US3844252A

US3844252A - Sheet removal device

Info

Publication number: US3844252A
Application number: US00362639A
Authority: US
Inventors: R Thettu
Original assignee: Xerox Corp
Current assignee: Xerox Corp
Priority date: 1973-05-21
Filing date: 1973-05-21
Publication date: 1974-10-29
Anticipated expiration: 1991-10-29
Also published as: IL44839A0; JPS5010248U; NL7406854A; BE814943A; AU6901374A; JPS5418921Y2; FI120474A; BR7404013D0; FR2230572B1; CA1000749A; FR2230572A1; ES426423A1; DE2419026C3; IT1012669B; DE2419026B2; SE390219B; DE2419026A1

Abstract

A sheet removal device for separating an image bearing support sheet from the surface of a heated fuser roll. The removal device is constructed in a configuration and of a material to prevent copy degradation and harming of the fuser roll during the sheet separating operation.

Description

United States Patent 11 1 1111 3,844,252 Thettu Oct. 29, 1974 SHEET REMOVAL DEVICE 447,012 2/1891 Knowlton 61 al. 118 245 1 1 Invent Raghulinga Theflu, Webster, 3321331 21138; 5123113351: jiiijjii 13/332 1,080,959 12/1913 Eaton 118/262 2,314,051 3/1943 OSgOd.... 118/245 [73] Asslgnee' gel-ox corporat'on Stamford 2,330,530 9/1943 Tuttle 118 101 ux Om 2,360,044 10 1944 Dermody ll8/245 x [22] Filed; May 1973 3,357,401 12 1967 Wood 118/637 [21] Appl. No; 362,639

Primary ExaminerMorris Kaplan [52] US. Cl 118/60, 34/D1G. 3, 118/70, 118/245, 432/ 51 Int. Cl G03g 13/08 [57] ABSTRACT 81 Fleld of Search 118/601 A sheet removal device for separating an image bear- 118/104, 124, 126, 245, 261, 262, 203, 204; ing support sheet from the surface of a heated fuser 355/3 15 101/425 429; 34/DIG- 3; roll. The removal device is constructed in a configural 17/ 1 NO; 432/6 15/25651; 271/DIG- tion and of a material to prevent copy degradation and 2; 162/1 NO; /1 NO; 72/1 NQ harming of the fuser roll during the sheet separating operation. [56] References Cited UNITED STATES PATENTS 15 Claims, 6 Drawing Figures 246,728 9/1881 Crich et a1. 118/124 X SHEET REMOVAL DEVICE This invention relates to apparatus for fixing a toner image to a final support sheet and, in particular, to means for facilitating the removal of a toner bearing support sheet from a heated pressure roll fusing mechamsm.

In the process of xerography, a light image of an original to be copied is conventionally recorded in the form of a latent electrostatic image upon a photosensitive plate and the latent image then rendered visible by the application of a heat sensitive toner material. The visual image can be either fixed directly upon the photosensitive plate or transferred from the plate to a sheet of final support material, such as plain paper or the like, and the image affixed thereto. One prevalent method of accomplishing image fixing is through means of a heat pressure roll technique wherein the toner bearing support material is passed through the nip of two cooperating pressure rolls with the image side of the support material contacting one of the roll surfaces which is maintained at an elevated temperature. Sufficient energy is transferred, under pressure, from the heated roll surface to the image bearing support material to accomplish the desired image fixing. A typical pressure roll fusing system of this type is disclosed in US. Pat. No. 3,256,002 which issued in the name of Hudson.

As described in the above-noted Hudson patent, the outer surface of the heated roll is generally provided with a release agent which serves to prevent the toner images carried on the support sheet from offsetting from the sheet onto the fuser roll surface. Silicone based oils, which possess relatively low surface energies, have been found to be a material that is suitable for use in the heated roll fuser environment. A thin layer of oil is applied to the contact surface of the heated roll which interfaces between the roll surface and the toner images carried on the support material. A low energy profile is thus presented to the toner as it passes through the fuser nip which, under most conditions, prevents the toner from adhering to the heated fuser roll surface. Although the low surface energy oils generally act as a non-wetting fluid in regard to most support materials, it has been found that a mechanical flowing of the release agent from the roll onto the support material will occur if an excess of oil is allowed to accumulate in a region where it can come in contact with the copy sheet. Accordingly, the amount of oil applied to the roll surface is usually metered under controlled conditions to maintain a relatively thin coating of the release agent upon the roll surface.

As the toner'image bearing support sheet passes through the nip of the fuser roll, the support sheet, because of the geometry of the system and the forces involved, will most generally want to remain in contact with the heated roll surface. As a result, the copy sheet is carried along on the surface of the heated roll as the sheet passes beyond the fusing nip and some instrumentality, such as a stripper blade or the like, must be introduced between the sheet and the roll surface to affect removal. The sheet removal device, because it comes into contact with the thin layer of oil maintained on the heated roll surface, is capable of paddling or accumulating an excess of oil at the point where the sheet is separated from the roll surface. The trailing portion of the sheet, which is then pulled through the puddle of excess oil, picks up the oil thus degrading the quality of the copy produced.

A further difficulty associated with this type of mechanism is caused by toner adhering to the pick off device. The heated toner, coming in contact with the pick off mechanism is in a highly tackified viscous state and, as such, wants to stick to any surface it contacts. As a result, the images on the copy sheet moving thereover will generally cling to the pick off mechanism causing image degradation and impede or even stop the sheets movement.

It is therefore an object of the present invention to improve heated pressure roll image fixing devices.

A further object of the present invention is to facilitate the removal of a support sheet from the surface of a heated image fixing roll.

Yet another object of the present invention is to eliminate support sheet jams within a pressure roll image fixing system.

A still further object of the present invention is to provide a non-deleterious sheet removal device suitable for use in a pressure roll image fixing apparatus.

Another object of the present invention is to remove a toner image bearing support sheet from the surface of a heated fuser roll without harmfully disturbing the release agent carried on the fusing roll surface or the toner images carried upon the support material.

These and other objects of the present invention are attained by means of a sheet removal device which is adapted to move between the surface of an oil coated heated fuser roll and an image bearing support sheet carried thereon the removal device having a cutting edge which is shaped to prevent oil from accumulating in and about the contact region, the sheet removal device being formed of a material which is incapable of mechanically of chemically interacting with toner images brought in contact therewith thus preventing the toner from adhering to the contact surface. Further means, operatively associated with the sheet removal device, are also provided to remove the blade from within the sheet contact region upon the sensing of a support sheet jam condition whereby potential damage to the fuser roll is averted.

For a better understanding of the present invention as well as other objects and further features thereof, reference is had to the following detailed description of the invention to be read in connection with the accompanying drawings wherein:

FIG. 1 is a perspective view in partial section illustrating a heated pressure roll image fixing assembly employing the sheet removal apparatus of the present invention;

FIG. 2 is an end view in partial section of the lower fuser roll of the assembly shown in FIG. 1 illustrating the sheet removal apparatus of the present invention positioned in an operative condition;

FIG. 3 is an end view in partial section of the lower fuser roll of the assembly illustrated in FIG. -1 showing the sheet removal apparatus of the present invention positioned in an inoperative condition;

FlG. 4 is a top plan view showing the contour of a sheet stripping blade employed in the apparatus of the present invention;

FIG. 5 is a partial end view in section of the lower fuser roll illustrated in FIG. 1 showing a second embodiment of the sheet removal device suitable for use in the present invention;

FIG. 6 is also a partial end view illustrating another embodiment of the present invention.

Referring now to FIG. I, there is shown a typical heat pressure roll fixing system utilizing the sheet removal apparatus of the present invention. This system is similar to that disclosed in regard to the above-noted Hudson patent. A pair of co-acting fuser rolls, including a lower heated roll 11 and an upper back up roll 12, are rotatably mounted within a support frame 13 and have drive means (not shown) operatively associated therewith for rotating the rolls at synchronous speeds in the direction indicated. As disclosed by Hudson, one of the roll members, in this particular case the bottom roll 12, is provided with an internal source of heat energy and is arranged so that its outer surface contacts the toner image bearing side of a copy sheet 15 as the sheet is transported through the nip of the fuser roll assembly. The lower or heated fuser roll 11 is formed of a resilient blanket 16, which is placed over a copper core 17, and having a thin layer of relatively abhesive material 18, as for example triflouroethylene, placed thereover. Running axially through the interior of the copper core is a quartz heating lamp I9 which functions to transfer sufficient energy to the roll member so as to raise the surface temperature thereof to a predetermined operating level.

The upper or back up fuser roll 12 is made up of a relatively rigid cylindrical substrate 20, preferably being fabricated of a stainless steel, over which a relatively thick sleeve 21 of trifiouroethylene is fitted. In assembly, the two co-acting rolls are mounted in the frame so that the lower resilient heated roll is deformed against the more rigid upper roll thus creating an extended nip therebetween through which the copy sheet is passed during the fusing process. During passage of the sheet, sufficient pressure and heat energy is transferred from the fuser assembly to the copy sheet to affect the desired image fixing.

Although the present invention will be described with reference to the above-noted pressure roll image fixing system, it should be clear to one skilled in the art that the instant invention is not necessarily limited or restricted in its usage to this particular fixing system and that it can be similarly utilized in a wide variety of pressure roll fixing systems presently known and used in the art.

In order to prevent the toner image carried by the final support sheet from being offset onto the heated roll surface, as the sheet is drawn through the fuser nip, the heated roll is provided with a layer of oil containing a release agent capable of preventing the toner image from adhering to the heated roll surface. Silicone based oils have been found to be a suitable release agent for this intended purpose. An oil applicating mechanism, generally referenced 25, is positioned adjacent to the lower portion of the heated fuser roll as illustrated in FIG. I. An applicator wick 26 is mounted in the upper part of housing 27 and is arranged to contact the lower portion of the heated roll surface. A rotating oil metering cylinder 28 is located directly beneath the wick and serves to transport a regulated amount of oil from the housing sump region 29 upwardly into contact with the wick surface. Sufficient oil is carried to the wick by the metering roll to allow the wick to apply to the outer pe' riphery of the heated fuser roll a relatively thin homogeneous coating of oil. The oil coating applied to the fuser roll surface must be thick enough to act as an interface between the roll surface and the copy sheet to prevent toner offsetting but yet must be thin enough to prevent wetting of the copy sheet as it moves through the fuser nip. For further information concerning this type of oil metering system reference is had to US. Pat. No. 3,718,116.

As previously noted, the image bearing support sheet, as it passes through the nip of the fuser roll assembly, tends to remain in contact with the lower heated pressure roll surface. As a consequence, some instrumentality must be provided to effect the removal of the support sheet from the roll surface after image fixing is accomplished. To this end, a pair of pick off fingers 30 are mounted slightly downstream from the nip of the fuser roll assembly. The fingers are arranged to move between the lower fuser roll surface and the copy sheet in process. The copy sheet, as it leaves the fuser nip, is carried forward by the roll and thus caused to come into contact with the upper surface of the stripper fingers. The fingers, moving between the sheet and the roll, redirect the sheet along a second predetermined path of travel away from the roll thus effecting the desired separation.

Conventionally, when this type of sheet pick off device has heretofore been employed in a heated pressure roll fuser system, the pick off blade element invariably would doctor the oil carried on the heated roll surface thus producing a puddle of excess oil to build up at the tip and top face of each finger. This copious amount of oil, which is accumulated within the sheet removal region, poses an ever present danger to the sheet in process supply because the amount of oil is such that mechanical offsetting of the oil to the sheet cannot be avoided.

The apparatus of the present invention, among other things, is specifically designed to eliminate any harmful oil accumulations in and about the sheet pick up region. Excessive oil build ups are prevented by the present apparatus by first shaping the tip of the pick off finger to permit oil to flow around the blade and secondly by providing means for collecting excess oil flowing over the top of the finger and carrying the oil away from the region where it is capable of contacting the support sheet.

As illustrated in FIGS. 1, 2 and 4, the sheet removal apparatus of the present invention includes two bladelike fingers 31 which are pivotably mounted upon the free ends of pivot pins 32. The pivot pins, in turn, are anchored at one end in a vertical support member 34 which is secured to a horizontal tie bar 35. Each finger is provided with a cutting edge 36 which is formed by the joinder of the top surface 38 and incline surface 39 formed in the body of the finger. The fingers are supported in the assembly so that the inclined lower surface 39 thereon rests under the influence of gravity upon the heated lower pressure roll surface. The finger contacts the roll along a line of contact that is tangent to the roll surface which is located about 0.001 inches back from the cutting edge of the finger.

As seen in FIG. 4, the cutting face of each finger is provided with an arcuate shape which permits the oil carried upon the heated roll surface to conveniently flow about each side of the fingers. The side rake in the face of the finger is created by forming a radius at the tip of the finger which is substantially normal to the top surface of the finger. It has been found that good flow characteristics can be obtained when the radius (r) formed in the finger is at least as great or greater than the radius (R) of the heated fuser roll.

It has also been found that the oil carried on the fuser roll, when brought into moving contact with the stripper fingers, will tend to move or flow over the upper surface of the fingers. The oil, coming into contact with the relatively cooler body portion of the finger, continues to walk up the cooler surface via capillary action and where if left unchecked, the oil will begin to build up in dangerous amounts. As can be seen, therefore, shaping the cutting edge of the sheet stripping device will, not in itself, prevent an oil build up from occurring within or along the intended path of travel of a copy sheet as it is removed from the fuser roll.

in order to prevent an excess of oil from building up on the top surface of the stripper fingers, a clear aperture 40 is formed in the main body of each finger directly behind the cutting edge into which the excessive oil is capable of falling and being collected. Preferably, the opening should be positioned so that the oil passing therethrough falls back into contact with the fuser roll surface directly below the point where it is removed by the finger tip. In this way, a continuous flow of oil is produced around the tip wherein the oil removed during the sheet stripping operation is put back on the roll surface in the depleted regions. As shown in FIG. 2, an absorptive pad 41 is mounted within the opening 40 which serves as an oil reservoir to store the oil so accumulated. The pad also serves as a metering device for feeding oil back to the upper surface of the pick off fingers to wet the surface thereof with a thin coating of oil for preventing toner from adhering to the surface as the copy sheet is moved thereover. Oil pads formulated of wool or of high density Dacron, having a relatively high oil retention capacity, have been found to be capable of metering oil back to the finger surface via capillary action at a rate that will maintain a thin film of oil upon the top surface of the finger. It should be clear to one skilled in the art, however, that the present invention is not limited or restricted to the above-named material and any suitable material capable of producing the desired results can be herein utilized without departing from the teachings of the present invention.

A second embodiment illustrating another finger configuration is shown in FIG. 5. A recess or step 57 is formed in the top surface 58 of the blade-like finger 59 into which excessive oil flowing over the top of the blade is caused to drop thus preventing the oil from contacting the main body of the copy sheet as it moves thereover. As in the previous finger configuration, an aperture 60 is also provided in the body of the finger through which excessive oil collected in the recess can be exhausted from the system. Alternatively, the aperture 60 can be filled with an absorbent pad 61 capable of collecting and storing excessive oil delivered thereto.

Referring to FIG. 6, there is illustrated another embodiment of a finger 80 for controlling the puddling of oil within the sheet pick off region. The top surface of the finger 81 is stepped to provide a recess 82 into which oil moving over the blade is collected. Along both side walls of the finger there is provided an oil channel 83 for directing the oil collected in the recess downwardly toward the bottom surface of the finger. The oil collected within the recess 82 is directed into horizontal gutters 85 formed in the top surface of the recess and is guided into the side wall channels 83. The bottom surface of the finger is V-shaped in construction with the apex 84 of the V pointed at the moving surface of the fuser roll. In operation, the oil collected in the recess 82 is directed downwardly via the channel 83 and then moves along the bottom of the finger where it collects at the apex 84. When sufficient oil is collected at the apex to overcome the surface energies involved, the oil is released from the finger and falls into contact with the roll surface thus automatically replenishing the oil supply thereon directly below the area wherein the blade acts to deplete the oil supply. A continuous flow of oil is thus established wherein substantially the same amount of oil is delivered back onto the roll as is removed by the action of the finger. The channel 83 can take almost any form. In practice it was found that a shallow groove machined in the finger side wall would operate to establish the desired oil flow. Similarly, a protruding boss in the side walls also provides the same results.

To further prevent toner from adhering from the top surface of the finger, as a copy sheet is drawn thereover, the fingers are preferably constructed of a material that will neither mechanically or chemically interact with the toner in a manner to cause the toner to adhere to the finger surface. Such materials, as aromatic polyesters, as for example, Econol as manufactured by the Carborumbum Co., of Sanbornn, N.Y., which are loaded with a triflouroethylene filler; amide imides, as for example Amoco Al-llL 4 as supplied by the Amoco Chemical Company of Syemor, lnd., which are loaded with a graphite and triflouroethylene filler; polymides, as for example Vespel as manufactured by the duPont Co., which are coated with a layer of triflouroethylene have all been found to exhibit non-adhering characteristics to toner and are well suited for use in the construction of the sheet removal fingers.

Similarly, it has been found that by keeping the sheet contacting surface of the fingers at a temperature that is relatively cooler than the fixing temperature of the toner material, adhesion of the toner to the finger can also be inhibited. It is believed that the relatively hot toner leaving the fuser roll will rapidly pass from a tacky semi-liquid state into a more stable solidified state upon contacting the cooler blade surface thus placing the toner in a non-offsetting condition. A finger, which is constructed of a metal having a high coefficient of thermal conductivity, such as aluminum or the like, and which is coated with a thin layer of triflouroethylene has been found to work well in the practice of the present invention. In this embodiment, the main body of the fingers should have sufficient mass so that it acts as a relatively large heat sink in regard to the blade edge region whereby a heat build up at the cutting edge is rapidly dissipated into the massive body of the blade. By maintaining the finger surface temperature at or below F, satisfactory toner release characteristics can be obtained.

It should be further noted that this type of blade has the capability of working well in conjunction with dry fuser rolls as well as with those coated with a release agent.

A further safety feature is also provided for in the present apparatus in order to protect the heated roll surface from being abraided or otherwise harmed by the sheet stripping fingers. When, for reasons beyond the control of the present sheet stripping apparatus, a copy sheet becomes misaligned or otherwise inadvertently becomes attached or otherwise enmeshed with the sheet removal fingers, the fingers are caused, due to the forces involved, to work harder against the roll surface. This, in turn, causes the blade edges of the fingers to dig into the generally sensitive roll surface. Under extreme conditions, the edge of the blade can cause sufficient damage to the roll surface whereby the roll must be replaced within the fuser assembly.

As illustrated in FIGS. 2 and 3, the body of each finger is supported upon the pivot pin 32 by means of a spring clip 70. Both ends of the clip are anchored in the end wall 71 of the finger with the extended body of the clip being turned so that it is carried within an elongated opening 73 provided for in the main body of the finger. A circular detent 75 (FIG. 3), capable of engaging the pivot pin 32, is formed in the clip which serves to support the clip in an operative position upon the pin in the manner shown in FIG. 2. Upon the occurrence of a sheet jam condition, whereby the finger is caused to exert undue pressure against the roll surface, the tinger is forced back against the holding pressure of the pivot pin with sufficient pressure to cause the pin to be released from the detent. The finger is thus permitted to fall away from the roll surface to an inoperative condition as illustrated in FIG. 3. It should be clear that the detent release pressure of the spring is set at a point whereby the pressure required to release the finger is below that at which the fingers could harm the roll surface. In this sense, the spring apparatus has the ability to sense the impending occurrence of a jam condition and automatically take appropriate corrective action before any damage can be sustained by the roll surface.

While this invention has been described with reference to the structure disclosed herein, it is not necessarily confined to the details as set forth and this application is intended to cover such modifications or changes as may come within the scope of the following claims.

What is claimed is:

1. In a reproduction machine wherein a developed electrostatic image is transferred to a suitable image bearing support sheet and permanently affixed thereto by heat-pressure means including a heated pressure roll, the improvement comprising:

means applying a release agent coating to the heated pressure roll;

a blade-like element having a cutting edge formed along one side thereof; and

means for supporting said blade-like element in close proximity to an upper portion of the heated pressure roll with the cutting edge of the blade in a position to strip a support sheet moving therefrom, said blade having a recess formed therein behind the cutting edge thereof and extending through the blade, said recess overlying a lower portion of the heated pressure roll whereby release agent removed from the roll by said blade is returned to the roll.

2. The apparatus of claim 1 wherein the cutting edge of said blade has a radius formed therein that is greater than the radius of the fuser roll.

3. The apparatus of claim 2 wherein said recess is a aperture formed in the body of the blade behind the cutting edge thereon.

4. The apparatus of claim 3 wherein said aperture is filled with a material capable of absorbing said removed oil.

5. The apparatus of claim 1 wherein said cutting edge contacts the roll surface along a contact line that is tangent to the surface of said roll.

6. The apparatus of claim 1 wherein the blade has means operatively associated therewith for removing the blade from contacting said roll when the contact force between the roll and the blade exceeds a predetermined pressure.

7. The apparatus of claim 1 wherein said blade is formed of an aromatic polyester filled with triflouroethylene.

8. The blade of claim 1 wherein said blade is formed of a polymide which is filled and covered with triflouroethylene.

9. The blade of claim 1 wherein said blade is formed of an amide-imide.

10. The apparatus of claim 1 wherein said blade if formed of a metal having relatively high thermal conductivity.

11. The apparatus of claim 10 wherein said metallic blade is coated with a layer of triflouroethylene.

12. The apparatus of claim 4 wherein said absorbent material comprises an oil reservoir holding a quantity of said removed oil which is metered to the blade surface by capillary action.

13. The apparatus of claim 12 wherein said absorbent material comprises a high density wick which is embedded below the sheet contacting surface of said blade.

14. The apparatus of claim 1 wherein said recess is a channel running along at least one side wall of said blade.

15. The apparatus of claim 1 wherein said recess is an embossed ridge running along at least one side wall of said blade.

Claims

1. IN A REPRODUCTION MACHINE WHEREIN A DEVELOPED ELECTTROSTATIC IMAGE IS TRANSFERRED TO A SUITABLE IMAGE BEARING SUPPORT SHEET AND PERMANENTLY AFFIXED THERETO BY HEAT-PRESSURE MEANS INCLUDING A HEATED PRESSURE ROLL, THE IMPROVEMENT COMPRISING: MEANS APPLYING A RELEASE AGENT COATING TO THE HEATED PRESSURE ROLL; A BLADE-LIKE ELEMENT HAVING A CUTTING EDGE FORMED ALONG ONE SIDE THEREOF; AND MEANS FOR SUPPORTING SAID BLADE-LIKE ELEMENT IN CLOSE PROXIMITY TO AN UPPER PORTION OF THE HEATED PRESSURE ROLL WITH THE CUTTING EDGE OF THE BLADE IN A POSITION TO STRIP A SUPPORT SHEET MOVING THEREFROM, SAID BLADE HAVING A RECESS

9. The blade of claim 1 wherein said blade is formed of an amide-imide.