JPH0213786B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a double-sided image forming apparatus such as a copying machine that forms images on both sides of a transfer material (hereinafter referred to as a sheet). In particular, the present invention relates to a double-sided image forming apparatus that achieves power saving in a fixing device that fixes a toner image on a sheet.

The following is an explanation using a double-sided copying machine as an example.

Conventionally, in a copying machine using electrophotography, it has been considered to perform so-called double-sided copying in which copied images are formed on both the front and back sides of a sheet of copy paper. Furthermore, various copying machines have already been proposed and realized for achieving such double-sided copying. For example, a normal one-sided copy is performed on one side of a sheet, and the sheet that has been copied on one side is fed back to the original paper feed section or another second paper feed section, and then the opposite side of the sheet is transferred. There is a method in which the side surface is sent to the copy processing section again and the back surface is copied in the same way as the front surface. This is the most practical double-sided copying machine because only one set of copy processing units is required and the structure is simple and compact.

However, in such conventional double-sided copying machines, fixing is performed at the same set temperature for both the first side (front side) and the second side (back side) of the sheet. Therefore, when fixing the second side of the sheet, residual heat from fixing the first side remains in the sheet, so the temperature of the sheet may rise above the required fixing temperature. This may cause the sheet to expand, contract or curl unnecessarily.

SUMMARY OF THE INVENTION Therefore, the present invention provides a double-sided image forming apparatus that eliminates the drawbacks of the conventional apparatus described above and also realizes power saving.

As described above, the present invention includes an image carrier for carrying a toner image, a transfer means for transferring the toner image on the image carrier onto a recording material, and a predetermined method for heat-fixing the toner image on the recording material. In a double-sided image forming apparatus that has a heating body maintained at a set temperature and fixes the toner image transferred on the first side of the recording material and then fixes the toner image transferred on the second side, The set temperature for fixing the toner image on the second side is lower than the set temperature for fixing the toner image on the first side.

Hereinafter, one embodiment of the present invention will be described in detail using the drawings.

FIG. 1 is a side view of a double-sided copying machine to which an embodiment of the present invention is applied.

In the figure, an original 1 is placed on a transparent plate 2 of an original table, and an optical system includes movable reflecting mirrors 3, 4, and a lens 5.
and fixed reflection mirrors 6 and 7. That is, the original 1 has an equal optical path length due to the movable reflective mirror 3 that moves together with the illumination lamp 8 and the movable reflective mirror 4 that moves in the same direction at half the moving speed of the movable reflective mirror 3. While being maintained, the light is further subjected to slit exposure through a lens 5 and fixed reflection mirrors 6 and 7, and is imaged onto a photosensitive drum 9. Here, the surface of the photosensitive drum 9 is composed of a photoconductor whose photoconductive layer is covered with a transparent insulating layer, and the photoconductor is first positively charged by a positive charger 11 that is supplied with a positive high voltage from a high voltage power supply 10. Becomes electrically charged. Subsequently, when reaching the exposure section 12, the original 1 on the transparent plate 2 of the original table is illuminated by the illumination lamp 8, and an image is formed on the drum 9 by the movable reflection mirrors 3, 4, the lens 5, and the fixed reflection mirrors 6, 7. be done. The photosensitive drum 9 is exposed to the original image and at the same time is connected to the high voltage power supply 1.
AC discharger 1 supplied with AC high voltage from 0
3 receives an alternating current discharge. Next, the photosensitive drum 9 is exposed to light by the full-surface exposure lamp 14.
An electrostatic latent image is formed on the surface and enters the developing device 15. Development is performed by powder development using a magnetic sleeve method, and the electrostatic latent image is visualized. Next, the sheet is sent out from the paper feed section, and the relay tray 17 and first paper feed tray 18 of the paper feed section are of the cassette type, and the second paper feed tray 19 is equipped with an automatic paper lifting device. It is a deck type that can load a relatively large number of sheets. Here, the relay tray 7 is also used as a paper feed tray during double-sided copying. And paper feed sections 17, 18,
A sheet sent from one of the drums 19 is brought into close contact with the drum 9. Therefore, the transfer charger 20 positively charges the sheet using the high-voltage power supply 10, and transfers the image on the drum 9 onto the sheet. After the transfer, the sheet is separated from the drum 9 by a separation section 21 and guided to a fixing device 23 via a conveyance path 22. The fixing device 23 is composed of a fixing roller 24 having a heat source 24a and a pressure roller 25 having a rubber layer on the surface. A sheet having a powder image passes between the rollers that are in pressure contact with each other, and is fixed by pressure and heat. The powder image is fixed on the sheet. The sheet that has passed through the fixing device 23 is sent to a conveyance path 27a in the case of double-sided copying, and is further stored in the relay tray 17 with the image formed on the first side facing upward. A set number of sheets are stacked in the relay tray 17 through a similar copying process. Next, a signal from the copy button (not shown) turns on.
The sheet in the relay tray 17 is sent out to the conveyance path 46, and after the image is transferred to the second side of the sheet,
Conveyance path 22, fixing device 23, and conveyance path 27b
Alternatively, it is discharged into the sorter 30 or tray 31 via 27c. The same copying process is then repeated for the set number of copies. Note that during single-sided copying, the sheet that has passed through the fixing device 23 is guided to the conveyance path 27b or 27c and then transferred to the sorter 30 or tray 31.
It is carried inside. Also, the conveyance route is normally 27 (solid line).
It is located at position c, and if necessary, it receives a signal and moves to dotted line 2.
It can be switched to the position 7a or 27b.

The fixing device 23 of this embodiment includes a hollow cylindrical fixing roller 24 having a halogen heater 24a therein as a heat source, a pressure roller 25 whose surface is coated with a rubber layer 25b on a core metal 25a, and this roller. A hollow cylindrical roller 32 that also has a halogen heater 32a inside it and is in contact with the pressure roller.
It is made up of. Further, a thermistor 33 is provided on the surface of the roller 24 as a temperature detection device, and a thermistor 34 is provided on the roller 25 as well. The outer peripheral surface of the metal pipe portion of the fixing roller 24 is coated with a thin film such as tetrafluoroethylene coating or silicone rubber to prevent offset. Furthermore, the pressure roller 25, which rotates in pressure contact with the fixing roller 24, is made of iron, aluminum or
A rubber layer 25b such as silicone rubber is adhesively coated on the surface of a metal core 25a made of SUS or the like. The roller 32 is a hollow cylindrical roller made of copper with good thermal conductivity, and its outer peripheral surface is coated with a thin tetrafluoroethylene coating to prevent offset. In addition, each roller 24, 25, 32 transfers the driving force of the motor M to a belt 35, gears 36, 37, 3.
8, 39, 40, and 41 to rotate.

In this embodiment, during warm-up, standby, or image formation on the first surface,
The surface temperature of the fixing roller 24 is 180°C.
The detection temperatures of the thermistors 33 and 34, which are temperature detection devices, are set so that the surface temperature of the sensor 5 is 160°C. Then, the set temperatures of the thermistors 33 and 34 are set respectively by a signal from a copy button (not shown) turned on to start image formation on the second side (back side).
At the same time, the temperature is shifted to 170°C and 150°C, and the control unit 35 lowers the voltage supplied to the heaters 24a and 32a, which are heat sources, so that the surface temperature of the fixing roller 24 is lowered.
The surface temperature of the pressure roller 25 is controlled at 170°C and 150°C. This control state is shown in FIG. In the figure, the vertical axis is the roller temperature (° C.), the horizontal axis is the elapsed time (seconds), and the temperature change of the fixing roller 24 is shown by a curve a, and the temperature change of the pressure roller 25 is shown by a curve b.

As a result, in this embodiment, the temperature of the sheet does not increase unnecessarily even when fixing the second side (back side), and the surface of the sheet is prevented from becoming rough, expanding, contracting, curling, etc. Power saving can also be achieved.

According to the applicant's experiments, the degree of residual heat varies depending on the conveyance speed of the copying machine, machine configuration layout, etc., but in copying that can produce about 30 double-sided copies (A4 size sheets) per minute, Although the temperature immediately before the fixing device during copying on the second side is about 30 to 40°C higher than room temperature, by using the fixing device of this embodiment, the second side can be copied without causing the above-mentioned problems. I was able to fix it.

Still another embodiment is shown in FIG.

In this embodiment, a heating element having a configuration as shown in FIG. 4 is provided in a heat source built into one or both of the rollers 24, 32. In this embodiment, the heat source 42 is provided with a main heating element 42a and an auxiliary heating element 42b.When fixing the first surface, both the main heating element 42a and the auxiliary heating element 42b are energized, and when fixing the second surface, the main heating element 42a and the auxiliary heating element 42b are supplied with electricity. A control unit (not shown) controls the power supply only to the body 42a. In this embodiment, if the amount of heat generated by the auxiliary heating element 42b is determined in advance, the surface temperature of the roller can be easily lowered during fixing on the second surface.

Further, according to the present invention, (i) only the set temperature on the fixing roller 24 side is lowered. (ii) It is also possible to perform control such as reducing only the set temperature on the pressure roller 25 side. Further, according to the present invention, the first
The fixing temperature of the surface or the second surface can be determined arbitrarily and is not limited to the examples. Further, in this embodiment, an external heating type fixing device has been described as an example, but the present invention is not limited to this. For example, an internal heating type fixing device may be used, or a roller fixing device may be used. Of course, the invention is not limited to this and can also be applied to a hot plate fixing device.

As described above, the present invention prevents roughening, curling, etc. of the sheet surface during fixing by setting the fixing temperature when forming an image on the second side lower than the fixing setting temperature when forming an image on the first side. The purpose of the present invention is to provide a double-sided image forming apparatus that realizes power saving while also achieving power saving.

[Brief explanation of drawings]

FIG. 1 is a side view of a double-sided copying machine to which an embodiment of the present invention is applied, FIG. 2 is a perspective view of its fixing device, FIG. 3 is a state diagram of temperature control, and FIG. 4 is a diagram of other heat sources. FIG. 3 is a side view of the embodiment. In the figure, 23...fixing device, 24...fixing roller, 24
a...Halogen heater, 25...Pressure roller, 32
...Roller, 32a...Halogen heater, 33,
34...Thermistor.

Claims (1)

[Scope of Claims] 1. An image carrier for carrying a toner image, a transfer means for transferring the toner image on the image carrier onto a recording material, and a predetermined device for heat-fixing the toner image on the recording material. In a double-sided image forming apparatus which has a heating body maintained at a set temperature and fixes a toner image transferred onto a first side of a recording material and then fixes a toner image transferred onto a second side of the recording material, The temperature setting when fixing the toner image on the second side is the first temperature.
A double-sided image forming apparatus characterized in that the temperature is lower than a set temperature when fixing a toner image on a surface. 2. The double-sided image forming apparatus according to claim 1, wherein the heating body is a heat roller heated by a heat source.