JPS6222149B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device using a fixing roller.

Conventionally, a thermal atmosphere fixing method, a pressure fixing method, a roller heating fixing method, etc. have been used to fix the toner powder image supported on a toner support. Among the above methods, the roller heating fixing method is widely used because it is said that uniform roller surface temperature improves fixing performance and paper conveyance.One specific configuration is shown in Figure 1, where one of the rollers is used for both conveyance and conveyance. The outer circumferential surface of one roller is coated with a material with good mold releasability such as Teflon, the outer circumferential surface of the other roller is coated with a heat-resistant elastic material such as silicone rubber, and the inner surface of both rollers is coated with a material with good mold release properties such as Teflon. A heater is provided, and the heater heats the roller to heat the toner support sandwiched between the two rollers, but the uniformity of the temperature of the roller surface and the deformation of the roller are contrary to each other. In particular, in the case of silicone rubber, etc. provided on the outer peripheral surface of the roller, when the roller is heated, the rubber layer expands, but both ends of the roller tend to lose heat to the surrounding area. The roller will sag from the center, and the diameter of both ends will be smaller than the diameter of the center of the roller, resulting in a so-called cylindrical shape.

This causes problems such as the ends of the rollers not coming into contact with the opposing rollers or the specified contact pressure being unable to be obtained, and therefore, even though there is not much difference in the surface temperature of the rollers between the center and both ends. However, there is a risk that the toner may be poorly fixed to the support at the end of the roller.

Moreover, due to the difference in diameter between the center and both ends of the roller, a difference in circumferential speed occurs between the center and both ends, which causes the toner support to be brought to the center of the roller, causing wrinkles on the toner support. do.

In order to prevent wrinkles from occurring on the toner support, the diameter at both ends of one roller is made larger than the diameter at the center, as shown in Figure 2, to reduce the amount of deformation that occurs at both ends of the roller during heating. Although countermeasures have been taken, the processing is extremely troublesome and it is also difficult to set the amount of deformation.

In order to solve the above-mentioned disadvantages of the conventional fixing device, the present invention provides a fixing device in which the temperature of the heater that heats both ends of the roller is set higher than the temperature of the heater that heats the center of the roller. It provides equipment.

The present invention will be explained below with reference to an embodiment shown in the drawings.

FIG. 3 shows a connection circuit for the heaters disposed on each roller shown in FIG. 4.

In FIG. 3, the thermistor TH ₁ is the first thermistor that heats both ends of the roller 21, as shown in FIG.
It is one of _the heating _control means for the heater of
It is connected to DC and generates a voltage between both ends according to the surface temperature of the roller 21.

Operational amplifier IC ₁ operates by resistors R ₃ and R ₄ connected in series between the ends of DC power supply DC at the same time that the voltage across this thermistor TH ₁ is input to the non-inverting input terminal via resistor R ₂ . A set voltage is input to the inverting input terminal via resistor _R5 , these two input voltages are compared, and the difference voltage is output. That is,
When the surface temperature of the roller 21 becomes lower than the set temperature, an output voltage is generated.

The output voltage of the operational amplifier IC ₁ is used to turn on the heater 1 using the semiconductor relay SSR ₁ . Therefore, the surface temperature of the roller 21 is controlled by the first heater heating control means including the thermistor TH ₁ mentioned above, the variable resistor VR ₁ which is the input system to the operational amplifier IC ₁ , and the resistors R ₁ to R ₅ . Therefore, the temperature is controlled to a set temperature, and the set temperature can be arbitrarily set by the variable resistor _VR1 .

Further, as shown in FIG. 4, the thermistor TH ₂ is one of the heating control means for the second heater that heats the central part of the roller, and is connected in series with a resistor R ₆ and a variable resistor VR ₂ . It is connected to a direct current power supply DC, and generates a voltage between both ends according to the surface temperature of the roller 20.

Operational amplifier IC ₂ is operated by resistors R _{8 and} R ₉ connected in series between the ends of DC power supply DC at the same time that the voltage across this thermistor TH ₂ is input to the non-inverting input terminal via resistor R ₇ . The terminal voltage is input to the inverting input terminal via the resistor _R10 , and the two input voltages are compared and the difference voltage is output. The output voltage of this operational amplifier is applied to AND gate IC ₄ ,
Also, the voltage across the thermistors TH ₁ and TH ₂ is R ₁₁ ,
They are input to operational amplifier IC ₃ via R ₁₂ respectively. The operational amplifier IC ₃ compares these input voltages and produces the difference voltage, i.e. produces an output voltage when the surface temperature of the roller 20 is lower than the surface temperature of the roller 21, and applies the output voltage to an AND gate.
Add to IC ₄ .

Therefore, the variable resistor VR ₂ which is the input system to the thermistor TH ₂ and the operational amplifier IC ₂ mentioned above, and the resistance
The heating of the second heater is controlled by a second heater heating control means including R ₆ to R ₁₀ , a shadow computational amplifier IC ₃ , and an AND gate IC ₄ . The gate IC ₄ outputs an output voltage when the surface temperature of the roller 20 is lower than the surface temperature of the roller 21 and at the same time when the surface temperature of the roller 20, that is, the roller with the second heater arranged in the center, is lower than the set temperature. This output voltage drives the semiconductor relay SSR ₂ to turn on the heater 2.

Here, the surface temperature of the rollers 20 and 21 is controlled by variable resistors VR _{1 and 21} so that the former is lower than the latter.
Set by VR ² ₂ .

As a result, the surface temperature at the ends of the roller 21 is maintained higher than the surface temperature at the center of the roller 20, thereby minimizing deformation at both ends of the roller. It is possible to prevent wrinkles on the toner support without using any special means, and when a narrow toner support is used for fusing, with only the central area of the roller being fixed, the surface temperature of that area can be reduced. Since the second heater heating control means can control the second heater to maintain the surface temperature of the roller at the set temperature even if the temperature drops below the set temperature, it is possible to continuously fix a narrow toner support. Even if the fixing effect is lowered due to a temperature drop in that part, the fixing effect will not be reduced.

The fixing device of the present invention can also be applied to a device that fixes a toner powder image on a toner support using a fixing roller and a conveyor belt, as shown in FIG.
That is, a heater 1 that heats the ends of the roller and a heater 2 that heats the center are disposed inside the fixing roller 25, and a conveyor belt 26 that presses against the roller is disposed below the roller. A toner support placed on the belt may be conveyed between rollers and fixed by heated rollers.

Furthermore, the device of the present invention can be applied to fixing devices that use heating rollers other than those described above.

[Brief explanation of the drawing]

1 and 2 are schematic configuration diagrams showing an example of a conventionally used roller heat fixing device, FIG. 3 is an electric circuit diagram showing an embodiment of the device of the present invention, and FIG.
The figure is a schematic configuration diagram showing one embodiment of the device of the present invention, and FIG. 5 is a schematic configuration diagram showing another embodiment of the device of the present invention. 11, 12... Heater, 20, 21... Fixing roller, 30... Fixing device.

Claims (1)

[Scope of Claims] 1. In a fixing device using a roller heating method for heating and fixing a toner powder image supported on a toner support, a first heater that heats an end of the roller that comes into contact with the toner support. and a first heater heating control means having means for detecting the surface temperature of the roller heated by the first heater, and turning on the first heater when the surface temperature is below a set temperature. and a second heater that heats the central portion of the roller; and a means for detecting the surface temperature of the roller heated by the second heater, and when the surface temperature is equal to or lower than the set temperature. and a second heater heating control means for turning on the second heater when the surface temperature of the roller heated by the first heater is lower.