JP3598684B2 - Paper feed mechanism of image forming apparatus - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to a paper feeding mechanism of an image forming apparatus that feeds paper such as an electrophotographic apparatus as an image forming apparatus, a printer, a copier, a facsimile, and the like.
[0002]
[Prior art]
Among the many paper feeding methods used in the paper feeding mechanism of the image forming apparatus, there is a method using a half-moon-shaped paper feeding roll as one of relatively simple and inexpensive structures. In such a paper feeding mechanism using a half-moon-shaped paper feeding roll, a paper loading plate that slides in the vertical direction is moved up and down by an elevating mechanism to apply paper feeding pressure to the paper.
[0003]
Thus, the uppermost sheet is pressed against the half-moon-shaped paper feed roll. By rotating the paper feed roll, a frictional force is generated between the paper feed roll and the uppermost sheet in the paper feeding direction, and the paper is fed between the uppermost sheet and the next sheet below this sheet. A friction force is generated in the direction opposite to the paper direction. Here, if the frictional force between the paper feed roll and the uppermost sheet is made larger than the frictional force between the uppermost sheet and the sheet located below the sheet, the sheets are sequentially fed. .
[0004]
The conventional paper feeding mechanism is provided with a lever provided with a separation claw in order to prevent double feeding (feeding of the lowermost sheet together with the uppermost sheet) at the time of sheet feeding. There is something. Further, in the conventional paper feeding mechanism, an over-elevation prevention mechanism for limiting the upper limit position of the paper in the vertical direction when paper is not fed (when paper is not fed) is arranged. As the over-elevation prevention mechanism, for example, there is a system in which the above-mentioned separation claw is disposed, and this separation claw also serves as an over-elevation prevention mechanism.
[0005]
That is, the over-elevation prevention mechanism restricts the upper limit position of the separation claw by providing a locking projection on the lever, providing a stopper on the apparatus body side, and locking the locking projection to the stopper. However, in such a mechanism, when the paper supply roll rotates until the paper is separated from the uppermost layer paper during paper supply, the locking projection provided on the lever collides with the stopper provided on the apparatus main body side, The impact noise caused noise.
[0006]
As a mechanism for preventing an impact sound that causes noise during paper feeding, for example, there is a method using a circular ring 80 as shown in FIG. 8 (Japanese Patent Laid-Open No. 8-133504).
[0007]
In the paper feed mechanism of this image forming apparatus, a half-moon-shaped paper feed roll 82 and a lever 84 are arranged. The lever 84 has a separation claw 84A. The sheet stacking plate 85 on which sheets are stacked is urged upward by a spring member (not shown).
[0008]
When the paper feed roll 82 rotates, the paper stacking plate 85 is urged upward by a spring member, so that the uppermost paper 86 abutting on the paper feed roll 82 is fed in the paper feeding direction (the direction of arrow FW in FIG. 8) by frictional force. Is fed to
[0009]
Further, when the cutout portion 82A of the paper feed roll 82 faces the paper 86, the paper 86 comes into contact with the circular ring 80, so that the member of the lever 84 does not collide with a hard part, thereby preventing the generation of an impact sound. Is done.
[0010]
[Problems to be solved by the invention]
If the circular ring 80 is not used, the next sheet other than the uppermost layer is prevented from being fed (double feed) by the separating operation of the lever 84 (separating claw 84A), and only one sheet 86 of the uppermost layer is fed. The paper is fed, and the rotation of the paper feed roll 82 ends. When the paper feed roll 82 is separated from the uppermost sheet 86, the uppermost sheet 86 is conveyed by a roll (not shown) arranged on the downstream side, and the other next sheets no longer receive a conveying force (frictional force). Although it returns in the direction opposite to the sheet feeding direction (the direction of arrow RW in FIG. 8) due to the elastic force of the sheet 86 itself (the force for returning the sheet 86 bent by the sheet feeding roller 82 to the original state), the circular ring 80 is used. Is pressed against the uppermost sheet 86, the next sheet 86 other than the uppermost layer cannot return in the direction opposite to the sheet feeding direction, is gradually pressed against the separation claw 84A of the lever 84, and finally the heavy Cause transmission. Further, there is a problem in that the frictional resistance between the sheets when the sheet supply roller 82 is not rotating causes double feeding, thereby impairing the transportability of the sheets 86.
[0011]
In view of the above, it is an object of the present invention to provide a sheet feeding mechanism of an image forming apparatus that prevents the generation of an impact sound at the time of sheet feeding without impairing sheet transportability.
[0012]
[Means for Solving the Problems]
The paper feed mechanism of the image forming apparatus according to claim 1, wherein the urging means for urging the stacked plurality of supply sheets with an urging force, and a rotating shaft facing one surface of the outermost layer sheet, A substantially half-moon-shaped paper feed roll that rotates under the driving force and feeds the outermost layer paper by frictional force, and a positioning mechanism that positions the outermost layer paper urged by the urging means when paper is not fed, It is rotatably disposed on opposite vital axis on one surface of the outermost layer of the sheet, a large-diameter portion and a small diameter portion of the small diameter provided at different positions around the axis than the large diameter portion, in the sheet feeding roll After the paper is fed, the large-diameter portion presses the uppermost paper and has a cam that moderately raises the positioning mechanism .
[0013]
In the sheet feeding mechanism of the image forming apparatus according to the first aspect, the plurality of supply sheets stacked by the urging unit are pushed up, for example, upward. The paper feed roll rotates by receiving the driving force, and the paper feed roll sends out the outermost layer (uppermost layer) by frictional force. Immediately after the end of the feeding, the large-diameter portion of the cam comes into pressure contact with the uppermost sheet of paper, so that the elevation of the positioning mechanism is moderated . Therefore, it is possible to prevent an impact between the hard portions of the positioning mechanism, thereby preventing the generation of an impact sound.
[0014]
Further, in the paper feed mechanism of the image forming apparatus according to the first aspect, the paper is conveyed and the cam rotates after the paper feed roll sends out the uppermost paper. When the small diameter portion of the cam faces one surface of the uppermost sheet, the position of one surface of the uppermost sheet is determined by the positioning mechanism. Therefore, during the conveyance of the sheet, the small-diameter portion of the cam is kept separated from the uppermost sheet, and the cam is in contact only with the uppermost sheet.
[0015]
Therefore, according to the paper feeding mechanism of the image forming apparatus of the present invention, the urging force of the urging means does not act on the small diameter portion of the cam during the conveyance of the sheet, and the conveyance resistance of the sheet during the conveyance does not occur. Further, according to the paper feeding mechanism of the image forming apparatus according to the first aspect, the next sheet located below the uppermost sheet can return (return to a predetermined position) in the direction opposite to the transport direction. Double feed is prevented without impairing the transportability of the paper.
[0016]
Sheet feeding mechanism of the image forming apparatus according to claim 2 is provided with a sheet stacking plate for stacking the paper before Symbol one by one image forming unit a plurality of sheets stacked on said sheet stacking plate by sheet feed roller An engaging portion and a separation claw that feed paper and have at least one cam coaxial with the feed roll, and the positioning mechanism also has an over-raising prevention function of limiting an upper limit position of the paper in the vertical direction. And a locking portion for locking the engaging portion.
[0017]
In the paper feed mechanism of the image forming apparatus according to the second aspect, the upper limit position of the outermost layer of the paper in the vertical direction is limited by the engaging portion and the locking portion which also have the function of preventing excessive rise.
[0018]
According to a third aspect of the present invention, the center of gravity of the cam is located substantially on a line connecting the axis of the cam and the maximum radius of the cam.
[0019]
In the paper feed mechanism of the image forming apparatus according to the third aspect, immediately after the paper feed roll feeds the uppermost sheet, the cam rotates by its own weight, and the large diameter portion of the cam presses against the upper surface of the uppermost sheet. I do.
[0020]
According to a fourth aspect of the present invention, the outer diameter of the cam is gradually reduced from the maximum radius.
[0021]
In the paper feed mechanism of the image forming apparatus according to the fourth aspect, when the paper feed roll starts feeding paper and the paper feed roll rotates until it is separated from the uppermost layer of paper, the cam is pressed and the paper is rotated with the rotation of the cam. It rises gently, so that the rigid parts of the positioning mechanism come into gentle contact with each other, so that the impact is buffered.
[0022]
Further, in the paper feed mechanism of the image forming apparatus according to the present invention, since the cam is gradually pressed against the paper, the impact while the cam is interlocked with the movement of the paper is suppressed, and the image is stably formed. It is formed.
[0023]
The paper feeding mechanism of the image forming apparatus according to claim 5, wherein a maximum radius of the paper feeding roll is equal to a maximum radius of the cam, or a maximum radius of the paper feeding roll is longer than a maximum radius of the cam. Is longer than the distance from one surface of the outermost sheet of paper positioned by the positioning mechanism to the center of rotation of the cam, and the distance from one surface of the sheet of the outermost layer to the center of rotation of the cam is greater than the distance of the cam. It is characterized by being longer than the minimum radius.
[0024]
In the paper feed mechanism of the image forming apparatus according to the present invention, the maximum radius of the paper feed roll and the maximum radius of the cam are the same, or the maximum radius of the paper feed roll is longer than the maximum radius of the cam. The cam rotates without any trouble while the paper roll is feeding the top layer paper. Further, since the maximum radius of the cam is longer than the distance from the upper surface of the uppermost sheet of paper positioned by the positioning mechanism to the rotation center of the cam, the cam immediately after the paper feed roll has sent out the uppermost sheet of paper. The large-diameter portion is pressed against the uppermost sheet of paper. Further, since the distance from the upper surface of the uppermost sheet to the rotation center of the cam is longer than the minimum radius of the cam, the position of the upper surface of the uppermost sheet is determined by the positioning mechanism, and therefore, when the sheet is not fed. The small diameter portion of the cam is kept separated from the uppermost sheet and the cam is only in contact with the uppermost sheet. Therefore, according to the sheet feeding mechanism of the image forming apparatus according to the fifth aspect, the function of the sheet feeding mechanism can be reliably exhibited.
[0025]
According to a sixth aspect of the present invention, in the sheet feeding mechanism of the image forming apparatus, the cam is rotatably supported on a rotation axis of the sheet feeding roll.
[0026]
In the paper feeding mechanism of the image forming apparatus according to the sixth aspect, since the cam is mounted on the rotating shaft of the paper feeding roll, a separate shaft for mounting the cam is not required, and the number of parts does not increase. Similarly, the positional relationship between the paper feed roll and the cam with respect to the rotating shaft is constant, so that the accuracy after the mounting of the paper feed roll and the cam is improved.
[0027]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, a sheet feeding mechanism of an image forming apparatus according to an embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a cross-sectional view showing the overall configuration of a laser beam printer LBP to which a paper feeding mechanism of an image forming apparatus is applied, FIG. 2 is a perspective view of a paper feeding mechanism S shown in FIG. 1, and FIG. FIG. 4 is a side view of the cam shown in FIG. 3, and FIG. 5 is a front view of the drive mechanism shown in FIG.
[0028]
In the apparatus main body 10 of the laser beam printer LBP shown in FIG. 1, paper cassettes 12 and 14 are detachably mounted at a lower portion thereof and are arranged in two upper and lower stages. Then, the paper 11 in the paper cassettes 12 and 14 is conveyed by paper feed rolls 13 and 15.
[0029]
A manual tray 16 is installed in the apparatus main body 10 above a paper cassette 14, and the paper 11 set in the manual tray 16 is transported by a paper feed roll 17. The manual feed tray 16 is normally folded and covered by a manual feed tray storage cover 18, and is set as shown in FIG. 1 when executing the process in the manual feed mode.
[0030]
On the downstream side in the transport direction of each of the paper feed rolls 13, 15, and 17, the posture of the paper 11 is corrected and the synchronization of the transport of the paper 11 and an image forming process by an image forming unit 26 as an image forming unit described later is synchronized. Registration rolls 20, 22, and 24 are provided, respectively. The orientation of the paper 11 is corrected by the registration rolls 20, 22, and 24, and the paper 11 is conveyed to the image forming unit 26 at a timing synchronized with the image forming processing.
[0031]
On the other hand, a laser scanner 28 that outputs a laser beam based on image data to be formed, a photosensitive drum 30 that receives the laser beam from the laser scanner 28, and a laser beam The image forming unit 26 includes an electrostatic recording type image forming unit 26 including a developing unit (not shown) for developing a latent image formed on the photosensitive drum 30 formed by the above-described process, a transfer roll 32 for heating, and the like. A fixing unit 36 and other main components constituting the electrostatic recording system are provided.
[0032]
In the image forming unit 26, a laser beam based on image data to be formed from a laser scanner 28 scans the rotating photosensitive drum 30 at a constant angular velocity, and a latent image is formed on the photosensitive drum 30. After the latent image is developed by a developing device (not shown) and visualized (a toner image is formed on the surface), the toner image on the photosensitive drum 30 is transported between the photosensitive drum 30 and the transfer roll 32. The image is transferred to the paper 11. Thus, the toner image is placed on the surface of the sheet 11.
[0033]
The transferred sheet 11 is conveyed to a fixing unit 36, and the transferred image (toner) is fixed to the sheet 11 by a fixing roll 34. Thus, the image forming process (printing process) on the sheet 11 is completed. Note that the image-formed sheet is hereinafter referred to as a recording sheet P to distinguish it from the sheet 11 on which no image is formed.
[0034]
The recording paper P having an image formed on one side in this manner is discharged to a tray 40 provided on the upper surface of the apparatus main body 10 by the discharge roll 38, and the recording paper P is stacked and stored in the tray 40.
[0035]
The configuration of the sheet feeding mechanism (including the sheet cassette 12) S according to the present invention will be described with reference to FIG. In FIG. 2, arrow RE indicates the right side, and arrow LE indicates the left side.
[0036]
A sheet stacking plate 42 is pivotally supported by the sheet feeding cassette 12, and a spring member 44 as an urging unit shown in FIG. 1 is disposed on a lower surface of the sheet stacking plate 42. The sheet feeding pressure is applied to the sheet 11 (see FIG. 1) by the spring member 44. Further, a pair of guide plates 46 are provided on both left and right sides of the sheet feeding cassette 12 in the transport direction (the direction of arrow FW in FIG. 2), and a pair of levers are provided between the guide plate 46 and the main body frame 52 on the transport side. 48 is rotatably supported around a support shaft 50.
[0037]
The lever 48 is provided with a separation claw 48A having a substantially V-shaped tip so as to face the paper 11 on the transport side thereof. Further, as shown in FIG. 3, the lever 48 is formed with an engaging portion 48B which constitutes a part of the positioning mechanism. The paper cassette 12 facing the engaging portion 48B is formed with an L-shaped engaging portion 48C that forms a part of the positioning mechanism, and is formed with a groove 48D for releasing the engaging portion 48B. I have. When the engaging portion 48B is locked by the locking portion 48C, the upper limit position PX of the separation claw 48A in the vertical direction is determined, and the stacked paper 11 is prevented from being excessively raised.
[0038]
As shown in FIG. 2, a rotating shaft 58 to which four half-moon-shaped paper feed rolls 13 disposed at positions facing the paper 11 at the left end are fixed on the main body frame 52 at the left end. It is supported in a state. Further, a cam 60 is mounted on the rotating shaft 58 so as to be rotatable with respect to the rotating shaft 58 coaxially with the toothless gear 54 and the paper feed roll 13. That is, the rotational force of the paper feed roll 13 is not transmitted to the cam 60.
[0039]
According to the present embodiment, since the cam 60 is rotatably supported on the rotary shaft 58, a separate shaft for mounting the cam 60 is not required, and the number of parts does not increase. Further, according to the present embodiment, the positional relationship between the paper feed roll 13 and the cam 60 with respect to the rotation shaft 58 becomes constant, so that the accuracy after the mounting of the paper feed roll 13 and the cam 60 is improved. Note that the cam 60 does not have to be coaxial with the paper feed roll 13.
[0040]
A total of two cams 60 are arranged one by one between the paper feed rolls 13. Further, the cam 60 is provided inside the minimum paper size of the paper 11 (a size capable of feeding the paper 11, for example, a standard size of an envelope or a postcard). Note that rubber or the like is attached to the outer peripheral surface of the paper feed roll 13 so that the coefficient of friction with the paper 11 is increased.
[0041]
As shown in FIG. 4, a hole 60 </ b> A through which the rotating shaft 58 is inserted is formed in the cam 60, and a cylindrical portion 61 forming a peripheral surface of the hole 60 </ b> A is formed with a hole 60 </ b> A as a rotation center of the cam 60. It protrudes along the axis QX direction. The cam 60 has a substantially fan shape, and the large-diameter portion 60C formed over a range of approximately 90 degrees (angle θ) from the linear surface 60B has an axis of the hole 60A (same as the axis of the rotating shaft 58) QX. Has the same radius (maximum radius) RZ. This maximum radius RZ is the same as or slightly smaller than the radius of the paper feed roll 13.
[0042]
Further, the cam 60 is formed with a reduced-diameter surface 60D whose outer diameter is gradually reduced from the large-diameter portion 60C having the maximum radius RZ on the opposite side of the linear surface 60B, and the cam 60 has a small-diameter portion 60E having the minimum radius RY. It is the same as the outer peripheral surface of the cylindrical portion 61.
[0043]
That is, the maximum radius RU of the paper feed roll 13 (see FIG. 3) and the maximum radius RZ of the cam 60 are the same, or the maximum radius RU of the paper feed roll 13 is longer than the maximum radius RZ of the cam 60. Therefore, the cam 60 rotates without any trouble while the paper feed roll 13 is feeding the uppermost paper 11.
[0044]
Further, the maximum radius RZ of the cam 60 is based on the distance LU (see FIG. 3) from the upper surface of the uppermost sheet 11 positioned by the positioning mechanism (the engaging portion 48B and the locking portion 48C) to the rotation center QX of the cam 60. Is also getting longer. Therefore, immediately after the paper feed roll 13 sends out the uppermost sheet 11, the large diameter portion 60 </ b> C of the cam 60 comes into pressure contact with the uppermost sheet 11.
[0045]
Further, the distance LU from the upper surface of the uppermost sheet 11 to the rotation center QX of the cam 60 is longer than the minimum radius RY of the cam 60. Therefore, the position of the upper surface of the uppermost sheet 11 is positioned by the positioning mechanisms 48B and 48C, and the small-diameter portion 60E of the cam 60 when paper is not fed is maintained in a state separated from the uppermost sheet 11 (see FIG. 3). ) And the straight surface 60B of the cam 60 is only in contact with the uppermost sheet 11. Therefore, according to the present embodiment, the function of the sheet feeding mechanism can be reliably exhibited.
[0046]
The center of gravity BW of the cam 60 is located on the maximum radius RZ side near the linear surface 60B between the maximum radii RZ. In the initial position shown in FIG. I have. The center of gravity BW is a position that faces vertically downward when the cam 60 is suspended around the rotation shaft 58 by its own weight.
[0047]
That is, as shown in FIG. 3, in the initial position, the straight surface 60B of the cam 60 comes into contact with the uppermost sheet 11 by its own weight, and the cam 60 rotates by its own weight by the rotation of the paper feed roll 13. It rotates about an axis 58.
[0048]
At the initial position, the load of the cam 60 that is in contact with the uppermost sheet 11 by its own weight does not prevent the next sheet 11 other than the uppermost sheet from returning in the direction opposite to the transport direction. That is, according to the present embodiment, the next sheet 11 located below the uppermost layer sheet 11 can return in the direction opposite to the transport direction (return to the position shown in FIG. 3), so that the transport property of the sheet 11 can be improved. , And double feed is prevented.
[0049]
Although the cam 60 is rotated by its own weight with respect to the rotation shaft 58 in the present embodiment, the cam 60 may be forcibly guided by a spring member (not shown).
[0050]
When the cassette 12 is inserted into the main body frame 52, the sheet stacking plate 42 is raised by the spring member 44, and the stacked sheets 11 are pushed upward. Since the lever 48 provided on the guide plate 46 is rotatable about the support shaft 50, the separation claw 48 </ b> A comes into contact with the uppermost sheet 11 by the weight of the lever 48. Further, as shown in FIG. 4, the position in the vertical direction is restricted by the engagement of the engagement portion 48B with the engagement portion 48C.
[0051]
As shown in FIG. 2, the paper feed roll 13 for transporting the paper 11 from the paper cassette 12 is rotated about a rotation shaft 58 by a driving force from a motor (not shown), and the outer peripheral surface of the paper feed roll 13 is The paper 11 other than the uppermost layer is prevented from being fed (double feed) by the separating operation of the lever 48 (separating claw 48A) while being in contact with the uppermost layer, and has an intermittent structure in which the uppermost layer of the paper 11 is conveyed one by one. I have.
[0052]
Hereinafter, the intermittent structure will be described with reference to FIG. The toothless gear 54 can be meshed with the drive gear 62, and a locking claw 54 </ b> B formed on the toothless gear 54 can be engaged with a locking member 64 </ b> A connected to the solenoid 64.
[0053]
A cam 66 is formed on the toothless gear 54, and a rod 68 is rotatably supported so as to correspond to the cam 66. One end of a spring 70 is hooked on an intermediate portion of the bar-shaped member 68, and the spring 70 constantly urges the bar-shaped member 68 in a counterclockwise direction (the direction of arrow CCW in FIG. 3).
[0054]
A predetermined voltage is applied to the solenoid 64 based on a paper feed start signal from a control unit (not shown) of the image forming unit 28 shown in FIG. 1, and the locking member 64 </ b> A is pressed by the solenoid 64 against the urging force of the spring 65. When pulled, the locking member 64A separates from the locking claw 54B.
[0055]
Then, the rod-shaped member 68 rotates the cam portion 66, that is, the paper feed roll 13 in the clockwise direction (the direction of arrow CW in FIG. 5) by the urging force of the spring 70, and the toothless portion 54 </ b> A of the toothless gear 54 and the drive gear 62 move. From the opposed non-meshed state, the paper feed roll 13 and the drive gear 62 are brought into a meshed state.
[0056]
In this meshing state, the rotating shaft 58 shown in FIG. 2 connected to the toothless gear 54 is driven to rotate the paper feed roll 13. The rotated paper feed roll 13 feeds one sheet of paper 11 on the top of the paper stacking plate 42, and the fed paper 11 is conveyed into the apparatus main body 10 shown in FIG. After the paper feed roll 13 makes one rotation, the locking claw 54B of the toothless gear 54 is locked by the locking member 64A as shown in FIG. 5, and stops in the non-meshing state shown in FIG.
[0057]
Note that the main body frame 52 has a rotating shaft 72 supported rotatably on its transport side in a horizontal state. The registration roll 22 is attached to the rotation shaft 72.
[0058]
Hereinafter, the operation of the present embodiment will be described with reference to FIGS. When the paper feed roll 13 rotates from the initial state shown in FIG. 3, the cam 60 rotatably provided coaxially with the paper feed roll 13 rotates by its own weight, as shown in FIG. Since the center of gravity BW of the cam 60 is on the side of the maximum radius RZ (see FIG. 4) between the paper feed roll 13 and the linear surface 60B, the center of gravity BW moves downward, and one end of the large diameter portion 60C having the maximum radius RZ is attached to the sheet 11. Contact.
[0059]
Further, in a state where the paper feed roll 13 is rotated and the paper 11 is sent out halfway and the paper feed roll 13 is separated from the paper 11, the paper 11 is nipped and transported by the registration roll 22, as shown in FIG. Is done. Therefore, the cam 60 comes into pressure contact with the paper 11, and the cam 60 is rotated by the frictional force between the large diameter portion 60 </ b> C and the paper 11.
[0060]
Then, as shown in FIG. 3, when the small diameter portion 60E of the cam 60 faces the upper surface of the uppermost sheet 11, the position of the upper surface of the uppermost sheet 11 is positioned by the positioning mechanisms 48B and 48C. Therefore, during the conveyance of the sheet 11, the small diameter portion 60 </ b> E of the cam 60 is kept separated from the uppermost sheet 11, and the straight surface 60 of the cam 60 contacts the uppermost sheet 11. State.
[0061]
Therefore, in the present embodiment, the urging force of the spring member 44 does not act on the small-diameter portion 60E of the cam 60 during the conveyance of the paper 11, and the conveyance resistance of the paper 11 during the conveyance does not occur.
[0062]
In the present embodiment, there is almost no difference in the outer diameter between the paper feed roll 13 and the cam 60 when the paper feed roll 13 is separated from the paper 11 and when the cam 60 comes into contact with the paper 11. The paper 11 smoothly moves from the diameter portion 60C to the reduced diameter surface 60D (if the maximum outer diameter RZ of the cam 60 is slightly smaller than the radius of the paper feed roll 13, the paper 11 rises slightly). Moving.
[0063]
Therefore, according to the present embodiment, the large-diameter portion 60C and the reduced-diameter surface 60D of the cam 60 move smoothly with respect to the sheet 11, so that the sheet stacking plate 42, the sheet 11, and the separation contacting the sheet 11 by its own weight. The claw 48A is gently pushed upward, and the engaging portion 48B provided on the lever 48 smoothly contacts the locking portion 48C, so that the impact is buffered and the generation of an impact sound is prevented.
[0064]
Further, according to the present embodiment, since an impact transmitted to the photosensitive drum 30 or the laser scanner 28 shown in FIG. 1 is prevented, an image is formed in a stable state, and the image being written is not affected.
[0065]
Note that the configuration, operation, and effects of the upper paper cassette 14 of the paper cassette 12 are the same as those of the above-described paper cassette 12, and thus description thereof is omitted.
[0066]
【The invention's effect】
Since the present invention is configured as described above, it is possible to prevent an impact between the rigid portions of the positioning mechanism when the cam is pressed against the outermost layer of paper, thereby preventing the generation of an impact sound. Further, since the next sheet can return in the direction opposite to the transport direction, the transportability of the sheet is not impaired.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view illustrating an overall configuration of a laser beam printer according to an embodiment.
FIG. 2 is a perspective view of the sheet feeding mechanism shown in FIG.
FIG. 3 is a sectional view of the sheet feeding mechanism shown in FIG.
FIG. 4 is a side view of the cam shown in FIG. 3;
FIG. 5 is a front view of the drive mechanism shown in FIG.
FIG. 6 is a cross-sectional view illustrating a sheet feeding state of the sheet feeding device.
FIG. 7 is a cross-sectional view illustrating a sheet feeding state of the sheet feeding device.
FIG. 8 is a cross-sectional view showing a conventional paper feed mechanism.
[Explanation of symbols]
Reference Signs List 10 Main body 11 Paper 12,14 Paper cassette 13,15 Paper feed roll 26 Image forming unit (image forming unit)
42 paper loading plate 44 spring member (biasing means)
48 lever (positioning mechanism)
48A Separating claw 48B Engagement part (positioning mechanism)
48C Locking part (positioning mechanism)
48D Groove 52 Body frame 58 Rotary shaft 60 Cam 60C Large diameter portion 60E Small diameter portion PX Upper limit position QX Axis (rotation center)
BW Center of gravity RZ Maximum radius of cam RY Minimum radius of cam RU Maximum radius of paper feed roll LT Distance from top surface of uppermost layer paper to rotation center of cam S Paper feed mechanism LBP Laser beam printer

Claims (6)

Urging means for urging the stacked plurality of supply sheets with an urging force;
A substantially half-moon-shaped paper feed roll that is arranged on a rotating shaft facing one surface of the outermost layer paper, rotates under a driving force, and feeds the outermost layer paper by frictional force,
A positioning mechanism for positioning the outermost layer of paper energized by the urging means during non-feeding;
It is arranged rotatably around the axis, facing one surface of the outermost layer paper,
A large diameter portion and a small diameter portion smaller in diameter than the large diameter portion are provided at different positions around the axis,
After the paper is sent out by the paper feed roll, the large-diameter portion presses the uppermost layer of paper, and a cam that moderately raises the positioning mechanism ,
A sheet feeding mechanism for an image forming apparatus. Comprising a sheet stacking plate for stacking the sheet, a plurality of sheets stacked on said sheet stacking plate in front Symbol sheet feed roller to feed the one by one image forming unit, and the cam at least one said sheet feeding A lever provided coaxially with the roll, wherein the positioning mechanism locks the engaging portion with a lever having an engaging portion and a separating claw that also has an over-raising prevention function of limiting an upper limit position of the sheet in the vertical direction. The paper feed mechanism of the image forming apparatus according to claim 1, further comprising a stop. The paper feed mechanism of the image forming apparatus according to claim 1, wherein a center of gravity of the cam is located substantially on a line connecting an axis of the cam and a maximum radius of the cam. 3. The sheet feeding mechanism according to claim 1, wherein the outer diameter of the cam is sequentially reduced from the maximum radius. The maximum radius of the paper supply roll and the maximum radius of the cam are the same or the maximum radius of the paper supply roll is longer than the maximum radius of the cam, and the maximum radius of the cam is the outermost layer positioned by the positioning mechanism. The distance from one surface of the sheet to the center of rotation of the cam, and the distance from one surface of the sheet of the outermost layer to the center of rotation of the cam is longer than the minimum radius of the cam. 3. The paper feeding mechanism of the image forming apparatus according to 2. The paper feed mechanism according to claim 1, wherein the cam is rotatably supported on a rotation shaft of the paper feed roll.

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