JP2009003047A - Fixing device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To control a temperature distribution on the outer circumferential face in the axis direction of a fixing roll in a fixing device heating and pressurizing an unfixed toner image for fixing it on a storage medium. <P>SOLUTION: External heating rolls 6 and 7 are brought into contact with the outer circumferential face of the fixing roll 2 having a heating source. The fixing roll is provided with an elastic layer along the circumferential face. In the external heating roll having the built-in heating source, the outside diameter is formed into a crown-shape that gently expands in the center of the axial line. By means of temperature detection means 4a and 4b, a circumferential face temperature in use of a small-size storage medium in a paper passing area and that in a non paper passing area in the axial line direction of the fixing roll are detected, and based on the detection values, the pressing force of the external heating rolls to the fixing roll is switched and the axial directional temperature distribution of the fixing roll is controlled. When a layout is set so that the axial line of the fixing roll and that of the external heating roll make a predetermine angle α, when viewed from the back side of the external heating roll pressed against the fixing roll, the axial direction temperature of the fixing roll can be controlled. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a fixing device that is used in an image forming apparatus such as a printer, a copying machine, or a facsimile machine, and heats and pressurizes an unfixed toner image held on a recording medium to fix it on the recording medium.

As a fixing device of an image forming apparatus that forms a visible image using toner, a fixing device having a fixing roll and a pressure member pressed against the fixing roll is widely used. In this fixing device, at least the fixing roll is rotationally driven in a state where the fixing roll and the pressure member are in pressure contact with each other, the recording medium is fed into the pressure contact portion (nip portion), and the indeterminate state held on the recording medium. The received toner image is heated and pressurized.
The fixing roll includes a hollow cylindrical cored bar such as aluminum and a heating source such as a halogen lamp inside, and the peripheral surface is heated to a temperature suitable for fixing the toner image.

  Such a fixing roll is likely to have a difference in the peripheral surface temperature of the fixing roll between the passing area and the non-passing area depending on the size of the recording medium to be conveyed. That is, in the passing area of the recording medium, heat moves to the recording medium and the peripheral surface temperature decreases, but in the non-passing area, heat does not move to the recording medium and the peripheral surface temperature increases.

Patent Document 1 describes a fixing device that attempts to suppress an excessive rise in temperature near the end of a heating roll depending on the size of the recording medium used.
In this fixing device, an elastic layer is provided on a base material of a heating roll having a built-in heat source, and a pressure contact portion is formed by pressing a pressure member, and a recording paper is sandwiched between the pressure contact portions to fix a toner image. Is. And an external heating roll shall be press-contacted to the outer peripheral surface of a heating roll, and the heat source is arrange | positioned so that a heating may be suppressed in the axial direction vicinity of this external heating roll. Further, it is described that the cooling roll is pressed against the outer peripheral surface at both ends in the axial direction of the heating roll, and the surface temperature of the heating roll is lowered in this region.
JP 2003-295658 A

  In the fixing device that heats the toner image with the heating roll as described above, a heating source is provided so that the entire width can be sufficiently heated corresponding to the width of the recording medium of the maximum size that is generally used. In this fixing device, when a recording medium having a size smaller than the maximum size is continuously used, heat is removed from the heating roll to the recording medium in a sheet passing area of the small size recording medium. When the temperature of this portion is detected and the heating source is controlled so as to achieve a proper fixing temperature, the temperature of the non-sheet passing region rises, and an overheating state occurs. In such a state, when there are halftone images near both ends in the width direction of the recording medium, toner offset may occur due to the influence of the non-sheet passing region that has become high temperature. In addition, when a large temperature difference occurs between the paper passing area and the non-paper passing area, defects such as uneven glossiness occur in the fixed image when a recording medium having a large size is subsequently used.

  For example, an image forming apparatus that uses a so-called A3 novi size recording medium that is slightly larger than the A3 size and can form an image in a range larger than the A3 size may cause the following defects. In such a fixing device of the image forming apparatus, the toner image can be fixed by sufficiently heating in the range of A3 Nobi size. For this reason, if A3 size recording media are used continuously, only the vicinity of the end of the fixing roll becomes hot, and if there are halftone images near both ends in the width direction of the A3 size image, a so-called non-visual offset is generated. The tendency to occur becomes stronger. Such an offset is not noticeable at first glance, but it causes image smearing. Similar problems may occur when using a recording medium smaller than the A3 size.

  On the other hand, as described in Patent Document 1, when an external heating roll in which the heat supply amount from the heating source is reduced near both ends is used, when a recording medium of the maximum size is used, Both ends cannot be heated sufficiently. In particular, when the heating roll is rapidly heated such as when the image forming apparatus is started up, a temperature difference is generated in the axial direction of the heating roll. In addition, using rolls having different heating ranges corresponding to all sizes of recording media to be used leads to an increase in the size of the apparatus and an increase in manufacturing costs.

  The present invention has been made in view of the circumstances as described above, and an object of the present invention is to control the temperature distribution of the outer peripheral surface in the axial direction of the fixing roll, and to achieve excellent fixing for the maximum size recording medium to be used. An object of the present invention is to provide a fixing device capable of obtaining an image and preventing an image defect due to overheating of a non-sheet passing area even when a recording medium having a small size is used.

  In order to solve the above-mentioned problem, the invention according to claim 1 is characterized in that a heating source is provided therein, and is rotationally driven. A pressure member that sandwiches and presses a recording medium holding a toner image, a plurality of temperature detection units that detect surface temperatures of the fixing roll at different positions in the axial direction of the fixing roll, and the fixing roll One or a plurality of external heating rolls that are arranged so as to be in contact with each other along the axial direction and have a heating source therein, and at least one of the fixing roll and the external heating roll is: An elastic layer that is deformed by the contact pressure between them is provided over the entire circumference, and the temperature detecting means includes a sheet passing area through which a recording medium of all sizes to be conveyed and a conveyed medium are conveyed. Detecting at least two temperatures of a non-sheet-passing area through which a recording medium having a width dimension smaller than that of a large-sized recording medium passes without contacting, and based on a detection signal from the temperature detecting means, Provided is a fixing device that changes the distribution of contact pressure in the axial direction between a heating roll and the fixing roll.

  The invention according to claim 2 is the fixing device according to claim 1, wherein the external heating roll has an outer diameter that changes gently in the axial direction, and the axial direction between the external heating roll and the fixing roll The distribution of the contact pressure is changed by changing the pressure contact force between the external heating roll and the fixing roll based on the detection signal of the temperature detection means.

  According to a third aspect of the invention, there is provided the fixing device according to the second aspect, wherein the external heating roll gradually changes so that an outer diameter of the external heating roll expands at a central portion from an end portion in the axial direction. The external heating roll and the fixing roll support both end portions and change the pressing force.

  According to a fourth aspect of the present invention, in the fixing device according to the second or third aspect, when the external heating roll is viewed from a rear side of a position in contact with the fixing roll, the external heating roll It is assumed that the axis and the axis of the fixing roll are supported at a predetermined angle.

  According to a fifth aspect of the present invention, in the fixing device according to the first aspect, the external heating roll has an axis of the external heating roll and the fixing when viewed from the rear side of the position in contact with the fixing roll. The axial line of the roll is supported at a predetermined angle, and the distribution of the contact pressure in the axial direction between the external heating roll and the fixing roll is determined based on the detection signal of the temperature detection means. The pressure is changed by changing the pressure contact with the fixing roll.

  According to a sixth aspect of the present invention, in the fixing device according to the first aspect, the external heating roll has an axis of the external heating roll and the fixing when viewed from the rear side of the position in contact with the fixing roll. The angle α formed with the roll axis can be changed within a range including the positions where these axes are parallel, and the distribution of the contact pressure in the axial direction between the external heating roll and the fixing roll is as follows: The angle α is changed by changing the detection signal of the temperature detecting means.

  According to a seventh aspect of the present invention, in the fixing device according to any one of the first to third aspects, at least one of a type, a size, a thickness, and a basis weight of the recording medium and a detection signal by the temperature detection unit Based on the above, the distribution of the contact pressure in the axial direction between the external heating roll and the fixing roll is changed.

  According to the configuration of the first aspect of the present invention, the axial distribution of the contact pressure at which the external heating roll comes into contact with the fixing roll is changed based on the detection signal detected by the temperature detecting means, whereby the fixing roll The distribution of the heat supply amount in the axial direction can be controlled. That is, in the range where the contact pressure is large, the elastic layer of the fixing roll or the external heating roll is greatly deformed and the circumferential length of the contact area is increased. Accordingly, it is possible to increase the amount of heat supplied from the external heating roll to the fixing roll in a range where the contact pressure is large. In addition, the amount of heat supplied can be reduced in a range where the contact pressure is small. As a result, the temperature rise in the non-sheet passing region can be suppressed, and image defects due to overheating near the end of the fixing roll can be suppressed.

  According to the configuration of the second aspect of the invention, the contact pressure with the fixing roll is increased at the portion where the outer diameter of the external heating roll is enlarged, and the contact width is widened. As a result, the amount of heat supplied from the external heating roll to the fixing roll is increased at the portion where the outer diameter is enlarged. Further, by adjusting the pressing force of the external heating roll, it can come into contact with the fixing roll in a range where the outer diameter is enlarged, and can be separated from the fixing roll in a range where the outer diameter is small. On the other hand, when the external heating roll is strongly pressed against the fixing roll, it contacts in a wide range in the circumferential direction over the entire width of the peripheral surface of the fixing roll. In such a state, the difference in the contact range in the circumferential direction due to the difference in the outer diameter of the external heating roll is a small ratio, and the difference in the amount of heat supplied is also a small ratio. Therefore, the peripheral surface of the fixing roll can be heated almost uniformly over the entire width.

  According to the configuration of the invention of claim 3, the amount of heat from the external heating roll can be increased at the central portion in the axial direction of the fixing roll and can be decreased at the end. In particular, by adjusting the pressure contact force small, the external heating roll can be separated from the fixing roll in the vicinity of the end portion, and the heat conduction to the vicinity of the end portion can be cut off. On the other hand, when the external heating roll is strongly pressed, it contacts the external heating roll in a wide range in the circumferential direction of the fixing roll. And when both ends are pressed and the external heating roll is pressed, the bending of the axis of the external heating roll is generated, and the effect of increasing the contact pressure at both ends in the axial direction is produced. This cancels out the fact that the outer diameter is enlarged at the central portion, resulting in a distribution with little difference in contact pressure in the axial direction. Therefore, by adjusting the pressing force of the external heating roll against the fixing roll, it is possible to switch between a state in which the heat supply amount is small at both ends in the axial direction and a state in which a substantially uniform heat amount is supplied along the axial direction. It becomes possible.

  According to the configuration of the invention of claim 4, the external heating roll is strongly pressed against the fixing roll in a partial range in the axial direction of the fixing roll, and press-contact is performed so that the contact pressure decreases as the distance from the range increases. it can. Therefore, it is possible to set a large difference in the amount of heat supplied between a range where a large amount of heat is supplied from the external heating roll and a range where a small amount of heat is supplied.

  According to the configuration of the fifth aspect of the invention, it is possible to increase the amount of heat supplied to the fixing roll by strongly pressing the external heating roll against the fixing roll in a partial range in the axial direction of the fixing roll. And the range in which a large amount of heat is supplied can be enlarged or reduced by changing the pressure contact force. This makes it possible to adjust the temperature distribution in the axial direction of the fixing roll.

  According to the configuration of the sixth aspect of the invention, it is possible to increase the amount of heat supplied to the fixing roll by strongly pressing the external heating roll against the fixing roll in a partial range in the axial direction of the fixing roll. When the axis of the fixing roll and the axis of the external heating roll overlap when viewed from behind the external heating roll, that is, when these axes are arranged so as to be parallel, the amount of heat is almost evenly distributed in the axial direction. Supplied. Accordingly, it is possible to appropriately adjust the temperature distribution in the axial direction of the fixing roll.

  According to the configuration of the seventh aspect of the invention, even if the temperature difference generated in the fixing roll differs depending on the recording medium used, the temperature distribution corresponding to this can be set to a satisfactory image fixing. Can do.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic configuration diagram illustrating a fixing device according to an embodiment of the present invention.
The fixing device 1 includes a fixing roll 2 supported so as to be rotatable around a central axis, two temperature detecting means 4 a and 4 b for detecting the surface temperature of the fixing roll 2, and an outer peripheral surface of the fixing roll 2. An endless belt 8 stretched between two external heating rolls 6 and 7 for auxiliary heating from the outside, a pressure roll 9 and two support rolls 11 and pressed against the fixing roll 2, and an endless belt 8 A main part is constituted by a pressure applying member 10 which is supported by being in contact with the inner peripheral surface and presses the endless belt 8 along the outer peripheral surface of the fixing roll 2. Around the fixing roll 2, a release agent supply device 12 that supplies a release agent and a cleaning device 13 that removes toner and paper dust attached to the outer peripheral surface of the fixing roll 2 are disposed. When a recording sheet P (recording medium) holding an unfixed toner image is sent to the pressure contact portion between the fixing roll 2 and the endless belt 8 that are rotationally driven, the toner image is heated by heat transfer from the fixing roll 2. At the same time, the pressure is applied to the recording sheet. The recording sheet on which the toner image is fixed is guided by the guide member 14 and sent out of the apparatus by the discharge roll 15.

The fixing roll 2 has a cylindrical metal core 2a having conductivity, and a heat-resistant elastic layer 2b and a release layer 2c are laminated around the core 2a. The core 2a is rotatably supported by a main body frame (not shown) of the image forming apparatus by a flange and a support shaft.
For the cylindrical cored bar 2a of the fixing roll 2, a metal such as aluminum, iron, and stainless steel having excellent thermal conductivity and rigidity can be used. In this embodiment, a cylindrical body made of aluminum is used as a core metal, and silicone rubber is used for the elastic body layer 2b. For the release layer 2c, PTFE resin or the like in which silicon carbide powder is dispersed can be used.
As shown in FIG. 1, a halogen lamp 2 d is disposed inside the fixing roll 2 as a heating source, and heat is supplied almost uniformly over the entire length of the fixing roll 2 in the axial direction. Yes.

As the temperature detecting means 4, a temperature sensor that detects the temperature in contact with the outer peripheral surface of the fixing roll 2 is used. As shown in FIG. 3, these are the first temperature detecting means 4a for detecting the temperature of the outer peripheral surface of the fixing roll in the sheet passing area, and the second temperature detecting means 4b for detecting the temperature of the non-sheet passing area. Is included.
The first temperature detection unit 4 a is disposed in contact with the outer peripheral surface of the fixing roll 2 at a substantially central portion in the axial direction of the fixing roll 2. That is, the temperature of the outer peripheral surface of the fixing roll 2 is detected in a region through which recording sheets of all sizes conveyed with reference to the central portion of the fixing roll pass.
The second temperature detection means 4 b is arranged so as to detect the temperature of the outer peripheral surface in the vicinity of the end of the fixing roll 2 in the axial direction. That is, the position at which the temperature is detected by the second temperature detecting means 4b is a range through which the maximum size recording sheet passes, but is deviated from the range through which the small size recording sheet passes.

The temperature detection means 4a and 4b measure the temperature in contact with the peripheral surface of the fixing roll 2, and use a thermocouple using the Seebeck effect, a thermistor using an element having a large temperature coefficient of resistance, or the like. It is done. Since these contact-type temperature sensors are inexpensive, the cost of the apparatus can be reduced.
As the temperature sensor, a sensor that detects the temperature without contact with the surface of the fixing roll can be used.
Further, in the present embodiment, the two temperature detecting means 4a and 4b are arranged, but the temperature distribution can be detected more finely by arranging at three or more places.

  The endless belt 8 is formed of a heat-resistant resin film such as polyimide, and includes two support rolls 11 disposed at positions away from the fixing roll 2 and a pressure roll 9 disposed so as to be pressed against the fixing roll 2. It is wound around. The pressure roll 9 is pressed to such an extent that the elastic layer of the fixing roll 2 is largely deformed, and the recording sheet P passing through the pressure contact portion of the pressure roll 9 is easily peeled off from the fixing roll 2.

  As shown in FIG. 1, the pressure applying member 10 is formed by laminating an elastic layer 10b and a low friction layer 10c on a base plate 10a, and the base plate 10a is fixed to the fixing roll 2 by a compression coil spring 10d. It is energized towards. The base plate 10a is a stainless steel member.

  The release agent supply device 12 is disposed in contact with a tank 12a for storing the release agent, a pumping member 12b made of a porous material for pumping the release agent from the tank 12a, and a pumping member 12b. Supply roll 12c that holds the mold, coating roll 12d that contacts the supply roll 12c and the fixing roll 2 and applies the release agent supplied from the supply roll 12c to the surface of the fixing roll 2 almost evenly, and the supply roll The main part is composed of a release agent regulating member 12e that regulates the amount of the release agent supplied to the surface of 12c and adjusts the amount of the release agent supplied to the coating roll 12d.

  The cleaning device 13 gradually sends out a cleaning roll 13a for cleaning the surface of the fixing roll 2, a belt-like cleaning web 13b pressed against the cleaning roll 13a and the external heating roll 6, and a wound cleaning web 13b. The main part is composed of a feed roll 13c, a take-up roll 13d that winds the cleaning web 13b fed from the feed roll 13c, and a pressing roll 13e that presses the cleaning web 13b from the back to the cleaning roll 13a and the external heating roll 6. It is configured.

  The cleaning web 13b is a series of strip-shaped members in which a nonwoven fabric is impregnated with silicone oil. And it is press-contacted to the surrounding surface of the external heating roll 6 and the cleaning roll 13a until it is pulled out from the delivery roll 13c by which the unused part was wound, and is wound up by the winding roll 13d. Therefore, these peripheral surfaces are cleaned by rotating the external heating roll 6 and the cleaning roll 13a. The cleaning web 13b is wound around the take-up roll from the feed roll at a slow speed, so that a new part always comes into contact with the peripheral surfaces of the external heating roll 6 and the cleaning roll 13a, and is good for a long period of time. It can be cleaned.

As shown in FIG. 1, the external heating rolls 6 and 7 are rolls configured by laminating release layers 6b and 7b on cylindrical metal cores 6a and 7a having conductivity. It is supported and pressed against the outer peripheral surface of the fixing roll 2. The external heating rolls 6 and 7 are internally provided with halogen lamps 6c and 7c as heating sources, and these halogen lamps 6c and 7c supply heat almost uniformly in the axial direction of the external heating rolls 6 and 7. It has become. The heating rolls 6 and 7 are in contact with the peripheral surface of the fixing roll 2 to heat the outer peripheral surface of the fixing roll 2 from the outside.
The heating source for the external heating rolls 6 and 7 is not limited to the halogen lamps 6c and 7c. The number of external heating rolls disposed may be one or more.

As shown in FIG. 2, both ends of the external heating roll 6 are supported so as to be able to advance and retreat with respect to the axis of the fixing roll 2, and the fixing roll 2 is connected via a cam 17 that is rotationally driven by a stepping motor 16. It is pressed to the side. That is, when the cam 17 rotates, the support shaft 6d of the external heating roll 6 is displaced, and the pressing force of the external heating roll 6 to the fixing roll 2 is controlled. The force that presses the external heating roll 6 by the cam 17 is changed in three stages: a first pressing force, a second pressing force that is weaker than this, and a state in which the external heating roll 6 is separated from the fixing roll 2. ing.
The pressing force can be adjusted using a solenoid or the like instead of the cam 17.

  Further, as shown in FIG. 3, the external heating rolls 6 and 7 have a shape in which the outer diameter continuously expands toward the central portion rather than the end portion in the axial direction, that is, a crown shape. By having this shape, when the external heating roll 6 is pressed against the outer peripheral surface of the fixing roll 2 with a large pressing force by the rotation of the cam 17, the external heating roll 6 has a substantially entire length in the axial direction. In contact with the outer circumferential surface. Further, as conceptually shown in FIG. 4 (a), the fixing roll 2 and the external heating roll 6 are strongly pressed in a state where they are supported at both ends, so that both axes are bent so as to bend. As shown in FIG. 4B, the distribution of the contact pressure is nearly uniform in the axial direction. Therefore, the distribution of the amount of heat transfer from the external heating roll 6 to the fixing roll 2 is substantially uniform as shown in FIG.

  On the other hand, when the pressing force to the fixing roll 2 is reduced, the axial end of the external heating roll 6 is separated from the peripheral surface of the fixing roll 2 as shown in FIG. Are touching. Accordingly, a large amount of heat is supplied from the external heating roll 6 to the fixing roll 2 in the vicinity of the central portion in the axial direction of the fixing roll 2, and heat conduction is blocked in the vicinity of the end portion. In this way, the pressure applied to the fixing roll 2 by the external heating roll 6 is changed, the distribution of the amount of heat moving to the fixing roll 2 is changed in the axial direction of the fixing roll 2, and the temperature distribution of the fixing roll 2 is controlled. It has become.

In the present embodiment, both of the two external heating rolls 6 and 7 have the crown shape, but only one of them may have a crown shape.
Further, the curve in which the outer diameter of one external heating roll 6 changes in the axial direction may be different from the change curve of the other external heating roll 7.
Further, the pressing force can be controlled for each external heating roll.
Thus, the temperature in the axial direction of the fixing roll 2 can be accurately controlled by changing the pressing force, the presence or absence of the crown shape, or the change curve of the outer diameter of the crown shape for each external heating roll.

Further, as shown in FIG. 6A, when the external heating roll 6 pressed against the fixing roll 2 is viewed from behind, the axis of the external heating roll 6 has a predetermined angle α with the axis of the fixing roll 2. It can also be arranged in a state.
By arranging the external heating roll 6 in this way, the distribution of the contact pressure between the external heating roll 6 and the fixing roll 2 increases near the central portion in the axial direction of the fixing roll 2 and decreases near the end. As a result, as shown in FIG. 6B, the circumferential length of the contact area is increased at the central portion in the axial direction of the fixing roll 2, and the heat from the external heating roll 6 is near the end portion and at the central portion. The difference in the amount of movement increases.
When there are two or more external heating rolls, the angle α can be changed for each external heating roll.

Next, a process of controlling the pressing force of the external heating rolls 6 and 7 against the fixing roll 2 based on the temperature detected by the temperature detection means 4 and the size of the recording sheet will be described.
FIG. 7 is a flowchart showing control of the pressing force.
When the running of the paper is started, the external heating rolls 6 and 7 are pressed against the fixing roll 2 by the first pressing force which is the initial setting, and heat is supplied to the entire length of the fixing roll 2 in the axial direction (ST1). ). Then, the paper size is recognized from information input to the apparatus or a signal detected by a sensor or the like (ST2). If the recognized paper size is the maximum size that can be used with this apparatus, the first pressing force acting on the external heating rolls 6 and 7 is maintained (ST3). Then, based on the detection signal of the first temperature detecting means for detecting the temperature in the sheet passing area, the heating source 2d incorporated in the fixing roll 2 and the heating sources 6c and 7c of the external heating roll are controlled, and the surface of the fixing roll 2 is controlled. The temperature is controlled to a temperature suitable for fixing (ST4). In this state, an image fixing operation is performed (ST5). When a predetermined number of fixing operations are completed, the running of the sheet is terminated.

  On the other hand, if the recognized paper size is not the maximum size, the temperature of the non-sheet passing area of the fixing roll 2 is detected by the second temperature detecting means 4b (ST6), and the temperature detected by the first temperature detecting means 4a is detected. Compare (ST7). If these temperature differences are less than or equal to a preset value, the fixing operation is performed while maintaining the first pressing force (ST8, ST9, ST10). The sheet is continuously run, the temperature of the non-sheet passing area rises, and the difference between the detected temperatures of the first temperature detecting means 4a and the second temperature detecting means 4b is larger than a set predetermined temperature difference. If so, the pressing force of the external heating rolls 6 and 7 to the fixing roll 2 is switched to the second pressing force (ST11). Further, the sheet is continuously run with the second pressing force (ST9, ST10), and when the temperature difference is smaller than a predetermined value, the pressing force of the external heating rolls 6, 7 is again the first pressing force. The pressing force is set to 1 (ST8). When the external heating roll 6 is pressed against the fixing roll 2 by the second pressing force, the heat transfer to the end portion of the fixing roll 2 is reduced, and the temperature difference between the central portion and the end portion in the axial direction is reduced. Cases can also arise. Thereafter, when it is confirmed that all the set number of fixing operations have been completed, the sheet running is ended.

The temperature difference is changed according to the type of paper used and the basis weight, and is set as shown in Table 1, for example.
Here, the basis weight refers to the weight of one recording sheet per square meter, and the types of recording sheets are for plain paper and coated paper. The first pressing force is a pressing force in which the entire axial length of the external heating rolls 6 and 7 having a crown shape is in contact with the outer peripheral surface of the fixing roll 2 and is set to a force stronger than the second pressing force. To do. On the other hand, the second pressing force is weaker than the first pressing force, and both end portions in the axial direction of the external heating rolls 6 and 7 are separated from both end portions of the fixing roll 2.

  In the embodiment described above, the outer heating roll has a so-called crown shape whose outer diameter is enlarged at the center portion, but the fixing roll axis and the outer side when viewed from behind the outer heating roll are used. When the heating roll is arranged so that the axis of the heating roll is at a predetermined angle α, an external heating roll having the same diameter in the axial direction can also be used. Even if such an external heating roll is used, the distribution of the contact pressure can be changed by changing the pressing force against the fixing roll 2.

  On the other hand, in the embodiment described, the angle α formed between the axis of the fixing roll and the axis of the external heating roll when viewed from behind the external heating roll is constant, but this angle α can be changed. You can also. The mechanism for changing the angle can be realized by moving the position of the bearing that supports the external heating roll using a solenoid or a stepping motor.

  In such a fixing device, when the external heating roll is supported so that the external heating roll and the fixing roll are parallel, that is, the angle α is 0 °, the external heating roll is applied to the entire area in the axial direction of the fixing roll. It can be pressed against the fixing roll. Heat can also be supplied from the external heating roll to the end of the fixing roll. On the other hand, by setting the angle α to a predetermined value, the external heating roll and the fixing roll are separated from each other in the vicinity of the end portion, and heat conduction to the end portion of the fixing roll can be blocked.

In the fixing device in which the angle α formed between the axis of the external heating roll and the axis of the fixing roll changes as described above, a roll having a constant outer diameter in the axial direction can be used as the external heating roll.
When the angle α is changed as described above, the force for pressing the external heating roll against the fixing roll may be changed, but may be constant.
Moreover, when providing a some external heating roll, the said angle (alpha) can also be controlled independently for every external heating roll. By controlling in this way, the angle α can be set to be different for each external heating roll, and the distribution of the amount of heat supplied to the fixing roll can be controlled more appropriately.

  Further, in the fixing device in which two or more external heating rolls are in pressure contact with the fixing roll, for some of the external heating rolls, the pressing force on the fixing roll is changed, assuming that the outer diameter changes in the axial direction, Other external heating rolls can also change the angle α between the axis of the external heating roll and the axis of the fixing roll when viewed from behind. When three or more external heating rolls are arranged, each external heating roll may be controlled independently, or may be controlled separately for each of a plurality of groups.

  In the fixing device described above, the shape of the external heating roll is crowned on the premise of a device that employs a so-called center register that controls the position of the recording sheet P at its center. Further, when the external heating roll pressed against the fixing roll is viewed from the back side, the fixing roll axis and the external heating roll axis intersect at the center in the axial direction of the fixing roll, and the contact pressure is the highest at the center. Is set to be larger. On the other hand, in a fixing device that employs a so-called side registration in which the position of the recording sheet P is controlled by its side edge, as shown in FIG. What is reduced in the vicinity can be used. Further, as shown in FIG. 8B, when viewed from the back side of the external heating roll 23 pressed against the fixing roll 22, the axis of the fixing roll 22 and the axis of the external heating roll 23 are near one end. Can be dealt with by crossing and pressing so that the contact pressure becomes maximum near the end.

1 is a schematic configuration diagram illustrating a fixing device according to an embodiment of the present invention. FIG. 2 is a schematic view showing a mechanism for pressing an external heating roll against a fixing roll of the fixing device shown in FIG. 1. FIG. 2 is a schematic front view showing an external heating roll pressed against a fixing roll of the fixing device shown in FIG. 1. FIG. 2 is a diagram conceptually illustrating a state in which the fixing roll and the external heating roll of the fixing device illustrated in FIG. 1 are in contact with each other and the external heating roll is strongly pressed against the fixing roll. FIG. 2 is a diagram conceptually illustrating a state in which the fixing roll and the external heating roll of the fixing device illustrated in FIG. 1 are in contact with each other and the external heating roll is pressed against the fixing roll with a weak force. FIG. 6 is a diagram of an external heating roll pressed against the fixing roll as viewed from behind, and is a schematic view showing a state in which the axis of the external heating roll has a predetermined angle α with the axis of the fixing roll 2. It is a flowchart which shows the process of controlling the pressing force which presses an external heating roll to a fixing roll. It is the schematic which shows the shape and arrangement | positioning of the external heating roll in the fixing device which is other embodiment of this invention.

Explanation of symbols

1: fixing device, 2: fixing roll, 2a: metal core, 2b: elastic layer, 2c: release layer, 2d: halogen lamp (heating source), 4: temperature detection means, 6, 7: external heating roll, 6a, 7a: Metal core, 6b, 7b: Release layer, 6c, 7c: Halogen lamp (heating source), 8: Endless belt, 9: Pressure roll, 10: Pressure applying member, 11: Support roll, 12: Release Mold supply device, 13: Cleaning device, 14: Guide member, 15: Discharge roll, 16: Stepping motor, 17: Cam

Claims (7)

A fixing roll provided with a heating source therein and driven to rotate;
A pressure member that is pressed against the outer peripheral surface of the fixing roll and sandwiches and presses a recording medium in which an unfixed toner image is held in a pressure contact area with the fixing roll;
A plurality of temperature detecting means for detecting the surface temperature of the fixing roll at different positions in the axial direction of the fixing roll;
One or a plurality of external heating rolls arranged on the outer peripheral surface of the fixing roll so as to contact along the axial direction and having a heating source inside,
At least one of the fixing roll and the external heating roll is provided with an elastic layer that is deformed by contact pressure therebetween, over the entire circumference.
The temperature detecting means includes a paper passing area through which all sizes of the recording medium to be transported and a non-paper passing area through which a recording medium having a smaller dimension in the width direction than the maximum size of the recording medium to be transported does not contact. It detects at least two temperatures,
A fixing device that changes an axial contact pressure distribution between the external heating roll and the fixing roll based on a detection signal from the temperature detection unit. The external heating roll has an outer diameter that changes gently in the axial direction,
The distribution of the contact pressure in the axial direction between the external heating roll and the fixing roll is changed by changing the pressure contact force between the external heating roll and the fixing roll based on the detection signal of the temperature detection means. The fixing device according to claim 1.   The external heating roll changes gradually so that the outer diameter expands from the end in the axial direction at the center, and the external heating roll and the fixing roll support the respective end portions and press contact force The fixing device according to claim 2, wherein the fixing device is changed.   The external heating roll is supported so that the axis of the external heating roll and the axis of the fixing roll are at a predetermined angle when viewed from the rear side of the position in contact with the fixing roll. The fixing device according to claim 2 or 3. The external heating roll is supported so that the axis of the external heating roll and the axis of the fixing roll are at a predetermined angle when viewed from the rear side of the position in contact with the fixing roll,
The distribution of the contact pressure in the axial direction between the external heating roll and the fixing roll is changed by changing the pressure contact force between the external heating roll and the fixing roll based on the detection signal of the temperature detection means. The fixing device according to claim 1. The external heating roll has an angle α formed by the axis of the external heating roll and the axis of the fixing roll when viewed from the rear side of the position in contact with the fixing roll. It is possible to change within the range to include,
The distribution of the contact pressure in the axial direction between the external heating roll and the fixing roll is changed by changing the angle α based on a detection signal of the temperature detection means. The fixing device according to 1. Changing the axial contact pressure distribution between the external heating roll and the fixing roll based on at least one of the type, size, thickness or basis weight of the recording medium and a detection signal from the temperature detection means. The fixing device according to any one of claims 1 to 6, wherein the fixing device is characterized in that:

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