, the drive rolleris disposed on the upper surface side of the transfer sheet S, and the driven rolleris disposed on the lower surface side of the transfer sheet S, but the configuration of the drive rollerand the driven rolleris not limited thereto.

A lift that raises and lowers the sheet traywill be described below. As illustrated in, a sheet bundle of the transfer sheets S is stacked on the sheet trayvia a pallet, and the sheet traycan be raised and lowered by a lift. The liftincludes a pair of pulleysanda pair of chainsanda pair of weightsandan upper limit detection sensor, and a lower limit detection sensor. The transfer sheet S may be directly stacked on the sheet traywithout using the pallet.

The pair of pulleysandare rotatably supported by a housing of the image forming apparatusat positions above the sheet tray. The pulleyand the pulleyare separated from each other in the sheet conveyance direction indicated by arrow A. The pair of chainsandare respectively wound around the corresponding pulleysandand one ends of the chainsandare connected to the sheet tray, and the other ends of the chainsandare respectively connected to the corresponding weightsand

When the pulleysandrotate in a first direction (the pulleyrotates clockwise and the pulleyrotates counterclockwise in), the sheet traymoves upward and the weightsandmove downward. On the other hand, when the pulleysandrotate in a second direction opposite to the first direction (the pulleyrotates counterclockwise and the pulleyrotates clockwise in), the sheet traymoves downward and the weightsandmove upward.

The upper limit detection sensordetects whether the uppermost transfer sheet S stacked on the sheet trayreaches an upper limit position to which the transfer sheet S is allowed to be raised by the lift. The upper limit detection sensoris disposed above the sheet tray. The upper limit detection sensoris, for example, a reflective optical sensor including a light emitter that outputs light and a light receiver that receives the light, which is output from the light emitter and reflected by the transfer sheet S.

The upper limit detection sensoroutputs a detection signal to a controller when the transfer sheet S is on a detection optical path of the upper limit detection sensor, i.e., when the uppermost transfer sheet S stacked on the sheet trayreaches the upper limit position. On the other hand, the upper limit detection sensordoes not output the detection signal when the transfer sheet S is not on the detection optical path. The upper limit detection sensormay be a transmissive optical sensor instead of the reflective optical sensor. When the controller receives the detection signal of the upper limit position, the controller immediately stops a raising operation of the sheet tray.

The lower limit detection sensordetects whether the sheet trayreaches a lower limit position to which the sheet trayis allowed to be lowered, with the transfer sheets S of the maximum capacity stacked on the sheet tray. The lower limit detection sensoris disposed at a position facing the weightwhen the sheet trayis fully loaded. The lower limit detection sensoris, for example, a reflective optical sensor similar to the upper limit detection sensor.

The lower limit detection sensoroutputs a detection signal to the controller when the sheet trayis on a detection optical path of the lower limit detection sensor, i.e., when the sheet trayis fully loaded and the sheet trayreaches the lower limit position. On the other hand, the lower limit detection sensordoes not output the detection signal when the sheet trayis not on the detection optical path. The lower limit detection sensormay be a transmissive optical sensor instead of the reflective optical sensor. When the controller receives the detection signal of the lower limit position, the controller immediately stops a lowering operation of the sheet tray.

A sheet conveyance process by the first sheet stacking devicedescribed above will be described below. The stacking of the transfer sheets S in the first sheet stacking deviceand the stacking of the transfer sheets S in the second sheet stacking devicecan be achieved by like configuration and control, and thus only the first sheet stacking devicewill be described below.

First, the first sheet stacking deviceacquires the size data including the length of the transfer sheet S to be conveyed and stacked. Specifically, the size data based on the length and width of the transfer sheet S detected by the sheet size detection sensoror the size data of the transfer sheet S input by a user from the control panelis used. Then, when the transfer sheet S on which an image is formed by the sheet feeding device, the sheet position correction device, and the image forming deviceis conveyed to the first sheet stacking device, the supply roller pairstarts conveying the transfer sheet S, which is fed after the image is formed by the image forming device, and the sheet conveyance mechanismis driven. At this time, the guide mechanismis stopped in a standby state illustrated inin which the holderis stopped at the standby position, and the blower fanstarts blowing constantly at a constant air volume.

After that, the controller determines whether the sheet leading end detection sensorhas detected the leading end of the transfer sheet S. When the controller determines that the leading end of the transfer sheet S has been detected, the controller measures a first predetermined time which is an elapsed time from a leading end detection time of the transfer sheet S. The first predetermined time is determined in advance in accordance with the size of the transfer sheet S to be conveyed. When the first predetermined time has elapsed, the conveyance beltstarts rotating, and the holderthat has been stopped at the standby position starts moving in the sheet conveyance direction. At this time, since the conveyance speed of the transfer sheet S by the sheet conveyance mechanismis faster than the moving speed of the holder, the leading end of the transfer sheet S enters the holderfrom the openingand the leading end that has entered the holderis nipped and held by the nipping portion

The controller controls the moving speed of the holder, i.e., the driving speed of the motorto rotate the conveyance beltso that the conveyance speed of the transfer sheet S by the sheet conveyance mechanismand the moving speed of the holderare equal to each other when the transfer sheet S has entered the holder. Accordingly, the leading end of the transfer sheet S enters the holderdue to the speed difference until the moving speed of the holderbecomes equal to the conveyance speed of the transfer sheet S by the sheet conveyance mechanism. The time from when the holderstarts moving until the transfer sheet S has entered the holderis defined as a second predetermined time. At this time, the amount of the leading end of the transfer sheet S entering the holdercorresponding to the first and second predetermined times is a predetermined amount C illustrated in.

When the holderholds the transfer sheet S, i.e., when the amount of the leading end of the transfer sheet S entering the holderreaches the predetermined amount C, the controller accelerates the moving speed of the holder(i.e., a first acceleration) and measures a third predetermined time corresponding to the size data of the transfer sheet S acquired in advance.

The sheet conveyance mechanismand the guide mechanismtogether start conveying the transfer sheet S with the speed difference between the conveyance speed of the transfer sheet S by the sheet conveyance mechanismand the moving speed of the holder, which is generated by the first acceleration. At this time, the moving speed of the holderbecomes faster than the conveyance speed of the transfer sheet S by the sheet conveyance mechanism, and the holderconveys the transfer sheet S while pulling the leading end of the transfer sheet S. As a result, the transfer sheet S can be prevented from bending (warping) as compared with the case of equal speeds (without the speed difference). During this conveyance, the force of the holderholding the transfer sheet S is smaller than the friction force between the sheet conveyance mechanismand the transfer sheet S. Accordingly, the transfer sheet S is gradually drawn out from the holder, but the holderkeeps holding the transfer sheet S from a holding position where the transfer sheet S is held to a releasing position where the transfer sheet S is released.

When the third predetermined time has elapsed after the holderholds the transfer sheet S, the controller accelerates the moving speed of the holder(i.e., a second acceleration). As a result, the moving speed of the holderis increased, and the holderreleases the transfer sheet S. Even if the transfer sheet S is pulled out of the sheet conveyance mechanismbefore the transfer sheet S is released from the holder, the transfer sheet S is released from the holderby the inertial force of the transfer sheet S.illustrates the transfer sheet S released from the holder. In, the holderis accelerated at an acceleration position D of the second acceleration and releases the transfer sheet S at a release position E.

illustrates a small-size transfer sheet S, which has a smaller size than the transfer sheet S, used in the first sheet stacking deviceinstead of the transfer sheet S. As illustrated in, the controller adjusts the acceleration position D and the release position E in accordance with the small-size transfer sheet S, and the small-size transfer sheet Sis released from the holderby the speed difference between the conveyance speed of the small-size transfer sheet Sby the sheet conveyance mechanismand the moving speed of the holder, which is generated by the second acceleration.

The transfer sheet S or the small-size transfer sheet SI that has been pulled out of the sheet conveyance mechanismand has been released from the holderreceives the wind force from the blower fan, falls toward the sheet tray, and is stacked on the sheet tray.