JPH0697372B2 - Double-sided image forming device - Google Patents

Description

The present invention relates to a double-sided image forming apparatus such as a copying machine that forms an image on both sides of a transfer material (hereinafter referred to as a sheet), and more particularly to a fixing apparatus for fixing a toner image on a sheet. The present invention relates to an improved double-sided image forming apparatus.

Conventionally, various proposals have been made to realize a copying machine for performing so-called double-sided copying in which copy images are formed on both front and back surfaces of a sheet by using an electrophotographic method. For example, ordinary one-sided copying is performed on one side of a sheet, the sheet that has been subjected to the one-sided copying is guided again to the original sheet feeding section or another second sheet feeding section, and then the other side of the sheet is copied again to the copy processing section. There is a type that can be sent to and copied to the back side in the same way as the front side. This is the most practical double-sided copying machine because it has a single copy processing unit and the structure is simple and compact. As a fixing device for fixing a toner image on a sheet in this double-sided copying machine, a heat roller fixing device that performs fixing by passing the sheet between a pair of heated and pressure-contacted rollers is known to have high efficiency. Has been. In this heat roller fixing, a factor that influences the degree of fixing is the nip amount. The nip amount is a function of the nip width generated by the pressing force of the roller, the heating amount, and the moving speed of the sheet, and determines the fixing degree.

By the way, in the conventional double-sided copying machine, the fixing of the first side and the fixing of the second side are both performed with the same nip amount, and also with the same amount of heat transfer of the pressure contact force. However, the state of the sheet to be fixed differs greatly between the first surface fixing and the second surface fixing.

In addition, the sheet usually contains water before fixing, and the sheet subjected to the first surface fixing is more likely to cause a thermogenic curl due to the removal of moisture by heat than a curl due to the pressure contact force. As described above, the sheet curled by the fixing on the first side is jammed during conveyance in the machine for the subsequent second side copying, storage failure in the relay tray, re-feeding failure from there, transfer failure, etc. Will interfere with the process. Therefore, it is not a good idea to perform fixing on the first surface and fixing on the second surface with the same nip amount as in the conventional case.

SUMMARY OF THE INVENTION The present invention provides a double-sided image forming apparatus that solves the above-mentioned drawbacks of the conventional apparatus, prevents curling which is an obstacle, and saves power.

The gist of the present invention is to have a heating roller and a pressure roller that pressurizes the heating roller to form a nip, and nips and conveys an unfixed image carried on the first surface of the recording material at the nip. In a double-sided image forming apparatus for fixing and then fixing the unfixed image carried on the second surface of the recording material by nipping, the roller set temperature at the first surface fixing in the case of double-sided image formation Is lower than that when fixing the second surface,
A double-sided image forming apparatus is characterized in that the roller contact pressure at the time of fixing the second surface is made lower than that at the time of fixing the first surface.

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

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

In the figure, a document 1 is placed on a transparent plate 2 of a document table, and an optical system is composed of moving reflecting mirrors 3 and 4, a lens 5 and fixed reflecting mirrors 6 and 7. That is, the original 1 has the same optical path length due to the moving reflection mirror 3 that moves integrally with the illumination lamp 8 and the moving reflection mirror 4 that moves in the same direction at a moving speed half that of the moving reflection mirror 3. While being maintained, slit exposure is performed via the lens 5 and the fixed reflection mirrors 6 and 7, and an image is formed on the photosensitive drum 9. Here, the surface of the photosensitive drum 9 is composed of a photoconductor in which a photoconductive layer is covered with a transparent insulating layer.
First, it is positively charged by the positive charger 11 which is supplied with a positive high voltage from the high voltage power source 10. Then, when it reaches the exposure unit 12, the transparent plate 2 of the document table illuminated by the illumination lamp 8
The image of the original document 1 is formed on the drum 9 by the movable reflection mirrors 3 and 4, the lens 5, and the fixed reflection mirrors 6 and 7. The photosensitive drum 9 is exposed to the image of the original, and at the same time, is subjected to an AC corona discharge by an AC corona discharger 13 to which an AC high voltage is supplied from a high voltage power supply 10. Then, the entire surface is exposed by the entire surface exposure lamp 14, an electrostatic latent image is formed on the surface of the photosensitive drum 9, and then the developing device 15 is reached. The development is performed by powder development using a magnetic sleeve method, and the electrostatic latent image is visualized. On the other hand, although the sheet is sent out from the paper feed unit, the relay tray 17 and the first paper feed tray 18 of the paper feed unit are cassette type, and the second paper feed tray 19 has an automatic paper lifting device. The relay tray 17 is a deck type capable of stacking a large number of sheets, and is also used as a paper feed table during double-sided copying. The first surface of the sheet sent from any one of the sheet feeding units 17, 18 and 19 is brought into close contact with the drum 9. Then, the transfer charger 20 positively charges the sheet by the high voltage power source 10 and transfers the image on the drum 9 onto the sheet. The transferred sheet is separated from the drum 9 by the separating unit 21, and is guided to the fixing device 23 via the conveyance path 22. The fixing device 23 is composed of a fixing roller 51 having a heating source 53 and a pressure roller 52 having a rubber layer on the surface, and a sheet having a powder image passes between these rollers in pressure contact with each other. To fix the powder image on the sheet.

The sheet that has passed through the fixing device 23 is
The paper is sent to the transport path 27a, and then first to the relay tray 17.
The image formed on the surface is stored with the image side as the upper surface. A set number of sheets are stacked in the relay tray 17 through the same copying process. Next, when the copy button (not shown) is turned on, the first-side copied sheet on the first tray in the relay tray 17 is conveyed.
After being sent to the sheet 46, the toner image on the photosensitive drum 9 is transferred to the second surface of the sheet, and then the transport path 22, the fixing device 23, and the transport path 27b or 27c, and the sorter 30 or the tray 31.
Is discharged inside. Thereafter, the same copying process is performed for the set number of sheets. In the case of only one-sided copying, the sheet that has passed through the fixing device 23 is guided to the conveyance path 27b or 27c and is carried out into the sorter 30 or the tray 31. As described above, the transport path is normally located at the position of the solid line 27c, and receives a signal and switches to the position of the dotted line 27a or 27b if necessary.

Next, the fixing device 23 shown in FIG. 1 will be described in detail with reference to FIGS. 2, 3, and 4. FIG. 2 shows a cross section when no paper is passed, FIG. 3 is a cross section when one-sided copy or double-sided copy is on the first side, and FIG. 4 is a cross section when two-sided copy is on the second side.

In these figures, 51 is a fixing roller, which has a heat source 53 inside. 52 is a pressure roller. Fusing roller
A thermistor 55 for controlling the surface temperature is pressed against the surface of the 51, and the thermistor 55 allows the heat source
53 is controlled to be turned on and off. An arm 57 that supports both ends of the pressure roller 52 has one end pivotally supported and the other end coupled to one end of a lever 59 via a compression spring 58. The lever 59 has a pin of a cam 60 at the other end. 60 'is engaged, and the rotation of the cam 60 causes the compression spring 58 to be compressed and extended by swinging in the direction A or B in the figure around the point b. 67 is a surface elastic layer of the pressure roller.

When the paper is not passed, the lever 59 moves to the cam 60 as shown in FIG.
The pressure roller 52 is not biased by the fixing roller 51.
Is in a remote state. On the other hand, when the paper is passed, the lever 59 is eccentrically oscillated by the rotation of the cam 60 by a motor (not shown) and oscillates in the direction A, and the arm 57 is rotated about the axis a by the spring force of the compression spring 58. Thus, the pressure roller 52 is brought into pressure contact with the fixing roller 51.

Now, the fixing operation in this fixing device will be described below. First, in the case of copying on only one side, the fixing roller 51 and the pressure roller 52 are started to rotate by the drive motor (not shown) in response to the copy start signal, and the pressure motor (not shown) operates to operate the cam 60. Is rotated, and its pin 60 'biases the lever 59 to press the pressure roller 52 against the fixing roller 51 as shown in FIG. A concave portion 64 provided on the outer peripheral portion of the cam 60 is provided with a sensor 61 provided near the cam 60.
Is detected, the pressure motor and therefore the cam 60 are stopped,
A brake mechanism included in the motor itself locks the pair of rollers 51 and 52 so that the pressed state of the rollers 51 and 52 is maintained. This state is shown in FIG. It should be noted that the stop position of the cam 60 is preferably set to a relief position with respect to the lever 59 in order to automatically cause the movement of the cam 60 at the time of releasing pressure thereafter. By such movement of the lever 59,
The arm 57 receives the spring force of the compression spring 58 to bring the pressure roller 52 into pressure contact with the fixing roller 51, and these rollers rotate in a pressure contact state.

On the other hand, the heating source 53 built in the roller 51 has a structure as shown in FIG. That is, the main heating element 53a and the auxiliary heating element 53b are provided, and in the case of single-sided copying, the main heating element 5a
The surface temperature of the fixing roller 51 is controlled by the thermistor 55 such that the surface temperature of the fixing roller 51 reaches a set temperature of 190 ° C. by supplying electricity to the 3a and the auxiliary heating element 53b. This is 20 ° C. higher than the set temperature of 170 ° C. for fixing the first side in double-sided copying, which will be described later.

In the case of single-sided copying under the above conditions, the sheet having the unfixed toner image is fixed by passing between the rollers. Normally, when the one-sided copying is completed, the copy sheet is discharged to the outside of the apparatus via the above-mentioned path 27c or 27b. The rotation of the rollers 51, 52 is stopped by the signal of the completion of the discharge from the machine
And the brake of the pressure motor for driving the cam 60 is released. At this time, since the cam 60 is in contact with the lever 59 in a free-running state as described above, when the brake of the motor is released, the repulsive force of the spring 58, the weight of the roller 52 and the like cause a stable contact position with the lever 59. It is reversely rotated up to the position shown in FIG.

Further, also in the case of the first side copy in the double sided copy, the cam 60 takes the same stop position as in the case of the above single sided copy. The stop position when the sensor 61 detects the concave portion 64 as in the case of the one-sided copy described above or the first-side copy of the double-sided copy is referred to as a first stop position. However, in the case of the first-side copying, unlike the case of the single-sided copying, the auxiliary heating element 53b is not energized but only the main heating element 53a is energized. As described above, the surface temperature of the fixing roller 51 is the set temperature 170. It is controlled so that it becomes ℃.

Next, in the case of the second side copy in the double sided copy, the rotation of the roller pair and the rotation of the cam 60 are similarly started by the copy start signal, but in this case, as shown in FIG.
When the sensor 61 detects the concave portion 63 provided on the outer peripheral portion of the 60, the brake mechanism described above stops and locks the cam 60 at this position, and the roller pair is held in a pressured state corresponding thereto. The second surface is fixed by passing between the pair of rollers under pressure. This state is shown in FIG. The stop position when the sensor 61 detects the recess 63 as in the case of the second-side copy of the above-described double-sided copy is referred to as a second stop position.

The concave portion 63 is located downstream of the concave portion 64 when viewed in the driving and rotating direction of the cam 60, and the cam 60 is driven by a pressure motor (not shown) in the case of first-side copying of single-sided copying and double-sided copying. When the sensor 61 detects the second concave portion, that is, the concave portion 64 by rotating in the direction of the arrow, the rotation of the pressure motor is stopped when the copying is completed.
The cam 60 is reversely rotated to a stable contact position with the lever 59 by the repulsive force of 58 and the weight of the roller 52. In the case of the second-side copying of the double-sided copying, the cam 60 stops rotating when the sensor 61 detects the first concave portion, that is, the concave portion 63. In the case of the second surface copy, the main surface heat source 53a as well as the auxiliary heat source 53b is energized by the second surface copy start signal, and the set temperature is also changed to 190 ° C. as described above. When the copying of the second surface is completed, the cam 60 rotates in the reverse direction to release the pressurization state as in the case of the first surface.

As is apparent from FIGS. 3 and 4 and the above description, the roller pressing pressure contact force is different between the fixing at the first position and the fixing at the second position, and the fixing at the first position is more than the pressing force at the second position. It is getting bigger. It is known that a factor that determines the fixing degree is a nip amount, and the nip amount is expressed by time x heating amount x nip width. In the present embodiment, fixing is performed under the condition that the roller pressure is high and the temperature is low in the first side copy, and conversely in the second side copy, the fixing is performed under the condition that the pressure is low and the temperature is high. Be seen. Therefore, the nip amount is fixed under substantially the same conditions. However, residual heat remains on the sheet on which fixing of the first side is completed, and moisture contained in the normal sheet is removed to some extent, so that fixing of the second side is more difficult than fixing of the first side. Since the same fixing can be performed with a low nipple amount, the pressing force or the set temperature may be changed to set the nip amount for the second surface fixing smaller than the nip amount for the first surface fixing.

As described above, in the fixing of the first side, the thermal curl of the sheet can be suppressed to a small level by lowering the set temperature, and the processes such as conveyance and transfer up to the second side fixing can be stably performed. In this case, the moisture of the sheet is removed to some extent and the influence of heat on the curl is small, so the curl due to the pressure can be reduced by raising the set temperature and instead lowering the applied pressure, and the sheet to the discharge tray or sorter can be reduced. The storage of can be improved.

FIG. 6 is a flow chart showing the first and second surface fixing operations in this embodiment.

As described above, according to the present invention, it is possible to obtain a double-sided image device in which wrinkles, curls, and the like of a sheet can be reduced, and rationalization and power saving can be realized.

[Brief description of drawings]

FIG. 1 is a side sectional view of a double-sided copying machine according to an embodiment of the present invention, and FIGS. 2, 3, and 4 are sectional views showing different states of a fixing device of the same embodiment, and FIG. Is a cross-sectional view of the heat source of the identification fixing device, and FIG. 6 is a flowchart showing the pressing and releasing operations of the fixing device. 9 ... Photosensitive drum, 17 ... Relay tray, 18, 19 ... Paper feed table, 20 ... Transfer charger, 23 ... Fixing device, 30 ... Sorter, 31 ... Discharge tray, 51 ... Fixing roller, 52 ... Pressure roller, 53 … Heating source, 55… Thermistor, 57… Arm, 58… Compression spring, 59… Lever, 60… Cam, 61… Sensor, 63, 64… Recessed part.

Continuation of the front page (56) Reference JP-A-54-92749 (JP, A) JP-A-58-136073 (JP, A) JP-A-58-120283 (JP, A) JP-A-58-142363 (JP , A) JP 60-142373 (JP, A) JP 60-142379 (JP, A) JP 60-142363 (JP, A) Actual development Sho 60-44061 (JP, U) Actual development Sho 60-44062 (JP, U) JP-B 2-13786 (JP, B2) JP-B 2-1784 (JP, B2)

Claims (1)

[Claims] 1. An unfixed image carried on the first surface of a recording material at the nip is sandwiched and conveyed and fixed by a heating roller and a pressure roller that presses the heating roller to form a nip. In the double-sided image forming apparatus that performs fixing and then holds and conveys the unfixed image carried on the second surface of the recording material in the nip, the roller set temperature at the time of fixing the first surface in the case of double-sided image formation is set. A double-sided image forming apparatus characterized in that it is lower than that during second surface fixing, and the roller contact pressure during second surface fixing is lower than that during first surface fixing.