Electrical contacting device for fusing roller

A fusing roller of the type having a thin internal resistance heating layer is electrically contacted by an internal conductive annular element positioned adjacent the end of the roller core. The resistance layer is applied to a common surface formed by the outside of the core and the annular element. Preferably, the resistance layer is covered by a protective layer. With this structure, the contacting device is protected from external damage, for example, from that caused by release oil contamination.

RELATED APPLICATION 
This application is related to co-assigned U.S. patent application Ser. No. 
07/139,994, entitled Fusing Roller, filed concurrently herewith, in the 
names of Carl T. Urban, Mark A. Lewis and David A. Glocker. 
TECHNICAL FIELD 
This invention relates to electrostatography, and more particularly to a 
device for electrically contacting the resistive heating layer of a fusing 
roller. 
BACKGROUND ART 
U.S. Pat. No. 4,395,109 describes a roller fusing mechanism for fusing 
toner to paper or another substrate in which a thin resistive heating 
layer connectable to an electrical power supply is positioned close to the 
surface of a fusing roller. The resistive heating layer is insulated from 
a metal core and is covered by a protective layer having an abhesive 
fusing surface. This type of structure permits the heat generated within 
the resistive heating layer to be conducted rapidly and efficiently to the 
fusing surface. Consequently, the surface temperature can be controlled 
more accurately and the power requirement for the fusing mechanism is 
reduced. 
In this prior structure, electrical contact is provided to the resistive 
heating layer by copper conductive elements of substantial thickness 
positioned on the surface of the roller in a location at which the 
resistive heating layer is uncovered by the protective layer. These 
conductive elements are electrically contacted as the roller rotates, by 
brushes or the like connected to the power supply. 
Sizeable conductive elements of this type are readily contactable, but 
interfere with other aspects of the apparatus. For example, most fusing 
rollers need the application of a release oil to prevent offset of toner 
in operation. Oil can corrode the conductive elements and the elements 
themselves can provide a conduit for oil to travel deeper into the roller 
where it can cause damage. 
DISCLOSURE OF THE INVENTION 
It is the object of the invention to provide a fusing roller generally of 
the type described, but which can be connected to a power supply with less 
damage from release liquid or other outside agents. 
This and other objects are accomplished by an electrical contacting 
structure which is internal to the roller and protected from oil and other 
problems. The contacting structure includes a conductive annular element 
around the fusing roller which contacts the inner surface of the resistive 
heating layer and means for electrically connecting the conductive annular 
element to the power supply. According to a preferred embodiment, the 
fusing roller has a core with an insulative surface. The conductive 
annular element adjoins the core and forms a continuous cylindrical 
surface with the insulative surface. The resistive heating layer is 
supported by and contacts the continuous cylindrical surface.

BEST MODE OF CARRYING OUT THE INVENTION 
According to FIG. 1 a fusing roller 10 is part of a fusing mechanism of a 
type well known in the art. The fusing mechanism includes a pressure 
roller 50 for providing a heating nip and a wicking mechanism 60 for 
applying release oil to prevent toner offset onto the fusing roller. 
FIG. 2 shows the fusing roller 10 comprising a core 16, a resistive heating 
layer 14, and a protective layer 12 providing a fusing surface. The 
resistive heating layer is positioned between the core and the protective 
layer. To limit heat loss and electrical shorting at the core 16 of the 
fusing roller, the surface of core 16 is both thermally and electrically 
insulative, for example, the entire core can be of glass or another 
insulative material or a layer of insulative material can be positioned 
between the core and the heating layer 14. 
Resistive heating layer 14 is electrically connected to a power supply 28 
through an electrical contacting structure. This structure provides 
thorough contact which allows electrical current to be evenly distributed 
to the resistive heating layer 14. This electrical contacting structure 
includes conductive annular elements, such as ring 18A and 18B, which 
provide broad area contact with layer 14. Conductive annular elements 18A 
and 18B adjoin core 16 and comprise sections 19A and 19B with outside 
diameters corresponding to the outside diameter of the insulative surface 
on core 16, and annular extensions 21A and 21B with outside diameters 
corresponding to the inside diameter of the core 16. Conductive 
cylindrical elements such as plugs 22A and 22B, are positioned at the axis 
of fusing roller 10 and are connected to conductive rings 18A and 18B by 
connecting means, for example, screws 20A and 20B. The heads of screws 20A 
and 20B are covered with a protective material 38 to decrease release oil 
damage and provide insulation. 
Insulative annular elements 24A and 24B, for example rings made from a 
phenolic material, support conductive plugs 22A and 22B and protect the 
roller ends and the conductive rings 18A and 18B from heat loss and 
release oil damage. Insulative rings 24A and 24B comprise sections 25A and 
25b having outside diameters which correspond to the outside diameter of 
the fusing roller 10, and annular extensions 26A and 26B whose outside 
diameters correspond to the inside diameter of the conductive rings 18A 
and 18B. 
The electrical current needed to heat the resistive heating layer 14 is 
supplied by the power supply 28. Electrical contact between the power 
supply 28 and the conductive plugs 22A and 22B can be accomplished by any 
known axial connecting mechanism. A preferred design is shown in FIG. 2 
and includes ball conductors 30A and 30B which are urged by springs 36A 
and 36B into relative, sliding rotational movement with hemispherical 
cavities 32A and 32B in the ends of conductive plugs 22A and 22B. 
In operation, electrical current provided by the connected power supply 28 
flows through ball conductors 30A and 30B, conductive end plugs 22A and 
22B, screws 20A and 20B, conductive rings 18A and 18B, and resistive 
heating layer 14. The resistive heating layer materials, in response to 
the electrical current flow, produce the desired heating effect of the 
fusing roller 10. The insulative core 16 and insulative rings 24A and 24B 
minimize heat loss within the system. 
The contacting structure eliminates several problems associated with the 
external contacting structure of the prior art. The release oil usually 
required in electrostatographic fusing systems often collects on and 
corrodes the external conductive brushes. This inhibits the electrical 
contact needed to maintain the required current flow, and thus alters the 
fusing roller surface temperature. The external contacting structure also 
acts as a conduit for release oil, allowing the oil to penetrate and 
damage the fusing roller materials. In addition, the external contacting 
structure is directly exposed to the operating environment which increases 
the required operating space, and the possibilities of mechanical and 
electrical malfunctions such as element deterioration and electrical 
shorting. 
The internal electrical contacting structure shown in FIGS. 1 and 2 is 
almost entirely insulated and protected from the release oil and the 
operating environment. Therefore, the problems of element corrosion and 
fusing roller damage due to release oil are decreased. The possibilities 
for mechanical and electrical malfunctions are decreased because the 
majority of the contacting structure is housed within the fusing roller. 
Improved electrical contact is maintained because the axially located 
conductors connecting the power supply 28 to the conductive end plugs 22A 
and 22B are positioned at each end of the fusing roller and consequently, 
less exposed to the release oil. In addition, the required operating space 
is reduced. 
Electrical continuity of the resistive heating layer 14 maintains 
uniformity of the heat applied to the surface to be fused. Damage to the 
resistive heating layer, such as cracking, will occur if the resistive 
heating layer becomes separated from the core during manufacture or use. 
Fusing roller materials having dissimilar thermal expansion coefficients 
will experience varying amounts of expansion when heated during 
manufacture or use, thus increasing the possibility of resistive heating 
layer and core separation. For example, the curing process in applying the 
outer protective layer 12 may require a high temperature which invites 
such separation. Therefore, materials used for the resistive heating layer 
and core should exhibit excellent bonding characteristics and have similar 
coefficients of thermal expansion. 
Many metallic or metallic alloy resistive layer materials which have 
resistive properties particularly useful in this type of fusing roller 
have a coefficient of thermal expansion between 30.times.10.sup.-7 to 
120.times.10.sup.-7 linear distance per distance per degree C. Most glass 
compositions also fall in this range. Thus, glass is an excellent material 
to be used for the core. One or more glasses can be matched with each 
resistive material in this respect. 
The preferred embodiment shown in the FIGS. includes a resistive heating 
layer made from a metal alloy of about 29% nickel and 71% iron. Because of 
a close match in thermal expansion properties, this alloy maintains 
excellent bonding with a core made of an alkali barium borosilicate glass. 
However, many other usable materials also bond well with the same or other 
glasses. For example, a tungsten resistive heating layer matches well with 
a borosilicate, soda borosilicate, or soda lime borosilicate glass core. 
Titanium resistive heating layers are applied to potash soda lime or 
alkali barium glass cores, and tantalum resistive heating layers are used 
with lead borosilicate, soda zirconia, or soda borosilicate glass cores. 
Resistive heating layers made of certain carbon steels are applied to 
glass cores made of potash soda lime, or potash lead. Stainless steels 
containing 17% and 28% chromium are applied to glass cores made of potash 
lead, alkali barium, or soda potash lead. A metal alloy containing 
approximately 42% nickel, 6% chromium, and 52% iron is applied to glass 
cores made from potash soda lead, soda lime, potash lead, lead zinc 
borosilicate, alkali barium, alkali lead, or soda barium fluoride. Glass 
cores made of alkali barium borosilicate, alkali borosilicate, soda 
borosilicate, borosilicate, aluminosilicate, alkali earth aluminosilicate 
also maintain the desired bonding and thermal expansion properties when 
coated with a resistive heating layer made of molybdenum. These cores also 
bond well with metal alloys containing approximately (1) 29% nickel and 
71% iron, (2) 40.5-41.75% nickel-cobalt and 59.5-58.25% iron, and (3) 17% 
cobalt and 83% iron. 
The thickness of the resistive heating layer is dependent on the 
composition of the material used and the amount of available power. For 
example, when the resistive heating layer 14 is made of the preferred 
nickel-iron alloy its thickness can range from 0.1 microns to 0.3 microns. 
The protective layer 12 includes at least one material that provides good 
toner release properties, for example, silicone rubber or 
polytetrafluoroethylene, as is well known in the art. For example, a 
protective layer of polytetrafluoroethylene having a thickness ranging 
from 1.0 mils to 2.0 mils gives good results when coated directly on the 
preferred nickel-iron alloy resistive heating layer previously coated on 
an alkali barium borosilicate glass core. 
Manufacture of the described fusing roller includes completely inserting 
annular extensions 21A and 21B of conductive rings 18A and 18B into each 
end of core 16. The outside surfaces of sections 19A and 19B of conductive 
rings 18A and 18B form a continuous surface with the outside surface of 
the core 16. The method for joining these components is dependent on the 
types of materials used. For example, thermal properties of a glass core 
and conductive rings made of a nickel-iron alloy are similar; therefore, 
permanent contact between the core 16 and conductive rings 18A and 18B can 
be established by means such as welding. 
The resistive heating layer 14 is then applied as a coating to the 
continuous surface formed by the core 16 and attached conductive rings 18A 
and 18B, for example, by sputtering. Once the desired resistive heating 
layer thickness is obtained, the outside surface of the resistive heating 
layer 14 is cleaned, for example, by chemical etching. Bonding strength 
between the resistive heating layer 14 and the protective layer 12 is 
further increased by this cleaning process. The protective layer 12 is 
then applied over the entire exposed surface of the resistive heating 
layer 14, for example, by spraying. 
Annular sections 26A and 26B of insulative rings 24A and 24B are then 
completely inserted into the centers of conductive rings 18A and 18B 
respectively. The continuous outside surface of the fusing roller is 
maintained by the outside surfaces of sections 25A and 25B of insulative 
rings 24A and 24B. Section 25B of ring 24B has a larger axial width than 
section 25A of ring 24A in order to accommodate means for driving the 
fusing roller, such as slot 34 in which a drive gear is mounted. 
Conductive end plugs 22A and 22B are then inserted into the centers of the 
insulative rings 24A and 24B, extending into the portions 26A and 26B to 
provide additional support to the fusing roller 10. 
Electrical contact between the conductive end plugs 22A and 22B and the 
conductive rings 18A and 18B is established by inserting conductive means 
such as screws 20A and 20B into the ends of the fusing roller 10 from the 
outer surface of said roller toward the axis of the core 16. These screws 
20A and 20B pass through and contact the resistive heating layer 14, 
conductive rings 18A and 18B, insulative rings 24A and 24B, and extend 
into the conductive end plugs 22A and 22B respectively. The exposed heads 
of screws 20A and 20B are protected from the operating environment by a 
coating 38, such as silicone rubber. 
After the means for driving the fusing roller, such as a drive gear is 
attached to the insulating ring 24B by means of slot 34, the completed 
fusing roller 10 is mounted into an electrophotographic machine by 
conventional mounting means and connected to the power supply by snapping 
the spring mounted ball conductors 30A and 30B into the hemispherical 
cavities 32A and 32B, located on the ends of the conductive end plugs 22A 
and 22B. 
The invention has been described in detail with particular reference to a 
preferred embodiment thereof, but it will be understood that variations 
and modifications can be effected within the spirit and scope of the 
invention as described hereinabove and as defined in the appended claims.