JPS60142379A - Both-surface image forming device - Google Patents

Abstract

PURPOSE:To prevent curling and wrinkling, save electric power, and prolong the life of a roller, bearing motor, etc., by setting the degree of fixation lower in 1st surface fixation than in one-surface image formation, and setting the fixation degree of the 2nd surface lower than that of the 1st surface at the time of both- surface image formation. CONSTITUTION:A heat source 53 is provided with a main heating body 53a and two auxiliary heating bodies 53b and 53c. All the heating bodies are powered on in the fixation of one-surface copying operation, the main heating body 53a and auxiliary heating body 53c are powered on in the 1st surface copying of both-surface copying operation, and only the main heating body 53a is powered on with the signal for the copy start of the 2nd surface. The detection level of a thermistor is varied to control the set surface temperature of the fixing roller 51 to 190 deg.C in the 1st surface copying of both-surface copying operation and 160 deg.C in the 2nd surface copying. Consequently, the heating value applied to a sheet is reduced successively and the degree of fixation is decreased.

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), and particularly to a fixing device that fixes a toner image on a sheet. The present invention relates to a double-sided image forming apparatus that has been improved.

Conventionally, various copying machines have been proposed and implemented for performing so-called double-sided copying, in which copy images are formed on both the front and back sides of a sheet using electrophotography. For example, a normal one-sided copy is performed on one side of a sheet, the first side of the sheet is guided again to the original paper feed section, or another second paper feed section, and then the other side of the sheet is copied again. There is one that sends the paper to a processing section and copies the back side in the same way as the front side. This is a double-sided copying machine with a practical claw because only one set of the MII section is required and the structure is simple and compact. In this type of double-sided copying machine, the most efficient fixing device is a heated roller fixing device that fixes the toner image on the sheet by passing the sheet between a pair of rollers that are heated and pressed together. known as. In this heat roller fixing, the factor that influences the degree of fixing is the nip amount. The nip amount is a function of the width of the roller produced by the pressing force of the roller, the amount of heating, and the moving speed of the sheet, and determines the degree of fixation.

By the way, in conventional double-sided copying machines, not only the fixing of the first side and the fixing of the second side are performed with the same nip amount, but also with the same pressing force, heating amount, and moving speed -t. However, the state of the sheet to be fixed on the first surface is significantly different from that when the first surface is fixedly fixed and when the second surface is fixed. That is, the moisture normally contained in the sheet has been removed to some extent after the first side has been fixed, and the sheet after the first image has been fixed has residual heat.

Also, if the first side is fixed at a high fixing rate, the sheet will wrinkle.

Curling is likely to occur, and this may interfere with subsequent processes such as sheet conveyance for second-side copying, storage in a relay tray, refeeding from there, and transfer of second-side images.

Therefore, it is not necessarily a good idea to perform fixing on the first side and fixing on the second side with the same chive f amount as in the past.

SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a double-sided image forming apparatus which eliminates the drawbacks of the conventional apparatus and which prevents the occurrence of curls and wrinkles, saves power, and extends the life of rollers, bearing motors, etc.

The gist of the present invention is to provide a double-sided image forming apparatus having a common heat roller fixing device that fixes a toner image formed on a first side of a sheet and then fixes a toner image formed on a second side of a sheet. In the case of double-sided image formation, the degree of fixation at the first fixation is lower than the degree of fixation in the case of single-sided image formation, and the degree of fixation at the second time in the case of double-sided image formation is lower than the degree of fixation at the first time. A double-sided image forming apparatus is characterized in that:

An embodiment of the present invention will be described in detail below with reference to the drawings.

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

In the figure, an original 1 is placed on a transparent plate 2 of an original table, and an optical system is composed of movable reflecting mirrors 3, 4, a lens 5, and fixed reflecting mirrors 6, 7.

That is, the document 1 is moved between the movable reflection mirror 3 that moves together with the illumination lamp 8 and 1/1 of the movable reflection mirror 3.
While the optical path length is kept equal by the movable reflecting mirror 4 which moves in the same direction at a moving speed of 2, the lens 5
The light is subjected to slit exposure through fixed reflection mirrors 6 and 7, and is imaged onto a photosensitive drum 9. Here, the surface of the photosensitive drum 9 is made of a photosensitive member with a photoconductive layer covered with a transparent insulating layer.
As the photoreceptor rotates, it is first positively charged by a glass charger 11 to which a high positive voltage is supplied from a high voltage power source 1o. Subsequently, when reaching the exposure section 12, the image of the document 1 on the transparent plate 2 of the document table illuminated by the illumination lamp 08 is reflected by the movable reflection mirrors 3, 4, the lens 5, the identification reflection mirror 6, and the image of the document 1 on the transparent plate 2 of the document table.
An image is formed on the optical drum 9 by 7. The photosensitive drum 9 receives an AC corona discharge from an AC corona discharger 13 to which an AC high voltage is supplied from a high voltage power supply 10 at the same time as the original image is exposed to the photosensitive drum 9 . Next, an electrostatic latent image is formed on the surface of the photosensitive drum 9 by full exposure by the full surface exposure lamp 14, and then reaches the developing device 15. Development is performed by powder development using a magnetic sleeve method, and the electrostatic latent image is visualized. On the side, the sheets are fed out from the paper feed section, but the relay tray 17 and first paper feed table 18 of the paper feed section are automatic paper feed trays, and the second paper feed table 19 is an automatic paper feed section. It is a deck type that has a lifting device and can load a relatively large number of sheets. The relay tray 17 is also used as a paper feed table during double-sided copying. The first side of the sheet fed from one of the paper feed sections 17, 18, and 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 51 having a heat source 53 and a pressure roller 52 having a rubber layer on its surface. A sheet for narrowing the powder image passes between these rollers that are in pressure contact with each other. , the powder image is fixed onto the sheet by pressure and heat.

The sheet that has passed through the fixing device 23 is sent to the conveyance path 27a in the case of double-sided copying, and is further transferred to the first relay tray 17.
It is stored with the image formed on the surface facing up. A set number of sheets are stacked in the relay tray 17 through a similar copying process. Next, in response to a signal from a copy button (not shown) turned on, the first side copy method sheet in the relay tray 17 is sent to the conveyance path 46, and the toner on the photoreceptor drum 9 is applied to the second side of the sheet. After the image is transferred, it is discharged into the sorter 30 or tray 31 via the conveyance path 22, the fixing device 23, and the conveyance path 27b or 27c. Repeat the same copying process for the set number of copies.

Note that in the case of only one-sided copying, the sheet that has passed through the fixing device 23 is guided to a conveyance path 27b or 27e, and is carried out into a sorter 30 or a tray 31. In this way, the conveyance path is normally set at the position 27c shown by the solid line, and is bent to the position shown by the dotted line 27a or 27b in response to an optional signal.

FIG. 2 shows the fixing device 23 shown in FIG. 1 in this embodiment.
5 shows a detailed diagram of the heat source 53 of FIG.

That is, the heat source 53 includes a main heating element 53a and two auxiliary heating elements 5.
3b and 53c are provided, and during the fixing of single-sided copying, the main heating element 53a1 and the auxiliary heating elements 53b and 53c are all energized, but in the case of copying on the first side of double-sided copying, when the copying starts. According to the signal, the power to the auxiliary heat generating element 53b is cut off, and only the main heat generating element 53a and the auxiliary heat generating element 53c are energized. In this state, the first side copying is completed, and in response to the signal to start the second side copying, the auxiliary heating element 53e is also cut off, and only the main heating element 53a is energized. In the above, the surface temperature of the fixing roller 51 is set at 1.90 for single-sided copying. ? When copying the first side of double-sided copying, the level is 170C; when copying the second side, the level is 160C. The amount of heat is gradually reduced and the degree of fixing is lowered. Although this temperature change is somewhat less responsive, it is effective when making a large number of double-sided copies.

3, 4, and 5 are sectional views of fixing devices according to other embodiments of the present invention, which correspond to fixing device $23 in FIG. 1. The overall configuration of the double-sided copying machine according to this embodiment is the same as that shown in FIG.

Figure 3 shows the cross section when paper is not passing through, Figure 4 shows the cross section when copying on one side.
FIG. 5 is a sectional view when the first side of the duplex copy is being passed.

In these figures, 51 is a fixing roller, which has a heat source 53 inside. 52 is a pressure roller. A thermistor 55 for controlling the surface temperature is pressed against the surface of the fixing row 251, and the thermistor 55 turns on and off the heat source 53. Also, an arm 5 supporting both ends of the pressure roller 52 is provided.
7 has one end supported by a shaft and the other end connected to one end of a lever 59 via a compression spring 58. The other end of this lever 59 is engaged with a pin 60' of a cam 60, and the rotation of this cam 6o It is provided so as to compress and expand the compression/gun 58 by swinging in the direction A or B in the figure around point 9b. 67 is a surface elastic portion of the pressure roller.

When paper is not being passed, the lever 59 is not biased by the cam 60 as shown in FIG. 3, and the pressure roller 52 is spaced IF from the fixing roller 51. On the other hand, when the paper is oiled, the lever 59 is biased and swung in the A direction when the Shikamuro 0 is rotated by a motor (not shown), and the arm 57
When the fixing roller 52 is rotated about the axis a by the spring force of the compression spring 58, the pressure roller 52 is brought into pressure contact with the fixing roller 51. The fixing operation of this fixing device will be described below. First, in the case of copying only one side, the drive motor (not shown) is activated by the copying start signal to fix the fixing roller 5.
1 and the pressure roller 52 start rotating, and the pressure motor (not shown) operates to rotate the cam 60, and the bottle 60' biases the lever 59 to apply pressure as shown in FIG. The roller 52 is brought into pressure contact with the fixing roller 51. When the sensor 61 installed near the cam 6o detects the recess 64 on the outer periphery of the cam 6o, the pressure motor and the cam 6
0 is stopped, and the pair of rollers 5 and 52 are locked in a pressurized state by the brake mechanism of the motor itself. This state is shown in FIG.

It is preferable that the stop position of the cam 6o is set at a free position with respect to the lever 59 so that the cam 6o will automatically move when the pressurization is released later. Due to this movement of the lever 59, the arm 57 is moved by the compression spring 5.
The pressure roller 52 is brought into pressure contact with the fixing roller 51 under the force of a spring 8, and these rollers rotate in a state of pressure contact. In the case of single-sided copying, the sheet with the unfixed image is fixed by passing between the rollers.

The fixing operation at the stop position when the sensor 61 detects the fourth part 64 as in the case of the one-sided object described above is performed in the first
This is called position fixation.

Normally, when the single-sided copying is completed, the copy sheet is ejected from the machine via the path 27c or 27b, and in response to this signal indicating completion of ejection, the rollers 51 and 52 stop rotating and the cam 60 is driven. Pressure motor brake 11
(Removal is carried out. At this time, as mentioned above, the cam 60 is in contact with the lever 59 in the release state, so when the brake of the motor is released, the repulsive force of the spring 58 and the N-stroke of the roller 52, etc. Stable contact position #i with lever 59 due to
’ (position shown in Figure 3)! , the rotation is reversed.

In the case of copying the first side of double-sided copying, the copying start signal causes the rotation of the roller pair and the pressure motor, as well as the cam 6.
00 rotation starts in the same way, but in this case, as shown in Figure 5,
When the Sentsu 61 detects the four parts 63 on the outer circumference of the cam 60, the cam 60 stops, and the brake mechanism described above
Locked at this position, the roller pair is maintained under pressure corresponding to the break. The first surface is fixed by passing the pressurized sheet as described above between a pair of rollers. This state is shown in FIG.

The fixing operation at the stop position when the sensor 61 detects the concave portion 63 of the copy, as in the first side copy (/,) of the double-sided copy described above, is referred to as second position fixing.

Next, in the case of copying on the second side of double-sided copying, the rotation of the roller pair and the rotation of the cam 60 are similarly started in response to the copy start signal. When the cam 60 is detected, the cam 60 stops and is locked in this position by the brake mechanism described above, and the roller pair is maintained in a pressurized state corresponding to this. The second surface is fixed by passing the sheet between the pair of rollers under pressure. The second copy of both copies mentioned above.
The fixing operation at the stop position when the sensor 61 detects the four portions 63 as in the case of the surface is referred to as third position fixing.

When viewed in the drive rotational direction (arrow) of the cam 60, the recess 62, the recess 63, and the recess 64 are sequentially located on the downstream side, and the lever 59 is closest to the lowest point at the stop position of the cam 60 with respect to the recess 64. Therefore, the pressing force on the second side and 11F1 on one side of the first side increases by -5 (1) The degree of fixing increases in this order.

FIG. 6 is a flow chart showing the three pressurizing operations described above.

As in the two embodiments described above, by changing the roller setting temperature or pressing force, it is possible to
The fixing degree can be changed so that the first side>the second side, but in order to achieve this constant 7j degree order, it is necessary to change the roller temperature or pressing force to 33+1p as in the above two embodiments. It is possible without providing. For example, the heat temperature classification shown in Part 2 is set to only the main heat generating source 53a1 and the auxiliary heat generating source 53b, and the recesses of the cam shown in Figs. 3, 4, and 5 are set to only 63 and 64. It would be better if the stopping positions m of the cam 60 were set to only the first position and the second position.

It is good to change both the roller setting temperature and the pressing force.

- To give an example, the fixing temperature for single-sided copying is set to 19
0C, the pressure position is set at the first position, the first image fixing of double-sided copying is carried out at the set temperature 170C, the pressure position is set at the first position, and then the second fixing is carried out at the set temperature 170C, the pressure position is set at the second position. It is good to do it in a certain position. Further, in the above example, the temperature was changed in the first image fixing, and then the pressure was changed in the second fixing, but even in the opposite case, the fixing degree of the above-mentioned 11@ order can be achieved. That is,
The pressing force may be changed during the first image fixing, and the set temperature may be changed during the second image fixing.

In order to set the degree of fixing in the present invention to one side, the first side, and the second side, it is possible to use a combination of changing the roller setting temperature and pressing force, and the setting temperature, pressing force, etc. Considering this, many combinations can be considered.

By setting the fixing degree to one side, the first side, and the second side, a low fixing degree is given to the first side even when one side is printed as temporary adhesion, and the sheet used is thin. In the case of a letter, the heat is sufficiently removed during the first image fixing and some residual heat remains, so the degree of fixing is further lowered in the second image fixing to fully achieve the purpose of fixing. This tendency is strong even in high-speed machines with high copy processing capacity, so the degree of fixation in the above order is effective. Further, depending on whether the degree of fixation of the toner is strongly dependent on temperature or pressure, the degree of fixation does not immediately become the amount of nigration, and effective fixing is possible in the order of the degree of fixation described above.

As described above, according to the present invention, it is possible to obtain a double-sided image device that can reduce wrinkles, curls, etc. of sheets, and also realizes rational power saving and long life.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a double-sided copying machine according to an embodiment of the present invention, and FIG. 2 is a diagram showing a heat source of a fixing device in the same embodiment.
3, 4, and 5 are diagrams showing different states of the fixing device in another embodiment of the present invention, and FIG. 6 shows the roller pressing and releasing operations of the fixing device in the embodiment. 'This is a flowchart. 9... Photosensitive drum 17... Relay tray 18.19
...Paper feed tray 20...Transfer charger 23...Fixing device 30...Sorter 31...Ejection tray 51...
-Fixing roller 52...Pressure roller 53...Heat source 55...Thermistor 57...Arm 58...
・Compression spring 59...Lever 60...Cam 61・
...Sensor 63.64...Four parts 5 diagrams

Claims (1)

[Claims] In the case of double-sided image formation in a double-sided image forming apparatus having a common thermal roller fixing device that fixes the toner image formed on the first side of the sheet and then fixes the toner image formed on the second side of the sheet. The degree of fixation during fixation on the first side is lower than the degree of fixation in the case of single-sided image formation, and the degree of fixation on the second side in the case of double-sided image formation is lower than the degree of fixation on the first image. Image forming device.