JPS63142367A - Electrophotographic copying machine - Google Patents

Abstract

PURPOSE:To reduce the staining of a fixing roller by switching one of conditions of electrostatic charging, development, and transfer at the time of half-fixation mode and making the amount of developing toner stuck on a photosensitive body smaller than that in a normal fixation mode. CONSTITUTION:A switching means 34 is connected through a varistor 33 to a grid electrode 32 arranged between the corona wire 31 of an electrostatic charger 6 and the photosensitive body 5 and the switching means 34 is connected to a CPU as a control means. Then when, for example, the half-fixation mode is selected with a mode selection key, part of the varistor is short-circuited through the operation of the switching means 34 to hold an electrostatic charging potential lower than that in the normal mode. Thus the electrostatic charging potential to the electrostatic charger 6 is lowered to make the amount of developing toner stuck on the image part on the photosensitive body 5 at the time of development smaller than that in normal fixation mode. The amount of developing toner transferred to transfer paper is therefore decreased. Consequently, the quality of a copy image is improved, the reliability is increased, and maintenance intervals become long.

Description

Detailed Description of the Invention The present invention includes the steps of forming a latent image on a photoconductor, developing it, copying it, and fixing it, and fixing it on transfer paper using normal fixing to obtain a fixed copy. The present invention relates to an electrophotographic copying machine that can be selected between a mode and a semi-fixing mode in which weak fixing is performed to the extent that it can be easily erased.

Conventional electrophotographic copying machines of the type described above are already known. This type of copying machine was created in response to the demand that it would be convenient to be able to correct a portion of a copy made from an original by simply erasing it with an eraser or the like.

In the semi-fixing mode, the heat of the fixing roller is not sufficiently supplied to the toner layer in the copy produced, so the toner's welding state to the transfer paper is insufficient, and the toner layer adheres to the fixing row, causing the fixing roller to 7η There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide an electrophotographic copying machine which can solve the above-mentioned conventional problems and can achieve a desired semi-fixed state by reducing stains on the fixing roller.

In order to achieve the above object, the present invention is characterized in that in the semi-fixing mode, the amount of developed toner attached to the photoreceptor is reduced compared to the normal fixing mode by switching at least one of charging, developing, and transfer conditions. shall be.

The structure and operation of the present invention will be explained in detail based on the embodiment shown in the drawings.

FIG. 1 is a diagram showing the overall general configuration of an embodiment of an electrophotographic copying machine according to the present invention.

An original placed on a contact glass l provided on the top surface of the copying machine is optically scanned by the left and right swinging illumination units 2, and an image is formed on the photoreceptor drum 5 via a lens 3 and a mirror 4. The photoreceptor is exposed to light.

Around the photosensitive drum 5, a charging charger 6, an erase unit 7, an exposure position, a developing device 8, a transfer charger 9, a separation recess conveying belt 10, a static elimination charger 11, and a cleaning unit 12 are arranged in the rotational direction indicated by the arrow. has been done. Upper, middle, and lower paper feed trays 1 are located on the right side of the camera.
3, 14, and 15 are provided, and the transfer paper is fed to the transfer section constituted by the transfer charger 9 via the paper feed path 16. The toner image formed on the surface of the photoreceptor drum by the known electrophotographic process by each of the above-mentioned process units is transferred by the transfer charger 9 to the transfer paper fed at the same timing, and then transferred by the separation & feeding unit 10. After being conveyed to the fixing unit 17 and fixed, the sheet is discharged onto the copy receiver 18, or, in the case of double-sided copying, is reversed and discharged onto the intermediate copy receiver 19.

The configuration described up to this point is the same as that of a conventional copying machine.

The fixing unit 17 of the copying machine of this embodiment is a hot cola type fixing device, and as shown in detail in FIG. A possible pressure roller 22 is provided.

The pressing force of the pressure roller 22 is variable by a cam 25 that engages with a cam follower 24 provided at the tip of a lever 23 that supports the pressure roller 22. Cam 25 is the third
As shown in the figure, the cam follower 24 is rotated to two predetermined positions by a rotary solenoid 26, thereby displacing the cam follower 24 as shown by the arrows in FIG.
The pressing force of the pressing roller 22 is switchable. The operation panel of the copying machine is equipped with a mode selection key that allows you to arbitrarily select between normal fixing mode and semi-fixing mode.
The rotary solenoid 26 is turned on and off by operating this selection key.

Furthermore, in the copying machine of this embodiment, as shown in FIG. A paper transport path 29 is provided which branches from the transport path leading to the normal transfer section on the discharge side and directly leads to the fixing unit 17. A conveyance path switching pawl 30 is provided at a branch point between the normal conveyance path 16 and this conveyance path 29. Conveyance rollers made of a material such as sponge whose friction coefficient and pressing force are not very large are provided at key points of the conveyance path 29. Further, a re-fixing mode selection key is provided on the operation panel, and by operating this key, the above-mentioned conveyance path switching claw 30 is moved to a position for guiding the paper to the conveyance path 29, and the pressure roller 22 is also applied. Set the pressure to the pressure for normal fixing.

The operation of producing a semi-fixable copy using this apparatus will be explained below.

When the operator selects the semi-fixing mode by operating the mode selection key on the operation panel, the rotary solenoid 26 turns on, rotates the cam 25, and moves the cam follower 24 engaged with it to the right in the second position. Pressure roller 2 is moved to
The pressing force on the fixing roller 21 of No. 2 is reduced to the pressing force in a predetermined semi-fixing mode. As a result, the toner image on the transfer paper sandwiched and conveyed by the fixing roller 21 and the pressure roller 22 is fixed in a semi-fixed state, and
Excreted during the day.

As mentioned above, this semi-fixed state is set to such a level that it can be easily erased with an eraser like a pencil-written document, and that the image will not rub or peel off even with normal handling. The pressing force of the pressure roller in the semi-fixing mode is determined according to this.

The resulting copy can therefore be easily modified.

However, if copies in a semi-fixed state are stored as they are, it is difficult to maintain them in perfect condition because they are touched by human hands over time or the sheets are rubbed against each other. Therefore, it is desirable to make the necessary corrections and then completely fix them.

Therefore, when the re-fixing mode is selected using the re-fixing mode selection key on the operation panel of the copying machine, the conveyance path switching claw 30 is switched to the position where it guides the paper toward the conveyance path 29, and the corrected paper is transferred from the paper insertion slot. When a semi-fixed copy is inserted, the copy is ejected to the intermediate copy tray 19 by the conveyance roller 28, inserted into the conveyance path 29 by the paper feed roller of the intermediate copy tray, and transferred to the fixing unit 17 by the conveyance roller provided on the conveyance path. sent. At this time, the fixing unit 17
Since the pressing force of the pressure roller 22 is normally the pressing force for fixing, the semi-fixing copy is completely fixed and is discharged on the first day of receiving the copy.

A semi-fixable copy can be obtained by changing the fixing temperature, the nip width between the fixing roller and the pressure roller, and the passing speed of the fixing section, in addition to changing the pressing force of the fixing roller shown in the above embodiment. Of these, the nip width changes in relation to the fixing pressure. Furthermore, it is practically difficult to change only the passing speed of the fixing section separately from other conveyance paths. Therefore, in addition to changing the pressing force, it is highly possible to change the fixing temperature. In the case of a flash fixing device, the degree of fixing can be changed by changing the amount of light.

Fixing conditions such as pressing force and fixing temperature to obtain an optimal semi-fixing copy vary depending on the type of transfer paper.

Therefore, it is preferable to set fixing conditions in advance according to the type of transfer paper, and to change the fixing conditions by inputting a transfer paper type designation key.

Further, in the semi-fixing mode, special transfer paper or toner suitable for the semi-fixing mode may be used.

When making a copy using normal fixing, by operating the mode selection key on the operation panel and selecting the normal fixing mode, the cam 25 is moved to the pressure roller 2 as shown in FIG.
2 to the right so that it is sufficiently pressed against the fixing roller 21.

The following copies can be obtained by copying and fixing as usual.

When comparing the case of normal fixing and the case of semi-fixing, there is a difference in the dirt on the fixing roller 20, as shown in FIG.

In Figure 4, where the horizontal axis is the fixing pressure and the vertical axis is the amount of dirt on the fixing roller, the amount of dirt on each curve is larger in the case of semi-fixing at the fixing pressure P2 than in the case of normal fixing at the fixing pressure P1. One thing is clear. The curves in Figure 4 show the changes in the amount of toner attached to the transfer paper when the amount of toner attached to the transfer paper is controlled, and the amount of toner attached to the transfer paper is decreased in the order of curves A, B, and C. Indicate the case.

From FIG. 4, it was found that even with the same fixing pressure, the amount of staining on the fixing roller varied greatly depending on the amount of developed toner attached. In particular, when two or more layers of toner adhere to the transfer paper and the amount of developed toner is large, the amount of stain becomes several to several tens of times larger than when the amount of developed toner is small.

From this point of view, in the present invention, when the semi-fixing mode is selected, the amount of developing toner adhering to the transfer paper is automatically reduced.

As a specific example of reducing the amount of developed toner adhering to the transfer paper, as shown in FIG. A switching means 34 is connected thereto, and the switching means 34 is connected to a cPU as a control means.

When the semi-fixing mode is selected by the mode selection key, a part of the varistor is short-circuited by the operation of the switching means 34, and the charging potential is lowered than in the normal mode.

As the charging potential by the charging charger 6 is lowered, the amount of developing toner that adheres to the image area of the photoreceptor 5 during development becomes smaller than in the normal fixing mode. Therefore, the amount of developing toner transferred to the transfer paper is also reduced. In this way, the state shown by curve C in FIG. 4 can be obtained, and the amount of dirt on the fixing roller can be kept almost the same as in the normal fixing mode.

As another example, as shown in FIG. 1, a variable power power source 36 is connected to the halogen lamp 35 for exposure, a variable voltage power source a38 is connected to the developing sleeve 37 of the developing device 8, and the variable power source 36 and the variable voltage power source 38 are connected to the developing sleeve 37 of the developing device 8. a38 is controlled by the CPU.

In this case, when the semi-fixing mode is selected, the power amount of the variable power power source 3G is lowered to lower the light amount of the exposure halogen lamp 35, and the voltage of the variable voltage power source tA38 is increased to reduce the voltage applied to the developing sleeve 37. increase. As a result, the photoreceptor 5
The difference between the potential of the developing area and the potential of the developing sleeve 37 becomes smaller, and the amount of developing toner adhering to the photoreceptor decreases. That is, the amount of developing toner on the transfer paper can be reduced.

In contrast to the example in which both the power of the halogen lamp and the voltage of the developing sleeve are controlled, it is sufficient if the difference between the potential of the developing area of the photoreceptor and the potential of the developing sleeve can be reduced by controlling either one.

Furthermore, as shown in FIG. 6, a transformer 39 is connected to the developing sleeve, a variable AC power source 40 and a variable DC power source 41 are connected to the transformer 39, and the variable AC power source 40 and variable DC power source 41 are controlled by the CPU: It is also possible to use development bias control that uses PI. In normal fixing mode, AC voltage and DC voltage are applied, but in semi-fixing mode, the AC voltage component is reduced to ○FF. to control.

The control flow in the example of FIG. 5 may be as shown in FIGS. 7 and 8, but what is the control flow in particular? l
Since the content of the invention does not lie in the flow of Il itself, its explanation will be omitted.

It is only necessary to reduce the amount of developing toner attached to the transfer paper in the semi-fixing mode, so in addition to the above example, it is possible to switch and control the distance between the photoreceptor and the developing sleeve, and to switch and control the speed of the developing sleeve during development. The object of the present invention is also achieved.

According to the present invention, it has become possible to significantly reduce the staining of the fixing roller by a simple method of switching the amount of developing toner that adheres to the transfer paper between the normal fixing mode and the semi-fixing mode. This has the effect of improving the quality of copied images, increasing reliability, and lengthening maintenance intervals.

[Brief explanation of the drawing]

1 is a schematic front sectional view of an example of an electrophotographic copying machine according to the present invention, FIG. 2 is a schematic sectional view of an example of a fixing unit, and FIG. is a diagram showing the relationship between the fixing pressure and the amount of dirt on the fixing roller; FIGS. 5 and 6 are schematic diagrams showing different embodiments in which the amount of attached developing toner is switched and controlled;
FIGS. 7 and 8 are an example of a flowchart in the case of control (2) according to the example of FIG. 2... Lighting unit 5... Photoreceptor 6... Charger 8... Developing device 9... Transfer charger 32... Grid electrode 33... Varistor
34...Switching means 35...Halogen lamp 36...Variable power source 37...Developing sleeve 38...Variable voltage power source 39...Transformer
40... Variable AC power supply 41... Variable DC power supply

Claims (4)

[Claims] (1) It has a process of forming a latent image on a photoreceptor, developing it, copying it, and fixing it, and fixing it on transfer paper in a normal fixing mode to obtain a normal fixed copy, and in a normal fixing mode to obtain a fixed copy. In an electrophotographic copying machine that can be selected between a semi-fixing mode in which weak fixing is performed, the amount of developed toner attached to the photoreceptor can be changed to a normal fixing mode by switching at least one of charging, developing, and transfer conditions in the semi-fixing mode. An electrophotographic copying machine characterized by the following: (2) The electrophotographic copying machine according to claim 1, wherein the absolute value of the charging potential of the photoreceptor during charging is set lower in the semi-fixing mode than in the normal fixing mode. (3) A patent claim characterized in that the potential of the developing sleeve during development is switchable so that the difference between the potential of the developing area of the photoreceptor is smaller in semi-fixing mode than in normal fixing mode. The electrophotographic copying machine according to item 1. (4) The alternating current component of the voltage applied to the developing sleeve during development is changed so as to be smaller in the semi-fixing mode than in the normal fixing mode. Electrophotocopy machine.