JPH02302777A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain stable transfer characteristics by impressing bias whose polarity is the same as an electrifying means electrifying an image carrier on a transfer means when a transfer means does not exist at a transfer part, detecting a current at this time, and setting a proper transfer bias voltage value. CONSTITUTION:The transfer material P is supplied to the transfer part matching with an image formed on an image carrier 1, and the transfer bias is impressed on the transfer means 2. At this time, when the transfer material P does not exist at the transfer part, the bias voltage of a prescribed voltage value of a polarity the same as the electrifying means 3 is impressed thereon. Based on the current detected at this time, the transfer bias voltage proper for the transfer material P is impressed by a transfer means 2. Therefore, stable transfer characteristics can be always obtained regardless of the environments.

Description

DETAILED DESCRIPTION OF THE INVENTION (1) Object of the Invention (Field of Industrial Application) The present invention relates to an image forming apparatus using an electrostatic transfer process, such as an electrostatic copying machine and a printer thereof.

(Prior Art and Problems to be Solved) The image carrier is equipped with a transfer means that comes into contact with the image carrier, such as a transfer roller and a transfer belt, and a transfer site that is formed as a nip between the two. In a well-known image forming apparatus, which includes a step of inserting a transfer material such as paper and applying a transfer bias to the transfer means, the toner image on the image carrier side is transferred to the transfer material. It is known that there are two types of transfer bias for transfer: a constant voltage control method and a constant current control method.

However, in this type of apparatus, the transfer means is in contact with the image carrier, and the resistance value of the transfer means is large (varies) depending on the environment, so that the following drawbacks cannot be avoided.

That is, when performing constant voltage control, normal temperature (23℃
, 60% RH: hereinafter referred to as N/N).
%RH (hereinafter referred to as L/L) environment, the resistance of the transfer means such as a transfer roller becomes high, making it impossible to apply sufficient charge to the transfer material, resulting in transfer failure.

Further, in a high temperature (32° C., 85% RH: hereinafter referred to as H/H) environment, the resistance of the transfer means is low (as a result, excessive bias is applied), which inevitably causes deterioration of image quality.

Furthermore, when constant current control is performed, it is not affected by environmental fluctuations in the resistance of the transfer means, and it is possible to apply a fixed amount of charge to the transfer material. However, if a small transfer material such as a postcard is used in an L/L environment, most of the current will flow through the non-paper passing area where the image bearing member and the transfer means are in direct contact, and the transfer material will not have enough charge. A problem arises in that the film is not applied and transfer defects occur.

The present invention has been made to deal with such a situation, and in an image forming apparatus that uses a transfer means such as a transfer roller or a contact quib, there is a transfer material between the transfer means and the image carrier. applying a bias having the same polarity as the polarity when charging the image carrier when the image carrier is not being charged, and setting the transfer bias when the next transfer material passes based on this; It is an object of the present invention to provide an image forming apparatus that can perform stable and good transfer at all times without being affected by changes in the environment.

(2) Structure of the invention (technical means for solving the problem, its effect) In order to achieve the above object, the present invention provides an image carrier, a charging means for charging the surface of the image carrier, and a charging means that contacts the image carrier. and a transfer means for forming a transfer site by applying a transfer material to the transfer site in synchronization with the image formed on the image carrier, and applying a transfer bias to the transfer means. In the forming apparatus, a bias voltage having a predetermined voltage or current value of the same polarity as that of the charging means is applied to the transfer means when no transfer material is present at the transfer site, and based on the current or voltage detected at this time. The present invention is characterized in that an appropriate transfer bias voltage is applied to the transfer material by the transfer means.

With this configuration, in an image forming apparatus equipped with a contact type transfer means such as a transfer roller,
Stable transferability can be obtained at all times regardless of the environment.

(Description of Embodiments) FIG. 1 is a schematic side view of the main parts showing the configuration of a laser beam printer suitable for applying the present invention. A rotating cylindrical image carrier (hereinafter referred to as a photoconductor) has a photosensitive layer made of an organic semiconductor on its surface, and the photosensitive layer is uniformly negatively charged by a wide charger 2. .

Next, the charged surface is irradiated with an image-modulated laser beam 7 by a laser scanner 5, and the potential of the irradiated portion is attenuated to form an electrostatic latent image.

Then, when this latent image reaches a developing area opposite to the developing device 9, negatively charged toner is supplied from the developing device and adheres to the latent image portion to form a toner image.

When the photoconductor 1 further rotates and this latent image arrives at a transfer site where the photoconductor 1 and the conductive transfer roller 2 come into contact to form a transfer site, the latent image is aligned with the timing of the latent image, and
The transfer material P is guided to this transfer site, and at the same time, a transfer bias is applied to the transfer roller 2 by the bias applying means 4, so that the toner image on the photoreceptor side is transferred to the transfer material.

Thereafter, the transfer material separates from the photoreceptor 1 and reaches a fixing site (not shown), where the toner image is fixed and fixed on the transfer material and is then discharged from the machine, leaving the toner image on the photoreceptor 1 without contributing to transfer. The residual toner is eliminated by the cleaner 10, and the residual charge is eliminated by the pre-discharging lamp 8, and the photoreceptor 1 is ready for the next step.

By the way, in the illustrated apparatus, the transfer roller 2 is made of a metal core with a diameter of 8 mm, carbon dispersed in EPDM, and a volume resistivity of 10' to 1010 ΩcII+ and a hardness of 25 to 25.
A medium resistance material adjusted to 30° (Asker-C hardness) was formed to have an outer diameter of 20''.

However, as mentioned above, this transfer roller is also easily affected by environmental humidity. Specifically, a roller with a length of 220 mm is pressed against a conductive flat plate with a nip width of 2 mm, and there is a gap between the two. When IKV voltage is applied and the resistance value is actually measured, it is approximately 09Ω under L/L fM environment, approximately 4XIO'Ω under N/N environment, and approximately 5~5Ω under H/H environment.
l OX 10'Ω thick (it was found that it varies.

Of course, this value varies slightly depending on the material, manufacturing method, etc., but it has been difficult to significantly change the characteristics as described above by such means.

The present invention has been achieved in view of the above situation, and it is possible to apply a voltage of the same polarity as that of the wide charger 3 between adjacent transfer materials (referred to as "paper gap") during pre-rotation and continuous printing. is applied to the transfer roller 2, the resistance value of the roller is estimated based on the current value at that time, and based on this, the optimum bias voltage is applied when the next sheet is passed.

Figure 2 shows the current-voltage characteristics between the photoreceptor 1 and the transfer roller 2 in various environments, with A, B, and C showing good results under L/L, N/N, and H/H environments, respectively. This shows the range in which transferability can be obtained.

In this case, the reason why the current value when applying a negative voltage to the transfer roller is small is because the photoreceptor is previously negatively charged (usually -600
This is because the photoreceptor and transfer roller have a slight rectifying property.

In FIG. 3, the horizontal axis represents the current value when a voltage of 13 KV is applied to the transfer roller, and the vertical axis represents the optimum transfer voltage value during transfer relative to this value.

In other words, even if the resistance value of the transfer roller changes due to environmental changes, an appropriate bias setting period is provided between sheets during the previous rotation, and a predetermined voltage of the same polarity as that of the charger is applied to the transfer roller, so that the current at this time can be adjusted. Depending on the value, the optimum transfer bias can be set for the next transfer.

FIG. 4 is a schematic diagram of a device that makes the above possible, in which the bias applying means 4 is composed of a variable constant voltage power source 13, an ammeter 14, and a controller section 15.
As shown in the timing chart in the figure, a voltage of -3 V is applied to the transfer roller 2 during the pre-rotation, the current value at this time is determined by the ammeter 14, and the corresponding voltage is determined from Figure 3. , this voltage is applied as a transfer bias when transferring the first sheet.

The reading of the ammeter may be taken as an average value over the entire area where -3KV is applied, or may be sampled by dividing the area. In addition, in order to achieve synchronization on the surface of the photoreceptor, the transfer bias is shifted by Δ from the laser exposure.

Similarly, -3 KV is applied between the first and second sheets, and the transfer bias for the second sheet is determined from the current value at this time.

In this case, in order to obtain the voltage VT from the read current iT in the control section, the V
It may be determined by T = -I T Xa+β (α and β are constants), or it may be determined by calculation by a computer or by a look-up table.

According to the present invention, since a bias having the same polarity as that of the charger is applied between sheets, transfer memory does not occur. In laser beam printers, it is common to perform APC control in which the amount of light is controlled to be constant by performing laser exposure between sheets of paper. part is bright potential,
When the area is attenuated to about -100V and this area is charged with a positive potential by the transfer roller, transfer memory is more likely to occur than in the dark potential area that is not exposed (-600V), and this causes the transfer of the next transfer material. It is possible to prevent image quality deterioration such as background blur and excessive density in halftone areas.

Of course, it goes without saying that even when APC control is not performed, it is effective in preventing the occurrence of transfer memory.

In addition, by applying a voltage of opposite polarity to the transfer roller to the transfer roller in this manner, there is an effect of returning the toner adhering to the surface of the roller to the photoreceptor, that is, there is an effect of cleaning the transfer roller.

FIG. 6 is a timing chart showing another embodiment of the present invention.

Although it has already been mentioned that the application of the present invention has the effect of cleaning the toner adhering to the transfer roller, it is quite possible that the transfer roller becomes extremely contaminated, especially when a jam occurs. Therefore, this embodiment is suitable for such a case.

As shown in the figure, after the main switch is turned on, a preparatory rotation is performed as appropriate, and at this time the charger 3 is turned off to maintain the photoreceptor surface potential at almost zero potential (at this time, the main motor is synchronized with the main motor). Preferably, the pre-exposure lamp 8 is turned on).

Further, by starting the preparatory rotation when the former roller of the fixing device, which normally consists of a roller equipped with a heat source and a roller that is in pressure contact with the fixing device, reaches an appropriate temperature, there is an effect of warming the latter roller.

By initially applying a voltage of -3 KV to the transfer roller 2 at the start of the preparatory rotation, the transfer roller can be effectively cleaned since the photoreceptor is in an uncharged state (over OV).

Then, the voltage applied to the transfer roller was switched to +3KV.

This eliminates the reverse fog toner (
In this case, the positively charged toner) is also transferred to the photoreceptor 1,
The surface of the transfer roller will be thoroughly cleaned.

In this process, the resistance value of the transfer roller may be estimated while a negative voltage is applied to the transfer roller, and the optimum transfer voltage may be determined based on this estimate.

In this case, since the surface of the photoreceptor 1 has zero potential, the transfer current value when a negative voltage is applied to the transfer roller is larger than that in the above-mentioned embodiment, and the accuracy of estimating the optimum transfer voltage is improved. It turns out.

FIG. 7 shows still another embodiment of the present invention, in which a bias applying means 16 to the transfer roller 2 is used.
sets the constant voltage power supply 17 with positive polarity and the constant current power supply 18 with negative polarity, the current value of the constant current power supply 18, and detects the voltage of the power supply 18, thereby changing the voltage value of the constant voltage power supply 17. It consists of a controller 19 for setting the power source, and a switch 20 for switching between the two types of sources.

When the power supply 18 is set so as to obtain a constant current of -10 μA, the voltage at this time varies between -3.5 KV and -2 KV depending on the environment, as shown in the graph of FIG. 2. in this case,
The optimal voltage for transfer is the shaded area in the positive voltage area in Figure 2, and varies from +3.7 to +1.7K depending on the environment.
It varies between V.

This situation is shown in solid lines in FIG.

, In the same figure, the horizontal axis is the output voltage of the constant current power supply 18 ■A, (
The vertical axis is the optimum transfer voltage Vya (positive voltage) estimated from this value.

The dotted line E in the same figure is an approximation line to the solid line. Using this line, the controller 19 can calculate V T, knee α×vA, (α is a constant), the application power of the constant voltage power supply 17 can be easily determined.

+i The VTI detection timing is as shown in FIG.
During the pre-rotation, a constant current is applied between the sheets, the voltage at this time is detected and set as vy+, and from now on as mentioned above, V T
2 is determined and applied during the next transfer.

As can be seen from FIG. 2, the optimum transfer bias value is the voltage V
, changes considerably due to changes in the environment, but the current i
T is concentrated around 20 μA. In other words, it can be said that the current value is more appropriate as a guideline for optimizing the transfer bias.

Therefore, it can be said that the method of performing constant current control to set an appropriate voltage as in this embodiment provides higher reliability.

Although the present invention has been described above with respect to an embodiment using a transfer roller, the present invention is not limited to this (it goes without saying that it can also be applied to an embodiment that uses a transfer belt as a transfer means, and Needless to say, the charging means for the photoreceptor is not limited to the corona discharger type, and a charging roller, a contact type charging means, or a blade-shaped charging means can also be used.

In this case, when applying a superimposed direct current to alternating current as a charging power source, the polarity of the charging means is that of the direct current component.

(3) As described in the detailed description of the invention, according to the present invention, in an image forming apparatus equipped with a transfer means that contacts an image carrier, such as a transfer roller, when there is no transfer material between the two, , applying a bias of the same polarity to the transfer means as the charging means for charging the image carrier and detecting the current at this time;
By setting an appropriate transfer bias voltage value based on this current value, stable transfer performance can be obtained at all times regardless of the environment, and this has a remarkable effect on obtaining high-quality images.

[Brief explanation of the drawing]

FIG. 1 is a schematic side view of the main parts of an image forming apparatus suitable for applying the present invention, FIG. 2 is a graph showing differences in current-voltage characteristics due to differences in environment, and FIG. 3 is a detailed diagram of the present invention. Graphs for explanation; FIG. 4 is a schematic diagram showing the structure of the device shown in FIG. 1 near the transfer site; FIG. 5 is a timing chart showing the same operation; FIG. 6 is a timing chart showing another example. 7 is a schematic diagram showing the configuration near the transcription site showing still another embodiment. FIG. 8 is a timing chart showing the operation of the above. FIG. 9 is a graph for explaining the operation of the above. . ■... Photoreceptor, 2... Transfer roller, 3... Charger, 4.16... Bias application means, 13... Constant voltage power supply, 14... Ammeter, 15.19. ... Controller, 17... Constant voltage power supply, 19... Constant current power supply. Fig. 3 0 -10-20-30-401T (PA) Fig. 2 Fig. 6 Fig. 1: Racer''-surprise) 0FF

Claims (2)

[Claims] (1) An image carrier, a charging means for charging the surface of the image carrier,
a transfer unit that contacts the image carrier to form a transfer site, supplies a transfer material to the transfer site in synchronization with the image formed on the image carrier, and applies a transfer bias to the transfer unit; In the image forming apparatus configured to apply voltage, a bias voltage having a predetermined voltage value having the same polarity as that of the charging means is applied to the transfer means when no transfer material is present at the transfer site, and the current detected at this time is An image forming apparatus characterized in that the transfer means applies an appropriate transfer bias voltage to the transfer material. (2) When there is no transfer material at the transfer site, applying a bias of a predetermined current value of the same polarity as the charging means to the transfer means,
The image forming apparatus according to claim 1, wherein a transfer bias voltage is applied to the transfer means based on the voltage value detected at this time.