Sheet discharging apparatus, sheet processing apparatus, and image forming system

A sheet discharging apparatus includes a discharging portion configured to discharge a sheet, a supporting portion configured to support the sheet discharged by the discharging portion, a lifting portion configured to lift and lower the supporting portion, a transmissive sensor configured to output an output signal that changes in accordance with a position of an upper surface of the sheet supported by the supporting portion, a reflective sensor configured to output an output signal that changes in accordance with the position of the upper surface of the sheet supported by the supporting portion, and a controller configured to control the lifting portion and including a first determining portion configured to determine whether or not sheet detection by the transmissive sensor is possible and a second determining portion configured to determine whether or not sheet detection by the transmissive sensor is needed.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a sheet discharging apparatus that discharges a sheet, a sheet processing apparatus that processes a sheet, and an image forming system that forms an image on a sheet.

Description of the Related Art

An image forming system of an electrophotographic system includes a sheet discharging apparatus that discharges a sheet on which an image has been recorded and then a process such as a binding process has been performed if necessary. As such a sheet discharging apparatus, an apparatus that lifts and lowers a tray on which discharged sheets are supported such that the height of the upper surface of the sheets supported on the tray is maintained at a constant height is known. Japanese Patent Laid-Open No. 2001-335236 discloses a transmissive sensor in which a light emitting portion and a light receiving portion are respectively disposed on the left side and the right side of the tray and which detects the position of the upper surface of the sheets when the sheets block an optical axis between the light emitting portion and the light receiving portion.

The light receiving portion of the transmissive sensor is known to be affected by disturbance light such as sunlight in some cases. If the apparatus is configured to always stop discharging a sheet to suppress erroneous operation relating to ascent and descent of the tray in the case where there is disturbance light, there might be generated a time in which the apparatus cannot be used. Japanese Patent Laid-Open No. 2009-286515 discloses disposing two transmissive sensors which have arrangements of the light emitting portion and the light receiving portion reversed from each other, and performing lifting/lowering control of the tray by using one of the sensors that is not affected by the disturbance light.

However, in the configuration according to Japanese Patent Laid-Open No. 2009-286515, two sensors that only differ from each other in the arrangement of the light emitting portion and the light receiving portion and that have substantially the same function are used, which allows the cost to increase to address the disturbance light.

SUMMARY OF THE INVENTION

The present invention provides a sheet discharging apparatus, a sheet processing apparatus, and an image forming system that can reduce influence of disturbance light with a simple configuration.

According to one aspect of the invention, a sheet discharging apparatus includes a discharging portion configured to discharge a sheet, a supporting portion configured to support the sheet discharged by the discharging portion, a lifting portion configured to lift and lower the supporting portion, a transmissive sensor including a first light emitting portion configured to emit light and a first light receiving portion configured to detect the light received from the first light emitting portion, the transmissive sensor being configured to output an output signal that changes in accordance with a position of an upper surface of the sheet supported by the supporting portion, a reflective sensor including a second light emitting portion configured to emit light and a second light receiving portion configured to detect the light emitted from the second light emitting portion and then reflected on a sheet, the reflective sensor being configured to output an output signal that changes in accordance with the position of the upper surface of the sheet supported by the supporting portion, and a controller configured to control the lifting portion and including a first determining portion configured to determine whether or not sheet detection by the transmissive sensor is possible and a second determining portion configured to determine whether or not sheet detection by the transmissive sensor is needed, wherein the controller is configured to, in a case where the first determining portion has determined that sheet detection by the transmissive sensor is possible, lift or lower the supporting portion by the lifting portion on a basis of the output signals of the transmissive sensor and the reflective sensor, in a case where the first determining portion has determined that sheet detection by the transmissive sensor is not possible and the second determining portion has determined that sheet detection by the transmissive sensor is not needed, lift or lower the supporting portion by the lifting portion on a basis of the output signal of the reflective sensor, and in a case where the first determining portion has determined that sheet detection by the transmissive sensor is not possible and the second determining portion has determined that sheet detection by the transmissive sensor is needed, stop discharge of a sheet to be discharged by the discharging portion.

According to another aspect of the invention, a sheet discharging apparatus includes a discharging portion configured to discharge a sheet, a supporting portion configured to support the sheet discharged by the discharging portion, a lifting portion configured to lift and lower the supporting portion, a transmissive sensor including a first light emitting portion configured to emit light and a first light receiving portion configured to detect the light received from the first light emitting portion, the transmissive sensor being configured to output an output signal that changes in accordance with a position of an upper surface of the sheet supported by the supporting portion, a reflective sensor including a second light emitting portion configured to emit light and a second light receiving portion configured to detect the light emitted from the second light emitting portion and then reflected on a sheet, the reflective sensor being configured to output an output signal that changes in accordance with the position of the upper surface of the sheet supported by the supporting portion, and a controller configured to control the lifting portion and including a first determining portion configured to determine whether or not sheet detection by the transmissive sensor is possible and a second determining portion configured to determine whether or not sheet detection by the transmissive sensor is needed, wherein the controller is configured to, in a case where the first determining portion has determined that sheet detection by the transmissive sensor is possible, lift or lower the supporting portion by the lifting portion on a basis of the output signals of the transmissive sensor and the reflective sensor, in a case where the first determining portion has determined that sheet detection by the transmissive sensor is not possible and the second determining portion has determined that sheet detection by the transmissive sensor is not needed, lift or lower the supporting portion by the lifting portion on a basis of the output signal of the reflective sensor, and in a case where the first determining portion has determined that sheet detection by the transmissive sensor is not possible and the second determining portion has determined that sheet detection by the transmissive sensor is needed, lift or lower the supporting portion by the lifting portion on a basis of information about a sheet to be discharged by the discharging portion.

According to still another aspect of the invention, a sheet discharging apparatus includes a discharging portion configured to discharge a sheet, a supporting portion configured to support the sheet discharged by the discharging portion, a lifting portion configured to lift and lower the supporting portion, a transmissive sensor including a first light emitting portion configured to emit light and a first light receiving portion configured to detect the light received from the first light emitting portion, the transmissive sensor being configured to output an output signal that changes in accordance with a position of an upper surface of the sheet supported by the supporting portion, a reflective sensor including a second light emitting portion configured to emit light and a second light receiving portion configured to detect the light emitted from the second light emitting portion and then reflected on a sheet, the reflective sensor being configured to output an output signal that changes in accordance with the position of the upper surface of the sheet supported by the supporting portion, and a controller configured to control the lifting portion, wherein the controller is configured to, in a case where an amount of light received by the first light receiving portion in a state in which the first light emitting portion is not emitting light is a first amount, lift or lower the supporting portion by the lifting portion on a basis of the output signals of the transmissive sensor and the reflective sensor, and in a case where the amount of light received by the first light receiving portion in the state in which the first light emitting portion is not emitting light is a second amount larger than the first amount, (i) if a grammage of the sheet to be discharged by the discharging portion is a first grammage, lift or lower the supporting portion by the lifting portion on a basis of the output signal of the reflective sensor, (ii) if an environmental humidity is a first humidity, lift or lower the supporting portion by the lifting portion on the basis of the output signal of the reflective sensor, and (iii) if the grammage of the sheet to be discharged by the discharging portion is a second grammage smaller than the first grammage and the environmental humidity is a second humidity higher than the first humidity, stop discharge of the sheet to be discharged by the discharging portion.

According to still another aspect of the invention, a sheet discharging apparatus includes a discharging portion configured to discharge a sheet, a supporting portion configured to support the sheet discharged by the discharging portion, a lifting portion configured to lift and lower the supporting portion, a transmissive sensor including a first light emitting portion configured to emit light and a first light receiving portion configured to detect the light received from the first light emitting portion, the transmissive sensor being configured to output an output signal that changes in accordance with a position of an upper surface of the sheet supported by the supporting portion, a reflective sensor including a second light emitting portion configured to emit light and a second light receiving portion configured to detect the light emitted from the second light emitting portion and then reflected on a sheet, the reflective sensor being configured to output an output signal that changes in accordance with the position of the upper surface of the sheet supported by the supporting portion, and a controller configured to control the lifting portion, wherein the controller is configured to, in a case where an amount of light received by the first light receiving portion in a state in which the first light emitting portion is not emitting light is a first amount, lift or lower the supporting portion by the lifting portion on a basis of the output signals of the transmissive sensor and the reflective sensor, and in a case where the amount of light received by the first light receiving portion in the state in which the first light emitting portion is not emitting light is a second amount larger than the first amount, (i) if a grammage of a sheet to be discharged by the discharging portion is a first grammage, lift or lower the supporting portion by the lifting portion on a basis of the output signal of the reflective sensor, (ii) if an environmental humidity is a first humidity, lift or lower the supporting portion by the lifting portion on the basis of the output signal of the reflective sensor, and (iii) if the grammage of the sheet to be discharged by the discharging portion is a second grammage smaller than the first grammage and the environmental humidity is a second humidity higher than the first humidity, lift or lower the supporting portion by the lifting portion in response to discharge of a sheet by the discharging portion.

DESCRIPTION OF THE EMBODIMENTS

First Embodiment

As illustrated inFIG. 1, an image forming system1S according to a first embodiment is constituted by an image forming apparatus1, an image reading apparatus2, a document feeding apparatus3, and a sheet processing apparatus4. The image forming system1S forms an image on a sheet serving as a recording material, processes the sheet by the sheet processing apparatus4if necessary, and then outputs the sheet. Simple description of each apparatus will be given below, and then the sheet processing apparatus4will be described in detail.

The document feeding apparatus3conveys a document placed on a document tray18to image reading portions16and19. The image reading portions16and19are each an image sensor that reads image information from a document surface, and both surfaces of the document are read in one time of document conveyance. The document whose image information has been read is discharged onto a document discharge portion20. In addition, the image reading apparatus2can read image information from a still document set on a platen glass by reciprocating the image reading portion16by a driving device17. Examples of the still document include documents not compatible with the document feeding apparatus3such as booklet documents.

The image forming apparatus1is an electrophotographic apparatus including an image forming portion1B of a direct transfer system. The image forming portion1B includes a cartridge8including a photosensitive drum9, and a laser scanner unit15disposed above the cartridge8. In the case of performing an image forming operation, the surface of the photosensitive drum9that is rotating is charged, and the laser scanner unit15exposes the photosensitive drum9on the basis of image information to draw an electrostatic latent image on the surface of the photosensitive drum9. The electrostatic latent image borne on the photosensitive drum9is developed into a toner image with charged toner particles, and the toner image is conveyed to a transfer portion where the photosensitive drum9and a transfer roller10oppose each other. A controller of the image forming apparatus1serving as a printer controller executes an image forming operation by the image forming portion1B on the basis of image information read by the image reading portions16and19or image information received from an external computer via a network.

The image forming apparatus1includes multiple feeding apparatuses6that each feed a plurality of sheets serving as recording materials one by one at predetermined intervals. A sheet fed from one of the feeding apparatuses6is conveyed to registration rollers7, the skew thereof is corrected by the registration rollers7, then the sheet is conveyed to the transfer portion, and the toner image borne on the photosensitive drum9is transferred onto the sheet in the transfer portion. A fixing unit11is disposed downstream of the transfer portion in the sheet conveyance direction. The fixing unit11includes a rotary member pair that nips and conveys the sheet, and a heat generation member such as a halogen lamp for heating the toner image, and performs a fixing process of the toner image by heating and pressurizing the toner image on the sheet.

In the case of discharging the sheet on which an image has been formed to the outside of the image forming apparatus1, the sheet having passed through the fixing unit11is conveyed to the sheet processing apparatus4through a horizontal conveyance portion14. In the case of a sheet on a first surface of which an image has been formed in duplex printing, the sheet having passed through the fixing unit11is passed onto reverse conveyance rollers12, is switched back and conveyed by the reverse conveyance rollers12, and is then conveyed to the registration rollers7again through a reconveyance portion13. Then, the sheet passes through the transfer portion and the fixing unit11again, thus an image is formed on a second surface thereof, and then the sheet is conveyed to the sheet processing apparatus4through the horizontal conveyance portion14.

The image forming portion1B described above is an example of an image forming portion that forms an image on a sheet, and an electrophotographic unit of an intermediate transfer system that transfers a toner image formed on a photosensitive member onto a sheet via an intermediate transfer member may be used as the image forming portion. In addition, a printing unit of an inkjet system or an offset printing system may be used as the image forming portion.

Sheet Processing Apparatus

The sheet processing apparatus4includes an inlet path91, an in-body discharge path92, a first discharge path93, and a second discharge path94as conveyance paths for conveying sheets, and an upper discharge tray25and a lower discharge tray37as discharge destinations to discharge the sheets to. The lower discharge tray37is disposed below the upper discharge tray25in an up-down direction V that is a gravity direction. The inlet path91serving as a first conveyance path is a conveyance path in which a sheet is received and conveyed from the image forming apparatus1. The in-body discharge path92serving as a second conveyance path is a conveyance path which is disposed below the inlet path91and in which a sheet is received from the inlet path91and guided toward a binding processing portion4A. The first discharge path93is a conveyance path through which the sheet is discharged onto the upper discharge tray25, and the second discharge path94serving as a third conveyance path is a conveyance path which extends from an intermediate supporting portion39toward bundle discharge rollers36and in which the sheet is guided to the bundle discharge rollers36.

The sheet discharged from the horizontal conveyance portion14of the image forming apparatus1is received by inlet rollers21serving as a conveyance portion disposed on the inlet path91, and conveyed toward pre-inversion rollers22through the inlet path91. An entrance sensor27whose output value such as a voltage value or an output signal changes on the basis of the presence or absence of a sheet at a detection position between the inlet rollers21and the pre-inversion rollers22is provided on the inlet path91. The pre-inversion rollers22convey the sheet received from the inlet rollers21toward the first discharge path93.

To be noted, the sheet conveyance speed of the inlet rollers21may be set to a value higher than that in the horizontal conveyance portion14such that the sheet conveyance speed increases when the sheet is received by the inlet rollers21. In this case, it is preferable that a one-way clutch is provided between a conveyance roller in the horizontal conveyance portion14and a motor that drives the conveyance roller, and the conveyance roller freewheels in the case where the sheet is pulled by the inlet rollers21.

In the case where the discharge destination of the sheet is the upper discharge tray25serving as a first supporting portion, the sheet is guided to the first discharge path93by a guide member23provided at a branching portion between the inlet path91and the in-body discharge path92. Reverse conveyance rollers24serving as a first discharging portion are provided on the first discharge path93, and the reverse conveyance rollers24discharge the sheet received from pre-inversion rollers22onto the upper discharge tray25.

In the case where the discharge destination of the sheet is the lower discharge tray37serving as a second supporting portion, the reverse conveyance rollers24serving as a reverse portion switch back the sheet received from the pre-inversion rollers22and convey the sheet to the in-body discharge path92. Specifically, the sheet is guided to the first discharge path93in a state in which the guide member23has pivoted in a C2 direction. Then, after the trailing end of the sheet has passed an inversion sensor41, the reverse conveyance rollers24rotate in a reverse direction, and the guide member23pivots in a C1 direction. As a result of this, the sheet is conveyed to the in-body discharge path92. That is, the in-body discharge path92guides the sheet in a direction opposite to the inlet path91. The inversion sensor41functions as a discharge destination switching sensor used for switching the discharge destination of the sheet from the upper discharge tray25to the lower discharge tray37.

In-body discharge rollers26, intermediate conveyance rollers28, and kick-out rollers29each serving as a rotary member pair disposed on the in-body discharge path92sequentially pass the sheet received from the reverse conveyance rollers24onto each other and convey the sheet toward the binding processing portion4A. A pre-intermediate supporting sensor38detects the sheet at a position between the intermediate conveyance rollers28and the kick-out rollers29. As the entrance sensor27, the pre-intermediate supporting sensor38, and the inversion sensor41, for example, optical sensors that detect the presence or absence of a sheet at the detection position by using light, or flag sensors that each include a flag pressed by the sheet are used.

The binding processing portion4A serving as a processing portion includes a bundle pressing flag30, the intermediate supporting portion39serving as a third supporting portion, a stapler57, a bundle discharge guide34, and a driving belt35, and performs an alignment process on sheets. The intermediate supporting portion39is constituted by an intermediate upper guide31and an intermediate lower guide32, and a plurality of sheets are supported thereon as a sheet bundle. The sheet bundle discharged toward the intermediate supporting portion39by the kick-out rollers29constituted by a roller pair is pressed against the intermediate lower guide32by the bundle pressing flag30.

Then, the sheet bundle discharged onto the intermediate supporting portion39is guided downward along the intermediate lower guide32, and brought into contact with a longitudinal alignment plate provided at a downstream end portion of the intermediate supporting portion39in the sheet conveyance direction by a semicircular roller33. In addition, the sheet bundle aligned in the sheet conveyance direction by the longitudinal alignment plate is aligned in a width direction perpendicular to the sheet conveyance direction by unillustrated lateral alignment plates. To be noted, the semicircular roller33is set to have such a conveyance pressure on the sheet bundle aligned on the intermediate supporting portion39as to slip on the sheet bundle.

After such an alignment process has been performed, the sheet bundle is subjected to a binding process by the stapler57serving as a processing portion. Then, the bound sheet bundle is pushed out by the bundle discharge guide34fixed to the driving belt35, and is passed onto the bundle discharge rollers36through the second discharge path94. The sheet bundle is discharged to the outside by the bundle discharge rollers36serving as a second discharging portion, and is supported on the lower discharge tray37. To be noted, the stapler57is an example of a processing portion, and a processing portion that performs a different process on the sheets may be used. Examples of the different processing portion include a processing unit that performs a center binding process in which the sheet bundle is folded in half, that is, folded at the center, and the center portion of the sheet bundle is stapled. In addition, examples of the process performed on the sheet also include a process so-called jog discharge in which sheets are discharged while displacing the alignment position of the sheet bundle for every predetermined number of sheets.

The lower discharge tray37is movable in the up-down direction V, which is an approximate vertical direction, with respect to the casing of the sheet processing apparatus4. The sheet processing apparatus4includes a sensor that detects the presence or absence of a sheet supported on the lower discharge tray37, a sensor that detects the position of the upper surface of sheets supported on the lower discharge tray37, that is, the height of the uppermost sheet in the up-down direction V, and so forth. The discharge tray37is controlled on the basis of output signals of these sensors so as to descend in an A2 direction as the amount of sheets supported on the discharge tray37increases. In addition, the discharge tray37is controlled to ascend in an A1 direction toward an initial position when the sheets are removed from the discharge tray37. A sheet discharging portion100including the lower discharge tray37capable of ascending and descending will be described below.

To be noted, in the configuration example of the present embodiment, the upper discharge tray25is a fixed member fixed to the casing of the sheet processing apparatus4. However, the upper discharge tray25may be also configured to be capable of ascending and descending similarly to the lower discharge tray37. In this case, a configuration similar to that of the sheet discharging portion100that will be described later may be applied to the upper discharge tray25.

Sheet Discharging Portion

FIGS. 2A and 2Billustrate a configuration of the sheet discharging portion100serving as a sheet discharging apparatus of the present embodiment.FIG. 2Ais a section view of the sheet discharging portion100illustrating a schematic configuration thereof.FIG. 2Bis a perspective view of the sheet discharging portion100illustrating a schematic configuration thereof. In the description below, a direction in which the sheet is discharged to the outside from the sheet processing apparatus4will be referred to as a “sheet discharging direction D”, and a direction perpendicular to the sheet discharging direction D and the up-down direction V, that is, the rotation axis direction of the bundle discharge rollers36will be referred to as a “sheet width direction W”.

The sheet discharging portion100includes the bundle discharge rollers36serving as a discharging portion and the discharge tray37serving as a supporting portion or a stacking portion. The bundle discharge rollers36are a roller pair that nips a sheet bundle processed by the binding processing portion4A and convey the sheet bundle in the sheet discharging direction D to discharge the sheet bundle to the outside of the sheet processing apparatus4. The discharge tray37is a lifting tray that ascends and descends with respect to the sheet processing apparatus4.

In addition, the sheet discharging portion100includes a sheet presence/absence sensor50, an upper limit sensor53, a lower limit sensor54, a transmissive upper surface sensor51, and a reflective upper surface sensor52. Each sensor will be schematically described below.

The sheet presence/absence sensor50is a sensor for detecting whether or not at least one sheet is supported on the discharge tray37. The sheet presence/absence sensor50includes a flag member50aprojecting upward from a center portion in the sheet width direction W of the upper surface of the discharge tray37serving as a sheet supporting surface, and a photo-interrupter that is shielded from light by the flag member50a. When a sheet is supported on the discharge tray37, the flag member50ais pressed by the sheet and swings, and the photo-interrupter is switched from a transmitting state to a shielded state. When no sheet is supported on the discharge tray37, the flag member50aprojects upward from the discharge tray37, and the photo-interrupter takes the transmitting state. As a result of this, a signal corresponding to the presence or absence of a sheet on the discharge tray37is output.

The upper limit sensor53is a sensor that detects the discharge tray37being at an upper limit position in a lifting/lowering range thereof in the up-down direction V. The lower limit sensor54is a sensor that detects the discharge tray37being at a lower limit position in the lifting/lowering range thereof in the up-down direction V. As the upper limit sensor53and the lower limit sensor54, photo-interrupters shielded from light by a light shielding portion provided on the discharge tray37may be used. When the discharge tray37moves to the upper limit position or the lower limit position, the corresponding one of the photo-interrupters switches from the transmitting state to the shielded state. When the discharge tray37is positioned between the upper limit position and the lower limit position, the photo-interrupters are both in the transmitting state. As a result of this, the upper limit sensor53outputs a signal corresponding to whether or not the discharge tray37is at the upper limit position, and the lower limit sensor54outputs a signal corresponding to whether or not the discharge tray37is at the lower limit position.

The transmissive upper surface sensor51is provided below the bundle discharge rollers36in the up-down direction V. The transmissive upper surface sensor51is a photoelectric transmissive sensor constituted by a light emitting portion51aserving as a first light emitting portion and a light receiving portion51bserving as a first light receiving portion, and the light emitting portion51aand the light receiving portion51boppose each other in a space above the discharge tray37. The light receiving portion51bis disposed on an optical axis L51of light emitted from the light emitting portion51a. The direction of the optical axis L51is preferably parallel to the sheet width direction W. In this case, the light emitted from the light emitting portion51areaches the light receiving portion51bby passing through a space above the discharge tray37in the sheet width direction W.

In the case where no sheet is present on the optical axis L51, the light emitted from the light emitting portion51areaches the light receiving portion51b, and the light receiving portion51boutputs an output signal such as a voltage value corresponding to the amount of received light. In the case where a sheet is present on the optical axis L51, the light emitted from the light emitting portion51ais blocked by the sheet, thus the amount of light received by the light receiving portion51bdecreases, and the output signal of the light receiving portion51bchanges. As a result of this, the transmissive upper surface sensor51outputs an output signal serving as a detection signal corresponding to the position of the upper surface of the sheet supported on the discharge tray37.

The reflective upper surface sensor52is provided below the bundle discharge rollers36in the up-down direction V. The reflective upper surface sensor52is a photoelectric reflective sensor constituted by a light emitting portion52aserving as a second light emitting portion and a light receiving portion52bserving as a second light receiving portion that are disposed on a substrate, and is disposed on the upstream side of the discharge tray37in the sheet discharging direction D. The direction of an optical axis L52of the light emitted from the light emitting portion52apreferably intersects with the direction of the optical axis L51of the transmissive upper surface sensor51. More preferably, the direction of the optical axis L52is a direction along the sheet discharging direction D, that is, a direction toward the downstream side in the sheet discharging direction D. The light receiving portion52bis capable of detecting light incident from the downstream side in the sheet discharging direction D.

In the case where a sheet is present on the optical axis L52, the light emitted from the light emitting portion52aand then reflected by the sheet is incident on the light receiving portion52b, and thus the light receiving portion52boutputs an output signal such as a voltage value corresponding to the amount of light received by the light receiving portion52b. In the case where no sheet is present on the optical axis L52, the light emitted from the light emitting portion52ais not reflected by a sheet, thus the amount of light received by the light receiving portion52bdecreases as compared with the case where a sheet is present on the optical axis L52, and the output signal of the light receiving portion51bchanges. As a result of this, the reflective upper surface sensor52outputs an output signal serving as a detection signal corresponding to the position of the upper surface of the sheet supported on the discharge tray37.

The light emitting portions51aand52aof the transmissive upper surface sensor51and the reflective upper surface sensor52are each constituted by, for example, a light emitting diode: LED, and the light receiving portions51band52bare each constituted by, for example, a phototransistor. In addition, the “light” that the transmissive upper surface sensor51and the reflective upper surface sensor52use for detection of a sheet in the present embodiment may be infrared light.

The discharge tray37ascends and descends in a direction along the up-down direction V by being driven by a lifting motor55illustrated inFIG. 4serving as a lifting portion. At this time, as will be described later, a lifting controller80illustrated inFIG. 5controls the lifting motor55on the basis of output signals of the sensors50to54described above, and thus the lifting/lowering control of the discharge tray37is performed.

Specific examples of a mechanism for driving the discharge tray37by the driving force of the lifting motor55include the following. The sheet supporting surface of the discharge tray37is supported by a stay supported by the casing of the sheet processing apparatus4, and this stay is slidable in the up-down direction V along a rail fixed to the casing and extending in the up-down direction V. In addition, the stay is coupled to a belt stretched in the up-down direction V by a driving pulley connected to the lifting motor55and another pulley. When the lifting motor55rotates in a normal direction or a reverse direction, the belt is rotated via the driving pulley, and thus the discharge tray37ascends or descends in accordance with the amount of rotation of the lifting motor55.

The function of the transmissive upper surface sensor51and the reflective upper surface sensor52will be further described with reference toFIGS. 3A to 3D.FIG. 3Ais a schematic view of the sheet discharging portion100as viewed from the downstream side in the sheet discharging direction D.FIG. 3Bis a schematic view of the sheet discharging portion100in the state ofFIG. 3Aas viewed in the sheet width direction W. The optical axis L51of the transmissive upper surface sensor51is disposed slightly below the optical axis L52of the reflective upper surface sensor52in a direction Y1, that is, a normal direction of the sheet supporting surface of the discharge tray37in which sheets S are stacked on the discharge tray37. In the present embodiment, in design, the optical axis L51of the transmissive upper surface sensor51is positioned 3 mm below the optical axis L52of the reflective upper surface sensor52. Therefore, in the case where the sheets S are stacked approximately flat without occurrence of curling or leaning described below, the transmissive upper surface sensor51detects the sheets S first. In the case where only one reflective upper surface sensor52is provided, the reflective upper surface sensor52is preferably disposed in a central region in the sheet width direction W to secure detection precision even with the curling and leaning of the sheets. The central region is a region at the center in the case where a region from the light emitting portion51ato the light receiving portion51bof the transmissive upper surface sensor51is equally divided into three regions in the sheet width direction W.

FIG. 3Cis a diagram illustrating the sheet discharging portion100as viewed from the same viewpoint as inFIG. 3A, and illustrates a state in which curling indicated by an arrow Y2 is generated in the sheets S supported on the discharge tray37. The position of the discharge tray37is the same as inFIG. 3A. The curling mentioned herein refers to a state in which at least one end portion of the sheets S in the sheet width direction W is lifted as compared with the center portion of the sheets S in the sheet width direction W, or a state in which the center portion is lifted as compared with the end portions in the sheet width direction W. In the state in which curling is generated in the sheets S, the signal level of the light receiving portion51bof the transmissive upper surface sensor51changes when an end portion of the curled sheets S blocks the optical axis L51.

FIG. 3Dis a diagram illustrating the sheet discharging portion100as viewed from the same viewpoint as inFIG. 3B, and illustrates a state in which the sheets S supported on the discharge tray37are leaning on a wall surface4aof the sheet processing apparatus4. The position of the discharge tray37is the same as inFIG. 3B. The trailing end, that is, the upstream end in the sheet discharging direction D of the sheets S supported on the discharge tray37abut the wall surface4adue to the inclination of the discharge tray37inclined upward toward the downstream side in the sheet discharging direction D, and thus the wall surface4aserves as an alignment standard for the sheets S in the sheet discharging direction D. The leaning of the sheet S refers to a state in which the trailing end of a newly discharged sheet S comes into contact with the wall surface4abefore landing on the sheet supporting surface of the discharge tray37or on the upper surface of an already supported sheet, thus the trailing end is held by the wall surface4aby leaning on the wall surface4aand has not landed on the supporting surface or on the upper surface of a sheet. In the case where the leaning of the sheet S occurs, the signal level of the light receiving portion52bof the reflective upper surface sensor52changes when the leaning sheet S blocks the optical axis L52.

As described above, the transmissive upper surface sensor51and the reflective upper surface sensor52, while both having a function of detecting the position of the upper surface of the sheets S, have different detection characteristics with respect to the shape and orientation of the sheets S supported on the discharge tray37. By using sensors of different detection characteristics in combination, the lifting/lowering control of the discharge tray37can be performed appropriately. That is, in the present embodiment, in the case where both the transmissive upper surface sensor51and the reflective upper surface sensor52are capable of detecting a sheet, the two sensors can be used in combination and thus the detection results thereof can be complemented by each other. For example, in the case of detecting the upper surface position of the sheets S by only the transmissive upper surface sensor51, there is a possibility that the output signal of the transmissive upper surface sensor51indicates that there is no sheet on the optical axis L51although actually a leaning sheet covers a nip portion of the bundle discharge rollers36. In this case, there is a possibility that the leaning sheet hinders discharge of a new sheet and discharge failure of a sheet or droppage of a sheet from the discharge tray37occurs. Similarly, also in the case of detecting the upper surface position of the sheets S by only the reflective upper surface sensor52, there is a possibility that a curled sheet hinders discharge of a new sheet and discharge failure of a sheet or droppage of a sheet from the discharge tray37occurs. In contrast, by performing the lifting/lowering control of the discharge tray37while monitoring the upper surface position of the sheets S while using the transmissive upper surface sensor51and the reflective upper surface sensor52in combination, the possibility of occurrence of the issues described above can be lowered.

Hardware Configuration

FIG. 4is a block diagram illustrating a hardware configuration of the image forming system1S according to the present embodiment. As illustrated inFIG. 4, the image forming system1S includes a main controller101of the sheet processing apparatus4, a controller119, and an image forming apparatus controller301. The controller119performs overall control of the image forming apparatus1and the sheet processing apparatus4. The image forming apparatus controller301controls the image forming apparatus1. The main controller101controls the sheet processing apparatus4.

The controller119is connected to the image forming apparatus controller301and the main controller101respectively via transmission signal lines302and304, and transmits commands and data to the image forming apparatus controller301and the main controller101by serial communication. The image forming apparatus controller301is connected to the controller119via a transmission signal line303, and transmits data to the controller119by serial communication. The main controller101of the sheet processing apparatus4is connected to the controller119via a transmission signal line305, and transmits data to the controller119by serial communication. When performing an image forming operation, the controller119transmits a command to the image forming apparatus controller301and the main controller101, and receives data from the image forming apparatus controller301and the main controller101. As described above, in the case where a plurality of apparatuses are connected to and cooperate with each other, the controller119integrally manages the control and status of each apparatus, and thus maintains the consistency of operation between the apparatuses.

The main controller101of the sheet processing apparatus4serving as a controller according to the present embodiment includes a central processing unit: CPU306, a random access memory: RAM308, a read-only memory: ROM307, a communication portion315, and an I/O port310. The CPU306is a central processing unit that controls various operations of the sheet processing apparatus4. The RAM308is a volatile memory that temporarily stores control data required for operation of the sheet processing apparatus4. The ROM307is a nonvolatile memory that stores a control program for the sheet processing apparatus4, and a control table required for the operation of the sheet processing apparatus4. The communication portion315communicates with the controller119.

The CPU306, the RAM308, the ROM307, and the communication portion315are connected to the I/O port310via a bus309, and the I/O port310is connected to each constituting element of the sheet processing apparatus4. That is, via the I/O port310, the main controller101outputs control signals for operating various actuators of the sheet processing apparatus4, and receives input of detection signals from various sensors of the sheet processing apparatus4.

More specifically, the main controller101is connected to the lifting motor55via a driving circuit (i.e., lifting motor driving circuit)65. In the present embodiment, a stepping motor is used as the lifting motor55. The lifting motor55is connected to a lifting mechanism of the discharge tray37via an unillustrated drive transmission mechanism such as gears. The discharge tray37ascends when the lifting motor55rotates in a first direction, and descends when the lifting motor55rotates in a second direction opposite to the first direction. The discharge tray37ascends or descends by a predetermined distance, for example, 0.01 mm, in accordance with a 1-step rotation operation of the lifting motor55.

In addition, the main controller101is connected to the light emitting portion51aand the light receiving portion51bof the transmissive upper surface sensor51respectively via a light emitting circuit61aand a light receiving circuit61b, and is connected to the light emitting portion52aand the light receiving portion52bof the reflective upper surface sensor52respectively via a light emitting circuit62aand a light receiving circuit62b. The light receiving portion51bof the transmissive upper surface sensor51and the light receiving portion52bof the reflective upper surface sensor52input low-level signals to the main controller101via the light receiving circuits61band62bin the case where the light receiving portions51band52bare not receiving light, and input high-level signals to the main controller101in the case where the light receiving portions51band52bare receiving light. Further, the main controller101is connected to the upper limit sensor53, the lower limit sensor54, and the sheet presence/absence sensor50respectively via input circuits63,64, and60, and receive signals output from the sensors.

Functional Configuration

FIG. 5is a block diagram illustrating a functional configuration of the image forming system1S. The main controller101is constituted by a motor controller75, a photosensor controller71, a photo-interrupter detection portion70, a lifting controller80, and a communication controller79.

The motor controller75controls the lifting motor55to rotate in the first direction, rotate in the second direction, or stop rotation, in accordance with a command from the lifting controller80. In the case where a driving step number of the lifting motor55that is a stepping motor is specified, the motor controller75controls the lifting motor55to rotate in a specified direction by the specified number of steps. The photosensor controller71performs control to repeatedly turn on and off the light emitting portion51aof the transmissive upper surface sensor51and the light emitting portion52aof the reflective upper surface sensor52. In addition, the photosensor controller71obtains signal levels of the light receiving portions51band52bwhen the light emitting portions51aand52aare on, and signal levels of the light receiving portions51band52bwhen the light emitting portions51aand52aare off. In the configuration example of the present embodiment, the light emitting portions51aand52aare repeatedly turned on and off at a period of 50 milliseconds.

The photo-interrupter detection portion70detects the position of the discharge tray37and the presence or absence of a sheet on the discharge tray37on the basis of signals obtained from the photo-interrupters of the upper limit sensor53, the lower limit sensor54, and the sheet presence/absence sensor50. Specifically, the photo-interrupter detection portion70detects the discharge tray37being at the upper limit position on the basis of the upper limit sensor53being in the shielded state, and detects the discharge tray37being at the lower limit position on the basis of the lower limit sensor54being in the shielded state. In addition, the photo-interrupter detection portion70detects the presence of a sheet on the discharge tray37on the basis of the photo-interrupter of the sheet presence/absence sensor50being in the shielded state.

The communication controller79controls communication with the controller119described above. The lifting controller80obtains information about a sheet to be discharged onto the discharge tray37via communication with the controller119. Examples of the information about the sheet include the type of the sheet, the grammage of the sheet, the grain direction of the sheet, that is, the direction of fiber of the sheet, information about a surface of the sheet on which printing is to be performed, that is, which of simplex printing and duplex printing is to be performed, the size of the sheet, the number of sheets, the type of processing to be performed on the sheet, the temperature and humidity of the environment in which the sheet is placed, and so forth.

The lifting controller80includes a first sheet presence/absence determining portion81that determines whether or not a sheet is present on the basis of the output signal of the transmissive upper surface sensor51, and a second sheet presence/absence determining portion82that determines whether or not a sheet is present on the basis of the output signal of the reflective upper surface sensor52. The lifting controller80further includes a detectability determining portion83that determines whether or not sheet detection by the transmissive upper surface sensor51is possible, and a detection necessity determining portion84that determines whether or not sheet detection by the transmissive upper surface sensor51is needed. The lifting controller80performs lifting/lowering control of the discharge tray37by commanding the motor controller75to drive the lifting motor55on the basis of the information obtained from the photosensor controller71, the photo-interrupter detection portion70, and the communication controller79.

The first sheet presence/absence determining portion81determines whether or not a sheet is present on the optical axis L51of the transmissive upper surface sensor51on the basis of the information obtained from the photosensor controller71. Specifically, whether or not a sheet is present is determined by using the signal level of the light receiving portion51bof the transmissive upper surface sensor51when the light emitting portion51ais on, on the basis of a relationship shown in Table 1. To be noted, “Low” in Table 1 indicates a signal level corresponding to a state in which the amount of light received by the light receiving portion51bis a first amount smaller than a predetermined standard, and “High” in Table 1 indicates a signal level corresponding to a state in which the amount of light received by the light receiving portion51bis a second amount larger than the predetermined standard.

TABLE 1SIGNAL LEVEL OF LIGHT RECEIVINGPORTION OF TRANSMISSIVEDETERMINATIONUPPER SURFACE SENSOR WHENOF PRESENCE/LIGHT EMITTING PORTION IS ONABSENCE OF SHEETLOWPRESENTHIGHABSENT

The second sheet presence/absence determining portion82determines whether or not a sheet is present on the optical axis L52of the reflective upper surface sensor52on the basis of the information obtained from the photosensor controller71. Specifically, whether or not a sheet is present is determined by using the signal levels of the light receiving portion52bof the reflective upper surface sensor52when the light emitting portion52ais on and off, on the basis of a relationship shown in Table 2. To be noted, “Low” in Table 2 indicates a signal level corresponding to a state in which the amount of light received by the light receiving portion52bis smaller than a predetermined standard, and “High” in Table 2 indicates a signal level corresponding to a state in which the amount of light received by the light receiving portion52bis larger than the predetermined standard.

The detectability determining portion83serving as a first determining portion according to the present embodiment determines, on the basis of the information obtained from the photosensor controller71, whether or not sheet detection by using the transmissive upper surface sensor51is possible. “Whether or not sheet detection by using the transmissive upper surface sensor51is possible” indicates whether or not it is appropriate or applicable to detect the presence or absence of a sheet on the optical axis L51by using the transmissive upper surface sensor51. Specifically, whether or not sheet detection by the transmissive upper surface sensor51is possible is determined by using the signal level of the light receiving portion51bof the transmissive upper surface sensor51when the light emitting portion51ais off, on the basis of a relationship shown in Table 3. In other words, in the case where the amount of light received by the first light receiving portion when the first light emitting portion is off is smaller than the predetermined standard, the first determining portion determines that sheet detection by the transmissive sensor is possible, and in the case where the amount of light received by the first light receiving portion when the first light emitting portion is off is larger than the predetermined standard, the first determining portion determines that sheet detection by the transmissive sensor is impossible.

The detection necessity determining portion84serving as a second determining portion according to the present embodiment determines, by using information about a sheet received from the controller119, whether or not sheet detection by the transmissive upper surface sensor51is needed. “Whether or not detection of a sheet is needed” indicates whether or not detection of presence or absence of a sheet on the optical axis L51by the transmissive upper surface sensor51is needed. Specifically, necessity of sheet detection by the transmissive upper surface sensor51is determined by using the information about a sheet received from the controller119on the basis of a relationship shown in Table 4.

In other words, the second determining portion, (i) if a grammage of the sheet discharged by the discharging portion is a first grammage, determines that detection of the sheet by the transmissive sensor is not needed, (ii) if an environmental humidity in which the sheet discharging apparatus is disposed is a first humidity, determines that sheet detection by the transmissive sensor is not needed, and (iii) if the grammage of the sheet discharged by the discharging portion is a second grammage smaller than the first grammage and the environmental humidity is a second humidity higher than the first humidity, determines that sheet detection by the transmissive sensor is needed. In the present embodiment, for example, the “first grammage” is 100 g/m2, the “second grammage” is 80 g/m2, the “first humidity” is 50 RH %, and the “second humidity” is 90 RH %. That is, in the case where the grammage of the sheet is smaller than a predetermined standard and the humidity is higher than a predetermined standard, the second determining portion determines that sheet detection by the transmissive upper surface sensor51is needed because there is a risk of occurrence of curling described below, and otherwise determines that sheet detection by the transmissive upper surface sensor51is not necessarily needed.

As described above with reference toFIG. 3C, the transmissive upper surface sensor51is configured to be capable of detecting an end portion of a sheet that is lifted up by curling in the case of a curled sheet. To lower the possibility of a discharge failure or the like caused by curling of a sheet, it is preferable that the lifting/lowering control of the discharge tray37is performed by using the transmissive upper surface sensor51in a situation in which occurrence of curling in the sheet is expected.

The curling of the sheet is known to be more likely to occur in the case where the degree of moisture absorption of the sheet to be used for image formation is higher and where the grammage of the sheet is smaller. Therefore, in the present embodiment, as predetermined conditions indicating that the possibility of occurrence of curling is high, the relative humidity [RH %] of the sheet-installed environment and the grammage [g/m2] of the sheet shown in Table 4 are used among information about the sheet. The “sheet-installed environment” refers to an environment in which a sheet to be used for image formation has been placed, specifically in the present embodiment, the environment in the storage chamber of the feeding apparatus6of the image forming apparatus1in which the sheet is accommodated. The relative humidity of the sheet-installed environment can be obtained as a detection result of the humidity sensor120included in the image forming apparatus1by communication via the controller119.

To be noted, a humidity sensor that detects the relative humidity of the environment in which the image forming system1S may be provided in the sheet processing apparatus4, and the detection result thereof may be referred to. In addition, the determination of whether or not sheet detection by the transmissive upper surface sensor51is needed may be made on the basis of the information about the sheet to be discharged, in accordance with conditions different from the conditions shown in Table 4. For example, at least one of the type of the sheet, the grain direction of the sheet, information indicating the surface of the sheet on which printing is to be performed, the size of the sheet, the number of sheets, the type of processing performed on the sheet, and the temperature of the sheet-installed environment may be used. Examples of the type of the sheet include thin paper sheets, plain paper sheets, and cardboards, and examples of the type of processing performed on the sheet include stapling. These conditions are appropriately used in combination in accordance with whether or not the condition is correlated with the likelihood of occurrence of curling of a sheet. For example, a configuration in which only the information about the grammage is used may be employed such that in the case where the grammage of the sheet to be discharged by the discharging portion is a first grammage, the second determining portion determines that sheet detection by the transmissive sensor is not needed, and in the case where the grammage of the sheet to be discharged by the discharging portion is a second grammage smaller than the first grammage, the second determining portion determines that detection of the sheet by the transmissive sensor is needed. For another example, a configuration in which only the information about the humidity is used may be employed such that in the case where the humidity of the environment in which the sheet discharging apparatus is installed is a first humidity, the second determining portion determines that sheet detection by the reflective sensor is not needed, and in the case where the humidity is a second humidity higher than the first humidity, the second determining portion determines that detection of the sheet by the transmissive sensor is needed.

Lifting/Lowering Control of Discharge Tray

Next, the lifting/lowering control of the discharge tray37by the main controller101according to the present embodiment will be described. After the power of the sheet processing apparatus4is turned on, the main controller101continues monitoring whether there is a job of an image forming operation in which the discharge tray37is set as a sheet discharge destination, and in the case where the job is executed, the main controller101performs the lifting/lowering control of the discharge tray37. In the lifting/lowering control, the discharge tray37is moved to the upper limit position in the case where no sheet is present on the discharge tray37, and in the case where a sheet is supported on the discharge tray37, the discharge tray37is lowered in accordance with the amount of sheets supported thereon such that the upper surface of the sheets on the discharge tray37is at a predetermined position.

The lifting/lowering control of the discharge tray37will be described in detail with reference to a flowchart ofFIG. 6. First, in step S100, the lifting controller80determines whether or not a sheet is present on the discharge tray37on the basis of the output signal of the sheet presence/absence sensor50. In the case where it has been determined that no sheet is present on the discharge tray37, the lifting controller80determines in step S101whether or not the discharge tray37is at the upper limit position on the basis of the detection result of the upper limit sensor53. In the case where it has been determined that the discharge tray37is at the upper limit position, the process returns to step S100, and the lifting controller80stands by until the output signal of the sheet presence/absence sensor50indicates that a sheet is present on the discharge tray37. In the case where it has been determined that the discharge tray37is not at the upper limit position in step S101, the lifting controller80rotates the lifting motor55in the first direction via the motor controller75, and thus lifts up the discharge tray37. Then, when the lifting controller80confirms that the detection result of the upper limit sensor53indicates that the discharge tray37is at the upper limit position, the lifting controller80stops the ascent of the discharge tray37in step S102.

According to the process described above, in the case where no sheet is present on the discharge tray37, the discharge tray37stands by at the upper limit position.

In the case where it has been determined that a sheet is present on the discharge tray37in step S100, the detectability determining portion83determines in step S103whether or not sheet detection by the transmissive upper surface sensor51is possible. In the case where it has been determined that sheet detection by the transmissive upper surface sensor51is “possible”, whether or not the transmissive upper surface sensor51and the reflective upper surface sensor52are detecting a sheet is determined in step S104by the first sheet presence/absence determining portion81and the second sheet presence/absence determining portion82as shown in Tables 1 and 2. In the case where the detection result of the transmissive upper surface sensor51or the reflective upper surface sensor52indicates that “a sheet is present”, in step S105, the lifting controller80rotates the lifting motor55in the second direction via the motor controller75, and thus lowers the discharge tray37. In other words, in the case where the transmissive sensor or the reflective sensor has output an output signal indicating that a sheet has been detected, the controller lowers the supporting portion by the lifting portion to a position where each of the transmissive sensor and the reflective sensor outputs an output signal indicating that no sheet is detected. Then, when the discharge tray37is lowered to a position where the detection results of both the transmissive upper surface sensor51and the reflective upper surface sensor52indicate that “no sheet is present”, the lifting controller80stops the descent of the discharge tray37. Alternatively, the lifting controller80stops the descent of the discharge tray37when the detection result of the lower limit sensor54indicates that the discharge tray37is at the lower limit position while lowering the discharge tray37. In the case where the detection results of both the transmissive upper surface sensor51and the reflective upper surface sensor52indicate that “no sheet is present” in step S104, the lifting controller80proceeds to step S106without lowering the discharge tray37.

In the case where the detectability determining portion83has determined that sheet detection by the transmissive upper surface sensor51is “possible” according to the process described above, lifting/lowering control using both the transmissive upper surface sensor51and the reflective upper surface sensor52is performed. In other words, in the case where the amount of light received by the first light receiving portion in a state in which the first light emitting portion is not emitting light is a first amount corresponding to Low in Table 3, the supporting portion is lifted or lowered on the basis of the output signals of the transmissive sensor and the reflective sensor. In this case, more reliable lifting/lowering control in which discharge of sheets can be continued even in the case where curling or leaning has occurred can be performed by making most of the detection characteristics of the transmissive upper surface sensor51and the reflective upper surface sensor52.

In the case where the detectability determining portion83has determined that sheet detection by the transmissive upper surface sensor51is impossible in step S103, the detection necessity determining portion84determines in step S107whether or not sheet detection by the transmissive upper surface sensor51is needed. In the case where it has been determined that sheet detection by the transmissive upper surface sensor51is “not needed”, the second sheet presence/absence determining portion82determines in step S108whether or not the reflective upper surface sensor52is detecting a sheet. In the case where the detection result of the reflective upper surface sensor52indicates that “a sheet is present”, in step S109, the lifting controller80rotates the lifting motor55in a second direction via the motor controller75, and thus lowers the discharge tray37. In other words, in the case where the reflective sensor has output an output signal indicating that a sheet has been detected, the controller lowers the supporting portion by the lifting portion to a position where the reflective sensor outputs an output signal indicating that a sheet is not detected. Then, when the discharge tray37is lowered to a position where the detection result of the reflective upper surface sensor52indicates that “no sheet is present”, the lifting controller80stops the descent of the discharge tray37. Alternatively, the lifting controller80stops the descent of the discharge tray37when the detection result of the lower limit sensor54indicates that the discharge tray37is at the lower limit position while lowering the discharge tray37. In the case where the detection result of the reflective upper surface sensor52indicates that “no sheet is present” in step S108, the lifting controller80proceeds to step S106without lowering the discharge tray37.

According to the process described above, in the case where the detectability determining portion83has determined that sheet detection by the transmissive upper surface sensor51is “impossible”, and the detection necessity determining portion84has determined that sheet detection by the transmissive upper surface sensor51is “not needed”, the lifting/lowering control is performed by using the reflective upper surface sensor52. In other words, in the case where the amount of light received by the first light receiving portion in a state in which the first light emitting portion is not emitting light is a second amount corresponding to High of Table 3 larger than the first amount, and the grammage of the sheet to be discharged by the discharging portion and the humidity of the environment in which the sheet has been placed do not satisfy predetermined conditions, which is a case corresponding to “Not needed” of Table 4, the supporting portion is lifted or lowered by the lifting portion on the basis of the output signal of the reflective sensor. In this case, although the transmissive upper surface sensor51is not used, since the likelihood of occurrence of curling of a sheet is low, appropriate lifting/lowering control can be performed by using the reflective upper surface sensor52.

In the case where the detection necessity determining portion84has determined that sheet detection by the transmissive upper surface sensor51is “needed” in step S107, the communication controller79notifies the controller119of stoppage of image formation on a sheet to be discharged onto the discharge tray37in step S110. When the notification of stoppage of image formation is received, the controller119stops a new image formation instruction in which the discharge tray37is set as a discharge destination. However, a sheet being conveyed in the image forming apparatus1and the sheet processing apparatus4is discharged onto the upper discharge tray25or the lower discharge tray37.

According to the process described above, in the case where the detectability determining portion83has determined that sheet detection by the transmissive upper surface sensor51is “impossible” and the detection necessity determining portion84has determined that sheet detection by the transmissive upper surface sensor51is “needed”, sheet discharge onto the discharge tray37is stopped. In other words, in the case where the amount of light received by the first light receiving portion in a state in which the first light emitting portion is not emitting light is a second amount corresponding to High in Table 3 and the grammage of the sheet to be discharged by the discharging portion and the humidity of the environment in which the sheet has been placed satisfy predetermined conditions, which is a case corresponding to “needed” in Table 4, the supporting portion is lifted or lowered by the lifting portion in response to discharge of a sheet from the discharging portion. In this case, since there is a possibility that curling of the sheet occurs, it is determined that it is difficult to perform appropriate lifting/lowering control with just the reflective upper surface sensor52, and therefore stoppage of sheet discharge, that is, stoppage of the image forming operation is determined.

Then, in step S111, a standby state is taken until the determination result of the detectability determining portion83indicates that sheet detection by the transmissive upper surface sensor51is “possible”. During the standby state, in step S113, elapsed time from step S110is measured. In the case where the elapsed time has reached a predetermined time Terr during the standby state, the communication controller79notifies the controller119of abnormality of the transmissive upper surface sensor51in step S114, and the lifting/lowering control of the discharge tray37is finished. When the determination result of the detectability determining portion changes to “possible” during the standby state, the communication controller79notifies the controller119of resuming image formation on the sheet to be discharged onto the discharge tray37in step S112. When the notification to resume the image formation is received, the controller119resumes the image formation instruction in which the discharge tray37is set as a discharge destination, and proceeds to step S106.

In step S106, the main controller101repeats the processing from step S100up to this step until the power of the sheet processing apparatus4is turned off.

Advantages of Present Embodiment

There is a possibility that the light receiving portion51bof the transmissive upper surface sensor51is affected by disturbance light from the outside due to the configuration thereof. For example, the light receiving portion51bcan be affected by sunlight. That is, sunlight can be incident on the light receiving portion51bat an incident angle close to that of the optical axis L51of the light emitted from the light emitting portion51a, depending on conditions such as the direction in which the sheet processing apparatus4is installed, the weather, and the time. In addition, the amount of the sunlight incident on the light receiving portion51bcan be as large as or larger than the amount of light that is incident on the light receiving portion51bafter being emitted from the light emitting portion51a.

In such a case, the amount of light received by the light receiving portion51bis approximately saturated even when the light emitting portion51ais off, and therefore the signal level of the light receiving portion51bhardly changes even when the light emitting portion51ais turned on. That is, the light receiving portion51boutputs an approximately constant signal regardless of whether the light emitting portion51ais on or off, and therefore it becomes inappropriate to determine whether or not a sheet is present on the optical axis L51on the basis of the signal of the light receiving portion51b.

In contrast, although disturbance light such as sunlight can be also incident on the reflective upper surface sensor52, since the light emitting portion52aand the light receiving portion52bare disposed close to each other, in the case where a sheet is present on the optical axis L52of the reflective upper surface sensor52, the disturbance light is shielded by the sheet. Therefore, the second sheet presence/absence determining portion82can appropriately detect the presence or absence of a sheet on the optical axis L52by determining whether or not a sheet is present by using the signal levels of the light receiving portion52bof the reflective upper surface sensor52when the light emitting portion52ais off and on in combination. That is, the reflective sensor is advantageous in that an appropriate detection accuracy can be more easily maintained than in the transmissive sensor in the presence of disturbance light.

In the present embodiment, in a configuration including the transmissive upper surface sensor51and the reflective upper surface sensor52, the lifting/lowering control of the discharge tray37is performed while selectively determining which of the transmissive upper surface sensor51and the reflective upper surface sensor52is used in accordance with the situation. That is, the detectability determining portion83serving as a first determining portion determines whether or not detection of the upper surface of a sheet by the transmissive upper surface sensor51is possible, and the detection necessity determining portion84serving as a second determining portion determines whether or not detection of the upper surface of a sheet by the transmissive upper surface sensor51is needed. Then, whether to perform lifting/lowering control on the basis of the output signals of the transmissive upper surface sensor51and the reflective upper surface sensor52, perform the lifting/lowering control on the basis of the output signal of just the reflective upper surface sensor52, or stop the sheet discharge is determined. As a result of this, the sheet discharge can be continued as long as possible while lowering the possibility of erroneous operation caused by the influence of disturbance light or the like, with a simple configuration.

Although the predetermined time Teri described above is set to 1 hour as an example in the present embodiment on the basis of time in which the light receiving portion51bcan be affected by sunlight, the time Terr can be appropriately changed. In addition, when a notification of stoppage of image formation is received, the controller119may display, on an unillustrated operation panel, a screen indicating that the image forming operation is stopped due to disturbance light so as to prompt the user to take a measure to prevent the disturbance light from entering.

To be noted, as an alternative method for reducing the influence of disturbance light on the transmissive upper surface sensor51, providing a plurality of transmissive upper surface sensors having different optical axis directions can be considered. However, in this configuration, a plurality of light emitting portions and a plurality of light receiving portions are disposed at positions apart from each other, and therefore the cost of the hardware increases. In addition, although disposing an aperture provided in front of the light receiving portion51bat a position as away from the light receiving portion51bas possible can be also considered, this leads to increase in the size of the apparatus. In contrast, according to the present embodiment, the influence of disturbance light can be reduced with a simple and compact configuration.

Second Embodiment

A sheet discharging portion according to a second embodiment will be described focusing on the difference from the first embodiment. The present embodiment is different in the details of the lifting/lowering control of the discharge tray37. In the description below, it is assumed that elements denoted by the same reference signs as in the first embodiment have substantially the same configuration and effects as in the first embodiment.

FIG. 7is a block diagram illustrating a functional configuration of an image forming system according to the present embodiment. The lifting controller80includes a tray descent amount calculation portion85in addition to the first sheet presence/absence determining portion81, the second sheet presence/absence determining portion82, the detectability determining portion83, and the detection necessity determining portion84. The tray descent amount calculation portion85calculates the descent amount of the discharge tray37on the basis of information about a sheet obtained by communication with the controller119.

Next, the lifting/lowering control of the discharge tray37in the present embodiment will be described with reference to a flowchart ofFIG. 8. To be noted, steps having the same processing as in the flowchart ofFIG. 6of the first embodiment are denoted by the same step numbers, and description thereof will be omitted.

In the case where the detection necessity determining portion84has determined that sheet detection by the transmissive upper surface sensor51is “needed” in step S107, the lifting controller80stands by for discharge of a sheet onto the discharge tray37in step S200. When no sheet is discharged onto the discharge tray37, the process returns to step S103. In the present embodiment, it is determined that a sheet has been discharged onto the discharge tray37at a timing at which the trailing end of the sheet has reached the bundle discharge rollers36. In the case where it has been determined that a sheet has been discharged onto the discharge tray37, the tray descent amount calculation portion85calculates a tray descent amount d by using the following formula (1) in step S201.
tray descent amountd[mm]=(number of sheets×sheet thickness)+base offset amount+post-processing offset amount  (1)

The number of sheets is the number of sheets in a sheet bundle discharged by the bundle discharge rollers36in one time. The sheet thickness is the thickness of each sheet in the sheet bundle discharged by the bundle discharge rollers36in one time. The main controller101obtains the number of sheets and the sheet thickness by communicating with the controller119. The sheet thickness is specified in units of 0.01 mm, for example. The base offset amount is a value set in consideration of deformation of discharged sheets, and is 1.5 mm in the present embodiment. The post-processing offset amount is determined in accordance with the type of processing performed on the sheet bundle to be discharged, and is 2 mm for a stapled sheet bundle, and 0 mm for a non-stapled sheet bundle in the present embodiment.

The method for calculating the tray descent amount d is not limited to the formula (1) described above as long as a value that enables suppressing occurrence of a jam caused by collision between sheets discharged from the bundle discharge rollers36with sheets already supported on the discharge tray37, and suppressing droppage of the already supported sheets from the discharge tray37. For example, the base offset amount may be set to a sufficiently large value, or a calculation formula for more accurately estimating the deformation of sheets by using the information about the sheets such as the grammage of the sheets, the grain direction of the sheets, information about a surface of sheets on which printing is to be performed, the size of the sheets, and the sheet-installed environment.

In the present embodiment, for example, in the case of a sheet bundle obtained by stapling10thick sheets each having a thickness of 0.12 mm, the tray descent amount d calculated on the basis of the formula (1) is 4.7 mm. Next, in step S109, the lifting controller80rotates the lifting motor55in the second direction by a number of steps corresponding to the tray descent amount d. In the present embodiment, since the lifting motor55is configured to lift or lower the discharge tray37by 0.01 mm by 1-step drive, in the case where the tray descent amount d is 4.2 mm, the number of steps is 420. In the case where the detection result of the lower limit sensor54indicates that the discharge tray37has reached the lower limit position while descending, the lifting controller80stops the lifting motor55to finish the descent of the discharge tray37, and proceeds to step S106.

As described above, in the present embodiment, in the case where the detectability determining portion83and the detection necessity determining portion84have determined that sheet detection by the transmissive upper surface sensor51is “impossible” and “needed”, that is, in the case where the result of step S103is NO and the result of step S107is YES, the lifting/lowering control is performed on the basis of an estimated tray descent amount d. In other words, in the case where the amount of light received by the first light receiving portion in the state in which the first light emitting portion is not emitting light is a second amount corresponding to High in Table 3 and the grammage of the sheet to be discharged by the discharging portion and the humidity of the environment in which the sheet has been placed satisfy predetermined conditions, which is a case corresponding to “Needed” of Table 4, the supporting portion is lifted or lowered by the lifting portion in accordance with discharge of sheets by the discharging portion. Therefore, by setting a calculation method for the tray descent amount d in advance in consideration of the influence of the curling of the sheets and the like, the discharge of sheets can be continued while suppressing the possibility of occurrence of a discharge failure or the like caused by the curling. That is, discharge of sheets can be continued as long as possible while suppressing the possibility of erroneous operation caused by the influence of disturbance light or the like.

Modification Example

Although the discharge tray37is lifted to the upper limit position on the basis of the detection result of the sheet presence/absence sensor50in the first embodiment and the second embodiment described above, the lifting control of the discharge tray37may be performed by a different method. As a modification example, a method of performing the lifting/lowering control of the discharge tray37by using the transmissive upper surface sensor51and the reflective upper surface sensor52will be described.

FIG. 9is a flowchart illustrating lifting/lowering control of the discharge tray37according to the present modification example. To be noted, steps of substantially the same processing as in the flowchart ofFIG. 8of the second embodiment will be denoted by the same step numbers and description thereof will be omitted.

First, in step S300, the lifting controller80obtains, from the controller119, whether or not there is a plan to discharge a sheet onto the discharge tray37. Processing performed in the case where there is a plan to discharge a sheet onto the discharge tray37is the same as in steps S103to S109and S200to S202of the flowchart ofFIG. 8according to the second embodiment, and redundant description will be omitted. In the case where there is no plan to discharge a sheet onto the discharge tray37in step S300, the lifting controller80performs lifting control of the discharge tray37by using the transmissive upper surface sensor51and the reflective upper surface sensor52by processing of steps S301to S306.

In step S301, the detectability determining portion83determines whether or not sheet detection by the transmissive upper surface sensor51is possible. In the case where sheet detection by the transmissive upper surface sensor51is “possible”, it is determined in step S302whether or not the detection results of both the transmissive upper surface sensor51and the reflective upper surface sensor52indicate that “no sheet is present”. In the case where the detection results of both the transmissive upper surface sensor51and the reflective upper surface sensor52indicate that “no sheet is present”, the lifting controller80rotates the lifting motor55in the first direction in step S303. Then, the discharge tray37is lifted up to a position where the detection result of one of the transmissive upper surface sensor51and the reflective upper surface sensor52indicates that “a sheet is present”. In addition, in the case where the detection result of the upper limit sensor53indicates that the discharge tray37has reached the upper limit position while the discharge tray37is ascending, the lifting controller80stops the lifting motor55to finish the ascent of the discharge tray37, and returns to step S300. In the case where the detection result of the transmissive upper surface sensor51or the reflective upper surface sensor52indicates that “a sheet is present” in step S302, the lifting controller80returns to step S300without lifting the discharge tray37.

In the case where sheet detection by the transmissive upper surface sensor51is “impossible” in step S301, the detection necessity determining portion84determines in step S304whether or not sheet detection by the transmissive upper surface sensor51is needed. In the case where sheet detection by the transmissive upper surface sensor51is “not needed”, whether or not the detection result of the reflective upper surface sensor52indicates that “no sheet is present” is determined in step S305. In the case where the result of the reflective upper surface sensor52indicates that “no sheet is present”, the lifting controller80rotates the lifting motor55in the first direction in step S306, and thus lifts up the discharge tray37to a position where the detection result of the reflective upper surface sensor52indicates that “a sheet is present”. In addition, in the case where the detection result of the upper limit sensor53indicates that the discharge tray37has reached the upper limit position while the discharge tray37is ascending, the lifting controller80stops the lifting motor55to finish the ascent of the discharge tray37, and returns to step S300. In the case where the detection result of the reflective upper surface sensor52indicates that “a sheet is present” in step S305, the lifting controller80returns to step S300without lifting the discharge tray37.

According to the processing described above, the discharge tray37can be lifted up to an appropriate position in accordance with the amount of supported sheets in a configuration in which the sheet presence/absence sensor50is omitted.

OTHER EMBODIMENTS

In the embodiments described above, the sheet processing apparatus4directly connected to the image forming apparatus1has been described as an example of a sheet processing apparatus. However, the present technique can be also applied to a sheet processing apparatus that receives a sheet from the image forming apparatus1via an intermediate unit. For example, the intermediate unit is a relay conveyance unit that is attached to a discharge space in an image forming apparatus of an in-body discharge type. In addition, examples of an image forming system include an image forming system in which modules having the functions of the image forming apparatus1and the sheet processing apparatus4are incorporated in a single casing.

In addition, the stapler57is an example of a processing portion that processes sheets, and for example, a sheet bundle aligned on the intermediate supporting portion may be discharged onto the discharge tray37without being stapled. In addition, the sheet discharging portion100provided in the sheet processing apparatus4is an example of a sheet discharging apparatus, and the present technique can be also applied to a sheet discharging apparatus that discharges a sheet serving as a recording material on which an image has been formed by the image forming apparatus to the outside of the image forming apparatus.

The discharging portion that discharges a sheet in the sheet discharging portion100is not limited to a roller pair that nips and conveys the sheet, and for example, sheets may be pushed out of the casing of the sheet processing apparatus4by the bundle discharge guide34serving as a discharging portion.

The inner configuration of the sheet processing apparatus4illustrated inFIG. 1and so forth is merely an example, and the layout of conveyance paths and so forth in the sheet processing apparatus may be changed. For example, instead of a configuration in which the discharge destination of sheets is switched in accordance with whether or not reverse conveyance by the reverse conveyance rollers24is performed, a flap-shaped guide member that switches a conveyance path between the conveyance path to the upper discharge tray25and the conveyance path to the binding processing portion4A may be disposed downstream of the inlet rollers21.

This application claims the benefit of Japanese Patent Application No. 2020-134814, filed on Aug. 7, 2020, which is hereby incorporated by reference herein in its entirety.