Image forming apparatus

An image forming apparatus includes a paper discharging tray and a paper detection part disposed at an upstream end of the paper discharging tray in a paper discharge direction. The paper detection part includes a base end member provided rotatably around a first axis extending in a direction perpendicular to a paper discharge direction and a tip member pivoted to the base end member to rotate around a second axis parallel to the first axis, and extending downwardly to incline toward an upstream side of the paper discharge direction in a state where the base end member is not subjected to pressure from the paper being discharged. The base end member is disposed to face a discharge opening when being at the reference position, and the image forming apparatus stops discharging paper from the discharge opening when the base end member rotates by a predetermined threshold or more with respect to the reference position.

BACKGROUND OF THE INVENTION

Field of the Invention

This invention relates to an image forming apparatus, in particular, for example, to an image forming apparatus including a paper discharging tray for stacking sheets on which an image is formed.

Description of the Background Art

Japanese Patent Laid Open Publication No. 2007-062928 discloses an image forming apparatus as an example of a background art. The image forming apparatus of the background art is provided with a paper discharging tray for stacking papers thereon, and the paper discharging tray is provided with a detection means including a detection lever positioned near a center of a discharging tray in a direction perpendicular to a paper discharge direction, an interlocking arm interlocking with the detection lever, and an auxiliary lever interlocking with the interlocking arm for detecting edges of papers with fully stacked.

However, the image forming apparatus of the background art has a problem that when a curl is generated, that is, in a case where a trailing edge of a paper discharged into the paper discharging tray is curved in the paper discharge direction, it is impossible to detect the curl. As a result, there is a problem that a paper stacking characteristics is deteriorated.

Therefore, a main object of the present invention is to provide a novel image forming apparatus.

Another object of the present invention is to provide an image forming apparatus capable of properly detecting a fully stacked condition of sheets discharged into a paper discharging tray or a curl generated on the sheet in the paper discharge direction, and preventing sheet stacking characteristics from being deteriorated.

SUMMARY OF THE INVENTION

In a first aspect of the invention, there is provided an image forming apparatus including: an image forming device to form an image on a sheet; a discharge opening for discharging the sheet on which the image is printed by the image forming device; a paper discharging tray on which the sheet discharged from the discharge opening is placed; a base end member provided at the discharge opening, and the base end member being rotatable around a first axis extending in a direction perpendicular to a sheet discharge direction; a tip member pivoted to the base end member to rotate around a second axis parallel to the first axis, the tip member extending downwardly to incline toward an upstream side of the sheet discharge direction in a state where the base end member is not subjected to pressure from the sheet being discharged, and the tip member coming into contact with the sheet when a height of a top surface of the sheet stacked on the paper discharging tray exceeds a predetermined height; a determiner to determine whether the base end member rotates by a predetermined threshold or more with respect to a reference position when no sheet is discharged; and a stopper to stop discharging the paper from the discharge opening in response that the determiner determines that the base end member rotates by the predetermined threshold or more with respect to the reference position. Furthermore, the base end member is disposed to face the discharge opening when being at the reference position, and the base end member and the tip member respectively rotate in response to the pressure from the sheet being discharged from the discharge opening.

In a second aspect according to the first aspect of the invention, the image forming apparatus further includes a first forcing member to force the tip member around the second axis and toward the upstream side of the sheet discharge direction.

In a third aspect according to the second aspect of the invention, when the tip member is at the reference position, a tip of the tip member is positioned at an upstream side with respect to the discharge opening in the sheet discharge direction.

In a fourth aspect according to the third aspect of the invention, the paper discharging tray includes a vertical wall surface that is formed at the upstream side with respect to the discharge opening in the sheet discharge direction, when the tip member is at the reference position, the tip of the tip member abuts on the vertical wall surface.

In a fifth aspect according to any one of the first to fourth aspects of the invention, the image forming apparatus further includes a second forcing member to force the base end member around the first axis and toward the upstream side of the sheet discharge direction.

In a sixth aspect according to any one of the first to fifth aspects of the invention, the image forming apparatus further includes a lock device that locks a posture of the tip member when the tip member is rotated by the pressure from the sheet being discharged from the discharge opening by an angle of a predetermined degrees or more.

In a seventh aspect according to the sixth aspect of the invention, the lock device releases the lock of the posture of the tip member when the base end member returns to the reference position.

In a eighth aspect according to any one of the first to seventh aspects of the invention, the image forming apparatus further includes an auxiliary member provided at an end of the discharge opening in a sheet width direction, the auxiliary member being rotatable around the first axis working with the base end member, and the auxiliary member coming into contact with the sheet when the height of the top surface of the sheet stacked on the paper discharging tray exceeds a predetermined height.

According to the present invention, it is possible to properly detect a fully stacked condition of sheets discharged into the paper discharging tray or a curl generated on the sheet in the paper discharge direction, and prevent sheet stacking characteristics from being deteriorated.

The above or other objects, features, and advantages of the present invention will be better understood by reading the following detailed description of embodiments with reference to the drawings.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

First Embodiment

FIG.1is a schematically cross-sectional view illustrating an internal structure of an image forming apparatus10according to a first embodiment of the present invention. Referring toFIG.1, the image forming apparatus10is a multifunction peripheral (MFP) having a photocopying function, a printer function, a scanner function, a facsimile function, etc., and forms a multi-color image or a monochromatic image on a recording medium (for example, a paper) by means of electrophotographic manner. However, the recording media is not limited to the paper sheets, overhead projector (OHP) films other than the paper sheets are available as the recording media, for example.

Hereinafter, throughout the specification, a left side and a right side in a horizontal direction as seen from a front side of the image forming apparatus10are defined as a left direction and a right direction, respectively. Furthermore, a front side (i.e., a near side) and a rear side (i.e., a depth side) of the image forming apparatus10in a depth direction of the image forming apparatus10as seen from above (or down) the image forming apparatus10are defined as a forward direction (also referred to as a front direction) and a backward direction (also referred to as a rear direction), respectively.

First, an outlined configuration of the image forming apparatus10will be described. As shown inFIG.1, the image forming apparatus10includes an apparatus body12and an image reader14disposed above the apparatus body12.

The image reader14includes a document laying table16made of a transparent material. A document pressing cover18is attached on the document laying table16with a hinge or the like in a freely open-and-close manner. The document laying cover18is provided with an auto document feeder (ADF)24which automatically feeds documents laid on a document laying tray20one by one to an image reading position22. Not shown in the drawings, an operation part (such as a touch panel or operation buttons) to receive operational inputs from a user is provided on a front side of the image reader14.

Furthermore, the image reader14accommodates an image reading part26which includes a light source, a plurality of mirrors, an imaging lens, a line sensor, etc. The image reading part26exposes a surface of a document to the light source, and leads a reflected light reflected from the surface of the document to the imaging lens with the plurality of mirrors. Then, the reflected light is imaged on the light receiving element of the line sensor by the imaging lens. The line sensor detects luminance or chromaticity of the reflected light imaged on the light receiving element, and generates image data based on an image depicted on the surface of the document. A CCD (Charge Coupled Device), a CIS (Contact Image Sensor) or the like is available as the line sensor.

The apparatus body12accommodates a control unit (not shown) which includes a CPU, a memory, an auxiliary memory unit and the like, and an image forming device30, etc. The control unit transmits control signals to each part of the image forming apparatus10in response to operation instructions input from the operation part such as the touch panel, and causes the image forming apparatus10to perform various operations.

The image forming device30is provided with an exposure unit32, a developing unit34, a photoreceptor drum36, a cleaner unit38, a charging unit40, a transfer unit42, and a fixing unit46, etc. The image forming device30forms an image on a paper transported from a paper feeding tray48or a manually feeding tray50and discharges an image-formed paper into a paper discharging tray52. The image data, which are read by the image reading part26or transmitted from an external computer or the like, are used as the image data for forming the image on the paper.

The image data handled by the image forming apparatus10correspond to a multi-color image using four colors consisting of black (K), cyan (C), magenta (M), and yellow (Y). Therefore, the developing unit34, the photoreceptor drum36, the cleaner unit38and the charging unit40are provided four each so that four types of latent images corresponding to four colors are formed, and thus constitute four image stations. The four image stations are arranged in a horizontal line along a traveling direction (i.e., a left-right direction) of a surface of an intermediate transfer belt54.

The photoreceptor drum36is an image carrier in which a photosensitive layer is formed on a surface of a cylindrical base body having conductivity, and the charging unit40is a member to charge the surface of the photoreceptor drum36to a predetermined potential. Furthermore, the exposure unit32is configured as a laser scanning unit including a laser diode (LD) and a polygon mirror, etc., and located below the photoreceptor drum36. The exposure unit32exposes the surface of the charged photoreceptor drum36to form on the surface of the photoreceptor drum36an electrostatic latent image in accordance with the image data. The developing unit34visualizes the electrostatic latent image formed on the photoreceptor drum36with toners of four colors (i.e., Y, M, C, and K). Furthermore, the cleaner unit38removes a residual toner remaining on the surface of the photoreceptor drum36after performing the development and image transfer.

The transfer unit42is provided with the intermediate transfer belt54, a driving roller56, a driven roller58, four intermediate transfer rollers60and a transfer roller (also referred to as a secondary transfer roller)44, and disposed above the photoreceptor drums36in the image stations.

The intermediate transfer belt54is an endless belt having flexibility and is made of a synthetic resin or rubber, etc. in which conductive materials such as a carbon black are blended as appropriate. The intermediate transfer belt54is suspended by the driving roller56and the driven roller58, and is located so that an outer peripheral surface of the intermediate transfer belt54comes into contact with an outer peripheral surface of the photoreceptor drum36. The intermediate transfer belt54circulates in a predetermined direction with a rotary drive of the driving roller56.

The driving roller56is provided rotatably around an axis of the driving roller56with a drive unit (not shown). The driven roller58rotates with a circulation of the intermediate transfer belt54as well as applies a certain tension to the intermediate transfer belt54to prevent the intermediate transfer belt54from loosening.

The intermediate transfer rollers60are arranged at positions in which the intermediate transfer rollers60face the photoreceptor drums36across the intermediate transfer belt54, respectively. During image forming process, a transfer electric field is formed between the photoreceptor drum36and the intermediate transfer belt54by applying a predetermined voltage (i.e., a primary transfer voltage) to the intermediate transfer roller60. By the action of the transfer electric field, a toner image formed on the outer peripheral surface of the photoreceptor drum36in each of the image stations is transferred to the outer peripheral surface of the intermediate transfer belt54.

A secondary transfer roller44is provided to press the intermediate transfer belt54between the secondary transfer roller44and the driving roller56. During image forming process, the transfer electric field is formed between the intermediate transfer belt54and the secondary transfer roller44by applying a predetermined voltage (i.e., a secondary transfer voltage) to the secondary transfer roller44. By the action of the transfer electric field, the toner image formed on the outer peripheral surface of the intermediate transfer belt54is transferred (i.e., secondarily transferred) to a paper while the paper passes through a transfer nip area between the intermediate transfer belt54and the secondary transfer roller44.

Returning toFIG.1, the fixing unit46is provided with a heating roller62and a pressure roller64. The fixing unit46is disposed above the secondary transfer roller44. The heating roller62is set to be a predetermined fixing temperature, and as the paper passes through the nip area between the heating roller62and the pressure roller64, the toner image transferred to the paper is heated and pressed, so that the toner image is thermally fixed to the paper.

Inside the apparatus body12, there is formed a first paper transport path L1for transporting the paper from the paper feeding tray48or the manually feeding tray50to the paper discharging tray52via a resist roller68, the secondary transfer roller44, and the fixing unit46. Furthermore, there is also formed a second paper transport path L2for returning the paper passing through the fixing unit46after a front side of the pater is printed to the first paper transport path L1at the upstream side of the secondary transfer roller44in a paper transport direction in order to perform a duplex printing on the paper. In the first paper transport path L1and the second paper transport path L2, there are provided a plurality of transport rollers66to provide an auxiliary propulsion to the paper as appropriate.

The resist roller68, which is also referred to as a paper stop roller (i.e., PS roller), transports the paper at the same speed as a process speed at which the image forming device30performs the image formation process on the paper. For example, the resist roller68stands by (or pauses) while nipping the transported paper with the transport rollers66, and then starts transporting the paper in synchronization with the transfer unit42.

In case of performing a simplex printing in the image forming apparatus10, the paper is led one by one from the paper feeding tray48or the manually feeding tray50into the first paper transport path L1, and then transported to the resist roller68with the transport rollers66. The resist roller68transports the paper to the secondary transfer roller44(i.e., a secondary transfer nip part) at a timing when a tip of the paper and a tip of the image information on the intermediate transfer belt54are aligned each other, and the toner image is transferred on the paper. Then, an unfixed toner on the paper is thermally fixed by passing through the fixing unit46(i.e., a fixing nip part), and the paper is discharged onto the paper discharging tray52via the paper discharging roller70in the vicinity of the paper discharging tray52.

On the other hand, in case of performing a duplex printing, when a trailing edge of the paper passing through the fixing unit46after the front side of the pater is printed reaches the paper discharging roller70, the paper reversely travels and is led to the second paper transport path L2by reversely rotating the transport rollers66. The paper led to the second paper transport path L2is transported through the second paper transport path L2with the transport rollers66, and then led to the first paper transport path L1at the upstream side of the resist roller68in a paper transporting direction. At this time, as the front and back surfaces of the paper are inverted, a printing process is performed on the back side of the paper by passing through the resist roller68, the secondary transfer roller44, and the fixing unit46in order.

Now, the specific configuration of the paper discharging tray52according to the present embodiment and a peripheral thereof will be described below with reference to the drawings. As shown inFIGS.2to4, the paper discharging tray52includes a horizontal surface52a,an inclined surface52bleading to the horizontal surface52a,and a vertical wall surface52c.The horizontal surface52ais located at a downstream side of the paper discharging tray52in the paper discharge direction (or a sheet discharge direction), and the inclined surface52bis located at an upstream side of the paper discharging tray52in the paper discharge direction. In addition, the inclined surface52bhas a downward slope toward the upstream side in the paper discharge direction. The vertical wall surface52cextends upwardly from an end of the upstream side of the inclined surface52bin the paper discharge direction, and is located at an upstream side with respect to a discharge opening70ain the paper discharge direction.

the paper discharging tray52slides down by its own weight the inclined surface52btoward an upstream side (i.e., a discharge opening70aside) in the paper discharge direction, and is brought into contact with the upstream end (i.e., the vertical wall surface52c) of the paper discharging tray52in the paper discharge direction. In other words, the trailing edge (i.e., an end of the upstream side in the paper discharge direction) of the paper placed on the paper discharging tray52is positioned at the end of the upstream side of the paper discharging tray52in the paper discharge direction. Meanwhile, there is provided a plurality of ribs leading in the paper discharge direction on an upper surface of the paper discharging tray52(i.e., an upper surface of the horizontal surface52aand an upper surface of the inclined surface52b), and upper surfaces of these ribs may function as a paper laying surface.

The image forming apparatus10is provided with a paper detection part80for detecting a condition of the paper on the paper discharging tray52. As shown inFIGS.2to4, the paper detection part80is provided in the vicinity of the discharge opening70a(i.e., at the end of the upstream side of the paper discharging tray52in the paper discharge direction), and includes a shaft member80a,a first detection part82, a second detection part (as an auxiliary member)84, and a shielding section86.

The shaft member80ais a columnar or cylindrical member, and is rotatably pivoted to the apparatus body12. Furthermore, an axis of the shaft member80a(also referred to as a first axis) extends in a direction, which is perpendicular to the paper discharge direction and along a discharge opening70a.Furthermore, the first axis is substantially parallel to a surface of the paper discharged from the discharge opening70a.Moreover, each of the first detection part82, the second detection part84, and the shielding section86is attached (e.g., fixed) to the shaft member80a.Therefore, each of the first detection part82, the second detection part84, and the shielding section86integrally rotates around the first axis working with the shaft member80awhen the shaft member80arotates.

In addition, the first detection part82, the second detection part84, and the shielding section86are located at a downstream side with respect to the discharge opening70ain the paper discharge direction. Furthermore, not shown in the drawings, between the apparatus body12and the shaft member80a,there is provided a second forcing member (e.g., a torsion spring) to force the shaft member80atoward an upstream side in the paper discharge direction (i.e., toward a direction closer to the discharge opening70a) so that the first detection part82, the second detection part84, and the shielding section86rotate around the first axis. However, the force of the second forcing member is set to the extent that it does not prevent the paper from being discharged from the discharge opening70a.

Hereinafter, in a state where the first detection section82, the second detection section84, and the shielding section86receive no pressure from the paper being discharged from the discharge opening70aas well as do not abut on (or come into contact with) the upper surface of the paper placed on the paper discharging tray52, it is referred that the first detection section82, the second detection section84, and the shielding section86is respectively arranged in a predetermined aspect (i.e., at a reference position).

The first detection part82includes a base end member82a,a tip member82b,a shaft member82c,and a first forcing member82d,and is disposed at a substantial center of the paper discharging tray52in the front-back direction (i.e., a paper width direction).

The base end member82ais a rod-like member whose one end is attached to the shaft member80a.When being at the reference position, the base end member82atakes a posture that gradually heads down as it goes toward a downstream side in the paper discharge direction (i.e., gradually heads up as it goes toward an upstream side in the paper discharge direction).

Furthermore, as shown inFIG.3, when being at the reference position, the base end member82ais disposed to face the discharge opening70a.Accordingly, when the paper is discharged from the discharge opening70a,the leading edge of the paper (an end of a downstream side of the paper in the paper discharge direction) comes into contact with the base end member82a.

As shown inFIGS.2to4, the tip member82bis a rod-like member whose one end is rotatably pivoted to the base end member82a.Specifically, one end of the tip member82bis pivoted to a shaft member82cprovided at the other end portion of the base end member82a.An axis of the shaft member82c(referred to as a second axis) extends in a direction, which is perpendicular to the paper discharge direction and along a discharge opening70a.In other words, the second axis is substantially parallel to the first axis. Namely, the tip member82bis provided to be rotatable around the second axis which is substantially parallel to the first axis.

Furthermore, when being at the reference position, the tip member82btakes a posture that gradually heads down as it goes toward a downstream side in the paper discharge direction (i.e., gradually heads up as it goes toward an upstream side in the paper discharge direction). Moreover, when being at the reference position, the other end (i.e., a tip potion) of the tip member82bis located at an upstream side with respect to the discharge opening70ain the paper discharge direction.

As described above, the base end member82aand the tip member82bare bent at a predetermined angle around the shaft member82c(second axis) as seen from the front (or back) side.

The first forcing member82dis a torsion spring (e.g., a twist spring, a torsion coil spring, etc.) which is wound around the shaft member82c,and forces the tip member82bto rotate around the second axis toward the upstream side in the paper discharge direction (i.e., in a direction approaching the discharge opening70a). However, the force of the first forcing member82dis set to the extent that it does not prevent the paper from being discharged from the discharge opening70a.

As shown inFIGS.2and4, the second detection section84is a plate-like member and is disposed at one end of the paper discharging tray52in the front-back direction (i.e., the paper width direction). When being at the reference position, the second detection section84is located so as to gradually heads down as it goes toward the downstream side in the paper discharge direction, that is, located diagonally in the same direction as the base end member82a.Furthermore, the second detection section84is provided to correspond to each of end positions in the width direction of various sizes of papers used in the image forming apparatus10. Specifically, in the front-to-back direction (i.e., in a paper width direction) of the second detection section84, there is provided the second detection section84so as to cover a range from a position of the width direction end of the smallest-sized paper used in the image forming apparatus10to a position of the width direction end of the largest-sized paper used in the image forming apparatus10.

Furthermore, the image forming apparatus10is provided with a detection sensor72that detects position information (e.g., a rotation angle) of the base end member82a(or the shaft member80a). The detection sensor72is, for example, a photo sensor having a light emitting element and a light receiving element, and is connected to the control unit (CPU). In one case where the rotation angle of the base end member82aexceeds a predetermined threshold relative to the reference position, a shielding wall86aof the shielding section86is positioned between the light emitting element and the light receiving element, so that light from the light emitting element is blocked by the shielding wall86aand thus not received by the light receiving element. On the other hand, in another case where the base end member82ais positioned at the reference position or the rotation angle of the base end member82adoes not exceed the predetermined threshold relative to the reference position, the light from the light emitting element is not blocked and thus received by the light receiving element. The detection sensor72outputs to the CPU a signal indicating whether the light from the light-emitting element is received by the light-receiving element, and the CPU detects a full stack (or full) of papers or a curl generated on the paper in the paper discharge direction in response to the output signal of the detection sensor72. Furthermore, when the CPU detects the full stack of papers or the curl generated on the paper in the paper discharge direction, it determines that a condition to stop transporting the paper is met and then stops discharging the paper (i.e., transporting the paper through the paper transport paths L1and L2).

Next, in an event that the paper is discharged from the discharge opening70ain the image forming apparatus10according to the present embodiment, an operation of the paper detection part80will be described below.

First, when the paper is discharged from the discharge opening70a, the leading edge of the paper abuts on the base end member82a.At this time, as the force of the second forcing member is set to the extend that it does not prevent the paper from being discharged from the discharge opening70a, when the leading edge of the paper abuts on the base end member82a,the base end member82arotates toward the downstream side in the paper discharge direction (i.e., a direction away from the discharge opening70a) against the force from the second forcing member. When the base end member82arotates by a predetermined angle toward the downstream side in the paper discharge direction, the leading edge of the paper abuts on the tip member82b.At this time, as the force of the first forcing member82dis also set to the extend that it does not prevent the paper from being discharged from the discharge opening70a,the tip member82brotates toward the downstream side in the paper discharge direction (i.e., a direction away from the discharge opening70a) against the force from the first forcing member82d.

As shown inFIG.5, the entire the base end member82aand the tip member82bis located at a position above the surface of the paper being discharged from the discharge opening70a(hereinafter, referred to as a paper through position). When being at the paper through position, a longitudinal direction (i.e., an extension direction) of the base end member82aand a longitudinal direction (i.e., an extension direction) of the tip member82bare identical. Namely, the base end member82aand the tip member82bare aligned on a substantial straight line.

Here, since the force from the second forcing member is acting on the base end member82a,the base end member82anever rotates excessively in a direction opposite to a direction of the force from the second forcing member. Similarly, since the force from the first forcing member82dis acting on the tip member82b,the tip member82bnever rotates excessively in a direction opposite to a direction of the force from the first forcing member82d. Optionally, there may be provided a limiting part (also referred to as a base end member limiting part) that physically limits the base end member82ato rotate in excess of a predetermined angle in the direction opposite to the direction of the force from the second forcing member, and a limiting part (also referred to as a tip member limiting part) that physically limits the tip member82bto rotate in excess of a predetermined angle in the direction opposite to the direction of the force from the first forcing member82d, respectively.

When the trailing edge of the paper passes through the paper detection part80(specifically, a tip of the tip member82b), the base end member82aand the tip member82bare forced to return from the paper-through position to the reference position by the force from the first forcing member82dand the force from the second forcing member. In the case where the base end member82aand the tip member82breturn from the paper through position to the reference position, if the tip of the tip member82bdoes not abut on (or come into contact with) the paper stacked on the paper discharging tray52, the base end member82aand the tip member82breturn to the reference position (seeFIG.3).

On the other hand, as shown inFIG.6, in a state (fully stacked state) where higher number of papers than a predetermined number of papers (e.g., the maximum number of papers that can be stacked) are stacked on the paper discharging tray52, when the base end member82aand the tip member82breturn from the paper through position to the reference position, the tip of the tip member82bcomes into contact with the paper, so that the base end member82aand the tip member82bare suspended at a predetermined position between the paper through position and the reference position. In other words, the base end member82aand the tip member82bdo not completely return to the reference position. At this time, as the base end member82ais suspended with rotating by a predetermined angle from the reference position toward the downstream side in the paper discharge direction, the shielding wall86aof the shielding section86is positioned between the light emitting element and the light receiving element, so that it is determined that the condition to stop transporting the paper is met, and thus an operation of discharging the paper is stopped.

Furthermore, as shown inFIG.7, even if the number of the stacked papers lie within the tolerance (i.e., not a fully stacked state), in such a case that the trailing edge of the paper is curved and thus so-called curl is generated in the paper discharge direction (i.e., a paper discharge direction curl generation state), the tip of the tip member82bcomes into contact with the paper, so that the base end member82aand the tip member82bare suspended at a predetermined position between the paper through position and the reference position. Therefore, as the base end member82ais suspended with rotating by the predetermined angle from the reference position toward the downstream side in the paper discharge direction, so that it is determined that the condition to stop transporting the paper is met and thus the operation of discharging the paper is stopped, similarly to the fully stacked state.

According to the present embodiment, it is possible to properly detect a fully-stacked condition of the papers on the paper discharging tray52or a curl generated on the papers in the paper discharge direction, and prevent a paper stacking characteristics from being deteriorated.

Furthermore, according to the present embodiment, as there is provided the first forcing member82dto force the tip member82btoward the upstream side in the paper discharge direction, it is possible to completely return the tip member82bto the reference position when the condition to stop transporting the paper is not met, for example the papers are not fully stacked or no curl generated on the paper in the paper discharge direction, so that erroneous detection can be prevented.

Furthermore, according to the present embodiment, as there is provided the second forcing member to force the shaft member80aand the base end member82aattached thereto toward the upstream side in the paper discharge direction, it is possible to completely return the base end member82ato the reference position when the condition to stop transporting the paper is not met, so that the erroneous detection can be prevented.

Furthermore, according to the present embodiment, when being at the reference position, as the tip of the tip member82bis positioned at the upstream side with respect to the discharge opening70ain the paper discharge direction, it is possible to precisely detect the curl generated on the trailing edge of the paper.

In the present embodiment, although the tip of the tip member82bis apart from the vertical wall surface52when being at the reference position, it may abut on the vertical wall surface52c.In this case, the tip of the tip member82bwhen being at the reference position may be positioned at the upstream side with respect to a rotation axis of the paper discharging roller70in the paper discharge direction. By configuring in this way, it is possible to more precisely detect the curl generated on the trailing edge of the paper.

Furthermore, as shown inFIG.8, even if the number of stacked papers lies within the tolerance, in a state where the curl, which curves an end portion in a width direction of the paper, is generated (referred to as a paper width direction curls generation state), the end portion in the width direction of the paper comes into contact with the second detection part84, and thus the second detection part84is pushed up. As described above, since each of the first detection part82, the second detection part84, and the shielding section86integrally rotates around the first axis working with the shaft member80a,when the second detection part84is pushed up by the paper, the base end member82arotates by a predetermined angle toward the downstream side with respect to the reference position in the paper discharge direction. As a result, it is determined that the condition to stop transporting the paper is met, and thus the operation of discharging the paper is stopped. Therefore, it is possible to properly detect the curls generated in the paper width direction and prevent the paper stacking characteristics from being deteriorated.

Second Embodiment

Since the image forming apparatus10according to the second embodiment is identical to the image forming apparatus10according to the first embodiment except for including a lock device for locking the posture of the tip member82b,there will be described only different points from the first embodiment to avoid overlapping descriptions.

As shown inFIG.9, the paper detection section80according to the second embodiment is provided with a lock device88. The lock device88includes a protrusion88aand an elastic part88b.The protrusion88ais disposed adjacent to the first detection part82(or a base end member82a) and protrudes from the shaft member80atoward the paper discharge direction (i.e., a side of the paper discharging tray52). Specifically, the protrusion88aextends from the shaft member80ain the same direction as the first detection part82(or the base end member82a).

The elastic part88bis provided at a tip of the protrusion88a(i.e., at the end in the paper discharge direction). In addition, the elastic part88bis provided so that a part thereof overlaps the first detection part82(or the tip member82b) in the front-back direction (i.e., an axial direction of the shaft member80aor an axial direction of the shaft member82c). Furthermore, the elastic part88bis provided between the first detection part82(or the tip member82b) when positioned at the reference position and the first detection part82(or the tip member82b) when positioned at the paper-through position.

Therefore, when the first detection part82(or the tip member82b) is rotated between the reference position and the paper through position, the first detection part82(or the tip member82b) abuts on the elastic part88b, so that the rotation of the first detection part82(or the tip member82b) is disrupted by the elastic part88b.

However, the elastic part88bis deformed into such a shape that the elastic part88bdoes not disrupt the rotation of the first detection part82(or the tip member82b) when it is subjected to pressure equivalent to pressure applied by the paper being discharged from the discharge opening70a.Therefore, as shown inFIG.10, the first detection section82(or the tip member82b) gets free from the elastic part88band rotates from the reference position to the paper-through position.

On the other hand, the elastic part88bdoes not significantly deform when it is subjected to pressure equivalent to pressure applied by both the weight of the tip member82band the force from the first forcing member82d.Accordingly, the rotation of the first detection section82(or the tip member82b) is disrupted. Therefore, when the first detection part82(or the tip member82b) once gets free from the elastic part88band then is positioned at a position close to the paper-through position with respect to the elastic part88b,the first detection part82(or the tip member82b) comes to be supported by the elastic part88b.In other words, the posture of the tip member82bis locked. At this time, since the first detection part82(or the tip member82b) is positioned above the upper surface of the paper discharged from the discharge opening70a,the weight of the first detection part82(or the tip member82b) by itself and the force from the first forcing member82dnever act on the paper being discharged from the discharge opening70a.

However, the elastic part88bdeforms into such a shape that it does not disrupt the rotation of the first detection part82(or the tip member82b) when the entire paper detection part80is subjected to pressure (inertia of the paper detection part80) which allows the first detection part82to return from the paper through position to the reference position. As a result, the first detection part82(or the tip member82b) gets free from the elastic part88band rotates from the paper-through position to the reference position. Namely, the lock of the posture of the tip member82bis released.

According to the second embodiment, since the tip member82bis locked when rotating from the reference position by an angle of a predetermined degrees or more, it is possible to prevent the posture of the paper being discharged from the discharge opening70afrom being disturbed and thus prevent the paper stacking characteristics from being deteriorated.

In each of the above described embodiments, although the image forming apparatus10is configured as a color multifunction machine, the image forming apparatus according to the present invention may be configured as a monochrome printing machine or a monochrome multifunction machine.

In each of the above described embodiments, although the image forming apparatus10is configured as a multifunction machine, the image forming apparatus according to the present invention may be configured as a printer, a copier, or a facsimile if including even the paper discharging tray.

Furthermore, it should be noted that the specific shapes and the like given in the above-described embodiments are only examples, and they can be changed or modified as appropriate depending on actual products.