Hot roll fuser for a xerographic copier

Abstract

 In a hot roll fuser for a xerographic copier, the hot roll 14 is mounted at a fixed axial position and the back-up roll 16 is mounted on pivot arms 36 for pivotal movement about axis 38 to and from the hot roll. A further pivot arm assembly is mounted on an axis 42 positioned between the axes of the rolls. This assembly includes two arms 40, each of which extends round the axis 34 of the back-up roll to a mounting position 60. At each end of the back-up roll, a compression spring 50 is mounted between the roll axis 34 and mounting position 60. Arms 40 each include a cam follower surface 44 which engages the surface of a cam 46. As cam 46 rotates it causes movement of the arms between a position at which back-up roll 16 is separated from roll 14 and a position at which roll 16 is urged into contact with roll 14 by springs 50. At this latter position, the axis 34 of the back-up roll is positioned on a line between pivotal axis 42 and mounting position 60.

Description

[0001] The present invention relates to xerographic copying apparatus and in particular to a hot roll fuser therefor.

[0002] Hot roll fusers comprise a heatable roll and a back-up roll which, in operation, are brought together to form a fusing nip through which copy sheets carrying toned images are passed to cause fusing of the images to the sheets. The present invention is concerned with a mechanism for effecting relative movement between the rolls in a hot roll fuser to position them between an open position at which they are apart and a closed position at which they provide a fusing nip, and is characterised by a first pair of link arms (36) arranged for pivotal movement about a first common axis (3&) and having means for supporting respective ends of one of said rolls to provide arcuate movement thereof about said first common axis (38), a second pair of link arms (40) arranged respectively at the ends of said one of said rolls for pivotal movement between two predetermined limits about a second axis (42) and having spring mounting means (60) positioned thereon remote from the pivot point (42), and a pair of compression springs (50) positioned respectively at each end of said one of said rolls and coupled between said spring mounting means (60) and said means for supporting on the respective link arms, the arrangement being such that when the seconi pair of link arms (40) is positioned at the first of said two predetermined limits, the roll supporting means is positioned on a line running between the second axis (42) and the spring mounting means (60), and the springs bias the rolls into engagement.

[0003] An embodiment of the invention will now be described with reference to the drawings, in which:

FIGURE 1 is a general view of a copier incorporating a hot roll fuser system;

FIGURE 2 is a simplified cross-sectional view of the Fiure 1 fusing system;

FIGURE 3 is a diagrammatic view of the fusing system showing its roll closure mechanism;

FIGURE 4 is a diagrammatic view of a fusing assembly as in FIGURE 3, but seen from the opposite side;

FIGURES 5 and 6 are exploded diagrammatic views of the solenoid, pivoting link and clutch shown in FIGURE 4;

FIGURE 7 is a diagrammatic view of a mechanism used to move associated hardware in the fuser to facilitate access to the hot roll and backup roll area;

FIGURE 8 is a diagrammatic view as in FIGURE 7, with the associated hardware moved out of the way for access to the hot roll and cold roll;

FIGURE 9 is a perspective view of the fixed center drive for producing rotation of the backup roll, the backup roll's scraping blade cleaner and the fuser's paper exit guide transport roller; and

FIGURE 10 is an overall perspeczive view of the fusing assembly.

[0004] FIGURE 1 is a general view of xerographic copier 10 incorporating a fuser assembly 12 which is shown in its extended or pulled-out position in front of the copier. Fuser assembly 12 is slidably supported within copier 10. This is a non-operating position adapted to facilitate inspection, cleaning, repair and/or sheet jam clearance.

[0005] The slidably supported fusing assembly 12 includes a hot roll 14 and a backup roll 16. Generally, hot roll 14 is heated to an accurately controlled temperature by an internal heater 15, as seen in FIGURE 2, and an associated temperature control system which is not shown. Hot roll 14 preferably includes a deformable external surface formed as a thin elastomeric surface. This surface is designed to engage the toned side of a copy sheet, fuse the toner thereon and readily release the sheet with a minimum adherence of residual toner to the hot roll. As is conventional in hot roll fusers, the sheet toned side faces the hot roll.

[0006] Backup roll 16 is preferably a relatively cool and rigid roll. Both rolls 14 and 16 are circular cylinders and the fusing nip formed thereby defines a line (of some width due to deformation of hot roll 14) parallel to the axis of rolls 14 and 16.

[0007] The fusing nip formed by rolls 14 and 16 may be opened and closed in synchronism with the arrival and departure of the copy sheet's leading and trailing edges, respectively. This synchronism is achieved by a drum position sensing means which responds to the position of the photoconductor drum and effects opening and closing of the nip by means of a copier control system, all not shown. In the alternative, for a multi-copy run, the fusing nip may continuously remain closed until the trailing end of the last sheet has passed therethrough.

[0008] FIGURE 2 shows the fusing nip closed. Rigid backup roll 16 is shown to be in contact with resilient hot roll 14, thereby deforming the surface of hot roll 14 so as to form a fusing nip 18 of a certain width, measured in the direction of sheet movement 19. Feed roller 20 cooperating with idler roller 21 continues sheet movement 19 until a copy passing therethrough is free of fusing nip 18 and has passed through fuser exit-way or sheet transport channel 22.

[0009] In FIGURES 3 and 4, hot roll 14 is removably, rotationally mounted on a fixed position axis in mounting blocks 23 which are supported by way of positioning surfaces 24 formed in the ends of a single piece mointing main frame member 26. This main frame member 26 ireludes a hanger 28 which supports the fuser assembly by way of telescoping rails 30. Frame member 26 also includes rollers 32 which cooperate with a copier frame memb r to stabilize the fuser assembly position within the) copier.

[0010] As seen in FIGURES 3, 4 and 10, roll 16 is rot itonally supported, on axis 34, by way of pivoting cradle arms 36 at each end of frame member 26. These cradle arms are pivoted on the frame member at axis 38. Pivot arms 40, at each end of main frame member 26, are pivotably mounted to the frame member by way of pivot 42. Pivot arms 40 have downwardly extending projections 41 which support rollers 44 which cooperate with nip opening and closing cams 46. The other ends of pivot arms 40 have mounted thereon ends 48 of compressible force-cells 50. The other end 52 of force-cells 50 operates on cradle arm 36 to cause arms 36 to rotate clockwise about axis 38, as the fuser nip is closed. In addition to rotating arms 36, force-cells 50 provide controlled pressure to backup roll 16 through axis 34, and consequently the pressure to fusing nip 18 is controlled. The width of fusing nip 18 can also be adjusted by changing the pressure imparted thereto by force-cells 50. Springs 53, positioned between hanger 28 and pivot arms 40, provide a force causing roller 44 to follow cam 46.

[0011] The closing of fusing nip 18 is achieved by cams 46 which are rotationally mounted on axis 38. These cams include a low point 54 which, when positioned to cooperate with roller 44, establish a nip-open icondition. To close the nip, solenoid 56 is energized and clutch 58, shown in FIGURES 4-6, operates to rotate cams 46, in FIGURE 3, clockwise 235⁰ (counterclockwise if observing FIGURE 4) to the position shown, causing nip 18 to close.

[0012] During nip closure, pivot arms 40, in FIGURE '3, rotate counterclockwise causing fixed-position pivot 42, force-cell pivot 60 and axis 34 to come into substantial alignment. However, pivot point 60 does not move over center. Thus, subsequent rotation of cams 46, back to the nip open cam position 54, as a result of the de-energization of solenoid 56, allows force-cell 50 to rotate pivot arms 40 clockwise (when observed on FIGURE 3) about pivot 42, opening fusing nip 18.

[0013] Cams 46 rotate on axis 38 as long as clutch member 58 is free to rotate (see FIGURES 5 and 6). In the de-energized position of solenoid 56, dog 62 is held against rotation by tab 64 on pivoting link 66. Link 66 is pivoted at fixed position pivot 68. When solenoid 56 is energized, clutch member 58 and cam 46 are driven 235⁰ until dog 62 engages tab 70. Fusing nip 18 is now closed. Subsequently, when it is desired to open the fusing nip, solenoid 56 is de-energized, link 66 returns to its de-energized position, and clutch member 58 rotates until it is stopped by tab 64. Fusing nip 18 is now opened.

[0014] In the fragmented portion of FIGURE 4, a folded handle 72, for manually removing hot roll 14, is shown.

[0015] In FIGURE 10, a manually movable, rod-like handle 74 extends the length of the fuser assembly, parallel to axis 34. Opposite ends of this handle are attached to movable links 76, at each end of the fuser assembly. In FIGURES 7 and 8 it is seen that these links are pivoted on fixed-position axis 78. Both of the links have a notch 80, and a pivot point 82 for one end of a drive arm 84. In FIGURE 7, links 76 are shown in their operative positions, wherein hot roll 14 detach bar (not shown) and the fuser's output sheet transport channel (not shown) are located closely adjacent the downstream portion of fusing nip 18 (shown closed).

[0016] In FIGURES 7, 8 and 10, links 88 are pivoted on fixed-position axis 90. Each of links 88 has a projection 92 thereon for holding mounting blocks 23 securely within main frame 26. Links 88 carry locking pins 96 which lock links 88 (and the detach bar) in operative position by virtue of an interface at 98 between pin 96 and pivotable links 100. Links 100 are pivoted on fixed-position axis 102.

[0017] The ends of the above-mentioned output sheet transport channel are attached to links 106. These links are pivoted on backup roll axis 34. Axis 34 is not a fixed-positioned axis because during nip closure, axis 34 moves a slight distance downward, as represented by arrow 108 in FIGURE 7..

[0018] The upper end of links 106 carries a locking pin 110, cooperating with notch 80 formed in links 76. The lower end of links 106 carries lower pivot axis 112 for the end of drive arm 84 that is opposite pivot point 82.

[0019] In FIGURE 8, two tension springs 114 extend between pins 116 carried by links 76 and pins 118 carried by links 100. The springs provide a closing force between links 76 and links 100, when in jam-clearing position, as in FIGURE 8. In addition, springs 114 provide a contacting force between locking pins 96 and pivotable links 100, when in the operating position, as in FIGURE 7. The above-mentioned interface 98 is created by these latter two sets of links.

[0020] In order to move the above-mentioned detach bar 200 and output sheet transport channel 22 out of the way for jam clearance or to remove hot roll 14, the above-mentioned rod-like handle 74 and its links 76 are rotated counterclockwise about fixed-position axis 78, to the position shown in FIGURE 8. Opposite ends of detach bar 200 are attached to links 88, as by fasteners 201 (see FIGURES 3 and 4). Opposite ends of sheet transport channel 22 are connected to links 106 (see FIGURE 10). Counterclockwise rotation of handle 74 causes the detach bar to generally rotate clockwise about hot roll 14 away from fusing nip 18, and the output sheet transport channel to generally rotate counterclockwise about backup roll 16.

[0021] During such movement, pins 116 on links 76 engage links 100 and cause these links to pivot counterclockwise about their fixed-position axis 102. As a result, interface 98, as seen in FIGURE 7, created by contact between pins 98 and pivoted links 100 is broken. In FIGURE 8, as handle-actuated links 76 continue to rotate counterclockwise, notches 80 free pins 110. Counterclockwise rotation of links 76 transmits counterclockwise rotation to links 106 by virtue of drive arms 84. As pivot axis 112 moves counterclockwise as represented by arrow 120 in FIGURE 7, to its position in FIGURE 8, links 106 are pivoted clear of fusing nip 18. As counterclockwise rotation of links 76 continues, surfaces 122 formed thereon engage locking pin 96, causing links 88 to rotate clockwise about their fixed-position axis 90.

[0022] The detach bar and output sheet transport channel have now been moved out of the fusing nip for jam - clearance. In addition, link 88 has been pivoted clockwise, eliminating the interface between projection 92 on links 88 and mounting blocks 23. Links 88 can now be manually rotated clockwise, as represented by arrow 124 in FIGURE 8, in order that hot roll 14 can be removed from main frame 26.

[0023] In summary, interface 98 locks the detach bar in operative position, notch 80 and pin 110 lock the output sheet transport channel in operative position, spring 114 maintains interface 98, pin 116 lifts link 100 to interrupt interface 98, counterclockwise rotation of link 76 frees pin 110 and rotates link 106 by virtue of drive arm 84, and counterclockwise rotation of link 76 rotates link 88 clockwise as a result of interface with locking pin 96.

[0024] FIGURE 9 shows the fixed center drives for (1) producing rotation of the fuser's backup roll 16; (2) producing oscillatory movement of the backup roll's scraping blade cleaner 126; and (3) producing rotation of the fuser's paper exit guide transport roller 20. Roller 20 is supported by the exit paper transport guides, and engages the non-toner side of a sheet, as the sheet emerges from fusing nip 18. Additional information pertaining to the handle cleaner 126 appears in IBM TECHNICAL DISCLOSURE BULLETIN, Volume 18, No. 2, July 1975, pages 326-327.

[0025] Counterclockwise rotation of backup roll 16 is produced by gear 132 which meshes with continuously driven gear 134. Gear 132 is connected to the backup roll's axis 34 and causes counterclockwise rotation of this roll. When the fusing nip is being closed or opened, the backup roll's rotational axis 34 moves in.an arc about axis 38. Thus, gear 132 merely rolls about its meshing gear 134.

[0026] Cleaner 126 is supported by double helix lead screw 138. This lead screw is driven in a counterclockwise direction by virtue of gears 140-142 with gear 140 being fixedly mounted on an end of lead screw 138, gear 141 being rotatively mounted on fixed axis 144 and gear 142 being fixedly mounted on axis 34. Since all of these gears are carried by cradle arm 36, a fixed center relationship is maintained during nip opening and closing.

[0027] As a sheet of newly fused copy paper emerges from the fusing nip, and as it is driven by counterclockwise rotation of backup roll 16, its leading edge is guided into the output sheet transport channel (not shown in FIGURE 9). This sheet channel is supported by pivoting links 106. The link 106 which is located at the rear end of the fuser, and is shown in FIGURES 9 and 10, carries a pair of gears 146, 148 which mesh with a gear 150 which is integral with backup roll 16. Counterclockwise rotation of sheet transport roller 20 by gears 146, 148 and 150 transports the copy paper out of the fusing nip. Roller 20 cooperates with idler roller 21, shown in FIGURE 2, to trap the copy sheet therebetween. The idler roller engages the toned side of the copy sheet.

[0028] When the fuser's sheet detach bar and output sheet transport channel are manually moved out of the way, as for jam clearance, links 106 rotate in a counterclockwise direction as discussed above with reference to FIGURES 7 and 8. Since link 106 pivots about the backup roll's rotational axis 34, a fixed center is maintained for gears 146, 148 and 150, and gears 146 and 148 merely rotate in a circle about gear 150. Consequently, a constant center distance between the gears is maintained and transport roller 20 is driven with minimum backlash by the gearing.

[0029] In the high mechanical advantage toggle mechanism of this invention, cam follower roller 44, mounted on an extension of pivot arm 40, cooperates with nip opening/closing cam 46 as it is rotated. Cam 46 has high and low dwells with each having a detent to thereby stabilize the position of cam follower roller 44 in both the opened and closed positions. In FIGURE 3, a low detent can be seen at the cam low point 54. When a high dwell of rotating cam 46 approaches cam follower roller 44, the end of pivot arm 40 supporting the cam follower roller moves in a counterclockwise arc and the other end of the pivot arm on which force-cell 50 is mounted also moves in a counterclockwise arc. Simultaneously, cradle arm 36, with one end pivotally mounted on axis 38, pivots its other end, with backup roll 16, in an arc that is clockwise. Once high dwell detent has been achieved, rolls 14 and 16 are fully loaded together and fusing nip 18, as seen in FIGURE 3, is established. Rotating from high dwell to low dwell reverses the aforementioned movements until low dwell detent is achieved. At this position, rolls 14 and 16 are in their completely open position. A constant center distance is maintained between axis 34 and axis 38, regardless of whether fusing nip 18 is opened or closed.

[0030] As seen in FIGURES 9 and 10, counterclockwise rotation of backup roll 16 is produced by gear 132 which meshes with driven gear 134. During nip opening and closing, a constant center distance is maintained between axis 38 and axis 34 because the backup roll's rotational axis 34 moves in an arc about axis 38. Thus, with power input at driven gear 134, the backup roll is driven with minimum backlash by gears whose center distance is constant regardless of backup roll position.

[0031] In FIGURE 9, transport roller 20 is driven by gears 146, 148 and 150. Gears 146 and 148 are mounted on link 106 which pivots about the backup roll's axis 34. As a result of this fixed pivot, the center distance between the gears is constant and transport roller 20 is driven with minimum gear backlash.

[0032] As seen in FIGURES 9 and 10, backup roll scraping blade cleaner 126, driven by double helix lead screw 138, traverses back and forth along the length of backup roll 16. Gears 140-142, each of which is mounted on cradle arm 36, provide a driving force to lead screw 138. A benefit resulting from all three gears being mounted on cradle arm 36 is that the distance between the gears is always constant. Additionally, blade contact force as well as blade contact angle of cleaner 126 with backup roll 16 are also constant, regardless of the position of backup roll 16.

Claims

1. A hot roll fuser for a xerographic copier comprising a heatable roll and a backup roll arranged for relative movement between an open position and a closed position in which the rolls are engaged to form a fusing nip, characterised by a first pair of link arms (36) arranged for pivotal movement about a first common axis (38) and having means for supporting respective ends of one of said rolls to provide arcuate movement thereof about said first common axis (38), a second pair of link arms (40) arranged respectively at the ends of said one of said rolls for pivotal movement between two predetermined limits about a second axis (42) and having spring mounting means (60) positioned thereon remote from the pivot point (42), and a pair of compression springs (50) positioned respectively at each end of said one of said rolls and coupled between said spring mounting means (60) and said means for supporting on the respective link arms, the arrangement being such that when the second pair of link arms (40) is positioned at the first of said two predetermined limits, the roll supporting means is positioned on a line running between the second axis (42) and the spring mounting means (60), and the springs bias the rolls into engagement.

2. A hot roll fuser as claimed in claim 1 further characterised by a pair of cams (46) each mounted on said common axis at respective ends of said one of said rolls, and a cam follower arm (41) on each of the second pair of link arms (40) whereby rotation of the cams (46) causes said movement of the second link arms (40) through the cam follower arms (41).

3. A hot roll fuser as claimed in claim 1 or claim 2 further characterised by a lead screw (138) mounted on said first link arms along an axis parallel to the axis of said one of said rolls, a roll cleaner (126) mounted on the lead screw in contact with the surface of said one of said rolls for axial movement therealong as the lead screw rotates, and drive means (144) coupled to said one of said rolls and the lead screw for simultaneous drive thereof.

4. A hot roll fuser as claimed in claim 3 in which the drive means includes coupled gear pinions (140, 141, 142) mounted on one of the first pair of link arms (36).

5. A hot roll fuser as claimed in any of claims 1 to 4 further characterised in that said one of said rolls (16) is the backup roll and has a non-resilient surface, and the heatable roll (14) has a resilient surface.

6. A hot roll fuser as claimed in claim 5 in which the compression springs are adjustably mounted to vary the force with which the rolls contact when in the closed position thereby varying the width of the fusing nip.

Drawing