JPH02272590A - Image forming device - Google Patents

Abstract

PURPOSE:To keep the charge quantity per unit area of a transfer material constant irrespective of width of the transfer material and to stably execute a satisfactory transfer by providing a means for varying a transfer current by a bias applied to a transfer means in accordance with width of the transfer material. CONSTITUTION:When a transfer material of a specific size is contained, and a freely attachable and detachable cassette 5 is positioned in a fixed position in a device body, a cassette detecting part 6 for detecting it is provided. In this case, when a cassette, accordingly, width of the transfer material to be used is detected, an output signal of the cassette detecting part 6 is received, and by controlling a transfer power source 7 by a CPU 9, a current value is varied. That is, by setting a current value of an applied bias in accordance with width of the transfer material, even in any transfer material, the charge quantity per its unit area is kept constant and an appropriate transfer can be executed.

Description

Detailed Description of the Invention (1) Purpose of the Invention (Field of Industrial Application) This invention relates to an image forming apparatus that uses an electrostatic transfer process, such as an electrostatic copying machine or a printer, and particularly to a transfer apparatus thereof. .

(Prior Art and Problems to be Solved) The image forming apparatus described above is equipped with a moving image carrier and a transfer roller that runs in pressure contact with the image carrier, and a transfer roller mainly using paper is placed in the pressure nip between the two. Let the material pass through
A transferable toner image previously formed on the surface of an image carrier is superimposed on the toner image and the toner image is run in synchronization, a transfer bias is applied to the transfer roller, and the toner image is transferred to the transfer material by the action of the electric field formed. An image forming apparatus configured to do this has already been proposed.

Compared to devices that use conventionally well-known corona dischargers, such image forming devices are less likely to apply excessive charge to the transfer material during transfer, causing toner to fly away. In the case of reversal development, the charge on the image carrier side and that of the toner are of the same polarity, so the bias voltage applied to the transfer roller is low. Since the transfer material is firmly held, there are various advantages such as less transfer misalignment.

By the way, in this type of apparatus, it has been known that there are two types of means for applying a transfer bias: a constant voltage control method and a constant current control method. However, when handling transfer materials of various thicknesses, Constant current control is better
As the thickness increases, the resistance also increases and the voltage applied to the roller also increases, which has the advantage of preventing a decrease in the transfer electric field and maintaining transferability.

However, in this type of device, it is common to use transfer materials of various sizes, so if the width of the transfer material changes, especially if it becomes smaller,
There is a problem in that current flows directly from the transfer roller to the surface of the image carrier in areas where no transfer material is present, resulting in a drop in applied voltage and the occurrence of transfer defects.

This will be briefly described with reference to FIGS. 9A, 9B, 10A and 1OB.

In FIGS. 9A and 10A, a transfer roller 12 is in pressure contact with a rotating cylindrical image carrier 1a, and a wide transfer material 11 and an intermediate transfer material 11s are placed in a pressure nip between the two in a direction perpendicular to the plane of the paper. FIG. 2 is a cross-sectional view showing a configuration configured to be conveyed in a manner similar to that shown in FIG.

In FIG. 9A, the width of the transfer material 11 is almost the same as the length of the transfer roller 12, and in FIG. 10A, the width of the transfer material 11s is smaller than the length of the transfer roller 12, and a part of the nip portion is attached to the image carrier 1a. and the transfer roller 12 are in direct contact with each other.

FIG. 9B shows a simple equivalent circuit in the case shown in FIG. 9A, and symbols 1aR1LIR112R schematically represent the resistances distributed in the image carrier 1, the transfer material 11, and the transfer roller 12, respectively. It is something.

Further, FIG. 10B shows an equivalent circuit in the case shown in FIG. 10A. In this case, since the transfer material 11S does not exist at both end portions of the transfer roller 12, the resistance of the transfer material 11S at the corresponding portions increases. It is shown where it is zero.

From these two circuit diagrams, it can be easily understood that the combined resistance of the latter is smaller than that of the former (therefore, if the current flowing from the transfer roller to the image carrier is constant, the voltage will decrease).

FIG. 11 is a graph of an experimental example showing the above aspect, and the experimental conditions were as follows.

The film thickness of the image carrier 1a is 45 μm, and the specific resistance of the image carrier is 10′.
4ΩCm, specific resistance of transfer roller 10'Ωcm, roller length 21.6
cm, roller elastic layer thickness 6mm, roller hardness 20°
(Asker-C hardness), nip width 3 mtm.

Transfer current: 6 μA.

Process speed: 90 mm/sec.

The transfer material was paper with a basis weight of 80 gr/m. The graph in FIG. 11 shows the voltage change of the transfer roller when the width of the transfer paper was changed under the above conditions.

Along with such voltage changes, the amount of current concentrated in the area where the image bearing member and the transfer roller are in direct contact, where the resistance is low, and directed toward the transfer material decreases, and the amount of charge per unit area decreases. This will result in poor transfer.

The present invention has been made in order to cope with the situation described above, and is applicable to an image forming apparatus that uses a contact type transfer means such as a transfer roller and performs transfer by constant current control. Regardless of the relative width difference between the material and the transfer roller, a fixed amount of electric charge is always applied to the transfer material,
The object of the present invention is to provide a transfer device that can stably perform high-quality transfer.

(2) Structure of the invention (technical means for solving the problem and its operation) In order to achieve the above object, the present invention comprises an image bearing member and a transfer means that presses against the image carrier, and a transfer unit that is a pressure nip between the two. In an image forming apparatus configured to cause a transfer material to pass through a portion of the image forming apparatus and apply a constant current controlled bias to the transfer means at this time to transfer a toner image on the image bearing member side to the transfer material, an electric current is applied to the transfer means. The present invention is characterized in that it includes means for changing the transfer current caused by the bias according to the width of the transfer material.

With this configuration, the amount of charge per unit area, which is related to the width of the transfer material, can be kept constant and stable and good transfer can be performed at all times.

(Description of Embodiments) FIG. 1 is a schematic side view of the main parts of an image forming apparatus to which the present invention is applied, which includes an axis extending perpendicular to the plane of the paper,
A conductive elastic transfer roller 2 presses against a photoreceptor 1 rotating in the six directions of the arrows to form an appropriate nip portion.

The transfer material (not shown) supplied from the cassette 5 is transferred to the transport path 3.
It reaches the position of the pair of registration rollers 4, and at this position, it reaches the nip portion, which is the transfer site, in synchronization with the transferable toner image previously formed on the photoreceptor l, and further moves to the left in the figure. do.

While the transfer material is in the nip, the constant current power supply 7
A transfer bias is applied to the transfer roller 2, and the toner image on the photoreceptor 1 is transferred to the transfer material.Then, the toner image is further supplied to the fixing device 8 through the conveyance path 3, and after being fixed and fixed on the transfer material, it is transferred outside the device. It is assumed that - is discharged.

Although not shown, around the photoreceptor 1 there is a primary charger for uniformly charging the surface of the photoreceptor, and an image information device that applies an optical image signal to the primary charger to form an electrostatic latent image. means of giving,
The components necessary for image forming work are provided, such as a developing device that supplies toner to the latent image to make it visible, a cleaner that removes residual toner that remains on the photoreceptor even after transfer, and a pre-discharge means that removes residual charges. Of course it is.

Further, the above-mentioned apparatus is based on reversal development in which the polarity of the negative charge and the polarity of the toner are the same.

In the figure, reference numeral 9 is a CPU, reference numeral 10 is an I10 port 1'3-1, and reference numeral 11 is a pass line connecting the two, and reference numeral 12 is a memory.

In such an apparatus, the power supply 7 that applies the transfer bias is a constant current power supply, and when the transfer material of a specific size is stored and the removable cassette 5 is positioned in the main body of the apparatus, this A cassette detection section 6 is provided to detect the cassette detection section 6, and this section, along with other parts of the apparatus, is controlled by the CPU.

With such a configuration, when the width of the cassette and therefore the transfer material used is detected, the CPU 9 controls the transfer power source 7 in response to the output signal of the cassette detection section 6 to change the current value. do.

FIG. 2 shows the optimum current value of the bias applied to the transfer roller depending on the size of the transfer material.

In the graph shown, the film thickness of the photoreceptor 1 is 45 μm, and the specific resistance is t.
o”00m, transfer roller length 21.6111II+,
Specific resistance: 10"Ωcm, nip width: 3mm, process speed: 90mm/sec, transfer material weight: 8゜g
These are the results when using r/rr1'' paper.

As shown in the same graph, if the applied pie-scar current value is set according to the width of the transfer material, for any transfer material,
It is possible to perform appropriate transfer by keeping the amount of charge per unit area constant.

3A to 3D illustrate means for detecting the size of the transfer material using a cassette.

The end of the image forming apparatus main body B is formed with a part for attaching and detaching a cassette, and this part is provided with the cassette detection section 6 as described above. The section 6 is provided with two microswitches 6a and 6b.

Figures 3B to 3D show cassettes 51, 52, and 5 containing A4, B5, and A5 size transfer materials, respectively.
3 is shown, and when these are attached to the main body B, the cassette 51 has the switch 6a of the cassette detection unit 6, the cassette 52 has the switch 6b, and the cassette 53 has the switches 6a and 6b, respectively. Contacting convex portion 5C15d
is formed.

Therefore, no matter which cassette is attached to the main body B, the on/off mode of the microswitch is different depending on the cassette, so that the size of the cassette, and hence the transfer material, can be discriminated.

It is easy to understand that it is possible to detect transfer materials of other sizes or even more types of transfer materials in the same manner as described above.

Next, the current control of the transfer bias when there is no transfer material between the photoreceptor and the transfer roller will be explained, including the front rotation, the back rotation, the paper interval during continuous paper feeding, and when there is no transfer material between the photoreceptor and the transfer roller.

Conventionally, in the case described above (referred to as paper spacing), in order to prevent toner from adhering to the transfer roller, it is common to turn off the transfer bias at the time of paper spacing. In order to prevent toner of a predetermined polarity from adhering to the roller and to clean the adhering toner, a bias of opposite polarity is applied to the transfer roller between the sheets.
The applicant has proposed applying a weak bias to prevent the adhesion of so-called reverse fog toner, which is charged with a polarity opposite to the normal polarity.

Among these, the removal of reverse fog toner can be easily realized by switching the current value as described above at a time such as between sheets.

Figure 4 shows the transfer current and voltage when a transfer roller to which a constant current bias is applied is brought into contact with a photoreceptor charged to a dark area potential of -650V under the same conditions as shown in Figure 1 above. It is a graph showing the relationship between

In this case, it can be seen that a weak bias of about 150 V is applied at a current value of 6 μA.

On the other hand, as shown in the graph in Figure 2, the transfer current of 6 μA is the current value during maximum paper passing, and when printing multiple sheets with the transfer roller current between sheets of 6 μA, reverse fogging occurs. It was effective in preventing toner adhesion.

Of course, it goes without saying that cleaning the transfer roller is even more effective if a means for preventing adhesion of normally charged toner by applying a bias of opposite polarity is also used.

FIG. 5 shows another embodiment of the present invention, in which the transfer material taken out from the cassette passes through the pressure nip between the photoreceptor and the transfer roller and reaches the fixing device. There is no particular difference from the apparatus shown in FIG. 1 (corresponding parts are designated by the same reference numerals, and a description thereof will be omitted).

In this case, a protrusion 14 is formed on the side of the cassette 5 that is attached to the main body, and its length is made to vary depending on the size of the transfer material stored inside.

When the cassette 5 is attached to the main body, a movable member 15 is disposed at a position where it contacts the protrusion 14, and the movable member 15 comes into contact with the other end of a spring 13 whose one end is attached to a fixed position 16 in the main body.

With this structure, when the cassette 5 containing a certain size of transfer material is mounted on the main body, the movable member 15 is displaced to a position corresponding to the length of the protrusion 14 formed on the cassette. Become.

Since the movable member 15 is connected to a constant current power source 7 and a variable resistor 17 which is connected in parallel with the transfer roller, the resistance of the transfer bias circuit changes depending on the size of the transfer material. The larger the resistance, the larger the current flowing to the transfer roller side, and the smaller the resistance, the smaller the transfer current.The current value can be changed depending on the size of the transfer material.

With this configuration, there is no need to change the output current of the constant current power supply 7 itself, which simplifies the configuration of the power supply, and eliminates the need for a control circuit, which reduces the burden on the CPU and is advantageous in terms of cost. This also contributes to improved reliability due to the simpler structure.

FIG. 6 and FIG. 7 show still another embodiment of the present invention, in which FIG. 6 is a side view schematically showing the main part configuration of the device;
FIG. 7 is a perspective view showing a transfer material size detection area,
In this device as well, the same reference numerals are given to the parts corresponding to those of the above-described embodiments.

In the illustrated apparatus, the transfer material is placed on one plate 3a of a conveyance guide member consisting of a pair of plates 3a and 3b for guiding the transfer material from the cassette 5 to the transfer site via the registration roller pair 4. A slit extending in the middle direction is formed, and a light receiving element 18 is disposed on the other plate 3b at a position corresponding to the slit, and the light from the light source 20 reaches the light receiving element through the slit. It is arranged like this. Reference numeral 20a is a power source for the light source.

At this time, the light source and/or light-receiving element are appropriately arranged to match the size and position of the transfer material (thereby, it is possible to output a signal responsive to the position and size of the passing transfer material. Then, this can be transmitted to the CPU, and the bias current applied to the transfer roller can be controlled by the transfer power source 7 based on the time lag between the transfer material arriving at the transfer site from the above-mentioned detection position.

With this configuration, when an irregularly shaped object is used as a transfer material, for example, as shown in FIG. 8, it is also possible to transfer an opened envelope 11F as it is.

(3) As described in detail of the invention, according to the present invention, in a transfer device that uses a contact type transfer means such as a transfer roller and performs transfer by applying a constant current control bias, Since the amount of charge per unit area of the transfer material is always kept constant according to the size of the material, stable and good transfer can be performed, and this has a remarkable effect on obtaining high-quality images.

[Brief explanation of drawings]

FIG. 1 is a side view of the main parts of an image forming apparatus according to an embodiment of the present invention; FIG. 2 is a graph showing the relationship between the width of the transfer material and the current value in the same device; FIGS. 38 to 3D are cassettes. FIG. 4 is a graph showing the relationship between the current and voltage of the transfer roller in the case where no transfer material is present in the apparatus; FIG. 5 Image formation showing another embodiment of the present invention. FIG. 6 is a side view of the main parts of the image forming apparatus showing still another embodiment of the present invention; FIG. 7 is a perspective view showing the structure of the transfer material detection section; FIG. 8 is a side view of the main parts of the apparatus; FIG. 9A is an end view showing the relationship between the transfer material and the transfer roller when conveying a medium-wide transfer material, and FIG. 9B is the same as above. Figure 10A is an end view showing the relationship between the transfer material and the transfer roller when conveying the intermediate transfer material, Figure 10B is a diagram showing the equivalent circuit, and Figure 11 is a diagram showing the equivalent circuit. 7 is a graph showing the relationship between the width of the transfer material and the voltage when the transfer roller bias is controlled with a constant current. L... Photoreceptor, 2... Transfer roller, 3... Conveyance path, 4... Registration roller pair, 5... Cassette, 6...
...Cassette detection section, 7... Constant current power supply, 13...
Spring, 14...Protrusion, 15...Movable member, 17...
- Variable resistor, 18... Light receiving element, 20... Light source. Figure 3A Figure 38 Figure kire0-ra fL; Written amendment (method) % formula% ■, Indication of the case Patent Application No. 1-92937 2゜Name of the invention Image forming device 3゜Relationship with the case by the person making the amendment

Claims (1)

[Scope of Claims] An image bearing member and a transfer means that are in pressure contact with the image carrier are provided, and a transfer material is passed through a transfer site that is a pressure nip between the two, and at this time, a constant current control bias is applied to the transfer means. In an image forming apparatus configured to transfer a toner image on an image carrier side to a transfer material, the image forming apparatus is provided with means for changing a transfer current due to a bias applied to a transfer means in accordance with the width of the transfer material. transcription device.