JPH0362075A - Image forming device - Google Patents

Abstract

PURPOSE:To stably obtain satisfactory transfer properties from transfer material of any size under any environments by providing a control means controlling a transfer means by a voltage obtained by multiplying a stored voltage by a coefficient in terms of a constant voltage when the transfer material is in a transfer part. CONSTITUTION:Unless the transfer material is in the transfer part, a power source 8 controls the constant current of a transfer roller 2, holds or stores a voltage arising therein, then stops the constant current control. When paper is fed, that is, the transfer material is in the transfer part, a voltage obtained by multiplying the stored voltage of the transfer roller by a coefficient is applied to the transfer roller 2 to control a constant voltage. At this time, a coefficient varies with environmental conditions. Consequently, satisfactory transfer proper ties can be obtained constantly and stably under any environments regardless of the variation of transfer material size.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an image forming apparatus such as a copying machine or a printer using an electrophotographic method.

[Conventional technology]

An image carrier is provided with a transfer member that is in pressure contact with the image carrier, and a transfer material is passed between the two, and at this time, a bias voltage is applied to the transfer member to transfer the toner image on the image carrier side to the transfer material. Image forming apparatuses configured to do this have already been proposed.

FIG. 7 is a schematic side view showing a typical example of such an image forming apparatus. In the example shown in FIG. 7, the surface of a cylindrical photoreceptor l with a diameter of 30 mm, which has an axis perpendicular to the plane of the paper and rotates at a process speed of 24 mm/s in the direction of the arrow X shown in the figure, is V uniformly through a 12 mm charging roller 3. After the knee is charged to 600 V, image information is applied to the charged surface of the photoreceptor l by image-modulated laser beam slit exposure by the image information writing means 5, and the exposed portion of the photoreceptor l becomes vL= The electrostatic latent image is formed by attenuating to ~1oov.

Next, toner is supplied to this latent image by a developing device 6 to form a toner image. As the photoreceptor 1 rotates, this toner image is transferred to a transfer roller 2 with a diameter of 16.6 mm, which is a transfer member.
When the toner image reaches the transfer site, which is a nip portion where it comes into contact with the photoconductor 1, the transfer material P also arrives at this transfer site in synchronization with the toner image, and at this time, a transfer bias is applied to the transfer roller 2 to transfer the toner image. A charge having a polarity opposite to that of the toner is applied to the back surface of the material to transfer the toner image on the photoreceptor 1 to the transfer material.

In the illustrated apparatus, an OPC photoreceptor is used as the photoreceptor, a charging roller 3 is used as the charging means to press and follow the photoreceptor 1 and negatively charge it, and as a transfer means, it is also pressed and driven to the photoreceptor 1. A semiconductive transfer roller 2 was used to apply a positive charge to the back surface of the transfer material.

Image exposure is image exposure, and V Div ” is applied to the developing device 6.
When -370V is applied, reversal development is performed using negative toner.

[Problem that the invention is trying to solve]

Image forming apparatuses employing the above-mentioned contact transfer method do not require a high-voltage power source, and are therefore advantageous in terms of cost, compared to those using corona dischargers, which have been widely used in the past. In addition, since there are no electrode wires, there are no problems caused by dirt, and there is no generation of ozone or nitrogen oxides due to high-pressure discharge, and there is little deterioration of the photoreceptor or image quality due to these, among other advantages. However, on the other hand, it is known that the relationship between the voltage applied to the transfer roller 2 and the current flowing through it (referred to as V-1 characteristic) changes significantly due to changes in the environment of the transfer roller 2 (changes in temperature and humidity). - An example is shown in FIG.

As is clear from the example shown in Figure 8, for example, low temperature and low humidity (
15°C, 10%) environment (hereinafter referred to as L/L),
The resistance value of the transfer roller is several orders of magnitude higher than that at normal temperature (23°C, 64% or less N/N) (as is clear from the increase in the slope of the VI characteristic). On the other hand, high temperature and high humidity (32.5°C, 85% or less H/H)
Under the environment, the resistance value of the transfer roller is 1 to 1 compared to N/N.
It decreases by two orders of magnitude (this is clear from the fact that the slope of the vr characteristic becomes smaller).

In the case of the known apparatus shown in FIG. 7, experiments have shown that in order to perform good transfer, a transfer current of at least 0.5 to 0.6 .mu.A is required when a solid black image is passed through the sheet. Furthermore, it has been found that if the transfer current exceeds 5 μA when paper is not being transported, a positive potential transfer memory remains on the PC photoreceptor, causing ground blur on the image.

From this, the appropriate transfer bias in the known device is approximately 100 in the H/H environment, as is clear from FIG.
0V to about 2250V SN/N environment is about 1500V to about 2500V, and L/L environment is about 3000V to about 3
It turns out that the voltage is 500V. In the conventional example shown in FIG. 7, when constant voltage control is performed, the following problems occur.

In other words, if the transfer roller is controlled at a constant voltage of 2000V, for example, in order to perform appropriate transfer in the N/N environment, it will show almost the same transfer characteristics in the H/H environment, but in the L/L environment. Transfer current is 0.1~0.2μ
A, resulting in poor transfer.

In addition, if the voltage is set to improve transfer performance in L/L environments, positive transfer memory will occur on the PC photoconductor when paper is not passed in N/N and H/H environments, causing the output image to change. Produces yellowtail. Especially in H/H environment,
Since the transfer current increases even when paper is passed through, the charge passes through the transfer material and charges the negative toner on the surface of the photoreceptor to the opposite polarity, causing a transfer failure.

If constant current control is performed to cope with such a situation, the following problems will occur.

Generally, in this type of device, it is possible to use small transfer materials within the range of the maximum size transfer material that can be used. Sometimes, there will be a portion where the photoreceptor and the transfer roller are in direct contact. In the case of the above-mentioned known device, if constant current control is performed at 1 μA, when a small size transfer material is used, the current value per unit area flowing into the non-sheet passing portion directly in contact with the above will be approximately equal to the current value per unit area, so the transfer The voltage applied to the roller drops, and almost no current flows through the paper passing area, resulting in transfer failure.

In the above case, compared to when passing an A4 size paper, when an envelope is passed, it is more than 700 V in an H/H environment, about 1000 V in a N/N environment, and about 1500 V in an L/L environment.
The transfer voltage drops and the current flowing through the transfer material becomes 0.5 μA or less, causing transfer failure.

If you try to obtain sufficient transfer performance even when passing small-sized paper, the current density flowing into the relatively narrow non-transferring area, such as the difference between letter-size paper and letter-size paper, increases, causing the transfer to the photoreceptor surface. Memory blur occurs, causing stains on the back of the next letter-sized paper.

In short, with this type of known device, it is difficult to provide good transfer performance for all sizes of transfer materials in all environments, regardless of whether constant voltage control or constant current control is used. That was the current situation.

[Purpose of the invention]

The present invention has been made to deal with this situation, and it eliminates the above-mentioned drawbacks and provides stable and good transfer performance for transfer materials of all sizes under all environments. The object of the present invention is to provide an image forming apparatus that can be used.

[Structure of the invention]

In order to achieve the above object, according to the present invention, an image bearing member, an image forming means for forming an image on the image bearing member, and an image forming means for forming an image on the image bearing member are arranged opposite to the image bearing member, and the image forming means forms an image on the image bearing member. , an image forming apparatus having a transfer means for transferring a transfer material to the transfer material by contacting and passing the transfer material through a transfer site between the image carrier and the image carrier,
When there is no transfer material at the transfer site, at least the transfer means is controlled with a constant current, and the voltage value generated at this time is held or stored, and when the transfer material is present at the transfer site,
The present invention is characterized in that it has a control means for controlling the transfer means at a constant voltage using a voltage value obtained by multiplying the voltage value by a coefficient, and the coefficient varies depending on the voltage value during the constant current control.

Alternatively, in order to achieve the above object, according to the present invention, an image bearing member, an image forming means for forming an image on the image bearing member, and an image forming means for forming an image on the image bearing member are arranged opposite to the image bearing member, and the image forming means forms an image on the image bearing member. ,
In an image forming apparatus having a transfer means that transfers a transfer material to the transfer material by passing the transfer material in contact with the transfer region between the image carrier and the image carrier, at least the transfer means is controlled with a constant voltage when the transfer material is not present at the transfer region. , the control means holds or stores the voltage value generated at this time, and when a transfer material is present at the transfer site, controls the transfer means at a constant voltage with a voltage value that is the voltage value multiplied by a coefficient, and the coefficient is set as above. This is characterized in that the current value is varied depending on the current value flowing through the transfer means during constant voltage control.

〔Example〕

FIG. 1 is a schematic side view showing a configuration example of an image forming apparatus according to the present invention. First, the surface of an OPC photoconductor 1 with a diameter of 30 mm rotating in the direction of arrow X at a process speed of 24 mm/s is negatively charged in a - direction by a charging roller 3, and then image information such as a laser scanner 5 is applied to the charged surface. An image-modulated laser beam is projected by the writing means to attenuate the potential of that portion, thereby forming an electrostatic latent image. The potential attenuated portion of this electrostatic latent image is developed with negative polarity toner in a developing device.

On the downstream side of the developing device as seen in the traveling direction of the photoreceptor 1,
A semiconductive material (for example, 10' to 1010
Ω) The transfer roller 2 is arranged in pressure contact, and the pressure nip portion between the two forms a transfer site. Here, the transfer roller 2 does not need to be in pressure contact with the photoconductor 1, and the gap between the transfer roller and the photoconductor 1 is smaller than the thickness of the transfer material, and the transfer roller 2 transfers only when the transfer material passes through this gap. The material P may be pressed against the transfer site. When the negative toner image reaches the transfer site, a transfer material P (transfer paper) is supplied from the conveyance path 7 to the transfer site at the same timing, and a positive bias applied to the transfer roller causes the photosensitive material to be exposed. The toner image on the body surface is transferred to the transfer material.

The above charging roller 3. For the transfer roller 2, constant voltage/
It is assumed that a power supply 8 capable of constant current control applies a predetermined current/voltage at a predetermined time point. This power supply 8 is controlled by a signal from the CPU as described later.

In this device, the power supply 8 is turned on when paper is not passing, such as during multiple rotations during fuser warm-up, before rotation before printing, and between sheets during continuous paper feeding, that is, when there is no transfer material at the transfer site. The transfer roller 2 is controlled with a constant current, the voltage value generated there is held or memorized, and then the constant current control is stopped and the previously memorized transfer roller A voltage value obtained by multiplying the voltage value by a coefficient is applied to the transfer roller 2 to perform constant voltage control. At this time, the coefficients are made to vary depending on the environmental conditions.

Figure 2 shows the relationship between the voltage applied to the transfer roller and the current flowing to the roller under different environmental conditions (transfer V-1
characteristics). To explain this using the transfer roller 2 (the same roller as in the conventional example) under an N/N environment, the photoreceptor is at V when no paper is passing through the transfer site (when there is no transfer material). (
= -600V), and if the current flowing through the transfer roller 2 is controlled to be 2 μA by constant current control, the voltage applied to the roller 2 at that time is approximately 1500V, and at this voltage, when paper passes The solid black transfer current is about 0.5 μA. However, in order to output a stable solid black image, it is approximately 1 μA.
Since a transfer current of 1500V is required to be applied to the transfer roller, a voltage of 1800V is applied to the transfer roller by multiplying the held or memorized voltage by 1500V -1-1,2, and the solid black transfer current is reduced to 1μA.
shall be. That is, by controlling the voltage and current of the transfer roller in this way, in an N/N environment, the transfer roller is controlled to a constant voltage of about 1800 V when paper is passed, and at this time, a solid black transfer current of about 1 μA flows. It can be seen that good transfer is performed.

Although this is the case when A4 size transfer material is passed, the same result is obtained even when using small size paper because constant voltage control is performed.

Looking at the above in the H/H, L/L environment,
When using the same transfer roller as the one used in the measurement under the N/N environment described above, in the N/N environment, if the current flowing to the transfer roller is controlled at a constant current of 2 μA when paper is not passing, At that time, the voltage applied to the roller is about 1250V, and if this voltage is held and controlled at a constant voltage of about 1375V, which is multiplied by 1.1, a current of about 1 μA will flow when solid black paper is passed.

For L/L, the current flowing to the transfer roller when paper is not passing is 2
When controlling the constant current with μA, the applied voltage during control is approximately 230
When the voltage is 0V and constant voltage control is performed using a voltage 1.3 times this voltage, a current of 1 μA flows at approximately 3000V when solid black paper is passed.

In this way, by controlling the current flowing through the transfer roller at a constant current when no transfer material is present at the transfer site, and observing the operating voltage to the transfer roller at that time, the transfer characteristics depending on the environment can be determined. Next, when a transfer material is present at the transfer site, that is, at the time of transfer, the operating voltage value is held and memorized in order to apply an appropriate transfer bias suitable for the environment, and then the voltage value is multiplied by a factor (for example, As in, 1.1 times H/H.

(1.2 times for N/H and 1.3 times for L/L), a sufficient transfer current flows during transfer to prevent transfer defects from occurring. This is effective in compensating for the environmental characteristics of the transfer roller.

Note that the constant current control of the current flowing through the transfer roller as described above may be performed at least part of the time when no transfer material is present at the transfer site.

In Example 1 above, the voltage value for constant voltage control when paper is passing is the hold/memory voltage value for constant current control when paper is not passing, multiplied by a coefficient that varies depending on the environment. Since it also changes depending on the resistance value, H/
The coefficient at H time is 1.1 times.

The coefficient for N/N is not limited to 1.2 times, and the coefficient for L/L is not limited to 1.3 times. FIG. 3 shows the VI characteristics when a transfer roller having a resistance value lower than that of the transfer roller described above is used. In this case, the suitability coefficient value is 1. 1 at Q5゜N/N,
1. L/L is 1.2.

As described above, the appropriate coefficient value differs depending on the resistance value of the transfer roller.

In addition, in the above embodiment, in order to apply a voltage appropriate for the environment to the transfer roller when a transfer material is present at the transfer site, the environmental condition is detected by some method and the coefficient of the hold/memory voltage as described above is determined. Must. The detection method includes voltage detection as described above. The power supply 8 in FIG. 1 controls the transfer roller with a constant current when there is no transfer material at the transfer site, detects the voltage held and stored by the power supply 8, and uses a variable resistor etc. to adjust the detected voltage. The coefficient values are determined in a one-to-one correspondence (this coefficient value determination is performed based on the characteristics of a graph prepared in advance showing the relationship between the hold/memory voltage and the coefficient, as shown in FIG. 4). Since changes in the resistance value of the transfer roller due to the environment are mainly affected by humidity, an appropriate transfer voltage can be obtained in any humidity environment because the coefficient is determined based on the hold/memory voltage.

In this way, when there is no transfer material at the transfer site in Fig. 4,
In other words, there was a one-to-one correspondence between the hold/memory voltage and the coefficient value during non-paper-passing constant current control, but another effective method is to divide the hold/memory voltage by a certain size and calculate the coefficient value within that category. There is one in which all voltages are multiplied by the same factor. For example, as shown in FIG. 5, the hold/storage voltage during 2 μA constant current control is about 3000 V, and the solid black transfer current at that time is about 1 μA. Therefore, for example, when the hold/storage voltage is detected by the hold/storage voltage detection device, the coefficient is 1 when the hold/storage voltage is above a certain voltage (3000 V in the case of Figure 5), and the coefficient α is lower than that (in the case of Figure 5, the coefficient is greater than l). ), the magnitude of the storage voltage is divided into 3000 V or more and less than 3000 V, and the former classification is set to a coefficient of 1, and the latter is set to a coefficient α.

In all of the embodiments described above, the coefficient value is determined based on voltage detection when there is no transfer material at the transfer site, but it is also possible to determine the coefficient based on current detection when there is no transfer material at the transfer site. That is, when there is no transfer material at the transfer site, the transfer roller is controlled with constant voltage instead of being controlled with constant current.

For example, in FIG. 6, assume that the transfer roller is controlled at a constant voltage of 1500 V when there is no transfer material at the transfer site. Then, the transfer roller receives 2.8 μA in H/H.

A current of 1.8 μA flows in N/N and 0.8 μA in L/L. Therefore, the current is detected, and each coefficient value for multiplying 1500V by a coefficient is determined based on the magnitude of the current. In Figure 6, the coefficient is H/Hte 0.9
(1350V), N/N Te1.2 (1800V),
L/L is 2.0 (3000V), and if the transfer roller is controlled at a constant voltage when the paper passes through with transfer material at the transfer site using a voltage multiplied by the respective coefficients, the transfer current for solid black is approximately Iμ.
A will flow. Furthermore, division coefficient multiplication based on the detected current can be carried out in the same manner as shown in FIG.

In the above embodiments, as shown in FIGS. 2 and 3, the relationship between the voltage applied to the transfer roller and the current flowing through the roller is determined by humidity,
As the temperature increases, the slope becomes thicker. Therefore, the larger the voltage or current detected when no transfer material is present at the transfer site, the larger the coefficient is preferably set.

In the above description, a case has been described in which a transfer roller is used as the transfer means, but it is of course possible to use a transfer belt as the transfer means. Furthermore, it is not limited to so-called image exposure and reversal development methods that expose the portion of the photoreceptor where a toner image is formed, but also so-called background exposure and regular development that exposes the background portion of the photoreceptor that does not form a toner image. Of course, similar effects can be obtained in other cases as well.

〔Effect of the invention〕

As explained above, according to the present invention, in an image forming apparatus equipped with an image bearing member and a transfer means facing the image bearing member, the image forming apparatus can always Stable and good transferability can be obtained, so
It has a remarkable effect on obtaining good quality images.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an embodiment of the image forming apparatus of the present invention, and FIGS. 2, 3, 5, and 6 are V-I of a transfer roller applicable to the image forming apparatus of the present invention. A graph showing the characteristics, Fig. 4 is a graph showing the relationship between the voltage applied to the transfer roller and the coefficient, Fig. 7 is a cross-sectional view explaining a conventional image forming apparatus, and Fig. 8 is a transfer roller of the conventional image forming apparatus. It is a graph which shows the VI characteristic of. 1... Image carrier 2... Transfer roller 3... Charging roller 4... High voltage power source 5... Optical scanner 6... Developing device 7... Transfer entrance guide 8... Constant current・Constant voltage source P...transfer material

Claims (2)

[Claims] (1) An image bearing member, an image forming means that forms an image on the image bearing member, and an image forming means that faces the image bearing member and transfers the image formed by the image forming means to a transfer site between the image bearing member and the image bearing member. In an image forming apparatus having a transfer means for transferring a transfer material to the transfer material by passing the transfer material in contact with the transfer material, at least the transfer means is controlled with a constant current when there is no transfer material at the transfer site, and the voltage value generated at this time is held or and a control means for controlling the transfer means at a constant voltage with a voltage value obtained by multiplying the voltage value by a coefficient when a transfer material is present at the transfer site, and the coefficient is determined according to the voltage value during the constant current control. An image forming apparatus characterized by being different. (2) An image bearing member, an image forming means for forming an image on the image bearing member, and facing the image bearing member, the image formed by the image forming means is transferred to a transfer site between the image bearing member and the image bearing member. In an image forming apparatus having a transfer means for transferring a transfer material onto the transfer material by passing the transfer material in contact therewith, at least the transfer means is controlled at a constant voltage when there is no transfer material at the transfer site, and the voltage value generated at this time is held or The control means controls the transfer means at a constant voltage with a voltage value multiplied by a coefficient when the transfer material is present at the transfer site, and the coefficient is a current value flowing through the transfer means during the constant voltage control. An image forming apparatus characterized in that the image forming apparatus is different depending on the image forming apparatus.