JPH04251276A - Transfer device for image forming device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention can be applied to electrophotographic photoreceptors, electrostatic recording dielectric materials, magnetic recording magnetic materials, etc. by electrophotography, electrostatic recording, magnetic recording, and other conventionally known appropriate image forming process means. The present invention relates to a device for transferring a transferable image formed on a first image carrier such as a paper or a plastic sheet to a second image carrier such as a paper or plastic sheet.

More specifically, a second image carrier is superimposed on a first image carrier on which a transferable image is formed, and a charge is applied to the back surface of the second image carrier by a transfer means to produce a transferable image. The present invention relates to a transfer device of an image forming apparatus that transfers an image to a second image carrier.

0003

2. Description of the Related Art FIG. 5 is a schematic diagram showing an example of a transfer device in a conventional image forming apparatus.
After being rotated at a speed (process speed) and uniformly charged by a primary charging roller 2, an electrostatic latent image is formed by image exposure 3. Next, toner 5, which is a charged particle, is applied by a developing device 4 in accordance with the electrostatic latent image to form a transferable developed image 6.

On the other hand, a transfer material 7, which is a second image carrier, is transferred from a paper feeding section (not shown) to a transfer roller 8, which is a transfer means, in synchronization with the movement of the developing image 6 on the photosensitive drum 1 due to drum rotation. The toner 5 is fed into the nip portion of the photosensitive drum 1, and by the action of the bias voltage applied to the transfer roller 8 via the core bar 9 by the power source 10, an electric charge of opposite polarity to the toner 5 is applied to the back surface of the transfer material 7. The developed image 6 on the photosensitive drum 1 is transferred to the transfer material 7 by the electric charge.

After the transfer, excess charge on the back surface of the transfer material 7 is removed by a charge eliminating needle 13, and the transfer material 7 is sent to a fixing device (not shown) with the transferred developed image on it, and the developed image is transferred to the transfer material 7. Fixed permanently. After passing through the transfer section, the surface of the photosensitive drum is cleaned of residual toner by a cleaning device 14, and is used again for image formation.

Regarding the bias voltage of the transfer roller 8, the present applicant has developed an automatic transfer voltage control system (hereinafter referred to as AT) that can always obtain good transfer performance even when environmental conditions change.
(referred to as the VC method) was previously proposed in Japanese Patent Application No. 63-27610. In this ATVC method, prior to the image forming process, the photosensitive drum 1 is pre-rotated, a bias voltage is applied to the transfer roller 8 during this pre-rotation, the output current value at this time is measured with an ammeter 11, and this measured value is controller 1
Give feedback to 2. Then, the bias voltage of the power supply 10 is adjusted by the controller 12 so that the output current value becomes a predetermined value, and a constant voltage of the adjusted voltage as it is or a value corrected by a coefficient etc. is transferred. Even if the impedance of the transfer roller 8 varies greatly depending on the environment, a transfer bias with appropriate constant voltage characteristics can always be obtained.

[0007]

However, in the above-mentioned conventional apparatus, the transfer roller 8 is adjusted so that the current value becomes a predetermined value when the photosensitive drum 1 and the transfer roller 8 are in direct contact with each other.
Because the constant voltage bias applied to the transfer roller was adjusted, 1) when the impedance of the transfer material 7 is high (for example, when using thick paper or when trying to print on the back side of the transfer material 7 that has been printed once), and 2) when the transfer roller There was a problem in that transfer failure occurred when the impedance of 8 was low.

This problem will be explained with reference to a voltage-current characteristic curve diagram of a power source that applies a bias voltage to the transfer roller 8 shown in FIG. In FIG. 6, a curve A is a curve showing the relationship between the bias voltage V of the transfer roller 8 and the output current I when the photosensitive drum 1 and the transfer roller 8 are rotated in direct contact with each other. A voltage V0 is determined to obtain a current I0, and this voltage V0 is used as a constant voltage bias for the transfer roller 8 in the transfer process during the image forming process.

When paper is used as the transfer material 7 and the paper a is sandwiched between the photosensitive drum 1 and the transfer roller 8, the V-I
Since the curve is like curve P1, constant voltage bias V0
is applied, the transfer current becomes I1. The problem is whether or not a sufficient amount of transfer current I1 can be secured, but as shown in FIG. It is done.

However, when a transfer material with high impedance is used, such as thick paper b, the V-I
The characteristic becomes curve P2, which approaches the V axis, so at bias voltage V0, only I2 flows, and I2<I.
L, resulting in poor transfer.

In FIG. 6, curve A' shows the V-I and characteristics when the impedance of transfer roller 8 is smaller than curve A, and in this case, the voltage corresponding to the predetermined current value I0 during the pre-rotation is V0. ', and the constant voltage bias value applied during transfer is V0'. Then, the transfer current for paper a also becomes lower than the critical transfer current value IL,
This will result in poor transfer. In reality, the curves P1 and P2 appear as curves slightly farther away from the V axis as corresponding to the curve A', but since the difference from the solid line is small, they are omitted for the sake of simplifying the explanation.

In order to ensure transfer performance, it is necessary to ensure a sufficient supply of charge to the transfer material 7, that is, to ensure that the current values I1 and I2 are greater than or equal to the critical transfer current value IL.
The conventional ATVC method assumes that the current value I0 during pre-rotation and the current value I1 (or I2) during transfer have a constant proportional relationship, so the impedance of the transfer material 7 may change or the transfer When the impedance of the roller 8 changes, transfer defects inevitably occur as described above.

The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a transfer device that does not cause transfer defects.

[0014]

[Means for Solving the Problems] The present invention provides a method for overlapping a second image bearing member on a first image bearing member on which a transferable image is formed, and charging the back surface of the second image bearing member by a transfer means. In a transfer device of an image forming apparatus that transfers a transferable image to a second image carrier by applying a voltage, a power source for applying a bias voltage having a constant voltage characteristic to the transfer means, and a power source for applying a bias voltage having a constant voltage characteristic to the transfer means, a current detector for measuring the output current of the power source in a state where the two image carriers are overlapped; The present invention provides a transfer device for an image forming apparatus, characterized in that the transfer device includes a controller that changes a bias voltage applied to a transfer device.

[0015]

[Operation] According to the present invention, the output current of the power source is measured by a current detector in a state where the second image carrier is interposed between the first image carrier and the transfer means, and the measured current is By feeding back to the controller and controlling the bias voltage of the power supply so that the output current becomes a predetermined value,
Regardless of the impedance of the second image carrier, etc., transfer defects can be reliably prevented and high-quality images can always be obtained.

[0016]

Embodiments Embodiment 1 FIG. 1 shows a cross-sectional view of essential parts of the apparatus of the first embodiment, and the same parts as in the conventional apparatus shown in FIG. The transfer material 7 is conveyed in the direction of the arrow, and while the transfer material 7 moves a distance l0 from the leading edge in the traveling direction while being sandwiched between the photosensitive drum 1 and the transfer roller 8, the ammeter 11 measures the voltage from the power source 10. Output current is measured.

[0017] This measurement result is sent to the controller 12, and a current value I2 averaged over the distance l0 is obtained. If the current value I2 is smaller than the critical current value IL that causes transfer failure, the controller 12 switches the power supply 10 to
The output voltage is increased to obtain a current value Il sufficient for transfer.

FIG. 2 shows how the output voltage V and output current I change according to the distance L from the leading edge of the transfer material 7 under the control of the controller 12. Here, for the initial applied voltage V0, a predetermined constant value may be used, or a voltage value determined by the ATVC method described above may be used.

Note that in the above case, transfer defects occur over a distance l0 from the tip of the transfer material 7;
By setting the distance l0 sufficiently small, the above-described control can be performed using an area where no printing is done in most cases of printing. Furthermore, in EDP output, there are cases where a header print with an extremely small print amount is output before the main text, and in such a case, the above-mentioned control may be performed using the margin of this header print. In continuous printing, it goes without saying that the appropriate voltage value obtained when printing the first sheet may be applied to the second and subsequent sheets.

Experimental Example As the photosensitive drum 1, an aluminum cylinder with an outer diameter of 30 mm and an organic semiconductor formed thereon was used, and a peripheral speed of 50 mm was used.
It was rotated at a speed of mm/sec and uniformly charged to a dark area potential of -600V by a charging roller 2. Next, image exposure 3 is performed to obtain a bright area potential of -150V, and after forming a latent image using image exposure 3 as an appropriate pattern, reversal development is performed using developer 4 to apply toner 5 to the bright area to develop the image. 6
I got it. Toner 5 used had a volume average particle size of 6.5 μm and an average charge amount of 10 μc/gr. As the transfer roller 8, EPDM is placed on a stainless steel core metal 9 with an outer diameter of 8 mm.
An elastic layer with a specific resistance of approximately 108 Ω・cm and an Asker C hardness of 30° is formed by dispersing metal oxide inside, and the outer diameter is 20 mm.
The following was used. This transfer roller 8 has a total pressure of 1000
gr to the photosensitive drum 1 to form a nip of about 2 mm, and transfer was performed to the back side of a high impedance transfer material (paper b) that had been printed on one side.

First, as a reference example, when V0 = 1.7 KV was obtained according to I0 = 10 μA using the conventional ATVC method and transferred to paper b, the transfer current was I2 = 2.
．． The current value was 5 μA, which was less than the critical transfer current value IL=3 μA, resulting in defective transfer, resulting in scattering around the characters and disturbance of the half-tone image.

According to this embodiment, from the tip of the transfer material 7
After detecting I2=2.5 μA at 0=30 mm, the output voltage of the power source 10 was controlled from V0=1.7 KV to V1=2.5 KV so that the current I1 became I1=4 μA. When the transfer was performed in this manner, no transfer failure occurred as in the above-mentioned reference example. <Embodiment 2> FIG. 3 is a plan view of the main parts of the apparatus of the second embodiment, and the same parts as in FIG. In FIG. 3, 7 and 7a both indicate transfer materials, and while the transfer material 7 has a width that covers the entire length of the transfer roller 8, the transfer material 7a has a narrower width than the transfer material 7. In the transfer process, portions W1 and W2 are created where the transfer roller 8 and the photosensitive drum 1 are in direct contact with each other.

In these contact portions W1 and W2, current flows more easily than in the portion via the transfer material 7a, and the ammeter 11
It is necessary to calculate the current value flowing through the transfer material 7a by subtracting the current flowing directly through the photosensitive drum 1 from the measured value, and to control the current value by comparing it with a reference value.

To explain this with reference to FIG. 3, when the full width W0 of the transfer roller 8 comes into contact with the photosensitive drum 1 at the applied voltage V0, a current value I0 is obtained, so the current value flowing through the widths W1 and W2 is I0×( (W1+W2)/W0).

[0025] Therefore, if the current value obtained when the transfer material 7a passes is Ia, then Ia-I0×((W1+W2)/W0) is
Therefore, this current value is IL×((W
0-W1-W2) /W0), increase the voltage of the power supply 10 and calculate [Ia'-I0'×(W1
+W2) /W0)]
>IL×((W0-W1-W2
) /W0) In other words, Ia'>IL×((W0-W1-W2)/W0
)
+I0'×((W1+W2)/W0). Here, I0' is the boosted output voltage value V
1, this is the current value that flows when the transfer roller 8 and the photosensitive drum 1 are in direct contact across their entire width. Embodiment 3 FIG. 4 shows the main parts of a third embodiment of the apparatus, and the same parts as in FIG. 1 are given the same reference numerals and redundant explanation will be omitted. 15 is a cassette, 16 is an intermediate tray, 17 is a paper feed roller, 18 is a paper refeed roller, 19 is a register roller, and 20 is a fixing device.

Reference numerals 21, 22, and 23 are three conveyance paths for the transfer material 7, and the transfer material 7 is conveyed as follows. First, when printing is performed on one side of the transfer material 7, the transfer material 7 is taken out one by one from the cassette 15 by the paper feed roller 17 and is conveyed along a conveyance path 21 shown by a broken line. That is, it is synchronized with the photosensitive drum 1 by the register roller 19 and guided to the nip between the transfer roller 8 and the photosensitive drum 1.
After passing through the fixing device 20, it is stored in the intermediate tray 16, in preparation for image formation on the second side. When printing only on one side, the transfer material 7 passes through the fixing device 20 and then passes through the conveyance path 23.
is discharged.

When forming an image on the second side, the transfer material 7 taken out from the intermediate tray 16 by the paper refeed roller 18 is
The paper passes through the transport path 22 to reach the register roller 19, then passes through the transport path 21 to the fixing device 20, and after leaving the fixing device 20, passes through the transport path 23 and is discharged to the outside.

In this embodiment, in the pre-rotation step before the image forming step, the transfer material 7 is taken out from the single-transfer cassette 15 through the conveyance path 21 and guided to the nip between the transfer roller 8 and the photosensitive drum 1. At this time, the appropriate transfer bias is determined by the controller 12 based on the measured value obtained by the ammeter 11. At this time, since there is no developing image 6 on the photosensitive drum 1, the transfer material 7 remains blank and passes through the fixing device 20.
stored in the intermediate tray.

The above is the pre-rotation process, and in the image forming process for the first side, the transfer material 7 is taken out from the intermediate tray 16 by the paper refeed roller 18, passes through the conveyance path 22, the register roller 19, and is transferred to the transfer roller 8. and is guided to the nip of the photosensitive drum 1. At this time, the bias value of the power source 10 is maintained at the value determined during the above-mentioned pre-rotation, and the developed image 6 is transferred onto the first surface of the transfer material 7. After passing through the fixing device 20, in the case of single-sided printing, it is carried out through the conveyance path 23, and in the case of double-sided printing, it is stored in the intermediate tray 16 again via the conveyance path 21, in preparation for image formation on the second side. The transfer bias value during image formation on the second side is maintained at the same value as on the first side.

According to this embodiment, the output voltage of the power source 10 is always maintained at a constant value at the time of transfer in the image forming process, so that the transfer performance is more stable than in the first and second embodiments. is obtained.

Although the first to third embodiments have been described using a transfer roller as the transfer means, the gist of the present invention is not limited to the transfer roller, and may be applied to a corona transfer method, a belt transfer method, Needless to say, it can be applied to any transfer drum method or the like.

[0032]

As described above, the present invention provides a method for adjusting the output current of a power source to a predetermined value when the second image carrier is interposed between the first image carrier and the transfer means. Since the bias voltage of the power source is controlled, it is possible to obtain a high-quality image without transfer defects without being influenced by the impedance of the second image carrier or the like.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram of main parts of a first embodiment device.

FIG. 2 is a diagram showing changes in transfer bias voltage and current value from the leading edge to the trailing edge of the transfer material.

FIG. 3 is a plan view of the main parts of the device of the second embodiment.

FIG. 4 is a schematic diagram of the main parts of the device of the third embodiment.

FIG. 5 is a schematic diagram of an example of a conventional image forming apparatus.

FIG. 6 is a voltage-current characteristic curve diagram of a bias power source for a transfer roller.

[Explanation of symbols]

1 Photosensitive drum (first image carrier) 5 Toner (
Charged particles) 6 Developing image 7 Transfer material (second image carrier) 8 Transfer roller (transfer means) 10 Power source 11 Current detector 12 Controller

Claims (1)

[Claims] Claim 1: A second image bearing member is placed on top of a first image bearing member on which a transferable image has been formed, and a charge is applied to the back surface of the second image bearing member by a transfer means to form a transferable image. In a transfer device of an image forming apparatus that transfers images to a second image carrier, a power source for applying a bias voltage having constant voltage characteristics to the transfer means overlaps the first image carrier and the second image carrier. a current detector for measuring the output current of the power source in the current state, and a bias voltage to control the power source and apply to the transfer means according to the measured value of the current detector so that the output current becomes a predetermined value. 1. A transfer device for an image forming apparatus, comprising a controller for changing the transfer rate.