Electrophotography – Image formation – Fixing
Reexamination Certificate
2001-10-29
2003-06-24
Pendegrass, Joan (Department: 2852)
Electrophotography
Image formation
Fixing
C219S619000, C219S672000
Reexamination Certificate
active
06584298
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a fixing device of an induction heating type for use in an image forming apparatus such as a copying machine, a printer, and a facsimile machine and an image forming apparatus equipped with this fixing device.
Up to now, a fixing device for use in an image forming apparatus such as a copying machine, a printer, and a FAX machine has a structure such that a heating roller for heating a transfer material carrying a toner image composed of a powder developer and a pressing roller for conveying and pressing it are provided, and the toner particles on this transfer material are fused and melted to be fixed on it by the passage of the transfer material through the fixing point which is the pressing contact portion (nip portion) of these heating roller and pressing roller.
A generally known fixing device uses a halogen lamp, which is provided inside a metallic roller to heat the roller by radiant heat, as a heat source of the heating roller. However, in recent years, as a fixing device employing a technique of induction heating, there has been proposed a method of heating in which an eddy current is made to flow in a fixing roller in a structure having a shape composed of a coil supporting member provided along the rotary axis of the fixing roller having a heat applying coil wound round on it.
Such a fixing device is capable of making the position of heat generation come as close as possible to toner particles by generating an eddy current in the fixing roller by a magnetic flux to generate heat based on Joule's heat, and is also capable of achieving improved efficiency of energy consumption as compared to a heating roller employing a halogen lamp. In addition, such a fixing device is capable of performing temperature control easily and with a high precision.
However, as shown in FIG.
28
(
a
) and FIG.
28
(
b
), in the case where a heat applying coil
101
is uniformly wound around a coil supporting member
100
, as shown in
FIG. 29
, the magnetic flux density is small at both ends of the fixing roller in the longitudinal direction. As a result, heat generation is decreased to cause a temperature drop to occur, which produces poor fixing.
By making the length of the fixing roller longer than the part that is required for fixing in order to get rid of the problem of this temperature drop, the temperature of the part that is required for fixing is secured. In that case, however, the length of the heat applying coil becomes long, electric power consumption becomes high, and it is not possible to make the size compact, which causes the device to have a large size. Further, there is a problem that, for example, manufacturing cost is increased because the heat applying coil and the supporting member must be made large-sized.
SUMMARY OF THE INVENTION
This invention was made in view of the above-mentioned points, and it is an object to provide a fixing device and an image forming apparatus which are capable of securing the heat generation area with a simple structure, and which can be made small in size and at a low manufacturing cost.
For the purpose of solving the above-mentioned problems and accomplishing the object, this invention has any one of the structures described below.
A fixing device according to a first aspect of the invention comprises a cylindrical fixing roller to be heated, a coil supporting member disposed along the inside of this fixing roller, a heat applying coil formed by winding a wire round on the circumference of this coil supporting member for heating the fixing roller by inducing an induced current in the fixing roller, and a pressing roller that forms a nip portion with the fixing roller, conveys a transfer material which is gripped by the nip portion between the fixing roller and the pressing roller, and a toner image formed on the transfer material being fixed by heat energy given from the fixing roller, characterized in that the heat applying coil is formed by winding a wire round in such a way as to have a shape which is longer in the longitudinal direction of the coil supporting member and parts parallel to the longitudinal direction of the coil supporting member and parts lying along the circumference of the coil supporting member, and with respect to this heat applying coil, the winding density of the parts lying along the circumference of the coil supporting member is made higher than the winding density of the parts parallel to the longitudinal direction of the coil supporting member.
According to this aspect of the invention, by making the winding density of the parts of the heat applying coil lying along the circumference of the coil supporting member higher than the winding density of the parts of the heat applying coil parallel to the longitudinal direction of the coil supporting member, the magnetic flux density at the end portions in the longitudinal direction of the fixing roller is made higher, and heat generation becomes higher accordingly; thus, the distribution of heat generation in the fixing roller is improved thereby making possible to suppress the temperature drop at the end portions in the longitudinal direction, and it is possible that the length of the heat applying coil is made as short as possible, a sufficient heat generation area is secured with a simple structure, and the size is made small and the manufacturing cost is lowered.
According to a second aspect of the invention, the wire of the heat applying coil has a cross-sectional shape such that the lengths of the vertical axis and the lateral axis intersecting each other perpendicularly at the center are different, and the heat applying coil is formed by winding the wire round in such a way that, in the parts parallel to the longitudinal direction of the coil supporting member, the long axes of the wire cross-section are directed to one another, and in the parts lying along the circumference of the heat applying coil, the short axes of the wire cross-section are directed to one another.
According to the second aspect of the invention, by forming the coil in such a way that, in the parts of the heat applying coil parallel to the longitudinal direction of the coil supporting member, the long axes of the wire cross-section are directed to one another, and in the parts lying along the circumference of the coil supporting member, the short axes of the wire cross-section are directed to one another, the magnetic flux density at the end portions in the longitudinal direction of the fixing roller is made higher, and heat generation becomes higher accordingly; thus, the distribution of heat generation in the fixing roller is improved thereby making it possible to suppress the temperature drop at the end portions in the longitudinal direction, and it is possible that the length of the heat applying coil is made as short as possible, a sufficient heat generation area is secured with a simple structure, and the size is made small and the manufacturing cost is lowered.
According to a third aspect of the invention, a fixing device is provided wherein, with respect to the heat applying coil, the number of stacked layers are different between the parts of the heat applying coil parallel to the longitudinal direction of the coil supporting member and the parts of the heat applying coil lying along the circumference of the coil supporting member, and the number of stacked layers in the parts of the heat applying coil lying along the circumference of the coil supporting member is made greater than the number of stacked layers in the parts of the heat applying coil parallel to the longitudinal direction of the coil supporting member.
According to the third aspect of the invention, by making the number of stacked layers in the parts of the heat applying coil lying along the circumference of the coil supporting member greater than the number of stacked layers in the parts of the heat applying coil parallel to the longitudinal direction of the coil supporting member, the magnetic flux density at the end portions in the longitudinal directio
Omoto Tetsuko
Toyoda Miho
Frishauf Holtz Goodman & Chick P.C.
Konica Corporation
Pendegrass Joan
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