JPS60125875A - Control system for fixation temperature - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION Technical Field of the Invention The present invention relates to a fixing temperature control system for a heat fixing section using silk as a heat roller and a pressure roller used in an electrophotographic printing or copying apparatus, and particularly to The purpose is to feedhack the surface temperature of the pressure roller side, which does not have the same temperature, to obtain better fixing characteristics.

Conventional technology and problems A heating roller with a built-in heating element and a pressure roller that presses the paper to which toner has adhered to the roller to obtain the required nip length (temperature control of the fixing section) Conventionally, this is performed by detecting the surface temperature of the heating roller. However, in this method, the temperatures of the paper and the 1-ner change due to changes in the temperature of the pressure roller, resulting in uneven fixing performance. In other words, the heating roller and the pressure roller need to be rotated in a pressed state by a motor or the like in order to fix the paper and toner and send it ill. At this time, since heat is transferred from the heating roller surface to the pressure roller surface, the surface temperature of the pressure roller gradually increases even though the pressure roller itself does not have a built-in heating element. When the paper and toner are conveyed and fixed in this state, the paper and toner are also heated from the pressure roller side. Therefore, if only the temperature of the heating roller surface is controlled, the temperature of the toner may rise too much and proper fixing cannot be obtained (occurrence of hot offset). If the fixing temperature of the toner is too high, the toner will stick to the paper.
If it is too low, problems such as toner falling off the paper may occur, so it is necessary to set it appropriately.

Purpose of the Invention The present invention attempts to obtain better fixing characteristics by detecting the surface temperature of the pressure/pressure roller side in the above-mentioned heat fixing section and feed-hacking this to the temperature control circuit of the heat roller. It is.

Structure of the Invention The present invention detects the surface temperature of a heating roller in a heating fixing unit that is a combination of a heating roller with a built-in heating element and a pressure roller that presses a sheet of paper with toner attached to the heating roller. A fixing device including a first temperature detection sensor and a heating roller surface temperature control circuit that receives the output of the sensor and changes the amount of heat generated from the heating element so that the surface temperature reaches a constant control target value. A second temperature detection sensor is provided to detect the surface temperature of the pressure roller, and the output of the second temperature detection sensor is fed to the temperature control circuit to increase the surface temperature of the pressure roller. The present invention is characterized in that the control target value is controlled in a direction that decreases as the control target value increases, and this will be explained in detail below with reference to the illustrated embodiment.

Embodiment of the Invention FIG. 1 is a schematic diagram of the entire electrophotographic printing or copying apparatus, in which 1 is a hopper for storing printing sheets P, 2 is a paper feeding mechanism for taking out printing sheets P one by one from the hopper 1, 3
, 4.5 show some of the components of the printing section that prints on the printing sheet 1-P, 3 is a photosensitive drum, 4 is a transfer section, 5
is the fixing part.

On the photosensitive drum 3, a latent image is formed by image projection, and development is performed by applying l.toner.In the transfer section 4, an electric charge is applied to the paper, and the toner image on the drum is transferred to the paper by electrostatic force. Transcription takes place.

The fixing section 5 heats the toner image on the paper transferred by the transfer section 4 and fuses it to the paper. 6 is a feed roller that sequentially feeds the sheet P after fixing, and 7 is a stacker that stores the sheet P after printing. In the figure, the dashed line indicates the traveling route of the printing sheet (P).

FIG. 2 is a detailed sectional view of the heat fixing section 5 according to the present invention, and 8 is a heating roller. The surface till of this roller 8 is made of silicone rubber or funosol resin coated with silicone oil. The inner layer 12 is a metal pipe (aluminum or iron), and a heating element such as a heater (lamp) 9 is arranged inside. The surface temperature of the heating roller 8 heated by the heater 9 is detected by the thermistor 10.

On the other hand, 13 is a pressure roller, the surface layer 15 of which is made of an elastic material such as silicone rubber. The surface layer 15 is made of an elastic material so that the surface layer is depressed along the surface of the heating roller 8 when pressed, and the printing sheet P comes into contact with the surface of the heating roller within a certain range (2.knob length). It's for a reason. 16
is a metal pipe (aluminum or iron) with no heating element inside. In this example, a thermistor 14 is provided to detect the surface temperature of the surface layer 15. The rollers 8.13 in FIG. 2 correspond to the upper and lower rollers of the fixing section 5 in FIG. 1, respectively. Thermistors 10 and 14 are placed opposite to the roller through a small gap or in contact with the roller with light contact pressure. Toner T is electrostatically attached to the printing sheet P, and is heated and fixed on the sheet P when it passes between the heating roller 8 and the pressure roller 13.

At this time, only the heating roller 8 is heated by the heater 9, but when the heating roller 8 and the pressure roller 13 rotate to fix the sheet after toner transfer, the surface temperature of the pressure roller 13 also increases. It receives heat from the heating roller 8 and rises. When the temperature of the pressure roller 13 increases in this way, the temperature of the printing sheet P and toner T held between the pressure roller 8 and the pressure roller 13 also increases because it depends on the temperature of the pressure roller 13. As a result, the fixing temperature cannot be maintained at a desired value. Therefore, in the present invention, the temperature on the heating roller 8 side is controlled by also detecting the surface temperature on the pressure roller 13 side.

FIG. 3 shows a heating roller surface temperature control circuit showing an embodiment of the present invention, and TI and T2 are thermistors 10 and 14 of FIG.
It is. The thermistor T1 on the heating roller side is connected in series with the resistor RI and has a constant voltage E.

A voltage El is generated by resistor-dividing the voltage El. This voltage E+ is expressed as RTI, which is the internal resistance of the thermistor T1. On the other hand, the thermistor T2 on the pressure roller side is connected in series with the resistor R2 and generates a voltage E2 which is a divided voltage of the constant voltage EO.However, since the insertion point of the thermistor T2 is opposite to the thermistor T1, the thermistor T2? Let RT2 be the internal resistance of .

The temperature characteristics of both thermistors TI and T2 are shown in Figure 4, where the resistance value decreases as the temperature rises, so as the temperature rises, the voltage E+ in equation (1) decreases, and conversely, (2)
The voltage E2 in the equation increases.

The comparator 20 in FIG. 3 compares the two by inputting EI to one side and R2 to the + side. However, in order to explain the conventional configuration, if R2 is fixed and considered, El> The state of R2, that is, the surface temperature of the heating roller 8 is low and the thermistor T1
When the resistance value RTI is large, it is necessary to energize the heater 9 to raise the surface temperature of the heating roller 8. When the surface temperature rises to El-R2, further temperature rise is no longer desirable, so the power supply to the heater 9 is stopped. Therefore, R2 becomes the control target voltage for obtaining the optimum fixing characteristics, so under the above conditions, the output of the comparator 20 is O and the heater is ON11 and the heater is OFF.

However, if the surface temperature of the pressure roller 13 increases, the sheet P and toner T will be heated too much with the fixed control target value E2. Therefore, in this example, when the surface temperature of the pressure roller 13 rises by 2, the control target voltage E2 is increased and El>R2
In other words, the on-period of the heater 9 is shortened. A voltage divider circuit with thermistor T2 and resistor R2 makes this possible. In this case, if R1, R2, and TI are the same as before, you can choose one with appropriate characteristics for T2, but even in that case, R1, R2 should be a variable resistor G, or a combination of a fixed resistor and a variable resistor. It would be more convenient to make it adjustable. In addition, when the input to the comparative hot forest 20 is reversed, the output 1.0 may be used as a reverse center, and an infrared detector may be used as a temperature detection sensor other than a thermistor, and 1 may be used).

Effects of the Invention As described above, according to the present invention, it is possible to keep the amount of heat simultaneously applied to the sheet and the sheet from the heating roller that clamps the recording paper and the pressure roller in the heat fixing section constant. It has the advantage of being able to obtain stable fixing characteristics even if the surface temperature of the pressure roller (111) changes.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of an electrophotographic printing or copying apparatus, FIGS. 2 and 3 are diagrams showing an example of the present invention, and FIG. 2 is a detailed cross-section of a heat fixing section. 3 is a circuit diagram of a heating roller surface temperature control circuit, and FIG. 4 is a temperature characteristic diagram of a thermistor. In the figure, 8 is a heating roller, 9 is a heater, 10. T1 is the first
13 is a pressure roller, 14 and T2 are second temperature detection sensors, and 20 is a comparator of a heating roller surface temperature control circuit. Applicant Fujitsu Ltd. Representative Patent Attorney Minoru Aoyagi Figure 3 Figure 4

Claims (1)

[Claims] A first unit that detects the surface temperature of the heating roller for a heating fixing unit that includes a heating roller with a built-in heating element and a pressure roller that presses the paper to which the toner has adhered to the heating roller.
A fixing device including a temperature detection sensor, and a heating roller surface temperature control circuit that receives an output from the sensor and changes the amount of heat generated from the heating element so that the surface temperature reaches a constant control target value, A second temperature detection sensor is provided to detect the surface temperature of the pressure roller, and the output of the second temperature detection sensor is fed back to the temperature control circuit so that the surface temperature of the pressure roller increases. A fixing temperature control method characterized in that the control target value is controlled in a direction in which the control target value is decreased accordingly.