JP2704277B2 - 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 having an image carrier, such as an electrostatic copying machine and a printer, and a charging member capable of contacting the image carrier. The present invention relates to a forming apparatus.

(Problems to be Solved with the Related Art) An image carrier and a transfer member pressed against the image carrier are provided, and a transfer material is passed between the two members. An image forming apparatus configured to transfer a body side toner image 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.

After the surface of the cylindrical photoreceptor 1 having an axis perpendicular to the paper surface and rotating in the direction indicated by the arrow X in the drawing is uniformly charged by the power supply 4 via the charging roller 3, image information writing means is provided. By 7, image information is given to the charged surface by an image-modulated laser beam, slit exposure, or the like, and an electrostatic latent image is formed.

Next, toner is supplied to the latent image by the developing device 9 to form a toner image.

When the toner image reaches a transfer portion, which is a nip portion where the transfer roller 2 as a transfer member contacts the photoreceptor 1 with the rotation of the photoreceptor 1, the transfer material P is also transferred to the transfer material P in synchronization with the toner image. At this time, a transfer bias is applied to the transfer roller 2 to apply a charge of the opposite polarity to the toner on the back surface of the transfer material, thereby transferring the toner image on the photoconductor 1 to the transfer material.

In the illustrated apparatus, an OPC photoreceptor is used as the photoreceptor, the process speed is set to 23 mm / sec, a charging roller 3 is pressed against the photoreceptor 1 to negatively charge the photoreceptor 1 as a charging unit, and a transfer unit is a transfer unit. In this case, too, a transfer roller 2 having a low volume resistance, which is driven by pressure contact with the photoreceptor 1 and gives a positive charge to the back surface of the transfer material, was used.

The image exposure was an image exposure, and transfer development was performed by a developing device 9 using negative toner.

 FIG. 10 shows the sequence of the above device.

An image forming apparatus employing such a contact transfer method does not require a high-voltage power supply as compared with an apparatus using a corona discharger which has been widely used in the past. There are various advantages such as no obstacles due to contamination, no generation of ozone based on high-pressure discharge, no generation of nitrides, and less deterioration of the photoreceptor and image quality due to these. It is known that the relationship (referred to as VI characteristic) between the voltage applied to this and the current flowing therethrough varies greatly depending on the environment.

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

Variations in VI characteristics due to such environmental differences are described in
It is shown in the figure.

The solid line in the figure shows the voltage applied to the charging roller 3 in both L / L, N / N, and H / H states during pre-rotation, post-rotation, and during non-sheet passing such as between sheets, in both AC and DC components. The VI characteristic of the transfer roller 2 when the transfer roller 2 is turned on, and the broken line indicates the transfer characteristic of the transfer roller 2 when the A4 size transfer material passes through the above-described transfer portion in the same state as described above. The VI characteristics are shown.

In the case of such a known apparatus, according to an experiment, in order to perform good transfer, the transfer current at the time of paper passing is 0.5 to 4 μA.
It has been found that the necessity, and when this exceeds 5 μA, a positive potential transfer memory remains on the OPC photoreceptor and ground fog occurs in the image.

From this, an appropriate transfer bias in the known device is about 300 to 500 V for H / H, about 400 to 750 V for N / N, and
It turns out that it is about 1250-2000V in L / L.

When constant voltage control is performed by such a device, the following problems occur.

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

Also, if the voltage is set so as to improve the transferability in the L / L environment, the OP is set when the paper is not passed in the N / N or H / H environment.
Positive transfer memory is generated on the C photoconductor, and ground fog is generated in the output image. In particular, during H / H, the transfer current increases even during paper passing, so that electric charge penetrates the transfer material and charges the negative toner on the surface of the photoreceptor to the opposite polarity to cause transfer failure.

If the constant current control is performed to cope with such a situation, the following problem occurs.

In general, in this type of apparatus, it is common that a small-sized transfer material can be used within a range not more than the maximum size transfer material that can be used. For this reason, a small-size transfer material is used. At times, there is a portion where the photoconductor and the transfer roller are in direct contact. In the case of the above-described known apparatus, if the constant current control is performed at 1 μA, the current value per unit area flowing into the non-sheet passing portion directly contacting the above becomes 1 μA at the time of non-sheet passing such as a front rotation, a post rotation, and a sheet interval. Since the current value is equal to the current value per unit area when flowing, the voltage applied to the transfer roller drops, and almost no current flows in the paper passing area, causing transfer failure.

In the above case, the transfer voltage drops more than 200V for H / H, slightly less than 200V for N / N, and about 400V for L / L compared to when passing A4 size paper. Then, the transfer current becomes almost zero and transfer failure occurs.

In order to obtain sufficient transferability even when passing small-size paper,
For example, in a relatively narrow non-sheet passing portion such as the difference between letter size paper and A4 size paper, the current density flowing into this portion becomes large, and the background fog due to the transfer memory occurs on the surface of the photoreceptor. Back stain occurs on letter size paper.

In short, in this type of known apparatus, it is difficult to provide good transferability to transfer materials of all sizes in all environments by either the constant voltage control or the constant current control. That was the current situation.

The present invention has been made in order to cope with such a situation, and has as its object to provide an image forming apparatus which can solve the above-described disadvantages and can stably form a good image under any environment. Is what you do.

(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 an image from the image carrier to a transfer material at a transfer position. A transfer member for transferring, the transfer member being in contact with a surface of the transfer material sent to the transfer position on a side opposite to a surface on the image carrier side; and a voltage applying unit for applying a voltage to the transfer member. In the image forming apparatus, the voltage applying unit performs constant current control on the transfer member so that a current flowing from the transfer member to the image carrier becomes constant, and the transfer material is controlled by a voltage obtained during the constant current control. A constant voltage control is performed on the transfer member when the image is transferred to the transfer member.

According to another aspect of the invention, there is provided an image having a movable image carrier, a charging member that contacts the image carrier to charge the image carrier, and a voltage application unit that applies a voltage to the charging member. In the forming apparatus, the voltage applying unit performs constant current control on the charging member so that a current flowing from the charging member to the image carrier becomes constant, and the charging member uses a voltage obtained during the constant current control. Is characterized by performing constant voltage control.

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

FIG. 1 is a schematic side view showing a configuration of an image forming apparatus suitable for applying the present invention, and is a 30 mm diameter OPC photosensitive drum rotating at a process speed of 23 mm / sec in the direction of arrow X. After the surface of the body 1 is uniformly negatively charged by the charging roller 3, for example, an image-modulated laser beam is projected on the charged surface to attenuate the potential of the portion to form an electrostatic latent image. You.

When the latent image comes to a position facing the developing device 6 with the rotation of the photoconductor 1, negatively charged toner is supplied to the latent image, and a toner image is formed by a reversal developing method.

On the downstream side of the developing device as viewed in the running direction of the photoconductor 1,
A conductive transfer roller 2 serving as a charging member for pressing against the photosensitive member;
Are arranged in a press-contact manner, and the press-contact nip portion of both forms a transfer site as described below.

When the toner image arrives at the transfer site, the transfer material P is supplied to the transfer site from the conveyance path 7 at the same time as the toner image, and the toner image on the photoreceptor surface is transferred by the transfer bias applied to the transfer roller. Transfer to wood.

The constant voltage control and the constant current control (ATVC, Active Transfer
It is assumed that a predetermined voltage is applied at a predetermined point in time by a power supply 4 that can be used (called Voltage Control).

When the CPU 8 receives a print signal from an external device such as a computer, the CPU 8 sends a drive ON signal for the main motor to a motor drive circuit (not shown) for driving the photoconductor 1, and
At the same time, a primary high voltage ON signal is sent to the power source 4 to apply a charging bias to the charging roller 3 to charge the surface of the photoconductor 1 to, for example, a dark potential Vd-700V.

Next, the CPU drives an image information writing unit (not shown) to form an electrostatic latent image.

Next, it is assumed that the CPU 8 sends a transfer-on signal to the power supply 4, whereby the power supply 4 executes constant voltage and constant current control as described later.

Upon receiving the transfer ON signal, the power supply 4 controls the transfer roller 2 at a constant current. In the illustrated device, a current of 5 μA is assumed to flow.

Next, the power supply 4 holds the voltage generated on the transfer roller 2, then stops the constant current control and performs the constant voltage control (ATVC control) on the voltage of the transfer roller held earlier.

This will be described with reference to the VI characteristics of the transfer roller 2 under the N / N environment shown in FIG. 3. When the photoconductor is at the potential Vd when the paper is not passed, it is necessary to supply a transfer current of 5 μA. The voltage is about 750 V, and at this voltage, the transfer current during paper passing is about 2.25 μA.

In other words, by controlling the voltage and current of the transfer roller as described above, the transfer roller is controlled to a constant voltage of 750 V when the paper is passed under the N / N environment. At this time, 2.25 μA flows and good transfer is performed. It turns out that it is done.

As can be seen from the timing chart of FIG. 2, in the case of continuous paper passing, it can be easily understood that constant current control is performed between sheets and constant voltage control is performed during paper passing.

Next, the operation in various environments when the above-described control method is applied to the above-described device will be described with reference to FIG.

 Under H / H environment.

When paper is not passed, the power supply 4 supplies 5 μA to the transfer roller 2.
Is performed. As a result, 50
Since a voltage of 0 V is generated, this is held and the 500 V constant voltage control is performed at the next sheet passing.

As a result, in the case of A4 size transfer material passing, 1.
A transfer current of 5 μA is obtained, which is sufficient to achieve good transfer.

Also, in the case of small-size paper passing, since the voltage of 500 V is maintained in the paper passing portion of the transfer roller 2,
A transfer current of 1.5 μA was obtained, indicating that good transfer was possible.

Further, as described above, only a current of 5 μA flows when paper is not passed, so that there is no possibility that the transfer memory remains on the surface of the photoconductor and fog occurs.

Further, even in the non-sheet passing area of the difference between the large size paper and the small size paper, the constant voltage control is performed during the sheet passing.
In this case, the current density does not exceed about 5 μA, so that the transfer memory does not remain on the photoconductor.

The same applies to the N / N and L / L environments described below.

 Under N / N environment.

As described above, the constant current control of 5 μA is performed on the transfer roller 2 when paper is not passed.

At this time, a voltage of 750 V is applied to the transfer roller 2, and this voltage is held, and 75
It is assumed that 0V constant voltage control is performed.

As a result, when passing A4 size paper, 2.25
A transfer current of μA is obtained, which is a value sufficient to perform good transfer.

 Under L / L environment.

At the time of non-sheet passing, if the same constant current control as described above is performed, a voltage of 2 Kv is generated at the transfer roller 2.
Performs Kv constant voltage control.

At this time, since a transfer current of 2 μA flows through the transfer roller 2, good transferability can be obtained.

The constant current control is performed on the transfer roller so that the current flowing from the transfer roller to the photoconductor is constant, and the image forming conditions on the transfer material are determined based on the voltage applied to the transfer roller during the constant current control. Controlled.

As described above, by performing constant current control when paper is not passed and constant voltage control when paper is passed, good transferability can always be obtained regardless of the environment and transfer material size. A good quality image can be obtained without occurrence.

FIG. 5 shows another embodiment of the ATVC control according to the present invention.

In this case, the ATVC control is performed each time one sheet is output.
Control is running.

It was confirmed that a high-quality image can be obtained in all the environments in the same manner as described above even with this configuration.

In this case, it goes without saying that the ATVC control is not limited to every three sheets output.

FIG. 6 shows an embodiment in which the ATVC control according to the present invention is applied to printers such as laser beam printers, LED printers, LCS printers, and digital copiers using these printers.

In this device, when the print signal is input again within a predetermined time (reference numeral x in the figure) after the print signal is input to the CPU 8, the voltage held by the ATVC control performed at the time of the previous print signal is maintained, At this voltage, constant voltage control is also performed for the image output for the print input later, and when the print signal is input in this way, the ATVC is applied to the new signal.
Without performing the control, the constant voltage control by the first signal is continued.

If the next print signal is not input within the time x, the ATVC control is executed when the next signal is input.

Even in this case, the same effect as in the above-described respective cases is obtained. This is advantageous particularly when there is no change in the VI characteristic during one operation, and the ATVC control may be performed only during the pre-rotation. .

FIG. 7 shows an embodiment in which the ATVC control according to the present invention is applied to a copying machine.

In this case, it is assumed that the copy button is pressed, ATVC control is performed while the apparatus is performing pre-rotation, and constant voltage control is performed during the subsequent copy operation. FIG.
This shows a control mode when making one copy.

In the above description, the case where the transfer roller is used as the transfer means has been described. However, when the transfer belt is used as the contact transfer means, further, the image exposure is not limited to the reversal development method, Of course, the same effect can be obtained in the case of ground exposure and regular development.

FIG. 8 divides the ATVC control according to the present invention into a non-image area where no image is present in the image and an image area. In the former case, constant current control is performed, and the voltage at that time is held. This is a case where a constant voltage control is performed on an image area.

The figure will be described. The figure shows the V of the transfer roller 2 under a certain environment in the image forming apparatus having the above-described configuration.
It shows -I characteristics.

● indicates a non-image passing area, □ indicates a non-image area of the sheet passing area, and Δ indicates a VI characteristic of the image area of the sheet passing section.

As is clear from this graph, 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.

For this reason, even in non-image areas in the
By performing the control, it is possible to obtain the same operation as described above in which the above-described control is performed on the sheet passing portion and the non-sheet passing portion based on the presence or absence of the transfer material.

In the case of FIG. 8, in the non-image area of the paper passing portion, at 3 μA
By performing ATVC control, the same operation as in the case where control was performed at 5 μA in the non-sheet passing portion could be obtained.

In the above case, the constant current control is performed in the non-sheet passing portion and the non-image area. For example, in the non-sheet passing portion such as the pre-rotation and the sheet interval, the photoconductor is improved in cleaning property and developing property. It is also effective to perform ATVC control on this toner image, for example, in the case where toner is adhered by performing exposure and development on the toner image.

(3) Effects of the Invention As described above, according to the present invention, an image can be formed under image forming conditions according to the environment, so that there is a remarkable effect in obtaining a high-quality image.

[Brief description of the drawings]

FIG. 1 is a schematic side view showing a configuration of an image forming apparatus suitable for applying the present invention, FIG. 2 is a sequence showing an operation of the image forming apparatus, and FIG. 3 is a view showing V at normal temperature and normal humidity (N / N). FIG. 4 is a graph showing low-temperature and low-humidity (L / L), normal temperature and normal humidity, and high-temperature and high humidity (H
/ H) is a graph showing VI characteristics, FIGS. 5 to 7 are sequences each showing another control mode, and FIG. 8 is a difference in VI characteristics between an image area and a non-image area in a certain environment. 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, and FIG. 11 is V at low temperature, low humidity, normal temperature, normal humidity, and high temperature, high humidity in the above. It is a graph which shows -I characteristic. 1 photoconductor, 2 transfer roller, 3 charging roller,
4 high voltage power supply, 5 image information writing means, 6 developing device, 8 CPU.

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Yasushi Sato 3-30-2 Shimomaruko, Ota-ku, Tokyo Inside Canon Inc. (72) Inventor Toshio Miyamoto 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon (72) Inventor Kimio Nakahata 3-30-2 Shimomaruko, Ota-ku, Tokyo Canon Inc.

Claims (6)

(57) [Claims] A transfer member for transferring an image from the image carrier to a transfer material at a transfer position, the transfer member being transferred to the transfer position; Is an image forming apparatus having a transfer member that contacts the opposite surface and a voltage application unit that applies a voltage to the transfer member, wherein the voltage application unit is configured to maintain a constant current flowing from the transfer member to the image carrier. An image forming apparatus, wherein constant voltage control is performed on the transfer member, and constant voltage control is performed on the transfer member at the time of transferring an image onto a transfer material using a voltage obtained during the constant current control. 2. The image forming apparatus according to claim 1, wherein said constant current control is performed when a non-image area of said image carrier is at said transfer position. 3. The constant voltage value of the constant voltage control is constant from when the constant current control is performed until a plurality of images pass through the transfer position. Item 2. The image forming apparatus according to any one of Items 2 to 3. 4. The constant voltage value is constant until the predetermined number of images pass through the transfer position after the constant current control is performed, and the constant voltage value is constant after the predetermined number of images pass through the transfer position. The image forming apparatus according to any one of claims 1 to 3, wherein the constant current control is performed to determine a constant voltage value of the voltage control. 5. An image forming apparatus according to claim 1, wherein said transfer material is a rotating body. 6. An image forming apparatus comprising: a movable image carrier; a charging member that contacts the image carrier for charging the image carrier; and a voltage applying unit that applies a voltage to the charging member. In the apparatus, the voltage applying unit performs constant current control on the charging member so that a current flowing from the charging member to the image carrier becomes constant, and applies a voltage obtained during the constant current control to the charging member. An image forming apparatus that performs constant voltage control.