JPH0262866B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a hot plate type fixing device for thermally fusing toner images.

Conventionally, hot plate type fixing devices in electrophotographic recording devices such as copying machines have a sheet heating element such as a rubber heater glued to the back of an aluminum plate or iron plate, and a thermistor attached to the surface to control the temperature. It was hot. The heating plate used in this case has a thickness of 2
A relatively thin metal plate with a diameter of about 1.2 mm is used and is directly affected by the heat generated by the heater, so if the surface temperature of the heating plate is kept constant in the area where the paper touches and passes through, other areas will lose heat. Since there is less heat, the surface temperature of the hot plate increases. However, when the number of copies per minute is small as in a conventional copying machine, the temperature increase is small and does not pose much of a problem. However, in recent years, with the development of high-speed electrophotographic printing machines, a technology has been developed that prints and heat-fuses continuous slip paper, which is generally used as output paper for line printers, and the conventional hot plate type fixing device has been replaced with an auxiliary fixing roller. It is increasingly being used as a heating means.
In such devices, the amount of paper processed per unit time is several times to several tens of times that of a copying machine, and the temperature rise on the surface of the heating plate other than the paper passing section is extremely large, which can cause malfunctions. Become. Further, in the above-described printing apparatus, various paper sizes are used, and the temperature distribution on the surface of the hot plate becomes extremely uneven.

FIG. 1 shows such a conventional hot plate type fixing device, in which a toner image is formed on continuous paper 1 by an electrophotographic recording system (not shown). The continuous paper 1 is given an appropriate back tension by the suction device 2, contacts the preheating plate 3 with an appropriate contact pressure, is heated from the back side of the paper, and is further heated by the heating roller 4 and the back up roller 5. The paper is then heat-pressed and discharged from the fixing device by a pair of paper discharge rollers 6. The continuous paper 1 usually has a paper width of about 6 inches to 16 inches.
In such a case, if an attempt is made to uniformly heat a 16-inch wide sheet of paper, when a 6-inch wide sheet of paper is used, the temperature of the non-contact portion of the sheet will rise abnormally. FIG. 2 shows the temperature distribution of the preheating plate in the paper width direction in such a case. The thermistor for temperature adjustment of the preheating plate 3 is installed on the paper entry side at the center position in the paper width direction, and when adjusted to maintain the temperature at 80°C in that area, the temperature reaches the maximum temperature in the area where other paper is not passing through.
The temperature rises to around 200℃ and is released as unnecessary heat.
This may have an adverse effect on other equipment and cause malfunctions.
It also results in wasted energy consumption.

SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide a hot plate type fixing device that can eliminate these conventional drawbacks and can efficiently transfer heat to paper.

According to the present invention, in order to achieve the above object,
In a hot plate type fixing device that thermally fuses a toner image with a hot plate, a plurality of heat generating means are connected in parallel to a power supply unit for heating the hot plate, and a plurality of heat generating means are provided corresponding to each heat generating means. and a temperature control element, one of the temperature control elements controls the output from the power supply unit, and the other temperature control element controls energization from the power supply unit to the heat generating means. has been done.

Next, embodiments of the present invention will be described with reference to the drawings.
FIG. 3 is a view of the preheating plate seen from the back side, where A indicates the paper running direction and B indicates the paper width direction. Heater 11
is arranged at the center of the preheating plate, heaters 12 and 13 are arranged on either side of it, and heaters 14 and 15 are arranged on either side thereof. A thermistor 18 is attached to the heater 11, and a signal detected by the thermistor 18 controls the heaters 11, 12, 13, 14, and 15 to blink at the same time. A thermoswitch 17 is attached to the heater 12 and controls the blinking of the heaters 12 and 13. The heater 14 also has a thermo switch 16.
is attached to control the blinking of the heaters 14 and 15. The paper is configured to vary symmetrically about the centerline of the preheating plate.

These heaters 11-15 and thermoswitches 16-18 are connected to a circuit as shown in FIG. That is, a series circuit of heaters 12, 13, and thermoswitch 17, as well as heaters 14,
The series circuit of 15 and thermo switch 16 is heater 1
The thermoswitch 18 and the resistors 19 to 21 are connected in parallel to the AC power source 26, and the thermoswitch 18 is assembled in a bridge with the resistors 19 to 21, and the output thereof is connected to the comparator amplifier 23. The output of the comparator amplifier 23 is input to a commercially available SSR 25 including a resistor 22 and a light emitting diode 24.

In the above configuration, a change in the resistance value of the thermistor 18 due to a temperature change is extracted as an N-FF signal by a known bridge circuit composed of resistors 19 to 21 and a comparator amplifier 23.
The SSR 25 is driven to control energization to the heater.
In this way, the temperature near the heater 11 is controlled to be constant. Now, when fixing paper with a width equal to or smaller than that of the heater 11, the heaters 12, 13, 14, and 15 in the portion where the paper does not pass are controlled by the thermistor 18, so the temperature rise is larger than that of the heater 11. . By passing the narrow paper in this way, if the temperature near the heaters 12, 13 or heaters 14, 15 reaches the temperature determined by the thermostat 17 or thermostat 16, respectively, the respective Since the thermostat is opened, the heaters 12, 13 or the heaters 14, 15 can be controlled independently of the control by the SSR 15, and the heaters 12, 13 or the heaters 14, 15 can be controlled so that the temperature does not exceed a certain temperature. Can be done.

Further, for example, when the width of the paper is fixed to the same extent as that of the heaters 11, 12, and 13, only the thermoswitch 16 is activated to prevent excessive elevation of the portion where the paper does not pass. In this way, by setting the set temperature of the thermoswitch to a value that is slightly higher than or equal to the set temperature of the thermistor, it is possible to prevent the temperature from rising excessively in areas where the paper does not pass. Furthermore, by subdividing the thermistor and heater, more fine-grained control becomes possible for various paper widths.

As explained above, according to the present invention, the energization of the plurality of heating elements arranged in the direction perpendicular to the paper transport direction is individually controlled according to the temperature unevenness in the paper width direction caused by the paper width. As a result, the temperature distribution on the surface of the hot plate can be made uniform, and heat can be efficiently transferred to the paper to achieve stable thermal fixing.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a conventional fixing device, FIG. 2 is a diagram showing the temperature distribution of the preheating plate in the paper width direction, and FIG. 3 is a back view of the preheating plate of the fixing device according to the present invention. FIG. 4 is a circuit diagram for controlling the temperature of the preheating plate. 1...paper, 2...suction device, 3...preheating plate, 4...heating roller, 6...discharging roller, 11-15...heater, 16, 17...thermo switch, 18...thermistor, 25...SSR.

Claims (1)

[Scope of Claims] 1. A hot plate type fixing device that thermally fuses a toner image with a hot plate, comprising: a heating element compatible with small size paper that is controlled so that the temperature detected by a thermistor is constant; and a heating element that is compatible with small size paper; A heat plate type fixing device characterized by having a heating element connected in series with a thermoswitch that is compatible with large size paper but not compatible with large size paper.