SHEET FEEDING DEVICE AND IMAGE FORMING DEVICE

BACKGROUND

Field of the Disclosure

The present disclosure relates to a sheet feeding device and an image forming device, and in particular relates to the same provided with a sheet stacking member that is capable of being lifted and lowered and that stacks sheets on a sheet containing unit.

Description of the Related Art

Conventional image forming devices, such as printers, copiers, and facsimiles, include a sheet feeding device that feeds sheets that is contained in a sheet containing unit provided detachably to a main body of the device to an image forming unit by sending out the sheets with a sheet feeding unit. In the sheet feeding device, a lift plate that is a sheet stacking member on which the sheets are stacked is provided, so as to be capable of being lifted and lowered, in a sheet feeding cassette that is the sheet containing unit. When feeding the sheets, the lift plate is lifted such that the sheets are urged against a sheet feeding roller that is a sheet feeding unit. Furthermore, by having the sheet be in pressure contact with the feed roller, pressure contact force (hereinafter, referred to a sheet feeding pressure) is generated, and in a state in which the sheet feeding pressure is generated, the sheet feeding roller is rotated to send the sheets out.

Such a sheet feeding device is provided in the sheet feeding cassette with a lifter mechanism that is a lifting and lowering mechanism for lifting the lift plate, a gear and a motor that drives the gear is included in the main body of the device, and a drive unit that drives the lifter mechanism is provided. Furthermore, when the sheet feeding cassette is mounted, the lifter mechanism is connected to the drive unit, and subsequently, when the drive unit is driven, the lift plate is lifted with the lifter mechanism to a predetermined height that enables the sheet on the top to be sent out.

Incidentally, when replenishing the sheets, when changing the type of sheet, or when a sheet jam occurs, the sheet feeding cassette is drawn out from the main body of the device. When the sheet feeding cassette is drawn out as above, the connection between the lifter mechanism and the drive unit is released. In such a case, when the lift plate is in a lifted state, the lift plate is lowered by its own weight and the weight of the stacked sheets, and impacts the bottom surface of the sheet feeding cassette generating a noise with the impact. Note that the loudness of the sound of impact is prominent when there are no sheets stacked, in other words, when the sheet feeding cassette is drawn out when the lift plate is at its highest position.

Accordingly, in Japanese Patent Laid-Open No. 8-127434, in order to mitigate the sound of impact when the lift plate is lowered, for example, a damper is disposed inside a lifting and lowering mechanism and the lift plate is lowered slowly.

Note that in recent years, a need for sheet feeding devices to become more compact and to have a larger capacity is increasing. However, when a damper is disposed in the lifting and lowering mechanism, it makes it difficult to make the sheet feeding device more compact and the structure becomes complex, and further, since there will be a load caused by the damper when lifting the lift plate, load to the motor of the drive unit becomes larger.

SUMMARY

Accordingly, the present disclosure has been made in view of the present situation described above, and an object thereof is to provide, in a simple manner and at a low cost, a sheet feeding device and an image forming device that are capable of reducing the impact made when the lift plate (sheet stacking member) falls. The present disclosure provides a sheet feeding device including, a sheet containing unit detachably provided in a main body of the device, the sheet containing unit including a sheet stacking member on which a sheet is stacked, the sheet stacking member being capable of being lifted and lowered, a drive unit provided in the main body of the device, the drive unit including a drive gear and a driving source that drives the drive gear, a lifting unit that includes a pivoting member capable of pivoting in a direction in which the sheet stacking member is lifted and lowered, and a drive transmission gear connected to the pivoting member, the drive transmission gear being engaged with the drive gear when the sheet containing unit is mounted and releasing engagement with the drive gear when the sheet containing unit is dismounted, the lifting unit lifting the sheet stacking member to a first position, a brake unit that applies a braking force generated by frictional force to the drive transmission gear in a case in which the engagement between the drive gear and the drive transmission gear is released and the sheet stacking member is lowered from the first position, and a buffer member that absorbs force exerted to the drive transmission gear when the engagement between the drive gear and the drive transmission gear is released and the sheet stacking member is lowered.

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

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a schematic configuration of a laser printer that is an example of an image forming apparatus including a sheet feeding device according to a first embodiment of the present disclosure.

FIG. 2 is a perspective view a sheet feeding cassette of the laser printer, according to an embodiment of the present disclosure.

FIG. 3 is a control block diagram of the sheet feeding device, according to an embodiment of the present disclosure.

FIG. 4A is a perspective view illustrating a state in which the lift plate of the sheet feeding cassette is lowered to a position allowing the sheet to be stacked, according to an embodiment of the present disclosure.

FIG. 4B is a perspective view illustrating a state in which the lift plate is pivoted upwards, according to an embodiment of the present disclosure.

FIG. 5A is cross-sectional view illustrating a state in which the sheets are stacked on the lift plate, according to an embodiment of the present disclosure.

FIG. 5B is a cross-sectional view illustrating a state in which there is not sheet left on the lift plate, according to an embodiment of the present disclosure.

FIG. 6A is a cross-sectional view of an impact mitigating member provided in the sheet feeding device, according to an embodiment of the present disclosure.

FIG. 6B is a perspective view of the impact mitigating member, according to an embodiment of the present disclosure.

FIG. 7 is side view of a back side lateral plate of a cassette main body of the sheet feeding cassette, according to an embodiment of the present disclosure.

FIG. 8A is a diagram illustrating a state of the impact mitigating member in which the lift plate is lifted to its highest position, according to an embodiment of the present disclosure.

FIG. 8B is a diagram illustrating a state of the impact mitigating member when the lift plate has become slightly lower, according to an embodiment of the present disclosure.

FIG. 9 is a figure illustrating, in an enlarged manner, claws of a lifter gear being in pressure contact with the rib of the cassette main body, according to an embodiment of the present disclosure.

FIG. 10A is a diagram for describing a state of the impact mitigating member when the lift plate has been lowered and stopped at a position allowing the sheet to be stacked, according to an embodiment of the present disclosure.

FIG. 10B is a diagram for describing a state of the impact mitigating member in which the lift plate has been lowered to and stopped at a position that enables the sheets to be mounted thereon, according to a first exemplary embodiment of the present disclosure.

FIG. 11 is a diagram of an enlarged lock portion between the rib of the cassette and a claw of the lifter gear when the lift plate is in a static state, according to an embodiment of the present disclosure.

FIG. 12 is a perspective view for describing a configuration of an impact mitigating member of a sheet feeding device according to a second exemplary embodiment of the present disclosure, according to an embodiment of the present disclosure.

FIG. 13 is a side view of a back side lateral plate of the cassette main body of a sheet feeding cassette, according to an embodiment of the present disclosure.

FIG. 14 is a diagram for describing a cam surface of a rib of a cassette, according to an embodiment of the present disclosure.

DESCRIPTION OF THE EMBODIMENTS
Description of the Embodiments

Hereinafter, exemplary embodiments of the present discloser will be described in detail with reference to the drawings. FIG. 1 is a diagram illustrating a schematic configuration of a laser printer that is an example of an image forming apparatus including a sheet feeding device according to a first exemplary embodiment of the present disclosure. A laser printer 1 includes, inside a laser printer main body (hereinafter, referred to as a printer main body) 1A, an image forming unit 1B that forms an image on a sheet S and a sheet feeding device 1C that feeds the sheet S.

The image forming unit 1B includes a scanner unit 5, and four process cartridges 50 that form toner images of four colors, namely, yellow (Y), magenta (M), cyan (C) and black (Bk) and that include photosensitive drums 51. Furthermore, the image forming unit 1B includes an intermediate transfer unit 1D disposed above the process cartridges 50. The intermediate transfer unit 1D includes an intermediate transfer belt 52 wound around a drive roller 52a, a tension roller 52b, a driven roller 52c.

Furthermore, the intermediate transfer unit 1D includes primary transfer rollers 52d that are provided on the inner side of the intermediate transfer belt 52 and that abut against the intermediate transfer belt 52 at positions opposing the photosensitive drums 51. The intermediate transfer belt 52 is configured of a film-like member, is disposed so as to be in contact with the photosensitive drums 51, and is rotated in an arrow direction with the drive roller 52a driven by a drive unit (not shown).

By applying a transfer bias having a positive polarity to the intermediate transfer belt 52 with the primary transfer rollers 52d, toner images of various colors on the photosensitive drums 51, the toner images each having a negative polarity, are sequentially transferred in a superposed manner onto the intermediate transfer belt 52. Note that a secondary transfer roller 53 that transfers a full color image formed on the intermediate transfer belt 52 on the sheet S is provided at a position opposing the drive roller 52a of the intermediate transfer unit 1D. Furthermore, a fixing unit 6 is disposed above the secondary transfer roller 53.

The sheet feeding device 1C includes a sheet feeding cassette 2 serving as a sheet containing unit in which the sheets S are stacked, and a pickup roller 3 serving as a sheet feeding unit for sending out the sheets S stacked and contained in the sheet feeding cassette 2. Note that an image forming operation of the image forming unit 1B and a sheet feeding operation of the sheet feeding device 1C are controlled with a CPU 70 serving as a control member.

An image forming operation of the laser printer 1 configured in the above manner will be described next. When an image forming operation is started, the scanner unit 5 emits a laser beam according to image information from, for example, a personal computer (not shown) and sequentially exposes surfaces of the photosensitive drums 51, the surfaces of which are uniformly charged to a predetermined polarity and potential, to form electrostatic latent images on the photosensitive drums 51. Subsequently, the electrostatic latent images are developed and visualized with toner, and the visualized toner images are transferred onto the intermediate transfer belt 52 in a superposed manner with a primary transfer bias applied to the primary transfer rollers 52d. With the above, a full color toner image is formed on the intermediate transfer belt 52.

Furthermore, in parallel with the operation of forming the toner images, the sheet feeding device 1C sends out a sheet S that is contained in the sheet feeding cassette 2, and after the sheet S has been conveyed with a conveyance roller 4, the sheet S is conveyed to the secondary transfer unit. The full color toner image is transferred, with a secondary transfer bias that has been applied to the secondary transfer roller 53, onto the sheet S that has been conveyed to the secondary transfer unit. Subsequently, the sheet S onto which the full color toner image has been transferred is conveyed to the fixing unit 6. Heat and pressure is applied to the sheet S in the fixing unit 6 such that the toner of various colors are melted and mixed and are fixed as a full color image on the sheet S. After the above, the sheet S on which the image has been transferred is discharged to an output tray 9 with a pair of discharge rollers 8 provided downstream of the fixing unit 6.

Referring to FIG. 2, description of the sheet feeding cassette 2 will be given next. The sheet feeding cassette 2 is capable of containing sheets of variety of sizes, such as an A6 size to an LGL size. Furthermore, the sheet feeding cassette 2 is mounted in a mount space (not shown) provided in a lower portion of the printer main body 1A serving also as a sheet feeding device body, so as to be capable of being drawn out (so as to be detachable) in a width direction orthogonal to a sheet feed direction.

The sheet feeding cassette 2 includes a cassette main body 20 that contains the sheets S, and a pair of front lateral side restriction member 22 and back lateral side restriction member 23 that are provided in the cassette body 20 so as to be movable in the width direction and that serve as a pair of restriction member that restricts positions of lateral edges of the sheets S in the width direction. The front lateral side restriction member 22 and the back lateral side restriction member 23 are connected with a rack portion and a pinion gear (both not shown). Furthermore, when a user operates a lever (not shown) provided in the front lateral side restriction member 22, the front lateral side restriction member 22 and the back lateral side restriction member 23 move in the width direction in an interlocked manner and are disposed at positions corresponding to the sheet size.

The sheet feeding cassette 2 includes a rear end restriction member 24 that is provided in the cassette main body 20 so as to be capable of moving in the sheet feed direction and that restricts the positions of the rear ends of the sheets S, which are the upstream ends of the sheets S in the sheet feed direction. The rear end restriction member 24 is capable of being slid in the sheet feed direction. When the user operates a lever (not shown) of the rear end restriction member 24, the sheets S are disposed at positions that correspond to the sheet size.

The sheet feeding cassette 2 includes a lift plate 21 serving as a sheet stacking member supported by the cassette main body 20 so as to be pivotal (so as to be capable of being raised and lowered) in an up-down direction. The downstream end side of the lift plate 21 pivots in the up-down direction about supports 21a provided in the cassette main body 20. Note that in FIG. 2, only one of the supports 21a is illustrated.

In a portion between a bottom surface 20a of the cassette main body 20 and the lift plate 21, a lifter plate 25 serving as a pivoting member that pushes up the lift plate 21 towards the pickup roller 3 is disposed in a pivotal manner in the up-down direction that is a direction in which the lift plate 21 is raised and lowered. The pivoting edge of the lifter plate 25 is in contact with a back side of the lift plate 21 at a middle portion of the lift plate 21.

A lifter gear 26 serving as a fan-shaped drive transmission gear in which a teeth portion 26b is formed in the peripheral surface thereof is attached downstream of (hereinafter, referred to as a back side) of the lifter plate 25 in a cassette mounting direction illustrated by an arrow Y. Furthermore, the lifter plate 21 pivots integrally with the lift gear 26 about a lifter shaft 26x that is a shaft of the lifter gear 26 serving as a pivot axis illustrated in FIG. 6B.

A drive gear 31 that engages with the lift gear 26 when the sheet feeding cassette 2 is mounted is provided in the mount space and on the back side of the printer main body 1A. The drive gear 31 is driven (actuated) with a lifter motor 500 described above, illustrated in FIG. 3, serving as a driving source provided in the printer main body 1A. In the present exemplary embodiment, a drive unit 31A includes the lifter motor 500 and the drive gear 31.

In a state in which the drive gear 31 is engaged with the lifter gear 26, when the drive gear 31 is driven with the lifter motor 500 and is rotated in an arrow A direction, the lifter gear 26 is rotated in an arrow B direction. When the lifter plate 25 interlocked with the rotation of the lifter gear 26 pivots upwards about the lifter shaft 26x, the lift plate 21 is lifted and the sheets S stacked on the lift plate 21 is brought into pressure contact with the pickup roller 3. As described above, in the present exemplary embodiment, a lifting unit 30 that pushes up the lift plate 21 and brings the sheets S stacked on the lift plate 21 into pressure contact with the pickup roller 3 includes the lifter plate 25 and the lifter gear 26 that engages with the drive gear 31. Furthermore, the lift plate 21 can be lifted with the lifting unit 30 to a position (a first position) where the pickup roller 3 is capable of feeding the sheets S.

Note that when the sheet feeding cassette 2 is drawn out, the engagement (connection) between the lifter gear 26 and the drive gear 31 is released. When the engagement with the drive gear 31 is released in the above manner, the lifter gear 26 can rotate freely. With the above, for example, in a case in which the sheets S are stacked, when the sheet feeding cassette 2 is drawn out while the lift plate 21 is pivoting upwards, the lifter plate 21 becomes lowered with the weight of the sheets S and the lift plate 21 itself while the lifter gear 26 rotates freely, and in a case in which no sheet S is stacked, when the sheet feeding cassette 2 is drawn out while the lift plate 21 is pivoting upwards, the lifter plate 21 becomes lowered with the weight of the lift plate 21 itself while the lifter gear 26 rotates freely.

FIG. 3 is a control block diagram of the sheet feeding device 1C, and as illustrated in FIG. 3, a sheet feeding cassette detection sensor 600 that detects that the sheet feeding cassette has been accommodated in the mount space of the printer main body 1A is connected to the CPU 70. Furthermore, as described later and as illustrated in FIGS. 5A and 5B, a sheet surface detection sensor 601 the detects the stacked height of the sheets S, a sheet presence detection sensor 602 that is a detection member that detects whether there is a sheet S in the sheet feeding cassette, and a lifter motor 500 are connected to the CPU 70.

An operation of the lifting unit 30 will be described next. Note that the user draws out the sheet feeding cassette 2 from the printer main body 1A when installing the sheets S in the sheet feeding cassette 2. FIG. 4A illustrates a state in which the sheet feeding cassette with no sheets therein is drawn out from the printer main body 1A. In such a state, the lift plate 21 is lowered to a position where the sheets S can be stacked thereon.

When the user stacks the sheets S on the lift plate 21 of the sheet feeding cassette 2 and, subsequently, when the user returns the sheet feeding cassette 2 into the printer main body 1A, as it has been described already, the drive gear 31 becomes engaged with the lifter gear 26 of the sheet feeding cassette 2. When the sheet feeding cassette detection sensor 600 detects that the sheet feeding cassette 2 has been mounted in the mount space, the CPU 70 drives the lifter motor 500. With the above, as illustrated in FIG. 4B, the drive gear 31 rotates in the arrow A direction and upon rotation of the drive gear 31, the lifter gear 26 engaged with the drive gear 31 rotates in the arrow B direction.

As illustrated in FIG. 5A, the lifter plate 25 pivots upwards about the lifter shaft 26x with the rotation of the lifter gear 26. With the pivoting of the lifter plate 25, the lift plate 21 pivots upwards about the supports 21a to a position in which the sheet surface detection sensor 601 detects the sheets S on the lift plate 21. Subsequently, when the lift plate 21 pivots further upwards to a position in which the sheets S can be fed with the pickup roller 3, the CPU 70 stops the lifter motor 500. In the above manner, the sheets S are set to be in contact at a predetermined sheet feeding pressure with the pickup roller 3.

Subsequently, the CPU 70 drives the pickup roller 3 and, the sheets S are sent out in a sequential manner from the sheet Sa on the top. Note that when the sheets S are sent out in the above manner, the sheets S stacked on the lift plate 21 decreases and the stacked height of the sheets S stacked on the lift plate 21 becomes lower. The CPU 70 monitors the stacked height of the sheets S with the sheet surface detection sensor 601, and when the position of the sheet S on the top falls under a predetermined height, the CPU 70 receiving a signal from the sheet surface detection sensor 601 actuates the lifter motor 500 again. With the above, the lifter plate 25 pivots upwards again, and the lift plate 21 is lifted to a position where the top surface of the sheet S is in contact with the pickup roller 3 at an appropriate sheet feeding pressure.

The sheets S in the sheet feeding cassette is all sent out by repeating the above operation of sending out the sheets S with the pickup roller 3 and the above operation of pivoting the lift plate 21 upwards with the lifting unit 39. When there is no sheets S in the sheet feeding cassette, on the basis of a signal from the sheet presence detection sensor 602 illustrated in FIG. 5B indicating that there is no sheet S left in the sheet feeding cassette, the CPU 70 stops the sheet feeding operation and notifies the user of the above. Based on the notification, the user draws out the sheet feeding cassette 2 from the printer main body 1A to replenish the sheets S, and replenishes the sheets S.

Note that as illustrated in FIG. 5B, the lift plate 21 is pushed up to the top position immediately before the user draws out the sheet feeding cassette 2 from the printer main body 1A. In such a state, when the sheet feeding cassette 2 is drawn out from the printer main body 1A, the engagement between the lifter gear 26 and the drive gear 31 is released and the lifter gear 26 stops supporting the lift plate 21; accordingly, the lift plate 21 is lowered by its own weight.

Incidentally, as illustrated in FIGS. 6A and 6B, in the present exemplary embodiment, a groove G that has a shape that is concentric with the lifter shaft 26x is formed in a lateral side 26a of the lifter gear 26 on the cassette main body side. Furthermore, claws 26c and 26d that are pressure contact portions are provided so as to oppose each other are formed in the two facing inner wall surfaces of the groove G.

In the present exemplary embodiment, the claws 26c and 26d are each provided on the backside thereof with a slit hole 26e so as to allow a predetermined amount of elastic deformation to occur and are center beamed (bridged across); however, the claws 26c and 26d may be cantilevered. Furthermore, in the present exemplary embodiment, the interval between the claws 26c and 26d is about 1.4 mm.

Note that as illustrated in FIG. 6B, in the present exemplary embodiment, the lifter plate 25 is attached to the lateral side 26a of the lifter gear 26. Furthermore, as illustrated in FIG. 6A, in such a case as well, an opening portion 20c is formed in the back side lateral plate 20b of the cassette main body 20 so as to enable the lifter plate 25 to pivot in the up-down direction upon rotation of the lifter gear 26.

Meanwhile, as illustrated in FIG. 7, a rib 2b serving as a pressure contacted portion in which the claws 26c and 26d (hereinafter, referred to as sliding claws) of the lifter gear 26 slides while being in pressure contact therewith is provided in an outer wall surface of the back side lateral plate 20b of the cassette main body 20. The rib 2b (hereinafter, referred to as a cassette rib) moves inside the groove G of the lifter gear 26 when the lifter gear 26 rotates.

The cassette rib 2b has a shape that is concentric about the lifter shaft 26x of the lifter gear 26 so as not to disturb the rotation of the lifter gear 26. Furthermore, the cassette rib 2b includes a first portion 2b-1 in which a width (thickness) in a radial direction is narrow (thin), a second portion 2b-3 that has a wide width in the radial direction, a connection portion 2b-2 that connects the first portion 2b-1 and the second portion 2b-3 that has different widths, and a bevel portion 2b-4.

The surfaces of the first portion 2b-1, the connection portion 2b-2, and the second portion 2b-3 of the cassette rib 2b constitute sliding surfaces on which the sliding claws 26c and 26d being in pressure contact therewith slide when the sliding claws 26c and 26d slide, as described later. Note that in the present exemplary embodiment, in the cassette rib 2b, a width (a thickness) of the first portion 2b-1 positioned on the upstream side in the rotation direction, that is, on the upstream side in a first direction (a lowering direction) that is a direction in which the lifter gear 26 rotate together with the lift plate 21 when the lift plate 21 is lowered is about 1.4 mm. The width of the second portion 2b-3 positioned on the downstream side in the rotation direction of the lifter gear 26, that is, on the downstream side in the first direction is about 2.0 mm.

Furthermore, in the cassette rib 2b, a width of a boundary portion between the connection portion 2b-2 and the first portion 2b-1 is about 1.4 mm, and a width of a boundary portion between the connection portion 2b-2 and the second portion 2b-3 is about 2.0 mm. The width of the connection portion 2b-2 becomes larger towards the second portion 2b-3. Note that in the present exemplary embodiment, cassette rib 2b has a length that allows the sliding claws 26c and 26d to pass therethrough before the lift plate 21 reaches the lowest point, as described later. Furthermore, a surface of the bevel portion 2b-4 of the cassette rib 2b having such a length is provided at an end portion of the second portion 2b-3, and as illustrated in FIG. 11 described later, the surface configures a locking surface that locks the claws 26c and 26d that have passed through the cassette rib 2b.

Furthermore, as illustrated in FIGS. 6A and 6B, a spring 32 serving as an elastic member is provided between the lifter gear 26 and the cassette main body 20. Note that in the present exemplary embodiment, as illustrated in FIG. 6B, the spring 32 is provided in the lifter gear 26 while one end of the spring 32 is held by a spring holding portion 26f provided in the lifter gear 26.

Furthermore, when the lifter gear 26 rotates, the other end of the spring 32 abuts against a spring holding portion 2d provided on the outer wall surface of the back side lateral plate 20b of the cassette main body 20 illustrated in FIG. 7. Note that as illustrated in FIG. 6B, a groove G1 into which the spring holding portion 2d enters is formed in the lateral side 26a of the lifter gear 26. Furthermore, by having the spring holding portion 2d enter the groove G1, the other end of the spring 32 can be reliably abutted against the spring holding portion 2d when the lift gear 26 is rotated.

Note that the sliding claws 26c and 26d and the cassette rib 2b constitute a brake unit 40A, illustrated in FIG. 6A, which applies braking force caused by frictional force to the lifter gear 26 when the engagement between the drive gear 31 and the lifter gear 26 is released and the lift plate 21 is lowered. Furthermore, the spring 32 that is an elastic member constitutes a buffer member 40B that absorbs the force exerted to the lifter gear 26 when the engagement between the drive gear 31 and the lifter gear 26 is released and the lift plate 21 is lowered.

Furthermore, the brake unit 40A and the buffer member 40B configures an impact mitigating member 40 that mitigates the impact caused when the lift plate 21 is lowered. Note that the sliding claws 26c and 26d, the cassette rib 2b, and the spring 32 are disposed at positions in a rotatable range of the lifter gear 26 where the braking force can act on the lifter gear 26.

An operation of the impact mitigating member 40 described above will be described next. FIG. 8A illustrates the impact mitigating member 40 in a state in which the lift plate 21 is lifted up to the highest position. In such a state, the sliding claws 26c and 26d are positioned so as to meet the first portion 2b-1 of the cassette rib 2b.

However, as it has been described above, since the width of the first portion 2b-1 of the cassette rib 2b is about 1.4 mm and the interval between the claws is about 1.4 mm, even if the sliding claws 26c and 26d comes into contact with the cassette rib 2b, no frictional force will be generated in the above state. Furthermore, in the above case, the spring holding portion 26f of the lifter gear 26 and the spring holding portion 2d of the cassette main body 20 are separated from each other at a distance that is larger than the free length of the spring 32. Accordingly, no spring force (elastic force) exerted in a direction restricting the lift plate 21 from being lowered by the spring 32 is generated in the spring 32 provided in the lifter gear 26 such that no force exerted in the direction in which force is applied to the lifter gear 26 is absorbed.

When the sheet feeding cassette 2 is drawn out from the printer main body 1A in the above state, the engagement with the drive gear 31 is released and the lifter gear 26 becomes freely rotatable, such that the lift plate 21 becomes capable of being lowered as well. Note that since there is no frictional force between the sliding claws 26c and 26d and the cassette rib 2b and that the spring 32 exerts no effect immediately after the sheet feeding cassette 2 is drawn out, the lift plate 21 becomes lowered by its own weight, and receiving the load, the lifter gear 26 rotates in the first direction indicated by the arrow A.

FIG. 8B illustrates the impact mitigating member 40 in a state in which the lift plate 21 is slightly lowered. In such a state, the lifter gear 26 rotates slightly in the first direction, and with the rotation of the lifter gear 26, the sliding claws 26c and 26d move to a position meeting the connection portion 2b-2 of the cassette rib 2b. Note that, as described above, the width of the connection portion 2b-2 of the cassette rib 2b becomes larger towards the second portion. Accordingly, when the lift plate 21 is further lowered, the sliding claws 26c and 26d pinch the connection portion 2b-2 of the cassette rib 2b in the radial direction, and subsequently, come into pressure contact with the connection portion 2b-2 of the cassette rib 2b while becoming bent.

FIG. 9 is a figure illustrating an enlarged state in which the sliding claws 26c and 26d are in pressure contact with the connection portion 2b-2 of the cassette rib 2b while being bent. In such a state, when the lifter gear 26 rotates in the arrow direction A illustrated in FIG. 9, with an inclination created by the difference in width of the connection portion 2b-2 of the cassette rib 2b, the pressure contact force to the connection portion 2b-2 of the sliding claws 26c and 26d. Note that in the present exemplary embodiment, the contact angle between the connection portion 2b-2 of the cassette rib 2b and the sliding claws 26c and 26d is 10 degrees.

Furthermore, when the lift plate 21 is lowered, the sliding claws 26c and 26d pinching the cassette rib 2b pass through the connection portion 2b-2 of the cassette rib 2b and come into pressure contact with a second portion 2b-3. With the above, the frictional force between the sliding claws 26c and 26d and the cassette rib 2b becomes the largest and the braking force of the brake unit 40A becomes the largest; accordingly, the lowering speed of the lift plate 21 becomes further slow.

Note that in the present exemplary embodiment, when the sliding claws 26c and 26d come into pressure contact with the second portion 2b-3 of the cassette rib 2b, the other end of the spring 32 is locked to the spring holding portion 2d of the cassette main body 20 and starts to become compressed. With the above, the force exerted towards the lifter gear 26 starts to become absorbed by the spring 32, and with the function of the spring 32, the lowering speed of the lift plate 21 becomes further slow. In such a state, since the reaction forces of the two sliding claws 26c and 26d generated when the sliding claws 26c and 26d are bent are substantially the same in magnitude and are of opposing vectors, the reaction forces become cancelled out such that the bending amount of the sliding claws 26c and 26d becomes equal as a natural result.

FIG. 6A described above illustrates a state of the impact mitigating member 40 when the lift plate 21 is further lowered, accompanying the lowering of the lift plate 21, the lifer gear 26 rotates a predetermined amount, and the sliding claws 26c and 26d are detached from the cassette rib 2b. In the above, due to the frictional force between the sliding claws 26c and 26d and the cassette rib 2b and due to the function of the spring 32, the lowering speed of the lift plate 21 becomes zero such that the lift plate 21 stops before coming into contact with the bottom surface 20a of the cassette main body 20. With the above, contact between the lift plate 21 and the bottom surface 20a of the cassette main body 20 can be prevented and generation of an impact sound can be prevented.

In the above, since the sliding claws 26c and 26d are detached from the cassette rib 2b, no frictional force is generated; however, since the amount of compression of the spring 32 is at its largest, force that rotates in the opposite direction (an arrow A′ direction) is exerted to the lifter gear 26 with the spring force of the spring 32. In other words, when the lift plate 21 is lowered and the sliding claws 26c and 26d passes through the cassette rib 2b, while the lowering speed of the lift plate 21 becomes zero, a second force that lifts the lift plate 21 in the opposite direction with respect to the first direction is exerted to the lift plate 21 with the spring 32.

FIG. 10B illustrates the impact mitigating member 40 when the lift plate 21 is lowered and stopped at a position where the sheet can be stacked. In such a case, the lifter gear 26 is biased in the second direction illustrated by an arrow A′ with the spring 32, and the sliding claws 26c and 26d are locked to the bevel portion 2b-4 serving as a restriction portion of the cassette rib 2b. As described above, after the lift plate 21 is lowered and the sliding claws 26c and 26d are detached from the cassette rib 2b, when the lifter gear 26 is biased in the second direction with the spring 32, the sliding claws 26c and 26d are locked to the bevel portion 2b-4.

FIG. 11 is an enlarged figure of the lock portion between the sliding claws 26c and 26d and the bevel portion 2b-4 of the cassette rib 2b. In the above, the sliding claws 26c and 26d are locked to the bevel portion 2b-4 at a contact angle of 60 degrees. Note that the contact angle between the bevel portion 2b-4 and the claws 26c and 26d is larger than the contact angle with the connection portion 2b-2 in FIG. 9 described above.

As described above, by setting a contact angle, the sliding claws 26c and 26d and the bevel portion 2b-4 can be maintained in a locked state even if the lifter gear 26 is biased towards the arrow A′ direction with the spring 32, and the sliding claws 26c and 26d will not pass through the bevel portion 2b-4. With the above, the rotation of the lifter gear 26 is restricted, and the lift plate 21 is maintained at a position in which the sliding claws 26c and 26d and the bevel portion 2b-4 abut against each other and that enable the sheets S to be stacked. Note that desirably, the position is set at a position that allows the maximum number of sheets to be stacked on the lift plate 21.

Subsequently, after the sheets are stacked on the lift plate 21 and the sheet feeding cassette 2 is mounted in the printer main body 1A, the lifter gear 26 engages with the drive gear 31. When the drive gear 31 is rotated in the above state, the lifter gear 26 rotates in the arrow A′ direction illustrated in FIG. 10B. When the lifter gear 26 is rotated, with the rotational force of the lifter gear 26 and the spring 32, the sliding claws 26c and 26d passes through the bevel portion 2b-4 while being elastically deformed. Furthermore, with the rotation of the lifter gear 26, as illustrated in FIG. 5A, the lift plate 21 pivots upwards to a position in which the sheet surface detection sensor 601 detects the sheets S on the lift plate 21.

As described above, in the present exemplary embodiment, the lowering speed of the lift plate 21 is decreased with the frictional force caused by sliding between the sliding claws 26c and 26d and the cassette rib 2b and with the elastic force of the spring 32. Note that when, for example, the sliding friction is large, there may be cases in which the lift plate 21 does not become sufficiently lowered when the lowering speed of the lift plate 21 is reduced with only the sliding friction between the sliding claws 26c and 26d and the cassette rib 2b. Furthermore, in a case in which the sliding friction is small, the lowering speed of the lift plate 21 when the sliding claws 26c and 26d are detached from the cassette rib 2b does not become zero such that the lift plate 21 comes into contact with the bottom surface 20a of the cassette main body 20 generating an impact sound.

Furthermore, in a case in which the lowering speed of the lift plate 21 is reduced with only the spring 32, due to the release of the compressed spring 32 after the lift plate 21 has been lowered and due to the following repeated compression, reciprocal damping is caused in the lift plate 21 causing a different type of noise, or the appearance may become degraded. Furthermore, when the user stacks the sheet, because the position of the lift plate 21 does not become fixed since the lift plate 21 is made to float with the spring, work efficiency when replenishing the sheets S is disadvantageously decreased.

Conversely, when configured as in the present exemplary embodiment, the lift plate 21 can be lowered without generating an impact sound. Furthermore, after the lift plate 21 has been lowered, by locking the sliding claws 26c and 26d to the cassette rib 2b, occurrence of damage due to reciprocal damping can be prevented; accordingly, reciprocal damping being caused in the lift plate 21 generating a different type of noise and the appearance becoming degraded can be prevented.

As described above, in the exemplary embodiment, braking force created by frictional force is applied to the lifter gear 26 with the brake unit 40A, and the force exerted to the lifter gear 26 is absorbed with the buffer member 40B. With the above, when the lift plate 21 is lowered, the lowering speed of the lift plate 21 can be reduced without using a damper or the like, and the lift plate 21 can be prevented from coming into aggressive contact with the bottom surface of the cassette main body 20. As a result, the impact and the impact sound created when the lift plate 21 falls can be reduced easily with low cost.

Furthermore, even if reaction force of the compressed spring 32 is received after the lift plate 21 has been lowered, by locking the sliding claws 26c and 26d to the bevel portion 2b-4 of the cassette rib 2b, the lift plate 21 can be stopped. With the above, the lift plate 21 can be positioned at a position facilitating replenishment of the sheets S when the sheet feeding cassette 2 is drawn out from the printer main body 1A; accordingly, user operability can be improved.

Note that in the present exemplary embodiment, a rib is provided in the cassette main body 20, and claw shapes are provided in the lifter gear 26; however, not limited to the above, the rib may be provided on the lifter gear side, and the elastic claw shapes may be provided on the cassette main body 20 side. In other words, the rib may be provided in either one of the cassette main body 20 and the lifter gear 26, and the claw shapes may be provided on the other one of the cassette main body 20 and the lifter gear 26.

Incidentally, in the present exemplary embodiment, a case in which the claw shapes are slid while in pressure contact with the rib in the radial direction has been described; however, the claw shapes may be slid while in pressure contact with the rib in the axial direction of the shaft of the lifter gear.

A second exemplary embodiment of the present disclosure in which the claw shapes are slid while in pressure contact with the rib in the axial direction of the shaft of the lifter gear will be described next. FIG. 12 is a perspective view for describing a configuration of the impact mitigating member of the sheet feeding device according to the present exemplary embodiment, and FIG. 13 is a side view of the back side lateral plate of the cassette main body. Note that in FIGS. 12 and 13, reference numerals that are the same as those in FIGS. 6A to 7 that have already been described are the same or corresponding portions.

As illustrated in FIG. 12, an elastic claw shape 26g that is a claw-shaped projection is formed on the lateral side 26a that is on the cassette main body side of the lifter gear 26. A slit 26h is formed on both sides of the elastic claw shape 26g in the radial direction, accordingly, the elastic claw shape 26g is capable of elastic deformation in a thrust direction (an axial direction) with respect to the lifter shaft 26x of the lifter gear 26. Note that in FIG. 12, a slit on the teeth portion 26b side of the lifter gear 26 is not illustrated.

Furthermore, as illustrated in FIG. 13, a cassette rib 2b capable of being in pressure contact with the elastic claw shape 26g of the lifter gear 26 is provided so as to protrude towards the lifter gear 26 at the outer wall surface of the back side lateral plate 20b of the cassette main body 20. Furthermore, in the present exemplary embodiment, a brake unit 41A illustrated in FIG. 12 is constituted by the elastic claw shape 26g and the cassette rib 2b, and the spring 32 constitute a buffer member 41B illustrated in FIG. 12. Furthermore, the brake unit 41A and the buffer member 41B constitute an impact mitigating member 41.

Note that in the present exemplary embodiment, the cassette rib 2b, as illustrated in FIG. 14 that is a diagram taken along XIV-XIV of FIG. 13, includes a first portion 2b-5 in which the projection amount in the axial direction, that is, a projection amount towards the lifter gear side, is small, a second portion 2b-7 in which the projection amount towards the lifter gear side is large. Furthermore, the cassette rib 2b includes a connection portion 2b-6 connecting the first portion 2b-5 and the second portion 2b-7 that have different projection amounts, and a bevel portion 2b-8.

In the present exemplary embodiment, surfaces of the first portion 2b-5, the connection portion 2b-6, and the second portion 2b-7 constitute a sliding surface on which the elastic claw shape 26g comes in pressure contact. Furthermore, the projection amount of the connection portion 2b-6 increases towards the second portion 2b-7. In other words, in the cassette rib 2b, the gap between the cassette main body 20 and the lifter gear 26 in the axial direction is smaller on the downstream side than the gap on the upstream side in the first direction.

Furthermore, similar to the first exemplary embodiment, the contact angle between the cassette rib 2b and the elastic claw shape 26g at the connection portion 2b-6 is smaller than the contact angle at the bevel portion 2b-8 in which the surface thereof constitutes a locking surface. In the present exemplary embodiment, the contact angle between the cassette rib 2b and the elastic claw shape 26g at the connection portion 2b-6 is about 25 degrees, and the contact angle at the bevel portion 2b-8 is about 60 degrees. Note that, desirably, the angles are adjusted as appropriate according to the size of the lifter gear, the weight of the lift plate, and the like.

Note that as in the present exemplary embodiment, in a case in which the elastic claw shape 26g is slid while in pressure contact with the cassette rib 2b in the axial direction of the shaft of the lifter gear 26, a similar effect to that described in the first exemplary embodiment can be obtained. Furthermore, as in the present exemplary embodiment, the elastic claw shape 26g may be protruded on the lateral side 26a of the lifter gear 26, and the elastic claw shape 26g may be configured to slide while being in pressure contact with the cassette rib 2b in the axial direction of the lifter gear 26, so as to reduce the size of the lifter gear 26. Furthermore, the projection amount of the cassette rib 2b can be reduced. With the above, even in a case in which space is limited, the elastic claw shape and the rib can be formed and reduction in device size can be achieved.

Furthermore, in the description above, a sheet feeding device provided in a laser printer body has been described; however, the sheet feeding device can be applied to a sheet feeding device that is optionally mounted in a laser printer main body as well.

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

This application claims the benefit of Japanese Patent Application No. 2015-217439, filed Nov. 5, 2015, which is hereby incorporated by reference herein in its entirety.

SHEET FEEDING DEVICE AND IMAGE FORMING DEVICE

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