JP2008068948A - Sheet feeder, and image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sheet feeder and image forming device structured so as to stably feed a sheet. <P>SOLUTION: The sheet feeder is provided with a lifter 36 provided rotatably between an intermediate plate 35 and a cassette bottom surface 32a for pressing the sheet S stacked on the intermediate plate 35 to a feeding roller 101 by pushing up the intermediate plate 35 from beneath. The sheet S is stably fed when a sum of moment by force applied beneath on the intermediate plate 35 with respect to a contact 36c where the lifter 36 pushes up the intermediate plate 35 constantly acts in a direction for pressing a rotation supporting point 35a of the intermediate plate 35. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a sheet feeding apparatus and an image forming apparatus, and more particularly to a configuration of a sheet feeding cassette of a sheet that is detachably mounted on the apparatus main body.

  2. Description of the Related Art Conventionally, a copying machine provided with a sheet feeding device in which a sheet feeding cassette storing a plurality of sheets is detachably attached to the apparatus main body, and the sheets are taken out from the sheet feeding cassette one by one and conveyed to an image forming unit. An image forming apparatus such as a printer is known.

  FIG. 9 is a diagram illustrating an example of a conventional sheet feeding apparatus. A sheet feeding cassette 82 for storing a plurality of sheets S is detachably attached to a sheet feeding apparatus main body (not shown), and sheets S are stacked inside the frame of the sheet feeding cassette 82. A plate 85 and a lifter 86 for raising the middle plate 85 are provided. The middle plate 85 rotates in the vertical direction indicated by the arrow 85b with the rotation center 85a as a fulcrum, and the lifter 86 rotates in the vertical direction indicated by the arrow 86b with the rotation center 86a as a fulcrum. A paper feed roller 83 and a paper feed roller holder 84 that holds the paper feed roller 83 are provided above the paper feed cassette 82. Further, a paper surface sensor 88 for detecting the height of the paper surface is provided.

  The paper feed roller 83 is urged via a paper feed roller holder 84 by a spring or the like (not shown) so as to come into pressure contact with the upper surface of the sheet S stacked on the intermediate plate 85 with a predetermined pressing force (paper feed pressure). ing. The sheet feed roller 83 sequentially feeds the separation roller pair 89, 89 ′ from the uppermost sheet Sa in pressure contact. At this time, when a plurality of sheets S are sent to the pair of separation rollers 89 and 89 ', the separation roller 89' rotates in the direction opposite to the sending direction (89'a direction), and the sheet S to be conveyed is 1 The sheet is fed to the conveying roller 87 and fed to an image forming unit (not shown).

  When the above-described series of conveying operations is repeated and the sheets S are sequentially sent out, the sheet surface height (upper surface height) of the sheets S is lowered. When the paper surface height decreases, the paper surface sensor 88 detects this, and based on the detection signal from the paper surface sensor 88, the control unit (not shown) rotates the lifter 86 in the direction of the arrow 86b by a drive source (not shown). As a result, the intermediate plate 85 is rotated in the direction of the arrow 85b, and the paper surface height of the sheet S rises to a predetermined height.

  However, in the sheet feeding apparatus shown in FIG. 9, when the pressing force during the feeding operation of the sheet feeding roller 83 is applied to the upper surface of the sheet S, the force F indicated by the arrow is fed through the lifter 86. It is transmitted to the inner surface of the bottom plate portion 82a of the cassette 82. The bottom plate portion 82a is often formed to have a thin plate thickness in order to save space and reduce the weight of the apparatus. Therefore, the force F greatly increases the state shown by the broken line in FIG. The case where it bends occurs. When the bottom plate portion 82a is bent in this manner, the pressing force against the sheet S during the feeding operation becomes unstable, and the sheet cannot be fed stably.

  On the other hand, there is a structure shown in FIG. 10 as a structure that does not cause a large deflection in the bottom plate portion 82a of the sheet feeding cassette 82 as described above. In the sheet feeding cassette 82, the rotation center 96 a of the lifter 96 is provided in the vicinity of the pre-separation plate 90 formed on the downstream side in the sheet feeding direction in the frame of the sheet feeding cassette 82. Thus, since the rotation center 96a of the lifter 96 is provided at a location where the rigidity of the bottom plate portion 82a in the vicinity of the pre-separation plate 90 is large, large deflection of the bottom plate portion 82a can be suppressed. Accordingly, the lifter 96 is configured to rotate and move the intermediate plate 85 in the direction indicated by the arrow 85b by rotating in the opposite direction (arrow 96b direction) to the lifter 86 shown in FIG. 9 (for example, , See Patent Document 1).

JP-A-7-267385

  As described above, in the conventional sheet feeding apparatus as shown in FIG. 10, the rotation center 96 a of the lifter 96 is provided at a highly rigid position in the vicinity of the pre-separation plate 90. The bending at the bottom plate portion 82a hardly occurs. However, in this case, another problem arises due to the positional relationship between the contact point 83a of the sheet feed roller 83 with the sheet S, the contact point 96c of the lifter 96 and the intermediate plate 85, the rotation center 85a of the intermediate plate 85, and the like. This is because a clockwise moment MO1 indicated by an arrow centered on the contact point 96c is generated in the intermediate plate 85 due to the pressing of the sheet feeding roller 83 according to the sheet stacking amount of the intermediate plate 85. .

  In the sheet feeding device, the rotation fulcrum 85a of the intermediate plate 85 has a hinge structure, and the joint between the intermediate plate 85 and the cassette body has a mounting play caused by play of the hinge portion. Has occurred. Therefore, due to the moment MO1 described above, the intermediate plate 85 is lifted on the rotational fulcrum 85a side by the backlash in the vertical direction of the rotational fulcrum 85a, and the sheet supply of the intermediate plate 85 is performed using the contact point 96c between the lifter 96 and the intermediate plate 85 as a fulcrum. The downstream side in the feed direction (the pre-separation plate 90 side) is lowered. As a result, the contact position of the paper feed roller 83 and the pressing force (paper feed pressure) on the sheet S during the feeding operation of the paper feed roller 83 become unstable, and the sheet cannot be fed stably.

  SUMMARY An advantage of some aspects of the invention is that it provides a sheet feeding apparatus and an image forming apparatus that can stably feed sheets.

  The present invention includes a lifter that is rotatably provided between the middle plate and the bottom surface of the cassette body, and that pushes up the middle plate from below and presses the sheets stacked on the middle plate against a feeding roller. And a lifter that pushes up the intermediate plate from below, and the upward rotation direction of the intermediate plate and the upward rotation direction of the lifter are opposite to each other. The intermediate plate and the lifter are arranged so that when the sheet is fed, the sum of moments due to the force applied to the intermediate plate with respect to the support portion where the lifter contacts the intermediate plate is always It is configured to act in a direction to push down the rotation fulcrum.

  According to the present invention, the sum of moments applied downward to the intermediate plate with respect to the support portion that contacts the intermediate plate of the lifter always acts in the direction of pushing down the rotation fulcrum of the intermediate plate. Accordingly, the conveyance height of the sheets stacked on the intermediate plate can be stabilized, and the sheet feeding pressure can be stabilized and the sheets can be reliably fed.

  The best mode for carrying out the present invention will be described below in detail with reference to the drawings.

  FIG. 1 is a sectional view of a printer as an image forming apparatus 1 to which a sheet feeding apparatus 1002 according to the first embodiment of the invention is applied, and FIG. 2 is a block diagram of FIG.

  In FIG. 1, reference numeral 1000 denotes a printer, and the printer 1000 includes a printer main body 1001 and a scanner 2000 disposed on the upper surface of the printer main body 1001.

  Here, the scanner 2000 that reads a document includes a scanning optical system light source 201, a platen glass 202, and a document pressure plate 203 that opens and closes. Further, a lens 204, a light receiving element (photoelectric conversion) 205, an image processing unit 206, a memory unit 208 for storing image processing signals processed by the image processing unit 206, and the like are provided.

  When reading the original, the original (not shown) placed on the platen glass 202 is read by irradiating light with the scanning optical system light source 201. The read document image is processed by the image processing unit 206, is electrically encoded, converted into an electric signal 207, and transmitted to the laser scanner 111a serving as an image forming unit. Note that the image information processed and encoded by the image processing unit 206 may be temporarily stored in the memory unit 208 and transmitted to the laser scanner 111a as required by a signal from the controller 120.

  The printer main body 1001 includes a sheet feeding device 1002, a sheet conveying device 1004 that conveys the sheet S fed by the sheet feeding device 1002 to the image forming unit 1003, and a controller 120 that is a control unit for controlling the printer 1000. Etc.

  Here, the sheet feeding apparatus 1002 includes a separation unit including a sheet feeding cassette 100, a feeding roller 101, a feed roller 102, and a retard roller 103. The sheets S in the sheet feeding cassette 100 are separated and fed one by one by the action of a feeding roller 101 that moves up and down / rotates at a predetermined timing and a separation unit.

  The sheet conveying apparatus 1004 includes a conveying roller pair 105 (105a, 105b), and a registration roller unit 11 having a conveying roller pair 10 (10a, 10b) and a registration roller pair 30 (30a, 30b).

  Then, the sheet S fed from the sheet feeding apparatus 1002 is guided to the registration roller unit 11 after passing through a sheet conveying path 108 constituted by guide plates 106 and 107 by a conveying roller pair 105. Thereafter, when the skew is corrected in the registration roller unit 11, the sheet S is conveyed to the image forming unit 1003.

  A registration sensor 121 is provided near the upstream side of the registration roller pair 30 in the conveyance direction. A pre-registration sensor 104 is provided in the vicinity of the feed roller 102 in the conveyance direction downstream side. Output signals from these sensors are input to the controller 120 as shown in FIG. The registration roller pair 30, the conveyance roller pair 105, the feeding roller 101, the feed roller 102, and the retard roller 103 described above receive driving force from the main motor M shown in FIG. These are configured so that ON / OFF control is performed by the respective clutches 30b, 102b, and 105b via the respective drive circuits 30a, 102a, and 105a in accordance with signals from the controller 120, respectively.

  The image forming unit 1003 is of an electrophotographic type, and includes a photosensitive drum 112 as an image carrier, a laser scanner 111a as an image writing unit, a developing device 114, a transfer charger 115, a separation charger 116, and the like. .

  When forming an image, first, the laser beam from the laser scanner 111a is folded back by the mirror 113 and applied to the exposure device 112a on the photosensitive drum 112 that rotates in the clockwise direction. A latent image is formed. Further, the latent image formed on the photosensitive drum 112 in this way is thereafter visualized as a toner image by the developing device 114.

  Next, the toner image on the photosensitive drum 112 that has been visualized in this manner is then transferred to the sheet S by the transfer charger 115 in the transfer unit 112b. The distance from the exposure device 112a of the photosensitive drum 112 to the transfer unit 112b is lo.

  Further, the sheet S on which the toner image has been transferred in this manner is electrostatically separated from the photosensitive drum 112 by the separation charger 116 and then conveyed to the fixing device 118 by the conveyance belt 117 to fix the toner image. Thereafter, the paper is discharged by a discharge roller 119. Note that the photosensitive drum 112, the conveyance belt 117, the fixing device 118, and the discharge roller 119 described above are driven by the main motor M via the drive circuit 122 in response to a signal from the controller 120 as shown in FIG. Each is driven and controlled.

  Further, the printer 1000 and the scanner 2000 may be separate as shown in FIG. 1, but the printer 1000 and the scanner 2000 may be integrated. Even if the printer 1000 and the scanner 2000 are separate or integrated, if the processing signal of the image forming unit 1003 is input to the laser scanner 111a, it functions as a copying machine. If a fax transmission signal is input to the printer 1000, the printer 1000 functions as a fax. If a personal computer output signal is input, the printer 1000 functions as a printer.

  Conversely, if the processing signal of the image processing unit 206 is transmitted to another FAX, it functions as a FAX. Further, in the scanner 2000, if an automatic document feeder 250 as shown by a two-dot chain line is installed instead of the pressure plate 203, the document can be automatically read.

  Next, the sheet feeding apparatus 1002 in the present embodiment will be described with reference to FIG.

  As shown in FIG. 3, the sheet feeding apparatus 1002 includes a sheet feeding cassette 100 having a frame 100 a serving as a frame. An intermediate plate 35 provided in the frame 100a for stacking sheets, a feed roller 101 disposed above the intermediate plate 35 for feeding sheets S stacked on the intermediate plate 35, and the intermediate plate 35. And a lifter 36 that presses against the feeding roller 101. The lifter 36 is provided below the middle plate 35 downstream (relative to the arrow FL that is the feeding direction of the sheet S) and on the cassette bottom surface 32a of the sheet feeding cassette 100, and is rotated by a driving source (not shown). Driven.

  The feed roller 101 is held by the roller holder 150 at the upper periphery on the downstream side of the intermediate plate 35. The roller holder 150 is rotatably arranged around a fulcrum 150a. When the sheet S is fed, the roller holder 150 is urged in the direction of the arrow 150b by an unillustrated elastic member. The feeding roller 101 is pressed against the uppermost surface of the sheet S from above by an urging force applied to the roller holder 150.

  A feed roller 102 is disposed at the upper part on the downstream side of the paper feed cassette 100, and a retard roller 103 that is paired with the feed roller 102 is disposed below the feed roller 102. The sheet S fed from the feeding roller 101 is conveyed to the upper conveying roller pair 105 through these.

  The intermediate plate 35 is supported by a rotation fulcrum 35a having a hinge structure on the upstream side in the feeding direction (arrow FL) of the sheet S by the feeding roller 101, so that the downstream side thereof can be rotated in the vertical direction. It is formed as follows. In addition, in this rotation fulcrum 35a, the mounting play resulting from the play etc. of a hinge part can arise like the intermediate plate in the conventional cassette.

  The lifter 36 has a rotation center (base portion) 36 a disposed at a position having a large rigidity in the vicinity of the pre-separation plate 40 on which the sheet is preliminarily wound on the downstream side end portion of the intermediate plate 35. The occurrence of the bending shown by the broken lines described above with respect to 32 is prevented. The lifter 36 has a tip (contact portion) 36c that contacts the lower surface of the intermediate plate 35 as a contact (support portion) 36c. When the lifter 36 is rotated clockwise as indicated by an arrow 36b, the lifter 36 supports the intermediate plate 35 with the contact 36c. Then, the middle plate 35 is rotated upward. Thus, the upward rotation direction of the intermediate plate 35 and the upward rotation direction of the lifter 36 are set to be opposite to each other.

  Here, the feeding operation of the sheet feeding apparatus 1002 will be described.

  When performing the feeding operation, the feeding roller 101 is urged in the direction of the arrow 150 b by the roller holder 150, so that the feeding roller 101 is pressed against the upper surface of the sheets S stacked on the intermediate plate 35. Thereafter, the feeding roller 101 is rotationally driven in the direction of the arrow 101 a under the control of the controller 120. At this time, since a frictional force is generated between the feeding roller 101 and the sheet S, the uppermost sheet Sa in contact with the feeding roller 101 is fed toward the feed roller 102. Become.

When the feeding operation is repeated, the sheets S are sequentially fed, and the sheet surface height H of the stacked sheets S gradually decreases. Here, when the paper surface height reaches a predetermined height H ₀ , the controller 120 rotates the lifter 36 in the direction of the arrow 36b via a drive source (not shown) by a detection signal of the paper surface detection sensor 41. As a result, the intermediate plate 35 rotates in the direction of the arrow 35b, and the position of the upper surface of the stacked sheets S rises (hereinafter referred to as a lift-up operation). With this series of operations, the stacked sheets S are fed while maintaining a substantially constant paper surface height from the fully loaded state to the last sheet.

  As described above, the sheet feeding apparatus 1002 performs the feeding operation as described above. During this operation, various external forces are applied to the intermediate plate 35 of the sheet feeding apparatus 1002. Here, the force relationship applied to the intermediate plate 35 during the feeding operation will be described with reference to FIGS. 4 is a diagram illustrating an example of a force applied to the sheet feeding cassette 100 in the feeding operation state, FIG. 5 is a diagram illustrating an example of a force applied to the sheet feeding cassette 100 before the feeding operation, and FIG. 6 is a diagram illustrating the force in the feeding operation state. 6 is a diagram illustrating an operation example of the lifter 36 in the paper feed cassette 100. FIG.

As shown in FIG. 4, the force G generated at the center of gravity of the bundle of stacked sheets S and the feeding roller pressure F <b> 101 when urged by the roller holder 150 are directed downward in the vertical direction on the intermediate plate 35. Have joined. In addition, in the lower part of FIG. 4, an X-axis that extends to the left and right of the page and is defined in parallel with the bottom plate part 32 has the position of the contact 36c as the origin and the forward direction toward the downstream side in the sheet S feeding direction. It is shown to be. Force G mentioned above is intended to join from the origin in the X-axis at a distance L _1, the feed roller pressure F101 has become a applied at a distance L ₂ from the origin.

  In the sheet feeding apparatus 1002 according to the present embodiment, each variable based on the above definition satisfies the following equation of moment M regardless of the number of stacked sheets S.

M = G × | L ₁ | −F101 × L ₂ > 0 and L ₁ <0 (1)

  That is, the state in which this equation (1) is established means that the moment MO2 shown in FIG. 4 acts in the direction of the arrow (counterclockwise in the figure) about the contact point 36c with respect to the intermediate plate 35. It means being. In other words, if the composite moment MO2 is applied to the upstream side of the contact point 36c on the intermediate plate 35 (based on the feeding direction of the sheet S), the contact point of the intermediate plate 35 is satisfied. It is possible to prevent a force from acting so as to float the upstream side from 36c.

  Here, in the general cassette and the middle plate including the sheet feeding apparatus 1002 of the present embodiment, there is a current situation that a backlash can be generated at a rotation fulcrum that is a connecting portion thereof. On the other hand, when the moment MO2 is generated in the intermediate plate 35 so that the formula (1) is established, the moment MO2 acts in a direction in which the rotation fulcrum 35a of the intermediate plate 35 is pressed. The position of the fulcrum 35a is stabilized.

  As a result, the problem that the leading end side of the middle plate is lowered due to the floating fulcrum floating as in the conventional case does not occur, so that the sheet surface height of the stacked sheets S is stabilized, and the feeding roller 101 with respect to the sheets S is stabilized. The pressing force can be stabilized.

On the other hand, since the origin (position of the contact 36c) on the X axis moves with the lift-up operation of the lifter 36, the distances L ₁ and L ₂ shown in FIG. 4 are variables on the X axis. The movement associated with the lift-up operation of the lifter 36 is shown in FIGS. First, when the lifter 36 is in an initial state when the sheets S are fully loaded, as shown in FIG. 5, the position of the force G generated at the center of gravity of the bundle of sheets S and the feeding when urged by the roller holder 150 are provided. The position of the roller pressure F101 is at distances L ₁ ′ and L ₂ ′ from the origin. When the amount of stacked sheets S decreases, as shown in FIG. 6, the lifter 36 is lifted up so that the angle formed with the horizontal direction becomes an angle θ, and the original distances L ₁ ′ and L _{2 are obtained.} ′ Changes to distances L ₁ ″ and L ₂ ″. Here, assuming that the lifter 36 has a length l and a change based on the lift-up operation is added to the original distances L ₁ ′ and L ₂ ′, distances after the operation (for example, the distances L ₁ ″ and L ₂ described above). Therefore, equation (1) can be rewritten as follows.

G × | L ₁ ′ + l × (1-coSθ) |> F101 × {L ₂ ′ −l × (1-coSθ)}
And L ₁ ′ <l × (1-coSθ) (1) ′

  Here, a specific numerical example for the above formula (1) ′ will be described with reference to FIG. FIG. 7 is a graph showing the relationship between the moment MO3 acting on the intermediate plate 35 and the number of fed sheets.

For example, the minimum sheet size that can be set in the paper feed cassette 100 is B5 size (182 mm × 257 mm) (set so that the short side direction is the transport direction), the maximum number of stacked sheets is 500, and the upper limit of the stacking height is 50 mm. Suppose that In addition, the weight of 500 B5-size sheets to be set (the lightest type of available sheets) is 1500 Gf. Then, l = 60 mm, L ₁ ′ = −31 mm, and L ₂ ′ = 20 mm (when the rotation center 36a of the lifter 36 is provided at the same position as the sheet front end position on the X axis), and F101 = 200 Gf. At this time, the relationship between the moment MO3 acting on the intermediate plate 35 and the number of fed sheets is as shown in FIG. 7, and the moment MO3 applied during the sheet feeding operation is always a positive value from 1 sheet to 500 sheets (last sheet). . This indicates that regardless of the number of stacked sheets, the sheet surface height of the stacked sheets is stabilized and the pressing force of the feeding roller 101 on the sheets is stabilized. As a result, a highly reliable feeding operation can be performed.

  As described above, in the present embodiment, first, it is defined by the moment defined by the force G generated at the center of gravity of the sheet S and the feeding roller pressure F101 when the feeding roller 101 presses the upper surface of the sheet S. Find the moment.

  The sum of these moments is made to act on the upstream side of the contact point 36c in the intermediate plate 35 (with respect to the arrow FL that is the feeding direction of the sheet S). This prevents the generation of a force that pushes the rotation fulcrum 35a side upstream of the intermediate plate 35, that is, the contact point 36c in the intermediate plate 35.

  This means that the total sum of the moments applied to the middle plate 35 when the lifter 36 is pushed up by the contact 36c as a support portion is in a position to push the middle plate upstream from the contact 36c. Means.

  Accordingly, the downstream side of the intermediate plate 35 does not rotate so as to descend, and the sheet surface height of the sheets S stacked on the intermediate plate 35 is stabilized, so that the pressing force applied to the sheet S by the feeding roller 101 is increased. It becomes substantially constant, and the sheet can be fed stably.

  Next, a second embodiment of the present invention will be described with reference to FIG.

  FIG. 8 is a diagram illustrating a state of the sheet feeding cassette 100 during sheet feeding of the sheet feeding apparatus 1002 according to the present embodiment. Note that the basic configurations of the image forming apparatus 1 and the sheet feeding apparatus 1002 are the same as those in the first embodiment, and thus the description thereof is omitted, and the same reference numerals as those in FIGS. 3 to 6 are the same or equivalent. The part shall be indicated.

As shown in FIG. 8, in this embodiment, the roller holder 150 that supports the feeding roller 101 is formed longer than that shown in FIGS. As a result, the contact point 101b where the feeding roller 101 and the sheet S are in contact is positioned upstream of the contact point 36c at the tip of the lifter 36 in the sheet S feeding direction. Accordingly, the distance L ₂ on the X-axis from the position of the contact 36c to the contact point 101b which is the origin of the X-axis has a negative value.

Thus, in the sheet feeding cassette 100 shown in FIG. 8, a distance L ₁ and the distance L ₂ to the center of gravity position of the sheet S, irrespective of the number of stacked sheets S, and that apply the following conditional expression Become.

L ₁ <0 and L ₂ <0 (2)

According to the condition of the expression (2), the feeding roller 101 is configured to press against the upper surface of the sheet S between the contact point 36c on which the intermediate plate 35 is supported and the rotation fulcrum 35a on the intermediate plate 35. Will be operated. According to this, it is defined by the contact 36c which is the origin of the X-axis, moment by a force G and the distance L _1, and the sum of the moments by the feeding roller pressure F101 and the distance L _2, in the intermediate plate 35 It will act upstream from the contact 36c. Therefore, in the present embodiment, the moment MO4 applied to the intermediate plate 35 during the sheet S feeding operation is counterclockwise in the drawing. Further, when the sheet is fed in a state where L ₂ > 0 when the rigidity of the intermediate plate 35 is small, the area 35c surrounded by the broken line in the drawing is bent, and the paper surface height becomes unstable. The problem of becoming will be solved.

  As described above, the sheet feeding device and the image forming apparatus according to the present invention are useful for stably feeding a sheet, and in particular, the stability of the sheet feeding operation is continuously required. This is suitable for a sheet feeding apparatus and an image forming apparatus.

1 is a cross-sectional view of a printer as an image forming apparatus to which a sheet feeding apparatus according to a first embodiment is applied. It is a block diagram of FIG. FIG. 4 is a diagram illustrating a sheet feeding cassette during sheet feeding. It is a figure which shows the example of the force added to the paper feed cassette of a feeding operation state. It is a figure which shows the example of the force added to the paper feed cassette before feeding operation. It is a figure which shows the operation example of the lifter in the paper feeding cassette of a feeding operation state. It is a graph which shows the relationship between the moment which acts on a middle board, and the number of paper feed. FIG. 10 is a diagram illustrating a state of a sheet feeding cassette during sheet feeding of a sheet feeding apparatus according to a second embodiment. It is a figure which shows the example of the conventional sheet feeding apparatus. It is a figure which shows the example of the conventional sheet feeding apparatus.

Explanation of symbols

32a Cassette body bottom (cassette bottom)
35 Middle plate 35a Rotation fulcrum 36 Lifter 36c Support part (contact)
100 Feed cassette 101 Feed roller 1002 Sheet feeding device MO2 Sum of moments (moment)
S sheet

Claims (4)

In a sheet feeding device that feeds a sheet from a sheet feeding cassette that stores the sheet,
An intermediate plate provided in the cassette body of the paper feed cassette so as to be rotatable in the vertical direction and stacking sheets;
A feeding roller that is disposed above the middle plate and feeds the sheet by pressing the sheets stacked on the middle plate from above;
A lifter provided between the middle plate and the bottom surface of the cassette body, and pushing up the middle plate from below;
The intermediate plate and the lifter are arranged so that the upward rotation direction of the intermediate plate and the upward rotation direction of the lifter are opposite to each other,
When the sheet is fed, the sum of moments by the force applied to the intermediate plate with respect to the support portion where the lifter abuts on the intermediate plate always acts in a direction to push down the rotation fulcrum of the intermediate plate. A sheet feeding device characterized by the above. The force generated at the center of gravity of the sheets stacked on the intermediate plate is G, the distance from the support portion to the center of gravity is L ₁ , and the force by which the sheets stacked on the intermediate plate are pressed from above by the feeding roller. F, when the distance from the support portion to the position where the feeding roller presses is L ₂ , these G, L ₁ , F, L ₂ are
G × | L ₁ |> F × L ₂ and L ₁ <0
Satisfying the relational expression of
The sheet feeding apparatus according to claim 1. The relational expression is
G × | L ₁ |> F × L ₂ and L ₁ <0 and L ₂ <0
Is,
The sheet feeding apparatus according to claim 2, wherein the sheet feeding apparatus is a sheet feeding apparatus. The sheet feeding device according to any one of claims 1 to 3,
An image forming unit that forms an image on a sheet fed from the sheet feeding device,
An image forming apparatus.

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