Patent Grant
9371204
1. Field of the Invention
The present invention relates to a sheet feeding apparatus provided in an image forming apparatus, such as a copying machine, a facsimile machine, a laser beam printer, or a multifunction peripheral, and an image forming apparatus including the same.
2. Description of the Related Art
In the past, an image forming apparatus, such as a printer or a copying machine, has included a sheet feeding apparatus which separates sheets stacked on a sheet cassette or a sheet tray one by one and fed the separated sheet to an image forming portion. In such a sheet feeding apparatus, various separating methods are employed in a separating portion for separating the sheets one by one. For example, there is known a so-called slope separation method that separates a sheet by buckling a sheet while abutting a front edge of a sheet fed by feeding rollers against a separation slope in a feeding direction (see U.S. Pat. No. 5,622,364).
Recently, in the offices or homes, there has been an increasing demand for using a low-price small-sized printer or copying machine to be installed on a desk in use. In order to achieve this demand, one countermeasure is to further reduce the size and cost of a sheet feeding apparatus provided in a printer or a copying machine.
In a case where the sheet feeding apparatus employing the slope separation method described in Patent Literature 1 is used as the countermeasure, it is also easy to reduce the size of the low-cost apparatus. However, there is a problem that it is difficult to achieve the compatibility between separation performance for a sheet having a low rigidity (weak stiffness) (sheet having a thin thickness) and conveyance performance for a sheet having a high rigidity (strong stiffness) (sheet having a thick thickness) is difficult.
The present invention is directed to provide a sheet feeding apparatus capable of exhibiting stable separation feeding performance in both of a sheet having a low rigidity and a sheet having a high rigidity in a slope separation method, and an image forming apparatus including the sheet feeding apparatus.
According to the present invention, a sheet feeding apparatus includes: a sheet stacking unit on which sheets are stacked; a feeding unit which contacts a top sheet of the sheets stacked on the sheet stacking unit, and feeds the sheet in a sheet feeding direction; a conveying unit which receives the sheet fed by the feeding unit and conveys the sheet in a sheet conveying direction intersecting with the sheet feeding direction; a first separating unit which is disposed between the feeding unit and the conveying unit, and includes a separation slope inclined to be located in downstream in the sheet feeding direction as going to upside, so as to abut against a front edge of the sheet fed by the feeding unit and separate the sheet one by one; and a second separating unit which is disposed between the first separating unit and the feeding unit, and includes a separation nip portion which separates the sheet having passed through the separation slope one by one.
According to the present invention, a sheet feeding apparatus includes: a sheet stacking unit on which sheets are stacked; a feeding unit which contacts a top sheet of the sheets stacked on the sheet stacking unit, and feeds the sheet in a sheet feeding direction; a conveying unit which receives the sheet fed by the feeding unit and conveys the sheet in a sheet conveying direction intersecting with the sheet feeding direction; a separation slope which is disposed between the feeding unit and the conveying unit and is inclined to be located in downstream in the sheet feeding direction as going to upside, so as to abut against a front edge of the sheet fed by the feeding unit and separate the sheet one by one; a friction member which is disposed on the separation slope in a center of a width direction perpendicular to the sheet feeding direction, the sheet slidably contacting the friction member; an opposite member which is disposed to face the friction member; and a biasing unit which biases one of the friction member and the opposite member against the other.
According to the present invention, it is possible to exhibit stable separation feeding performance in both of a thin sheet having a low rigidity and a sheet having a high rigidity in a slope separation method.
Further features of the present invention will become apparent from the following description of exemplary embodiments with reference to the attached drawings.
Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. Also, the shapes and relative arrangements of components set forth in the embodiments may be appropriately changed according to configurations or various conditions of apparatuses to which the present invention is applied, and the scope of the present invention is not intended to be limited to the following embodiments.
First, an overall configuration of an image forming apparatus 100 equipped with a sheet feeding apparatus 1 according to a first embodiment of the present invention will be described with reference to
As illustrated in
The sheet feeding apparatus 1 includes a feeding roller 6 as a feeding unit which contacts a top sheet Sa of the sheets stacked on the sheet tray 2 and feeds the sheet in a sheet feeding direction (direction of an arrow D). Furthermore, the sheet feeding apparatus 1 includes a pair of intermediate conveying rollers 23 as a conveying unit which receives the sheet fed by the feeding roller 6 and feeds the sheet along a sheet conveying direction (direction of an arrow E) intersecting with the sheet feeding direction D. The sheet bundle S stacked on the sheet tray 2 is fed while being separated sheet by sheet by the feeding roller 6, a separation slope 10a of a fixed slope portion 10, and a sheet separation member 3, and is fed to a sheet conveyance path 24 within the apparatus body 100a.
The pair of intermediate conveying rollers 23 is disposed in the middle of the sheet conveyance path 24 within the apparatus body 100a, and the sheet S is conveyed toward an image forming portion 21 of downstream by the pair of intermediate conveying rollers 23. In an image formation by the image forming portion 21, a laser beam is irradiated on a photosensitive drum 21a as a previously-charged image bearing member from a laser exposure device 20 according to image information, and an electrostatic latent image is written on the photosensitive drum 21a. When the electrostatic latent image is formed on the photosensitive drum 21a, a toner is attached to the electrostatic latent image and developed by a development device (not illustrated), and the electrostatic latent image is visualized as a toner image.
In the image forming portion 21, a transfer roller 21b disposed to face the photosensitive drum 21a is pressed to configure a primary transfer portion. In the image forming portion 21, when the sheet S passes through a transfer nip portion between the photosensitive drum 21a and the transfer roller 21b, the toner image on the surface of the photosensitive drum 21a is transferred on the sheet S.
In downstream of the image forming portion 21 in the sheet conveyance path 24, a fixing device 22 is provided which includes a heating roller 22a and a pressure roller 22b disposed to face the heating roller 22a and pressed thereto. When the sheet S after the transfer of the toner image passes through a fixing nip portion between the heating roller 22a and the pressure roller 22b, the fixing device 22 fixes the toner image on the sheet S as an image. The image forming portion 21 as described above forms the image on the sheet S, which is fed by the sheet feeding apparatus 1, by the laser exposure device 20, the primary transfer portion configured by the photosensitive drum 21a and the transfer roller 21b, and the fixing device 22.
Then, the sheet S after the image fixation is conveyed more downstream, and the pair of discharge rollers 26 discharges the image plane downwards (facedown) to a discharge tray 27 formed on the upper surface of the apparatus body 100a.
Next, the configuration of the sheet feeding apparatus 1 provided in the apparatus body 100a will be described in detail. Incidentally,
In the sheet tray 2 in which the sheets S are stacked and set, width regulating portions 11a and 11b are disposed to be movable in a width direction. The width regulating portions 11a and 11b regulate a position of a sheet width direction (width direction, horizontal direction of
The feeding roller 6 is disposed above the downstream of the sheet feeding direction in the sheet tray 2. The feeding roller 6 is rotatably held to a pivot frame 8 that is pivotally supported in a vertical direction (direction of an arrow C of
One end of the pivot shaft 7 supports upstream of the sheet feeding direction of the pivot frame 8, and the other end of the pivot shaft 7 extending in a direction vertically separated from the pivot frame 8 is supported to a support frame 28 (see
Since the driving force of the drive motor is transmitted through the drive transmission mechanism, the feeding roller 6 rotates clockwise in
A feeding unit is provided with the feeding roller 6 which feeds the sheet S by rotating while abutting against the sheet S stacked on the sheet tray 2, and the pivot frame 8 which is pivotally provided to support the feeding roller 6. In the feeding unit, when an amount of stacked sheets S is reduced, the feeding roller 6 moves downward so that the abutting against the sheet S is maintained.
Next, the configuration of the portion which mainly separates the sheet in the sheet feeding apparatus 1 according to the present embodiment will be described with reference to
As illustrated in
The sheet separation member 3 is pivotally supported around the pivot point 3A as a supporting point, the pivot point 3A being provided downstream in the inside of the notch portion 10c, and a force is applied toward an opposite member 5 by a compression spring 4 as a biasing unit which is provided in a compressed state between a rear portion 10b of the inside and a rear surface of the sheet separation member 3. In this manner, a friction member 3B attached on the sheet separation member 3 is pressed against the opposite member 5 to constitute a separation nip portion n. In the present embodiment, the friction member 3B is biased against the opposite member 5 by the compression spring, but this relationship may be reversed. The opposite member 5 may be configured to be biased against the friction member 3B by the compression spring (not illustrated). The opposite member 5 has a curved surface 5a which guides the fed sheet S by sliding contact. Paths, through which the sheet can pass, are provided between the separation slope 10a and the opposite member 5 and between the sheet separation member 3 and the opposite member 5.
Therefore, the sheet separation member 3 is biased by the compression spring 4 which is movable to a protruding position (position of
Incidentally, the fixed slope portion 10 is disposed between the feeding roller 6 and the pair of intermediate conveying rollers 23 and configures a first separating unit having a separation slope 10a. Also, the sheet separation member 3, the opposite member 5, and the compression spring 4 are disposed between the fixed slope portion 10 and the pair of intermediate conveying rollers 23 and configure a second separating unit having the separation nip portion n which separates the sheet S having passed through the separation slope 10a one by one.
In the present embodiment, the sheet separation member 3 is biased against the opposite member 5 by the compression spring 4, but this relationship is not limited thereto. The opposite member 5 may be configured to be biased against the sheet separation member 3 by the biasing unit instead of the compression spring 4. Alternatively, the sheet separation member 3 and the opposite member 5 may be configured to abut against each other by the biasing unit.
The opposite member 5 is located on an opposite side of the sheet separation member 3 which is fixedly held to the support frame 28 (
Subsequently, a principle of separating the sheet S by the slope and feeding the separated sheet S will be described with reference to
That is, as illustrated in
On the other hand, when a friction coefficient between the top sheet Sa and a second sheet Sb is μp, the top sheet Sa receives a resistance force Rr1 (=μp·N) by the second sheet Sb, and thus, a conveyance force Fr1 generated in the top sheet Sa is expressed as Equation (1) below.
Fr1=Fr−Rr1=(μR−μp)N (1)
When the top sheet Sa is conveyed by the conveyance force Fr1 generated in the top sheet Sa, the front edge in the sheet feeding direction abuts against the separation slope 10a, and a conveyance resistance P1 generated in the top sheet is generated in a direction substantially horizontal to the sheet. Due to the resistance, a conveyance resistance P is generated in a direction substantially horizontal to the feeding roller 6.
When a plurality of sheets is taken out, the conveyance resistance P generated in the feeding roller 6 is the sum of conveyance resistances generated in the respective sheets. In the configuration of the feeding roller 6 according to the present embodiment, the feeding pressure N is changed according to the magnitude of the conveyance resistance P generated in the feeding roller 6.
Herein, the relationship between the conveyance resistance P and the feeding pressure N generated in the feeding roller 6 will be described below.
As illustrated in the graph of
Finally, when the conveyance force Fr1 generated in the top sheet Sa reaches a sheet buckling force Pz, the sheet is fed in a manner such that the front edge of the sheet buckles and gets on the separation slope 10a.
Subsequently, when a friction coefficient between the second sheet Sb and a third sheet Sc is μp′, the conveyance force Fr2 generated in the second sheet Sb is given as illustrated in
Fr2=FSa−Rr2=(μp−μp′)N (2)
In order not to cause a double feed, the conveyance force Fr2 generated in the second sheet Sb must not reach the sheet buckling force Pz. However, in the past, in the case of a sheet having a low rigidity (weak stiffness), such as a thin sheet, a sheet buckling force Pz is remarkably small, and the sheet easily gets on the slope portion with a small conveyance force even when the sheet is curled. Therefore, it is difficult to prevent a double feed.
The feature of the present invention, that is, the principle of separating a plurality of sheets in the separation nip portion n between the sheet separation member 3 and the opposite member 5, will be described below with reference to
For example, when two sheets are conveyed across the separation slope 10a in an overlapped state, the two sheets enter the separation nip portion n between the sheet separation member 3 and the opposite member 5, and a resistance force R is generated with respect to the two sheets. That is, the resistance force R acting on the sheet is the sum of a resistance force R1 acting on the top sheet Sa and a resistance force R2 acting on the second sheet Sb (R=R1+R2).
Also, the resistance force R acting on the sheet gives a force against the sheet feeding direction of the feeding roller 6, and the conveyance resistance P generated in the feeding roller 6 at that time has the same value as the resistance force R acting on the sheet (P=R).
In each of the sheets, since the front edge in the sheet feeding direction abuts against the friction member 3B attached to the sheet separation member 3, a resistance force R′ the sheet receives from the friction member 3B is generated. The sheet is conveyed while receiving the resistance force R′ received from the friction member 3B in the front edge in the feeding direction, and the top sheet Sa is conveyed separately from the second sheet Sb.
Herein, it is assumed that a friction coefficient between the opposite member 5 and the sheet is μs1, and an acting force of the compression spring 4 is Fsp. In this case, when two sheets enter the separation nip portion n, the resistance force R1 acting on the top sheet Sa and the resistance force R2 acting on the second sheet Sb can be expressed as Equations (3) and (4) below.
R1=R′+(μs1+μp)Fsp (3)
R2=R′−μp·Fsp (4)
In order to separately convey the two sheets, the conveyance force Fr1 generated in the top sheet Sa needs to exceed the value of the resistance force R1 acting on the top sheet Sa, and the conveyance force Fr2 generated in the second sheet Sb needs to be lower than the value of the resistance force R2 acting on the second sheet Sb. The above condition is expressed as Inequality below.
(Non-feed prevention condition)Fr1=(μR−μp)N>R′+(μs1+μp)Fsp
(Double-feed prevention condition)Fr2=(μp−μp′)N<R′−μp·Fsp
Herein, in a condition that the friction coefficient of the friction member 3B is 0.8, the acting force Fsp of the compression spring 4 is 150 gf (≈1.47 N (Newton)), and the angle of the sheet separation member 3 with respect to the horizontal direction is 70°, the sheet is fed in a state in which the front edge in the feeding direction of various sheets abuts against the friction member 3B. In this case, the measurement result of the resistance force R′ the sheet receives from the friction member 3B is illustrated in
In
The front edge of the sheet is conveyed over the friction member 3B at the moment when a resistance force of a thin sheet (basis weight 60 g/m2) becomes 240 gf (≈2.35 N), a resistance force of a plain sheet (basis weight 80 g/m2) becomes 280 gf (≈2.74 N), and a resistance force of a thick sheet (basis weight 160 g/m2) becomes 510 gf (≈5.00 N).
Whether the thin sheet can be separately conveyed is verified using the above calculation formula. The resistance force R′ the sheet receives from the friction member 3B is verified on the assumption that the resistance force of the thin sheet in
Also, the values of the above friction coefficients are set based on a value of a friction coefficient of a rubber roller usually used as the feeding roller of the image forming apparatus, or a value of a friction coefficient of a sheet frequently used, such as a so-called plain sheet.
In this case, the resistance force R1 acting on the top sheet Sa is 345 gf (≈3.38 N (Newton)), and the resistance force R2 acting on the second sheet Sb is 150 gf (≈1.47 N). Since the resistance force R acting on the sheet is the sum of these resistance forces, the resistance force R acting on the sheet is 495 gf (≈4.85 N), and the conveyance resistance P generated in the feeding roller 6 is also 495 gf (≈4.85 N).
Since the slope of the straight line in
Therefore, the conveyance force Fr1=579.2 gf generated in the top sheet Sa exceeds the resistance force R1=345 gf acting on the top sheet Sa. Also, since the conveyance force Fr2 (=128.7 gf) generated in the second sheet Sb is lower than the resistance force R2 (=150 gf) acting on the second sheet Sb, the sheet can be separately conveyed by the separation nip portion n.
Subsequently, a case where one sheet enters the separation nip portion n will be described with reference to
R1=R′+μs1·Fsp (5)
Herein, since the resistance force R acting on the sheet is only the resistance force R1 acting on the top sheet Sa, the resistance force R have the same value as the resistance force R1 (R=R1). In order to convey the sheet without jamming (conveyance failure) in the separation nip portion n, the conveyance force Fr1 generated in the top sheet Sa needs to exceed the value of the resistance force R acting on the sheet. The above condition is expressed as Inequality below.
(Non-feed prevention condition)Fr1=(μR−μp)N>R′−μs1·Fsp
Herein, in the same manner as the above-described condition, it is assumed that the resistance force R′ the sheet receives from the friction member 3B is 240 gf (≈2.35 N (Newton)), the friction coefficient μs1 between the opposite member 5 and the sheet is 0.1, and the acting force Fsp of the compression spring 4 is 150 gf (≈1.47 N). Also, on the assumption that the friction coefficient μR between the feeding roller 6 and the sheet is 1.5 and the friction coefficient μp between the top sheet Sa and the second sheet Sb is 0.6, a case where one thin sheet enters the separation nip portion n will be considered.
In this case, the resistance force R acting on the sheet is 255 gf (≈2.50 N), and the conveyance resistance P generated in the feeding roller 6 is also 255 gf.
Since the slope of the straight line in
Also, whether the thick sheet also can be conveyed without jamming in the separation nip portion n is verified.
It is assumed that the resistance force R′ the sheet receives from the friction member 3B is 510 gf (≈5.00 N) in the thick sheet of
Since the slope of the straight line in
Since the present embodiment is configured such that the feeding pressure N is changed according to the magnitude of the conveyance resistance P generated in the feeding roller 6, it is possible to change the feeding pressure N according to the magnitude of the sheet rigidity and to convey a wide variety of sheets.
In the sheet feeding apparatus 1 according to the present embodiment, the feeding roller 6 is configured to change the feeding pressure N according to the magnitude of the sheet conveyance resistance. Therefore, it is also possible to convey a sheet having a high rigidity, such as a thick sheet. Also, in a case where a plurality of sheets having a low rigidity, such as thin sheets, is simultaneously buckled and conveyed over the separation slope 10a, the sheet can be loosened in the separation nip portion n between the sheet separation member 3 and the opposite member 5. Therefore, it is possible to exhibit stable separation performance with respect to a wide variety of sheets.
According to the present embodiment described above, due to the separation member biased by the biasing unit and the opposite member disposed to contact the opposite position of the separation member, it is possible to obtain the effect of loosening the sheet in the separation nip portion between the separation member and the opposite member. Therefore, it is possible to obtain stable separation performance with respect to a wide variety of sheets, while achieving space saving and low-cost configuration.
That is, a thick sheet having a strong stiffness can be securely buckled at a value less than a set upper limit of the feeding pressure. Even when a plurality of sheets is buckled and conveyed over the separation slope, a thin sheet having a weak stiffness can be loosened in the separation nip portion n between the separation member separately provided and the opposite member disposed to face and contact the separation member.
Also, in the present embodiment, the opposite member 5 nipping the sheet with the sheet separation member 3 is provided as a fixed member, but is not limited thereto. That is, for example, as in a first modification illustrated in
Next, a sheet feeding apparatus 1 according to a second embodiment of the present invention will be described below with reference to
The present embodiment differs from the first embodiment in that the present embodiment further includes a separation member holder 9 which rotatably (pivotally) holds the sheet separation member 3. Also, the separation member holder 9 and the opposite member 5 are integrally movable in parallel to the separation slope 10a of the fixed slope portion 10, and the position of the separation nip portion n between the sheet separation member 3 and the opposite member 5 is movable.
In conjunction with the opposite member 5, the separation member holder 9 is provided to be movable in a vertical direction of the drawing, along a slide surface A continuously formed in the fixed slope portion 10 and the sheet tray 2, by a driving of a slide motor 30. In support portions 34 provided at both ends of the fixed slope portion 10 (only the right support portion is illustrated in
Next, the slide operation of the separation nip portion n will be described below with reference to
Above a sheet holding surface 2a of the sheet tray 2, a sheet surface detection lever 13 which detects a sheet surface position is vertically pivotally supported to the opposite member 5, with a rotation center 13a as a supporting point.
In the opposite member 5 which is integrally vertically movable with the separation member holder 9, a detection lever sensor 14 is disposed at a position where a rotation angle of the sheet surface detection lever 13 can be detected at the top of the sheet surface detection lever 13. The detection lever sensor 14 is provided with, for example, a transmission-type optical sensor such as a photo interrupter. The detection lever sensor 14 includes a light emitting portion 14a and a light receiving portion (not illustrated), and outputs a detection signal according to open and closed states of an optical path between the light emitting portion 14a and the light receiving portion. In
L1 is a vertical distance from the front edge of the top sheet Sa in the feeding direction in the state of
When the amount of the stacked sheets is smaller than a certain predetermined amount, as illustrated in
When the opposite member 5 moves downward, the sheet surface detection lever 13, the bottom portion of which abuts against the top surface of the sheet bundle S, is rotated clockwise. Thus, as illustrated in
A vertical distance L2 from the front edge of the top sheet Sa in the feeding direction in the state of
In the present embodiment described above, one of the second separating unit and the sheet stacking unit is movably supported to the other. That is, the sheet separation member 3 and the opposite member 5 as the second separating unit are movably supported to the sheet tray 2 as the sheet stacking unit. The controller 29 moves (lowers) the second separating unit toward the sheet tray 2 based on a reduced amount of sheets S on the sheet tray 2 (on the sheet stacking unit) with respect to the second separating units (3, 5). Therefore, the distances L1 and L2 between the top sheet Sa on the sheet tray and the separation nip portion n are substantially constantly maintained.
Thus, a variation in the position of the top sheet Sa of the sheet bundle according to the feeding can be detected by the sheet surface detection lever 13 and the detection lever sensor 14, and the vertical position of the separation nip portion n can be moved in parallel along the separation slope 10a according to the variation. Therefore, the vertical distance from the front edge of the top sheet Sa in the feeding direction to the separation nip portion n can be considered to be substantially constant without regard to the amount of the stacked sheets.
In the present embodiment, the above configuration can always stabilize the posture of the front edge of the sheet at the time of the entry into the separation nip portion n, and can separate and feed the sheet more stably from a fully stacked state to a slightly stacked state.
Next, a sheet feeding apparatus 1 according to a third embodiment of the present invention will be described below with reference to
The sheet support portion 16 as a sheet stacking unit is held to be rotated by a driving of a motor 31 based on control of a controller 29 provided in an apparatus body 100a. When a rotation angle of a pivot frame 8 exceeds a certain predetermined range, it is detected by a pivot frame sensor 15 being a transmission-type optical sensor. The controller 29 as a control unit controls a driving of the motor 31 based on a detection signal output the pivot frame sensor 15. Also, as in the first embodiment, the pivot frame 8 is rotatably supported by a pivot shaft 7.
The pivot frame sensor 15 can be provided with, for example, a transmission-type optical sensor such as a photo interrupter. In this configuration, the pivot frame sensor 15 includes a light emitting portion 15a and a light receiving portion (not illustrated), and outputs a detection signal according to opening or blocking of an optical path between the light emitting portion 15a and the light receiving portion by a shielding portion 8a protruding from a front edge upper portion of the pivot frame 8. In
The controller 29 controls the motor 31 based on the detection signal of the pivot frame sensor 15, such that the sheet support portion 16 is rotated around the rotation center 16a as the supporting point. Therefore, a top sheet Sa is always located within a constant height direction range without regard to a stacked amount of a sheet bundle S.
Since the top sheet Sa can be disposed at the same position by the sheet support portion 16, without regard to the stacked amount, the distance from a buckling point of the sheet to the separation nip portion n can be always constantly maintained. Therefore, it is possible to stabilize the behavior of the front edge of the sheet at the time of the entry into the nip portion.
Also, by maintaining the constant position of the top sheet Sa, a variation in an abutting angle of the pivot frame 8 against the top sheet Sa at the time of starting the feeding operation by a variation in the amount of the stacked sheets can be kept within a small range. Therefore, it is possible to minimize a variation in the feeding pressure N due to the amount of the stacked sheets and to more stably separate and feed the sheets from a state in which sheets are slightly stacked to a state in which sheets are fully stacked.
Subsequently, the principle of separating and conveying the sheets by the separation slope 10a according to the present embodiment will be described below with reference to
As illustrated in
On the other hand, when a friction coefficient between the top sheet Sa and a second sheet Sb is μp, the top sheet Sa receives a resistance force Rr1=μp·N by the second sheet Sb, and thus, a conveyance force Fr1 generated in the top sheet Sa is expressed as Equation (6) below.
Fr1=Fr−Rr1=(μR−μp)N (6)
When the top sheet Sa is conveyed by the conveyance force Fr1 generated in the top sheet Sa, the front edge in the sheet feeding direction abuts against the separation slope 10a, and a conveyance resistance P1 is generated in a direction substantially horizontal to the top sheet Sa. Due to the conveyance resistance P1, a conveyance resistance P is also generated in a direction substantially horizontal to the feeding roller 6.
When the feeding pressure N is increased by the conveyance resistance P generated in the feeding roller 6, the conveyance force Fr1 generated in the top sheet Sa is increased, and the conveyance resistance P1 generated in the top sheet Sa is also increased against the conveyance force Fr1. Finally, when the conveyance force Fr1 generated in the top sheet Sa reaches a sheet buckling force Pz, the sheet is fed in a manner such that the front edge of the sheet buckles and gets on the separation slope 10a.
When a friction coefficient between the second sheet Sb and a third sheet Sc is μp′, a conveyance force Fr2 generated in the second sheet Sb is as follows. That is, as illustrated in
Fr2=FSa−Rr2=(μp−μp′)N (7)
Next, the principle of separating a plurality of sheets in the separation nip portion n between the sheet separation member 3 and the opposite member 5 will be described below with reference to
For example, when two sheets are conveyed across the separation slope 10a in an overlapped state, the two sheets enter the separation nip portion n, and a resistance force R acting on the sheet is generated. The resistance force R acting on the sheet is the sum of a resistance force R1 acting on the top sheet Sa and a resistance force R2 acting on the second sheet Sb (R=R1+R2). Also, since the feeding roller 6 also receives a resistance having the same magnitude as the resistance force R acting on the sheet, the conveyance resistance P generated in the feeding roller 6 has the same value as the resistance force R acting on the sheet (P=R).
In each of the sheets, since the front edge (downstream end) in the sheet feeding direction abuts against the friction member 3B attached to the sheet separation member 3, a resistance force R′ received from the friction member 3B is generated. The front edge in the sheet feeding direction is conveyed while receiving the resistance force R′ received from the friction member 3B, and the top sheet Sa is conveyed separately from the second sheet Sb.
It is assumed that a friction coefficient between the opposite member 5 and the sheet is μs1, and an acting force of the compression spring 4 is Fsp. In this case, when two sheets enter the separation nip portion n, the resistance force R1 acting on the top sheet Sa and the resistance force R2 acting on the second sheet Sb can be expressed as Equations (8) and (9) below.
R1=R′+(μs1+μp)Fsp (8)
R2=R′−μp·Fsp (9)
In order to separately convey the two sheets, the conveyance force Fr1 generated in the top sheet Sa needs to exceed the value of the resistance force R1 acting on the top sheet Sa, and the conveyance force Fr2 generated in the second sheet Sb needs to be lower than the value of the resistance force R2 acting on the second sheet Sb. The above condition is expressed as Inequality below.
(Non-feed prevention condition)Fr1=(μR−μp)N>R′+(μs1+μp)Fsp
(Double-feed prevention condition)Fr2=(μp−μp′)N<R′−μp·Fsp
Subsequently, a case where one sheet enters the separation nip portion n will be described with reference to
R1=R′+μs1·Fsp (10)
Herein, since the resistance force R acting on the sheet is only the resistance force R1 acting on the top sheet Sa, the resistance force R have the same value as the resistance force R1 (R=R1). In order to convey the sheet without jamming in the separation nip portion n, the conveyance force Fr1 generated in the top sheet Sa needs to exceed the value of the resistance force R acting on the sheet. The above condition is expressed as Inequality below.
(Non-feed prevention condition)Fr1=(μR−μp)N>R′−μs1·Fsp
Since the above-described separating principle of the present embodiment is similar to that of the first embodiment, it can be seen that the separation conveyance is theoretically possible.
In the present embodiment described above, a sheet support portion 16 as a sheet stacking unit is movably supported to the sheet separation member 3 and the opposite member 5 as a second separating unit. The feeding roller 6 as a feeding unit is movably supported by following the movement of the sheet support portion 16 in a state of abutting against the sheet S on the sheet support portion 16. The controller 29 lifts the sheet support portion 16 together with the feeding roller 6, based on a moving amount of the feeding roller 6 lowered by following the reduction of the sheets S on the sheet support portion. Therefore, the distance between the top sheet Sa on the sheet support portion 16 and the separation nip portion n is substantially constantly held.
In the present embodiment, as compared with the first embodiment, it is possible to constantly maintain a distance between the buckling point of the sheet and the separation nip portion n on the separation slope 10a, without regard to the stacked amount of the sheet bundle, and it is possible to stabilize the behavior of the front edge of the sheet at the time of the entry into the separation nip portion n. Therefore, a better separation conveyance can be obtained. Also, since it is possible to minimize a variation in the feeding pressure N due to the amount of the stacked sheets, the sheet can be more stably fed.
Also, in the third embodiment, the motor 31 is used as a unit which pivotally rotates the sheet support portion 16, but the unit is not limited thereto. For example, as illustrated in a second modification of
Also, in the present embodiment, the sheet is buckled and separated in a manner such that the front edge of the top sheet Sa in the sheet feeding direction abuts against the separation slope 10a. However, for example, as illustrated in a third modification of
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 modifications, equivalent structures and functions.
This application claims the benefit of Japanese Patent Application No. 2013-003900, filed Jan. 11, 2013, which is hereby incorporated by reference herein in its entirety.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2013-003900 | Jan 2013 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5377970 | Kikuchi | Jan 1995 | A |
| 5622364 | Dutton et al. | Apr 1997 | A |
| 5823524 | Kawada | Oct 1998 | A |
| 7055818 | Furusawa | Jun 2006 | B2 |
| 7976014 | Kobayashi | Jul 2011 | B2 |
| 8439358 | Watanabe et al. | May 2013 | B2 |
| 8682240 | Fukita et al. | Mar 2014 | B2 |
| 8740215 | Watanabe et al. | Jun 2014 | B2 |
| 9073714 | Kim | Jul 2015 | B2 |
| 20060180989 | Seike | Aug 2006 | A1 |
| 20080122162 | Bokelman | May 2008 | A1 |
| 20080309000 | Tu | Dec 2008 | A1 |
| 20090026693 | Lim | Jan 2009 | A1 |
| 20110156340 | Otsuki | Jun 2011 | A1 |
| 20120080836 | Morisaki | Apr 2012 | A1 |
| 20120080838 | Osada | Apr 2012 | A1 |
| 20130142561 | Kim | Jun 2013 | A1 |
| Number | Date | Country |
|---|---|---|
| 1621097 | Oct 1997 | AU |
| 711844 | Oct 2013 | AU |
| 0798248 | Mar 1997 | EP |
| 0798248 | Oct 1997 | EP |
| 0798248 | Oct 1997 | EP |
| 05162876 | Jun 1993 | JP |
| 10-72142 | Mar 1998 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20140197591 A1 | Jul 2014 | US |
