JPS59123868A - System for controlling temperature of heat fixing roller - Google Patents

Abstract

PURPOSE:To prevent temp. drop at the time of multicopying, etc. and to prevent poor fixing by controlling temp. at T1 after the fixing roller has reached a temp. t2 higher than a normal set temp. t1. CONSTITUTION:When a thermistor 9 detects temp. t01 before reaching a set temp. t1, both rollers 1, 5 rotate, and then, the lower roller 5 rises in temp. rapidly, so the rise of temp. of the upper roller 1 becomes slow. Even when the roller 1 reaches t1, the supply of power to a heater 4 is not stopped, and when the thermistor 9 detects that it reaches a temp. t2, power supply to the heater 4 is stopped. At a time T2 after reaching a temp. t2, rotation of both rollers 1, 5 are stopped at the same time, and a temp. control circuit controls the temp. of the roller 1 at the temp. t1. In conclusion, the temp. control circuit first controls the temp. of the roller 1 at t2, and then, then, temp. control is carried out by changing over the set temp. to t1.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field The present invention relates to a heat fixing roller in a fixing unit of an electrophotographic copying machine or the like, which includes rollers pressed against each other, and particularly relates to temperature control of the rollers.

<Prior Art> In general, a heat fixing roller is composed of two rollers, an upper roller and an upper roller.Mainly, 1. The upper roller that comes into contact with the toner image transferred onto the copy paper is a heat roller that has a heater inside;
The lower roller is a pressure roller that is pressed against the heat roller. Normally, after the power is turned on for these two rollers, when the temperature at the temperature detection position of the upper roller reaches a predetermined temperature, the ready lamp will light to indicate that copying is possible, and printing will begin in this state. When the button is pressed, the drive motor rotates for the first time and is energized.

The heat fixing roller is constantly controlled at a temperature necessary to fix the toner image on the paper using a thermocouple, thermistor, or other sensor. The control temperature in this case is
There is only one point. This thermal stability varies. FIG. 1 shows an example of roller temperature control. When the power is turned on, the upper roller of the heat fixing roller is heated by the internal heater and gradually rises in temperature, and reaches the normal set temperature t1 after T1 time.

At this time, the power supply to the heater is cut off.

In the figure, the surface temperature of the roller further increases to t1' after T1 because it is heated by preheating of the heater. Thereafter, the roller is controlled to a temperature t1 by a temperature control circuit. In this way, from the time the power is turned on, the set temperature t1
Conventionally, it has been desired to shorten the waiting time T1 until reaching . Therefore, the above objective can be achieved by minimizing the heat capacity of the heat fixing roller.

On the other hand, by reducing the total power consumption of the entire copier,
Normally, the power consumption of the heater in the fixing roller tends to be kept low, especially in the case of medium-high speed machines, in order to reduce the power consumption to 5 Kw or less. Therefore, it was disadvantageous in terms of fixing properties during multi-copying. In other words, this is because the heater capacity used in the fixing section is limited. Further, even in low-speed machines, as the waiting time TI is shortened, the heat capacity of the rollers is reduced, which similarly makes it difficult to maintain temporary fixing performance during multi-copying.

FIG. 2 shows temperature changes of the upper and lower rollers during multi-copying in conventional temperature control. This figure is a characteristic diagram when the upper roller is provided with a heater and the lower roller is not provided with a heater. If multi-copying is started after T3 after the surface temperature of the rollers reaches the set temperature L1, both rollers will rotate. At this time, the upper roller not only loses heat from the paper passing through it, but also supplies heat to the lower roller. Therefore, while the temperature of the lower roller gradually increases, the surface temperature of the upper roller temporarily decreases to a value greater than the set temperature [1]. As a result, poor fixing of the toner image on the paper continues.

In order to prevent the above-mentioned fixing failure, it is possible to increase the pressing force of the upper and lower rollers. However, the roller surface is made of rubber or the like, which increases the compression set and may impede paper passing performance. It is also possible to prevent temporary fixing failure during multi-copying by increasing the set temperature 1>. In this case, PFA on the roller surface.

Considering the heat resistance of r'TFE, silicone rubber, etc., there is concern that their lifespans will be reduced. As a result, the original release properties, abrasion resistance, and abrasion resistance are significantly lowered, and the roller becomes useless as a fixing roller.

<Object of the Invention> In view of the conventional drawbacks, the present invention provides a temperature control method that can prevent fixing failure even during multi-copying.

<Example> FIG. 3 is a sectional view showing a heat fixing roller according to the present invention. In the figure, an upper roller 1 has a core metal 2 provided with a layer 3 coated with Teflon, for example, and further has a heater 4 inside. Further, the lower roller 5 is in pressure contact with the upper roller 1, and is constructed by covering a core bar 6 with a silicone rubber layer 7. This lower roller 5 is also provided with a heater 8 if necessary.

In the figure, reference numeral 9 denotes, for example, a thermistor for detecting the surface temperature of the upper roller l. Based on the temperature detection of the thermistor 9,
The surface temperature of the roller l is controlled by a control circuit (not shown).

An example of temperature control of the heat fixing roller of the present invention is shown in FIG. As shown in the figure, the thermistor 9 indicates the set temperature 1. The temperature to before reaching I.

If detected, both rollers 1 and 5 are rotated.

After this time ToH, the temperature of the lower roller 5 rises significantly. Therefore, the temperature increase rate on the upper roller 1 side is higher.

Thereafter, even if the temperature of the roller 1 reaches tl, the power supply to the heater 4 is not stopped and continues. Therefore, the temperature of the roller 1 further increases.

When the surface temperature of roller 1 reaches the set temperature t1, the rotational drive of rollers 1 and 5 is simultaneously stopped at time T2, and the temperature control circuit controls the temperature of roller 1 at the set temperature (, that is, temperature control The circuit controls the temperature of the roller 1 at t2, and then switches the temperature to the set temperature G at tl.

By controlling the temperature of the rollers as described above, the lower roller 5
The temperature of roller 1 can be raised to the required temperature in advance, and even when performing multi-copying, as shown in Figure 4,
The amount of Δt that falls below the set temperature t1 can be reduced. This makes it possible to quickly return the surface temperature of the roller 1 to the set temperature t1 and to prevent fixing failures.

An example of a failure is shown below.

In Figure 4, the upper roller has a core bar 2 with a wall thickness of 7 mm.
It is made of aluminum alloy 5056, and layer 3 is Teflon PF.
A, and the outer diameter was set to φ54.2 MIN. Then, the internal heater 4 is 80OW. Similarly to the roller, the lower roller 5 has a core metal 6 made of aluminum alloy, a silicone rubber layer 7 with a layer thickness of 4 mm, and a rubber hardness of 4.
0' was used. The lower roller 5 also has a power of 500 W.
heater 8 is used.

The upper and lower rollers 5 having the above structure are pressurized at 30 l (g, driven at a surface speed of 25.5 mm/s, the copying cycle time is 1.5 sec, and the temperature of the roller is t Q, , = I When the temperature reaches 80℃, the roller
Rotate 5. Also, "+ = 200℃, t2 = 2
Temperature control was performed by setting the temperature to 10°C.

In the above example, as a result of performing multi-copying of 100 sheets after reaching t2, the drop temperature ΔL from the set temperature t1 was 20°C. By the way, if a conventional temperature control method is implemented with a structure similar to that of this embodiment, the result of multi-copying 100 sheets Δt will be 3.
The temperature was 5°C.

As described above, it is clear that the temperature control method of the present invention reduces the temperature drop compared to the conventional method and is advantageous for fixing performance.

In this embodiment, the lower roller 5 is also provided with the heater 8, but
This was added to shorten the waiting time and is unrelated to the gist of the present invention. That is, the present invention is to control the temperature of the roller by switching the set temperatures t1 and t2 into two stages.

<Effects of the Invention> According to the temperature control method of the present invention, temperature control is performed at a temperature t2 which is higher than the normal set temperature 11, and after reaching temperature t2, temperature control is performed at the above set temperature. , temperature drop during multi-copying, etc. can be suppressed to a low level, and can greatly contribute to preventing fixing failures.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the relationship between roller temperature and time using conventional temperature control, Fig. 2 is a diagram showing temperature changes when performing multi-copying using conventional temperature control, and Fig. 3 is a diagram according to the present invention. FIG. 4 is a side sectional view showing an example of a heat fixing roller, and is a diagram showing temperature changes due to temperature control of the present invention. l: upper roller, 4: heater, 5: lower roller, 9: thermistor (temperature detection element), tl: normal set temperature,
[2; Second set temperature. Agent Patent Attorney Aihiko Fuku (and 2 others) g! glance at
r No. 1 1 7/ 醇目 r --- Figure 2

Claims (1)

[Claims] 1. In a thermal fixing roller composed of upper and lower rollers that are pressed against each other to fix a toner image formed on paper, the roller is heated at a second set temperature that is higher than the normal set temperature of the roller. A temperature control method for a heat fixing roller, characterized in that the temperature is controlled and, after reaching the second set temperature, the temperature of the roller is controlled at the normal set temperature.