Sheet discharging device and image forming apparatus incorporating same

A sheet discharging device, which is included in an image forming apparatus, includes a sheet discharging tray, a sheet discharging roller pair, a full state detection feeler pivotably supported and including a center feeler to measure a height of a center part of the recording medium and an edge feeler to measure a height of an edge part of the recording medium, and a full state detection sensor to detect a position of the full state detection feeler. A distance between a leading edge of the center feeler and an upper surface of the sheet discharging tray is smaller than a distance between a leading edge of the edge feeler and the upper surface thereof. The leading edge of the edge feeler is located closer to the upper surface of the sheet discharging tray than a common tangential line of the sheet discharging roller pair.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2013-038913, filed on Feb. 28, 2013 in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

1. Technical Field

Embodiments of the present invention relate to a sheet discharging device to discharge a sheet having an image thereon on a sheet discharging tray, and an image forming apparatus incorporating the sheet discharging device.

2. Related Art

Known image forming apparatus generally include a sheet discharging unit. In the sheet discharging unit, a pair of sheet discharging rollers conveys a recording medium such as a paper sheet to be discharged onto a sheet discharging tray. The sheet discharging unit has a full state detection feeler and a full state detection sensor disposed downstream from the pair of sheet discharging rollers in a sheet conveying direction to detect a vertical paper loadable position of recording media discharged on the sheet discharging tray. Some techniques have been disclosed to change the paper loadable height of recording media in the full state according to a state of paper curl of the recording medium or media on the sheet discharging tray, so as to prevent the recording media on the sheet discharging tray from falling off the sheet discharging tray and/or disarrangement of the discharging order of the recording media.

Japanese Patent Application Publication No. JP 2003-137479-A discloses a configuration of a paper delivery device of an image forming apparatus. The paper delivery device includes a full state detecting filler to detect a full state of a sheet discharging tray. By connecting an auxiliary filler to a filler main body and selectively changing a connecting position, the full state detecting filler determines the full state according to a paper condition. However, the center area of a recording medium in a lateral direction is the only detection target of the full state detecting filler, this technique is not effective to a paper curl at both side edges while being effective to a paper curl at the leading edge and/or the trailing edge. Moreover, it is not realistic the setting of the full state detecting filler is changeable according to type and size of various recording media.

Japanese Patent Application Publication No. JP 2003-128339-A discloses an image forming apparatus having a configuration in which a first contact member and a second contact member are attached at the top of an arm of an actuator included in a full state detection feeler. This configuration can cause respective contact surfaces in the paper sheet discharging direction to contact from mutually different directions with the top surface of the paper sheet on a discharging tray. This configuration is designed so that the contact surface of the first contact member or the contact surface of the second contact member contacts the top of the paper sheet reliably even when a curled paper sheet is discharged on the discharging tray. This configuration is expected to prevent misdetection in which a full state is detected due to curled paper sheet even if a relatively small amount of paper sheets is discharged on the discharging tray, thereby improving accuracy in the full state detection of paper sheets. However, because of the same reasons as JP 2003-137479-A, the technique disclosed in JP 2003-128339-A is not effective to a recessed paper curl at both side edges. Further, since the technique of JP 2003-128339-A is employed to a movable discharging tray, when a compact image forming apparatus in which the height of a discharging tray is fixed uses this technique, the full state of paper sheets is detected before the amount of paper sheets reaching a target number of paper sheets with respect to the paper sheets having a small amount of curl.

Japanese Patent Application Publication No. JP 2010-275056-A discloses a configuration that provides a technique to employ an actuator including a full state detecting section and a rear-end curling detecting section, so as to detect a sheet paper full state and a paper curl state with a simple configuration. However, this technique is literally targeted to detect the rear-end curls, and therefore is not effective to the recessed paper curl at both side edges. Rather than that, a paper regulating sheet is disposed to contact a paper sheet to be discharged to a discharging tray so as to correct the curves at both side edges in the lateral direction of the paper sheet. However, it is likely that friction generated due to the contact of the paper sheet with the paper regulating sheet causes friction can cause a paper discharging problem. Therefore, another countermeasure is required to this inconvenience.

Consequently, it is clear that the above-described techniques cannot prevent paper stacking failures when the stack of paper sheets discharged on a discharging tray includes has a paper curl at both side edges. In addition, it is difficult to secure the target number of paper sheets that can be discharged on the discharging tray. It has become general that a height from a discharging port to a discharging stack surface is set as small as possible to reduce a distance between the discharging port and the discharging stack surface. However, it is likely that this configuration causes paper stacking failures in discharged paper sheets notably.

It is strongly demanded in these days that image forming apparatuses have a characteristic to be used in various installation environments. When an image forming apparatus is installed under high humidity conditions, paper sheets containing moisture can increase an amount or degree of paper curl after passing through a fixing unit in which heat and pressure are applied to the paper sheets. If the paper sheets are curled, specifically on at least either side thereof, the leading edge of a subsequent paper sheet hits the trailing edge of a curled proceeding sheet on the discharging tray to push the discharged paper sheet, which can cause paper stacking failure. In the image forming apparatus having a full state detecting mechanism at a downstream side from a pair of conveying rollers in a sheet conveying direction to detect a paper loadable height on a discharging tray, a printing operation is stopped before such sheet force-out occurs to prevent occurrence of paper stacking failure. However, if the full state detection mechanism is set to operate when a paper curl is detected, the full state is detected before reaching the target number of paper sheets even when the small amount of curled papers is discharged. This problem can be solved by increasing the capacity (the depth) of the discharging tray. However, due to a strong demand from the market to reduce the size of an image forming apparatus, it is not easy to achieve a solution to sufficiently solve both problems.

SUMMARY

At least one embodiment of the present invention provides a sheet discharging device including a sheet discharging tray to which a recording medium having an image formed thereon is discharged, a sheet discharging roller pair to discharge the recording medium conveyed by a sheet conveying member disposed upstream from the sheet discharging roller pair to the sheet discharging tray, a full state detection feeler pivotably supported to measure a height of a stack of recording media including the recording medium on the sheet discharging tray and including a center feeler to measure a height of a center part of a flat surface of the recording medium in a direction perpendicular to a sheet conveying direction and an edge feeler to measure a height of an edge part of the flat surface of the recording medium in the direction perpendicular to the sheet conveying direction, and a full state detection sensor to detect a position of the full state detection feeler. A distance between a leading edge of the center feeler and an upper surface of the sheet discharging tray is smaller than a distance between a leading edge of the edge feeler and the upper surface of the sheet discharging tray. The leading edge of the edge feeler is located closer to the upper surface of the sheet discharging tray than a common tangential line of the sheet discharging roller pair.

Further, at least one embodiment of the present invention provides an image forming apparatus including an image forming unit to form an image on a surface of an image carrier, and the above-described sheet discharging device.

DETAILED DESCRIPTION

Descriptions are given, with reference to the accompanying drawings, of examples, exemplary embodiments, modification of exemplary embodiments, etc., of an image forming apparatus according to exemplary embodiments of the present invention. Elements having the same functions and shapes are denoted by the same reference numerals throughout the specification and redundant descriptions are omitted. Elements that do not demand descriptions may be omitted from the drawings as a matter of convenience. Reference numerals of elements extracted from the patent publications are in parentheses so as to be distinguished from those of exemplary embodiments of the present invention.

The present invention is applicable to any image forming apparatus, and is implemented in the most effective manner in an electrophotographic image forming apparatus.

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

A description is given of an entire configuration of an image forming apparatus100according to an embodiment with reference toFIG. 1.

The image forming apparatus100may be a copier, a facsimile machine, a printer, a multifunction peripheral or a multifunction printer (MFP) having at least one of copying, printing, scanning, facsimile, and plotter functions, or the like. According to the present embodiment, the image forming apparatus100is an electrophotographic color printer that forms color and monochrome toner images on recording media by electrophotography.

The image forming apparatus100includes a feed roller1, registration rollers2and3, transfer rollers4and5, photoconductors6,7,8, and9, a heat body10, a pressure body11, a sheet discharging driven roller12, a sheet discharging drive roller13, a separation claw15, a reverse driven roller16, a pair of duplex rollers17and18, a sheet discharging tray20, a full state detection feeler22, a full state detection sensor23, and a sheet discharging device24.

The feed roller1is disposed in a sheet feeding part located at a lower part of the image forming apparatus100. The feed roller1picks up and feeds a recording medium P from a stack of new recording media P1. After the recording medium P has reached the registration rollers2and3, the feed roller1continues the rotation to correct skew of the recording medium P at a nip area between the registration rollers2and3. Thereafter, the feed roller1stops the rotation temporarily. The registration rollers2and3starts the rotation again to synchronize with movement of a toner image to arrive the transfer rollers4and5.

Images formed based on image data in an image forming part are transmitted to the respective photoconductors6,7,8, and9via respective laser light beams. The images are transferred onto an intermediate transfer belt4a to form a composite toner image. By the time the composite toner image reaches the transfer rollers4and5, the recording medium P is conveyed by the registration rollers2and3so that the composite toner image is transferred onto the recording medium P.

After application of heat by the heat body10and pressure by the pressure body11, the recording medium P is conveyed to the sheet discharging driven roller12and the sheet discharging drive roller13to be discharged to the sheet discharging tray20. The sheet discharging driven roller12and the sheet discharging drive roller13form a sheet discharging roller pair.

When both sides of the recording medium P are to be printed by performing a duplex printing, the separation claw15powered up by a solenoid rotates clockwise to change a sheet conveying direction of the leading edge of the recording medium P conveyed from the heat body10and the pressure body11to the sheet discharging drive roller13and the reverse driven roller16. The sheet discharging drive roller13and the reverse driven roller16are a pair of rollers to reverse the recording medium before the recording medium P is discharged to the sheet discharging tray20. The rotation direction of the sheet discharging drive roller13changes and reverses its rotation direction at the timing the trailing edge of the recording medium P has not yet passed through the sheet discharging drive roller13and the reverse driven roller16. The reversed recording medium P is then conveyed to a duplex path where the pair of duplex rollers17and18are disposed. The recording medium P that has passed through a duplex path passes through the registration rollers2and3and a regular sheet conveying path to complete the duplex printing.

Here, a description is given of various examples of paper curl with reference toFIGS. 2A through 2H.

FIGS. 2A and 2Billustrate a state of a downward paper curl with both edges of a recording medium P in the sheet conveying direction lower than the center part of the recording medium P.FIGS. 2C and 2Dillustrate a state of an upward paper curl with both edges of the recording medium P in the sheet conveying direction higher than the center part of the recording medium P. A paper curl at the leading edge of the recording medium P in the sheet conveying direction as illustrated inFIGS. 2A and 2Cis referred to as a “face curl” and a paper curl at the trailing edge of the recording medium P in the sheet conveying direction as illustrated inFIGS. 2A and 2Cis referred to as a “back curl”.

FIGS. 2E and 2Fillustrate a state of a downward paper curl with both side edges of the recording medium P in a widthwise direction or a direction perpendicular to the sheet conveying direction lower than the center part of the recording medium P.FIGS. 2G and 2Hillustrate a state of an upward paper curl with both edges of the recording medium P in the direction perpendicular to the sheet conveying direction higher than the center part of the recording medium P. A paper curl at both edges of the recording medium P in the direction perpendicular to the sheet conveying direction as illustrated inFIGS. 2F and 2His referred to as a “side curl”. Further, a paper curl with both side edges curling downward as illustrated inFIGS. 2A and 2Fis occasionally referred to as a “projection curl” and a paper curl with both side edges curling upward as illustrated inFIGS. 2C and 2His occasionally referred to as a “recessed curl”.

There are various factors to cause paper curl. As described above with reference toFIGS. 2A through 2H, a side curl illustrated inFIG. 2Hhas a large amount of curl to which a measure to correct may need to be taken. Even though detailed mechanism of occurrence of paper curl is omitted here, the main factor is that an image on a printed side of the recording medium P contacts the heat body10and an image on a non-printed side of the recording medium P contacts the pressure body11.

Next, a description is given of the operation principles of a full state detection mechanism of the image forming apparatus100, with respect toFIGS. 3A through 3C.

The full state detection mechanism includes the full state detection feeler22and the full state detection sensor23. The full state detection feeler22extends vertically in a direction perpendicular to the sheet conveying direction, in other words, with respect to the sheet surface ofFIGS. 3A through 3C. Specifically, the full state detection feeler22is provided in the widthwise direction or the lateral direction over the recording medium P that is discharged by the sheet discharging driven roller12and the sheet discharging drive roller13. The full state detection feeler22is pivotably supported at both ends, as illustrated inFIG. 8. The full state detection feeler22moves in a direction as indicated by arrow inFIG. 1and pivots clockwise from a position illustrated inFIG. 3Ato a position illustrated inFIG. 3B.

The full state detection sensor23detects the position of the full state detection feeler22that is rotatable as described above.

It is to be noted that the position of the full state detection feeler22indicates an angular position of the full state detection feeler22, which is a posture in a plane perpendicular to a rotation axis of the full state detection feeler22. For example, the full state detection sensor23can be an optical sensor such as a photointerrupter. Together with a rotating disk disposed at a shaft end part of the full state detection feeler22, the optical sensor forms a rotary encoder that reads the position of a center feeler22aby detecting whether an optical path through which optical light travels from a light emitting element of the full state detection sensor23to a light receiving element thereof is blocked or not.

FIG. 3Aillustrates a state immediately before the leading edge of the recording medium P held between the sheet discharging driven roller12and the sheet discharging drive roller13hits the center feeler22aof the full state detection feeler22. Specifically,FIG. 3Ashows a state before the position of the center feeler22achanges, in other words, a state in which the full state detection sensor23is off or non-active.

FIG. 3Billustrates a state in which the recording medium P pushes up the center feeler22a. Therefore, the position of the center feeler22ais changed, that is, the full state detector sensor23is on or active.

The full state detection mechanism is designed such that an arithmetic logic unit (ALU determines, based on information from the active full state detection sensor23, whether or not the sheet discharging tray20is full. When the ALU determines that the sheet discharging tray20is full, a signal to stop the printing operation performed in the image forming apparatus100is issued. However, as illustrated inFIG. 3B, pushing up the full state detection feeler22is not regarded as the full state of the sheet discharging tray20. It is not until the active state of the full state detection sensor23continues more than a given time for at least one recording medium P to pass the full state detection feeler22that the sheet discharging tray20is detected as the full state and the signal to stop the printing operation is issued. At the same time, an alarm signal can also be issued. For example, a message to accelerate removal of the recording medium P on the sheet discharging tray20can be displayed on an operation panel of the image forming apparatus100. Instead of or in addition to this function, an audio message can be sent.

FIG. 3Cillustrates a state in which the sheet discharging tray20is full. A paper loadable height H of discharged recording media P2stacked on the sheet discharging tray20is indicated inFIG. 3C.

FIGS. 4A and 4Billustrate a comparative configuration of a sheet discharging device124that does not include the full state detection mechanism according to the present embodiment. InFIGS. 4A and 4B, a full state is detected when the recording medium P on the sheet discharging tray20has side curls (refer toFIG. 2H). Specifically,FIG. 4Aillustrates the comparative configuration of the sheet discharging device124. As illustrated inFIG. 4A, a center feeler122ameasures a paper loadable height H1′ at the center of the recording medium P on the sheet discharging tray20, so that the full state of the sheet discharging tray20is determined. InFIG. 4B, the center feeler122ais illustrated while the full state detection feeler22is omitted. The full state detection mechanism is set to turn on the full state detection sensor23when the center feeler122areaches the position corresponding to the paper loadable height H1′.

Due to incompletion of image forming, a subsequent recording medium P′ is further conveyed and discharged to the sheet discharging tray20even after the full state is detected. The subsequent recording medium P′ is to be discharged in a direction of a common tangential line T of the sheet discharging driven roller12and the sheet discharging drive roller13. Accordingly, the leading edge of the subsequent recording medium P′ hits edges Pa of the recording medium P with side curls onto the sheet discharging tray20to push the recording medium P stacked on the sheet discharging tray20. As a result, the paper stacking failure such as falling off and/or disarrangement of the discharging order of the discharged recording media P2can occur.

Now, a description is given of a sheet discharging device24according to the present embodiment with reference toFIGS. 5A through 5C.

FIGS. 5A and 5Billustrate a configuration of the sheet discharging device24with respect to the comparative configuration of the sheet discharging device124ofFIGS. 4A and 4B, and show the full state when the discharged recording media P2stacked on the sheet discharging tray20have side curls (refer toFIG. 2H).

FIG. 5Cis an enlarged view of the full state detection feeler22ofFIG. 5A. InFIG. 5B, the center feeler22aand edge feelers22bare illustrated while the full state detection feeler22is omitted. The center feeler22ais located at the center of the full state detection feeler22, which is also illustrated inFIG. 8A, and the edge feelers22bare disposed at both sides of the center feeler22a.

FIGS. 5A through 5Cshow that the full state of the sheet discharging tray20detected after the edge feelers22bhave measured one or both edges of the discharged recording media P2stacked on the sheet discharging tray20reaching the paper loadable height H2. The full state detection mechanism is previously set to turn on the full state detection sensor23when the edge feelers22breach a position corresponding to the paper loadable height H2. It is to be noted that the center feeler22aofFIG. 5Bhas the same structure and function as the center feeler122aofFIGS. 4A and 4B.

As illustrated inFIG. 5B, since the recording medium P has side curls (refer toFIG. 2H), the edges Pa of the recording medium P and the respective edge feelers22bcontact while the center feeler22adoes not contact the recording medium P. In this case, the full state is detected not based on the detection result obtained at the center of the recording medium P but based on the detection results obtained at the edges Pa of the recording medium P having the side curls.

Due to incompletion of image forming, the subsequent recording medium P′ is further conveyed and discharged to the sheet discharging tray20even after the full state is detected. The subsequent recording medium P′ is to be discharged in the direction of the common tangential line T of the sheet discharging driven roller12and the sheet discharging drive roller13.

As illustrated inFIGS. 5A and 5B, the paper loadable height H2of the edges Pa is located lower than the common tangential line T. In other words, respective lower edges or leading edges of the edge feelers22bare located closer to an upper surface of the sheet discharging tray20than the common tangential line T of the sheet discharging drive roller13and the sheet discharging driven roller12. This configuration can prevent the paper stocking failure caused by the subsequent recording medium P′ hitting the discharged recording media P2stacked on the sheet discharging tray20as illustrated inFIGS. 4A and 4B. By referring to the paper loadable heights in the full state illustrated inFIG. 5B, a paper loadable height H1at the center part of the recording medium P and the paper loadable height H2at the edges Pa have a relation of H1>H2. In other words, a distance between the leading edge of the center feeler22aand the upper surface of the sheet discharging tray20is shorter or smaller than a distance between each leading edge of the edge feelers22band the upper surface of the sheet discharging tray20. With this configuration, the paper stacking failure can be prevented in advance.

The paper loadable height H1′ at the center part of the recording medium P as illustrated inFIG. 4Band a paper loadable height H3as illustrated inFIGS. 5A and 5Bhave a relation of H1′>H3, which is likely that the number of stacked recording media decreases. However, in the present embodiment as illustrated inFIG. 5B, the edge feelers22bpress the curled edges Pa of the discharged recording media P2. Eventually, the number of stacked papers reduces by a smaller amount compared with the number of stacked recording media P2ofFIG. 4B. When the recording medium P has no curls, the center feeler22ameasures the height of the discharged recording media P2, and then the full state detection sensor23detects the full state of the sheet discharging tray20. Therefore, the paper loadable height in the full time corresponds to the paper loadable height Hi at the center part of the recording medium P. Further, a range of the edge feelers22bin an axial direction of the sheet discharging drive roller13extends the maximum printable paper width L of the recording medium P in the image forming apparatus100. With this configuration, any recording medium having side curl(s) can be detected.

Now, a description is given of operations of the full state detection feeler22while the recording medium P is passing thereby, with reference toFIGS. 6A and 6B.

As illustrated inFIG. 6A, the leading edge of the recording medium P conveyed by the sheet discharging drive roller13and the sheet discharging driven roller12hits the center feeler22a. Consequently, as illustrated inFIG. 6B, as the discharged recording media P2accumulates on the sheet discharging tray20, the discharged recording media P2push up the full state detection feeler22. During this movement, the position of the recording medium P and the position of the edge feelers22bare arranged so as to be separated away from each other without contacting. This positional arrangement of the recording medium P and the edge feelers22bis made because the contact of the recording medium P with the edge feelers22bcan increase risk to cause damage to the leading edge of the recording medium P and/or noise generated by the recording medium P and the edge feelers22brubbing against each other.

FIG. 7illustrates the state of the full state detection feeler22when the edge feelers22bmeasures the height of the recording media P2on the sheet discharging tray20, and the full state detection sensor23detects the full state of the sheet discharging tray20.

At the contact portion of the edge feelers22bwith the recording medium P as illustrated inFIG. 7, when the respective leading edges of the edge feelers22bare located within a range of ±θ based on the common tangent T, the full state detection sensor23is set to turn on according to the movement of the edge feelers22b. The reason why the range is based on the common tangent T of the sheet discharging driven rollers12and the sheet discharging drive roller13is that the recording medium P is discharged in the same direction as the common tangent T.

As an example, an angle θ can be approximately 5 degrees. The action that the full state detection feeler22presses the discharged recording media P2as described above with reference toFIGS. 5A and 5Bhas been taken into consideration to obtain the value of 5 degrees based on experimental evaluation of a range in which no paper stacking failures occur even when the subsequent recording medium P′ pushes the trailing edge of the discharged recording media P2stacked on the sheet discharging tray20. Alternatively, a distance from the sheet discharging driven roller12and the sheet discharging drive roller13to the edge feelers22b, a speed of discharging the recording medium P, rigidity of the recording medium P, and so forth can be considered to obtain an optimal angle θ of the sheet discharging device24.

FIG. 8Ais a diagram illustrating the full state detection mechanism, viewed from the discharging tray20to an upstream side in the sheet conveying direction. As illustrated inFIG. 8A, the center feeler22aand the edge feelers22bof the full state detection feeler22are connected serially, in other words, continuously without any slits in an axial direction of the sheet discharging driven rollers12and the sheet discharging drive roller13.

By contrast,FIG. 8Billustrates a comparative configuration in which the center feeler22aand the edge feelers22bare not connected serially and continuously. In this case, there seems to be cutouts or slits between the edge feelers22b, and therefore it is likely that the edges Pa of the side-curled recording medium P having a narrow width are caught by the slits, resulting in an operation failure of the full state detection feeler22and/or paper jam.

The full state detection feeler22can be integrally provided by the center feeler22aand the edge feelers22busing the same material, which can contribute to a reduction in cost. For example, an integrated plastic unit can be applied to the full state detection feeler22.

FIG. 8Cillustrates the full state detection feeler22integrally including the edge feelers22b.

FIG. 8Dillustrates the full state detection feeler22further including a weight container22con a lower surface of the center feeler22a. For example, when the edge feelers22bas illustrated inFIGS. 5A through 5Cmay need to further press recording medium P having side curls, one or more weights can be stored in the weight container22c. In this case, the optional number and type of weight may be selected.

FIGS. 9A and 9Billustrate a rotational locus of the sheet discharging tray20. As illustrated inFIGS. 9A and 9B, the sheet discharging tray20also functions as an openable exterior of the image forming apparatus100. For example, when a toner cartridge is replaced, the sheet discharging tray20can be opened. A rotational center of the sheet discharging tray20is illustrated inFIG. 1with reference numeral “19”. A large arc inFIGS. 9A and 9Brepresents the maximum rotational locus21of the sheet discharging tray20. A small arc inFIGS. 9A and 9Brepresents the maximum rotational locus of the full state detection feeler22. The large arc, which is the maximum rotational locus21of the sheet discharging tray20, and the small arc, which is the maximum rotation locus of the full state detection feeler22, share an intersection that is an area where the large arc and the small arc overlap as illustrated inFIG. 9A.

For example, when an operator opens the sheet discharging tray20while holding up the center feeler22aof the full state detection feeler22manually, the center feeler22aenters inside the maximum rotational locus21to interfere movement of the sheet discharging tray20as illustrated inFIG. 9A. When the rotation center19of the sheet discharging tray20is shifted to a further left side inFIG. 1, the full state detection feeler22can be retreated outside the maximum rotational locus21. However, shifting the rotation center19of the sheet discharging tray20increases the size of a housing of the image forming apparatus100.

To address this inconvenience, the full state detection feeler22according to the present embodiment is set movable without moving the rotation center19of the sheet discharging tray20. As described above, the full state detection feeler22is pivotably supported and is pushed up by the leading edge of the recording medium P to be conveyed to the sheet discharging tray20, as illustrated inFIG. 9A. Further, when the full state detection feeler22is in its natural state without application of any external force and with no recording medium P stacked on the sheet discharging tray20, the full state detection feeler22retreats to the outside of the maximum rotational locus21of the sheet discharging tray20by rotating counterclockwise along with the aid of gravity as illustrated inFIG. 9B.

As described above, the present embodiment(s) can achieve the following effects.

As shown in the above-described embodiment(s), even when the recording medium P has side curls, the sheet discharging device24can precisely detect the full state of the sheet discharging tray20before paper stacking failure occurs and, at the same time, can secure a sufficient paper loadable number when the recording medium P has a small degree of curl. Accordingly, by including the above-described sheet discharging device24, the image forming apparatus100that can prevent the paper stacking failure can be provided without adversely affecting a compact and low-cost configuration.

According to the action that the leading edge of the recording medium P conveyed by the sheet discharging drive roller13and the sheet discharging driven roller12contacts the center feeler22a, the full state detection feeler22remains pushed up until the trailing edge of the recording medium P passes the full state detection feeler22. While being contacting the center feeler22a, the recording medium P is set not to contact the edge feelers22b. This configuration can increase a risk to damage the leading edge of the recording medium P and/or to cause noise generated by the recording medium P and the edge feelers22brubbing against each other when the recording medium P and the edge feelers22bcontact.

The full state detection feeler22extends in an axial direction of the sheet discharging driven roller12and the sheet discharging drive roller13. The center feeler22ais located at the center in the axial direction of the full state detection feeler22and has the leading end to contact the discharged recording medium P or the discharged recording media P2stacked on the sheet discharging tray20. The edge feelers22bare located at both sides in the axial direction of the full state detection feeler22, interposing the center feeler22atherebetween. Since the respective edges of the edge feelers22bare continuously aligned in the axial direction of the full state detection feeler22, the edge feelers22bcan measure the paper loadable height of the discharged recording media P2on the sheet discharging tray20and the full state detection sensor23detects the full state of the sheet discharging tray20reliably regardless of the size of the recording medium P and the degree of side curls.

The respective edges of the edge feelers22bcontact the discharged recording media P2stacked on the sheet discharging tray20. According to the contact of the respective edges of the edge feelers22bto the recording medium P on the sheet discharging tray20, the position of the edges of the edge feelers22bat the full state detection of the sheet discharging tray20is within a range of ±5 degrees with respect to the common tangent T of the sheet discharging driven roller12and the sheet discharging drive roller13in a cross-sectional view vertical along the axial direction of the sheet discharging driven roller12and the sheet discharging drive roller13. By employing the configuration, even when the recording medium P has side curls, the full state of the sheet discharging tray20can be detected reliably. As a result, this configuration can prevent the paper stacking failure caused by the trailing edge of the recording medium P on the sheet discharging tray20pushing the subsequent recording medium P′.

The range of the edge feelers22bin the axial direction of the sheet discharging driven roller12and the sheet discharging drive roller13is set greater than the maximum width L of the printable paper width L used in the image forming apparatus100. By employing this configuration, any recording medium having side curls can be detected.

The center feeler22aand the edge feelers22bof the full state detection feeler22are connected continuously without any slits. With this configuration, together with the edges of the edge feelers22bserially connected in the axial direction of the sheet discharging driven rollers12and the sheet discharging drive roller13, any concern that the edges of the recording medium P having narrow side curls are caught in the slit to cause failure such as operational functions of the full state detection feeler22or paper jams can be prevented.

The full state detection feeler22includes the weight container22c. By storing an appropriate weight(s) in the weight container22cor changing the number of weights, the pressing force exerted by the full state detection feeler22to press the recording medium P can be adjusted.

The sheet discharging tray20is rotatable about its axial center. The maximum rotational locus21of the sheet discharging tray20and the maximum rotational locus of the full state detection feeler22share an intersection that is an area where the maximum rotational locus21and the maximum rotational locus overlap. With this configuration, the rotation center of the sheet discharging tray20is not shifted, which can contribute to a more compact image forming apparatus.

Further, when the external force is not applied, the full state detection feeler22pivots along with the aid of gravity and retreats to the outside of the maximum rotational locus21of the sheet discharging tray20. By so doing, an interference of the sheet discharging tray20and the full state detection feeler22can be prevented.