JPH07114294A - Fixing device - Google Patents

Abstract

PURPOSE:To provide a fixing device for preventing a temperature from rising at a non-paper passing part and also preventing a voltage from instanteneously and drastically dropping even in the case a high calorific power heater is used. CONSTITUTION:Two heaters 10A and 10B whose light distribution in a longitudinal direction of a fixing roller 1 constituted of a low light distribution area, a rise-up area, a high light distribution area and a peak area are arranged back to back so that one rise-up area may be laid over the other one. and thermistors 9A and 9B are installed near respective peak areas, and each heater is controlled so that the temperature difference between each detecting part may become within a prescribed value based on the temperature detected by the thermistors 9A and 9B.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a fixing device using a heat fixing system in an image forming apparatus.

[0002]

2. Description of the Related Art Conventionally, a fixing device used in an image forming apparatus which transfers a toner image onto a recording material and heat-fixes the toner image to obtain a permanent image has a structure as shown in FIG.

In FIG. 7, 101 is a fixing roller,
PFA, PTF on core metal 103 such as aluminum or iron
A releasable resin layer 104 such as E is provided, and the inside is heated by the heater 110. The surface temperature of the fixing roller 101 is detected by a temperature detecting element 109 that is in contact with the fixing roller 101, and is controlled to a predetermined temperature by adiabatically operating the heater 109 by a temperature control circuit (not shown). It

On the other hand, 102 is a pressure roller which rotates in pressure contact with the fixing roller 101. A sponge layer 107 having heat resistance and low hardness is provided on a metal core bar 106 such as aluminum or iron. It has a structure having a coating layer 108 made of a resin having a high releasing property such as PFA on the surface thereof.

A recording material 113 carrying a toner image 112
Is guided to the nip portion between the fixing roller 101 and the pressure roller 102 by the inlet guide 114, and is heated and pressed to be fixed. At this time, as a method of conveying the recording material 113, as shown in FIG.
3 is a so-called center reference method in which conveyance is performed with reference to the central portion as viewed from the traveling direction, and as shown in FIG. There are two types of transportation methods.

Among these, in the case of paper passing by the central reference, if a temperature detecting element is installed in the non-paper passing portion of the fixing roller 101, when a small-sized recording material is passed, the paper passing portion and the non-paper passing portion If the temperature difference between the parts becomes large and the temperature of the paper passing part cannot be detected accurately, or if the temperature detection element is a safety device such as a thermoswitch, the temperature rise at the edge is too large and the wire is erroneously disconnected. Inconvenience occurs. For this reason, the temperature detecting element has to be arranged near the center, and as a result, the fixing roller may be contaminated or scratched at the contact portion due to durability, toner fluffing, and the like, and the image may be significantly deteriorated.

On the other hand, in the case of the one-sided reference, if the temperature detecting element is installed in the non-paper-passing portion on the paper-passing reference side, the non-paper-passing portion and the paper-passing portion are close to each other, and the temperature is more accurate than in the case of the two-side reference. Not only can detection be performed, lateral registration is also easy, and since the temperature detection element contact portion can be arranged in the non-image area, image contamination due to fusing roller contamination and the like can be prevented. There is.

[0008]

However, according to the above-mentioned conventional example, in the one-sided reference system, the recording material of a large size or a small size is passed at the same reference end, so that the recording material of a small size is used. Then, the carry-out amount of heat in the non-sheet passing portion and the sheet passing portion on the opposite side with respect to the sheet passing standard greatly differ. At this time, in order to prevent damage to the fixing device due to a significant temperature rise in the non-sheet passing portion, the fixing roller 1
The heat capacity of No. 01 has to be increased, which causes the core thickness of the fixing roller to be unnecessarily thick, resulting in a long warm-up time and an increase in the cost of the fixing roller. there were.

Further, in both the central-referenced fixing device and the one-sided fixing device, as the paper feeding speed is increased, the heater 1
If the heat generation amount of 09 is not increased, the amount of heat taken out by the recording material 113 cannot be compensated. However, in the halogen heater mainly used as the conventional heater 109, the rush current at the time of lighting is higher than that in the steady state. Since it is extremely large, for example, when a halogen heater of about 700 W is turned on and off by a household power source, there is a problem that an instantaneous voltage drop occurs in the same power source line. The adverse effect of such a voltage drop is generally known to occur when a CRT image is momentarily distorted when a personal computer or the like is connected in the same line. There is also concern about the effects of malfunctions on the.

The present invention solves the above problems and does not cause a temperature rise in the non-sheet passing portion, and does not cause a large voltage drop instantaneously even when a heater having a large heat generation amount is used. To provide.

[0011]

According to the present invention, the above-mentioned object is provided with a pair of rollers, a fixing roller and a pressure roller, and a heating means which is disposed inside the roller and generates heat when energized. In a fixing device for fixing the unfixed developer image on the recording material by sandwiching the recording material carrying the developer image on the surface with the rollers and conveying the recording material while applying heat and pressure. Two heating means are provided in the roller, and the light distribution of each heating means is at least a peak area, and a high light distribution area and a low light distribution area which are continuous with the light distribution area of the recording material. , It is formed from the rising area from the low light distribution area to the high light distribution area, the peak area of one heating means is provided in the paper passing area near the end, and the peak area of the other heating means is on the opposite side. Provided near the end of the part of the rising area It is achieved by providing so as to overlap.

[0012]

According to the present invention, the respective peak areas are set at both ends of the fixing roller, and two rising areas from the low light distribution area to the high light distribution area which are continuous with the peak area are overlapped so as to overlap each other. Since the heating means is provided, each heating means is independently driven to provide an appropriate temperature environment according to the operating condition of the fixing device and the size of the recording material. First,
By providing the peak region of each heating means in the vicinity of the end of the fixing roller, the temperature drop due to heat release at the end of the fixing roller that has an opening and is in contact with the support member having a large heat capacity is compensated. Next, both heating means are arranged so that the rising areas from the low light distribution area to the high light distribution area overlap with each other, and prevent the temperature rise in the central portion where the heat emission is small. In addition, each heating means has a distribution in which a high light distribution area and a low light distribution area are combined, and one high light distribution area corresponds to the other low light distribution area. By adjusting the ratio appropriately, while preventing the temperature rise of the non-sheet passing area,
To realize an appropriate temperature distribution on the fixing roller according to the width of the recording material. Furthermore, each heating means can be independently energized, and by staggering the energization start timing of each other, an instantaneous increase in voltage drop is prevented.

[0013]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

<First Embodiment> First, a first embodiment of the present invention will be described with reference to FIGS. FIG. 2 is a diagram showing a schematic configuration of an image forming apparatus to which the fixing device of the present invention can be applied. In FIG. 2, reference numeral 21 denotes a photosensitive drum which is a latent image carrier and is rotatably arranged in the direction of the arrow. The surface of the photosensitive drum 21 is uniformly charged to a predetermined positive or negative potential by a primary charger 22 arranged above the photosensitive drum 21, and the charged surface is irradiated with a laser beam 23. By exposure, an electrostatic latent image having a pattern corresponding to the original image is sequentially formed on the surface of the photosensitive drum 21. Then, the electrostatic latent image formed on the surface of the photosensitive drum 21 is visualized as a toner image by the developing device 24 arranged on the side of the photosensitive drum 21, and is transferred to a portion facing the transfer charging roller 25. Be transported. On the other hand, cassette 2
The recording material in 8 is taken out of the cassette 28 one by one by the pickup roller 27 and fed by the paper feed roller 26. Then, the toner is introduced into the transfer portion between the photosensitive drum 21 and the transfer charging roller 25 at a predetermined timing by the registration roller 29, and comes into contact with the photosensitive drum 21 by receiving the transfer corona, so that the toner on the surface of the photosensitive drum 21 becomes visible. The images are sequentially transferred to the recording material. At this time, toner that has not been transferred remains on the surface of the photosensitive drum 21, but this residual toner is removed by the cleaning device 34. Then, as described above, the recording material that has passed through the transfer portion is guided to the fixing device via the conveyance belt 35 and the fixing inlet guide 14.

In this fixing device, as shown in FIG. 1A, a fixing roller 1 and a pressure roller 2 are arranged so as to be in pressure contact with each other, and the recording material on which the toner image is transferred is transferred to both rollers. It is designed to be pinched and transported by. This fixing roller 1 is provided with a releasable resin layer 4 such as PFA or PTFE on a thin metal cored bar 3, while the pressure roller 2 is provided on a metal cored bar 6 such as aluminum or iron. A sponge layer 7 having heat resistance and low hardness is provided, and P is formed on the surface of the sponge layer 7.
It has a structure having a coating layer 8 made of a resin having a high releasability such as FA.

Since the thickness of the core metal 3 of the fixing roller 1 determines the heat capacity of the fixing roller 1, it is a factor that determines the warm-up time of the fixing roller 1. Therefore, in order to reduce the warm-up time, it is preferable that the cored bar 3 is made of a metal material having high strength and high thermal conductivity with the thinnest possible thickness. The wall thickness depends on the core metal diameter and the set temperature, but is 1.5 mm or less, preferably 1 m.
It is better to be less than m.

Two halogen heaters 10A and 10B are provided inside the fixing roller 1 to heat the fixing roller 1. The heater 10A,
10B, as shown in FIG.
1, 32 can switch the conduction state with the AC100V input 33.
Reference numerals 1 and 32 are composed of triacs, SSRs (solid state relays), etc., and C as a temperature control circuit.
It is controlled by the PU 30.

Then, on the outer peripheral portion of the fixing roller 1, a portion corresponding to the vicinity of the peak area of the heaters 10A and 10B is provided.
Thermistors 9A and 9B as temperature detecting elements are provided respectively, and the surface temperature T _A at both ends of the fixing roller 1 is
It is configured to detect T _B. This temperature T _A , T
_B is input to the CPU 30 as shown in FIG. 2, and the switch circuits 31 and 32 are driven by the temperature control described later based on the temperatures T _A and T _B to drive the fixing roller 1. Is maintained at a predetermined temperature.

The axial light distribution of the heaters 10A and 10B in the fixing device of this embodiment as described above is shown in FIG. 1 (b).
The peak positions of the heaters are set near the reference end and the maximum paper feed end, respectively. The thermistors 9A and 9B are provided in a non-image area, preferably a non-paper passing area, in order to avoid the influence of scratches and the like due to durability. By providing the peaks in the heaters 10A and 10B in this way,
It is possible to prevent thermal sagging at both ends of the fixing roller 1. Further, a high light distribution region H region and a low light distribution region L region that are continuous with the peak, and a rising region that connects these regions are provided. Similarly, the light distribution of the heater 10B is H, in the opposite direction to the heater 10A.
L, the rising region is provided, the temperature detecting element 9B is provided near the peak, and the rising regions of the heaters 10A and 10B are arranged to partially overlap. By distributing the light in this way, the connection between the rising regions of the two heaters 10A and 10B can be made smooth without any peaks and valleys. If H and H or L and L of the heaters 10A and 10B are overlapped with each other, excessive temperature rise or temperature drop is likely to occur.

Next, a method of driving the heaters 10A and 10B will be described with reference to the flowchart of FIG. First, when the power of the printer is turned on, the switch circuit 31 is first turned on by the control signal of the CPU 30, and then the switch circuit 32 is turned on after about 0.2 seconds, and the AC10
The 0V input 33 is applied to the heater 10A and then 10B to heat the fixing roller 1. And the thermistor 9A
Thus, the surface temperature T _A of the fixing roller 1 is measured. Here, when T _A reaches a predetermined temperature T ₀ , the printer is ready to print and both heaters 10A and 10B are turned on.
FF is performed and a ready signal is output. When T <T ₀ , the heater 10A and 10B signals are kept in the ON state, so that both 10A and 10B are fully lit. This ready state continues according to the print command until printing is started, and the surface temperature of the fixing roller 1 is set to the heaters 10A and 10B.
It is maintained at about T ₀ by turning on and off.

Here, the lighting timing of each of the heaters 10A and 10B will be described in detail. In this embodiment, the lighting is basically performed by repeating the lighting cycle as shown in FIG. If the heaters 10A and 10B are alternately turned on and off in this manner, the heaters 10A and 10B
Since 10B does not turn on at the same time, it is possible to prevent power supply fluctuation due to inrush current. In the present embodiment, the lighting cycle t ₀ , the lighting time t _{1 of} the heater 10A, the time t ₂ from the lighting start of the heater 10A to the lighting start of the heater 10B, and the lighting time t ₃ of the heater 10B are varied as shown in the following table. change,
The heater is lit in a plurality of lighting modes.

[0022]

[Table 1]

As described above, in this embodiment, seven modes S =
Printing is performed by setting 1 to 7. First, at the start of printing, the mode S is set to 4 as shown in the flowchart of FIG. 3, the heaters 10A and 10B are lit at the same duty, that is, 5/6 of all lighting, and printing is performed.

During this printing, the temperature T of the thermistor 9A
_Since the temperature of the fixing roller 1 is adjusted so that _A becomes a predetermined temperature T ₁ , T _A becomes T _{1 as} shown in the flowchart of FIG.
In the following cases, the lighting in mode S = 4 is continued. Then, when T _A ≧ T ₁ , both heaters 10A and 10B are turned off, and the following lighting mode is reviewed.
It should be noted that the temperature T _A slightly rises due to overshoot for some time even after the heaters 10A and 10B are thus turned off.
_A <T ₁ .

First, when reviewing the lighting mode, the temperatures of the thermistors 9A and 9B are compared to determine whether or not the temperature difference between the thermistors 9A and 9B is larger than a predetermined value DT.
Next, when this temperature difference is less than the predetermined value DT, the mode S = 4 remains, but when it exceeds the predetermined value DT, the lighting mode is switched to perform control so that the difference is reduced. . Specifically, when DT is set to, for example, 10 ° C., and the detected temperature of the thermistor 9B is higher than that of the thermistor 9A by 10 ° C. or more, the mode is gradually shifted from 4 → 5 → 6 → 7, thereby heating the heater 10B. The amount of heat generation is relatively reduced to reduce the temperature difference between the thermistors 9A and 9B. Conversely, when the temperature detected by the thermistor 9A is higher than that of the thermistor 9B by 10 ° C. or more, the mode is set to 4
→ 3 → 2 → 1 should be gradually shifted. In either case, when | T _A −T _B | ≦ DT, the mode is returned to 4.

In this way, when the duty control of the heaters 10A and 10B is performed by switching the modes, the following effects can be obtained in addition to the warm-up reduction due to the usage of the thin fixing roller.

1) If small size paper (eg, envelope) is continuously fed along the reference end side, the temperature of the non-sheet passing portion rises, but as described above, the difference between the thermistors 9A and 9B becomes less than a predetermined value. By performing the duty control on the paper feed zone, it is possible to prevent the temperature rise in the non-paper feed section without placing a thermistor in the paper feed area. 2) Since the ON / OFF timings of the heaters 10A and 10B can be shifted, it is possible to prevent adverse effects on the power supply line due to the inrush current to the heaters. 3) Since the ON / OFF duty of the heaters 10A and 10B can be managed, power consumption management is easy. Particularly, if t ₁ + t ₃ ≦ t ₀ in Table 1, the heaters 10A and 10B are
Since the simultaneous lighting of is avoided, the maximum rated power during printer operation can be greatly reduced. 4) By setting a plurality of modes, the temperature distribution is not excessively corrected by duty control, and good control can be performed. 5) Correction by duty switching control is also effective against uneven temperature distribution due to variations in electric power with respect to the rated values of the heaters 10A and 10B, thickness of fixing roller, heat escape from end portions, and the like. Is. 6) By contacting the thermistors 9A and 9B with the paper non-passage area of the fixing roller, even if the thermistor contact portion is scratched due to durability, there is no risk of contaminating the image.

(Experimental Example) Even if the core metal 3 of the fixing roller 1 is made of carbon steel having a thickness of 0.7 mm, the surface of the core metal 3 has a thickness of 50 mm.
A fixing roller having an outer diameter of 35 mm and a length of 240 mm was formed by covering the PFA tube 4 of μm. Then, the halogen heaters 10A and 10B are both heaters rated at 400 W, and each has a light distribution distribution as shown in FIG.

As the pressure roller 2, a foamed silicone rubber layer 7 having a thickness of 7 mm is provided on the surface of a stainless steel core 6, and a PFA tube having a thickness of 30 μm is coated on the surface of the pressure roller 2 to have the same outer diameter as that of the fixing roller 1. Then, a pressure roller having substantially the same length was used.

The pressure roller 2 has a hardness of Asker-
It was 40 degrees at C. The fixing roller 1 and the pressure roller 2 were brought into contact with each other at a total pressure of 10 kgf to form a nip of about 5 mm.

The recording material 13 is the maximum size paper A
4 sizes are conveyed vertically and the minimum size is about 100 width.
It was decided to convey the mm envelope along the reference edge. At this time, the traveling speed of the recording material was 150 mm / sec. Under the above conditions, T0 = 160 ° C. and T1 = 190 described above.
Printing was performed according to the timing chart of FIG.

As a result, first, since the core metal of the fixing roller 1 can be thinned to 0.7 mm, it takes about 15 to 20 seconds, which is a very short time, from the power-on of the printer to the ready state. Became possible. Next, when 100 sheets of A4 size were continuously printed, as shown in FIG. 5A, the surface temperature of the fixing roller 1 was maintained at about 190 ° C. over the entire area even at the 100th sheet, which was excellent. Fixability was obtained. Next, when 100 envelopes were continuously printed in the same manner, a slight temperature decrease was observed in the non-sheet passing portion as shown in FIG. 5B, but a stable surface temperature should be maintained over almost the entire area. I was able to.

Further, since the halogen heaters 10A and 10B can be turned on by shifting the lighting timings from each other through the above-described operation, the inrush current at each lighting time can be suppressed to a small value, and the steady lighting is performed. In the state, the heat quantity of 400 W × 2 = 800 W can be obtained. For this reason, the amount of heat is the same as that of a heater of 800 W x 1
There was no bad influence such as voltage drop on the power supply line at N / OFF. Furthermore, the thermistor 9
By providing A and 9B in the non-sheet passing area, even if the surface of the fixing roller 1 is scratched due to durability, the image is not affected.

<Second Embodiment> Next, a second embodiment of the present invention will be described with reference to FIG. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment, an example is shown in which the paper passing size is not known in advance. On the other hand, when the paper passing size is known in advance, if the lighting mode of the heaters 10A and 10B is set in consideration of this information, quicker and smoother control is possible. FIG. 6 shows the apparatus configuration at this time. In FIG. 6, the paper 1 is placed in the cassette 28.
A detection pin 36 that records the size of 3 is provided,
This information is input to the CPU 30 by the sensor 37. Tables 2 and 3 below show examples of the lighting mode settings for the paper size information obtained in this way.

[0036]

[Table 2]

[0037]

[Table 3]

Table 2 shows the paper sizes A to D in descending order of width.
4 groups, the coefficient α is given to each group, and the mode S of the flowchart described in the first embodiment is used.
By weighting the length of t ₃ at α with α, the ON duty of the heater B is reduced as the paper width becomes smaller. By doing this,
By passing the paper, it becomes easier to balance the heat between the reference end side where heat is easily taken and the non-reference end side where heat is hard to be taken, and the temperature control becomes easier. In addition, if the control is performed by multiplying α only while the recording material is passing through the fixing roller 1 and the mode setting of Table 1 is used without multiplying α when the paper is not passing, the front and rear rotation is performed. It is more preferable because both the temperature control during the interval and the temperature control during the sheet passing can be optimally performed.

<Third Embodiment> Next, a third embodiment of the present invention will be described. The same parts as those of the first embodiment are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment, the case where the temperature control of the mode S is performed at the same time as the start of printing has been described. However, by utilizing the performance of the thin fixing roller 1, the standby temperature T ₀ is sufficiently lowered to save energy. In such a case, the first printing time can be shortened by turning on all the heaters A and B until the first recording material reaches the fixing roller 1. Specifically, in the flowchart of FIG. 3, one of the heaters A and B is turned on at the same time as the printing is started, and after about 0.2 seconds, the other one of the heaters is turned on and the pre-rotation is performed to detect the temperature detected by the thermistor A. Is the predetermined temperature T
_When the temperature becomes ₂ , the temperature control is switched to the mode S, and then the temperature is adjusted so that the detected temperature T _A of the thermistor A becomes T ₁ .

(Experimental example) Standby temperature T ₀ = 100
° C., the pre-rotation (when full lighting) the target temperature T ₂ = 180 ° C., was subjected to experiments as the target temperature T ₁ = 190 ° C. at the time of printing, T _A = laser beam 2 in FIG. 2 at the timing of a T ₂
If the image writing by means of 3 is started, when the leading end of the recording material 13 reaches the fixing roller 1, the fixing roller 1
Surface temperature is about 190 ° C and the target temperature T _{1 for} printing
It was found that the temperature can be adjusted at 190 ° C. As described above, it is possible to prevent the first printing time from being unnecessarily extended by raising the temperature to T ₂ = 180 ° C. in all lighting.

[0042]

As described above, according to the present invention,
Two heating means having a peak portion, a high light distribution area, a rising area, and a low light distribution area are arranged in opposite directions so that a part of the rising areas of each of them overlap with each other. Even if a thin fixing roller having a small heat capacity is used, it is possible to prevent the temperature rise in the non-sheet passing portion. Also, extremely fast warm-up performance can be realized,
Moreover, by overlapping the rising regions of the heating means, it is possible to prevent excessive temperature rise and temperature drop in the vicinity of the center. In addition, by shifting the energization start time of each heating means, the inrush current during energization can be kept small, adverse effects on peripheral equipment can be prevented, and stable control is possible against various fluctuation factors such as rating variations of each heating means. It became possible to do.

[Brief description of drawings]

FIG. 1 is a diagram showing a schematic configuration of a device according to a first embodiment of the present invention.

FIG. 2 is a diagram showing a light distribution of a heater used in the apparatus shown in FIG.

3 is an example of a flowchart of temperature control in the apparatus of FIG.

FIG. 4 is a timing chart of temperature control in the apparatus of FIG.

5 is a diagram showing a surface temperature distribution of a fixing roller of the apparatus shown in FIG.

FIG. 6 is a diagram showing a schematic configuration of a device according to a second embodiment of the present invention.

FIG. 7 is a diagram showing a schematic configuration of a conventional fixing device.

FIG. 8 is a diagram for explaining a sheet passing standard in a conventional fixing device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Fixing roller 2 Pressure roller 9A, 9B Temperature detection element 10A, 10B Heater (heating means) 13 Recording material

Claims (4)

[Claims] 1. A recording material, comprising a pair of a fixing roller and a pressure roller, and a heating means disposed inside the roller to generate heat by energization, the recording material carrying an unfixed developer image on the surface thereof. In the fixing device for fixing the unfixed developer image on the recording material by nipping it with the sheet and transporting it while applying heat and pressure, two heating means are provided in the fixing roller. , The light distribution of each heating means is at least the peak area, the high light distribution area and the low light distribution area connected to the peak area, and the rising area from the low light distribution area to the high light distribution area in the paper passing area of the recording material. It is formed, the peak area of one heating means is provided in the vicinity of the end of the paper passing area, the peak area of the other heating means is provided in the vicinity of the opposite end, and a part of the rising area is provided. Fixing characterized by being provided so as to overlap apparatus. 2. The fixing device according to claim 1, wherein two temperature detecting elements are provided in the vicinity of respective peak regions of each heating means. 3. The divided energization is performed by repeating the energization for each heating unit such that the energization start time and the energization stop period become a predetermined ratio for each heating unit so that the energization start timing of each heating unit does not coincide with each other. The fixing device according to claim 1 or 2, further comprising means for controlling a heating means. 4. The means for controlling each heating means has a plurality of modes of divided energization, and is set so as to appropriately change the mode of divided energization based on the temperatures detected by the two temperature detecting elements. The fixing device according to claim 3.