Media stripper, and fixing device and image forming apparatus employing same

A media stripper for use with a pair of first and second, opposed rotary members includes a stripper finger and a rotation restriction mechanism. The stripper finger has an operational edge thereof disposed adjacent to the first rotary member to strip a recording medium from the first rotary member. The stripper finger is rotatable around a pivot axis parallel to a rotation axis of the first rotary member either in a first rotational direction in which the operational edge approaches the first rotary member, or in a second rotational direction in which the operational edge approaches the second rotary member, so as to establish an operational position thereof relative to the first rotary member. The rotation restriction mechanism is disposed for contact with the stripper finger to restrict rotation of the stripper finger in the second rotational direction upon establishment of the operational position of the stripper finger.

CROSS-REFERENCE TO RELATED APPLICATIONS

This patent application is based on and claims priority pursuant to 35 U.S.C. §119 to Japanese Patent Application No. 2010-188115, filed on Aug. 25, 2010, in the Japan Patent Office, the entire disclosure of which is hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a media stripper, and a fixing device and an image forming apparatus employing the same, and more particularly, to a media stripper for use with a pair of rotary members disposed opposite each other to form a nip therebetween, and a fixing device and an electrophotographic image forming apparatus, such as a photocopier, facsimile machine, printer, plotter, or multifunctional machine, employing such a media stripper.

2. Description of the Background Art

In electrophotographic image forming apparatuses, such as photocopiers, facsimile machines, printers, plotters, or multifunctional machines incorporating several of those imaging functions, an image is formed by attracting toner particles to a photoconductive surface for subsequent transfer to a recording medium such as a sheet of paper. After transfer, the imaging process is followed by a fixing process using a fixing device, which permanently fixes the toner image in place on the recording medium by melting and settling the toner with heat and pressure.

Various types of fixing devices are known in the art, most of which employ a pair of generally cylindrical looped belts or rollers, one being heated for fusing toner (“fuser member”) and the other being pressed against the heated one (“pressure member”), which together form a heated area of contact called a fixing nip through which a recording medium is passed to fix a toner image onto the medium under heat and pressure.

One such fixing device includes a multi-roller, belt-based fuser assembly that employs an endless, flexible fuser belt entrained around multiple rollers, one of which is equipped with an internal heater, such as a radiant halogen heater, to heat the length of the fuser belt through contact with the heated roller. The fuser belt is paired with a pressure roller pressed against the outer surface of the fuser belt to form a fixing nip therebetween, at which a toner image is fixed in place with heat from the fuser belt and pressure from the pressure roller.

Owing to the fuser belt which exhibits a relatively low heat capacity and therefore can be swiftly heated, the belt-based fuser assembly eliminates the need for keeping the heater in a sufficiently heated state when idle, resulting in shorter start-up time and smaller amounts of energy wasted during standby, as well as a relatively compact size of the fuser assembly.

One important factor that determines imaging quality of a fixing device is the ability to properly convey a recording medium through the fixing nip without causing the recording medium to wrap around the rotary fixing member. Media wraparound occurs where the toner image heated through the fixing nip becomes sticky and thus adheres to the surface of the fixing member upon exiting the fixing nip. If not corrected, a recording medium wrapping around the fixing member would cause jam or other conveyance failure in the fixing nip.

For obtaining a fixing process with high immunity against media wraparound and concomitant conveyance failure, a fixing device may use a fuser roller or belt coated with a release agent such as fluorine resin where it contacts a heated, sticky toner image in the fixing nip, while equipped with a media stripping mechanism that allows a recording medium to properly separate from the fuser member at the exit of the fixing nip.

For example, in multi-color printing, a non-contact media stripping mechanism is used to strip a recording medium without touching a fuser roller, which often includes a cylindrical body covered by an outer elastic layer of silicone rubber or the like with a coating of oil or fluorine resin deposited thereon. Using the non-contact media stripper prevents the rubber-covered fuser member from damage due to continuous contact with the media stripping mechanism, which would otherwise result in streaks or other imperfections in a resulting image.

One example of such non-contact media stripper is a stripping plate having a thin-edged, wedge-shaped configuration with its thin operating edge directed toward a fuser member to engage a leading edge of a recording medium to strip it off the fuser member. The stripping plate may be provided with a flange or positioning mechanism, such as one that can contact the fuser member outboard of a maximum compatible width of recording medium, so as to maintain the operating edge in position spaced apart from the rotary member. Maintaining a spacing or gap between the stripping mechanism and the fuser member prevents damage to the fuser member as well as undesired offset or re-transfer of toner adherent, if any, from the stripping mechanism to the fuser member to potentially smear and degrade a resulting image.

BRIEF SUMMARY OF THE INVENTION

Exemplary aspects of the present invention are put forward in view of the above-described circumstances, and provide a novel media stripper for use with a pair of first and second, opposed rotary members disposed opposite each other to form a nip therebetween through which a recording medium is conveyed as the rotary members rotate together.

In one exemplary embodiment, the novel media stripper includes a stripper finger and a rotation restriction mechanism. The stripper finger has an operational edge thereof disposed adjacent to the first rotary member to strip the recording medium from the first rotary member. The stripper finger is rotatable around a pivot axis parallel to a rotation axis of the first rotary member either in a first rotational direction in which the operational edge approaches the first rotary member, or in a second rotational direction in which the operational edge approaches the second rotary member, so as to establish an operational position thereof relative to the first rotary member. The rotation restriction mechanism is disposed for contact with the stripper finger to restrict rotation of the stripper finger in the second rotational direction upon establishment of the operational position of the stripper finger.

Other exemplary aspects of the present invention are put forward in view of the above-described circumstances, and provide a novel fixing device.

Still other exemplary aspects of the present invention are put forward in view of the above-described circumstances, and provide a novel image forming apparatus.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, exemplary embodiments of the present patent application are described.

FIG. 1schematically illustrates an image forming apparatus200incorporating a fixing device100according to this patent specification.

As shown inFIG. 1, the image forming apparatus200is a high-speed, digital color imaging system that can print a color image on a recording medium such as a sheet of paper S according to image data, consisting of a generally upper, printer section200A, and a generally lower, sheet feeding section200B combined together to form a freestanding unit, on top of which may be deployed an appropriate image scanner that allows for capturing image data from an original document.

The printer section200A comprises a tandem color printer that forms a color image by combining images of yellow, magenta, and cyan (i.e., the complements of three subtractive primary colors) as well as black, consisting of four electrophotographic imaging stations201Y,201M,201C, and201K arranged in series substantially laterally along the length of an intermediate transfer belt210, each forming an image with toner particles of a particular primary color, as designated by the suffixes “Y” for yellow, “M” for magenta, “C” for cyan, and “K” for black.

Each imaging station201includes a drum-shaped photoconductor205rotatable counterclockwise in the drawing, having its outer, photoconductive surface exposed to an exposure device206while surrounded by various pieces of imaging equipment, such as a charging device202, a development device203accommodating toner of the associated primary color, an electrically biased, primary transfer device204, a cleaning device for the photoconductive surface, etc., which work in cooperation to form a primary toner image on the photoconductor205for subsequent transfer to the intermediate transfer belt210at a primary transfer gap defined between the photoconductive drum205and the primary transfer device204.

The intermediate transfer belt210is trained around multiple support rollers to rotate clockwise in the drawing, passing through the four primary transfer gaps sequentially to carry thereon a multi-color toner image toward a secondary transfer nip defined between a secondary transfer roller212and a backup roller211, at which the toner image is transferred to a recording sheet S fed from the sheet feeding section200B.

The sheet feeding section200B includes one or more sheet trays220each accommodating a stock of recording sheets S, as well as a sheet conveyance mechanism, including multiple rollers, guide plates, etc., which together define a sheet conveyance path for conveying a recording sheet S from the sheet tray220, then through the secondary transfer nip, and then through the fixing device100which fixes the toner image in place on the recording sheet S with heat and pressure, and finally to a sheet stacker215disposed outside the apparatus body to accommodate a finalized print for user pickup. The sheet conveyance path extends substantially laterally from the secondary transfer nip to the fixing device100.

During operation, each imaging station201rotates the photoconductor drum2counterclockwise in the drawing to forward its photoconductive surface to a series of electrophotographic processes, including charging, exposure, development, transfer, and cleaning, in one rotation of the photoconductor drum205.

First, the photoconductive surface is uniformly charged to a specific polarity by the charging device and subsequently exposed to a modulated laser beam emitted from the exposure device206. The laser exposure selectively dissipates the charge on the photoconductive surface to form an electrostatic latent image thereon according to image data representing a particular primary color. Then, the latent image enters the development device which renders the incoming image visible using toner. The toner image thus obtained is forwarded to the primary transfer device that electrostatically transfers the primary toner image to the intermediate transfer belt210through the primary transfer gap.

As the multiple imaging stations201sequentially produce toner images of different colors at the four transfer nips along the belt travel path, the primary toner images are superimposed one atop another to form a single multicolor image on the moving surface of the intermediate transfer belt210for subsequent entry to the secondary transfer nip between the secondary transfer roller212and the backup roller211.

Meanwhile, the sheet conveyance mechanism picks up a lowermost recording sheet S from the sheet stack in the sheet tray220, and then advances it in sync with the movement of the intermediate transfer belt210to the secondary transfer nip.

At the secondary transfer nip, the multicolor image is transferred from the belt210to the recording sheet S, which is then introduced into the fixing device100to fix the toner image in place under heat and pressure. The recording sheet S after fixing is forwarded along the sheet conveyance path to the sheet stacker215for stacking outside the apparatus body, which completes one operational cycle of the image forming apparatus200.

FIG. 2is an end-on, axial cutaway view schematically illustrating the fixing device100incorporated in the image forming apparatus200according to one embodiment of this patent specification.

As shown inFIG. 2, the fixing device100includes a rotary fuser belt51entrained tightly around a fuser roller52and a heat roller53, as well as a rotary pressure roller55pressed against the fuser roller52through the fuser belt51to form a fixing nip N therebetween, all of which extend in an axial, longitudinal direction perpendicular to the sheet of paper on which the FIG. is drawn, while accommodated in an enclosure housing100aof the fixing device100.

In the present embodiment, the fuser belt51comprises an endless, multilayered belt formed of a substrate of stiff material upon which is deposited at least an outer layer of elastic material. For example, the fuser belt51may be a bi-layered belt consisting of a substrate of nickel, stainless steel, or polyimide, coated with an elastic layer of silicone rubber deposited thereupon. A tension roller56is held against the belt51inside the belt loop to impart proper tension to the belt51between the belt supporting rollers52and53.

The fuser roller52comprises a metal-cored rubber roller, approximately 90 mm in diameter, for example, consisting of a cylindrical core of metal covered by an elastic layer of silicone rubber or the like deposited thereupon. To reduce warm-up time, sponged silicone rubber may be used to form the outer elastic layer, which does not absorb excessive heat to cause conductive heat loss where the rubber roller52contacts the fuser belt51.

The heat roller53comprises a hollow roller of thermally conductive metal, such as iron or aluminum, which accommodates a radiant halogen heater54or the like in its hollow interior to supply heat to the fuser assembly. Another heating mechanism, such as an electromagnetic induction heater (IH), may also be employed instead of a radiant heater. Operation of the heater54may be controlled according to readings of a thermometer or thermistor disposed adjacent to the heat roller53to detect temperature of the fuser belt51.

The pressure roller55comprises a metal-cored rubber roller, approximately 80 mm in diameter, for example, consisting of a hollow rotatable core of metal, such as iron, aluminum, or the like, covered by an elastic layer of silicone rubber or the like deposited thereupon. The pressure roller55is provided with a biasing mechanism that presses the pressure roller55against the fuser roller52via the fuser belt51to establish an adjustable, constant pressure in the fixing nip N, i.e., moves the pressure roller55toward the fuser roller52to increase the nip pressure, and moves the pressure roller55away from the fuser roller52to reduce the nip pressure. An optional, dedicated heater59may be provided in the hollow interior of the pressure roller55, so as to heat the pressure roller55to a desired temperature during fixing or where required.

Although the present embodiment depicts an endless fuser belt entrained around multiple rollers, alternatively, instead, the rotary fuser member51may be configured as any suitable rotatable member, such as an internally heated, hollow cylindrical roller, or a looped piece of thin film rotatable around a heated roll or pipe. Also, although the present embodiment depicts a hollow cylindrical pressure roller, alternatively, instead, the rotary pressure member55may be configured as an endless looped belt or other suitable rotatable member. Further, although the present embodiment depicts a motor-driven fuser roller to drive the rotary fixing members, alternatively, a rotary motor may be provided to a pressure roller, a heat roller, or other suitable portion of the fixing assembly.

During operation, the fuser roller52rotates in a given direction of rotation (i.e., clockwise inFIG. 2) to rotate the fuser belt51in the same rotational direction, which in turn rotates the pressure roller55held in contact with the rotating belt51. The fuser belt51during rotation is kept in proper tension with the tension roller56pressing against the belt51from inside of the belt loop, while having its circumference heated with the heat roller53to a given processing temperature sufficient for fusing toner at the fixing nip N.

In this state, a recording sheet S bearing an unfixed, powder toner image T enters the fixing device100, with its previously imaged side facing the fuser belt51and opposite side brought into contact with the pressure roller55. As the rotary fixing members51and55rotate together, the recording sheet S passes through the fixing nip N in a sheet conveyance direction (from right to left inFIG. 2), wherein heat from the fuser belt51causes toner particles to fuse and melt, while pressure from the pressure roller55causes the molten toner to settle onto the sheet surface, thereby fixing the toner image in place on the recording sheet S.

With continued reference toFIG. 2, the fixing device100is shown including a sheet stripper70disposed facing the fuser belt51downstream from the fixing nip N in the sheet conveyance direction. The sheet stripper70includes a stripper finger or plate75having an operational edge thereof disposed adjacent to, and apart from, the fuser belt51to strip the recording sheet S from the fuser belt51at the exit of the fixing nip N. Also, a contact sheet stripper58may be provided facing the pressure roller55downstream from the fixing nip N in the sheet conveyance direction, which has an operational edge thereof disposed in contact with the pressure roller55to prevent the recording sheet S from adhering to or wrapping around the pressure roller55at the exit of the fixing nip N.

The operational edge of the stripper finger75is positioned with a slight spacing or gap from the fuser belt51, so as to prevent potential damage caused by the finger operational edge touching and scratching the belt surface. Also, the finger operational edge is sufficiently close to the exit of the fixing nip N for preventing the outgoing sheet S from being excessively heated by prolonged contact with the fuser belt51, which would otherwise result in imaging defects, such as orange-peel texture, blistering, excessive gloss, hot offset or undesired transfer of toner, and the like.

For example, the operational edge of the stripper finger75may be positioned 5 mm away from the exit of the fixing nip N, and 2 mm away from the pressure roller55, where the fuser roller52has a diameter of 90 mm, and the pressure roller55a diameter of 80 mm, yielding a fixing nip N with a length ranging from 25.5 mm to 26 mm in the sheet conveyance direction.

During operation, where the recording sheet S after fixing adheres to the fuser belt51upon exiting the fixing nip N, the sheet stripper70allows separation of the outgoing sheet S from the belt surface as the stripper finger75engages the leading edge of the sheet S to force it away from the fuser belt51. On the other hand, where the recording sheet S after fixing adheres to the pressure roller55upon exiting the fixing nip N, the sheet stripper58allows separation of the outgoing sheet S from the roller surface by engaging the leading edge of the sheet S to force it away from the pressure roller55. Provision of the sheet strippers70and58to the rotary fixing members51and55, respectively, thus allows for proper conveyance of the recording sheet S immediately downstream from the fixing nip N, which can then proceeds to a suitable guide member to exit the fixing device100.

As used herein, the term “recording medium” herein includes any material, such as a sheet of paper, subjected to imaging process including passage through a nip defined between a pair of opposed rotary members disposed opposite each other. Also, the term “stripping” is used to describe removal of a recording medium from a rotary member forming a nip, and the term “stripper” or “stripper finger” refers to any device, such as wedge, blade, plate, or the like, held in contact with, or spaced apart from a rotary member forming a nip to strip a recording medium from the rotary member, as set forth herein.

FIG. 3is a perspective view schematically illustrating the sheet stripper70included in the fixing device100.

As shown inFIG. 3, the sheet stripper70comprises an elongated assembly including multiple stripper fingers75connected to a rotatable shaft73supported on an elongated stay72, which is in turn rotatably supported via the shaft73on a stationary frame71to be affixed to the enclosure housing100aof the fixing device100. Also included in the sheet stripper70is a pair of positioning flanges74disposed at opposed longitudinal ends of the stay72, each pointing outward from the shaft73beyond the stripper fingers75. Although relatively narrow eight stripper fingers are depicted inFIG. 3, the size, shape, number, or arrangement of stripper fingers is not limited to the embodiment described herein. For example, instead of multiple stripper fingers75, the sheet stripper70may be configured with only a single stripper finger75, in which case the stripper finger75may be an elongated plate extending along a length of the supporting shaft73.

The sheet stripper70is mounted in the fixing device100with the shaft73extending along the fuser roller52, so that the stripper fingers75are arranged in series in the axial, longitudinal direction of the fuser roller52, while the pair of positioning flanges74contacts the fuser belt51outboard of a width of the recording sheet S to form a spacing or gap between the operational edge of the stripper finger75and the fuser belt51.

Additionally, the sheet stripper70may have a biasing member, such as a spring, disposed between the frame71and the stay72to bias the stay71toward the fuser assembly, so that the flanges74slide against the fuser belt51rotating during operation. With the supporting stay72thus biased against the fuser belt51, each stripper finger75is properly positioned with respect to the fuser belt51with a desired, precise spacing between its operational edge and the fuser belt51.

FIG. 4is a sectional view of a sheet stripper70A mounted in the fixing device100according to a first embodiment of this patent specification.

As shown inFIG. 4, the sheet stripper70A includes the stripper finger75having a thin, operational edge thereof disposed adjacent to, and apart from, the rotary fuser belt51to strip the recording sheet S from the fuser belt51. The stripper finger75is rotatable around a pivot axis X parallel to a rotation axis of the fuser belt51either in a first rotational direction (indicated by an arrow R1in the drawing) in which the operational edge approaches the fuser belt51, or in a second rotational direction (indicated by an arrow R2in the drawing) in which the operational edge approaches the pressure roller55, so as to establish an operational position thereof relative to the fuser belt51.

In the present embodiment, the sheet stripper70A is configured as a non-contact stripper with a spacing or gap G defined between the operational edge of the stripper finger75and the surface of the fuser belt51as the positioning flange74contacts and slides against the fuser belt51. Also, the sheet stripper70A includes a gap adjuster screw77interposed between the stripper finger75and the stay72to allow positioning the stripper finger75through rotation either in the first rotational direction R1or in the second rotational direction R2, so as to adjust the width of finger-to-belt gap G during establishment of the operational position.

FIG. 5is a perspective view of an example of the sheet stripper finger75included in the sheet stripper70A ofFIG. 4.

As shown inFIG. 5, the stripper finger75comprises a tabbed base including a first, adjustment tab75adefining an oval slot75dfor accommodating the gap adjuster screw77therein, and a pair of second, mounting tabs75beach positioned generally perpendicular to the first tab75aand defining a through-hole75efor inserting the supporting shaft73therethrough, as well as a stripping tip75cshaped to form a thin, operational edge, combined together with the first and second base tabs75aand75bto form a single, integrated structure.

The stripper finger75may be formed of fluorine resin, such as PFA, or alternatively, may have its operational edge and bottom side (i.e., the side facing a recording medium stripped off the rotary member) provided with a coating of such fluorine resin. Also, the stripper finger75may be obtained as a molded piece of a single material, or an insert-molded piece of different materials.

For example, the stripper finger75may have the first and second tabs75aand75bformed of a relatively rigid resin, and the stripping tip75cformed of resin softer than that of the base tabs75aand75b, which are combined together through insert molding to form a composite structure of the tabbed base and the operational edge. Integrally forming the discrete parts of finger75through insert-molding allows for precise positioning of the stripping tip75crelative to the base tabs75aand75bdefining the slot75dand the through-hole75e, respectively, which leads to good stripping performance of the stripper finger75comparable to a stripper finger obtained through molding of a single material.

With further reference toFIG. 4, the stripper finger75is shown mounted by inserting the shaft73through the through-hole75eof the mounting tab75bto define the pivot axis X, with the stripping tip75cforming the operational edge directed to the fixing nip N, and the adjustment tab75adirected opposite the operational edge across the pivot axis X to face the stay72.

The gap adjuster screw77has its proximal end inserted loosely (i.e., with spacing around the screw shank) into the slot75ddefined in the adjustment tab75aof the stripper finger75, and its distal end screwed into a first screw hole72adefined in the stay72. A compression spring78is provided around the screw shank between the stay72and the stripper finger75, so as to elastically bias the stripper finger75in the first rotational direction R1around the pivot axis X. The gap adjuster screw77loosely engaging the slot75dmay be tightened or loosened to adjust the position of the stripper finger75around the pivot axis X, which allows for fine tuning of the gap G between the operational edge of the stripper finger75and the surface of the fuser belt51.

Specifically, loosening the screw77causes the stripper finger75to rotate around the pivot axis X in the first rotational direction R1to reduce the finger-to-belt gap G whereas tightening the screw77causes the stripper finger75to rotate around the pivot axis X in the second rotational direction R2to enlarge the finger-to-belt gap G.

Provision of the gap adjuster screw77to the sheet stripper70A thus allows for fine tuning of the finger-to-belt gap G in the range of, for example, from approximately 0.1 mm to approximately 0.6 mm, which ensures good stripping performance of the non-contact stripping finger75comparable to, or even more effective than, that of a contact stripping finger. Further, maintaining the finger-to-belt gap G in an appropriate range reliably protects the fuser belt51from damage due to rubbing against the stripper finger75, while reducing the risk of contaminating the stripper finger75with toner adherents, so that such adhesive toner, if present, does not re-transfer or offset from the stripper finger75to the fuser belt51, which would otherwise lead to imaging defects in a resulting print processed through the fixing nip N, as well as premature breakage of the fuser belt51.

With continued reference toFIG. 4, the sheet stripper70A is shown provided with a rotation restriction screw80A disposed for contact with the stripper finger75to restrict rotation of the stripper finger75in the second rotational direction R2upon establishment of the operational position of the stripper finger75, thereby preventing the operational edge of the finger75from contacting the pressure roller55.

Specifically, the rotation restriction screw80A is inserted into a second screw hole72bdefined in the stay72, which is located facing the adjustment tab75aand farther from the stripping tip75cthan the first screw hole72a, so that the screw80has its distal end in contact with the adjustment tab75awithout interfering the slot75daccommodating the gap adjuster screw77.

During assembly, the rotation restriction screw80A remains loosened in the screw hole72bof the stay72during adjustment of the finger-to-belt gap G through the gap adjustment screw77. After gap adjustment, the screw80A is screwed down toward the adjustment tab75aof the stripper finger75until the distal end of the screw80A becomes flush with the surface of the adjustment tab75a.

In such a configuration, the rotation restricting screw80A contacts the adjustment tab75ato restrict rotation of the stripper finger75in the second rotational direction R2around the pivot axis X, where the stripper finger75once set in the operational position is forced to rotate around the pivot axis X, for example, upon a recording sheet jamming the fixing nip N. Such rotation restriction capability prevents the finger-to-belt gap G from improperly enlarging, and prevents the stripper finger75from accidental contact with the pressure roller55, which would otherwise result in damage to the pressure roller55, particularly where the roller55has an outer circumferential surface formed of a soft, elastic material.

For comparison purposes and for facilitating an understanding of the sheet stripping mechanism according to this patent specification, consider a comparative example of sheet stripper170that does not have a rotation restriction mechanism with reference toFIG. 6.

As shown inFIG. 6, the overall configuration of the sheet stripper170is similar to that depicted above primarily with reference toFIG. 4, in which the sheet stripper170, disposed downstream from a fixing nip N defined between a pair of rotary fixing members, one being a fuser belt151entrained around a fuser roller152and the other being a pressure roller155having an elastic, rubber-covered outer surface, includes a thin-edged, stripper finger175having an operational edge thereof spaced apart from the fuser belt151to strip a recording sheet S from the fuser belt151, while rotatable either in a first rotational direction R1or in a second rotational direction R2around a shaft173supported on a stay172provided with a positioning flange174to define an edge-to-belt gap G which is adjustable through a spring-loaded, gap adjuster screw177disposed between the stripper finger175and the supporting stay172, except that the sheet stripper170does not include a rotation restriction mechanism.

Although effectively protected against accidental contact between the stripper finger175and the fuser belt151, the sheet stripper170occasionally fails to strip a recording sheet S from the fuser belt151, which then wraps around the fuser belt151to cause a jam in the fixing nip N. In such cases, the recording sheet S enters between the fuser belt151and the stripper finger175, thrusting against the finger operational edge to cause it to rotate around the pivot axis X in the second direction R2, and to eventually strike and damage the pressure roller155.

The problem is particularly pronounced in high-speed, color printing application using a pair of relatively large rotary fixing members, typically larger than 50 mm in diameter, where the stripper finger175has its operational edge shaped into an extremely thin-wedged configuration and disposed as close as possible to the exit of the fixing nip N for preventing the outgoing sheet S from being excessively heated by prolonged contact with the fuser belt151, which would otherwise result in imaging defects, such as orange-peel texture, blistering, excessive gloss, hot offset or undesired transfer of toner, and the like.

Not surprisingly, positioning the operational edge of the stripper finger175closer to the fixing nip N results in a reduced spacing Δ left between the finger operational edge and the pressure roller155, which makes the finger operational edge susceptible to contact with the pressure roller155upon rotation of the stripper finger175in the second rotational direction R2. In particular, contact with the finger operational edge can cause a significant damage to the elastic surface of the pressure roller155, where the finger operational edge is at a distance of 7 mm or shorter away from the exit of the fixing nip N with the opposed fixing rollers152and155both having a diameter of 80 mm or larger.

The problem encountered by the comparative example described above is effectively prevented in the sheet stripper70provided with the rotation restriction mechanism80according to this patent specification. That is, where a recording sheet S jamming between the fuser belt51and the stripper finger75thrusts against the finger operational edge to cause it to rotate around the pivot axis X, the rotation restriction screw80with its distal end contacting the adjustment tab75aof the stripper finger75counteracts the rotational force to hinder rotation of the stripper finger75in the second rotational direction R2. Hence, provision of the rotation restriction mechanism80allows for secure operation of the sheet stripper70, leading to high quality imaging performance of the fixing device100even in high-speed color printing applications.

FIG. 7is a sectional view of a sheet stripper70B mounted in the fixing device100according to a second embodiment of this patent specification.

As shown inFIG. 7, the overall configuration of the sheet stripper70B is similar to that of the first embodiment depicted above, except that the rotation restricting mechanism includes a screw or bolt80B combined with a locking nut81.

Specifically, the rotation restriction screw80B has its proximal end inserted loosely (i.e., with spacing around the screw shank) into the slot75ddefined in the adjustment tab75aof the stripper finger75, and its distal end screwed into a second screw hole72bdefined in the stay72, which is located facing the adjustment tab75aand farther from the stripping tip75cthan the first screw hole72a. The locking nut81is fitted on the shank of the rotation restriction screw80B between the stay72and the stripper finger75, so as to be driven toward the stay72when loosened, and toward the stripper finger75when tightened.

During assembly, the rotation restriction screw80B is inserted into the screw hole72bof the stay72with its locking nut81sufficiently loosened and not touching the stripper finger75during adjustment of the finger-to-belt gap G through the gap adjustment screw77. After gap adjustment, the locking nut81is torqued down toward the adjustment tab75aof the stripper finger75until it becomes flush with the surface of the base tab75a, thereby retaining the screw80B in place on the stripper finger75.

In such a configuration, the rotation restricting screw80B combined with the locking nut81contacts the adjustment tab75ato restrict rotation of the stripper finger75in the second rotational direction R2around the pivot axis X, where the stripper finger75once set in the operational position is forced to rotate around the pivot axis X, for example, upon a recording sheet jamming the fixing nip N. Such rotation restriction capability prevents the finger-to-belt gap G from improperly enlarging, and prevents the stripper finger75from accidental contact with the pressure roller55, which would otherwise result in damage to the pressure roller55, particularly where the roller55has an outer circumferential surface formed of a soft, elastic material.

In further embodiment, the sheet stripper70B may be configured with a stripper finger that has a dedicated slot for accommodating the rotation restriction screw80instead of an oval slot accommodating both the rotation restriction screw80as well as the gap adjuster screw77therein. An example of such a sheet stripper finger75is depicted inFIG. 8.

As shown inFIG. 8, the stripper finger75comprises a tabbed base including a first, adjustment tab75adefining a pair of first and second slots75dand75f, the former for accommodating the gap adjuster screw77and the latter for accommodating the rotation restriction screw80therein, and a pair of second, mounting tabs75beach positioned generally perpendicular to the first tab75aand defining a through-hole75efor inserting the supporting shaft73therethrough, as well as a stripping tip75cshaped to form a thin, operational edge, combined together with the first and second base tabs75aand75bto form a single, integrated structure. As is the case with the foregoing example, the stripper finger75may be a molded piece of fluorine resin, such as PFA, or alternatively, may have its operational edge and bottom side (i.e., the side facing a recording medium stripped off the rotary member) provided with a coating of such fluorine resin.

In these and other embodiments, the stripper finger75may have either of the configurations depicted inFIGS. 5 and 9, as well as any configuration other than those specifically described, depending on specific configuration of the sheet stripping mechanism.

FIG. 9is a sectional view of a sheet stripper70C mounted in the fixing device100according to a third embodiment of this patent specification.

As shown inFIG. 9, the overall configuration of the sheet stripper70C is similar to that of the foregoing embodiments depicted above, except that the rotation restricting mechanism includes a specially shaped screw or bolt80C combined with an E-ring82.

Specifically, the rotation restriction screw80C has its proximal end inserted loosely (i.e., with spacing around the screw shank) into the second slot75fseparate from the first slot75ddefined in the adjustment tab75aof the stripper finger75, and its distal end screwed into the second screw hole72bdefined in the stay72, which is located facing the adjustment tab75aand farther from the stripping tip75cthan the first screw hole72a. The E-ring82is fitted on the shank of the rotation restriction screw80C between the stay72and the stripper finger75.

With additional reference toFIGS. 10A and 10B, more specifically, the rotation restriction screw80C has its shank partially unthreaded and defining a recessed portion83adjacent to the proximal end for fitting the E-ring82therearound. The recessed portion83is located at a depth D from the screw head, substantially equal to a thickness T of the adjustment tab75aof the stripper finger75.

During assembly, the rotation restriction screw80C is inserted into the screw hole72bof the stay72without the E-ring82fitted therein, so that the screw80C may move relative to the stripper finger75during adjustment of the finger-to-belt gap G through the gap adjustment screw77. After gap adjustment, the screw80C is screwed down toward the adjustment tab75aof the stripper finger75until the head of the screw80C becomes flush with the surface of the adjustment tab75a. Then, the E-ring82is fitted in the recessed portion83of the screw80C, so that the screw80C no longer moves through the slot75f, thereby retaining the screw80C in place on the stripper finger75.

In such a configuration, the rotation restricting screw80C combined with the E-ring83contacts the adjustment tab75ato restrict rotation of the stripper finger75in the second rotational direction R2around the pivot axis X, where the stripper finger75once set in the operational position is forced to rotate around the pivot axis X, for example, upon a recording sheet jamming the fixing nip N. Such rotation restriction capability prevents the finger-to-belt gap G from improperly enlarging, and prevents the stripper finger75from accidental contact with the pressure roller55, which would otherwise result in damage to the pressure roller55, particularly where the roller55has an outer circumferential surface formed of a soft, elastic material.

In further embodiment, instead of a partially recessed screw combined with an E-ring, the rotation restriction screw80C may be configured as a shoulder screw or bolt combined with a locking nut, as shown inFIGS. 11A and 11B.

Specifically, the rotation restriction screw80C has its shank threaded to fit a locking nut84therearound, while defining an unthreaded shoulder85at the proximal end larger in diameter than the threaded portion. The shoulder85has a depth D from the screw head, substantially equal to a thickness T of the adjustment tab75aof the stripper finger75.

During assembly, the rotation restriction screw80C is inserted into the screw hole72bof the stay72with its locking nut84loosened sufficiently, so that the screw80C may move relative to the stripper finger75during adjustment of the finger-to-belt gap G through the gap adjustment screw77. After gap adjustment, the screw80C is screwed down toward the adjustment tab75aof the stripper finger75until the head of the screw80C becomes flush with the surface of the adjustment tab75a. Then, the nut84is torqued down toward the stripper finger75, so that the screw80C no longer moves through the slot75f, thereby retaining the screw80C in place on the stripper finger75.

In such a configuration, the rotation restricting screw80C combined with the locking nut84contacts the adjustment tab75ato restrict rotation of the stripper finger75in the second rotational direction R2around the pivot axis X, where the stripper finger75once set in the operational position is forced to rotate around the pivot axis X, for example, by a recording sheet jamming the fixing nip N. Such rotation restriction capability prevents the finger-to-belt gap G from improperly enlarging, and prevents the stripper finger75from accidental contact with the pressure roller55, which would otherwise result in damage to the pressure roller55, particularly where the roller55has an outer circumferential surface formed of a soft, elastic material.

Hence, the rotation restriction mechanism80according to this patent specification effectively prevents failures due to contact between the stripper finger75and the pressure roller55upon establishment of the operational position of the stripper finger75, wherein the rotation restriction member80, such as a screw or bolt, provided on the supporting stay72of the stripper finger75contacts the adjustment tab75adisposed opposite the operational edge across the pivot axis X of the stripper finger75, so as to restrict rotation of the stripper finger75in the second rotational direction R2around the pivot axis X.

Provision of the rotation restriction mechanism80allows for positioning the stripper finger extremely close to the exit of the fixing nip N, leading to secure, reliable performance of the sheet stripper70regardless of the type of recording sheet S in use. Further, restricting rotation of the stripper finger75by acting on the adjustment tab75aapart from the operational edge enables the operational edge to be positioned within an extremely small space adjacent to the fixing nip N. Furthermore, the rotation restriction member80provided on the supporting stay72can be positioned extremely close to the stripper finger75, so as to effectively act on the stripper finger75even where the sheet stripper70has a compact design with a reduced size of the stripper finger75. Moreover, use of inexpensive components, such as a screw or bolt, with or without a retaining member, as a rotation restrictor allows for low-cost production of the fixing device100incorporating the rotation restriction mechanism80.

Although in the embodiments described above, the rotation restriction mechanism80employs a rotation restriction member provided on the supporting stay72of the stripper finger75, alternatively, instead, it is possible to provide the rotation restriction member to the enclosure housing100aof the fixing member100which accommodates the rotary fixing members51and55. Several such embodiments are described below with reference toFIGS. 12 and 13.

FIG. 12is a sectional view of a sheet stripper70D mounted in the fixing device100according to a fourth embodiment of this patent specification.

As shown inFIG. 12, the overall configuration of the sheet stripper70D is similar to that of the foregoing embodiments depicted above, except that the rotation restricting mechanism includes a stationary flange80D affixed to the enclosure housing100aof the fixing device100, facing the adjustment tab75aof the stripper finger75.

Unlike the foregoing embodiments, the sheet stripper70D is configured as a non-contact stripper, i.e., with no spacing between the operational edge of the stripper finger75and the surface of the fuser belt51, wherein a tension spring86is disposed between the enclosure housing100aof the fixing device100and the adjustment tab75aof the stripper finger75to bias the stripper finger75in the first rotational direction R1, so as to press the finger operational edge against the fuser belt51.

The rotation restriction flange80D is spaced apart from the adjustment tab75awhere the stripper finger75is in position, which allows the stripper finger75to rotate by a limited amount in the second rotational direction R2around the pivot axis X. This amount of rotation does not exceed an amount of rotation required to bring the operational edge of the stripper finger75into contact with the pressure roller55.

In such a configuration, the rotation restricting flange80D, normally spaced apart from the adjustment tab75a, contacts the adjustment tab75ato stop rotation of the stripper finger75in the second rotational direction R2around the pivot axis X, where the stripper finger75once set in the operational position is forced to rotate by the limited amount around the pivot axis X, for example, upon a recording sheet jamming the fixing nip N. Such rotation restriction capability prevents the stripper finger75from accidental contact with the pressure roller55, which would otherwise result in damage to the pressure roller55, particularly where the roller55has an outer circumferential surface formed of a soft, elastic material.

FIG. 13is a sectional view of a sheet stripper70E mounted in the fixing device100according to a fifth embodiment of this patent specification.

As shown inFIG. 13, the overall configuration of the sheet stripper70E is similar to that of the foregoing embodiments depicted above, except that the rotation restricting mechanism includes a positionable screw80E screwed onto the enclosure housing100aof the fixing device100, facing the adjustment tab75aof the stripper finger75.

As is the case with the fourth embodiment, the sheet stripper70E is configured as a non-contact stripper, i.e., with no spacing between the operational edge of the stripper finger75and the surface of the fuser belt51, wherein a tension spring86is disposed between the enclosure housing100aof the fixing device100and the adjustment tab75aof the stripper finger75to bias the stripper finger75in the first rotational direction R1, so as to press the finger operational edge against the fuser belt51.

During assembly, the rotation restriction screw80E is screwed into position spaced apart from the adjustment tab75awhere the stripper finger75is in position, which allows the stripper finger75to rotate by a limited amount in the second rotational direction R2around the pivot axis X. This amount of rotation does not exceed an amount of rotation required to bring the operational edge of the stripper finger75into contact with the pressure roller55.

In such a configuration, the rotation restricting screw80E, normally spaced apart from the adjustment tab75a, contacts the adjustment tab75ato stop rotation of the stripper finger75in the second rotational direction R2around the pivot axis X, where the stripper finger75once set in the operational position is forced to rotate by the limited amount around the pivot axis X, for example, upon a recording sheet jamming the fixing nip N. Such rotation restriction capability prevents the stripper finger75from accidental contact with the pressure roller55, which would otherwise result in damage to the pressure roller55, particularly where the roller55has an outer circumferential surface formed of a soft, elastic material.

Hence, the rotation restriction mechanism80according to this patent specification effectively prevents failures due to contact between the stripper finger75and the pressure roller55upon establishment of the operational position of the stripper finger75, wherein the rotation restriction member80, such as a stationary flange or positionable screw, provided on the enclosure housing100aof the fixing device100contacts the adjustment tab75adisposed opposite the operational edge across the pivot axis X of the stripper finger75, so as to restrict rotation of the stripper finger75in the second rotational direction R2around the pivot axis X.

In addition to various beneficial effects described earlier, providing the rotation restriction member80, either stationary or positionable, on the enclosure housing100aof the fixing device100allows for a simple configuration of the rotation restriction mechanism70as well as a compact, inexpensive design of the fixing device100incorporating the rotation restriction mechanism70. Although the sheet stripper70in the fourth and fifth embodiments is configured as a contact sheet stripper, the rotation restriction flange and screw70D and70E may work with a non-contact sheet stripper, such as those described in the foregoing embodiments.

To recapitulate, the media stripper70according to this patent specification is used where a pair of first and second opposed rotary members51and55disposed opposite each other forms a nip N therebetween through which a recording medium S is conveyed as the rotary members51and55rotate together.

The media stripper70includes a stripper finger75and a rotation restriction mechanism80. The media stripper70has an operational edge thereof disposed adjacent to the first rotary member51to strip the recording medium S from the first rotary member51. The stripper finger75is rotatable around a pivot axis X parallel to a rotation axis of the first rotary member51either in a first rotational direction R1in which the operational edge approaches the first rotary member51, or in a second rotational direction R2in which the operational edge approaches the second rotary member55, so as to establish an operational position thereof relative to the first rotary member51. The rotation restriction mechanism80is disposed for contact with the stripper finger75to restrict rotation of the stripper finger75in the second rotational direction R2upon establishment of the operational position of the stripper finger75.

Although in several embodiments depicted above, the media stripper70is used in a fixing device that employs a pair of rotary fixing members forming a fixing nip therebetween, instead, the media stripping mechanism according to this patent specification may be used with any media conveyance device that includes a pair of opposed rotary members disposed opposite each other to form a nip therebetween through which a recording medium is conveyed as the rotary members rotate together.

Also, although in several embodiments depicted above, the fixing device is configured as a belt-based assembly including an endless, rotary fuser belt paired with a rotary pressure roller, the media stripping mechanism according to this patent specification may be applicable to any type of fixing device that includes a pair of rotary fuser and pressure members disposed opposite to each other to form a fixing nip therebetween.

Further, although in several embodiments depicted above, the image forming apparatus is configured as a tandem color printer that employs four imaging stations arranged sequentially along an intermediate transfer belt, alternatively, instead, the media stripping mechanism according to this patent specification may be applicable to any type of imaging system that includes a pair of opposed rotary members disposed opposite to each other to form a nip therebetween, in particular, one that incorporates a fixing capability to fix a toner image in place on a recording medium conveyed thorough a fixing nip.

For example, the printer section may employ any number of imaging stations or primary colors associated therewith, e.g., a full-color process with three primary colors, a bi-color process with two primary colors, or a monochrome process with a single primary color. The order in which the multiple imaging stations are arranged sequentially along the intermediate transfer belt may be different than that depicted herein.

Further, instead of a tandem printing system, the printing section may employ any suitable imaging process for producing a toner image on a recording medium, such as one that employs a single photoconductor surrounded by multiple development devices for different primary colors, or one that employs a photoconductor in conjunction with a rotary or revolver development system rotatable relative to the photoconductive surface.

Furthermore, the image forming apparatus according to this patent specification may be applicable to any type of electrophotographic imaging systems, such as photocopiers, printers, facsimiles, and multifunctional machines incorporating several of such imaging functions.