JPH10171284A - Fixing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To simplify the shape of a pressure roller, and to shorten the starting time by attaching both end parts of a pressure roller to a device main body side plate, and providing the supporting means therefore with a metallic positioning sleeve and a slide bearing of thermal insulation property. SOLUTION: In this fixing device, the positioning sleeve 7 is inserted into the both end parts of the pressure roller through the slide bearing 6. The pressure roller is movable only in the direction of a shaft center of a fixing roller being locat-supported by side plates 33. Both the end parts are passed through the sleeve 7, then the position in the direction perpendicular to the pressurizing force by both side edge parts of notched groove on the side plate 33. In this case, it is preferable to compose the slide bearing 6 of the resin with the thermal insulation-wear resistance property, and to make the sleeve 7 of ferrous sintered alloy. Namely, the slide bearing 6 made of the resin is restrained from expanding when expanding to some extent by being held by a core bar of the pressure roller however, a thermal expansion modulus of the inside sleeve 7 is minimum and the temp. rising is a little, therefore the bearing surface between the bearing 6 and the sleeve 7 is prevented from the rotation defect.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a fixing roller having a hollow cylinder having a heater therein, and a pressure roller having a hollow cylinder having a pressing shaft therein while being in pressure contact with the fixing roller. The present invention relates to a fixing device for an electrostatic recording device having two pressing members for pressing a cylindrical inner surface of a pressure roller on a pressure shaft.

[0002]

2. Description of the Related Art As a fixing device of an electrostatic recording apparatus such as an electrophotographic copying machine, a printer, and a facsimile, as shown in FIG. A fixing device including a pressure roller 3 having a heat-resistant rubber layer 3-2 is widely used.

In a large-size copying machine in which the width of a transfer sheet to be fixed is large, the lengths of a fixing roller and a pressure roller are increased. As shown in FIG. 19, 1-1 and 3-1 are often configured as thin hollow cylinders. However, in the case of a wide-width fixing device, the span between the bearings at both ends of the roller becomes long. Therefore, when pressure is applied at both ends, the pressure roller bends due to the pressing force, and the nip between the fixing roller 1 and the pressure roller 3 is formed. As shown in FIG. 20, the distribution in the length direction of the width is wider at both ends and narrower at the center, and as a result, the amount of heat applied to the transfer paper is smaller at the center than at both ends, resulting in uneven fixability. The paper conveyance force is different between the center and both ends, causing wrinkles.

In order to prevent this, cores 1-1, 3 of the fixing roller 1 and the pressure roller 3 formed as hollow cylinders are used.
If the rigidity is increased by increasing the thickness of -1, the mass of the core increases, and the rise time of heating becomes longer.

As a countermeasure against this problem, for example, Japanese Utility Model Laid-Open Publication No. 58-154962 discloses that a pressure roller is formed as a continuous hollow cylinder having a slightly larger diameter at both ends than at a central portion. A pressure shaft is provided, and 1
The bearing is provided with two bearings to support the pressing roller, and the pressing force applied to both ends of the pressing shaft is transmitted to the pressing roller via the pressing shaft and the bearing. There has been proposed a fixing device in which the pressure contact is performed. However, according to this method, when the roller becomes longer and the roller oscillates due to processing accuracy, the contact pressure becomes higher at the central portion, the nip width becomes larger than at both sides, and the transport speed at the central portion becomes larger than at both sides. As a result, there is a problem that paper is wrinkled. In addition, it is unavoidable that it takes time and effort to accurately form the roller into a continuous mold.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to solve the above-mentioned problems of the prior art, and in a wide fixing device such as a copying machine, a pressing member is moved from a pressing shaft having a pressing roller provided therein to a pressing member. A good pressure distribution can be obtained by applying pressure at the intermediate part through the intermediate part, the shape of the pressure roller can be made a simple cylindrical shape, and the rise time of the fixing device can be shortened by thinning the fixing roller. It is to provide a fixing device that contributes.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention comprises a fixing roller comprising a hollow cylinder having a heater inside, and a fixing roller comprising a hollow cylinder which is in pressure contact with the inside and has a pressure shaft inside. A fixing device for an electrostatic recording apparatus, comprising a pressure roller and having two pressing members for pressing the cylindrical inner surface of the pressure roller on the pressure shaft, wherein both ends of the pressure roller are in a pressure direction. Attached to the apparatus main body side plate by supporting means that can only move, the supporting means comprising a positioning sleeve and a slide bearing provided between the sleeve and both ends of the pressure roller, wherein the sleeve is It is characterized by being a sliding bearing made of metal and made of a heat-insulating resin.

[0008]

According to the present invention, the roller is twisted because both ends of the pressure roller are composed of a sleeve and a slide bearing and are attached to the apparatus side plate by a supporting means which can move only in the pressure direction. Also in this case, the positional accuracy of the roller pair is guaranteed.

Further, since the sleeve is made of metal and the slide bearing is made of a heat-insulating resin, the heat efficiency is reduced due to the escape of heat from the core of the pressure roller to the side plate, and the heat to other mechanical units in the apparatus is reduced. It is possible to prevent adverse effects due to transmission.

[0010]

Embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a perspective view showing a roller portion of the fixing device of the present invention. The fixing roller 1 is formed by coating a surface of a metal core bar 1-1 made of aluminum or iron with a heat-resistant resin such as a fluororesin. A heater 2 is provided inside. The surface temperature of the fixing roller 1 is 150 ° C.
The temperature is controlled in the range of 190 to 190 ° C. The pressure roller 3 is also formed by integrally molding a heat-resistant rubber layer 3-2 such as a silicon-based material on a metal core 3-1 made of metal, and has a pressure shaft 4 provided therein. . Two annular pressing members 5 whose thrust directions are fixed are attached to the pressing shaft 4, and the pressing force applied to both ends of the pressing shaft 4 is
Is transmitted to the fixing roller 1 via the pressure roller 3 by both pressing members 5. Positioning sleeves 7 are inserted at both ends of the pressure roller 3 via slide bearings 6.

FIG. 2 is a side view of the fixing device. The sleeve 7 is provided with a convex portion 7-1 which fits into a notch groove 33-2 parallel to a straight line passing through the center of both rollers 1 and 3 at the lower end of the notch groove 33-1 of the main body side plate 33. . Further, a tap 7-2 is provided on the sleeve 7, and a slide shoe 34 for guiding the pressure roller 3 along both edges of the cutout groove 33-1 of the main body side plate is provided with a tap 7-2. 2
Is fixed to the sleeve 7. Both side edges of the notch groove 33-1 are also parallel to a straight line passing through the centers of the rollers 1 and 3. With such a structure, the pressure roller 3 is
3 can move only in the direction of the axis of the fixing roller 1 positioned and supported by the fixing roller 3. On the other hand, the pressing shaft 4 is pressed in the direction of the fixing roller 1 by a pressing lever 32 urged by a pressing spring 31. Both ends thereof pass through the sleeve 7 and the positions in the direction perpendicular to the pressing force are determined by both side edges of the notch groove 33-1 of the side plate 33. As a result, the pressing forces applied to both ends are in the same vector direction, and no imbalance occurs in the pressing forces.

Next, the operation of the pressurizing method having the above-described structure will be described. Supports both ends of the roller, and calculates the deflection of the center point of the roller when the roller receives an equal load.
Assuming max

[0013]

(Equation 1)

[0014]

(Equation 2)

## EQU1 ## Here, w is the load per unit length, l is the roller length, E is Young's modulus, D ₁ is the outer diameter of the roller, D ₂ is a roller inside diameter. On the other hand, assuming that the rise time of the machine is t, from the relationship between the heat capacity of the roller and the heat source capacity,

[0016]

(Equation 3)

Is given by Where M is the roller mass,
ΔT is the temperature difference from the cold state to the predetermined temperature of the roller, Cp is the specific heat of the roller material, W is the wattage of the heater, and η is the efficiency. From the above, when the thickness of the roller is increased and the bending rigidity (EI) is increased, the deflection of the roller is reduced, but the mass of the roller is increased and the rise time t is increased.

FIGS. 3A and 3B show the results of calculating this relationship for the fixing roller of the fixing device. FIG.
(A) shows the relationship between the amount of deflection and the rise time with respect to the core thickness, and (b) of FIG. 3 is a curve diagram showing the relationship between the amount of deflection and the rise time.

Since the shorter the rise time, the better the performance of the machine is, the rigidity of the roller cannot be increased in order to increase the nip width at the center of the roller. In the present embodiment, as described above, the pressing shaft 4 is provided inside the pressing roller 3, whereby the pressing force is applied through the two pressing members 5 provided at the intermediate portion of the pressing roller 3. 3 to the fixing roller 1. If you do this,
Since pressing force is applied at two points of the pressing member 5, the fixing roller 1 bends but the pressing roller 3 does not bend, as shown in FIG.
Therefore, even if the thickness of the fixing roller is small, a nip width required for fixing can be obtained, and a good nip distribution can be achieved.

Incidentally, when the size of the paper handled by the copying machine becomes large and the total length of the rollers of the fixing device becomes, for example, 1,000 mm, the influence of the run-out of the rollers themselves cannot be ignored.

FIG. 5 shows the distribution of the nip width for each 1/6 rotation of the pressure roller 3 when the pressure position (▲) is changed when the pressure roller 3 has a runout of about 0.2 mm. Show. In the case of this embodiment, since the entire length of the pressure roller 3 is about 1000 mm, it is necessary to take into account the deflection of the pressure roller. FIG. 5 (a)
Is a case where the central portion of the pressure roller 3 is pressed. In this case, the nip distribution greatly changes depending on the rotation angle due to the influence of the swing of the pressure roller 3. In particular, since the nip width in the central portion is larger than the end portion depending on the angle, the transport speed in the central portion becomes faster than that at both ends, causing a problem that paper wrinkles occur. FIGS. 5B to 5D show the case where the pressing position is set to ／ to ５ of the entire length L from the roller end. In these cases, the nip distribution does not change significantly with the angle, and the influence of the shake is reduced. Also, since the nip width is larger at both ends than at the center, the transport speed is higher at both ends than at the center, and as a result, the effect of extending the paper wrinkles is produced. In the case of the nip distribution shown in FIGS. 5C and 5D, the same effect as the continuous effect of extending wrinkles in the vertical direction caused when the fixing roller itself has the continuous shape can be obtained. However, if the speed difference is too large, depending on the type of paper, the stress may cause the trailing edge of the paper to jump up, causing the unfixed image to be rubbed by the fixing entrance guide plate, disturbing the image, and causing rib wrinkles. Occurs. In the case of FIG. 5D, the nip width is small at the center, but it is within a practically acceptable range. From the above viewpoint, the two pressing members 5 are １ ／ L to 2 / L from both ends.
It can be said that a range of 5 L is desirable. In the above, the deflection of the fixing roller 1 is not considered. This is because a processing accuracy that does not cause a problem in the runout can be obtained. However, even when the fixing roller oscillates, the nip distribution has the same tendency as described above.

As described above, by pressing the inner surface of the cylinder of the pressure roller at two places to press the fixing roller, the thickness of the roller can be reduced, so that the rise time can be shortened. By providing the pressure position in the above-described range, the influence of roller runout on the nip distribution can be reduced.

In the apparatus of the above embodiment, when metal ball bearings are used as the two pressing members provided on the pressing shaft 4, the pressure is transmitted from the fixing roller 1 to the pressing roller core 3-1. Heat is applied to the pressing shaft 4 via the pressing member.
, The surface temperature of the fixing roller 3 near the contact of the pressing member, that is, the ball bearing, is reduced by, for example, about 5 ° C. as compared with the temperature in the vicinity thereof, which causes fixing unevenness.

As means for solving this problem, the pressing member for transmitting the pressing force from the pressing shaft to the inner surface of the core of the pressing roller may be formed of a heat insulating material. FIG. 6 and FIG. 7 are views showing the configuration near the pressing member of such an embodiment.

In this embodiment, the pressing member 8 is provided as a member separate from the bearing 9. The bearing 9 is configured as a sliding bearing, and the pressing member 8 is attached between the outer peripheral surface of the bearing 9 and the inner peripheral surface of the pressure roller core 3-1 as an annular member made of a heat insulating material. ing.

The pressing member 8 has heat resistance and abrasion resistance as well as heat insulation. Further, as the material, for example, a conductive resin having improved conductivity by mixing carbon particles with the resin is used.

Since this apparatus is constructed as described above, the heat transmitted from the fixing roller 1 to the pressing roller 3 during copying is transmitted to the pressing shaft 4 via the pressing member 8 as in the prior art. Thus, the surface temperature of the fixing roller in contact with the pressing member is prevented from lowering from the surface temperature in the vicinity thereof.

Although the pressure roller 3 is charged, the pressing member has a heat insulating property but is made of a conductive material, so that the static electricity is grounded, and the transfer paper is wound around the pressure roller by the static electricity. Jams and images are prevented from being scattered.

However, when the pressing members 8 provided at two positions of the pressing shaft 4 are solid members having no holes other than the holes fitted into the bearings 9, the core metal 3 between the two pressing members is not provided. There is no air flow in the space between the pressure roller 1 and the pressure shaft 4, heat is stored over time, and a temperature difference of, for example, about 5 ° C. is generated between the space outside the pressure member 8 and the pressure roller surface. Temperature unevenness and, consequently, fixing unevenness.

In order to solve the above-mentioned problems, minimize the unevenness of the pressure roller surface temperature, and improve the fixing unevenness caused by the unevenness, the space between the two pressing members is provided by the two pressing members 8. What is necessary is just to provide the vent hole connected to an outer space.

As shown in FIG. 8 and FIG.
If the annular opening 8a is provided with a stay 8b having a twisted airfoil section between the inner peripheral portion and the outer peripheral portion of the pressing member 8, the inner diameter of the pressing roller core 3-1 between the two pressing members can be reduced. The space between the peripheral surface and the outer peripheral surface of the pressure shaft 4 communicates with the space outside the pressing member 8, and when the pressure roller 3 rotates at the time of fixing, the twisted stay 8b becomes a blade of a blower to blow air. However, the stagnation of air between the pressing members 8 is eliminated, the temperature of the pressure roller becomes uniform, and the fixing unevenness is prevented.

In the embodiment shown in FIGS. 1 and 2, positioning sleeves 7 are inserted through sliding bearings 6 at both ends of the core of the pressure roller as positioning means in a direction perpendicular to the direction of the pressing force of the pressure roller 3. And a convex portion 7-
The guide shoe 1 and the guide shoe 34 are movably fitted into the cutout grooves of the main body side plate 33.

FIG. 10 is a sectional view showing a state in which the pressure roller 3 is attached to the main body side plate 33 by this method. When the copying machine or the like is on standby or copying, the fixing roller 1
The surface temperature of the pressure roller 3 becomes 150 to 190 ° C., and accordingly, the surface temperature of the pressure roller 3 also becomes 50 to 150 ° C. In this case, the core metal 3-1 of the pressure roller 3 also has a maximum temperature of 150 ° C. Therefore, when a material having low thermal conductivity is not used in the supporting method as shown in FIG.
The heat efficiency decreases due to the escape of heat from 1 to the side plate 33 via the bearing 6 and the sleeve 7, and the heat is transmitted to other units in the machine, adversely affecting them. Therefore, in the present invention, the sliding bearing 6 is made of a material having low thermal conductivity, for example, resin.

Alternatively, as shown in FIG.
Is a heat insulating resin, and a metal bearing 6
a (stainless steel needle bearing) is arranged. However, in this case, the thermal expansion coefficient of the resin of the sleeve 7 is larger than the thermal expansion coefficients of the bearing 6 and the pressure roller core 3-1. The load increases, and problems such as poor rotation or inability of the pressure roller 3 and slippage with the fixing roller 1 occur. For this reason, considering the thermal expansion, the sleeve 7
Although it is possible to reduce the diameter of the above, it is necessary to provide a considerable gap because the range of temperature change is wide as described above,
Positioning accuracy decreases.

This problem can be solved by forming the sliding bearing 6 from a material having a low thermal conductivity in FIG. That is, the temperature of the sleeve 7 does not increase so much because the heat conduction of the slide bearing 6 is small. In a preferred embodiment, the sliding bearing 6 is made of a heat-resistant and abrasion-resistant resin having heat insulating properties, and the sleeve 7 is made of an iron-based or sintered alloy. As a result, the core metal 3-1 of the pressure roller 3, respectively, the thermal expansion coefficient of the sliding bearing 6 and the sleeve _{7, β 1 = 23.9 × 10} - 6, β 2 = 5 × 1
_{^{0 - 5, β 3 = 11.9}} × 10 - becomes the ⁶ β ₃ ≦ β ₁ ≦ β ₂ relationship. With this configuration, when the sliding bearing 6 made of resin expands to some extent, it is held by the core of the pressure roller 3 and expansion is suppressed, but the coefficient of thermal expansion β ₂ of the inner sleeve 7 is minimized and the temperature rises. Since there is little rotation, there is no possibility of rotation failure on the bearing surface between the bearing 6 and the sleeve 7, the clearance can be regulated to be small, and the positioning accuracy can be improved.

FIGS. 12 and 13 show the respective states of thermal expansion due to temperature changes in the structures shown in FIGS. In FIG. 13, since the thermal expansion of the outer diameter B of the resin sleeve 7 is larger than that of the inner diameter A of the bearing 6, locking occurs in the region P due to the temperature rise. It is necessary to keep the size small from the beginning, and in this case, play occurs in the bearing in the Q region. On the other hand, in FIG. 12, the outer diameter of the resin bearing 6 is held at the inner diameter C of the pressure roller core 3-1. The inner diameter C ′ of the bearing 6 is larger than the outer diameter D of the sleeve 7,
No lock has occurred.

In this embodiment, the conductivity is improved by mixing carbon particles in the resin of the bearing 6. Pressure roller 3
Has a rubber layer 3-2, and is charged by peeling discharge during rotation. As a result, the transfer paper sticks to the pressure roller 3 due to static electricity and causes winding, which causes a jam. If the conductivity of the sliding bearing 6 is improved, jamming can be reduced.

Now, the pressing member for pressing the pressing roller is 2
In the heat roller fixing device of the present invention having a configuration in which the pressure member is provided, by changing the pressing position by the pressing member,
Even if the fixing roller is not in the form of a sword, but a straight cylinder, the squeezing effect that appears when the fixing roller is in the form of a squirt can be obtained. explained.

Therefore, in the configuration in which the fixing roller is formed in a continuous shape, the drawback that cannot be avoided depending on the use condition of the apparatus, that is, the rear end of the paper jumps due to the stress caused by the continuous effect depending on the paper quality, or the small-size paper When continuous paper is passed, the roller expands in the non-paper passing area and the squeezing effect becomes excessive, causing rib wrinkles.When passing long size paper, distortion due to stress accumulates and the paper flaps. Defects such as wrinkles and wrinkles can be easily avoided by increasing or decreasing the squeezing effect by changing the position of the pressing member that supports the pressing shaft according to the use conditions of the device. The amount of the squeezing effect that provides the optimum transport performance can be arbitrarily selected.

The positions of the pressing members shown in FIGS. 5A, 5B, 5C, and 5D
In terms of position, position, the amount of the spelling effect is in the relationship of position <position <position <position.

Therefore, according to the use conditions of the apparatus, for example, the type and size of the paper used, the number of continuous copies, and the temperature and humidity at the time of use of the machine, there is no wrinkle and no optimum curl at the rear end. The operator may specify a position at which the only effect is obtained, so that the pressing member is displaced to the specified position.

FIGS. 14 to 17 show an example of a means for displacing the pressing member formed as a bearing. In this example, the pressing shaft 4 is formed as a hollow cylinder, and a shaft 15 is provided in the inside thereof so as to be rotatable with respect to the pressing shaft coaxially with the pressing shaft. Screws 16 and 17 are cut in the shaft 15 so that the screw directions are reversed over two ranges symmetrically with respect to the center point. A feed nut 18 is screwed into each of the screws 16 and 17. The pressing shaft 4 is provided with two long holes 19 at upper and lower positions corresponding to the range of the screw of the shaft 15 as shown in the figure, and is slidable in the direction along the outer peripheral surface of the pressing shaft 4. A projection 20a protruding from the inner surface of the provided bearing holder 20 which is divided into upper and lower portions penetrates, and this projection 20a further engages with a recess 18a provided on the outer peripheral surface of the feed nut 18.

The inner surface of the inner ring of the pressing member 5 configured as a ball bearing is fitted to the outside of the bearing holder 20, and the outer surface of the outer ring is
1 is in contact with the inner peripheral surface.

Accordingly, when the shaft 15 is rotated, the feed nut 18 moves in a direction away from or near the center of the shaft according to the rotation direction, and the ball bearing 5 is also integrated via the bearing holder 20. Move away from or near the center of the axis.

A pulley 21 is fixed to one end of a shaft 15 in the pressure roller 3 as shown in FIG. 17, and can be rotated by a pulse motor 23 via a timing belt 22. A gear 24 is fixed to the other end of the shaft 15, and is shielded from light by a light shielding plate 25 provided integrally with a gear 24 'meshing with the gear 24. A home for detecting that the bearing has reached the home position and that the bearing has overrun. A position sensor 26 and an overrun sensor 27 are provided. At the end of copying, the bearing is returned to the home position by the pulse motor 23 and the home position sensor 2
6 and is held in that position. Since the rotation of the light-shielding plate is equivalent to the stroke distance of the bearing, even if the power is cut off halfway, it is possible to return to the home position. Prior to the start of copying, if the operator designates the position of the bearing according to the conditions using a button or the like provided on the operation unit, the pulse motor 23 sets the rotation speed of the shaft 15 for displacing the bearing from the home position to that position. The motor rotates and stops by the corresponding number of pulses. When the overrun sensor detects, the motor rotates reversely.

Instead of the operator designating the position of the pressing member constituted as a bearing by a button or the like provided on the operation section, a means for automatically detecting whether the operator uses the recording device or inputting the use conditions of the recording apparatus is provided. It is also possible to automatically control the position of the pressing member based on a detection signal of the use condition input or detected by this means.

In this case, a sensor for detecting the temperature and humidity of the atmosphere of the apparatus is provided, and the size of the transfer sheet, the quality of the transfer sheet, and the number of continuous copies are designated by an operator or automatically detected, and the signals are detected. Is input to the CPU, and the position of the pressing member suitable for the use condition of the apparatus is selected. FIG. 18 is the flowchart. The flow is clear from the figure, and will not be described in detail. In short, whether or not the paper size is a fixed size, whether or not the humidity is, for example, 65% or more, whether or not the paper quality is, for example, special paper such as tracing paper, or more than 100 continuous copies of small-size paper having a small width. Either position,... Is selected according to a preset program from the data as to whether or not.

In this example, a manual mode is provided so that the operator can manually set the position according to instructions in the instruction manual or judgment based on his / her own experience.

As described above, by displacing the position of the pressing member, the amount of the squeezing effect, which was conventionally uniquely determined by the squeezing shape of the fixing roller, can be reduced to an amount without side effects in accordance with the use conditions of the apparatus. Thus, it is possible to prevent the paper from wrinkling and jumping from the rear end, thereby improving the transportability.

[Brief description of the drawings]

FIG. 1 is a perspective view of a roller unit of a fixing device according to an embodiment of the present invention.

FIG. 2 is a side view of the fixing device shown in FIG.

3A is a curve diagram showing a relationship between a deflection amount and a rise time of a roller depending on a thickness of a roller core metal, and FIG. 3B is a curve diagram showing a relationship between a deflection amount and a rise time. FIG.

FIG. 4 is a curve diagram showing a nip distribution of a roller portion.

FIG. 5 is a curve diagram showing a nip distribution according to a pressing position when the pressing roller has a run-out;

FIG. 6 is a side sectional view showing another modification of the pressing member.

FIG. 7 is a sectional view taken along line VII-VII in FIG. 6;

FIG. 8 is a side sectional view showing still another modified example of the pressing member.

FIG. 9 is a cross-sectional view thereof.

FIG. 10 is a cross-sectional view showing a sleeve and a bearing according to the present invention provided in a portion where a pressure roller is attached to a main body.

FIG. 11 is a sectional view showing a modification of FIG. 10;

FIG. 12 is a curve diagram showing a state of thermal expansion of a sleeve, a bearing, and the like due to a temperature change of the structure shown in FIGS. 10 and 11;

FIG. 13 is another curve diagram showing a state of thermal expansion of a sleeve, a bearing, and the like due to a temperature change of the structure according to the present invention.

FIG. 14 is a side sectional view showing a modification in which the axial position of the pressing member is adjustable.

FIG. 15 is a top view of a part of FIG. 14;

FIG. 16 is a partial cross-sectional view of FIG.

FIG. 17 is an exploded perspective view showing the adjustment mechanism.

FIG. 18 is a flowchart when the adjustment is performed automatically.

FIG. 19 is a cross-sectional view illustrating a schematic configuration of a conventional heat roller fixing device.

20 is a diagram showing a nip width distribution in the fixing device of FIG.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Fixing roller 2 ... Heater 3 ... Pressure roller 4 ... Pressure shaft 5 ... Circular pressing member 6 ... Slide bearing 7 ......... Sleeve

Claims (1)

[Claims] An image forming apparatus comprising: a fixing roller having a hollow cylinder having a heater therein; and a pressure roller having a hollow cylinder having a pressure shaft therein while being in pressure contact with the fixing roller. In the fixing device of the electrostatic recording apparatus, which has two pressing members for pressing the inner surface of the cylinder, the both ends of the pressing roller are attached to the apparatus main body side plate by supporting means movable only in the pressing direction. The means includes a positioning sleeve and a slide bearing provided between both ends of the sleeve and the pressure roller. The sleeve is made of metal, and the slide bearing is made of a heat-insulating resin. A fixing device.