JPH10307493A - Belt nip type fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a belt nip type fixing device capable of obtaining an excellent reproduced image by closely sticking an image carrier such as a paper sheet to the periphery of a heating roller, without slipping and floating, while the image carrier passes through a nip part, in a belt nip type fixing device. SOLUTION: The fixing device constituted in such a manner that a belt 2 traveling in a state where a belt nip part is formed between the belt 2 and the periphery of the heating roller 1 is wound on an entrance side roller 3 and a pressure roller 4, is provided with a pressing means by one or plural supporting rollers 5 and 6 on a pad which can add a bearing force, in the loop of the belt 2. The belt 2 comes into close contact with the heating roller 1, within the range of the belt nip part and on the downstream side except the origin of the belt nip part, by the pressing means, so that the belt 2 in the belt nip part is restrained, to keep the degree of the contact higher.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device in an image forming apparatus such as a copying machine or various printers.
In particular, the present invention relates to a belt nip type fixing device in which a nip portion is formed by a heating roller and a belt.

[0002]

2. Description of the Related Art In various image forming apparatuses such as an electrophotographic copying machine and a laser printer, a toner image charged on a peripheral surface of a photosensitive drum is transferred to a sheet supplied as an image carrier, and thereafter, undetermined. A fixing device is provided for heating and melting the deposited toner image to fix it on paper. The basic configuration of this fixing device is such that a pair of a heat-fixing roller and a pressure roller are arranged in a path through which a sheet passes, and the pair of rollers heats the sheet while applying pressure to fix the toner image. It is to let.

In recent years, instead of such a roller type, a belt nip type which can secure a sufficient fixing time even when the sheet conveying speed is increased by adopting a long heating duration is adopted. Became. FIG. 5 is a schematic sectional view of the conventional belt nip type fixing device.

In FIG. 5, a sheet 50 on which a toner image 51 transferred from a transfer device (not shown) has been transferred is placed in a nip portion between the heating roller 1 and the belt 2 which is in contact with the peripheral surface thereof. The toner image 51 is fixed on the surface of the sheet 50 by heating and pressurizing when the toner image is supplied and passes through the nip portion.

The heating roller 1 is a hollow cylindrical body which is connected to an output shaft of a motor (not shown) and is driven to rotate in the direction of arrow A in the figure. Of the heater 1a. Belt 2
Is an endless type wound around a pressing roller 4 for applying pressure while holding the belt 2 between the entrance side roller 3 and the peripheral surface of the heating roller 1, and is, for example, a silicone rubber having a thickness of about 1 mm. A coating layer of fluorine or the like having good releasability is formed on the surface of a heat-resistant elastic body such as

The entrance roller 3 and the pressure roller 4 are both made of metal, and are idlers with their respective rotation axes parallel to the axis of the heating roller 1. The peripheral surface can be contacted within a range corresponding to the arc-shaped center angle. In the illustrated example, a heater 3a for heating the belt 2 is incorporated in the entrance roller 3.

[0007] Even in such a belt nip type fixing device, it is necessary to appropriately control the heating temperature at the time of fixing. For this control, the surface temperature of the heating roller 1 and the nip surface of the belt are required. A temperature sensor for detecting a temperature is provided, and the amount of heat generated by the heaters 1a and 3a is controlled by a controller based on the detected temperature.

The heating roller 1 is driven to rotate by the operation of a motor according to a print signal, and the belt 2 which is in contact with the peripheral surface of the heating roller 1 runs simultaneously by friction. The paper 50 supplied to the nip is discharged outside the apparatus through the nip. Then, when there is no input of this print signal or in the standby mode, the motor does not rotate, so that the belt 2 is kept stopped.

[0009]

However, when the heating roller 1 is rotated in the printing operation, the belt 2 runs at a high speed of, for example, about 200 mm / sec.
The deviation of the reproduced image often occurs due to a minute slip or the like between the heating roller 1 and the belt 2.

The fixing device of the belt nip type is characterized in that the nip length between the heating roller 1 and the belt 2 around the heating roller 1 is increased to increase the efficiency of heat fixing. However, since the nip between the heating roller 1 and the belt 2 is long, a speed difference between the peripheral speed of the heating roller 1 and the conveying speed of the paper 50 in the nip portion appears during the passage of the paper 50. Also causes a shift in the reproduced image.

Further, if the paper 50 is thick and has high rigidity, the copying deformation on the peripheral surface of the heating roller 1 is insufficient by the load of the belt 2 alone, and the adhesion is weakened. Or rise from the surface. Such a decrease in the adhesive strength of the sheet 50 or the lifting of the sheet 50 may cause the reproduced image to be disturbed. In particular, when the nip is long, the phenomenon of lifting the thick paper is remarkable.

On the other hand, for example, Japanese Patent Application Laid-Open No.
As described in Japanese Patent Publication No. 34-34, there is already known a configuration in which a point at which the belt starts to contact the peripheral surface of the heating roller is pressed by the roller.

However, this roller only presses the portion corresponding to the starting point of the nip, and does not exert a restraining force on the sheet passing through the nip where the fixing is actually performed. Therefore, the fact that the degree of adhesion of the sheet due to the long nip portion is not sufficient is the same as that of the configuration described in the conventional example. For example, in the case of heating and fixing thick paper, the floating or the like cannot be effectively prevented.

As described above, in the conventional belt nip type fixing device, slippage of the image carrier such as paper to the nip portion and insufficient or non-uniform adhesion of the image carrier occur. Can not.

According to the present invention, in a belt nip type fixing device, an image carrier such as a sheet is brought into close contact with the peripheral surface of a heating roller without slipping or floating during a period of passing through a nip portion, thereby achieving good reproduction. The purpose is to obtain images.

[0016]

SUMMARY OF THE INVENTION The present invention is directed to a heating roller which is driven to rotate, an input roller disposed on a receiving side of an image carrier such as a sheet, and a heating roller which is on a delivery side of the image carrier. A pressure roller disposed in close proximity, an endless belt that is wound around the entrance roller and the pressure roller so as to be able to rotate and forms a belt nip portion between the heating roller and the peripheral surface thereof, And pressing means for pressing the belt toward the heating roller on the downstream side of the area included in the belt nip and excluding the starting point.

According to this configuration, the pressing means presses the belt against the heating roller within the range of the belt nip, so that the degree of close contact of the belt with the heating roller can be increased, whereby the toner image on the image carrier can be improved. , And image reproduction with good image quality can be performed.

[0018]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The invention according to claim 1 is a heating roller which is driven to rotate, an input roller disposed on a receiving side of an image carrier such as a sheet, and a delivery side of the image carrier. A pressure roller disposed in close proximity to the heating roller, and an endless end that is wound around the entrance roller and the pressure roller so as to be able to rotate therearound and forms a belt nip between the heating roller and the peripheral surface thereof. A belt, and pressing means for pressing the belt toward the heating roller on the downstream side of the area included in the belt nip and excluding the starting point thereof. Has an effect of preventing fixing leakage and displacement.

According to a second aspect of the present invention, the pressing means is a rotatable support roller having an axis parallel to the axis of the heating roller in the loop of the belt, and the peripheral surface of the support roller is attached to the belt. The pressing surface of the
The proper arrangement of the support rollers has the effect of ensuring that the belt portion included in the belt nip is in close contact with the heating roller.

According to a third aspect of the present invention, the support rollers are arranged in a plurality of rows in the running direction of the belt, and the degree of adhesion of the belt is further increased by increasing the number of pressing points. Has an action.

According to a fourth aspect of the present invention, each of the entrance roller, the support roller, and the pressure roller is provided with a heater capable of transmitting heat to the belt, thereby increasing the amount of heat transmitted to the belt. Has an action.

According to a fifth aspect of the present invention, the pressing means is a pad made of an elastic material which is arranged in a loop of the belt and which can apply a surface pressure to the belt in a wide range in the running direction. In addition, it has the effect of reliably preventing the belt from rising from the heating roller due to the surface pressure load.

According to a sixth aspect of the present invention, the pad is elastically urged in the direction of the heating roller, and has an effect of ensuring that the running belt is closely adhered to the peripheral surface of the heating roller. Have.

According to a seventh aspect of the present invention, at least one of the pressure roller and the entrance roller has an inverted crown shape in which the outer diameter at the central portion in the axial direction is small and the diameter increases toward the end. In addition, it has the effect of making the degree of adhesion to the heating roller more stable by tightening the belt in the width direction.

Hereinafter, embodiments of the present invention will be described. (Embodiment 1) FIG. 1 is a schematic sectional view of a fixing device according to a first embodiment of the present invention, which is applicable to, for example, various color laser beam printers.

In FIG. 1, a heating roller 1, a belt 2,
The entrance roller 3 and the pressure roller 4 have the same configuration as that described in the conventional example, and the heating roller 1 and the entrance roller 3 have heaters 1a and 3a built therein, respectively. The heating roller 1 is driven by a variable speed drive motor (not shown).
When a print signal is input to the controller, the heating motor 1 rotates the heating roller 1 in the direction of arrow A in the figure, and the belt 2 contacting the peripheral surface of the heating roller 1 Force to run by force.

In such a configuration, the toner image 5 is transferred after the transfer.
1 is supplied, the paper 50 passes through a belt nip portion between the heating roller 1 and the belt 2, and heat transfer from the heating roller 1 and the belt 2 during this passage. Thus, the toner image 51 can be fixed on the sheet 50.

At a position included in the loop of the endless belt 2, a support roller 5 for applying a restraining force to the belt 2 toward the circumferential surface of the heating roller 1 is provided as a rotatable idler. This support roller 5
For example, it is a metal rod or hollow material having a diameter of about 8 to 20 mm, and is disposed with axes parallel to the respective axes of the heating roller 1, the entrance roller 3, and the pressure roller 4.

In FIG. 1, a point indicated by P represents a point at which the running belt 2 comes into contact with the peripheral surface of the heating roller 1, and a point indicated by Q represents the axis of each of the heating roller 1 and the support roller 5. Is the intersection of the line segment connecting. R is a distance between a line segment connecting the axis of the heating roller 1 and each of the axis of the support roller 5 and the pressure roller 4 and extending from the center of the heating roller 1 to the axis of the support roller 5. Represents the length of the arc of a circle whose radius is. Points indicated by S represent points at which the running belt 2 separates from the peripheral surface of the heating roller 1.

That is, the support roller 5 is located downstream of the point P in the running direction of the belt 2, and is located in the belt nip portion between the points P and S, which is expressed as the circumference of the heating roller 1. The belt 2 is pressed toward the heating roller 1 at the point included in the belt. It is preferable that the pressing force of the support roller 5 against the belt 2 is such that it does not act as a resistance when the belt 2 travels with the rotation of the heating roller 1.

In the illustrated example, the circumference of the belt nip (P
To S) is about 30 mm, and the outer diameter of the support roller 5 is about 8 to 20 mm as described above. The circumference of the heating roller 1 corresponding to the points P to Q is 2
It is preferably about 15 mm, and the support roller 5 is arranged such that the axis of the support roller 5 is located on a line segment included in the range of the circumference.

In the above configuration, the point that the support roller 5 presses the belt 2 is that the belt 2
Included in the area of the belt nip between the
The belt 2 is located downstream from the point where the belt 2 starts to enter the belt nip. Such a support roller 5
With this arrangement, the paper 50 can be pressed against the heating roller 1 in the belt nip portion against the paper 50 passing through the point P, and the adhesion of the paper 50 to the peripheral surface of the heating roller 1 can be reduced. Can be raised.

By improving the adhesion, the paper 50
Does not cause a slip even if the sheet is conveyed at a high speed, and the peripheral speed of the heating roller 1 and the moving speed of the sheet 50 can be matched to suppress the speed difference. For this reason, the position where the toner image 51 is carried on the sheet 50 does not shift, and the sheet 50 finally obtained as a reproduced image is not displaced.
Disorder of the above image is also prevented, and a good reproduced image can be output.

Further, Japanese Patent Application Laid-Open No. Hei 8-166734 mentioned above.
As described in Japanese Patent Application Laid-Open Publication No. H10-115, at the point where the paper 50 starts to enter the belt nip portion, that is, in the case where the support roller is disposed at the point P in FIG. Not something. Therefore,
The improvement in the degree of adhesion of the paper 50 by the support roller 5 in the present invention can be remarkably improved as compared with that described in this publication, and an extremely useful fixing device including reproduction of a color image is provided. Can be.

(Embodiment 2) FIG. 2 is a schematic sectional view of a fixing device according to a second embodiment of the present invention. In addition,
The same members as those shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

In this example, the support roller 5 shown in FIG.
Another second support roller 6 is arranged downstream of the second support roller 6. The outer diameter of the second support roller 6 is 8
It can be used as a common part with the support roller 5 arranged on the upstream side of about 20 mm, and the position of the support roller 5 on the upstream side only needs to satisfy the conditions shown in the example of FIG. Further, by arranging the two support rollers 5 and 6, the number of points for pressing the sheet 50 increases, so that the circumference of the heating roller 1 between the points P and Q is set to 20 points.
The support roller 5 may be arranged to correspond to about mm.

The axis of the second support roller 6 is arranged so that an arc length represented by T is within 20 mm with respect to a line segment passing through the axis of the heating roller 1 and the pressure roller 4 in FIG. Anything should do. That is, the points P to S
The contact point between the two support rollers 5 and 6 with respect to the belt 2 has an appropriate distance between the points P and S with respect to the belt nip portion represented as the circumference of the heating roller 1 up to the point. In this case, a configuration may be employed in which a uniform adhesive force can be applied to the sheet 50 passing through the belt nip portion.

By providing the two support rollers 5 and 6 as described above, the sheet 50 can be urged toward the peripheral surface of the heating roller 1 with a higher degree of adhesion than in the previous example. Therefore, for example, even when the paper 50 is a thick paper and has high rigidity, the paper 50 can be made to travel along the peripheral surface of the heating roller 1 while suppressing the rising of the paper 50. For this reason, regardless of the thickness of the sheet, the toner image 51 can be fixed without shifting the position, and a good reproduced image can be obtained.

(Embodiment 3) FIG. 3 is a schematic sectional view of a fixing device according to a third embodiment of the present invention. In addition,
Also in this example, the same members as those shown in FIG. 1 are designated by the same reference numerals, and detailed description thereof will be omitted.

As shown in FIG. 2, two support rollers 5 are included in a range corresponding to the belt nip portion.
6, the adhesion of the sheet 50 to the heating roller 1 is reduced by 1
This can be improved as compared with the case where the book support rollers are provided. Therefore, increasing the number of the support rollers leads to an increase in the adhesion, but in order to incorporate the support rollers in the limited space between the entrance side and the pressure rollers 3 and 4 within the loop of the belt 2, the support rollers There are restrictions on the outer diameter and the number of arrangements.

Therefore, in the present embodiment, a pad 7 made of an elastic material is provided to extend the pressing range on the belt 2, and the pad 7 enhances the adhesion.

The pad 7 is made of, for example, a heat-resistant rubber or sponge having an appropriate hardness, and is formed in a shape capable of pressing the entire length in a direction perpendicular to the feeding direction of the paper 50, and has an arc shape. It is fixed to a support plate 7a having a cross section. The support plate 7a is capable of swinging around a pin 7b fixed in the apparatus, and the pad 7 is belted by interposing a compression coil spring 7d between the support plate 7c and the base 7c in the apparatus. It is elastically biased on two sides.

The end face of the pad 7 facing the entry roller 3 is located downstream of the point P at which the belt 2 enters the belt nip portion between the heating roller 1 and the end face. Is about 2 to 20 mm, and preferably about 4 to 15 mm. The distance between the end surface of the pad 7 facing the pressure roller 4 and the point S is 10 to 10.
It is preferred to be about 20 mm.

By providing the pad 7 elastically urged by the coil spring 7d as described above, the support roller is pressed against the belt 2 by line contact, whereas the load of the surface pressure by the entire pad 7 is reduced. Joins belt 2. Therefore, even if the belt nip portion is long in the circumferential direction of the heating roller 1, the pad 7 presses the belt 2 over a wide range, so that the degree of adhesion of the belt 2 to the heating roller 1 can be further enhanced, and turbulence can be obtained. And a good reproduced image with no image can be obtained.

Although the adhesion of the belt 2 can be improved by combining a plurality of support rollers as described above, it is necessary to strictly control the processing accuracy and the assembly accuracy for all of these rollers. is there. On the other hand, when the pads 7 are provided, one support plate 7
In addition to the need for assembling only a, the elasticity of the pad 7 itself and the dimensional error due to the coil spring 7d can be absorbed, so that the machining accuracy and the assembly accuracy of the parts can be given a margin and the assembly can be simplified.

(Embodiment 4) FIG. 4 is a view showing an outline of a pressure roller according to a fourth embodiment of the present invention.
1A is a front view, and FIG. 1B is a perspective view.

In the first to third embodiments described above,
In each case, the belt 2 is pressed against the peripheral surface of the heating roller 1 by the support rollers 5 and 6 or the pad 7 to improve the adhesion. That is, even if the belt 2 is bent in the running direction, the belt 2 is passed through the belt nip portion while correcting the deformation by using the biasing force of the pressing body such as the roller or the pad, thereby securing the degree of adhesion. Thus, good fixation was realized.

On the other hand, since the belt 2 itself is an elastic band, it is obvious that the belt 2 is deformed not only in the running direction but also in the width direction. Therefore, when the belt 2 passes through the belt nip and generates a slight bending in the width direction, the adhesion to the heating roller 1 is lost, and this causes the image to be disturbed.

Therefore, in this embodiment, the belt 2
By providing the pressure roller 4 with a shape in which tension acts in the width direction, a fixing device capable of preventing disturbance of an image due to deformation in the width direction is provided.

As shown in the figure, the pressing roller 4 has a so-called inverted crown shape in which the outer diameter is the smallest at the center in the axial direction and the outer diameter increases toward the end. In the drawings, the difference in outer diameter is exaggerated, and the axial length of the pressure roller 4 is actually 380 mm.
In the case of (2), the outer diameter of the small-diameter portion at the center is 29.5 to 29.
The outer diameter of the large diameter portion at the end is about 30 mm.

The pressure roller 4 having such an inverted crown shape
It is known that, when the belt 2 is wound around at a high speed, the belt 2 is pulled in a direction indicated by an arrow in FIG. This is because, for an elastic belt such as rubber, when the rotation angle is the same, the larger the roller diameter, the longer the path of the belt, and the pulling force acts on the belt. Is moved to the larger roller diameter.

Therefore, the belt 2 is subjected to a load such that the end in the width direction spreads outward, and the belt 2 is subjected to a tension that is pulled in the width direction by this load. It can be run under tension. Since the pressure roller 4 is close to the heating roller 1 so as to be able to hold the belt 2, the belt 2 having a high degree of tension in the width direction can be passed through the belt nip. Therefore, the degree of adhesion of the belt 2 to the heating roller 1 is further improved,
A good reproduced image in which the occurrence of disturbance is suppressed more reliably can be obtained.

Also, instead of the pressure roller 4, the entry roller 3
In the same manner, the belt 2 can be made to pass by tensioning the width direction of the belt 2 and the pressure roller 4 and the entrance roller 3 are both formed into an inverted crown shape to increase the degree of tension. Running is also possible.

[0054]

DESCRIPTION OF THE PREFERRED EMBODIMENTS In the configuration having one support roller 5 shown in FIG. 1, the peripheral length of the belt nip was about 30 mm, and the outer diameter of the support roller 5 was about 8 to 20 mm. Then, in such a dimensional relationship, the results of observing the state of the reproduced image while changing the position of the support roller 5 are shown in (Table 1) and (Table 2).

[0055]

[Table 1]

[0056]

[Table 2]

As can be seen from Tables 1 and 2, the circumference of the heating roller 1 from point P to point Q is 2 to 17
If it is about mm, there is no significant disturbance of the image, and it has been confirmed that the preferable range of the circumference is 4 to 15 mm.

The distance R substantially corresponding to the distance between the support roller 5 and the pressure roller 4 is 10 to 22.
mm, and if it is more than this range, the degree of adhesion cannot be ensured. It has been confirmed that a preferable range is about 10 to 20 mm.

[0059]

According to the present invention, the belt is pressed toward the heating roller using the support roller or the pad within the range corresponding to the belt nip portion, so that the adhesion of the belt to the heating roller can be increased. It is possible to fix the toner image by heating and melting without shifting the carrying position of the toner image. Therefore, even if the belt is conveyed at a high speed and the nip length is long, a reproduced image without disturbance can be reliably obtained, and the image quality is greatly improved.

In the case where each of the entrance roller, the support roller, and the pressure roller is provided with a heater capable of transferring heat to the belt, the amount of heat transferred to the belt can be increased, so that the toner image can be more reliably heated and melted. , Good fixing is obtained.

Further, in the case where a plurality of support rollers are arranged or a pad which can apply a surface pressure is provided, the adhesion of the belt can be set more strongly. Similarly, a reproduced image without image disturbance can be obtained, and an image can be formed without being restricted by the image carrier.

Further, when the pressure roller or the like has an inverted crown shape, tension is also applied in the width direction of the belt and the belt is brought into close contact with the heating roller, so that a uniform and strong adhesion force is provided over the entire length in the width direction of the belt. Can be obtained, and an even better reproduced image can be obtained.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a fixing device according to a first embodiment of the present invention.

FIG. 2 is a schematic sectional view of a fixing device according to a second embodiment of the present invention.

FIG. 3 is a schematic sectional view of a fixing device according to a third embodiment of the present invention.

FIG. 4 is a diagram showing an outline of a pressure roller according to a fourth embodiment of the present invention.

FIG. 5 is a schematic sectional view of a conventional belt nip type fixing device.

[Explanation of symbols]

 Reference Signs List 1 heating roller 1a heater 2 belt 3 entrance roller 3a heater 4 pressure roller 5 support roller 6 second support roller 7 pad 7a support plate 7b pin 7c base 7d coil spring 50 paper 51 toner image

Claims (7)

[Claims] 1. A heating roller driven to rotate, an input roller disposed on a receiving side of an image carrier such as paper, and a pressure roller disposed on a delivery side of the image carrier and close to the heating roller. And an endless belt that is wound around the entrance roller and the pressure roller so as to be able to rotate and forms a belt nip between the heating roller and the peripheral surface of the heating roller, and a belt included in the belt nip. And a pressing means for pressing the belt toward the heating roller on the downstream side excluding the starting point thereof. 2. The pressing means is a rotatable support roller having an axis parallel to the axis of the heating roller in a loop of the belt, and the peripheral surface of the support roller serves as a pressing surface against the belt. The belt nip type fixing device according to claim 1, wherein: 3. The belt nip type fixing device according to claim 2, wherein the support rollers are arranged in a plurality of rows in the running direction of the belt. 4. The belt nip type fixing device according to claim 2, wherein each of the input roller, the support roller, and the pressure roller is provided with a heater capable of transmitting heat to the belt. 5. The device according to claim 1, wherein the pressing means is a pad made of an elastic material which is disposed in a loop of the belt and can apply a surface pressure to the belt in a wide range in the running direction. Belt nip type fixing device. 6. The belt nip type fixing device according to claim 5, wherein the pad is elastically urged toward the heating roller. 7. An apparatus according to claim 1, wherein at least one of the pressure roller and the entrance roller has an inverted crown shape in which the outer diameter at the central portion in the axial direction is small and the diameter increases toward the end. 7. The belt nip type fixing device according to any one of items 1 to 6,