Patent Grant
7539449
The present invention relates to an image heating apparatus for heating an image on a recording material. As the image heating apparatus, it is possible to use, e.g., a fixing apparatus for fixing an unfixed image formed on a recording material or a gloss-imparting apparatus for improving gloss of an image fixed on a recording material by heating the image.
An image forming apparatus for fixing a toner image on a recording material by circulating a heated fixing belt to contact the recording material onto which the toner image is transferred has been put into practical use. The fixation roller can realize a long heating length of the recording material by a relatively small apparatus structure similarly as in the case of using a large diameter fixation roller.
Japanese Laid-Open Patent Application (JP-A) 2004-341346 has disclosed an image forming apparatus in which a recording material is nipped and conveyed between a fixing belt and a pressure belt which are circularly driven while being pressed against each other to fix a toner image on the recording material. In the image forming apparatus, the fixing belt is heated by stretching the fixing belt around a heating roller provided with a heater at its central axis. The pressure belt is also heated by being circulated in contact with the heated fixing belt.
JP-A Hei 10-69208 has disclosed an image forming apparatus in which a fixing belt is heated by an induction heating (IH) method. In the image forming apparatus, a coil member is disposed opposite to an inner peripheral surface of the fixing belt having a metal layer. The fixing belt is induction-heated to be kept at a predetermined temperature range by applying a high-frequency current to the coil member to generate magnetic flux so as to be exerted on the fixing belt.
In the fixing apparatus using the fixing belt, it is necessary to prevent lateral deviation or dislodgement of the fixing belt by attaching a belt regulation member (so-called collar) at both end portions of a roller for stretching the fixing belt. Even in the case of employing a method wherein the lateral deviation of the fixing belt is prevented by detecting a position of the fixing belt in its width direction to control a degree of inclination of the roller, it is also necessary to employ the belt regulation member as a member for regulating the lateral deviation.
However, in the case where the fixing apparatus in which the fixing belt having the metal layer is stretched around the roller provided with the metal-made belt regulation member is operated, it has been found that large electromagnetic noise, radio wave, power supply ripple are caused to occur due to electromotive force generated in the fixing belt when a contact surface of the fixing belt with the roller is not electrically insulated. Particularly, it is difficult to ensure an electrical insulation distance between the fixing belt and the roller end portion.
An object of the present invention is to provide an image heating apparatus, for heating an image on a recording material by causing a belt member having an electroconductive layer to generate heat through induction heating, capable of reducing electromagnetic noise or the like generated by a potential difference caused between the belt member and a guide member for guiding the belt member.
According to an aspect of the present invention, there is provided an image heating apparatus, comprising:
magnetic flux generation means for generating magnetic flux;
a belt member having an electroconductive layer for generating heat by magnetic flux from the magnetic flux generation means, the belt member heating an image on a recording material; and
These and other objects, features and advantages of the present invention will become more apparent upon a consideration of the following description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings.
a) and 6(b) are schematic views for illustrating induced voltage of a fixing belt.
Hereinbelow, a fixing apparatus 50 as an embodiment of the present invention and a color electrophotographic printer 100 including the fixing apparatus 50 will be described with reference to the drawings. Incidentally, the fixing apparatus in the present invention is not limited to one using a fixing belt 1 and a pressure belt 2 as in this embodiment but may also be applicable to various fixing apparatuses including a fixing belt, having an electroconductive layer, for effecting induction heating, such as a fixing apparatus using a fixing belt and a fixation roller, a fixing apparatus for effecting only heating using a fixing belt without effecting pressure application, etc.
A fixing apparatus 50 (as shown in
Further, the fixing apparatus 50 and the color electrophotographic printer 100 in this embodiment are not limited to those employing combinations of constitutional members described below but may also be realized in other embodiments in which the constitutional members are partly or entirely replaced with their alternative members.
<Image Forming Apparatus>
Referring to
The color electrophotographic printer 100 includes a developing device 113 for colors of yellow (Y), magenta (M), cyan (C), and black (Bk). The developing device 113 includes a developing roller 113Y for Y (yellow), a developing roller 113M for M (magenta), a developing roller 113C for C (cyan), and a developing roller 113Bk for Bk (black). The respective developing rollers are moved to a position at which an associated developing roller contacts a photosensitive drum 121 as an image bearing member and develops an electrostatic latent image with toner of an associated color (Y, M, C or Bk) on the surface of the photosensitive drum 121.
Around the photosensitive drum 121, members including a primary charger 127, the developing device 113, a primary transfer device 123, and a cleaning apparatus 212 are disposed and subjected to formation and development of the electrostatic latent image by the rotation of the photosensitive drum in the following manner.
First, the surface of the photosensitive drum 121 cleaned by the cleaning apparatus 212 is electrically charged in a uniformly charged state by the primary charger 127. At the surface of the photosensitive drum 121 placed in the uniformly charged state, scanning with a laser beam modulated by an image signal is effected by a laser scanner 128. By the scanning exposure, on the surface of the photosensitive drum 121, electrostatic latent images for the respective colors are successively formed.
The respective electrostatic latent images are developed with associated color toners, respectively, by the developing device 113 to provide color toner images. A first toner image formed on the surface of the photosensitive drum 121 is primary-transferred onto the intermediary transfer belt 122 by the primary transfer device 123. Thereafter, a toner image of a subsequent color is formed on the surface of the photosensitive drum 121 and is superposed on the first toner image transferred on the intermediary transfer belt 122, in such a state that leading ends of the toner images are aligned with each other, in the same manner as in the case of the first toner image. The remaining two color toner images are also superposed on the previous color toner images on the intermediary transfer belt 122 in the same manner. As a result, on the intermediary transfer belt 122, a full-color toner image (including the four color toner images) is formed.
The thus formed full-color toner image formed on the intermediary transfer belt 122 is then a secondary-transferred onto the sheet S by a secondary transfer roller 221. Before the secondary transfer, the sheet S is fed from the paper feeding cassette 223 one by one by means of the paper feeding roller 224. The sheet S is placed in a stand-by state after subjected to correction of skew feeding by a pair of registration rollers 225. The pair of registration rollers 225 feeds the sheet S to a nip between the secondary transfer roller 221 and a separation roller 219 at timing in synchronism with the full-color toner image transferred onto the intermediary transfer belt 122. The sheet S onto which the full-color toner image is transferred by the secondary transfer roller 221 is conveyed into the fixing apparatus 50, where the toner image is fixed on the sheet S.
<Fixing Apparatus>
Referring to
The fixing belt 1 is a belt member extended under tension around a fixation roller 2 for rotationally driving the fixing belt 1 and a fixation tension roller 3, for stretching the fixing belt 1, as a heat source.
The fixing belt 1 has a 100 μm-thick base layer of nickel (1a in
As a material for the elastic layer, it is also possible to use other known elastic materials such as silicone rubber, fluorine-containing rubber and the like. In this embodiment, silicone rubber is used.
The fixation roller 2 is an elastic roller prepared by providing a silicone rubber layer 2a as an elastic layer on a surface of a core metal of iron alloy having an outer diameter of 20 mm and an inner diameter of 18 mm. By providing the elastic layer to the outer peripheral surface of the core metal, a friction transmission force is created, so that a driving force inputted from an unshown drive source via a drive gear train can be effectively transmitted to the fixing belt 1. By the silicone rubber layer 2a, an amount of heat conduction (transfer) to the core metal is decreased and a warm-up time is also effectively reduced.
The fixation tension roller 3 as a guide member for guiding the fixing belt 1 is an iron-made hollow roller (electroconductive portion), as an electroconductive member, having an outer diameter of 20 mm, an inner diameter of 18 mm, and a thickness of 1 mm, and is biased outwardly by an unshown stretching spring disposed at an axis end portion to apply tension to the fixing belt 1.
The fixing apparatus 50 further includes an induction heating (IH) unit 4 as a coil member for induction heating. The IH unit 4 is constituted by supporting two coils 4a and 4b in an electrical insulation manner. The coil 4a is disposed opposite to a flat portion of the fixing belt 1 (endless belt) as a member to be heated so as to exclusively heat the electroconductive layer of the fixing belt 1 by induction heating. The coil 4b is disposed opposite to the fixation tension roller 3 via the fixing belt 1 so as to induction-heat the electroconductive layer of the fixing belt 1 and the electroconductive portion of the fixation tension roller 3. The IH unit 4 has an opposite surface along an outer shape of the fixation tension roller 3, and a distance between the fixing belt 1 and the coils 4a and 4b is set to about 1.5 mm.
On the other hand, the pressure belt 2 is stretched around a metal pressure roller 20 as a pressing member and a pressure tension roller 22. The pressure roller 20 is rotated by mechanical power transmission from the fixation roller 2 even in such a state that it is moved away from the fixation roller 2. During the fixing operation, the pressure roller 20 is pressed against the fixation roller 2 at a pressing force of 300N. The pressure belt 21 is formed of the same material as the fixing belt 1. The pressure tension roller 22 is biased outwardly by an unshown stretching spring to apply tension to the pressure belt 21.
A fixation stay 23 formed of stainless steel (SUS material) is fixed on a fixation frame (not shown) so as to support the fixing belt from the back side of the fixing belt 1. A silicone rubber-made pressure pad 24 disposed opposite to the fixation stay 23 via the fixing belt 1 and the pressure belt 21 presses a nip, between the fixing belt 1 and the pressure belt 21, against the fixation stay 23 to apply a pressing force of 500N to the fixation stay 23.
An IH controller 10 supplies a triangular wave (AC 600 V, 25 kHz at maximum output) to the IH unit 4, so that magnetic flux is generated in the coils 4a and 4b to heat the fixing belt 1 and the fixation tension roller 3. The IH controller 10 increases and/or decreases its output on the bias of an output of a temperature sensor (thermistor) disposed at a central portion of the fixing belt 1 and downstream from the fixation tension roller 3, thus adjusting the temperature of the fixing belt 1 to 180° C. On the other hand, the pressure belt 21 is temperature-controlled to appropriately 100° C. by a heater (not shown) provided in the pressure roller 20.
During the fixation operation, the pressure belt 21 is raised and pressed against the fixing belt 1, so that a long pressure contact surface from the nip between the fixation roller 2 and the pressure roller 20 to the end portion of opposing surface between the fixation stay 23 and the pressure pad 24 is formed between the fixing belt 1 and the pressure belt 21. At the long pressure contact surface, when the sheet S on which the unfixed toner image is electrostatically adsorbed is supplied, nipped, and conveyed, the toner image subjected to application of heat and pressure is fixed on the sheet S.
As a material of the belt flanges 25a and 25b, a plastic material having a high heat resistance and a high sliding performance is used. By the belt flanges 25a and 25b, the fixing belt 1 is configured to be regulated in its deviation direction.
In the fixing apparatus 50 of this embodiment, the fixation tension roller 3 has a hollow roller 3a as a heat generation portion for generating heat by the action of magnetic flux from the coil 4b. Accordingly, cooling of the fixing belt 1 can be avoided by heat accumulation of the fixation tension roller 3, so that it is possible to ensure a sufficient temperature at the fixation nip without heating the fixing belt 1 up to high temperatures. Further, it is also not necessary to provide the fixation tension roller 3 with an additional heat means.
As a result, it is possible to realize resistance heating, with high reproducibility, such that passage of current between the nickel layer 1a (
Further, the thickness of the insulating members 26a and 26b provide gaps between the end portions of the hollow roller 3a and the belt flanges 25a and 25b. As a result, it is possible to obviate electrical conduction with reliability between the hollow roller 3a and the electroconductive layer of the fixing belt 1 even in the cases where the edge of the fixing belt 1 is locally bent by running against the belt flange 25a or 25b, where metal powder is deposited on portions adjacent to the belt flanges 25a and 25b, and where a length of the heat-shrinkable tube 27 is somewhat short. In the present invention, the electroconductive portion (hollow roller 3a) has an end surface which is electrically insulated at a position inside a regulation position at which the belt member (fixing belt 1) is regulated by the regulation portion (belt flange 25a or 25b).
As a result, it is possible to reliably prevent leakage of current from the fixing belt 1 and the nickel layer 1a (
Further, the nickel layer 1a of the fixing belt 1 and the hollow roller 3a of the fixation tension roller 3 are separated from each other by the heat-shrinkable tube 27, so that the eddy current is generated with high reproducibility between the nickel layer 1a and the hollow roller 3a, thus obviating irregular heating due to repetition of unstable contact and noncontact states.
The belt flanges 25a and 25b are formed of a plastic member (material) having a heat resistance and sliding performance and set to have an outer diameter larger than that of the fixation tension roller 3B. They are rotated together with the fixation tension roller 3B. In
In this embodiment, as shown in
As a result, it is possible to realize resistance heating, with high reproducibility, such that passage of current between the nickel layer 1a (
Further, the bent (interposed) portion of the heat-shrinkable tube 29 seals the end portions of the hollow roller 3a and the belt flanges 25a and 25b. As a result, it is possible to obviate electrical conduction with reliability between the hollow roller 3a and the electroconductive layer of the fixing belt 1 even in the cases where the edge of the fixing belt 1 is locally bent by running against the belt flange 25a or 25b, and where metal powder is deposited on portions adjacent to the belt flanges 25a and 25b.
As a result, it is possible to reliably prevent leakage of current from the fixing belt 1 to the casing (ground potential) of the fixing apparatus 50 even in the cases where the fixing belt 1 is electrically charged by continuously supplying the charged sheet S, where a voltage is induced in the fixing belt 1 by a high voltage supplied to the coils 4a and 4b, and where the eddy current by magnetic flux generates a potential at an end portion of the fixing belt 1.
<Induced Voltage of Fixing Belt>
a) and 6(b) are explanatory views of induced voltage of the fixing belt and
the coil 4b is disposed opposite to the fixing belt 1 via a spacing 4D, so that a distance d1 between the coil 4b and the nickel layer 1a is the sum of the spacing 4D and the thickness of the silicone rubber layer 1b. Further, a distance d2 between the hollow roller 3a of the fixation tension roller 3 and the nickel layer 1a is equal to a thickness of the heat-shrinkable tube 27.
An electrostatic capacity (capacitance) C created between two electrodes disposed with a spacing is generally represented by the following equation:
C=∈×S/d,
wherein ∈ represents a dielectric constant, S represents an area of electrode, and d represents a distance between electrodes.
Based on the above equation, as shown in the equivalent circuit shown in
Further, as shown in
V2=V1×C1/(C1+C2).
Here, strictly speaking, dielectric constants ∈ of the space, the rubber layer of the fixing belt, and the insulating heat-shrinkable tube (PFA) are different from each other. However, for simple evaluation, assuming that the dielectric constants ∈ are identical to each other and the areas S are also identical to each other, the voltage V2 is represented by the following equation:
V2=V1×d2/(d1+d2).
For example, when d1=1 mm, d2=80 μm, and V1=(AC 600 V, 25 kHz), V2 is approximately 44 V (25 kHz).
This voltage V2 is generated between the nickel layer 1a of the fixing belt 1 and the GND of the fixing apparatus 50, so that when a part of the nickel layer 1 of the fixing belt 1 is brought near the hollow roller 3a, an electric field therebetween is large since the electric field is inversely proportional to the distance therebetween. As a result, electric discharge from the nickel layer 1a (end surface) of the fixing belt 1 to a portion, at the GND potential, of the fixation tension roller 3 (end surface) is caused to occur, thus producing noise.
In these circumstances, in the case where the belt flanges 25a and 25b are formed of metal and directly contact the hollow roller 4a, a problem such as leakage or the like arises every time the distance between the end surfaces of the fixing belt 1 and the belt flanges 25a and 25b is decreased even when an electrical insulating layer is disposed at both of the inner surface of the fixing belt 1 and the surface of the fixation tension roller 3. For this reason, the belt flanges were not capable of being employed in order to regulate movement of the fixing belt in the width direction.
The above described problem has been solved by the fixation tension rollers 3 and 3B in First Embodiment and Second Embodiment according to the present invention, so that a simple belt regulation system is realized in a belt fixation-type fixing apparatus employing an external IH method and an endless belt. More specifically, even in such a constitution that the endless belt is externally heated by the IH method and belt flanges are provided to one roller of a plurality of stretching means for stretching the endless belt to effect regulation of lateral movement of the endless belt, it is possible to carrying out the constitution by a simple belt without causing leakage of current from the end surface of the belt to the end surface of the roller as the stretching means.
The image heating apparatus according to the present invention is not limited to the fixing apparatuses described in the aforementioned embodiments but may also be effectively applicable to other image heating apparatuses such as a temporary fixing apparatus for temporarily fixing an unfixed image on a recording material (to be heated), and a surface modifying apparatus for modifying an image surface property such as gloss or the like by reheating a recording material on which a fixed image is carried.
While the invention has been described with reference to the structures disclosed herein, it is not confined to the details set forth and this application is intended to cover such modifications or changes as may come within the purpose of the improvements or the scope of the following claims.
This application claims priority from Japanese Patent Application No. 265420/2005 filed Sep. 13, 2005, which is hereby incorporated by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-265420 | Sep 2005 | JP | national |
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| Number | Date | Country |
|---|---|---|
| 10-69208 | Mar 1998 | JP |
| 2004-341346 | Dec 2004 | JP |
| Number | Date | Country | |
|---|---|---|---|
| 20070212134 A1 | Sep 2007 | US |
