JPS63129378A - Heat roll fixing device for electrophotography - Google Patents

Abstract

PURPOSE:To prevent paper from burning and outer-most offset preventing layer from being damaged previously setting a time required for rise by a heat control temperature immediately after a switch is turned on and electrification time. CONSTITUTION:Receiving power from a brush 2, a resistance layer close to the surface in a heat roll 1 generates calorie and it is quickly heated. A thermistor 3 comes into contact with the surface of the heat roll and it is connected to a commercially available temperature controller. First, it reads an initial temperature, and sets a rise expectation time. The electrifying time is set to a timer so that the time is somewhat higher than the prescribed temperature 180 deg.C, and time required for the thermistor to catch up on detection is set to the timer as the non-electrifying time. The electrification starts. As for a temperature change caused by an infrared detector, overshoot in the rise is substantially reduced, compared with a conventional method, the deterioration of the offset preventing layer on the surface is minimized, and the paper burning in paper feed is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a heat roll fixing machine for electrophotography, and particularly to a fixing machine with short warming-up time and good paper release characteristics.

[Conventional technology]

Conventionally, to detect the heating status of a heat roll fuser,
Thermistors or temperature-measuring semiconductors were placed in contact with each other or with a slight gap between them, and the signals from these sensing elements were detected. After the required temperature has been reached, it has been common practice to judge based on these signals and control the temperature by turning ON-OFF or the like to keep the temperature constant. However, these sensors have poor responsiveness, and for this reason, fusers using heat rolls with small diameters and extremely short warm-up times have not yet been commercialized.

Problems to be solved by the invention C] In recent years, heat rolls having a heating element on the surface (for example, JP-A-55-60159) and heat rolls using induction heating (for example, JP-A-58-72179) have been developed. was developed, and it has now become possible to manufacture heat rolls with a diameter of 20φ or less, which was difficult to do with conventional heat rolls having a halogen lamp inside. For this reason, the fixing temperature (
It has now become possible to easily reduce the time required to reach the temperature (usually 160 to 200°C) to 20 seconds or less. Particularly when the diameter is 10φ or less, it is possible to reach a predetermined temperature in a few seconds.

However, conventional thermistors and temperature-measuring semiconductors have poor responsiveness, and the time it takes for commercially available products to rise to 2/3 of the temperature difference is between 1 to 3 seconds for fast ones and 8 to 10 seconds for slow ones.
When these are used, the detection performance of the temperature detector element is lower than the temperature rise characteristic of the fixing roller, so when the temperature detection element determines that the temperature is the specified temperature, the actual roll temperature will be much higher than this. , a so-called overshoot phenomenon occurs. Although this development occurs even with conventional rollers having a diameter exceeding 20 φ, the temperature thereof is usually within about 40° C. and does not cause any major problems. However, those that take less than 20 seconds to reach the specified temperature, especially those with a roll diameter of 20φ
This phenomenon is particularly severe for products with rise characteristics of less than 10 seconds, and in some cases it can reach up to 100°C.
This may cause burnt paper or damage to the outermost anti-offset layer.

On the other hand, there is a method to prevent the detection delay by using a non-contact detection element such as an infrared sensor, but this method is ineffective if paper gets stuck and can cause a fire. Furthermore, if a heat roll exceeding 20φ is used, there is a high probability that the paper will get stuck.

(Means for Solving the Problems) To solve the problems described above, it is effective to use one or a combination of two or more of the following methods.

(1) The initial temperature of the heat roll is estimated based on the output of the detection element being used immediately after the switch is turned on, or the output of another detection element installed to investigate the temperature of the heat roll, and from this, electricity is applied using a predetermined calculation method. A heating time is set, and after that time, electricity is temporarily stopped, and thereafter the temperature is controlled using a predetermined temperature control method.

(2) After reaching a predetermined temperature, the overshoot during ON-OFF is reduced by setting a preset amount of power smaller than the amount of power immediately before reaching the predetermined temperature.

(3) By using a direct heating method as the heating method, the roll diameter is set to 20φ or less. For faster warming-up, the diameter should be 10φ or less.

〔Example〕

Embodiments of the present invention will be described below based on the drawings.

FIG. 1 is a schematic diagram of a heat roll fixing machine for electrophotography.

FIG. 2 is a sectional view thereof. The heat roll 1 has a resistance heating element on its surface (having the structure shown in Japanese Patent Application No. 61-54463), has an outer diameter of 10φ, an inner diameter of 7φ, and the distance between the brushes 2 is 235 mil. The diameter of the rubber roller 4 is is 20φ.

Power is supplied from the brush 2, and the resistance layer near the surface generates heat.
heats up rapidly. The thermistor 3 is in contact with the heat roll surface and is connected to a commercially available temperature control device (not shown). The resistance value of heat roll 1 is 10 between brushes 2
．． It is adjusted to 4Ω (at room temperature).

Surface temperature was detected using an infrared sensor with almost no response delay. The voltage applied to the heat roll 1 was varied and the rise time from 20°C to 180°C was measured. Figure 3 shows the temperature rise curve at 950W (100V). Further, FIG. 4 shows the relationship between power and rise time. As described above, with a heat roll of 10φ, a rise time of 10 seconds or less can be easily obtained with a current capacity of 15 A or less of normal wiring. Furthermore, the setting of the rise time can be determined from the initial temperature and the time until rise.

Next, the results of temperature control using the electrophotographic heat roll fixing device of the present invention will be described.

FIG. 5 shows the case where the power is turned on at 950W (100V). This figure shows an example where the temperature rises above 20°C, but the same tendency occurs in other cases as well. Means 1 of the present invention first reads the initial temperature state from the controller (20° C. in this case). Next, the expected rise time is set from FIG. 3 (about 5.5 seconds in this case). A normal time is set in advance on a timer so that the temperature rises slightly higher than a predetermined temperature of 180° C., and a time (about 3 seconds in this case) until the detection of the thermistor catches up is set on the timer as a non-energizing time.

After that, power was started. The temperature change caused by the infrared detection device is shown in Figure 4. Compared to the conventional method, the overshoot at startup is significantly reduced, the deterioration of the anti-offset layer on the surface is also reduced, and the paper is Burnt spots also decreased. However, the ripple width during control was also large. Accordingly, in the second embodiment of the present invention, the voltage applied to the heat roll 1 is lowered to 60V at the end of the timer set in which no electricity is applied. As a result, the electric power added to the heat roll 1 is 36. It became OW and the ripple width decreased significantly. Even if you change the power during startup, the same effect will be 1q.
It will be done. In addition, when passing paper immediately after the rising edge, turn OFF.
Prevent the timer from running.

Although a timer was used in this actual droplet example, an electronic circuit can be easily constructed by storing the timer in advance in a microcomputer or by setting a sequence.

〔Effect of the invention〕

The present invention has the advantage of short rise time, small size, and good paper release properties.

It will help miniaturize electronic copying machines, optical printers, facsimile machines, etc., and will greatly contribute to industry.

[Brief explanation of the drawing]

Figure 1 is a schematic diagram of a heat roll fixing machine for electrophotography, Figure 2 is a sectional view of Figure 1, Figure 3 is a diagram showing the temperature rise of the heat roll used, and Figure 4 is the heat roll used. FIG. 5 is a diagram showing the relationship between power and rise time, and FIG. 5 is a diagram showing the effect of the temperature control means according to the present invention. 1...Heat roll, 2...Brush, 3...Thermistor, 4...Rubber roll. Figure 3 Figure 4

Claims (4)

[Claims] (1) In an electrophotographic heat roll fixing machine having at least one heat roll temperature detection means, it is preferable that the heat roll fixing machine for electrophotography has a mechanism for presetting the time until startup based on the heat roll temperature immediately after the switch is turned on, and setting the energization time. Features: Heat roll fixing machine for electrophotography. (2) The heat roll fixing machine for electrophotography according to claim 1, further comprising a mechanism for changing the electric power supplied to the heat roll immediately before or after the end of the set temperature rising time. (3) The heat roll fixing machine for electrophotography according to claim 1 or 2, wherein the diameter of the heat roll is 20φ or less. (4) The heat roll fixing machine for electrophotography according to claim 1 or 2, wherein the heat roll has a diameter of 10φ or less.