Patent ID: 12208981

The accompanying drawings are intended to depict embodiments of the present invention 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.

DETAILED DESCRIPTION

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.

Hereinafter, with reference to the drawings, a description is given of an image forming apparatus1according to an embodiment of the present disclosure.FIG.1is a schematic view illustrating an interior of the image forming apparatus1. The image forming apparatus1successively forms images on multiple sheets M. Examples of the sheet M as a sheet-shaped medium include paper (paper sheet), an overhead projector (OHP) transparency, thread, fiber, fabric, leather, metal, and plastic. As illustrated inFIG.1, the image forming apparatus1includes a sheet feed tray10, a conveyor20, an image forming unit30, a leading end guide40, a sheet ejection tray50(i.e., a tray), and an air exhaust60.

The sheet feed tray10stores a stack of sheets M before images are formed thereon. The conveyor20feeds the sheet M stored in the sheet feed tray10to a position facing the image forming unit30, and then ejects the sheet M to the sheet ejection tray50. The conveyor20includes a sheet feed roller21and a plurality of roller pairs22,23,24,25,26, and27.

The sheet feed roller21rotates while contacting the top sheet M among the stack of sheet M in the sheet feed tray10to feed the sheet M to a conveyance path of the sheet M. The plurality of roller pairs22to27is arranged at predetermined intervals along the conveyance path. The roller pairs22to27rotate while nipping the sheet M to convey the sheet M. The conveyance path indicated by a broken line inFIG.1is a space extending from the sheet feed tray10to the sheet ejection tray50via the position facing the image forming unit30.

Some of the roller pairs22to27convey the sheet M in different conveyance directions from others. The roller pair27is closest to the sheet ejection tray50among the roller pairs22to27. The conveyance direction of the sheet M by the roller pair27is a horizontal direction (i.e., from right to left inFIG.1). The “conveyance direction” simply cited in the present disclosure refers to the conveyance direction by the roller pair27.

The image forming unit30employs an inkjet method in which ink is discharged onto the sheet M to form an image on the sheet M. The image forming unit30includes multiple head modules that discharge inks of respective colors of cyan, magenta, yellow, and black. Each of the multiple head modules discharges the ink at a predetermined timing to form an image on the sheet M facing the image forming unit30. Alternatively, the image forming unit30may employ an electrophotographic method in which toner is fixed on the sheet M to form an image on the sheet M.

Among the components of the image forming apparatus1illustrated inFIG.1, the roller pair27(a part of the conveyor), the leading end guide40, the sheet ejection tray50, and the air exhaust60construct a sheet stacker that stacks multiple sheets M, for example.

The leading end guide40is disposed downstream from the roller pair27in the conveyance direction. The roller pair27and the leading end guide40are disposed above the sheet ejection tray50. The leading end guide40guides a leading end of the sheet M from the roller pair27to a downstream from the sheet ejection tray50in the conveyance direction, thereby facilitating the sheet M freely falling toward the sheet ejection tray50without conveyance failure of the sheet M such as collision between sheets M, a gap between the sheets M on the sheet ejection tray50, and a crease or a curl of the sheet M.

FIG.2is a schematic view of the sheet stacker of the image forming apparatus1, in which a guide44is at a holding position.FIG.3is a schematic view of the sheet stacker, in which the guide44is at a release position. As illustrated inFIGS.1to3, the leading end guide40includes a drive roller41, a driven roller42, an endless annular belt43, and multiple guides44and45.

The drive roller41and the driven roller42are rotatably supported by a housing of the image forming apparatus1at positions separated from each other in the conveyance direction. The endless annular belt43is stretched over the drive roller41and the driven roller42. As a motor transmits a driving force to the drive roller41, the drive roller41rotates, and the endless annular belt43rotates between the drive roller41and the driven roller42. The endless annular belt43rotates clockwise inFIGS.2and3. In other words, the endless annular belt43rotates in a direction in which a lower stretched portion thereof moves in the conveyance direction and an upper stretched portion thereof moves in the direction opposite to the conveyance direction.

The guides44and45are attached to the outer circumferential surface of the endless annular belt43at equal intervals. Accordingly, as the endless annular belt43rotates, the guides44and45move in the conveyance direction on the lower stretched portion of the endless annular belt43, and move in the direction opposite to the conveyance direction on the upper stretched portion of the endless annular belt43. The number of the guides44and45is not limited to two.

The guide44has an internal space for holding the leading end (downstream end in the conveyance direction) of the sheet M. More specifically, the guide44includes an opening portion44a, a middle portion44b, and a deep portion44c. Similarly to the guide44, the guide45includes an opening portion45a, a middle portion45b, and a deep portion45c. The structure of the guide44is described below.

When the guide44is positioned on the lower stretched portion of the endless annular belt43, the opening portion44ais open toward the upstream side in the conveyance direction (that is, the opening portion44afaces the roller pair27). When the guide44is positioned on the lower stretched portion of the endless annular belt43, the middle portion44bis positioned downstream from the opening portion44ain the conveyance direction. The middle portion44bhas a narrower gap than the opening portion44aand the deep portion44cin the vertical direction. When the guide44is positioned on the lower stretched portion of the endless annular belt43, the deep portion44cis positioned downstream from the middle portion44bin the conveyance direction. When the sheet M is inserted into the guide44through the opening portion44a, the leading end of the sheet M contacts the deep portion44c.

The gaps in the vertical direction of the opening portion44a, the middle portion44b, and the deep portion44care set to be larger than a thickness of the sheet M conveyed by the roller pair27. That is, the guide44holds the sheet M without nipping the sheet M between the upper wall and the lower wall thereof so that the sheet M is not hindered from moving forward and backward. Accordingly, the guide44does not scratch the sheet M entering or leaving from the guide44. The gap in the vertical direction of the middle portion44bis not limited to be narrower than the gaps of the opening portion44aand the deep portion44c. Alternatively, the opening portion44a, the middle portion44b, and the deep portion44cmay have the same gap in the vertical direction, or the deep portion44cmay have a narrower gap than the middle portion44bin the vertical direction.

When the guide44is positioned on the lower stretched portion of the endless annular belt43, the upper surface of the lower wall of the opening portion44ais inclined upward toward the middle portion44b. A surface of the opening portion44awhere the sheet M contacts is smooth without protrusions. Accordingly, a friction when the sheet M enters the internal space of the guide44can be reduced. When the portion of the guide44where the sheet M contacts is made of a material having high smoothness such as metal or resin, the sheet M can enter the guide44more smoothly.

At the start, the guide44is stopped at the holding position illustrated inFIG.2. The opening portion44aon the lower stretched portion of the endless annular belt43faces the roller pair27at the holding position. In other words, the guide44at the holding position can hold the leading end of the sheet M passing through the roller pair27. That is, the leading end of the sheet M conveyed by the roller pair27enters the internal space of the guide44through the opening portion44aand reaches the deep portion44c.

When the leading end of the sheet M enters the internal space of the guide44, the endless annular belt43starts rotating, and stops again when the guide45reaches the holding position. At that time, the speed (maximum speed) of the guide44moving to the downstream side in the conveyance direction is set to be faster than the conveyance speed of the sheet M by the roller pair27. Therefore, the leading end of the sheet M held by the guide44leaves from the guide44at a release position illustrated inFIG.3due to the speed difference between the conveyance speed of the sheet M by the roller pair27and the moving speed of the guide44.

The release position is downstream from the holding position in the conveyance direction on the lower stretched portion of the endless annular belt43. When the leading end of the sheet M leaves from the guide44, a trailing end (upstream end in the conveyance direction) of the sheet M is still nipped by the roller pair27. That is, the leading end guide40releases the leading end of the sheet M before the trailing end of the sheet M passes through the roller pair27. In other words, the trailing end of the sheet M passes through the roller pair27after the leading end of the sheet M is separated from the leading end guide40.

Thus, the sheet M freely falls toward the sheet ejection tray50. More specifically, the leading end of the sheet M starts freely falling at the release position, and then the trailing end of the sheet M that has passed through the roller pair27starts freely falling. That is, the guide44or45of the leading end guide40holds the leading end of the sheet M conveyed by the roller pair27at the holding position and releases the leading end of the sheet M at the release position to guide the sheet M to the sheet ejection tray50. The endless annular belt43rotates intermittently to eject each of the multiple sheets M to the sheet ejection tray50.

The endless annular belt43may start rotating when the leading end of the sheet M contacts the deep portion44cof the guide44, or may start rotating immediately before the leading end of the sheet M contacts the deep portion44cof the guide44. If the leading end of the sheet M does not contact the deep portion44c, the leading end of the sheet M can be prevented from being bent or creased. The position of the leading end of the sheet M conveyed by the roller pair27can be detected by a known position sensor (for example, an optical sensor, a rotary encoder, or a combination thereof).

The sheet ejection tray50stores a stack of sheets M on which images have been formed by the image forming unit30. The sheet ejection tray50is disposed downstream from the roller pair27in the conveyance direction and below the roller pair27and the leading end guide40. In other words, the sheet M is conveyed by the roller pair27, the leading end of the sheet M is guided by the leading end guide40, and then the sheet M freely falls toward the sheet ejection tray50.

FIG.4is a schematic view of an elevator51that raises and lowers the sheet ejection tray50. The sheet ejection tray50is movable in the vertical direction by the elevator51. The elevator51includes a pair of pulleys52aand52b, a pair of chains53aand53b, a pair of weights54aand54b, an upper surface sensor55, and a full-state sensor56. However, the specific configuration of the elevator51is not limited to the example illustrated inFIG.4.

The pair of pulleys52aand52bare rotatably supported by the housing of the image forming apparatus1at positions above the sheet ejection tray50and separated from each other. The pair of chains53aand53bare stretched over the corresponding pulleys52aand52b. One ends of the pair of chains53aand53bare connected to the sheet ejection tray50, and the other ends thereof are connected to the corresponding weights54aand54b.

When the pulleys52aand52brotate in a first direction (inFIG.4, the pulley52arotates clockwise and the pulley52brotates counterclockwise), the sheet ejection tray50moves upward and the weights54aand54bmove downward. On the other hand, when the pulleys52aand52brotate in a second direction opposite to the first direction (inFIG.4, the pulley52arotates counterclockwise and the pulley52brotates clockwise), the sheet ejection tray50moves downward and the weights54aand54bmove upward.

The upper surface sensor55detects the position of the top sheet M among the stack of sheets M on the sheet ejection tray50. The upper surface sensor55is disposed above the sheet ejection tray50, for example, at a position facing a duct61(seeFIGS.1to3) of the air exhaust60or at a position slightly above the duct61in the vertical direction. The upper surface sensor55is, for example, a reflective optical sensor including a light emitter that outputs light and a light receiver that receives the light output from the light emitter and reflected on the sheet M.

The upper surface sensor55outputs a detection signal to a controller100(seeFIG.6) described below when the sheet M is in an optical path thereof (that is, when the sheet M stacked on the sheet ejection tray50is detected). On the other hand, when the sheet M is not in the optical path, the upper surface sensor55stops outputting the detection signal. The upper surface sensor55is not limited to the reflective optical sensor, and may be a transmissive optical sensor.

The full-state sensor56detects that the sheet ejection tray50is full of sheets M. The full-state sensor56is disposed, for example, at a position facing the weight54bwhen the sheet ejection tray50is full. The full-state sensor56is, for example, a reflective optical sensor including a light emitter that outputs light and a light receiver that receives the light output from the light emitter and reflected on the weight54b.

The full-state sensor56outputs a detection signal to the controller100when the weight54bis in an optical path thereof (that is, when the sheet ejection tray50is full of the sheets M). On the other hand, when the weight54bis not in the optical path, the full-state sensor56stops outputting the detection signal. The full-state sensor56is not limited to the reflective optical sensor, and may be the transmissive optical sensor.

The air exhaust60exhausts a residual air70above the upper surface of the top sheet M among the stack of sheet M on the sheet ejection tray50to an upstream from the sheet ejection tray50in the conveyance direction. More specifically, as illustrated inFIG.3, the air exhaust60exhausts the residual air70between the top sheet M stacked on the sheet ejection tray50and the sheet M feely falling toward the sheet ejection tray50, to the upstream from the sheet ejection tray50in the conveyance direction.

The air exhaust60is disposed below the roller pair27and the leading end guide40, and above the sheet ejection tray50. The air exhaust60is disposed upstream from the sheet ejection tray50in the conveyance direction.FIG.5is a plan view of the sheet ejection tray50and the air exhaust60. The air exhaust60is disposed at a position facing the trailing end of the top sheet M stacked on the sheet ejection tray50in the vertical direction as illustrated inFIGS.1to3and in the width direction of the sheets M as illustrated inFIG.5. The air exhaust60includes the duct61and a fan62.

The duct61defines an air passage through which the residual air70above the upper surface of the top sheets M stacked on the sheet ejection tray50is exhausted to the outside of the image forming apparatus1. The duct61is disposed upstream from the sheet ejection tray50in the conveyance direction and directed against the upper surface of the top sheet M stacked on the sheet ejection tray50. Specifically, a leading end of the duct61is directed against the upper surface of the top sheet M among the stack of sheets M on the sheet ejection tray50on the upstream side of the sheet ejection tray50in the conveyance direction. The other end of the duct61is open to the outside of the image forming apparatus1. The leading end of the duct61, which is directed against the upper surface of the top sheet M stacked on the sheet ejection tray50, has an opening sufficiently larger than the thickness of the sheets M in the vertical direction and larger than the maximum width of the sheets M in the width direction of the sheet M.

The fan62generates an airflow toward the upstream from the sheet ejection tray50in the conveyance direction in the duct61. That is, the air exhaust60sucks the residual air70above the upper surface of the top sheet M stacked on the sheet ejection tray50to the upstream side in the conveyance direction. The fan62can change (increase or decrease) at least one of a velocity or an air volume of the generated airflow. A device for generating the airflow (i.e., an air flow generator) toward the upstream from the sheet ejection tray50in the conveyance direction is not limited to the fan62, and a known device such as a blower can be used. That is, examples of the airflow generator include the fan62and the blower.

FIG.6is a block diagram illustrating a hardware configuration of the image forming apparatus1. The image forming apparatus1includes a central processing unit (CPU)101as a control device, a random access memory (RAM)102as a storage device, a read only memory (ROM)103as a storage device, a hard disk drive (HDD)104as a storage device, and an interface (I/F)105, which are connected via a common bus109as a communication device. The CPU101, the RAM102, the ROM103, and the HDD104are examples of the controller100(i.e., circuitry).

The CPU101is an arithmetic device and controls the overall operation of the image forming apparatus1. The RAM102is a volatile storage medium that allows data to be read and written at high speed. The CPU101uses the RAM102as a work area for data processing. The ROM103is a non-volatile read only storage medium and stores programs such as firmware. The HDD104is a non-volatile storage medium with large storage capacity, in which data is read and written, and stores an operating system (OS), various control programs, application programs, and the like.

In the image forming apparatus1, the CPU101executes a control program stored in the ROM103, a data-processing program (application program) loaded into the RAM102from a recording medium such as the HDD104, and the like using an arithmetic function.

Such programs executed by the CPU configures a software control unit including various functional modules of the image forming apparatus1. The software control unit thus configured and the hardware resources installed in the image forming apparatus1, in combination, construct functional blocks that implement the function of the image forming apparatus1.

The I/F105connects the conveyor20, the image forming unit30, the leading end guide40, the elevator51, and the air exhaust60to the common bus109. That is, the controller100controls the operations of the conveyor20, the image forming unit30, the leading end guide40, the elevator51, and the air exhaust60via the I/F105.

FIG.7is a flowchart of a process of setting an air volume of the airflow to be generated (i.e., an airflow determination process). In the airflow determination process, the air volume exhausted by the air exhaust60(a flow rate of the airflow generated per unit time by the fan62) is determined. For example, the controller100executes the airflow determination process illustrated inFIG.7in response to an image forming instruction to successively form images on multiple sheets M.

The image forming instruction includes, for example, image data indicating an image to be formed on the sheet M, the number of sheets M (number of copies) on which the image is to be formed, and a size S of the sheet M on which the image is to be formed (in other words, the size S of the sheet M stacked in the sheet feed tray10). The size S of the sheet M refers to a size (for example, A4 or B5) of a surface of the sheet M on which an image is recorded. The controller100may acquire an image forming instruction from a user via a control panel, or may acquire an image forming instruction from an external device via a communication interface.

First, the controller100compares the size S of the sheet M in the image forming instruction with predetermined first and second thresholds Th1and Th2(S701and S702). The second threshold Th2is larger than the first threshold Th1. The number of thresholds to be compared with the size S is not limited to two in the airflow determination process. The controller100increases the air volume of the airflow generated by the air exhaust60with increasing the size S of the sheet M (S703to S705). 5 Values illustrated in steps S703to S705indicate the percentage (%) of the air volume when the maximum air volume the fan62can generate is defined as 100%. The values in steps S703to S705are examples, and the embodiments of the present disclosure are not limited thereto.

More specifically, when the size S of the sheet M is less than the first threshold Th1(Yes in S701), the controller100sets the air volume of the air exhaust60to 20% (S703). When the size S of the sheet M is equal to or greater than the first threshold Th1and less than the second threshold Th2(No in S701and Yes in S702), the controller100sets the air volume of the air exhaust60to 50% (S704). When the size S of the sheet M is equal to or greater than the second threshold Th2(No in S701and No in S702), the controller100sets the air volume of the air exhaust60to 80% (S705).

Then, the controller100drives the air exhaust60(more specifically, the fan62) at the air volume determined in steps S703to S705(S706). After the driving of the fan62is stabilized, the controller100starts a process of forming an image on the sheet M in accordance with the image forming instruction (S707). More specifically, the controller100causes the conveyor20to sequentially convey multiple sheets M, causes the image forming unit30to form an image on the sheet M conveyed by the conveyor20, and operates the leading end guide40in synchronization with the arrival of the sheet M conveyed by the roller pair27.

FIG.8is a flowchart of a process of moving the sheet ejection tray50in the vertical direction (i.e., a tray vertical movement process). In the tray vertical movement process, the elevator51moves the sheet ejection tray50in the vertical direction so as to move the upper surface of the top sheet M stacked on the sheet ejection tray50close to the leading end of the duct61while the image forming apparatus1successively forms images on multiple sheets M. For example, while the image forming apparatus1successively forms images on multiple 5 sheets M, the controller100executes the tray vertical movement process each time a predetermined time elapses (or a predetermined number of sheets M are stacked on the sheet ejection tray50).

First, the controller100determines whether the upper surface sensor55detects the sheet M (in other words, whether the upper surface sensor55outputs a detection signal) (S801). When the controller100determines that the upper surface sensor55detects the sheet M (Yes in S801), the controller100drives the elevator51to lower the sheet ejection tray50by a predetermined distance (S802).

As a result, the upper surface of the top sheet M stacked on the sheet ejection tray50is moved close to the leading end of the duct61so that the duct61of the air exhaust60is directed against the upper surface of the top sheet M stacked on the sheet ejection tray50. For example, in step S802, the controller100may cause the elevator51to lower the sheet ejection tray50by a predetermined fixed value (e.g., 5 mm) or to lower the sheet ejection tray50until the upper surface sensor55stops outputting the detection signal.

Then, the controller100determines whether the full-state sensor56detects that the sheet ejection tray50is full (in other words, whether the full-state sensor56outputs a detection signal) (S803). When the controller100determines that the sheet ejection tray50is full (Yes in S803), the controller100suspends image formation by the image forming apparatus1(S804). That is, the controller100stops operations of the conveyor20, the image forming unit30, and the leading end guide40. Further, the controller100instructs a user to remove the stack of sheets M on the sheet ejection tray50via the control panel.

After the user removes the stack of sheet M from the sheet ejection tray50, the controller100causes the elevator51to raise the sheet ejection tray50to a start position when the sheet ejection tray50is empty and resumes the image formation by the image forming apparatus1.

On the other hand, when the upper surface sensor55does not detect the sheet M (No in S801), the controller100ends the tray vertical movement process without executing the processes in step S802and beyond. When the controller100determines that the sheet ejection tray50is not full (No in S803), the controller100ends the tray vertical movement process without executing the process in step S804. Since the controller100repeatedly executes the tray vertical movement process, images are successively formed on multiple sheets M while keeping the duct61of the air exhaust60being directed against the upper surface of the top sheet M stacked on the sheet ejection tray50.

According to the above-described embodiment, the following operational effects, for example, are achieved.

According to the above-described embodiment, the air exhaust60can remove the residual air70between the top sheet M stacked on the sheet ejection tray50and the sheet M freely falling toward the sheet ejection tray50to reduce an air resistance of the free fall of the sheet M. As a result, even if the conveyance speed of the sheet M by the roller pair27is increased (in other words, the interval between the sheets M passing through the roller pair27is shortened), the sheets M successively conveyed is prevented from colliding with each other. That is, a throughput of the image forming apparatus1is improved.

The leading end guide40according to the above-described embodiment does not nip the leading end of the sheet M. In the above-described embodiment, the leading end of the sheet M is released by the guides44and45before the trailing end of the sheet M passes through the roller pair27. As a result, as illustrated inFIG.2, when the sheet M freely falls, the trailing end of the sheet M is positioned higher than the leading end of the sheet M. Therefore, the air exhaust60according to the above-described embodiment exhausts the residual air70to the upstream from the sheet ejection tray50in the conveyance direction to increase a velocity of the trailing end of the sheet M freely falling.

According to the above-described embodiment, the controller100executes the tray vertical movement process to causes the sheet ejection tray50to move in the vertical direction so that the upper surface of the top sheet M stacked on the sheet ejection tray50is moved close to the leading end of the duct61. Accordingly, when images are successively formed on multiple sheets M, a relative position between the air exhaust60and the sheet ejection tray50can be appropriately adjusted to exhaust the residual air70at an appropriate position. In the above-described embodiment, the sheet ejection tray50is moved up and down, but the air exhaust60may be moved up and down in another embodiment. That is, the air exhaust60may be movable in the vertical direction so that the leading end of the duct61is moved close to the upper surface of the top sheet M stacked on the sheet ejection tray50.

Further, according to the above-described embodiment, since the air volume is adjusted in response to the size S of the sheet M, the velocity of the sheet M freely falling can be appropriately controlled. Note that the controller100may adjust the wind speed of the airflow instead of the air volume, or may adjust both the air volume and the wind speed (i.e., the flow rate of the airflow generated by the fan62). That is, the controller100increases the flow rate of the airflow generated by the fan62with increasing the size of the sheet M conveyed by the roller pair27. In the present disclosure, the term “flow rate” includes the velocity and the air volume of the airflow generated by the fan62

Note that the present disclosure is not limited to specific embodiments described above, and numerous additional modifications and variations are possible in light of the teachings within the technical scope of the appended claims. It is therefore to be understood that the disclosure of this patent specification may be practiced otherwise by those skilled in the art than as specifically described herein, and such, modifications, alternatives are within the technical scope of the appended claims. Such modifications are also included in the technical scope of the present disclosure.

Any one of the above-described operations may be performed in various other ways, for example, in an order different from the one described above.

The functionality of the elements disclosed herein may be implemented using circuitry or processing circuitry which includes general purpose processors, special purpose processors, integrated circuits, application specific integrated circuits (ASICs), digital signal processors (DSPs), field programmable gate arrays (FPGAs), conventional circuitry and/or combinations thereof which are configured or programmed to perform the disclosed functionality. Processors are considered processing circuitry or circuitry as they include transistors and other circuitry therein. In the disclosure, the circuitry, units, or means are hardware that carry out or are programmed to perform the recited functionality. The hardware may be any hardware disclosed herein or otherwise known which is programmed or configured to carry out the recited functionality. When the hardware is a processor which may be considered a type of circuitry, the circuitry, means, or units are a combination of hardware and software, the software being used to configure the hardware and/or processor.