JPH04240683A - Image forming device - Google Patents

Abstract

PURPOSE:To uniformize a temperature distribution in the shaft direction of the fixing roller of a fixing device. CONSTITUTION:The heat source of the fixing roller 10 is constituted of two of first and second bar-like heaters 11 and 12 in which generated calorific value distributions are different along the shaft direction of the fixing roller 10, and either of which is selectively used. The first and the second heaters 11 and 12 are switched according to the number of the transferring paper P of a specified size to which the consecutive fixing processing is executed. That is, when the temperature of the non-paper passing part of the fixing roller 10 rises by executing the consecutive fixing processing of the transferring paper P of the specified size, the heat source of the fixing roller 10 is switched from the first heater 11 to the second heater 12, so that the temperature in the shaft direction of the fixing roller 10 is uniformized.

Description

[Detailed description of the invention]

[Industrial Application Field] In image forming devices such as copying machines, when a toner image is formed on a transfer paper, the transfer paper is transported to a fixing device, and the toner image is transferred as a permanent image onto the transfer paper. will be established. A heat roll type fixing device is often used as this fixing device. An example of such a fixing device will be described with reference to FIGS. 9 and 10. As shown in FIG. 9, the fixing device includes a fixing roller 10 that has a heater 100 inside and rotates in a predetermined direction;
It is composed of a pressure roller 20, etc., which rotates in pressure contact with the
By passing a transfer paper P carrying a toner image between a fixing roller 10 and a pressure roller 20, the toner image is heated and pressurized to fix and fix the toner image on the transfer paper P. As shown in FIG. 10, the fixing roller 10 is composed of a large diameter fixing section 10a and small diameter support sections 10b, 10b on both ends.
, 13 via ball bearings 14, 14. The heater 100 is disposed at the center of the fixing roller 10 along its axial direction from end to end, and a thermistor 21 is brought into contact with the intermediate portion of the outer surface of the fixing roller 10 . surface temperature is constantly detected. A heater control section for the fixing roller 10 is provided within the fixing device or on the main body side of the image forming apparatus, and the heater 100 is controlled to turn ON/OFF according to the temperature signal from the thermistor 21 by the temperature control section. No. 10 has its surface temperature maintained at a constant value.

However, although the fixing roller 10 is heated uniformly in the axial direction by the heater 100, both ends of the fixing roller 10 are heated by the bushes 13.
, 13 and the ball bearings 14, 14, the temperature of the fixing portion 10a of the fixing roller 10 is lower at both ends than in the middle, and the toner image is lowered at both ends of the fixing roller 10. There was an inconvenience that the fixation property of the film was poor. Further, for example, the transfer paper P may be attached to the fixing roller 10.
In the case of a center reference fusing device positioned at the center of the
As shown in FIG. 10, the fixing portion 10a of the fixing roller 10
When the transfer paper P having a length L2, which is sufficiently small in the width direction compared to the length L1, is continuously fixed, the amount of heat dissipated from the length L2 portion of the fixing roller 10 increases. 21, the ON time of the heater 100 becomes longer, but for this reason, the length L2 of the fixing roller 10 increases.
The temperature of the end portions other than the bushings 13, 13 increases.
, the ball bearings 14, 14, the pressure roller 20, and the oil applicators 22, 23 of the fixing roller 10 may be thermally damaged. This problem also occurs in the case of a one-sided fixing device in which the transfer paper P is positioned on one side of the fixing roller 10. The present invention has been made in view of the above problems, and an object thereof is to provide a fixing device that can maintain the surface temperature of the fixing roller uniformly over its axial direction.

[Means for Solving the Problems] In order to achieve the above object, the present invention provides a fixing roller that rotates with a heat source inside, a pressure roller that rotates in pressure contact with the fixing roller, and a surface of the fixing roller. In a fixing device having a detection means for detecting temperature, and a control means for controlling the heat source according to a signal from the detection means to control the surface temperature of the fixing roller to a predetermined temperature, the heat source is connected in the axial direction of the fixing roller. The heating element is composed of a plurality of rod-shaped heating elements, each of which has a different heat distribution along the axis, and one of which is selectively used, and the heating element is controlled by the control means in accordance with the number of sheets of transfer paper of a predetermined size to be continuously fixed. It is characterized by the ability to switch between uses. The present invention also provides a fixing roller that rotates and has a heat source inside, a pressure roller that rotates in pressure contact with the fixing roller, a detection device that detects the surface temperature of the fixation roller, and a signal from the detection device. In the fixing device, the heat source is controlled by a control means for controlling the surface temperature of the fixing roller to a predetermined temperature. 1
The first detection means is arranged in the normal paper passing area of the fixing roller, and the first detection means is arranged in the area where the transfer paper is least likely to pass. and a second detection means, and controls the heating element based on the temperature signal from the first detection means,
The control means is characterized in that the control means is provided with a function of switching and using the heating element based on the upper limit value and lower limit value of the temperature signal from the second detection means.

[Operation] The long surface temperature of the fixing roller is maintained at a constant value by the control means controlling the heat source within the fixing roller based on the detection signal from the detection means. However, when the transfer paper is passed, the transfer paper transfers heat from the surface of the fixing roller, so the surface temperature of the fixing roller differs between the paper passing area and the non-paper passing area, and the fixing roller If temperature control is performed based on the paper passing section, the temperature of the non-paper passing section will rise. This non-uniform temperature distribution varies depending on the size of the transfer paper. Therefore, in the invention according to claim 1, the heat source of the fixing roller is a plurality of rod-shaped heating elements, each of which has a different calorific value distribution along the axial direction of the fixing roller, and one of which is selectively used. If a part of the fusing roller becomes abnormally hot during continuous fusing processing, the heat source of the fusing roller is switched to a heating element with a different axial heat distribution, so that the axial temperature distribution of the fusing roller is uniform. I made it so that Further, in the invention according to claim 2, the first detection means is arranged in a normal paper passing area of the fixing roller, and the second detection means is arranged in an area where transfer paper is least likely to pass. The temperature control of the fixing roller is performed based on the temperature signal from the first detection means, and this causes the temperature of the part where the second detection means is disposed to be set to the upper limit or the lower limit. When the temperature approaches , the heating element is switched and used based on the temperature signal from the second detection means. That is, the second
Temperature adjustment in the part where the detection means is installed and which is most difficult to control is performed by switching the heating element, so the temperature distribution in the axial direction of the fixing roller is always uniform regardless of the size of the transfer paper etc. .

DESCRIPTION OF THE PREFERRED EMBODIMENTS Examples of the present invention will be described below with reference to the accompanying drawings. First, a first embodiment of the present invention will be described with reference to FIGS. 1 to 6. FIG. 2 shows a cross-sectional view of the fixing device 1 used in the image forming apparatus, and numeral 10 in the figure has two first and second heaters 11 and 12 as heat sources inside. The fixing roller 1 is rotated by the fixing roller 1.
A pressure roller 20 that is rotated while being pressed against the fixing roller 10 is disposed below the fixing roller 10 . The fixing roller 10 is a metal pipe whose outer surface is coated with a fluororesin or the like to prevent offset, and the pressure roller 20 is a metal pipe with an elastic member 20b such as silicone rubber adhered around a metal core 20a. A fixing nip N is formed at the pressure contact portion of the fixing and pressure rollers 10 and 20. A thermistor 21 for detecting the temperature of the fixing roller 10 is attached to an axially intermediate portion of the fixing roller 10.
The first and second heaters 1, which are heat sources, respond to the temperature signal from 1.
1 and 12 are controlled so that the surface temperature of the fixing roller 10 is maintained at a constant fixing temperature along its axial direction. Further, the fixing roller 10 is provided with a cleaning web 2.
2. A cleaning device including a pressure roller 23 and the like is attached, and the toner adhering to the fixing roller 10 is cleaned by sliding the cleaning web 22 against the fixing roller 10 via the pressure roller 23. Note that 24 and 25 are separating claws, and 26 is a carry-out roller. That is, the transfer paper P with the toner image T directed toward the fixing roller 10 side via the conveyance section 27 on the image forming apparatus main body side
is carried into the fixing device 1, this transfer paper P is fixed,
The toner image T on the transfer paper P is fixed while being held between the pressure rollers 10 and 20, and is heated and pressurized through the nip N of the pressure rollers 10 and 20, and then transferred to the transfer paper P. It is melted and fixed on top. The transfer paper P on which the fixing work has been completed is separated from the fixing roller 10 or the pressure roller 20 via the separation claws 24 and 25, and then transferred to the discharge roller 26.
It is carried out to the outside via. It should be noted that toner slightly attached to the fixing roller 10 during the fixing operation is removed by the cleaning web 22.
etc. to be cleaned. In this fixing device 1, as shown in FIG. 1, the transfer paper P is positioned at the center of the fixing and pressure rollers 10 and 20 (center reference). Next, the first, which constitutes a characteristic configuration of the present invention,
The configuration of the second heaters 11 and 12 and their control will be explained with reference to FIGS. 1, 3 to 6. Fixing roller 1
0, as shown in FIG.
, 14, and the first and second heaters 11, 12 are supported by the left and right support parts 10b, 1.
They are arranged parallel to each other in the axial direction of the fixing roller 10 up to the full length between 0b. First and second heaters 11, 12
The heaters are used in a switched manner with approximately the same capacity (for example, both have a rated power of 900 W), and are composed of halogen heaters in which filaments 11a and 12a are arranged in rod-shaped glass tubes 11b and 12b. There is. Also,
The first and second heaters 11 and 12 are filament 11a.
, 12a, the heat distribution in the axial direction of the fixing roller 10 can be changed. That is, the intermediate portion 11A of the first heater 11, the small size transfer paper P1 (the size is such that abnormal high temperatures are generated at both ends of the fixing roller 10 when the fixing device 1 performs continuous fixing processing, and specifically, (The size is smaller than the vertical feed width of B4 size.) The amount of heat generated in the approximately same length part as the paper passing area L1 is 11
The heat generation amount is set smaller than that of B and 11B. For example, as shown in FIG. 3(a), if the amount of heat generated at the intermediate portion 11A is 100, that at both end portions 11B, 11B is 12.
It is set to be 0. The second heater 12
Its axial heat generation distribution is determined to have an inverse relationship to that of the heater 11, and as shown in FIG.
The value of 2B is set to 80. Also,
As shown in FIG. 4, on the main body side of the image forming apparatus, there is a size detector 30 that detects the size (width direction size) of the transfer paper passing through the fixing device, and when continuously forming images on the transfer paper P. , a sheet number detector 31 that detects the number of sheets of transfer paper P to be continuously processed, and a first and second heater 11 based on signals from a size detector 30, a sheet number detector 31, and a thermistor 21.
, 12 is provided. Note that the heater control section 32 may be provided within the fixing device 1. The operation of the heater control section 32 will be explained below with reference to FIGS. 5 and 6. Furthermore, Figure 5 shows a small-sized transfer paper P.
, FIG. 6 relates to a full-size transfer paper P. When the main switch of the image forming apparatus is turned on, the first heater 11 of the fixing roller 10 is turned on as shown in FIGS. 5 and 6.
Power is supplied only to the first heater 11, and heating (warming up) of the fixing roller 10 is started by the first heater 11. In this case, the amount of heat generated at both end portions 11B, 11B of the first heater 11 is larger than that at the intermediate portion 11A. , 14, etc., and the temperature of the fixing portion 10a of the fixing roller 10 is uniformly raised in the axial direction by the first heater 11. When the thermistor detects that the temperature of the fixing roller 10 has reached a predetermined fixing temperature,
The fixing roller 10 is in a standby state as shown in FIGS. 5 and 6, and thereafter the first heater 11 is controlled to be turned ON/OFF by a signal from the thermistor 21. Next, the copy start key to start image forming work is turned on.
Then, a toner image is formed on the transfer paper P on the image forming apparatus main body side, and this is fixed by the fixing device 1. In this case, a signal of the width direction size of the transfer paper P from the size detector 30, and continuous transfer paper P from the sheet number detector 31
A signal indicating the number of images to be formed is transmitted to the heater control section 32. Here, a small size transfer paper P is selected, and the transfer paper P
In the case where images are formed continuously, the fixing roller 10 is initially
The fixing temperature is maintained at a predetermined temperature by the operation, but when the number of continuous fixing sheets exceeds a predetermined number n, the temperature is lowered by the thermistor 21 at the middle part of the fixing roller 10 which has a large amount of heat dissipated through the transfer paper P. is detected and controlled to maintain a predetermined fixing temperature), the temperature at both ends of the fixing roller 10, which has a small amount of heat dissipation, increases abnormally.
This will have an adverse effect on various parts within the fixing device 1. Therefore, when the number of consecutively fixed sheets of small-sized transfer paper P exceeds n sheets, as shown in FIG.
Switch to In the second heater 12, the amount of heat generated at the intermediate portion 12A is larger than that at both end portions 12B, 12B, and the temperature of the intermediate portion of the fixing roller 10 is controlled via the thermistor 21, etc., so that the temperature of the fixing roller 10 is controlled. If ON/OFF control is performed via this second heater 12, the temperature at both ends of the fixing roller 10 will gradually decrease even if a small-sized transfer paper P is continuously fixed. The temperature becomes uniform along its axis. Note that when the image formation (fixing) work on the small-sized transfer paper P is completed and the fixing device 1 enters the standby state, the fixing roller 10 is activated via the heater control section 32.
Heating is switched from the second heater 12 to the first heater 11 again. Also, full size (the size in the width direction is approximately equal to the length L2 of the fixing section 10a of the fixing roller 10, specifically when A3 or A4 size paper is fed horizontally or when using LEDGER size paper) ) is selected and when images are to be continuously formed on the transfer paper P, the fixing roller 10 is moved as shown in FIG.
is heated only by the ON/OFF operation of the first heater 11, and the second heater 12 remains in the OFF state and is not used. This is because the amount of heat dissipated in the axial direction of the fixing roller 10 via the transfer paper P is approximately equal, so the fixing roller 10
This is because an abnormally high temperature does not occur at 0. As described above, the two first and second heaters 11 and 12 having different heat distributions in the axial direction are attached to the fixing roller 10, and the first heater 11 is normally used to move the fixing roller 10 in the axial direction. In addition, when a predetermined amount or more of images are to be continuously formed on a small-sized transfer paper P, the heat source is switched from the first heater 11 to the second heater 12, Since the fixing roller 10 is designed to prevent abnormal heating on the end side of the fixing roller 10, even if the amount of heat dissipated on the end side is larger than that in the middle part, there is also a part where the transfer paper P is not passed. Even when the fixing roller 10 is heated, its axial temperature is kept substantially uniform, and the fixing roller 10 does not cause fixing problems, and the supporting parts 10b, 10b, etc. of the fixing roller 10 are not damaged by heat. Next, the second aspect of the present invention
An example will be described with reference to FIGS. 1, 7, and 8. Furthermore, the first
Components having the same functions as those in the embodiment are designated by the same reference numerals, and the description thereof will be omitted. In the fixing device according to the first embodiment, when using small size or full size transfer paper P of the same paper quality, the temperature distribution in the axial direction of the fixing roller 10 is kept substantially uniform, but the paper quality is different. Therefore, when using transfer paper P with different heat absorption amounts or intermediate size transfer paper P, the switching timing of the first heater 11 and the second heater 12 is different, making it difficult to precisely control the temperature in the axial direction of the fixing roller 10. Therefore, in this embodiment, two thermistors are used to detect the temperature of the fixing roller 10.
As shown in FIG.
It is arranged at the end of the fixing unit 10a (the part where the transfer paper P is least likely to pass), and detects the temperature not only at the middle part of the fixing roller 10 but also at the end part, and detects the temperature of the axis of the fixing roller 10. The directional temperature is controlled uniformly regardless of the quality or size of the transfer paper P. Here, also in this embodiment, it is assumed that the transfer paper P is positioned at the center of the fixing roller 10 (center reference), and the first and second heaters 11 and 12 are arranged on the same axis as in the first embodiment. It is assumed that there is a directional calorific value distribution. Further, as shown in FIG. 7, only the temperature signals from the first and second thermistors 40 and 41 are transmitted to the heater control section 32', and the heater control section 32' controls the first and second heaters. It is assumed that 11 and 12 are switched and controlled. The operation of the heater control section 32' will be explained below with reference to FIG. Note that the fixing roller 10 has a predetermined fixing temperature T.
o, the lower limit temperature T that does not cause any inconvenience to the fixing work.
1 and an upper limit temperature Th that does not cause any inconvenience to the fixing operation or equipment. When the main switch of the image forming apparatus is turned on, power is supplied only to the first heater 11 of the fixing roller 10.
Warm-up of the fixing roller 10 is started by this step. The fixing roller 10 is heated while its temperature is detected by the first thermistor 40.
detects the fixing temperature To, the fixing roller 10 goes into standby state, and then the first heater 1 turns ON/OFF.
controlled. Next, when the copy start key is turned on, a toner image is formed on the transfer paper P, and this is transferred to the fixing device 1.
However, small size or intermediate size transfer paper P
In this case, when images are continuously formed on the transfer paper P, the temperature of the intermediate portion of the fixing roller P is detected by the first thermistor 40, and the temperature is controlled so as to become the fixing temperature To. The temperature on the end side of the fixing roller 10 detected at 1 increases as indicated by A in the figure. When the second thermistor 41 detects that the end temperature has reached the upper limit Th as indicated by B in the figure, the heater control section 32' controls the heating of the fixing roller 10 to the first
The heater 11 is switched to the second heater 12, and the amount of heating at both ends of the fixing roller 10 is reduced compared to the middle part. After that, if images are continuously formed on small-sized or intermediate-sized transfer paper P, the fixing roller 1
0 is detected by the first thermistor 40, and the temperature there is controlled to become the fixing temperature To, so the temperature at the end of the fixing roller 10 decreases as shown by C in the figure. When the second thermistor 41 detects that the temperature on the end side has reached the lower limit Tl, as indicated by D in the figure, the heater control section 32' controls the heating of the fixing roller 10 by switching the heating of the fixing roller 10 to the second heater. 12 to the first heater 11
, and the amount of heating at both ends of the fixing roller 10 is increased compared to the middle part. Repeat this process below. As described above, the temperature of the fixing roller 10 is controlled by the first and second thermistors 4.
Detected at 0 and 41, the first and second heaters 11 and 12 are turned on.
/OFF control is performed based on the temperature detected by the first thermistor 40, and switching between the first heater 11 and the second heater 12 is performed based on the temperature detected by the second thermistor 41. Regardless of the size and quality of the paper P, the temperature distribution in the longitudinal direction of the fixing roller 10 can be maintained at a uniform temperature suitable for fixing, and the same effects as in the first embodiment can be obtained. Here, in both the first and second embodiments, the positioning of the transfer paper P with respect to the fixing roller 10 was performed based on the center reference, but even in the case of one side reference, the axial direction of the first and second heaters 11 and 12 Adjusting the heat distribution to this, the first and second heaters 11,1
Of course, if 2 is controlled in the same way, the same effect can be obtained. In addition, in both the first and second embodiments, the heat source inside the fixing roller 10 is replaced by two first and second heaters 11.
, 12 is not limited thereto, and a plurality of heaters generating different amounts of heat in the axial direction can be connected to the fixing roller 10.
Of course, it is also possible to provide an optimal one for the size of the transfer paper P, etc., as necessary. Furthermore, it goes without saying that the present invention is applicable even when the pressure roller 20 includes a heat source.

Effects of the Invention As is clear from the above description, according to the present invention, the heat source in the fixing roller is provided with a plurality of heat sources having different calorific value distributions along the axial direction of the fixing roller, and one of which is selectively used. The fuser roller is composed of a rod-shaped heating element, and if a temperature abnormality appears on the fuser roller, this heating element is switched to use, so the surface temperature of the fuser roller can be maintained uniformly along its axis. becomes. Therefore,
With this fixing roller, the toner image on the transfer paper is reliably fixed, and the bearing portion of the fixing roller is not damaged by heat.

[Brief explanation of the drawing]

FIG. 1 is a sectional view of a fixing roller of a fixing device according to a first embodiment.

FIG. 2 is a sectional view of the fixing device.

FIG. 3 is a diagram showing the distribution of heat generated in the axial direction of the first and second heaters of the fixing roller of the fixing device.

FIG. 4 is a control block diagram for explaining switching control of the first and second heaters of the fixing roller of the fixing device.

FIG. 5 is a diagram for explaining switching control of the first and second heaters of the fixing roller of the fixing device.

FIG. 6 is a diagram for explaining switching control of the first and second heaters of the fixing roller of the fixing device.

FIG. 7: The first fixing roller of the fixing device according to the second embodiment.
FIG. 2 is a control block diagram for explaining switching control of the second heater.

FIG. 8 is a diagram for explaining switching control of the first and second heaters of the fixing roller of the fixing device.

FIG. 9 is a cross-sectional view of a fixing device for explaining the prior art.

FIG. 10 is a sectional view of a fixing roller of the fixing device.

[Explanation of symbols]

10 Fixing roller 11 First heater (heating element) 12
Second heater (heating element) 20
pressure roller

Claims (2)

[Claims] 1. A fixing roller that has a heat source inside and rotates; a pressure roller that rotates while being in pressure contact with the fixing roller;
A fixing device comprising a detection means for detecting the surface temperature of the fixing roller, and a control means for controlling the heat source according to a signal from the detection means to control the surface temperature of the fixing roller to a predetermined temperature. The heating element is composed of a plurality of rod-shaped heating elements, each of which has a different heat distribution along the axial direction of the roller, and one of which is selectively used. A fixing device characterized in that the fixing device is provided with a function of switching and using the heating element. 2. A fixing roller that has a heat source inside and rotates; a pressure roller that rotates while being in pressure contact with the fixing roller;
A fixing device comprising a detection means for detecting the surface temperature of the fixing roller, and a control means for controlling the heat source according to a signal from the detection means to control the surface temperature of the fixing roller to a predetermined temperature. It is composed of a plurality of rod-shaped heating elements, each of which has a different heat generation distribution along the axial direction of the roller, and one of which is selectively used, and the detection means is a first one disposed in the normal paper passing area of the fixing roller. and a second detection means disposed in an area where transfer paper is least likely to pass through, and controls the heating element based on the temperature signal from the first detection means. A fixing device characterized in that said control means is provided with a function of switching and using a heating element based on an upper limit value and a lower limit value of a temperature signal from a detection means.