Patent Grant
6947172
The present invention relates to a fixing device incorporated into image-forming apparatus such as a copier, a printer, a facsimile and a composite apparatus having those functions, and also relates to a fixing roller employed for the fixing device.
Conventionally, a heat roller fixing method, in which a fixing roller, maintained at a required temperature, and a pressing roller, having an elastic layer and press-contacting to the fixing roller, apply heat and pressure to a non-fixed toner image transferred onto a transfer material, while conveying the transfer material, has been widely employed for the fixing devices incorporated into electro-photographic image-forming apparatus such as a copier, a printer, a facsimile, a composite apparatus having those functions, etc., ranging from low-speed apparatus to high-speed apparatus, and from monochrome apparatus to color apparatus.
In the fixing device employing the conventional heat roller fixing method, however, there have been problems that, since it is necessary to heat up the fixing roller having a large heat capacity when applying heat to toner and the transfer material, the efficiency of saving electronic energy is hardly improved and therefore the fixing device is disadvantageous in energy saving point of view, and further, it consumes much time to heat up the fixing device to the required temperature at an initial time of the image-forming operation, resulting in a long warming-up time required for starting the image-forming operation.
To overcome the abovementioned problems, fixing devices, employing a quick start fixing method, are set forth in Tokkaisho 52-106741, Tokkaisho 57-82240, Tokkaisho 57102736, Tokkaisho 57-102741 and Tokkaihei 11-327342, and are well known. In such a quick start fixing method, a fixing roller, which comprises a light-transmitting elastic layer equipped on an outer circumferential surface of a cylindrical light-transmitting base body and a heat absorptive layer equipped on an outer circumferential surface of the light-transmitting elastic layer, applies heat and pressure to a toner image on the transfer material, after the heat absorptive layer absorbs heat rays emitted from a halogen lamp disposed inside the light-transmitting base body.
As shown in
Further, in the conventional fixing device shown in
However, since a glass pipe or a polyimide resin material, etc., being good in heat-resistant property, strength, transparency, etc., while being bad in circularity accuracy of the outer diameters of them, is employed for light-transmitting base body 71a, unevenness around the outer circumferential surface of light-transmitting base body 71a would exist, or it is difficult to make the rotational axis of the outer-diameter of light-transmitting elastic layer 71b, formed on the outer circumferential surface of light-transmitting base body 71a, coincided with that of light-transmitting base body 71a. Accordingly, a certain deviation (for instance, around 0.5 mm) has occurred between both axes.
Accordingly, there has been a problem that, when bearing 71d is fitted on the outer circumferential surface of light-transmitting base body 71a to rotate fixing roller 71 as shown in
Further, there has been another problem that irregularities of the outer circumferential surface of light-transmitting base body 71a are transmitted to the nip portion, resulting in occurrences of wrinkles on the transfer material or non-uniformity of the fixed toner image.
Still further, there has been another problem that, since a bearing, etc., including oily lubricant, is conventionally employed for bearing 71d, a heat, transmitted from light-transmitting base body 71a in the thermal conducting process, promotes the evaporation of oily lubricant included in bearing 71d, and as a result, bearing 71d deteriorates within a very short time period.
Still further, since the length of pressing roller 72 is shorter than the length of fixing roller 71 in the conventional fixing device, stresses generated in light-transmitting elastic layer 71b for opposing the pressing force concentrate in the vicinity of both end portions of pressing roller 72. Accordingly, there has been a problem that the nip pressure in the vicinity of both end portions of pressing roller 72 becomes extraordinarily high, resulting in occurrences of wrinkles on the transfer material or unevenness of the fixed toner image in the width direction.
The invention has been achieved in view of the problems of the prior art stated above, and its first object is to provide a fixing device of a quick start type wherein a first light-transmitting elastic layer made of a material having hardness A1 is provided on the outside of a light-transmitting base body and a second light-transmitting elastic layer made of a material having hardness A2 is provided on the outside of the first light-transmitting elastic layer, while, hardness A2 is established to be lower than hardness A1 and a thickness of the second light-transmitting elastic layer is established to be greater than that of the first light-transmitting elastic layer, and thereby, fluctuation of nipping pressure caused by eccentricity at a nipping portion and unevenness of nipping pressure caused by unevenness on an outer circumferential surface of light-transmitting base body 71a are prevented, so that uniform fixing of toner images is made possible.
The second object of the invention is to provide a fixing device of a quick start type wherein a bearing member is made to fit on an outside diameter of a light-transmitting elastic layer or of a heat absorbing layer through a heat insulating member, a fixing roller is rotated around the central axis for rotation of an outside diameter of the light-transmitting elastic layer, and heat conduction to the bearing member is intercepted by the heat insulating member, so that prevention of fluctuation of nipping pressure caused by eccentricity at the nipping portion and prevention of deterioration of the bearing member are made possible.
The above object can be attained by the following structures.
a fixing roller comprising
a bearing to support the fixing roller rotatably, said bearing provided on an outer periphery of said light-transmitting elastic layer or an outer periphery of said heat ray absorbing layer.
a heat insulating member to intercepting heat transmission from said light-transmitting elastic layer or said heat ray absorbing layer to said bearing, wherein said heat insulating member is provided on an outer periphery of said light-transmitting elastic layer or an outer periphery of said heat ray absorbing layer and said bearing is provided on an outer periphery of said heat insulating member.
FIG. 6(a) is a front view of a gear-mounting section in the second embodiment of the invention, showing a side view that shows how gears are connected with a light-transmitting base body and FIG. 6(b) is a sectional top view of the inner side of the side plate of a fixing device main body.
An image-forming apparatus incorporating the fixing device, embodied in the present invention, will be detailed in the following, referring to drawings.
In the color printer, four sets of image-forming units, each of which comprises each of four sets of scorotron chargers (hereinafter, referred to as chargers) 2Y, 2M, 2C, 2K, each of four sets of image-exposing devices 3Y, 3M, 3C, 3K and each of four sets of developing devices 4Y, 4M, 4C, 4K, are arranged in a vertical direction along the periphery of endless-type flexible photoreceptor belt 1 (hereinafter, referred to as photoreceptor belt 1), serving as an image bearing element. Incidentally, a laser-beam scanning optical system is employed in each of image-exposing devices 3Y, 3M, 3C, 3K.
Photoreceptor belt 1, which is threaded on driving roller 11, lower roller 12 and upper roller 13 and stretched by tension roller 14, rotates clockwise in the arrow direction shown in
When the image-forming operation starts, the driving motor (not shown in the drawings) drives driving roller 11 to rotate photoreceptor belt 1 clockwise in the direction designated by the arrow, and photoreceptor belt 1 is charged at a certain electronic potential by the charging action of charger 2Y. After photoreceptor belt 1 is charged at a required electronic potential, image-exposing device 3Y exposes a laser-beam, modulated by the first image signals of yellow color Y, onto photoreceptor belt 1 to form a latent image, corresponding to a developed image of yellow color Y, on the surface of photoreceptor belt 1 with its rotating action (sub-scanning). Then, developing device 4Y conducts the reversal development in such a manner that the developer, adhered onto developer bearing sleeve 41Y, is conveyed to the developing region to develop the latent image of yellow color Y into a toner image of yellow color Y in a non-contacting state.
Next, photoreceptor belt 1 is charged again at a required electronic potential over the toner image of yellow color Y by the charging action of charger 2M, and image-exposing device 3M exposes a laser-beam, modulated by the second image signals of magenta color M, onto photoreceptor belt 1 to form a latent image, corresponding to a developed image of magenta color M, on the surface of photoreceptor belt 1 with its rotating action (sub-scanning). Then, developing device 4M conducts the reversal development of a non-contacting state in the same manner as that of yellow color Y to form a toner image of magenta color M, overlapped on the toner image of color Y.
In the same process as mentioned above, a toner image of cyan color C, corresponding to the third image signals of cyan color C, is formed by charger 2C, image-exposing device 3C and developing device 4C. Further, a toner image of black color K, corresponding to the fourth image signals of black color K, is formed by charger 2K, image-exposing device 3K and developing device 4K. Accordingly, the toner images of colors Y, M, C, K are sequentially formed on photoreceptor belt 1 while overlapping one by one, and as a result, a full color toner image is formed during one revolution of photoreceptor belt 1.
After charger 2F uniforms the electronic potential of the toner adhered on photoreceptor belt 1, the full color toner image, formed on the periphery surface of photoreceptor belt 1, is conveyed to a transferring region. Transfer material P, which is pulled out from either paper-feeding cassette 51 of paper-feeding device 5 or manual paper-feeding tray 53 by corresponding paper-feeding roller pair 52 or 54 and conveyed to resist roller pair 55, is fed to the transferring region in synchronism with the passing action of the full color toner image on photoreceptor belt 1 by the driving action of resist roller pair 55. Then, at the transferring region, the full color toner image is transferred onto transfer material P by means of transferring device 6 disposed opposite driving roller 11.
Transfer material P, on which the full color toner image is already transferred, is separated from the outer circumferential surface of photoreceptor belt 1 and conveyed to fixing device 7, in which the full color toner image is fused and fixed onto transfer material P. After the fixing process is completed, transfer material P is further conveyed to delivery tray 84 equipped on the upper side of the color printer by delivery roller pairs 81, 82, 83.
On the other hand, after transfer material P is separated from photoreceptor belt 1, cleaning blade 91 of cleaning device 9 cleans off the residual toner from the outer circumferential surface of photoreceptor belt 1. Incidentally, when the toner-image-forming operation of the next document is successively performed, the hysteresis of the previous electronic charged pattern is eliminated by exposing the outer circumferential surface of photoreceptor belt 1 by means of pre-discharger 92.
As shown in
Light-transmitting base body 71b is a hollow cylinder made of a heat-resistant glass material or a heat-resistant resin material. In the first embodiment of the present invention shown in
As shown in
Incidentally, hardness A1 of light-transmitting elastic layer 71q is set at, for instance, A1=56 (equivalent to the hardness of KE850, manufactured by Sinetu Chemical Co.) defined by JIS-K6301, while hardness A2 of light-transmitting elastic layer 71p is set at, for instance, A2=20 (equivalent to the hardness of KE520, manufactured by Sinetu Chemical Co.) also defined by JIS-K6301, namely, the values of A1 and A2 are selected under the condition of A1>A2, in which light-transmitting elastic layer 71p is softer than light-transmitting elastic layer 71q.
Further, thickness T1 of light-transmitting elastic layer 71q and thickness T2 of light-transmitting elastic layer 71p are set at, for instance, T1=1 mm and T2=1.5 mm, so that thickness T2 of light-transmitting elastic layer 71p is larger than thickness T1 of light-transmitting elastic layer 71q.
Since the hardness and thickness of the two layers of light-transmitting elastic layer 71b are set at the values as mentioned above, unevenness residing on the outer circumferential surface of light-transmitting base body 71a can be absorbed by light-transmitting elastic layer 71q.
In other words, since light-transmitting elastic layer 71q is formed by employing a mold put outside light-transmitting base body 71a, it is possible to improve roundness of an outside diameter of light-transmitting elastic layer 71q in an accuracy less than several tens μm. Further, absorbed unevenness on an outer circumferential surface of light-transmitting base body 71a is not transferred to the nipping section, because hardness of light-transmitting elastic layer 71q is set to be high, and its outer circumferential surface is covered by soft and thick light-transmitting elastic layer 71p.
Further, even when there exists eccentricity caused by deviation of the central axis for rotation of an outside diameter of the light-transmitting elastic layer 71b, it is possible to reduce an influence of fluctuation of nipping pressure caused by eccentricity at the nipping section, resulting in repression of occurrence the uneven fixing, because hardness of light-transmitting elastic layer 71p that comes directly into contact with the nipping section is set to be soft.
By providing two elastic layers as stated above, it is possible to design an elastic layer wherein functions are separated. For example, it is possible to realize elasticity that covers unevenness of light-transmitting base body 71a having a poor accuracy of an outside diameter and to realize elasticity capable of cooperating with a pressure roller and thereby of giving appropriate and uniform pressure. Namely, it is possible to give an optimum pressure while covering drawbacks of a light-transmitting base body.
It is further possible to use properly resistance to oil for fixing, resistance to heat and resistance to scratches in each layer by adapting to the level of the layer material. For example, with regard to the resistance to oil, stress is laid on a function to transmit no oil for an outer elastic layer and a material suitable for this function is used for the outer layer, and thereby, it is possible to prevent that oil soaks into an inner elastic layer. Namely, discoloration on an elastic layer caused by oil can be reduced remarkably, and thereby, light transmittance is maintained, and heat waves transmitted through a light-transmitting base body can be transferred effectively to a heat absorbing layer on the surface of a roller.
Next, in
Pressure roller 72 is one wherein an outer circumferential surface of hollow and cylindrical core metal member 72a made of metal such as aluminum alloy, for example, is covered by elastic member 72b such as silicone rubber. Both end portions of the core metal member 72a are supported rotatably by bearing members 72c. The bearing members 72c is urged by spring 72d to make the pressure roller 72 to be brought into pressure contact with fixing roller 71.
As shown in
The heat insulating sleeve 71f used here intercepts heat conduction from halogen heater 73 to bearing 71d through light-transmitting base body 71a and light-transmitting elastic layer 71b to prevent deterioration of bearing 71d caused by evaporation and solidification of lubricating oil. As a material of the heat insulating sleeve 71f, there is used, for example, 40% glass-reinforced polyphenylenesulfide (PPS) wherein heat deformation temperature under the load of 18.6 kg/cm2 defined by JIS-K7207 is 236° C. and heat conductivity is 0.3 W/mK.
Further, in the first embodiment of the invention shown in
When this cut-out section 71h is present, a length of a pressed area on the light-transmitting elastic layer 71b is shorter than a length of pressure roller 72 on an equivalent basis, and therefore, the light-transmitting elastic layer 71b is deformed uniformly by pressure, and stress concentration against the pressure generated within the light-transmitting elastic layer 71b in the vicinity of an end portion of pressure roller 72 can be avoided, resulting in a uniform nipping pressure for the entire area of fixing a transfer material.
In particular, when the outermost layer of the pressure roller is made of hard material having no elasticity, for example, when a hard roller made of metal is used as a pressure roller, the stress concentration mentioned above has been generated conspicuously in the vicinity of an end portion of pressure roller 72 in the conventional fixing device, and it has been difficult to obtain uniform nipping pressure.
In the case of the foregoing, a fixing device to which the invention is applied provides an effect in particular, on the other hand, and nipping pressure can be made uniform for the entire area for fixing transfer materials independently of hardness of a pressure roller to be used, and occurrence of wrinkles on a transfer material and occurrence of uneven fixing in the lateral direction can be prevented.
In the embodiment of the invention stated above, fixing roller 71 is rotated around the central axis for rotation of an outside diameter of the light-transmitting elastic layer 71b, and fluctuation of nipping pressure caused by eccentricity at the nipping portion is effectively repressed, because bearing 71d is fit on an outside diameter of light-transmitting elastic layer 71b through heat insulating sleeve 71f, with regard to fixing roller 71.
Next, in
Further, the gear 78 fixed on the fixing roller 71 is driven to rotate, with tooth portion 78a of the gear 78 engaged with a speed reduction gear connected to a driving means such as an unillustrated motor. When fixing roller 71 rotates, pressure roller 72 is driven by the fixing roller 71 to rotate in the arrow direction shown in
Further, when the stronger connection between the gear 78 and light-transmitting elastic layer 71b is required, it is also possible to make the protrusion 78b to cut into the inside of the light-transmitting elastic layer 71b after applying adhesive agents on the surface of an inside diameter of the gear 78 or on the protrusion 78b, when fitting the gear 78 on an outside diameter of the light-transmitting elastic layer 71b.
Since the first embodiment of the invention is constructed as stated above, it is possible to drive a fixing roller to rotate around the central axis for rotation of an outside diameter of the light-transmitting elastic layer, and even when the fixing roller 71 is supported rotatably around an outside diameter of the light-transmitting elastic layer 71b, there is no occurrence of fluctuations of an engagement position between gear 78a and a speed reduction gear connected to a driving means such as an unillustrated motor, and occurrence of uneven rotary speed of the fixing roller can be prevented.
Next,
In
On the portion that is on the left side from the point where gear 79 is mounted on fixing roller 71, there is not provided light-transmitting elastic layer 71b, and light-transmitting base body 71a is exposed. Therefore, the other end portion of connection member 79c that is set with screws is in contact with the light-transmitting base body 71a.
On the portion where the other end portion of the connection member 79c is in contact with the light-transmitting base body 71a, there are applied adhesive agents 79d so that the other end portion of the connection member 79c is fixed on the light-transmitting base body 71a, and gear 79 is connected mechanically to the light-transmitting base body 71a through the connection member 79c.
A material of the connection member 79c has only to be an elastic and heat-resistant sheet member, and it is preferable to use a metal sheet (for example, steel sheet and phosphor bronze).
Since a temperature rises to high temperature of about 200° C. at a portion where the other end portion of the connection member 79c is glued on the light-transmitting base body 71a, it is preferable to use adhesive agents having heat resistance for high temperature of 200° C. or more (for example, liquid state epoxy-belended resin 2285 made by Three Bond Company) as adhesive agent 79d.
Since the second embodiment of the invention is constructed as stated above, even when the central axis for rotation of an outside diameter of the light-transmitting elastic layer 71b does not agree with the central axis for rotation of an outside diameter of the light-transmitting base body 71a and deviation is caused accordingly, it is possible to transmit driving power for rotation to the light-transmitting base body 71a while connection member 79c absorbs the deviation flexibly.
Since gear 79 is fit on an outside diameter of light-transmitting elastic layer 71b, fixing roller 71 rotates around the central axis for rotation of an outside diameter of light-transmitting elastic layer 71b.
Therefore, it is possible to prevent occurrence of uneven rotary speed of a fixing roller caused by fluctuation of nipping pressure in the nipping section and fluctuation of an engagement position of gear 79 both arising from eccentricity, without giving an influence such as a load of driving power to light-transmitting elastic layer 71b.
Incidentally, the embodiment of the invention described above shows the best mode to which the invention is applied, and the structure and numerals described above do not limit the scope of the invention.
For example, though there is shown a mode wherein bearing 71d is fit on an outside diameter of light-transmitting elastic layer 71b through heat insulating sleeve 71f in the first embodiment shown in
Though an example wherein a color printer is equipped with the fixing device of the invention as an image forming apparatus has been shown in the embodiment stated above, it is naturally possible to apply the invention to a monochromatic copying machine, a monochromatic printer, a facsimile machine and all other image forming apparatuses requiring a fixing device for toner images, in the same way as in the embodiment stated above.
As explained in detail above, the inventions described in Structures (1)-(4) make it possible to obtain an effect to provide a fixing device wherein a first light-transmitting elastic layer made of a material having hardness A1 is provided on the outside of a light-transmitting base body and a second light-transmitting elastic layer made of a material having hardness A2 is provided on the outside of the first light-transmitting elastic layer, while, hardness A2 is established to be lower than hardness A1 and thickness T2 of the second light-transmitting elastic layer is established to be greater than thickness T1 of the first light-transmitting elastic layer, and thereby, unevenness of nipping pressure caused by unevenness on an outer circumferential surface of the light-transmitting base body at a nipping portion and fluctuation of nipping pressure caused by eccentricity of an outside diameter of the light-transmitting elastic layer are prevented, so that uniform fixing of toner images is made possible.
The inventions described in Structures (5)-(7) make it possible to obtain an effect to provide a fixing device wherein a bearing member is made to fit on an outside diameter of a light-transmitting elastic layer or of a heat absorbing layer through a heat insulating member, and thereby a fixing roller is rotated around the central axis for rotation of an outside diameter of the light-transmitting elastic layer, and heat conduction to the bearing member can be intercepted by the heat insulating member, so that fluctuation of nipping pressure caused by eccentricity of an outside diameter of the light-transmitting elastic layer at the nipping portion and deterioration of the bearing member of the fixing roller can be prevented.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2000-025216 | Feb 2000 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 5561511 | Mizunuma et al. | Oct 1996 | A |
| 5724638 | Isogai et al. | Mar 1998 | A |
| Number | Date | Country | |
|---|---|---|---|
| 20020018240 A1 | Feb 2002 | US |
