CA1129942A

CA1129942A - Heated web fusing apparatus for electrophotocopy machine

Info

Publication number: CA1129942A
Application number: CA332,306A
Authority: CA
Inventors: Christian A. Beck
Original assignee: Pitney Bowes Inc
Current assignee: Pitney Bowes Inc
Priority date: 1978-08-07
Filing date: 1979-07-20
Publication date: 1982-08-17
Also published as: JPS5525099A; DE2931871A1; GB2027640A; GB2027640B

Abstract

HEATED WEB FUSING APPARATUS
FOR ELECTROPHOTOCOPY MACHINE

Abstract of the Disclosure A fusing apparatus for an electrophotocopy machine has a flexible, steel web driven between a pair of pressure rollers. A heat source,such as a focused radiant energy lamp, heats the belt to a fusing temperature. A copy sheet bearing toner material is fed into the nip of the rollers where the heated web melts and fuses the toner to the copy sheet.

Description

j HEATED WEB FUSING APPARATUS
FOR ELECTROPHOTOCOPY MACHINE

Field of the Invention rne pre~An~ i ~7e ~tion relates to fusing electroscopic toner material to the surface of a carrier bearing the toner, and, more particularly, to an apparatus in which toner material is heated to an extent sufficient to fuse it to a copy sheet as it passes through the nip of a pair of rollers.

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There are a number of well-known devices that fuse or fix toner material to copy sheets by applying a combination of heat and pressure to a toner-bearing copy sheet. These devices generally pass the unfused copy sheet through a pair of rela-tively rlgid rollers, one or both o which are internally heated in order to soften and thereby fix the toner to the copy sheet. Other devices externally heat one or both rollers which are coated with a special, thermally conductive material.
Still another device passes the copy sheet through the nip of a feed roller and a thermally transparent rigid drum. Inside the drum is a radiant energy fuser which is focused on a line transverse to the plane of travel of the copy sheet. One such device is described in U.S. Patent No. 3,452,181.

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All heat assisted fusing devices, including the above, may pose a fire hazard in the event that a copy sheet becomes jammed in the fuser. A suitable jam dekection system is normally used to detect a paper jam in the fuser and to terminate power to the fuser heating element.
However, even after power is terminated the internally heated fuser rollers, with their relatively large thermal mass, may retain enough heat to ignite the jammed copy sheet. Likewise, a focused heat lamp could also readily ignite a jammed copy sheet before the lamp is extinguished and its heat dissipated.
Another problem associated with heat fusing devices is the presence of wrinkles in the unfused copy sheet.
Such wrinkles may be due to moisture or to damage incurred in feeding the copy sheet along its path. Wrinkles may cause a jarring of the unfused sheet thereby destroying some part or all of the desired image or wrinkles may additionally cause a crease when the pressure rollers engage the sheet.
Wrinkles may also result in fusing voids, i.eO local areas on the copy sheet where the toner ~ails to fuse to the sheet.
Accordingly, there have been many attempts to solve the foregoing problems by providing fire prevention and fire extinguishing systems as well as copy sheet guides to smooth out unwanted wrinkles. In spite of such attempts, there remains a relatively high likelihood of fire in the event of a paper jam in a heat assisted fuse~.

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Z~ 2 It is an object of this invention to reduce the fire hazard in a heat assisted fusing device.
It is another object to provide a relatively simple heated fusing apparatus.
It is still another object to provide a combination heat and pressure fixing device.
An additional object is to provide a heated fusing device with a heated element having a relatively low thermal mass.
According to one aspect of the present invention there is provided a method for applying pressure and heat to a developed electrostatic image on the surface of a copy sheet in order to fix the image on the sbeet, the method including the steps of feeding the copy sheet through a pair of oppositely driven, mutually biased, solid pressure fixing feed rollers and heating only a thermally conductive web disposed between the pressure fixing feed rollers, the web being contiguous with the rollers only at the juncture of the rollers. The image bearing surface of the copy sheet is contacted with the heated web as the copy sheet passes ` through the juncture of the pressure fixing feed rollers.
According to another aspect of the present invention, there is provided an apparatus for applying pressure and heat to a copy sheet bearing a developed electrostatic image on at least one surface thereof in orde to fix the image to the copy sheet. The apparatus has a pair of oppositely driven, mutually biased, solid pressure fixing feed~rollers. A thermally conductive web is disposed between the pressure fixing feed rollers for contacting the image bearing surface of a copy sheet fed -through the pressure fixing feed rollers, the web being contiguous with the rollers only at the juncture of the rollers. Means is provide~ for heating only the web so -- 3 ~
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that when a copy sheet bearing a developed image is fed between the feed rollers, the image on the copy sheet surface is fixed to the copy sheet by the combined heat and pressure applied to the copy sheet and to the image by the heated, thermally conductive web and the mutually biased, pressure fixing feed rollers.
The above described objects are thus fulfilled by the invention which provides a flexible, relatively thin, thermally conductive web disposed between the nip of a pair of fuser feed rollers. In a specific embodiment of the invention, the web in the form of an endless belt made out of a sheet of flexible, thin, stainless steel, is heated prior to passing through the nip of the rollers.
A copy sheet bearing fusible toner is fed by suitable means between the web and one of the rollers, with the toned side --; of the copy sheet facing the heated web. As the copy sheet passes between the heated web and the roller, the toner is melted or softened and becomes fixed to the copy sheet as the sheet emerges from between the web and the roller.
In the event of a paper jam, a suitable jam detecting means may be operable to interrupt power to the heat sou~ce.

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Due to the high thermal conductivity inherent in the low thermal mass of the web, the heat in the web is rapidly dissipated, thereby preventing the copy sheet from igniting.
The thin web of the invention has two surfaces. Either surface can be heated to achieve fusing due to the high thermal conductivity of the web. I

The thin stainless steel web may be additionally coated with a thin lay of permanent elastomeric material such as silicone to aid the release of the fixed copy sheet from the web and to aid thermal distribution of the lamps radiant energy across the web width.
The above summary and objects of the invention are further explained by references to the drawings, the follow-ing detailed description and to the appended claims which embody the spirit and scope of the invention.

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FIG. 1 is an elevation view of one preferred embodiment of the invention.
FIG. 2 is an elevation view of an alternate preferred embodiment of the invention.
FIG. 3 is a schematic diagram of the electrical controls of the invention.

Detailed Description Turning to FIG. 1, the fuser 8 of the invention is ~ener-ally shown ogether with a carrier or copy sheet 10 that ::

i 9~2 comprises a suitable material, such as paper. On one surface 12 of copy sheet 10 an image I (indicated by dashed lines above the surface 12) has been formed of toner particles that are lightly held to -the surface 12 by slight electrostatic forces. The copy sheet 10 is fed and positioned by suitable feeding and positioning means so that the toner image I on surface 12 faces the web comprising endless belt 14. The copy sheet is gently guided into the nip 17 defined by belt 14 and lower roller 16.
The belt 14 provides a low shallow tangent angle guide surface which meets the oncoming copy sheet 10, thereby helping to smooth any wrinkles within the leading edge of the copy ~ sheet 10. Such wrinkles are caused by ambient moisture ; that is absorbed by the copy sheet 10 or by unintentional paper handling abuse.
The belt 14 comprises a flexible, thermally conductive material, such as stainless steel.
Belt 14 is disposed between the rollers 16, 18.
The rollers extend across the width of belt 14 and are biased together to drive the belt 14 and the copy sheet ; 10. The belt 14 is laterally supported by three idler rollers 32, 34, 36. These rollers generally maintain and support the flexible belt in a roughly cylindrical configuration.
A heating element 20 is disposed inside the belt 14. The heating element 20 cGmprises a 600-900 wa-tt infra red lamp 21 and a curved reflector 22 for directing radiation from the lamp 21 toward the inner surface 13 of belt 14 in a ~ pc/~.

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direction away from upper roller 18. In this manner, the heat generated by lamp 21 is effectively applied to the belt 14 and not wasted upon heating the roller 18. Accordingly, roller 18 is partially shielded from the direct radiation of heat from lamp 21. Such direct radiation might interfere with the operation of roller 18 if it expanded due to the heat from lamp 21.

Those skilled in the art will know that there is provided sufficient, adequate insulation (not shown) surround-ing the fuser mechanism thereby ensuring that most of the generated heat is maintained within a local area of the copier.
Due to the relative thinness of belt 14, the heat applied to internal surface 13 is rapidly transmitted to external sur-face 15. As rollers 16,18 turn, the copy sheet 10 is fed into the nip 17 between the external surface 15 of belt 14 and the lower roller 16. As the heated external surface 15 contacts the toner image I on copy sheet 10, the toner material is softened or melted and thereby fixed to the copy sheet 10.
The fixing of image I to copy sheet 10 is enhanced by the mechanical pressure that is simultaneously applied to the copy sheet 10 as the sheet passes through nip 17 in contact with the heated surface 15 of belt 14.
The smooth operation of the fuser 8 is maintained by providing a silicone coating on the surfaces of rollers 18,16 and on both surfaces 13,15 of belt 14.
A torer agent is applied to the outer surface 15 of , , ~

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, belt 14 by applicator 30. The toner release agent inhibits the fused toner from sticking LO surface 15 after the copy sheet passes through nip 17. A scraper 38 engages the outer surface 15 for removing toner that may adhere to the belt 14 after the belt emerges from the nip 17. Scraper 38 is fixedly mounted at one end to a suitable support member 39. The scraper 38 extends along the length of the cylindrically shaped belt 14. In addition to removing toner particles, scraper 38 also serves to remove the copy sheet 10 if the latter becomes stuck to surface 15.
The invention is also provided with a nip release mech- ¦
anism 40 for moving lower roller 16 into and out of its copy sheet fusing and feed;ng position shown in FIG. 1. The nip release mechanism 40 includes roller support plates 46, one for each end of roller 16 which is rotatably mounted between the support plates 46. The plates 46 are supported at one end by a pivot 45 that is suitably secured to a structural member of the copy machine in which the invention is used. The other ends of plates 46 are supported by a biasing means 48 (such as a spring), which urges the plates 46 upward thereby keeping roller 16 biased against belt 14. A release bar 44 engages and extends between the support plates 46. Release arms 42 are coupled to the bar 44 on each side thereof. When arms 42 are pressed down in the direction indicated by arrow 47, support plates 46 turn counterclockwise about pivots 45, thereby- carrying lower roller 16 away from its normal engagement with belt 14 and opening the nip 17 between them.
In such nip release position, a paper jam in the fuser can be attende to and c]eared.

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¦ It is optional during warm up or shut down of fuser 8 to have the rollers 18 seperated by the nip release mechanism 40. Then, the rollers 32, 34, 36 keep the web 14 moving ¦ during either the start up mode and similarly disipates thermal energy uniformly and quickly during shutdown.
An alternate embodiment of the invention is shown in I FIG. Z. The fuser 8' of FIGo 2 is substantially the same as the one shown in FIGo 1 except for the eliptical, focused reflector 22 which has been substituted for the concave reflector 22 of FIG. 1. In addition, the lamp 21 is supported by any suitable means and is relocated off center inside belt 14 in order to have its output properly focused on a I predetermined section S of belt 14 that is disposed upstream of nip 17.
The belt 14 is supported by, single roller 36', 32' and by pairs of rollers 34' and 35'0 Any or all of support rollers 32', 34', 35' and 36' may be either driven rollers ~ or idler rollers. When drivenj such support roller assist ; in guidely and uniformly distributing the heat generated by focused lamp 21'. Support rollers 34' further assist in stiffening belt 14 at a point downstream from scraper blade ; 38.
Inasmuch as the focused lamp 21' concentrates the radiant energy on a relatively narrow bond across the width of web 14, the latter is very quickly raised to its operating, fusing temperature. For that reason, the embodiment of the invention shown in FIG. 2 is believed to be tne best mode of operation since the fuser warm up time is minimal. The : actual operating temperature is conventially controlled by thermal sensors (not shown) and is dependent upon, inter alia, the chemical composition of the toner.

, I , In order to conserve energy, the lamp 21 of both embodiments is operated by a control system 60 that is schematically shown in FIG. 3. A switch 60 is operatively disposed in the path of copy sheet 10. The switch 60 is closed when the leading edge of copy sheet 10 engages and operates switch arm 64, thereby allowing sufficient time to bring the lamp 21 to an operational intensity.
Switch 60 is a two-position switch that alternately connects a standard 110 A.C. source 70 to the lamp 21 either directly through conductor 66 or indirectly through standby resistor 68. Switch 60 is normally biased to connect the A.C. source 70 to the lamp 21 through the standby resistor 68. The resistor is sufficiently large enough to dissipate most of the A.C. voltage, thereby leaving a relatively small voltage across the lamp 21. The small voltage keeps the lamp filaments warm and helps cushion the shock to the filaments that is caused by full illumination. When the leading edge of the copy sheet engages switch arm 64, the switch 60 is moved to its second or full illumination position, thereby connecting the full voltage of source 70 across lamp 21. Accordingly, the temperature of belt 14 is quickly raised to a fusing level and the image I
(indicated by dashed lines) is fused to copy sheet 10. When the trailing edge of copy sheet 10 moves off switch arm 64, the switch 60 is returned by its bias to its normal or standby position. Those skilled in the art will recognize that switch 62 can be incorporated into a larger jam detection system. S~h a syste~ may monitor the passage of sheet I
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9~4;2 10 thro~gh fus~r ~ 2nd terrninate ~11 po~cr to lamp 21 iI-the copy sheet 10 has not passed thro~gh fuser 8 in a predetermined ~mount of time.
The motor is contin~ously driven by the A.C. source 70.
The drive from tile motor is taken from a motor sprocket 72 and coupled via drive chain 74 to a drive sprocket 76 that is-keyed to one end of upper roller 18.
Those skilled in the art will recognize that there is a tendency for the driven belt 14 to laterally drift from side to side. In order to provide lateral guidance to the web 14 due to this tendency the fuser 8 and ~' as shown in FIGS. 1 and 2, are provided with additional end restraining blocks 50 employed at ends of belt belt 14. The end blocks 50 are fixedly positioned perpendicular to the ends of web 14 and are circular in shape and diametrically larger than the ends of web 14. The blocks 40 are made of any suitable durable material that is able to withstand the ahrasion caused by the edges of .002" to .003"-stainless steel and has a low coefficient of friction relative to the stainless web 14~
One such material is known by the brand name of*Tufran, a product of General Magnaplate Corp., Linden, N.J.
An additional problem of balancing a semi rigid metal tube such as web 14 has been overcome by the nature of the placement of the balance rolers 32, 34 and 36. The balance of rollers 32~ 34 and 36 are positioned approximately 120 apart so as to peripherally support the web 14 on its external surface. While the balance rollers 34 and 326 support the web 14, they additionally ensure that minimum compressive or tensile stresses are exerted unto the , ~ *Trademark -10- ' ' . ' 11 A

web 14 during either functional moviny or static rnodes of the copy process, and particularly actual fusing of a copy sheet.
Those skilled in the art will recognize that the thick-ness of the belt 14 is inversely proportional to its thermal conductivity. In other words, belt 14 will dissipate heat quicker than a thick belt 14. Hence, a relatively thin belt is preferable in order to minimize the risk of igniting a copy sheet. On the other hand, too thin a belt may dissipate the heat before the image I is fused to the copy sheet 10. Hence, the thickness of the belt and its material (steel, aluminum, etc.), are chosen to suitably act with heating source 20 to deliver sufficient heat to the image I
to fuse it to the copy sheet 10. Additionally, suitable silicone elastomer or other material may be employed to aid release of the toner from the web 14 external surface. In the preferred embodiment, it has been discovered that a stainless steel belt 14 having a thickness between 0.002 and 0.003 inches works well. Of course, different toners and different copy sheets (e.g. plastic), may belts of other materials with different thicknesses. All such applica-tions of the invention are deemed to be within the spirit and scope of the appended claims.
It will also be appreciated that the invention may be employed in copiers that use either a direct or indirect means for forming a toner image on the copy sheet. Hence, it is useful in the so-called plain paper copiers as well as in the coated paper copiers. Further, the invention is also adapt-able to fixing image to other heat fusible surfaces, such as .' ~1 11 ~

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plastic and cloth. Accordingly, the invention described above is the preferred embodiment. That embodiment as well as further modifications that are within the ordinary skill of one trained in the fusing art are deemed to be within the spirit ~nd scope of the ollowing claims.

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Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. An apparatus for applying pressure and heat to a copy sheet bearing a developed electrostatic image on at least one surface thereof in order to fix the image to the copy sheet, said apparatus comprising:
A. a pair of oppositely driven, mutually biased, solid pressure fixing feed rollers, B. a thermally conductive web disposed between said pressure fixing feed rollers for contacting the image bearing surface of a copy sheet fed between the pressure fixing feed rollers, said web being contiguous with said rollers only at the juncture of said rollers; and C. means for heating only said web so that when a copy sheet bearing a developed image is fed between the feed rollers the image on the copy sheet surface is fixed to the copy sheet by the combined heat and pressure applied to said copy sheet and to said image by said heated, ther-mally conductive web and said mutually biased, pressure fixing feed rollers.

2. The invention of Claim 1 wherein said means for heating said web is operatively disposed adjacent the surface of the web that is opposite to said image.

3. The invention of Claim 1 wherein said means for heating said web comprises a radiant energy lamp disposed inside said web.

4. The invention of Claim 3 further comprising means for focusing the radiant energy lamp upon a portion of the web situated upstream of the juncture with said feed rollers.

5. The invention of Claim 3 further comprising means for shielding the feed rollers from said radiant energy lamp.

6. The invention of Claim 1 wherein said web comprises a relatively thin, flexible sheet of stainless steel.

7. The invention of Claim 6 wherein the stain-less steel sheet is from 0.002 to 0.003 inches thick.

8. The invention of Claim 1 further comprising means for releasing the pressure between said rollers in order to remove said endless belt.

9. The invention of Claim 1 wherein said web comprises an endless web.

10. The invention of Claim 9 wherein the web pro-vides a low shallow tangent angle guide surface for the copy sheet at the nip of the feed rollers.

11. A method for applying pressure and heat to a developed electrostatic image on the surface of a copy sheet in order to fix the image to the surface, comprising;
A. feeding the copy sheet through a pair of oppositely driven, mutually biased, solid pressure fixing feed rollers;
B. heating only a thermally conductive web disposed between said pressure fixing feed rollers, said web being contiguous with said rollers only at the juncture of said rollers; and C. contacting the image bearing surface of the copy sheet with the heated web as the copy sheet passes through the juncture of the pressure fixing feed rollers.