SHEET FEEDING APPARATUS AND IMAGE FORMING APPARATUS

Abstract

A sheet feeding apparatus including: a separation claw for restraining both end portions of leading edges of sheets in a width direction orthogonal to a sheet feeding direction, the sheets having reached a sheet feeding position, and separating, one by one, the sheets fed by a pickup roller; and a photosensor detecting that the separation claw has reached a separation position for separating the sheets when a sheet stacking board is raised to detect that the sheets have reached the sheet feeding position, in which the separation claw, which is movable in an up-and-down direction, is moved to the separation position, the photosensor detects that the sheets supported by the sheet stacking board have reached the sheet feeding position of being feedable by the pickup roller, by rise of the sheet stacking board.

Description

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a sheet feeding apparatus and an image forming apparatus, in particular, a sheet feeding apparatus and an image forming apparatus, which separate sheets one by one by using a separation claw and feed the separated sheets.

2. Description of the Related Art

In recent years, an image forming apparatus such as a printer, a copying machine, or a facsimile machine includes a sheet feeding apparatus for separating sheets one by one and feeding the separated sheets to an image forming portion. As the above-mentioned sheet feeding apparatus, for example, there is known an apparatus configured to raise and lower a sheet supporting portion, which has the sheets stacked thereon, by drive from a driving source such as a motor. In the sheet feeding apparatus, the sheet supporting portion is raised so that an uppermost sheet of the stacked sheets can be located at a position in a height direction (that is, sheet feeding position), where it becomes possible to feed the sheets by a feed roller.

Then, in order to continuously feed the sheets, it is necessary to keep the height of the uppermost sheet on the sheet supporting portion, at such a height (sheet feeding position) at which the uppermost sheet can be fed by the feed roller. Therefore, heretofore, the sheet feeding apparatus is provided with an optical sensor and a sensor flag. The sensor flag pushed up by the uppermost sheet shields the optical sensor from sensor light, to thereby detect that the uppermost sheet has reached the sheet feeding position. Then, the optical sensor detects that the height of the uppermost sheet is lowered from the sheet feeding position as a result that the sheets are fed, and based on such detection, the rise of the sheet supporting portion is controlled so that the height of the uppermost sheet can be maintained at the sheet feeding position. This technology is disclosed in Japanese Patent Application Laid-Open No. 2003-165633.

Further, heretofore, as a sheet feeding apparatus configured to feed sheets prone to be adhered to one another, there has been an apparatus including a mechanism for loosening a sheet bundle, which is stacked in order to be fed, by blowing air thereto. In this case, in order to enable surely a feed of the sheets prone to be adhered to one another, for example, air is blown by air blowing means to a side end of an upper portion of the sheet bundle stacked on the sheet supporting portion, and air is allowed to pass through among the sheets, so that the sheets are released from being adhered to one another. Note that, in the sheet feeding apparatus as described above, a sheet holding-down member for suppressing flotation of the sheets to which air is blown is provided. This technology is disclosed in Japanese Patent Application Laid-Open No. 2008-87906.

However, in the conventional sheet feeding apparatus, when the sheets are sequentially fed, a height of the sheet bundle is thereby lowered, and following this, the sensor light of the optical sensor becomes unshielded, then the sheet supporting portion rises. At this time, when air is blown to trailing edges of the sheets, a sheet surface against which the sensor flag abuts floats up because the sheet holding-down member is arranged at a position apart from the sheet surface. Then, in a case where the sheet surface against which the sensor flag abuts floats up as described above, then the sensor flag is pushed up, the sensor light becomes shielded before the uppermost sheet reaches the sheet feeding position, and the uppermost sheet cannot be held at the sheet feeding position.

Further, for example, in a case where leading edge portions of the sheets stacked on the sheet supporting portion are curled upward, a height of the sheet surface against which the sensor flag abuts and a surface height of the leading edges of the sheets differ from each other. In this case, when a height of the sheet supporting portion is controlled based on a signal from the optical sensor, the leading edges of the sheets become located more upward than the sheet feeding position in terms of height. Therefore, when the sheets are fed in this state, there is apprehension that the leading edges of the sheets cannot smoothly enter a nip between conveyor rollers located downstream thereof resulting in sheet jamming.

SUMMARY OF THE INVENTION

In view of the above-mentioned circumstances, the present invention has been made, and therefore, it is an object of the present invention to provide a sheet feeding apparatus and an image forming apparatus, which are capable of surely detecting that the sheets have reached the sheet feeding position.

According to the present invention, there is provided a sheet feeding apparatus configured to feed sheets, including:

a rising and lowering sheet supporting portion configured to support the sheets;

a raising and lowering mechanism configured to raise and lower the sheet supporting portion;

a feed roller configured to feed out an uppermost sheet of the sheets supported by the sheet supporting portion;

a detecting portion configured to detect the uppermost sheet of the sheets supported by the sheet supporting portion;

a separation claw, which is movable up and down and configured to separate, one by one, the sheets fed by the feed roller, by restraining a side end of leading edges of the sheets in a width direction orthogonal to a sheet feeding direction; and

• • a control portion configured to control the raising and lowering mechanism based on a detection by the detecting portion,

wherein the detecting portion is arranged to detect a position of the separation claw, and the control portion controls the raising and lowering mechanism based on the detection by the detecting portion so that the uppermost sheet of the sheets supported by the sheet supporting portion is located at a position of being feedable by the feed roller.

Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a view illustrating a schematic configuration of a laser beam printer as an example of an image forming apparatus including a sheet feeding apparatus according to a first embodiment of the present invention.

FIG. 2 is a view illustrating a configuration of a sheet feeding deck as the sheet feeding apparatus.

FIG. 3 is a block diagram for performing control of a sheet stacking board provided in the sheet feeding apparatus.

FIG. 4 is a view illustrating a separation claw provided on the sheet feeding deck.

FIG. 5 is a view illustrating a configuration of a sheet feeding deck as a sheet feeding apparatus according to a second embodiment of the present invention.

FIG. 6 is a view illustrating another configuration of the sheet feeding deck.

DESCRIPTION OF THE EMBODIMENTS

A description will be provided below in detail of embodiments for implementing the present invention with reference to the accompanying drawings. FIG. 1 is a view illustrating a schematic configuration of a laser beam printer as an example of an image forming apparatus including a sheet feeding apparatus according to a first embodiment of the present invention. In FIG. 1, the laser beam printer 1, a laser beam printer main body 1A (hereinafter referred to as a printer main body), and a deck-type sheet feeding apparatus 2 (hereinafter referred to as a sheet feeding deck) mounted under the printer main body 1A are illustrated. An image forming portion 1B is provided in the printer main body 1A, and forms an image by an electrophotographic method. The image forming portion 1B includes: a photosensitive drum 14 on which a toner image is formed; a laser exposure device 17 as a laser exposure optical system configured to irradiate the photosensitive drum 14 with a laser beam according to an image signal; and a transfer roller 15 configured to transfer, to a sheet S, the toner image formed on the photosensitive drum 14. The photosensitive drum 14 is incorporated in a process cartridge 13 detachably mounted to the printer main body 1A. In a lower portion of the printer main body 1A, a cassette 20 configured to stack and contain the sheets S therein is detachably mounted to the printer main body 1A, and the sheets S contained in the cassette 20 are appropriately fed out in order from an uppermost one by a pickup roller 21 provided in the printer main body 1A.

In FIG. 1, a feed roller 23 is provided in the printer main body 1A, and a retard roller 24 rotates at a predetermined torque through a torque limiter (not shown) in a direction of returning the sheets conveyed by the feed roller 23. By the feed roller 23 and the retard roller 24 provided in the printer main body 1A, the sheets S fed out by the pickup roller 21 are separated and fed one by one. Pairs of conveyor rollers 11 and 12 are provided in the printer main body 1A, and the pairs of conveyor rollers 11 and 12 sequentially receive the sheets S fed by the feed roller 23, and convey the received sheets S toward a registration roller pair 25. The sheet S on which a toner image is transferred is subjected to heating and pressing treatments at the time of passing through a fixing device 16, so that the toner image is fixed to the sheet S.

In the laser beam printer 1 configured as described above, when an image forming operation is started, first, the photosensitive drum 14 is irradiated with light according to the image signal by the laser exposure device 17, and then a latent image is formed on the photosensitive drum by such irradiation of the light according to the image signal. Next, this latent image is developed by toner contained in the process cartridge 13, to thereby form the toner image (visible image) on the photosensitive drum. In parallel with such a toner image forming operation, for example, the sheets S stacked on the cassette 20 are fed out in order from the uppermost one by the rotation of the pickup roller 21. After that, the sheets S are separated and conveyed one by one by a separation portion including the feed roller 23 and the retard roller 24.

After that, the sheet S fed by the feed roller 23 is conveyed toward the standstill registration roller pair 25 by the pairs of conveyor rollers 11 and 12 provided in the printer main body 1A, and then leading edge of the sheet S is allowed to abut against a nip portion of the registration roller pair 25 so that a loop is formed in the sheet S, to thereby correct the skew feed of the sheet S. After that, the registration roller pair 25 starts to rotate in synchronization with the image formed on the photosensitive drum 14, and conveys the sheet S to a nip portion between the photosensitive drum 14 and the transfer roller 15 opposite thereto. Further, when the sheet S is fed from the sheet feeding deck 2 configured as described later, the sheet S is also conveyed to a transfer portion comprising the photosensitive drum 14 and the transfer roller 15, by the registration roller pair 25 in synchronization with the image formed on the photosensitive drum 14. In the transfer portion, a bias is applied to the transfer roller 15, so that the toner image is transferred to the sheet S which comes from the cassette 20 or to the sheet S which comes from the sheet feeding deck 2. After that, the sheet S on which the toner image is thus transferred is conveyed to the fixing device 16, and is pressed and heated in the fixing device 16, so that the toner image is fixed thereto. After that, the sheet S is delivered by a delivery roller 18 to a delivery tray 19 provided in an upper portion of the printer main body.

The sheet feeding deck 2 includes a sheet stacking board 55 that is provided, as being capable of rising and lowering, in a sheet storage 2a as a sheet containing portion configured to contain the sheets S therein, and is a sheet supporting portion configured to stack and support a bundle of the sheets S. Further, the sheet feeding deck 2 includes a trailing edge regulating plate 56 configured to regulate a position of a trailing edge as an upstream side edge of a sheet bundle Sa in a sheet feeding direction. Here, the sheet bundle Sa is stacked on the sheet stacking board 55. Further, the sheet feeding deck 2 includes a door 2c to be opened at the time of stacking the sheet bundle Sa on the sheet stacking board 55. The door 2c is arranged on a front side of the printer main body 1A. When the door 2c is opened, the sheets S can be loaded and unloaded from an operation side of the printer main body 1A.

Further, as illustrated in FIG. 2, the sheet feeding deck 2 includes side regulating plates 57 and 58 as a pair of regulating members configured to regulate a position of the sheet bundle Sa in a width direction orthogonal to the sheet feeding direction. Here, the sheet bundle Sa is stacked on the sheet stacking board 55. The sheet stacking board 55 is suspended through wires 60a to 60d, each having an end fixed to a wire winding shaft 59. By rotating the wire winding shaft 59 forward and reverse by a raising and lowering motor (not shown), the wires 60a to 60d are wound in and wound off, to thereby move (raise and lower) the stacking board 55 in an up-and-down direction. In this embodiment, a raising and lowering mechanism 60 configured to raise and lower the sheet stacking board 55 includes: the raising and lowering motor (not shown); the wires 60a to 60d; and the wire winding shaft 59.

Further, the sheet feeding deck 2 includes a sheet feeding portion 2b configured to feed out an uppermost sheet S1 of the sheet bundle Sa stacked on the sheet stacking board 55. The sheet feeding portion 2b includes a pickup roller 51 as a feed roller configured to feed out the sheets S1, which are stacked on the sheet feeding board 55, in order from the uppermost one. Further, the sheet feeding portion 2b includes: a feed roller 52 and a retard roller 53, which serve as a separation portion configured to separate and feed one by one the sheets S1 fed out by the pickup roller 51; and a conveyor roller 54 configured to convey the sheet S1, which is separated one by one by the separation portion, to the printer main body 1A. Still further, in the vicinity of the trailing edge regulating plate 56, a fan 30 as an air blowing portion configured to blow air toward a trailing edge of an upper portion (in the vicinity of the uppermost sheet S1) of the sheet bundle Sa is arranged.

Further, as illustrated in FIG. 2, a drive gear 103 is driven by a drive motor Md illustrated in FIG. 3, and the drive gear 103 is fixedly attached to a roller shaft 104. Then, at the time of feeding the sheets, the drive gear 103 is driven, to thereby rotate the roller shaft 104. Following the rotation of the roller shaft 104, a moment in a direction of allowing the pickup roller 51 to abut against the sheets S1 is generated in a pick arm 106 from the roller shaft 104 taken as a fulcrum. In this manner, the pickup roller 51 rotatably held on a rotation end of the pick arm 106 abuts against the sheets S1. By reverse rotation of the roller shaft 104, a moment in a direction of moving the pickup roller 51 to be spaced apart from the sheets S1 is generated in the pick arm 106, and the pickup roller 51 is spaced apart from the sheets S1.

Further, a sheet feeding pressure is changed depending on a friction coefficient between the sheet S1 and the pickup roller 51, and a reaction force acts on the pickup roller 51 in a direction reverse to the sheet feeding direction, by reaction force from the sheet S1 at the time of feeding the sheet. Then, the roller shaft 104 (rotation fulcrum) of the pick arm 106 is arranged upstream in the sheet feeding direction, and hence a component force in a direction of being brought into pressure contact with the sheet S1 is generated in the pickup roller 51 by the reaction force that acts on the pickup roller 51. The sheet feeding pressure is set based on the component force and the own weight of the pickup roller 51. Therefore, a force by which the pickup roller 51 is brought into pressure contact with the sheet at the time of feeding the sheet S1 is changed depending on the friction coefficient between the sheets S1 and the pickup roller 51. For example, for the sheets S1 in which a friction coefficient thereamong is small and feeding with small feeding force is necessary, the sheet feeding pressure is also reduced, and double feeding becomes less likely to occur. On the contrary, for the sheets S1 in which the friction coefficient thereamong is large and a large feeding force is necessary, the sheet feeding pressure is also increased, and an occurrence of a feeding failure of the sheets can be prevented. As described above, the sheet feeding pressure with which the pickup roller 51 abuts against the sheets S1 is generated in such a manner that the pickup roller 51 is brought into pressure contact with the sheet S1 by the moment generated in the pick arm 106 when a driving force is transmitted to the pick arm 106 and the reaction force when the pickup roller 51 feeds the sheet S1.

Then, in the sheet feeding deck 2 configured as described above, when the stacking of the sheet bundle Sa onto the sheet stacking board 55 is ended, and the door 2c is closed, a detection sensor (not shown) detects the close of the door 2c. Based on the detection of the detection sensor, a control portion C illustrated in FIG. 3 rotates a raising and lowering motor ML. In this manner, the wire winding shaft 59 rotates so that the wires 60a to 60d are wound in, and the sheet stacking board 55 is raised. After moving to a position capable of feeding the uppermost sheet S1, the sheet stacking board 55 is controlled to rise and lower, so as to maintain the position, by the control portion C based on a signal coming from a photosensor 61 to be described later. After that, the feeding of the sheets S1 is started by the pickup roller 51 that has abutted against the sheets S1 raised to the position (hereinafter referred to as a sheet feeding position) capable of feeding the sheets S1 by the pickup roller 51. Note that, the sheet feeding position is located within a certain range in the height direction capable of feeding the sheets, and if the uppermost sheet is located within the range, it is possible to feed the uppermost sheet because the sheet feeding pressure generated between the pickup roller 51 and the uppermost sheet remains within the range capable of feeding the sheets. Here, in a case of feeding the sheets S1, first, air is blown to the trailing edge of the upper portion of the sheet bundle Sa by the fan 30, so that end portions of the sheets are floated up (lifted by the blown air). After that, the uppermost sheet S1 of the sheet bundle Sa stacked on the sheet stacking board 55 is fed out by the pickup roller 51, and after that, the sheets in the sheet bundle Sa are separated one by one by the separation portion, followed by feeding, and further, are conveyed to the printer main body 1A by the conveyor roller 54.

By the way, as illustrated in FIG. 2, the side regulating plates 57 and 58 are provided with, a pair of separation claws 101 and 102, which are arranged so as to be engaged with both corner portions as both end portions of the leading edges (downstream edges in the sheet feeding direction) of the sheets in the width direction. Those separation claws 101 and 102 separate the sheets by using deflection of the sheets, which is caused by stiffness thereof. Specifically, when the each of sheets is fed out by the pickup roller 51, both corner portions of the leading edge of the sheet are restrained by the separation claws 101 and 102, and the sheet in which the leading edge is restrained is deflected at both corner portions. When the deflection reaches a predetermined amount or more, the leading edge flicks and climbs over the separation claws 101 and 102. As a result, one sheet is separated from the others. Note that, upward movements of the separation claws 101 and 102 are restricted by stoppers 57a and 58a so that the separation claws 101 and 102 can flick out one sheet while deflecting the one sheet at the time of the separation thereof. The stoppers 57a and 58a are formed on the side regulating plates 57 and 58 in this embodiment. Further, after elastically flicking out of the separation claws 101 and 102 as described above, the sheet S is fed to the separation portion including the feed roller 52 and the retard roller 53.

Here, in this embodiment, the separation claws 101 and 102 are provided to the side regulating plates 57 and 58 so as to be swingable (movable) in the up-and-down direction through a swing shaft (not shown). Further, on the side regulating plate 58 as one of the pair, the photosensor 61 is provided, which is a detecting portion configured to detect that the uppermost sheet S1 of the sheet bundle Sa has reached the sheet feeding position. Note that, in a case where the uppermost sheet S1 has reached the sheet feeding position as described above, when the uppermost sheet S1 is fed by the pickup roller 51, the uppermost sheet S1 can smoothly enter a nip (hereinafter referred to as a separation nip) between the feed roller 52 and the retard roller 53. Further, on one-side swing ends of the separation claws 101 and 102, claw portions 101a and 102a which are engaged with corner portions of the sheets are provided. Further, in this embodiment, on the other-side swing end of the separation claw 101 as one of the pair, a sensor light shielding portion 101b configured to shield sensor light of the photosensor 61 is provided.

Here, in this embodiment, in the separation claws 101 and 102, the claw portions 101a and 102a are located at lower positions until the sheet stacking board 55 is raised. At this time, the sensor light shielding portion 101b of the separation claw 101 as one of the pair has moved to a position of not shielding the sensor light of the photosensor 61, the position being located above the photosensor 61. In this state, when the sheet stacking board 55 is raised, the corner portions of the uppermost sheet S1 and the claw portions 101a and 102a are shortly engaged with each other, and after that, the separation claws 101 and 102 swing while the claw portions 101a and 102a are raised together with the sheets on the sheet stacking board.

When the separation claws 101 and 102 swing as described above, the separation claws 101 and 102 move in time to separation positions of separating the sheets fed by the pickup roller 51. At the separation positions, the separation claws 101 and 102 abut against the above-mentioned stoppers 57a and 58a which restrict the upward movement thereof. Then, when the separation claws 101 and 102 move to the separation positions as described above, the sensor light shielding portion 101b provided on the separation claw 101 shields the sensor light of the photosensor 61, and the photosensor 61 outputs a trigger signal. Based on this trigger signal, the control portion C determines that the uppermost sheet S1 has moved to the sheet feeding position, and stops the raising and lowering motor ML, to thereby stop the rise of the sheet stacking board 55. In this manner, the sheet feeding deck 2 completes feeding preparation thereof, and turns to a standby state. When a feeding start signal is sent from the printer main body 1A to the sheet feeding deck 2 after the sheet feeding deck 2 turns to the standby state, the control portion C controls the drive motor Md of the feeding portion of the sheet feeding deck 2, and rotates the pickup roller 51, to thereby start a feeding operation of the sheet. At this time, the drive of the fan 30 is started, and air is blown to the trailing edge of the upper portion of the sheet bundle Sa on the sheet stacking board, so that adherence between the uppermost sheet S1 and the sheet in the vicinity thereof is released.

By the way, the sheet feeding operation is repeated so that the sheets are sequentially fed, with the result that a height of the sheet bundle Sa is lowered, and following this, the separation claws 101 and 102 gradually swing in a direction in which the claw portions 101a and 102a lower. Then, when the separation claws 101 and 102 swing as described above, the sensor light shielding portion 101b provided on the separation claw 101 is raised, and then, becomes unshielding the sensor light of the photosensor 61. In this manner, the control portion C detects that the uppermost sheet S1 has lowered in position than the sheet feeding position, and drives the raising and lowering motor ML of the raising and lowering mechanism 60 to raise the sheet stacking board 55 so that the uppermost sheet S1 can be maintained at the sheet feeding position. Though the sheets in the vicinity of the uppermost sheet turn to a state of floating upward due to an influence of air blown thereto from the fan 30 at this time, the leading edge portions of the sheets, on which the separation claws 101 and 102 are arranged, and particularly, the corner portions of the sheets are held in a state of being adhered to one another by weight of the separation claws 101 and 102. Specifically, in this embodiment, the separation claws 101 and 102 also have a function to hold down the sheets for the purpose of suppressing the flotation of the leading edge portions of the sheets by air blown thereto by the fan 30. In other words, even in a case where air is blown to the separation claws 101 and 102, the positions of the separation claws 101 and 102 are not changed. Accordingly, if the positions of the separation claws 101 and 102 are detected, then the uppermost sheet S1 can be maintained at the sheet feeding position without being affected by the air.

As described above, in this embodiment, when the sheet stacking board 55 is raised, the separation claws 101 and 102 which have moved to the separation positions are detected, so that it can be surely detected that the uppermost sheet has reached the sheet feeding position. In other words, when the sheet stacking board 55 is raised, it is detected that the separation claws 101 and 102 have moved to the separation positions, so that it can be surely detected that the uppermost sheet has reached the sheet feeding position. Further, the sensor light shielding portion 101b is provided on any one of the separation claws 101 and 102 as in this embodiment, to thereby increase an amount of the stacked sheets as compared with the case of providing the sensor light shielding portion above the sheets. Further, in this embodiment, the photosensor is used for detecting the position of the uppermost sheet, however, other detection units may also be applicable as long as similar effects can be obtained.

Though the sheets are separated by the separation claws 101 and 102 in this embodiment, the sheets do not sometimes come out of the separation claws 101 and 102 if engaging amounts of the separation claws 101 and 102 with respect to the sheets are increased. Therefore, in order that the sheets can surely come out of the separation claws 101 and 102, it is preferred to reduce the engaging amounts of the separation claws 101 and 102 with respect to the sheets. However, preferred engaging amounts differ depending on types of the sheets. For example, in a case of special sheets such as label sheets, which are perforated, if the engaging amounts of the separation claws are reduced, such sheets are prone to be bent at perforated portions. Therefore, at the time of feeding the special sheets, the sheets cannot push back reaction force coming from the separation claws 101 and 102 to thereby cause buckling on the perforated portions, leading to a feeding failure.

Accordingly, in this embodiment, the perforated portions of the perforated special sheets are covered with the separation claws 101 and 102, so that the reaction force coming from the separation claws 101 and 102 may be received by portions other than the perforated portions. In this embodiment, for example, as illustrated in FIG. 4, an engaging amount Wb of the separation claw 101 in the sheet feeding direction is set at 3.5 times or more an engaging amount Wa thereof in the sheet width direction. The same applies to the separation claw 102 as the other of the pair. Further, as illustrated in FIG. 2, the pickup roller 51 is provided in the vicinity of the center in the width direction between the pair of separation claws 101 and 102, and distances for ensuring a sufficient sheet deflection amount are set between the pickup roller 51 and the separation claw 101 and between the pickup roller 51 and the separation claws 102. With such a configuration, even the perforated special sheets are not buckled at the perforated portions, and can be stably separated and fed.

By the way, in the description above, the positions of the separation claws are detected, to thereby hold the uppermost sheet at the sheet feeding position without being affected by air blown from the fan 30. However, the present invention is not limited to this. For example, in some cases, sheets of which leading edges are curled are stacked on the sheet stacking board. At this time, the height of the sheet surface against which the sensor flag abuts and the height of the sheet surface at the leading edges of the sheets differ from each other as already mentioned. In this case, if the height of the sheet stacking board 55 is controlled based on the signal coming from the photosensor, the height of the leading edges is located more upward than a nip (hereinafter referred to as a separation nip) between the feed roller 52 and the retard roller 53, for example, in a case where the leading edges of the sheets are curled upward. When the sheets are fed in this state, the leading edges of the sheets cannot smoothly enter the separation nip. However, even in a case of feeding the sheets in which the leading edges are curled, the leading edges of the sheets can be allowed to smoothly enter the separation nip if the positions of the separation claws are detected.

FIG. 5 is a view illustrating a configuration of a sheet feeding deck as described above as a sheet feeding apparatus according to a second embodiment of the present invention. In FIG. 5, the same reference symbols as those already mentioned in FIG. 2 denote the same or equivalent portions. Further, a description of the same operations as those in the first embodiment is omitted. Here, until the sheet stacking board 55 is raised, the separation claws 101 and 102 swing so that the claw portions 101a and 102a can be located at lower positions. At this time, the sensor light shielding portion 101b of the separation claw 101 as one of the pair has moved to the position of not shielding the sensor light of the photosensor 61, the position being located above the photosensor 61. In this state, when the sheet stacking board 55 is raised, for example, the corner portions of the uppermost sheet S1 in which the leading edge portion is curled upward and the claw portions 101a and 102a are engaged with each other, so that the separation claws 101 and 102 swing in the direction in which the claw portions 101a and 102a is raised. When the separation claws 101 and 102 swing as described above, the sensor light shielding portion 101b provided on the separation claw 101 shields the sensor light of the photosensor 61, and the photosensor 61 outputs the trigger signal.

Then, based on this trigger signal, a control portion (not shown) detects that the uppermost sheet S1 of the stacked sheet bundle Sa is moved to the sheet feeding position in which the uppermost sheet S1 can be fed by the pickup roller 51 to smoothly enter the separation nip. Then, the control portion stops the rise of the sheet stacking board 55 based on the detection, to thereby complete the feeding preparation. Then, the sheet feeding deck 2 turns to the standby state. Here, in this embodiment, the separation claws 101 and 102 is raised in accordance with the rise of the uppermost sheet S1 curled upward, and thus, the position where the sheet stacking board 55 stops is a position where the leading edge of the sheet can smoothly enter the separation nip. Specifically, in a case of detecting the positions of the separation claws 101 and 102 as in this embodiment, the sheet stacking board 55 can be stopped at the position where the leading edge of the sheet can smoothly enter the separation nip even if the sheet is curled.

In the description above, the position control for the sheet stacking board 55 is performed based on the position of the separation claw 101 as one of the pair. However, the present invention is not limited to this. For example, as illustrated in FIG. 6, photosensors 61 and 62 may be provided on the two side regulation plates 57 and 58, respectively, and the sensor light shielding portions 101b and 102b may be provided on the other-side swing ends of the two separation claws 101 and 102. Note that, in this case, the wires 60a and 60b which support one of side end portions of the sheet stacking board 55 are wound in or wound off by a wire winding shaft 65. Further, the wires 60c and 60d which support the other side end portion of the sheet stacking board 55 are wound in or wound off by a wire winding shaft 64. Specifically, in a case where the photosensors 61 and 62 are provided to the side regulating plates 57 and 58, respectively, two raising and lowering mechanisms 60A and 60B are provided in order to raise and lower the sheet stacking board 55.

With the configuration as described above, when the sheet stacking board 55 is raised, the claw portions 101a and 102a are engaged with the corner portions of the uppermost sheet S1 in which the leading edge portion is curled upward, so that the separation claws 101 and 102 swing in the direction in which the claw portions 101a and 102a is raised together with the uppermost sheet. When the separation claws 101 and 102 swing as descried above, the sensor light shielding portions 101b and 102b provided on the separation claws 101 and 102 shield the sensor light of the photosensors 61 and 62, and the photosensors 61 and 62 output the trigger signals. Based on the trigger signals, the control portion stops the raising and lowering mechanisms 60A and 60B, so that the sheet stacking board 55 can be stopped at the position where the uppermost sheet S1 reaches the sheet feeding position.

Here, a curl amount sometimes differs between both corners of the leading edge of the sheet. When the sheet is fed in this state, then in some cases, the leading edge of the sheet does not smoothly enter the separation nip, and the sheet is skew-fed. However, even in a case where there is a difference in the curl amount as described above, the drive of the two raising and lowering mechanisms 60A and 60B is individually stopped in response to the detection of the separation claws 101 and 102 by the photosensors 61 and 62, to thereby control a rising and lowering amount of the sheet stacking board 55 in the width direction. With such a configuration, even in a case where the curl amount differs between both corners of the leading edge of the sheet, both corners of the leading edge of the sheet can be maintained at the sheet feeding position, and as a result, the leading edge of the sheet can be allowed to smoothly enter the separation nip without skew-feeding the sheet.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of Japanese Patent Application No. 2009-181086, filed Aug. 3, 2009, which is hereby incorporated by reference herein in its entirety.

Claims

1. A sheet feeding apparatus configured to feed sheets, comprising:

a rising and lowering sheet supporting portion configured to support the sheets;

a raising and lowering mechanism configured to raise and lower the sheet supporting portion;

a feed roller configured to feed out an uppermost sheet of the sheets supported by the sheet supporting portion;

a detecting portion configured to detect the uppermost sheet of the sheets supported by the sheet supporting portion;

a separation claw, which is movable up and down and configured to separate, one by one, the sheets fed by the feed roller, by restraining a side end of leading edges of the sheets in a width direction orthogonal to a sheet feeding direction; and

a control portion configured to control the raising and lowering mechanism based on a detection by the detecting portion,

wherein the detecting portion is arranged to detect a position of the separation claw, and

the control portion controls the raising and lowering mechanism based on the detection by the detecting portion so that the uppermost sheet of the sheets supported by the sheet supporting portion is located at a position of being feedable by the feed roller.

2. A sheet feeding apparatus according to claim 1, further comprising an air blowing portion configured to blow air to trailing edges of the sheets supported by the sheet supporting portion,

wherein leading edge portions of the sheets in which the air is blown to the trailing edges by the air blowing portion are held down by the separation claw.

3. A sheet feeding apparatus according to claim 1, further comprising a pair of regulating members configured to regulate positions of the sheets in the width direction, the sheets being supported by the sheet supporting portion,

wherein the separation claw is provided on each of the pair of regulating members so as to move in an up-and-down direction.

4. A sheet feeding apparatus according to claim 3, wherein the detecting portion is provided on each of the pair of regulating members,

the raising and lowering mechanism comprises two raising and lowering mechanisms, which support, raise and lower both ends of the sheet supporting portion in the width direction, respectively, and

when raising the sheet supporting portion, the control portion stops drive of each of the two raising and lowering mechanisms in response to detection of the separation claw by the detecting portion provided on each of the pair of regulating members.

5. An image forming apparatus comprising a sheet feeding apparatus configured to feed sheets and an image forming portion configured to form an image on each of the sheets fed by the sheet feeding apparatus, the image forming apparatus comprising:

a rising and lowering sheet supporting portion configured to support the sheets;

a raising and lowering mechanism configured to raise and lower the sheet supporting portion;

a feed roller configured to feed out an uppermost sheet of the sheets supported by the sheet supporting portion;

a detecting portion configured to detect the uppermost sheet of the sheets supported by the sheet supporting portion;

a separation claw, which is movable up and down and configured to separate, one by one, the sheets fed by the feed roller, by restraining a side end portion of leading edges of the sheets in a width direction orthogonal to a sheet feeding direction; and

a control portion configured to control the raising and lowering mechanism based on a detection by the detecting portion,

wherein the detecting portion is arranged to detect a position of the separation claw, and

the control portion controls the raising and lowering mechanism based on the detection by the detecting portion so that the uppermost sheet of the sheets supported by the sheet supporting portion is located at a position of being feedable by the feed roller.

6. An image forming apparatus according to claim 5, further comprising an air blowing portion configured to blow air to trailing edges of the sheets supported by the sheet supporting portion,

wherein leading edge portions of the sheets in which the air is blown to the trailing edges by the air blowing portion are held down by the separation claw.

7. An image forming apparatus according to claim 5, further comprising a pair of regulating members configured to regulate positions of the sheets in the width direction, the sheets being supported by the sheet supporting portion,

wherein the separation claw is provided on each of the pair of regulating members so as to move in an up-and-down direction.

8. An image forming apparatus according to claim 7, wherein the detecting portion is provided on each of the pair of regulating members,

the raising and lowering mechanism comprises two raising and lowering mechanisms, which support, raise and lower both ends of the sheet supporting portion in the width direction, respectively, and

when raising the sheet supporting portion, the control portion stops drive of each of the two raising and lowering mechanisms in response to detection of the separation claw by the detecting portion provided on each of the pair of regulating members.