JPH0210427B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a heating roller fixing device for a copying machine,
In particular, it relates to the temperature control device.

A heating roller fixing device has a fixing roller and a pressure roller as a pair of rollers, and transfer paper with the image side facing the fixing roller is sandwiched and conveyed between the rollers. Usually, both rollers have a heater inside. It's summery.

This is intended to shorten the warm-up time by providing a heater on the pressure roller and transmitting this heat to the fixing roller. And since both rollers are rotating during warm-up,
Heat is transferred efficiently and evenly.

FIG. 1 shows a temperature characteristic diagram of a conventional example.

In the figure, the vertical axis is temperature t, and the horizontal axis is time T.
It is. A is the surface temperature of the pressure roller, which will be described later, and B is the surface temperature of the fixing roller. Further, _T1 is the time until the temperature of B rises, that is, the warm-up time.

Figure a shows the characteristics when the set temperature of the pressure roller heater is set to a sufficiently high temperature. In this case, the warm-up time T ₁ will certainly be short, but
After warm-up, there is a large temperature difference between immediately after the surface of the fixing roller reaches the set temperature and after the fixing roller has been allowed to rotate for a sufficient period of time, resulting in a disadvantage that the temperature control width W becomes large. This is because the set temperature of the pressure roller is higher than the set temperature of the fixing roller, and therefore, even after the fixing roller reaches the set temperature, there is heat conduction from the pressure roller.

If, in consideration of this point, the set temperature of the pressure roller is set lower, there is a disadvantage that the warm-up time _T1 becomes longer, as shown in FIG. 2B.

The present invention has been made in view of such conventional examples, and its purpose is to reduce the temperature control range after the set temperature is reached in this type of heating roller fixing device without prolonging the warm-up time. The idea is to suppress it.

An explanation will be given below based on one embodiment of the present invention.

FIGS. 2a and 2b are sectional views of the fixing roller and the pressure roller, respectively.

First, the fixing roller shown in FIG. 1A will be described. The fixing roller 1 is provided with a heater penetrating inside a cylindrical core member 2, and further provided with a silicone rubber layer 4 on its surface. Both ends of this core metal member 2 have a small diameter, and are supported by a fixed front plate 5 and a fixed rear plate 6, respectively. Further, a driving gear 7 is provided on the outside of the rear side plate 6 and fixed to one end of the core metal member 2. The silicone rubber layer 4 is not provided over the entire large diameter portion of the core member 2, but is sufficient as long as it is wide enough to contact the entire width of the transfer paper. A temperature sensor 8 consisting of a thermistor is provided in contact with.

Figure b shows the pressure roller 9, and a heater 10 is provided inside. Further, the surface of this pressure roller 9 is coated with a synthetic resin coating. Similarly to the fixing roller 1, a drive gear 11 and a temperature sensor 12 are provided.

The drive gears 7 and 11 are in mesh with each other, and each roller rotates while being in contact with each other. Also, 13 is
This is a pressure lever for pressing the pressure roller 9 in the direction of the fixing roller 1 .

FIG. 3 is a block diagram showing a temperature control mechanism after temperature detection by these temperature sensors 8 and 12.

In the figure, 14, 15, 16 are comparison circuits, and the comparison circuit 14 compares the temperature sensor 8 on the fixing roller 1 side with the reference temperature, and the comparison circuits 15, 16
The temperature sensor 12 on the pressure roller 9 side is compared with each reference value. Here, the comparison circuit 14
The reference value in is the set temperature on the fixing roller 1 side, the reference value in the comparison circuit 15 is a high set temperature _t1 , which will be described later, and the reference value in the comparison circuit 16 is the low set temperature _t2 , which will also be described later. .
Reference numeral 17 denotes a control circuit that takes in the comparison outputs of these comparison circuits 14, 15, and 16 and performs various judgment controls internally. Further, 18 and 19 are switch circuits, respectively. The switch circuit 18 is connected to the heater 3 on the fixing roller 1 side, and the switch circuit 19 is connected to the heater 10 on the pressure roller 9 side.

The temperature sensor 8 of the fixing roller 1 is provided on the core member 2 as described above, but this was done in consideration of roller damage (peeling of the contact surface between the core member 2 and the silicone rubber layer 4). It is. In this case, the thermal conductivity of the silicone rubber layer 4 is extremely poor, so there is a temperature difference between the surface of the silicone rubber layer 4 and the core metal member 2, which is particularly noticeable during warm-up.

For this purpose, it is necessary to conduct heat to the surface of the silicone rubber layer 4 by the pressure roller 9, especially during warm-up.

Next, the operation of the block diagram shown in FIG. 3 will be explained.

First, the detection signal from the temperature sensor 8 on the side of the fixing roller 1 is compared with a reference value in the comparison circuit 14, and if it exceeds this reference value, a signal is sent to the control circuit 17. The control circuit 17 receives this signal and switches the switch circuit 18.
Send the switch circuit drive signal to switch circuit 1
8, in response to this, the heater 3 is controlled to be turned on and off.

On the other hand, the detection signal from the temperature sensor 12 on the pressure roller 9 side enters the comparison circuits 15 and 16, but first, an output is output from the comparison circuit 16 side, which has the low set temperature _t2 as a reference value. However, in the control circuit 17, this signal is not processed at this point. Next, the output signal from the comparator circuit 15 having the high set temperature t ₁ as a reference value is taken into the control circuit 17 . Then, for the first time at this point, the control circuit 17
takes in the output signal of the aforementioned control circuit 16,
Start decision control. Then, the control output is sent to the switch circuit 19, and based on this, the switch circuit 19
is for controlling the heater 10 to turn on and off.
Of course, in this case, the heater 10 is controlled at the low set temperature _t2 .

The temperature characteristics when performing this kind of control are as follows.
As shown in the figure.

As is clear from the figure, the temperature on the pressure roller 9 side is at the high set temperature t ₁ until the end of warm-up (after T ₁ hour has elapsed), but is switched to the low set temperature t ₂ after the end of warm-up. In this case, t ₂ can be considered to be approximately equal to the optimum fixing temperature.

Since the temperature on the pressure roller 9 side is switched in this way, the fixing roller 1 side does not receive unnecessary heat after reaching the set temperature, so the temperature control width W can be kept extremely small.

As described above, the present invention controls the temperature of the pressure roller side to be set high during warm-up and to shorten the warm-up time, while switching to a low temperature after warm-up is completed. Therefore, the temperature control width can be kept small.

[Brief explanation of drawings]

Figures 1a and b are temperature characteristic diagrams in the conventional example, Figure 2a is a vertical sectional view of the fixing roller, Figure 2b is a vertical sectional view of the pressure roller, and Figure 3 is a temperature control block diagram according to the present invention. , FIG. 4 is a temperature characteristic diagram according to the present invention. DESCRIPTION OF SYMBOLS 1... Fixing roller, 3... Heater, 4... Silicon rubber layer, 9... Pressure roller, 10... Heater.

Claims (1)

[Scope of Claims] 1. A fixing roller provided with a heating element inside and a heat-resistant elastic layer formed on the outer periphery, and a pressure roller provided with a heating element inside and whose outer periphery comes into pressure contact with the fixing roller. , a fixing roller temperature detection means for detecting the surface temperature of the fixing roller; a pressure roller temperature detection means for detecting the surface temperature of the pressure roller; A control means for controlling energization of the heat generating element for the fixing roller and the heat generating element for the pressure roller based on the detection signal, and an image surface is placed on the fixing roller side between the fixing roller and the pressure roller. In a heating roller fixing device configured to nip and convey a sheet of transfer paper directed toward the user and to conduct heat from a pressure roller to the elastic layer during warm-up of the device, a first heating element of a heating element provided on the pressure roller is provided. a first reference temperature setting means for setting a reference temperature; a second reference temperature setting means for setting a second reference temperature lower than the first reference temperature of the heating element provided on the pressure roller; a temperature control mode based on the first reference temperature;
and a mode switching means for switching between a temperature control mode based on the second reference temperature, and the mode switching means controls the temperature of the pressure roller in the temperature control mode based on the first reference temperature when the apparatus is warmed up. , after the device warms up, the temperature of the pressure roller is controlled in a temperature control mode based on the second reference temperature;
A temperature control device for a heating roller fixing device characterized by switching modes.