JPS58129450A - Fixing device - Google Patents

Abstract

PURPOSE:To prevent fixability difference between the central part and the side end part of a transfer paper, even if the paper changes in size, by providing large and small heaters separately in 2 heat fixing rollers. CONSTITUTION:When a narrow transfer paper P1 is passed through rollers 10, 11, surface temp. of the region A10 of the roller 10 lowers, and a heater 12 is actuated with a temp. detector 14. When surface temps. of regions B10, B'10 exceed set temp., a temp. detector 15 actuates the heater 13 of the lower roller 11 to heat the region A11. The region 11 of the roller 11 also heats the paper P1. As a result, the difference between the region A10 and B10, B'10 in heat expansion amt. is kept in an allowable range, and accordingly, when a wide paper P2 is heated, the difference between the parts corresponding these regions in fixability can be prevented.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a fixing device that heats and fixes a toner image using a pair of rollers.

Conventionally, this type of device has generally fixed a toner image by passing paper supporting the toner image between a heat roller into which a halogen heater is inserted and a pressure roller that is in pressure contact with the heat roller. The temperature of the surface of the roller that corresponds to the paper passing portion of the heat roller is detected by a temperature detection means such as a thermistor, and the halogen heater is controlled so that the surface temperature of the row 2 is always constant. The temperature distribution on the longitudinal surface of the heat roller generally shows a convex curve with the ends lower than the center due to heat conduction losses from both ends of the standby line to the bearings, support frame, etc. In order to keep the temperature of the paper passing section constant, heat is supplied from the halogen heater 1, and a large temperature rise is seen in the non-paper passing section compared to the paper passing section.

On the other hand, there are various width sizes of paper (length of paper in the direction perpendicular to the paper conveyance direction). Therefore, when small-width paper is passed continuously, the difference between the amount of thermal expansion in the non-paper passing area and the thermal expansion amount in the paper passing area for the narrow-width paper becomes inappropriate. When passing a paper of this size, the roller part that was a non-paper passing part for small-width paper also passes as a paper passing part, so the difference in the amount of thermal expansion mentioned above is in an inappropriate range. This causes problems such as wrinkles occurring in this large-sized paper, or a difference in fixing performance at the center of the paper and at one end.

SUMMARY OF THE INVENTION An object of the present invention is to provide a fixing device that can solve the above-mentioned disadvantages.

The present invention will be described in detail below with reference to the drawings.

FIG. 1 is an explanatory diagram of an electrophotographic apparatus that can utilize the fixing device of the present invention. In the figure, this is an electrophotographic photoreceptor mounted on the surface of a drum 2 that rotates in the direction of the arrow. As the photoreceptor l rotates, it is first uniformly charged by a charger 3, and then a desired beam of light is projected through a lens 4, thereby forming an electrostatic latent image. This latent*Fi is then developed using toner by a developer 5, and the obtained toner image is transferred to a transfer paper conveyed through a transfer paper conveyance path 5 under the action of a transfer charger 7. After the transfer, the surface of the photoreceptor 10 is cleaned by a cleaning device 8, and the photoreceptor 1 is reused.

The transfer paper on which the toner image has been transferred is guided to a fixing device 9. The fixing device 9Fi has heaters 12 and 13 inside each, and has cylindrical rollers 10 and 11 that are in pressure contact with each other and rotate in the directions of the arrows.
0.11, and the toner image is heated and fixed on this paper. Note that the unfixed toner image supporting surface of the paper is
10.

FIG. 2 is an explanatory diagram of the fixing device according to the present invention used in the apparatus shown in FIG. P, is a small size transfer paper, and P, is a wide size transfer paper. Roller l for small width size 0 paper P1
To the area of O. , and the area A1 of the roller 11, and the area A1 of the roller 11 is clamped and conveyed, and the large size is transferred to the area of the roller lO.
It is held and conveyed to BIX. That is, area B of roller IO,
. , B1゜', and areas B■, B, , / of the roller 11 are non-passing areas for notebook size paper P, but for large size paper P! This is the paper passing area. Furthermore, Laura
Area A1° of O and area A1m of roller 11 are for both papers P.
, , P! This is the paper passing area.

The heater (10 gen/Z lamp, etc.) disposed in the roller 10 is located in area B. It has a heat generating part 12' having a length that is approximately the same as the axial length of the part 1 person, BI,' (same as this length, or slightly shorter, or in the illustrated example, ty longer than the above-mentioned maximum length). Then, the area Bn -An -Bl@' t jxJ is heated from the inside of the roller IO.

Heater 13t'i area A arranged in the friend roller 11
It has a heat generating part 13' having a length approximately equal to the axial length of the portion 11 (same as this length, slightly longer, or slightly shorter than this length in the illustrated example), and Area At5t is heated.

Reference numerals 14 and 15 are temperature detectors such as thermistors, which have a characteristic that as the temperature increases, the low resistance value decreases. Temperature detector 14U area A of roller 10. For example, in area A, to detect the temperature of area A. The temperature sensor 15 is in contact with or in close proximity to the intermediate surface of the roller 10, while the temperature sensor 15 is in the region B of the roller 10.

For example, area B, for detecting the temperature of. is in contact with or close to the intermediate surface of the The temperature sensor 15 is placed in contact with or close to, for example, the intermediate surface of the area B1.'. ′
Alternatively, the temperature of the sensor may be detected. The temperature detector 14 controls the heater 12 to maintain the surface temperature of the roller lO at a temperature at which the toner image can be heated and fixed.

An example of the control circuit is shown in FIG.
It is incorporated into the bridge circuit together with resistors 1, 2 and -R3. 16 is a comparator, and 17 is a switch circuit interposed between the power source 18 and the heater 12. Here, roller 1
0 area. When the surface temperature of the temperature sensor 14 decreases from a temperature at which a toner image can be properly fixed, for example 170° C., and the resistance of the temperature detector 14 increases more than the resistance corresponding to 170° C., the comparator 16 outputs a level 1 output signal. , switch circuit 1
7e Close. Accordingly, power is supplied from the power source 8 to the heater 12. The heat generating portion 12' of the heater 12 generates heat, and the area B1°, AHo, B, of the roller 10 is generated. ′
heat up. Thus area A of roller 10. When the surface temperature exceeds 170"0, the comparator 16 stops outputting the signal, and this opens the switch circuit 17, so the power supply from the power source 18 to the heater 12 stops and the heater stops generating heat. .

Temperature detector 15 is also incorporated into a circuit similar to that described above. However, as the comparator 16, a comparator that outputs a level 1 output signal when the resistance of the temperature detector 15 falls below a predetermined value is used, contrary to the standard. To be more specific, the area B of the roller IO. (or B□') rises above the set value, for example 180°C, and the resistance of the temperature detector 15 becomes smaller than the resistance corresponding to 180°C, the comparator 16
outputs a level 1 output signal, which closes the switch circuit 17 and supplies power from the power source 19 to the heater 13. In this way, the heat generating portion 13' of the heater 13 generates heat, and 1. heat up. On the other hand, when the surface temperature of the area BI0 (or B, .') of the roller IO has not reached the set temperature of 180°C, the comparator 16 does not output an output signal, and at this time the switch circuit 17 is open and the power is turned on. 18
The heater 13 is not energized and the heater 13 does not generate heat.

In addition, each resistance value of the resistance R+ -k'q-k'3 of the bridge circuit 1 in which the temperature detector 14 is incorporated, and each resistance value of the resistance tag, tow, and tortoise of the bridge circuit in which the temperature detector 15 is incorporated are as follows. They are appropriately selected depending on the set temperature (170'0.180°C), respectively.

In the above, when the narrow paper P is passed, the area A of the roller IO. Since heat is removed from the paper PtK and the surface temperature of this area A16 decreases, the heater 12 is activated by the action of the temperature detector 14. This heater is not limited to area A1° as mentioned above, but also area B. *Since B16' is also heated,
As described above, if the narrow paper P continues to be passed continuously, the area B, . . .

B, ·' will be abnormally heated, but in the device to which the present invention is applied, the area B1°, B, o' is the set temperature f.
(1 go DEG C.) When the temperature exceeds t-, the heater 13 of the lower roller 11 is activated by the action of the temperature detector 150 to heat the area AHt of the roller 11. Therefore, the phoenix in the area of the roller 11 also applies heat to the paper P1 and the roller A. It saves the heat carried away from paper P, to area A,.

and B. , B1.7 can also be kept within the permissible range, and even when a large size paper P is passed next, wrinkles will not occur in this paper. Also large size paper P,
The area of people,. There is no difference in fixability between the portion corresponding to the area B10+B■' and the area corresponding to the area B10+B■'. Furthermore, as described above, by heating the area A11 of the roller 11, the roller l
Since the amount of heat taken out of the area A1° of O is reduced, the heater 12 can be turned on and off more frequently, and thermal deterioration of the roller can also be prevented.

As described above, according to the present invention, the difference in thermal expansion between the paper passing part and the non-paper passing part of the roller can be suppressed to a small value to prevent paper from wrinkling. In addition, thermal deterioration of the rollers can be prevented.

[Brief explanation of the drawing]

FIG. 1 is an explanatory diagram of an example of an electrophotographic apparatus that can utilize the present invention;
FIG. 2 is a detailed explanatory diagram of the present invention, and FIG. 3 is an example of a control circuit. This is a diagram of the throat. 10.11 is a roller, 12.13 is a heater, 14°15
is a temperature sensor, P is a small size paper, and Fold. It is a large size paper. Applicant: Canon Corporation, Saji.

Claims (1)

[Scope of Claims] In a fixing device that pinches and conveys a toner image support material between a first and second roller and heats and fixes the toner image on the support material, a first width size of a tenth roller is provided. a first heat source that heats a region through which the toner image support material passes; and a second heat source that heats a region of the second roller through which the toner image support material having a second width size smaller than the first width size passes. a heat source, and a temperature detection means for detecting the temperature of a portion of the first row 2 through which the toner image supporting material of the first width size passes but the toner image supporting material of the second width size does not pass; A fixing device patented as comprising: control means for operating the second heat source when the temperature rises above a set temperature.