SHEET FEEDING DEVICE AND IMAGE FORMING APPARATUS INCORPORATING THE SHEET FEEDING DEVICE

A sheet feeding device includes a sheet feeding body, a sheet separating body, a loading body, a support, and a pressing body. The sheet feeding body is configured to feed a recording sheet. The sheet separating body is configured to separate the recording medium and convey the recording medium together with the sheet feeding body. The loading body is configured to load the recording medium to be fed by the sheet feeding body. The support is disposed above the sheet separating body. The pressing body is made of metal and rotatably supported by the support between the loading body and the sheet separating body. The pressing body includes a part-shaped face to contact or face the recording medium. A surface of the part is covered with a metal plating.

CROSS-REFERENCE TO RELATED APPLICATION

This patent application is based on and claims priority pursuant to 35 U.S.C. § 119(a) to Japanese Patent Application No. 2019-043919, filed on Mar. 11, 2019, in the Japan Patent Office, the entire disclosure of which is hereby incorporated by reference herein.

BACKGROUND

Technical Field

This disclosure relates to a sheet feeding device and an image forming apparatus incorporating the sheet feeding device.

Background Art

Various types of sheet feeding devices are known to include a sheet metal part (also referred to as a metal plate in the Background Art section) processed with a metallic pressure plate that functions as a pressing body, in addition to a sheet separation roller that functions as a sheet separating body, for the purpose of separating and conveying a sheet that functions as a recording medium.

The metal plate is used for pressure application before sheet separation, that is, a sheet separation method in which pressure is applied before sheet separation is performed by the sheet separation roller even when additional sheets are supplied, so that multi-sheet feeding failure is prevented. With pressure application before sheet separation using such a metal plate, a tip of the metal plate that contacts a sheet feed roller or a sheet is bent into an R-shaped curve, so that the following inconveniences are prevented.

To be more specific, the above-described bending process of the edge of the metal plate is known to prevent (1) deviation of contact to a sheet feed roller by increasing the rigidity of the bent portion of the metal plate due to plastic deformation of the metal plate, (2) loss of safety and easy wear of the sheet feed roller with a sharp tip of the metal plate, and (3) scraping of sheet and generation of paper dust caused by contact with the sharp tip of the metal plate.

SUMMARY

At least one aspect of this disclosure provides a novel sheet feeding device including a sheet feeding body, a sheet separating body, a loading body, a support, and a pressing body. The sheet feeding body is configured to feed a recording sheet. The sheet separating body is configured to separate the recording medium and convey the recording medium together with the sheet feeding body. The loading body is configured to load the recording medium to be fed by the sheet feeding body. The support is disposed above the sheet separating body. The pressing body is made of metal and rotatably supported by the support between the loading body and the sheet separating body. The pressing body is configured to contact and separate with respect to the sheet feeding body at an edge of the pressing body. The pressing body includes a part-shaped face to contact or face the recording medium. A surface of the part is covered with a metal plating.

Further, at least one aspect of this disclosure provides an improved image forming apparatus including an image forming device and the above-described sheet feeding device. The image forming device is configured to form an image on a recording medium. The sheet feeding device is configured to feed the recording medium to the image forming device.

DETAILED DESCRIPTION

FIG. 1is schematic diagram illustrating an image forming apparatus1according to an embodiment of this disclosure. InFIG. 1, the image forming apparatus1is a color printer. Note that, in other embodiments, the image forming apparatus is not limited to a color printer but may be a monochrome printer or another type of image forming apparatus such as a copier or a multifunction peripheral. The image forming apparatus1includes a housing la that includes four image forming units2Y,2C,2M, and2K, a primary transfer unit3, a secondary transfer roller4, an optical writing device5, a sheet feeding device6that functions as a target recording medium sheet feeder, a fixing device7, a pair of sheet ejection rollers8, and a sheet ejection tray11.

The image forming units2Y,2C,2M, and2K are disposed at substantially a center of the housing la. The image forming units2Y,2C,2M, and2K correspond to yellow image, cyan image, magenta image, and black image, respectively, and include respective photoconductor drums12Y,12C,12M, and12K, each of which functions as an image bearer. Further, the image forming units2Y,2C,2M, and2K include charging rollers13Y,13C,13M, and13K, developing devices14Y,14C,14M, and14K, and photoconductor cleaning devices15Y,15C,15M, and15K, respectively. It is to be noted that the image forming units2Y,2C,2M, and2K are occasionally referred to as the “image forming unit2” in a single form without suffixes. Similarly, the charging rollers13Y,13C,13M, and13K, the developing devices14Y,14C,14M, and14K, and the photoconductor cleaning devices15Y,15C,15M, and15K are also occasionally referred to as the “charging roller13”, the “developing device14”, and the “photoconductor cleaning device15”, respectively, in a singular form. The optical writing device5emits light to irradiate a surface of the photoconductor drum12(i.e., the photoconductor drums12Y,12C,12M, and12K), so that an electrostatic latent image that corresponds to the image is formed on the surface of the photoconductor drum12. Toner is supplied from a toner bottle16(i.e., toner bottles16Y,16C,16M, and16K) to the developing device14(i.e., the developing devices14Y,14C,14M, and14K) to develop the electrostatic latent image into a visible toner image.

The primary transfer unit3is disposed above the image forming unit2. The primary transfer unit3includes an entrance roller17, a drive roller18, an opposing roller19, a backup roller20, a support roller21, and a transfer belt22stretched over these rollers. The primary transfer unit3further includes primary transfer rollers23Y,2523C,23M, and23K. The primary transfer rollers23Y,23C,23M, and23K are disposed facing the photoconductor drums12Y,12C,12M, and12K, respectively, via the transfer belt22. The single toner images having respective colors of yellow, cyan, magenta, and black formed on the photoconductor drums12Y,12C,12M, and12K are sequentially overlaid on the surface of the transfer belt22.

The secondary transfer roller4is disposed at a position facing the drive roller18via the transfer belt22. A bias applying unit applies a bias to the secondary transfer roller4. By so doing, the secondary transfer roller4transfers the composite toner image formed on the surface of the transfer belt22, collectively onto a sheet P that is fed from the sheet feeding device6.

The optical writing device5is disposed below the image forming unit2. The optical writing device5has a known configuration including a light source, a polygon mirror, various mirrors and lenses. The optical writing device5forms an electrostatic latent image corresponding to an image input from an external device such as a personal computer onto the surface of the photoconductor drum12.

The sheet feeding device6is disposed in a lower part of the housing la and includes a sheet tray24, a sheet feed roller26, and a sheet separation roller27. The sheet tray24includes a bottom plate24athat functions as a sheet loader that loads a sheet P that functions as a sheet-shaped recording medium. The sheet feed roller26functions as a sheet feeding body to feed out the sheet P form the sheet tray24. The sheet separation roller27functions as a sheet separating body to separate and convey the sheet P together with the sheet feed roller26. The sheet feeding device6further includes a pair of sheet conveying rollers28, a pair of registration rollers29, a bypass tray30, a secondary sheet feed roller31, and a friction pad32. The secondary sheet feed roller31feeds the sheet P from the bypass tray30. The friction pad32separates the sheet P and conveys the sheet P together with the secondary sheet feed roller31.

The sheet tray24that is located at the lowest part of the housing la is pulled out to the right inFIG. 1when a cover that is supported by the housing1ato open and close relative to the housing1ais opened. The bottom plate24ais attached to the sheet tray24to be vertically movable. A plurality of sheets P is loaded on an upper face of the bottom plate24a.The sheet feed roller26is disposed above the bottom plate24ato contact with an uppermost sheet P on top of the plurality of sheets P loaded on the bottom plate24a.The sheet feed roller26is driven by a drive unit to rotate in a counterclockwise direction inFIG. 1. The sheet separation roller27has a material with high friction resistance, such as rubber, around the circumferential surface. The circumferential surface, such as rubber, of the sheet separation roller27is pressed against a circumferential surface of the sheet feed roller26by a biasing body. Details of the biasing body are described below.

The pair of sheet conveying rollers28includes a drive roller and a driven roller. Both the drive roller and the driven roller are rotatably supported by the housing1a.The drive roller of the pair of sheet conveying rollers28is driven by a drive unit to rotate, thereby rotating the driven roller that is pressed against the drive roller, to convey the sheet P. The pair of registration rollers29is disposed downstream from the pair of sheet conveying rollers28in a sheet conveyance direction. The pair of registration rollers29includes a drive roller and a driven roller. The drive roller of the pair of registration rollers29is also driven to rotate by a drive unit to convey the sheet P toward a downstream side in the sheet conveyance direction at a given timing.

The bypass tray30is supported by the cover to open and close relative to the cover. Sheets are loaded on the bypass tray30when the bypass tray30is open. The secondary sheet feed roller31is also supported by the cover to open and close relative to the cover. The secondary sheet feed roller31separates and feeds the sheet P loaded on the bypass tray30, one by one, cooperating with the friction pad32. It is to be noted that the cover also rotatably supports the secondary transfer roller4and a pressure roller35. When the cover is to open, a sheet conveyance passage emerges to allow the sheet P to pass through.

The fixing device7is disposed downstream from the secondary transfer roller4in the sheet conveyance direction. The fixing device7includes a heat roller34and a pressure roller35and is disposed at the upper part of the housing la. The heat roller34includes a heater inside and is rotatably supported by the housing la. The heat roller34is rotated by a drive unit. The pressure roller35is rotatably supported by the cover. A biasing force applied by a biasing body causes the circumferential surface of the pressure roller35to closely contact and press against a circumferential surface of the heat roller34, so that the pressure roller35is rotated along with rotation of the heat roller34. The toner image formed on the surface of the sheet P that passes between the heat roller34and the pressure roller35is fixed to the sheet P by application of heat and pressure.

The pair of sheet ejection rollers8is disposed downstream from the fixing device7in the sheet conveyance direction. The pair of sheet ejection rollers8includes a drive roller and a driven roller. As the drive roller of the pair of sheet ejection rollers8is rotated by a drive unit, the driven roller is rotated along with the rotation of the drive roller, so that the sheet P is ejected to the outside of the housing la. After having been ejected by the pair of sheet ejection rollers8, the sheet P is ejected to and stacked in the sheet ejection tray11that is an integral part of the upper face of the housing1a.

According to the above-described configuration, the sheet P loaded on the bottom plate24ais held between (gripped by) a pad24band the sheet feed roller26for image formation to the sheet P. By so doing, when two or more sheets P are conveyed, the two or more sheets P are conveyed to the downstream side in the sheet conveyance direction and are separated one by one between the sheet feed roller26and the sheet separation roller27, so that only a single sheet P at a time is further conveyed. Consequently, the sheet P that has been separated and fed from the sheet tray24is conveyed by the pair of sheet conveying rollers28and the pair of registration rollers29. Then, the toner image is transferred onto the sheet P by the secondary transfer roller4. The sheet P having the toner image then passes through the fixing device7. When passing through the fixing device7, the toner image is fixed to the sheet P. Then, the sheet P is guided to the pair of sheet ejection rollers8to be ejected to the sheet ejection tray11.

Similar to a known sheet feeding device, the sheet feeding device6of the image forming apparatus1has a configuration designed to eliminate an increase in frequent occurrence of multi-sheet feeding failure of the sheets P when the sheets P are added to the sheet tray24. To be more specific, insertion of additional sheets P reduces a friction force generated between the sheets P at a position of insertion of the additional sheets or additional sheet bundle. When the friction force generated at the sheet adding position falls below a friction force generated at another position between other sheets, a few sheets before the sheet adding position are not separated reliably. Consequently, the sheet P is separated from the sheet adding position, resulting in a multi-sheet feeding failure involving a bundle of sheets. In order to separate the sheets P to feed the sheets P one by one reliably, a constant friction force is applied between the sheets P and the lower sheet P remains without being conveyed together with the upper sheet P when the upper sheet P is being fed.

FIG. 2is a cross-sectional view illustrating a sheet feed tray unit24A of the sheet feeding device6according to an embodiment of this disclosure.FIG. 2illustrates a state in which the sheet feed tray unit24A is inserted and set to the housing1a.

The sheet feed tray unit24A includes the sheet tray24, the bottom plate24a,the pad24b,and the sheet separation roller27, as indicated by a broken line inFIG. 2. The sheet feed tray unit24A includes (a pair of) rotary bodies36, compression springs37, and a pressure plate38(seeFIG. 3). The (pair of) rotary bodies36, the compression springs37, and the pressure plate38compose a regulator40that functions as a pre-separation pressure mechanism illustrated inFIGS. 3 and 7.

When the cover that is openably closable and supported relative to the housing1ais opened, the sheet feed tray unit24A is pulled in a tray removal direction Xa (that is, to the right inFIG. 2) so as to additionally supply the sheet P or sheets P. Further, the sheet feed tray unit24A is configured to be inserted in a tray insertion direction Xb (that is, to the left inFIG. 2) after the additional sheets P are supplied.

In order to additionally supply the sheets P, a user holds a handle24c that functions as an integrally formed part with the sheet tray24, pulls out the sheet feed tray unit24A in the tray removal direction Xa, and loads the sheets P onto the bottom plate24afrom above ofFIG. 3. Thereafter, insertion of the sheet feed tray unit24A to the state illustrated inFIG. 1completes preparation for separating and conveying the sheets P one by one as described above.

FIG. 3is a cross-sectional view illustrating a main part of the sheet feeding device6according to an embodiment of this disclosure.

InFIG. 3, the sheet feed roller26is rotatably supported by the housing la and is driven by a drive unit to rotate in a counterclockwise direction inFIG. 3. When the sheet feed tray unit24A illustrated inFIG. 2has been inserted in the tray insertion direction Xb (that is, to the left inFIG. 2) and completely set to the housing la, the sheet feed roller26comes to contact the sheet separation roller27.

The pad24bis disposed at a tip of the bottom plate24a.The pad24bincludes a high friction resistance member to prevent a multi-sheet feeding failure of the sheets P. The pad24bprevents the sheet bundle of sheets P from being excessively fed or causes the force for feeding the sheets P to be sufficiently transmitted.

The bottom plate24ais lifted by a sheet feed pressure spring so that a force is applied to move the bottom plate24ain an upward direction inFIG. 3. The sheet loaded on the bottom plate24ais pressed against the sheet feed roller26by the force of the sheet feed pressure spring, and then obtains a force to convey the sheet to the subsequent process.

FIG. 4is a perspective view illustrating a schematic configuration of the main part of the sheet feeding device6according to an embodiment of this disclosure.FIG. 5is an enlarged perspective view illustrating the main part of the sheet feeding device6ofFIG. 4. The sheet separation roller27is disposed below the sheet feed roller26. The width of the sheet separation roller27is smaller than the width of the sheet feed roller26. It is to be noted that the width of the sheet separation roller27may be equal to the width of the sheet feed roller26or greater.

As illustrated inFIGS. 2 to 5, the sheet separation roller27is rotatably supported by a movable bracket9. A fixed base10is fixedly mounted on the sheet tray24. As illustrated inFIG. 4, the movable bracket9is rotatably supported by the fixed base10at a fulcrum9a.In other words, the movable bracket9has the fulcrum9athat is rotatably supported by the fixed base10to swing (rotate) about the fulcrum9awithin a given angle range in clockwise and counterclockwise directions inFIG. 4.

A compression spring33is interposed between the movable bracket9and the fixed base10. The compression spring33applies a biasing force to the movable bracket9in a direction in which the sheet separation roller27is pressed against the sheet feed roller26. The biasing force of the compression spring33causes the sheet separation roller27to be pressed against the sheet feed roller26, so that the sheet separation roller27closely contacts the sheet feed roller26to form a region through which the sheets are conveyed to be separated. As described above, the movable bracket9, the sheet separation roller27, and the compression spring33compose the pressure pre-separation mechanism.

As illustrated inFIG. 5, a torque limiter27ais provided coaxially with the sheet separation roller27so that the torque limiter27ais built inside the sheet separation roller27. According to the torque limiter27a,the sheet separation roller27idles when the excessive torque is generated. With this configuration, a region that has been occupied by a torque limiter in the configuration of a known sheet feeding device may be used as an open space. Accordingly, the open space made by reducing the length of the support shaft of the sheet separation roller27may be used to provide other parts or to reduce the size of a device, that is, the pre-separation pressure mechanism including the pair of rotary bodies36, the compression springs37, and the pressure plate38.

FIG. 6is a perspective view illustrating a schematic configuration of a fixed guide cover25in the sheet feeding device6according to an embodiment of this disclosure. The fixed guide cover25functions as a support and is disposed above the sheet separation roller27.

The fixed guide cover25is disposed so that the sheet P passes over the upper surface of the fixed guide cover25. The fixed guide cover25is arranged to cover the support shaft of the sheet separation roller27and has an upper face to guide the sheet P to be conveyed along the upper face.

As illustrated inFIG. 6, the fixed guide cover25has an opening through which the circumferential surface of the sheet separation roller27is exposed. The fixed guide cover25is detachably attached to the fixed base10with screws or engaging members.

FIG. 7is a schematic view illustrating the regulator40of the sheet feeding device6according to an embodiment of this disclosure.FIG. 8is a perspective view illustrating a schematic configuration of the fixed guide cover25and the regulator40in the sheet feeding device6according to an embodiment of this disclosure. As illustrated inFIGS. 7 and 8, the pair of rotary bodies36is disposed inside the fixed guide cover25and the respective rollers of the pair of rotary bodies36are located at respective positions outside support positions of the sheet separation roller27. It is to be noted that, hereinafter, for convenience, the pair of rotary bodies36and the compression springs37are occasionally referred to in the singular form, for example, the “rotary body36” and the “compression spring37.”

The rotary body36is rotatably supported by the fixed guide cover25on a support shaft36a.The compression spring37functions as a biasing body and is mounted on the rotary body36, at a position downstream from the support shaft36ain the sheet conveyance direction Xc. One end of the compression spring37is fixed to the projection25aof the fixed guide cover25.

A pressure plate38is disposed at an upstream side end of each of the pair of rotary bodies36in the sheet conveyance direction Xc. The pressure plate38functions as a plate-shaped pressing member formed by pressing and blanking and includes a metal material such as stainless steel. The pressure plate38is attached to the pair of rotary body36by a double tape and glues. The rotary body36is biased by the biasing force of the compression spring37to rotate about the support shaft36ain the counterclockwise direction inFIG. 7. According to this configuration, the edge of the pressure plate38is pressed with a given contact pressure against the circumferential surface of the sheet feed roller26at a position downstream from the support shaft36ain the sheet conveyance direction Xc. The pressure plate38is configured to swing (rotate) about the support shaft36atogether with the rotary body36within a given movable angle range of the rotary body36in clockwise and counterclockwise directions inFIG. 7.

As illustrated inFIG. 8, the compression springs37are configured to be attached at two places, one compression spring37on the left side and the other compression spring37on the right side, of the sheet separation roller27disposed at the center of the sheet feeding device6. As illustrated inFIG. 5, by providing the torque limiter27aprovided inside the roller part of the sheet separation roller27, the open space is effectively used to press the sheet separation roller27in a well-balanced manner.

In a case in which the pressure plate38is a thin metal plate, the pressure plate38has good strength even if the plate is thin, and therefore the metal plate is inserted between the sheet feed roller26and the sheet separation roller27without damaging the edge of the metal plate. In addition, the pressure plate38is excellent in contact durability with sheets, and therefore achieves a maintenance-free configuration having a long service life.

FIG. 9Ais a plan view illustrating the schematic configuration of the main part of the sheet feeding device6according to an embodiment of this disclosure.FIG. 9Bis a side view illustrating the schematic configuration of the main part of the sheet feeding device6according to an embodiment of this disclosure, viewed from the sheet tray24of the sheet feeding device6.

As illustrated inFIGS. 9A and 9B, the pressure plate width, in other words, the length of the sheet width direction of the pressure plate38in a sheet width direction perpendicular to the sheet conveyance direction Xc is greater than the width of the sheet feed roller26. As described above, the pressure plate38is pressed against the sheet feed roller26and is in pressure contact. The pressure contact portion of the pressure plate38is also referred to as a pressure portion.

Similar to a pressing member (that is, a pressure plate) of a known sheet feeding device, the pressure plate38keeps the sheet P straight since the pressure plate38supports the sheet P even in an area beyond the width of the sheet feed roller26. Consequently, when multiple sheets P enter between the sheet feed roller26and the sheet separation roller27, the multiple sheets P remain straight in a stable condition. Accordingly, a frictional state between any adjacent sheets P in the multiple sheets is stabilized, and therefore the sheets P are separated reliably. In other words, by increasing the pressure plate width of the pressure plate38in the sheet width direction to be wider (greater) than the width of the pressure portion, sheet behavior is stabilized to provide good separation.

As described above, in the sheet feeding device6according to this disclosure, the edge of the pressure plate38contacts and separates from the circumferential surface of the sheet feed roller26. According to this configuration, the multiple sheets P are conveyed between the sheet feed roller26and the sheet separation roller27. At this position, when the multiple sheets P pass through the pressure portion that is the pressure contact portion of the pressure plate38, a lower sheet P of the multiple sheets P contacts a sloped face of the pressure plate38. Due to the contact with the sloped face of the pressure plate38, the lower sheet P receives a sheet conveyance load (resistance), which prevents the lower sheet P from climbing over the pressure plate38. Consequently, the upper sheet P alone of the multiple sheets P is conveyed to the sheet separation roller27. According to the above-described operation, sheet separation is performed in two steps, thereby conveying the sheet P without causing a multi-sheet feeding error even if any additional sheet is inserted to the sheet tray.

FIG. 10is a schematic diagram illustrating movement of the pressure plate38used in the sheet feeding device6according to an embodiment of this disclosure.

Each of the pair of rotary bodies36is supported by the fixed guide cover25at the support position that is the position of the support shaft36a.The support position is located upstream from the contact position of the pressure plate38and the sheet feed roller26in the sheet conveyance direction Xc.

With this configuration, as illustrated inFIG. 10, even when the multiple sheets P enter the contact position between the pressure plate38and the sheet feed roller26, the pressure plate38rotates together with the rotary body36in the clockwise direction, as indicated by arrow inFIG. 10, against the biasing force of the compression spring37. Accordingly, since the pressure plate38moves to the downstream side in the sheet conveyance direction Xc to avoid the multiple sheets, a paper jam is prevented.

Known sheet feeding devices have a configuration including a fixed separation plate and another sheet pressing mechanism to press the upper side of a sheet. However, since this known configuration does not include a movable separation plate, a thick paper could not be conveyed or a rubber employed to a sheet separation roller was scraped, and therefore the durability was unstable. A comparative configuration includes a fixed guide cover that functions as a supporting member having such a separation plate. The fixed guide cover25according to this disclosure achieves the above-described effect by attaching to the fixed base10instead of a fixed guide cover provided to the comparative configuration. Accordingly, the effect of this disclosure is obtained easily without changing the comparative configuration significantly.

Further, while a pickup roller is provided to the comparative configuration, the sheet feeding device6according to an embodiment of this disclosure employs a pickup less mechanism that does not include a pickup roller. Therefore, even without a pressing mechanism, the sheet feeding device6achieves the separation performance at low cost.

It is to be noted that, in the sheet feed tray unit24A including the regulator40(seeFIG. 2), the rotary body36illustrated inFIG. 7is rotatable about of the support shaft36awithin a given angle range. InFIG. 2, a stopper mechanism is provided to prevent the pressure plate38from contacting the sheet feed roller26. With the stopper mechanism, when the sheet feed tray unit24A is pulled out in the tray removal direction Xa, the pressure plate38and the rotary body36are restricted from rotating excessively in the counterclockwise direction by the biasing force of the compression spring37. Further, a rotary body retaining mechanism is provided to prevent the rotary body36from coming off from the fixed guide cover25due to excessive rotation.

Further, when the sheet feed tray unit24A is inserted in the opposite direction,30in other words, when the sheet feed tray unit24A is inserted intentionally in the tray insertion direction Xb as illustrated inFIG. 2, the pressure plate38and the sheet separation roller27contact the sheet feed roller26excessively. In order to prevent this excessive contact with the sheet feed roller26, a rotation restricting mechanism is provided to the sheet feeding device6.

FIG. 11is a schematic diagram illustrating a pressure plate44that is another pressure plate used in the sheet feeding device6according to an embodiment of this disclosure.

The structure of the pressure plate44illustrated inFIG. 11is basically identical to the structure of the pressure plate38illustrated inFIG. 7, except that the pressure plate44ofFIG. 11includes a folded portion44aat the edge. The folded portion44aof the pressure plate44indicates a bending edge formed by folding a flat metal plate. The edge of the pressure plate44includes a part of the folded portion44aon the side that contacts with the sheet feed roller26. The pressure plate38and the pressure plate44are identical to each other in structure, where the pressure plate38and the pressure plate44are processed by pressing and blanking a stainless steel plate, for example. The folded portion44ais formed by deforming (folding) the edge of the pressure plate44into an R-shape portion44b.More specifically, the folded portion44ais formed by folding the folded portion44aat an angle of approximately 180 degrees. In other words, the folded portion44ais formed by the hemming (folding).

With respect to the pressure plate44illustrated inFIG. 11, the folded portion44ais stronger, less damaging to a sheet P to contact due to a round-shaped (R-shaped) portion of the folded portion44a,and lengthens a distance to the sheet separation roller27due to no projection of the folded portion44ato the sheet separation roller27. According to this configuration, it is less likely that the pressure plate44contacts the sheet separation roller27, and therefore the configuration prevents the sheet separation roller27from being damaged by the pressure plate44.

The sheet P to be conveyed does not directly contact the pressed end face of the pressure plate38(which indicates the end face in the thickness direction of the outer peripheral shape of the pressure plate38inFIG. 7) and the pressed end face of the pressure plate44(which indicates the end face in the thickness direction of the outer peripheral shape of the pressure plate44inFIG. 11). However, if rust occurs due to, for example, a change over time, it is likely that the rust is exposed on the sheet conveyance passage, which may be a major factor that hinders conveyance of the sheet.

Further, unless some sort of processing is performed, the surfaces of the steel plate (for example, stainless steel plate) of the pressure plate38and the pressure plate44remain in the initial state of the steel plate. Since the sheet P is conveyed while the surface of the sheet P contacts the surfaces of the steel plate of the pressure plate38and the pressure plate44, the condition (coefficient of friction) of the surface of the steel plate is not controlled in this state. The obstructing force against the sheet moving force changes depending on the coefficient of friction of the steel plate surfaces of the pressure plate38and the pressure plate44with respect to the sheet P and the sheet feed roller26, which greatly affects the function of sheet conveyance while separating the sheet P.

In order to address this inconvenience, in one embodiment of this disclosure, the pressure plate38and the pressure plate44, both of which function as metallic pressing members, are metal-plated after pressing and blanking the surface that contacts or faces at least the sheet P and the sheet feed roller26.

By performing the metal plating on the surfaces of the pressure plates38and44as described above, rust due to the change of time is prevented from occurring, in particular, at the edges formed by pressing and blanking and, at the same time, the coefficient of friction is changed according to the separation characteristics. Since the metal-plated surface does not affect adhesion for fixing the pressure plates38and44, the entire configuration is maintained as in the case without metal plating.

If the hemming is not performed, the punched edges of the pressure plates38and44are exposed in a direction perpendicular to the sheet conveyance passage. Occurrence of rust without the hemming is more affected than when the hemming is performed. Even in such a case without the hemming, the above-described metal plating is performed to restrain occurrence of rust, so that the above-mentioned concern may be eliminated.

For example, in a case in which electroplated bright nickel plating is performed as a specific metal plating onto the pressure plates38and44that are formed by pressing an electrolytic zinc-plated metal steel plate, the coefficient of friction of the steel plate, which is a base material of the pressure plates38and44, to the sheet feed roller26including rubber material is changed by approximately 10 percent (%) from 1.8 to 1.6.

According to the classification by a film formation mechanism, any method may be used for performing the above-described metal plating process. Examples of the method include electroplating, hot-dip plating, and electroless plating. In particular, since hot-dip plating (in other words, immersion dipping) is a process in which a steel material is immersed in a molten metal and is plated, the entire surfaces of the pressure plates38and44to be metal-plated (including the punched edges formed by pressing) are plated with a thick film in a short time. With this method, the entire surfaces of the pressure plates38and44, including the areas contacting or facing the sheet P, are formed with a metal plating film easily.

In addition, according to the classification by apparatus and process, any method may be employed for performing the above-described metal plating process. Examples of the method include rack plating, barrel plating, and hoop plating.

The above-described metal plating is performed after forming the shapes of members and components such as the pressure plates38and44. “Forming the shapes of members and components” refers to cutting, bending, or both. This process achieves an effect of protecting the cut surface forming the part and an effect of retaining a stable surface property when compared with the bending after the processing. In other words, the metal plates are formed on the surfaces of the pressure plates38and44, at least on the surface shaped (cut, bent, or both) as a part that contacts or faces the sheet P and the sheet feed roller26.

As described above, the configuration according to an embodiment of this disclosure achieves basic effects, which are to prevent the rust of the pressing member from occurring and to change the friction coefficient of the pressing member to the sheet as the recording medium.

The sheet feeding device according to this disclosure includes a pressing member made of metal, for example, the pressure plate38illustrated inFIG. 7and the pressure plate44illustrated inFIG. 11. However, the pressing member applicable to this disclosure is not limited to the pressure plate38and the pressure plate44. For example, pressure plates employed in a comparative sheet feeding device may be applied to this disclosure. To be more specific, a pressure plate in the comparative sheet feeding device is a stainless steel plate that includes a folded portion at the edge. The folded portion is formed by bending the leading end of the pressure plate at an angle of substantially 90 degrees toward a direction opposite to a sheet feed roller of the comparative sheet feeding device. Another pressure plate of the comparative sheet feeding device includes a folded portion and has a structure simpler than the above-described pressure plate. Different from the above-described pressure plate, the bending of this pressure plate begins at a portion closer to the root. Yet another pressure plate of the comparative sheet feeding device also includes a folded portion and has a round shape at the edge. These pressure plates of the comparative sheet feeding device may be applied to this disclosure.

Here, an additional description is given of the above-described comparative sheet feeding device. The comparative sheet feeding device includes the configurations in which the above-described pressure plates are used as pressing members made of metal plates to separate and convey a sheet functioning as a cording target medium. The comparative sheet feeding device has the configuration similar to the configuration of the sheet feeding device6according to an embodiment of this disclosure, in that a pressing member of made of a metal plate is employed.

However, the comparative sheet feeding device cannot prevent occurrence of rust on the pressing member, and therefore the coefficient of friction of the pressing member to a recording medium cannot change.

As described above, this disclosure is applicable to the sheet feeding device6having the configuration illustrated inFIGS. 1 and 7and the sheet feeding device6having the configuration employing the sheet feed roller, the sheet separation roller, and the pressing member of the comparative sheet feeding device. However, the configuration applicable to this disclosure is not limited to the above-described configurations. For example, this disclosure may be applicable to another configuration of the comparative sheet feeding device including a pickup roller, a sheet feed roller, and a pressing member and yet another configuration of the comparative sheet feeding device including a sheet feed roller, a friction pad, and a pressing member.

In the above-described embodiments, the term “image forming apparatus” indicates an apparatus in which an image is formed on a recording medium such as paper, OHP (overhead projector) transparencies, OHP film sheet, thread, fiber, fabric, leather, metal, plastic, glass, wood, and/or ceramic by attracting developer or ink thereto; the term “image formation” indicates an action for providing (i.e., printing) not only an image having meanings such as texts and figures on a recording medium but also an image having no meaning such as patterns on a recording medium; and the term “sheet” is not limited to indicate a paper material but also includes the above-described plastic material (e.g., an OHP sheet), a fabric sheet and so forth, and is used to which the developer or ink is attracted. In addition, the “sheet” is not limited to a flexible sheet but is applicable to a rigid plate-shaped sheet and a relatively thick sheet.

Further, the size (dimension), material, shape, and relative positions used to describe each of the components and units are examples, and the scope of this disclosure is not limited thereto unless otherwise specified. Further, it is to be noted in the following examples that: the term “sheet conveying direction” indicates a direction in which a recording medium travels from an upstream side of a sheet conveying path to a downstream side thereof; the term “width direction” indicates a direction basically perpendicular to the sheet conveying direction.

It is to be noted that reference sign “X” indicates is a direction from the front20side to the rear side of the image forming apparatus1, reference sign “Y” indicates is a direction from the left side to the right side of the image forming apparatus1, and reference sign “Z” indicates is a direction perpendicular to the direction X and the direction Y. In the above-described embodiments, the sheet P for image formation is employed as a recording medium on which an image is formed. However, the sheet P is not limited to the recording medium but also includes thick paper, postcard, envelope, plain paper, thin paper, coated paper, art paper, tracing paper, and the like. The sheet P further includes a non-paper material such as OHP sheet, OHP film, resin film, and any other sheet-shaped material on which an image may be formed.

The effects described in the embodiments of this disclosure are listed as the examples of preferable effects derived from this disclosure, and therefore are not intended to limit to the embodiments of this disclosure.

The embodiments described above are presented as examples to implement this disclosure and are not intended to limit the scope of this disclosure. These novel embodiments can be implemented in various other forms, and various omissions, replacements, or changes can be made without departing from the gist of this disclosure. These embodiments and their variations are included in the scope and gist of this disclosure, and are included in the scope of this disclosure recited in the claims and its equivalent.