JPS6367189B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heat roller fixing device, and more particularly to a heat roller fixing device in which a control sensing element is installed at the highest temperature portion of the heat roller.

There are many types of heat fixing methods for electrophotographic copying machines, such as a heater direct heating method, an oven method, and a roller fixing method.

However, the roller fixing method is superior in that it does not catch fire even if paper jams occur.
There is specification No. 3196766. ).

Although this roller fixing method is superior in the above points, compared to, for example, a heater direct heating method, it takes longer to start up the fixing process, that is, after the fuser is energized, the roller surface reaches a temperature that allows heat fixing. It has the disadvantage that it takes a long time. For this reason, many studies have been conducted to shorten the start-up time of the roller fixing system, but even with improved roller fixing devices, the start-up time still takes 2 to 5 minutes.

A second problem with roller fusing systems is accurate control of the heated roller surface temperature. In order to perform this control accurately, it is necessary to accurately follow slight temperature changes, and for this purpose it is necessary not only to select a temperature sensing element, but also to place the temperature sensing element in close contact with the surface of the thermal roller. is desirable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a heat roller fixing device that has a short rise time, controls the overshoot phenomenon on the surface of the heat roller, and enables accurate temperature control.

An example of a heat roller fixing device is shown in Figures 1 and 2.
This will be explained using figures. 1 is an upper roller, which is usually an aluminum roller with a wall thickness of 4 to 5 mm and whose surface is coated with 40 to 80 μm Teflon (trademark). 2 is an infrared lamp installed inside the roller. 3 is a lower roller for sandwiching the copy paper between it and the upper roller and passing it through;
It is usually a roller made of silicone rubber or coated with silicone rubber.

4 is a bearing that supports the rotating roller, and 5 and 6 are gears that rotate the upper roller and the lower roller.

A sensor 7 is located approximately in the center of the roller and close to its circumferential surface, and is a thermosensitive resistance element such as a thermocouple or a thermistor made of chromel, alumel, or the like. 8 is a cover to prevent wind from directly hitting the temperature sensor.

Shortening the startup time of the fixing device means increasing the capacity of the infrared lamp 2 and decreasing the heat capacity of the upper roller 1. However, if the method described above is adopted so that the rising time is about 1 minute, the temperature overshoot as described later will be extremely large, and the temperature at the end of the roller will be considerably lower than that at the center. It has been found that the distribution is no longer uniform and temperature control becomes very difficult. These causes are thought to be as follows.

Overshoot refers to a phenomenon in which the roller surface temperature, which begins to rise as electricity is applied to the upper roller 1 in FIG. 3, exceeds the control set temperature point A and reaches point B.

When the temperature sensing element 7 is in contact with the roller surface, when the roller surface temperature reaches point A, the temperature sensing element issues a control signal and activates the control circuit to cut off the power to the lamp 2. The surface temperature of the roller reaches point B, causing an overshoot phenomenon.

The cause of this is the temperature gradient between the lamp 2 and the surface of the upper roller 1, so by the time the temperature sensing element detects the surface temperature of the roller 1 and cuts off the electricity, the amount of heat inside the upper roller 1 has already increased considerably. This phenomenon appears more strongly as the capacity of the lamp 2 increases.

Moreover, the overshoot phenomenon is greater when the temperature sensing element is not in contact with the roller than in a configuration where the temperature sensing element is in contact with the roller.

Next, the reason why the surface temperature at both ends of the upper roller 1 is lower than that at the center is as shown in Fig. 2.
As shown in the cross-sectional view AA′, firstly, the light emitting part of the infrared lamp 9 does not reach the bearings 12 at both ends of the upper roller 1, and secondly, the bearings 12 have a large heat capacity and It may be mentioned that there are bearings 4 and gears 5 which are thermally coupled, such as other gears or panels. This phenomenon in which the surface temperature at both ends of the upper roller 1 is lower than that at the center is particularly likely to occur in a fixing device with a short startup time. That is, by reducing the thickness of the upper roller 1, the conduction of heat in the longitudinal direction of the roller becomes poor, and by shortening the startup time of the fixing device, the bearing 4 and gear 5 are This is because the fixing device reaches the usable state before being sufficiently heated, and thus the fixing device reaches the usable state before the heat has sufficiently diffused to the end portion of the roller 1.

In general, if the fixing temperature is too low, an under-fixing (or insufficient fixing) phenomenon occurs, in which the toner image is easily removed from the support, and if the fixing temperature is too high, an offset phenomenon occurs, in which the toner image is easily removed. It is well known that a phenomenon occurs in which a part of the image is fused from the support to the upper roller and, after one revolution, the image is transferred to another part of the support.

Therefore, even in a fixing device with a short start-up time, it is extremely problematic in practice unless the above-mentioned overshoot and non-uniformity of temperature distribution on the roller surface are improved.

Upper roller outer diameter 40mm, wall thickness 4mm, capacity 800W
The configuration of the conventional fixing device, in which the infrared lamp and temperature control detection element are located in the center of the roller, has been slightly changed, the upper roller has a thickness of 2.7 mm, and the capacity of the infrared lamp has been increased to 1300W. If you use a lamp that makes the light distribution uniform on the roller surface during normal operation and has the highest temperature between the center and the edge when starting up, you can raise the roller surface temperature from room temperature (18℃) to 180℃. It only takes 1 minute to get up.

However, in this case, even if a temperature control sensing element (chromel, alumel, etc.) was used in contact with the roller surface, the overshoot at the center of the roller reached 23°C (the highest temperature part would be even higher). Needless to say.) Furthermore, if a temperature control sensing element is placed 1mm above the roller surface, the temperature will reach approximately 40°C.
An overshoot occurred.

As a result of study, the present inventor found that the above-mentioned problem was solved by a roller with a built-in heater for fixing a toner image made of a thermoplastic resin on an image support, and a control sensor for controlling the surface temperature of the roller. In a thermal roller fixing device that has an element and a control circuit, after the heater is energized, when the roller surface temperature reaches the set temperature, the highest temperature distribution in the axial direction of the roller is at the midpoint between the end and center of the roller. It has been found that the problem can be solved by using a heat roller fixing device in which a control detecting element is installed in the highest temperature part at the time of rising.

Hereinafter, the present invention will be explained with reference to the drawings.

First, as shown in FIG. 4, the light distribution of the infrared lamp on the roller was designed so that the roller surface temperature at the time of rising was highest in the middle between the center of the roller and the end of the roller.

In the present invention, even though the light distribution of the lamp is higher at the roller ends, the heat escapes to the roller ends more, so the temperature distribution on the roller surface has a maximum temperature at the center of the roller than at the roller ends. When a temperature control sensing element was installed at the maximum temperature part of the surface of the heat roller, overshoot could be suppressed extremely well as shown in FIG. In other words, in Fig. 6, point f on the roller surface is g
Since the light distribution of the infrared lamp is higher than at point e, and there is less heat escaping to the roller end than at point e, the set control temperature is reached faster than other parts, and the temperature control detection element is activated to turn off the power to the infrared lamp. . Next, the overshoot begins, and the fifth
As shown in the figure, in the present invention, f of the roller surface is
When the part reaches the point C, the part g is in a low state such as the temperature D (the same goes for the part e and the part f).
Heat is diffused to e, and overshoot is suppressed. According to the inventor's measurements, points e, g, and i, where the roller surface temperature is low, reach the set temperature within a few seconds after cutting off the current, and in the subsequent continuous control, points e, f, g, h, and i All parts of
Temperature changes began to show consistent movements.
This is because the initial heat absorption occurs at both the roller center and the roller ends, and when the roller is warmed up, it is estimated that the temperature will be close to the maximum temperatures f and h at the time of rising.

On the other hand, if the temperature control sensing element is installed at the center of the roller, the temperature rise at the center of the roller is slow, so when the set temperature is detected and the infrared lamp is turned off, the end of the roller will be the same as the center of the roller. , the temperature has almost reached the set temperature, but the roller f
Since the areas indicated by and h reach a higher temperature than the roller ends and the roller center, the overshoot is large at any part of the roller.

Therefore, in order to prevent overshoot in the temperature control detection element in the center, the control circuit must be designed in such a way that the infrared lamp is turned off at a temperature lower than the set temperature, and is controlled at the set temperature in steady state. It must be heavily configured. On the other hand, in a fixing device that rises quickly, if a temperature control sensing element is installed in the center of the roller, the temperature at the end of the roller during rise will be insufficient, causing a problem as described above. In addition, we have gone one step further and set the temperature at the center of the roller to the maximum while minimizing the temperature gradient (temperature drop) toward the ends of the roller. Even if the element is installed and the infrared lamp is turned off at the set temperature, overshoot will be large because heat will not diffuse from the center of the roller to the ends of the roller.

Examples of the present invention will be described below.

The outer diameter of the upper roller is 40 mm, and the wall thickness of the roller is 2.7 mm.
mm, in a fixing device with an infrared lamp power of 1300W, the infrared lamp was selected in relation to the roller so that points f and h had the highest temperature, and the tip of the thermocouple was placed in contact with point f on the roller surface. In this case, the overshoot at the center g of the roller was significantly improved by 10°C, compared to 23°C when the temperature control sensing element was placed at the center of the roller.

Furthermore, a temperature control sensing element is installed from the roller surface.
When installed at a distance of mm (the control temperature of the sensing element is adjusted accordingly so that the roller surface is controlled to the set position), the overshoot at the center of the roller was 22°C; When the sensing element was installed in the area, the temperature was 40°C, which was a huge improvement.

Next, improved embodiments of the present invention will be shown.

The outer diameter and wall thickness of the upper roller, the power of the infrared lamp, and the light distribution of the lamp to the upper roller were the same as in the previous example, and only the temperature control sensing element was improved as follows. In other words, the temperature control sensing element is placed 0.32 mm parallel to the chromel-alumel roller axis.
The thermocouple was installed over the length of the roller, and its joint was placed at point f on the roller surface. In this improved fixing device, the overshoot at the center of the roller could be kept at 4°C. Also, the roller surface point f and h of the highest temperature part
We were also able to keep the point overshoot to 4°C.

Note that this value of 4° C. is within the ripple range of the steady control region. This effect is clearly superior to the overshoot of 22° C. at the center of the roller when the tip of the thermocouple was simply placed above the 1 mm gap at point f on the roller surface in the previous embodiment. Also,
When a thermistor is installed at point f on the roller surface with a 1mm gap, and its lead wire is installed parallel to the roller axis over a length of 40mm, the overshoot at the center of the roller is obvious when compared to 26℃. It can be seen that it is excellent.

As described above, according to the configuration of the present invention, when the roller surface temperature rises to the set temperature after the heater is energized, the highest temperature is obtained at the intermediate portion between the roller end and the center, so that the entire area of the roller is heated. Heat conduction is smooth and rapid, and the temperature sensing element is placed in contact with the roller surface at the highest temperature point, allowing for more precise detection than in the case of non-contact, while also preventing the overshoot phenomenon. It has revolutionary effects such as reduction of power consumption and accurate temperature control.

[Brief explanation of drawings]

FIG. 1 is a perspective view of a heat roller fixing device, FIG. 2 is a sectional view along AA′ of the heat roller fixing device shown in FIG. 1, FIG. 3 is a temperature curve of the surface of a heat roller of a conventional heat roller fixing device, The figure shows a temperature distribution curve on the surface of the heat roller during startup of the heat roller fixing device of the present invention, FIG. 5 shows a temperature curve on the surface of the heat roller of the heat roller fixing device of the present invention, and FIG. FIG. 3 is a front view of a heat roller section and a temperature sensor section in the fixing device. 1... Upper roller, 2... Infrared lamp, 3... Lower roller, 4... Bearing, 5 and 6... Gear, 7
...Temperature sensor, 8...Cover, 9...Light emitting part of the infrared lamp, 10...Base of the infrared lamp, 11...Insulator, 12...Bearing part.

Claims (1)

[Scope of Claims] 1. A roller having a built-in heating element for fixing a toner image made of a thermoplastic resin on an image support;
A thermal roller fixing device comprising: a temperature detection element for detecting a surface temperature of the roller; and a control circuit for controlling energization of the heating element based on an output signal of the temperature detection element; Maintain the relationship between the roller and the heating element so that when the roller surface temperature rises to the set temperature after energizing, the highest temperature is obtained at the middle part between both ends and the center of the roller. ,
A thermal roller fixing device characterized in that a temperature sensing element is disposed at the highest temperature part in contact with the roller surface. 2. The thermal roller fixing device according to claim 1, wherein the temperature sensing element is a thermocouple stretched in parallel over a predetermined range.