JP2770187B2 - Image forming device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Industrial Application Field) The present invention relates to an image carrier, such as an electrostatic copying machine and a printer, and a transfer member forming a nip between the image carrier and the image carrier. And an image forming apparatus having the same.

(Problems to be Solved with the Prior Art) An image carrier and transfer means such as a transfer roller and a transfer belt which are pressed against the image carrier are provided. An image forming apparatus including a step of applying a transfer bias to a transfer material to transfer a toner image on the image carrier to a transfer material has already been proposed.

FIG. 9 is a schematic side view showing a typical example of such an image forming apparatus, having an axis perpendicular to the paper surface,
The cylindrical OPC photosensitive member 1 rotating at a process speed of 23 mm / sec in the direction of arrow X is uniformly negatively charged by a power source 4 via a charging roller 3, and the charged surface is irradiated with a laser beam 5 image-modulated. Then, the potential of the irradiated portion is attenuated to form an electrostatic latent image.

When the latent image arrives at the developing position facing the developing device 6 as the photoconductor 1 rotates, the negatively charged toner adheres to the irradiated portion of the latent image to perform reversal development to form a toner image. You.

When the photosensitive member 1 further rotates and the toner image reaches a transfer portion where the transfer roller 2 made of an elastic material having a medium volume resistance and the photosensitive member 1 are pressed against each other, the toner image is transferred to the toner image in synchronization with the timing. The material P is supplied to the portion. At this time, a positive transfer bias is applied to the transfer roller 2 by the power supply 4, and the toner image on the photoconductor 1 is transferred to the transfer material by the action of the electric field formed thereby.

 FIG. 10 is a sequence showing the above operation.

An apparatus employing such a contact-type transfer means is advantageous in terms of cost because it does not require a high-voltage power supply as compared with an apparatus utilizing a corona discharger which has been widely used in the past, and is advantageous in terms of cost. Since there is no contamination, there is no deterioration in image quality due to contamination, and generation of ozone, nitrogen oxides, etc. due to discharge is extremely small, so there is virtually no risk of failure due to these adhering to the photoreceptor. However, on the other hand, transfer means such as a transfer roller, which is usually formed of a material such as rubber, is included in a circuit for applying a transfer bias, and the resistance of the transfer means fluctuates significantly depending on the environment. Accordingly, the relationship between the voltage applied to the transfer roller and the current at this time (referred to as VI characteristic) is inevitably changed.

That is, in a low-temperature and low-humidity environment (hereinafter, referred to as L / L), the resistance value of the transfer roller increases by several orders of magnitude compared to that in a normal-temperature, normal-humidity environment (hereinafter, referred to as N / N). H / H), it is reduced by one or two orders of magnitude compared to N / N.

The change in VI characteristics due to such a difference in environment is described in the eleventh embodiment.
Schematically shown in the figure.

In the drawing, solid lines indicate L / L, N / N, and H / H, when the voltage applied to the charging roller 3 is AC / DC when the paper is not passing through, for example, before rotation, after rotation, or between sheets. The VI characteristics of the transfer roller 2 when both components are ON, and the broken lines indicate the VI characteristics of the transfer roller 2 when the A4-size transfer material passes through the transfer site in each environment. The characteristics are shown respectively.

In the case of the known apparatus as described above, according to experiments, in order to perform good transfer, the transfer current during paper passing is 0.5 to 4 μm.
A, and the transfer current when paper is not passed is 5 μA in L / L environment and 10 μA in N / N, H / H environment.
It has been found that a positive potential transfer memory remains on the OPC photoreceptor when the temperature exceeds the limit, and ground fogging occurs in the image.

From the above, it can be said that the appropriate transfer bias in the apparatus is about 300 to 500 V for H / H, about 400 to 750 V for N / N, and about 1250 to 2000 V for L / L.

When the constant voltage control is performed by the above-described known device, the following problems occur.

That is, so that proper transfer is performed under N / N environment,
For example, when the transfer roller is controlled at a constant voltage of 500 V, the transfer characteristics are almost the same in H / H, but the transfer current becomes almost zero in the L / L environment, resulting in poor transfer.

Further, if the voltage is set so as to improve the transferability in the L / L environment, a transfer memory occurs in the N / N and H / H environments, and the image fog occurs.

Particularly in an H / H environment, the transfer current becomes excessive during paper passing, and electric charges penetrate the transfer material, and the negatively charged toner on the surface of the photoreceptor is charged to the opposite polarity, causing transfer failure.

Further, if the constant current control is performed to cope with the above situation, the following problem occurs.

Generally, in this type of apparatus, a smaller transfer material can generally be used within a range not larger than the maximum usable size of the transfer material. In the case where is used, there is naturally a portion where the photosensitive member directly contacts the transfer roller.

For example, if constant current control is performed at 1 μA,
Since the current value per unit area flowing into the portion where the photoconductor and the transfer roller directly contact each other is almost equal to the current value per unit area when 1 μA flows during non-sheet passing such as between sheets, the voltage applied to the transfer roller , And almost no current flows in the paper passing area, causing transfer failure.

In this case, if the envelope is passed through the A4 size paper, the transfer voltage drops by about 200V for H / H, slightly less than 200V for N / N, and about 400V for L / L. Is almost zero, which causes transfer failure.

In order to obtain sufficient transferability even when a small-size transfer material is passed, if a non-sheet passing portion to be formed is relatively small, such as a letter size and an A4 size, a current flowing into the non-sheet passing portion is required. As the density increases, background fogging due to the transfer memory occurs on the photosensitive member, and the back surface of the subsequent transfer material is stained.

In short, in this type of known apparatus, it is not possible to provide good transferability to transfer materials of all environments and all sizes by either constant voltage control or constant current control. It was difficult at present.

The present invention has been made in view of the above circumstances, and has as its object to provide an image forming apparatus capable of stably obtaining good transferability regardless of the size and environment of a transfer material. is there.

(2) Configuration of the Invention (Technical Means for Solving the Problems, Action of the Invention) In order to achieve the above object, the present invention provides a movable image carrier and a transfer member forming a nip with the image carrier. In the image forming apparatus having a transfer member for transferring an image from the image bearing member to a transfer material at the nip portion, and a voltage applying unit for applying a voltage to the transfer member, the voltage applying unit may be a transfer member. Performs the first constant voltage control on
When an image is transferred to a transfer material by the transfer member, a second constant voltage control is performed on the transfer member with a voltage based on a current flowing through the transfer member during the first constant voltage control. In the image forming apparatus (1) or (1), the first constant voltage control is performed when a non-image area of the image carrier is in the nip portion. In the forming apparatus (2), or any one of the above (1) or (2),
The image forming apparatus (3), wherein the first constant voltage control is performed when there is no transfer material in the nip portion.
Alternatively, in any one of the above (1) to (3), the second constant voltage control is performed until a predetermined number of transfer materials pass through the nip after the first constant voltage control is performed. The constant voltage value is constant, and the first constant voltage control is performed to determine the constant voltage value of the second constant voltage control after a predetermined number of transfer materials have passed through the nip portion. In the image forming apparatus (4) described above, or in any one of the above (1) to (4), the transfer member is a roller-shaped image forming apparatus (5).

With such a configuration, it is possible to always perform good transfer stably on a transfer material of any size regardless of the environment.

FIG. 1 is a schematic side view showing the configuration of an image forming apparatus suitable for applying the present invention.

A 30φ cylindrical OPC photosensitive member 1 extending in the direction perpendicular to the paper surface and rotating in the direction of the arrow X at a process speed of 23 mm / sec,
After being uniformly negatively charged by the charging roller 3, the charged surface is irradiated with an image-modulated laser beam 5, and the potential at that portion is attenuated to form an electrostatic latent image.

When the latent image arrives at a developing site facing the developing device 6 with the rotation of the photoconductor 1, negatively charged toner is supplied from the developing device and a toner image is formed by reversal development.

On the downstream side of the developing device 6 when viewed in the traveling direction of the photoconductor 1, a conductive transfer roller 2 is disposed in pressure contact with the photoconductor 1, and
The nip portion of both forms a transfer site.

When the toner image formed on the surface of the photoreceptor 1 reaches the transfer portion as the photoreceptor rotates, a transfer material P is supplied from the guide 7 to the transfer portion at the same time as the toner image is rotated. , As described below,
At a predetermined time, a predetermined voltage is applied to the transfer roller 2, and the toner image is transferred from the photoconductor 1 to the transfer material P.

When the CPU 8 receives the print signal, the CPU 8 sends a drive-on signal to a main motor (not shown) for driving the photoconductor 1,
At the same time, a primary high voltage ON signal is sent to the power source 4 to charge the charging roller 3
To uniformly charge the surface of the photoconductor 1 to, for example, -700V.

Next, the CPU 8 activates an image signal writing unit (not shown) to form an electrostatic latent image on the charged surface.

Next, the CPU 8 sends a transfer-on signal to the power supply 4, whereby the power supply 4 performs a transfer voltage control as described later, and a constant voltage control of +1000 V in the illustrated apparatus.

When the constant voltage control is performed, the current detection circuit 9 detects the current at this time and inputs the signal to the CPU 8.

The CPU 8 having received the signal converts the voltage into an appropriate transfer voltage value according to a voltage-current correspondence table held in advance as shown in FIG. 2 and sends this signal to the power supply 4.
Starts constant voltage control at this voltage value.

Such a control operation is performed for each image output, and the operation sequence is shown in FIG.

Next, the operation and effect of the above-described device will be described with reference to VI-VI shown in FIG.
This will be described with reference to a graph showing characteristics.

First, in the N / N environment, as shown in the figure, the transfer current when a transfer voltage of +1000 V is applied when paper is not passed is about 7 μA, and as can be seen from FIG. The constant voltage control is performed with this voltage when the paper is passed.

As shown in Fig. 4, the constant voltage control of 750V is about 1.6μ.
It can be seen that a transfer current of A was obtained and good transfer was performed.

In the H / H environment, when a constant voltage control of 1000 V is performed during non-sheet passing, a current of about 8.4 μA flows by this, and this is converted by the table of FIG.
Is performed.

As a result, a transfer current of about 1.6 μA is obtained with an A4 size transfer material, and this value is sufficient for performing good transfer.

Even with a transfer material smaller than A4 size, a voltage of 750 V in N / N and 500 V in H / H is maintained in the paper passing area, so a 1.6 μA current is secured in this area and good transfer is achieved. It is possible.

Also, when paper is not passed, about 7μA for N / N and about 8.4μ for H / H
Since only the current of A flows and all are 10μA or less, N / N, H
With / H, the transfer memory does not remain on the photoreceptor surface and fog does not occur.

Further, in the non-sheet passing area, which is the difference between the large-size sheet and the small-size sheet, as can be seen from FIG. 4, the current density during non-sheet passing, such as between sheets, is A4 size, N 5μ at / N
A, H / H is 4 μA, and the level at which the transfer memory appears is 10 μA or less, and the transfer memory does not remain on the photoconductor.

Next, in the case of the L / L environment, when the same constant voltage control as described above is performed when paper is not passed, a current of about 1.0 μA flows through the transfer roller, and from FIG. 2KV constant voltage control is performed when passing paper.

As a result, a current of 1.6 μA flows through the transfer roller (see FIG. 4), and good transfer can be performed.

Also, the transfer memory is about 1.0μ when paper is not passing.
Only A flows, and this value is less than 5 μA, which is the level at which transfer memory occurs in L / L, so that ground fog due to the transfer memory does not occur.

Furthermore, a good output image can be obtained for a small size as in the case of N / N and H / H.

As described above, by applying the transfer control means according to the present invention, good transferability is always obtained regardless of the environment and the size of the transfer material, and a high-quality image can be obtained without generating ground fog. Obtainable.

FIG. 5 is a sequence diagram showing another embodiment of the present invention.

In the above-described embodiment, the above-described transfer control is performed every time one sheet of image is output. In this embodiment, however, the transfer current detection and
Corresponding voltage setting and constant voltage control of the transfer roller by the voltage are performed.

Normally, the characteristics of the transfer material printed at a time can be regarded as almost constant depending on the environmental conditions at that time,
Even if this is done, the expected effect can be expected.
It is easy to understand that the present invention is not limited to the execution for each sheet.

FIG. 6 shows the transfer control according to the present invention, which includes a laser beam printer, an LED printer, an LCS printer, and the like;
This shows an embodiment when applied to a digital copying machine using these.

In this device, as can be seen from the figure, when a print signal is input again for a certain period of time (reference numeral x) after the print signal is input to the CPU 8, the voltage set by the transfer control performed at the time of the previous signal is maintained. Subsequently, the constant voltage control is performed at this voltage also in the subsequent printing.

If the next print signal is not input within the time x, the transfer control according to the present invention is performed when the next signal is input.

If there is no change in the VI characteristics during the work, such a method is effective, and the transfer control according to the present invention may be performed only during the pre-rotation or the pre-multi-rotation during the warm-up.

FIG. 7 shows a sequence when the transfer control according to the present invention is applied to a copying machine.

In this case, the transfer control according to the present invention is performed while the pre-rotation is performed by pressing the copy button, and thereafter, the constant voltage control is performed at the set voltage.

The figure shows a control mode when three copies are made.

Although the present invention has been described above with respect to a case where an image is formed by reversal development using a transfer roller, the present invention is not limited to this. For example, although a transfer belt is used, the present invention is applied to an apparatus for performing normal development. Needless to say, this can also be applied.

FIG. 8 divides one image into a non-image area where no image is present and an image area where an image is present. In the former case, constant voltage control is performed, and the current at that time is converted into a corresponding voltage. This shows the VI characteristic when the latter part is controlled at a constant voltage by this voltage.

The figure shows the characteristics of the transfer roller in a certain environment,
● indicates the non-image area of the sheet passing section, □ indicates the non-image area of the sheet passing section, and Δ indicates the VI characteristics of the image area of the sheet passing section.

As can be seen from the drawing, even in the paper passing portion, the characteristics are different between the image area and the non-image area due to the difference in the surface potential of the photoconductor.

Therefore, by performing the transfer control according to the present invention even in the non-image area in the sheet passing portion, it is possible to obtain the same operation and effect as described above in which the transfer control is executed according to the presence or absence of the transfer material.

In the case of FIG. 8, by performing the constant voltage control of 1200 V in the non-image area of the paper passing portion, the same operation as that of controlling at 1000 V in the non-paper passing portion can be obtained. The conversion table between current and voltage in this case is the same as that shown in FIG. 2 as in the first embodiment.

Incidentally, it has been already proposed to apply toner for cleaning the photoconductor, improving the developing property, etc. in a non-paper passing portion such as a pre-rotation, a paper interval, but in such a case, It is also effective to perform the transfer control according to the present invention on the toner image when the toner image on the photoreceptor surface reaches the transfer site.

In this case, if a voltage having the same polarity as that of the toner is applied to the toner image shown earlier in the non-image area and the current flowing to the transfer roller is detected, the toner image does not adhere to the transfer roller. There is no danger that the transfer roller can be cleaned at the same time.

When transferring the image area, the detection current may be converted so that a voltage having a polarity opposite to that of the toner image can be applied.

(3) Effects of the Invention As described above, according to the present invention, good transferability can be stably obtained regardless of the size and environment of the transfer material, and this greatly contributes to obtaining good quality images. .

[Brief description of the drawings]

FIG. 1 is a schematic side view of an image forming apparatus suitable for applying the present invention, FIG. 2 is a detection current-voltage change table of the above, FIG. 3 is an operation sequence of the above, and FIG. 5 to 7 are graphs showing VI characteristics in low humidity, normal temperature, normal humidity, and high temperature and high humidity environments, FIG. 5 to FIG. 7 are operation sequences showing another embodiment of the present invention, and FIG. 8 is an image area in one image. FIG. 9 is a side view schematically showing the configuration of a known image forming apparatus, FIG. 10 is an operation sequence of the above, FIG. 11 is a low-temperature and low-humidity It is a graph which shows VI characteristic at the time of normal temperature normal humidity, and high temperature and high humidity. 1 photoconductor, 2 transfer roller, 3 charging roller,
4. Power supply for bias voltage application, 5 ... Image signal writing means, 6 ... Developing device, 8 ... CPU, 9 ... Current detection circuit.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G03G 15/16

Claims (5)

(57) [Claims] A transfer member for forming a nip between the movable image carrier and the image carrier, wherein the transfer member transfers an image from the image carrier to a transfer material at the nip portion; An image forming apparatus having a voltage application unit for applying a voltage to a transfer member, wherein the voltage application unit performs a first constant voltage control on the transfer member, and transfers an image to a transfer material by the transfer member. An image forming apparatus, wherein a second constant voltage control is performed on the transfer member with a voltage based on a current flowing through the transfer member during the first constant voltage control. 2. The image forming apparatus according to claim 1, wherein the first constant voltage control is performed when a non-image area of the image carrier is in the nip. 3. The image forming apparatus according to claim 1, wherein the first constant voltage control is performed when there is no transfer material in the nip portion. 4. The constant voltage value of the second constant voltage control is constant from the time when the first constant voltage control is performed to the time when a predetermined number of transfer materials pass through the nip portion. The first constant voltage control is performed after a predetermined number of transfer materials have passed to determine the constant voltage value of the second constant voltage control. The image forming apparatus according to any one of the above items. 5. The image forming apparatus according to claim 1, wherein said transfer member has a roller shape.