JPH08123211A - Image forming device - Google Patents

Abstract

PURPOSE: To obtain stable transfer performance irrespective of use environment and the condition of a transfer material when transferring a toner image by bringing transfer member, such as a transfer roller into contact with an image carrier. CONSTITUTION: Before the paper 23 reaches, a prescribed voltage is applied to the transfer roller 16 rotating in contact with a photocounductive drum 12. And according to a transfer current flowing in the transfer roller 16 at the time, a transfer voltage which is applied to the transfer roller is determined. During the transfer of the toner image onto the paper 23, this transfer current is monitored, and the voltage applied to the transfer roller 16 is corrected by calculating the transfer voltage each time the transfer current exceeds a permissible range.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus for forming an image, such as a copying machine, a printer, a facsimile machine, etc., and more specifically, a toner image on an image bearing member such as a transfer roller or a transfer belt. The present invention relates to an image forming apparatus configured to transfer to a transfer material such as paper by a transfer member.

[0002]

2. Description of the Related Art In an image forming apparatus, for example, an electrostatic latent image is formed on a photosensitive drum, and this is developed by a developing device to form a toner image. The toner image thus created is transferred onto a transfer material such as paper using a transfer device. A corotron called a transfer corotron may be used for transfer at this time, but a toner image is transferred by applying a bias voltage to a transfer member such as a roller because of the advantages of easy position adjustment and easy maintenance. There are also those that are adapted to be transferred to a material. In the image forming apparatus using the latter transfer device,
As a method of applying a bias voltage, a method of using a constant voltage control method for controlling a constant voltage and a method of using a constant current control method for controlling a constant current are generally used.

In an image forming apparatus using a constant voltage control system, a transfer member such as a transfer roller used as a transfer device is usually one in which conductive particles are dispersed in rubber and its volume resistivity is appropriately adjusted. I'm using it. Since the volume resistivity greatly changes depending on the environment in which the image forming apparatus is used, it is difficult to always obtain stable transfer characteristics when applying one type of bias voltage having a fixed value.

For example, it is assumed that an optimum bias voltage is set in a normal temperature and normal humidity environment (hereinbelow, an environment of a temperature of 22 ° C. and a relative humidity of 55%).
If this is changed to a low-temperature and low-humidity environment (hereinafter referred to as an environment of 10% C and 15% RH in this specification), the resistance values of both the transfer member such as the transfer roller and the transfer material such as the paper become large. , Transfer failure occurs. On the contrary, in a high temperature and high humidity environment (hereinbelow, referred to as an environment of 85% RH at a temperature of 32 ° C.), the resistance values of both the transfer member such as the transfer roller and the transfer material such as the paper become extremely large. Becomes smaller. As a result, an excessive current flows into the transfer member or the transfer material, and part of the toner is converted to the same polarity as the transfer bias. In this way, the toner whose polarity has been reversed to the original polarity of the toner does not transfer to the transfer material and causes the phenomenon of transfer omission. In addition, an excessive current may flow into the photoconductor itself to change the potential corresponding to the image, which may cause a so-called transfer memory and adversely affect the image during the next image forming cycle. became.

In order to avoid such a problem, in JP-A-3-62075, constant voltage or constant current control is performed in the non-sheet passing portion of the image carrier where the transfer material does not exist at the transfer portion. Then, the voltage to be applied when passing the transfer material is determined according to the current value and the voltage value obtained at that time, and the toner image is transferred by the constant voltage control method when the paper is passed.

Further, in Japanese Patent Laid-Open No. 4-258980, the output voltage at the time of transfer is calculated via software by the output voltage value and the current detected by the current detecting means. Then, the toner image is transferred by the constant voltage control method using the voltage obtained by the calculation.

[0007]

In these image forming apparatuses, the transfer device itself can cope with environmental changes by such measures. However, since the voltage value for transfer is determined before the start of the transfer operation in which the transfer material has not yet arrived at the transfer site, the problem in transfer characteristics due to the difference in the transfer material has not been solved. That is, the transfer material such as paper has a different water content and a different resistance value depending on the environment or the environment, and a transfer material having a large resistance value has a disadvantage that the charge necessary for the transfer is insufficient. In addition, the nip pressure and the nip width of the contact portion of the image carrier and the transfer member such as the transfer roller may change due to the difference in the thickness of the transfer material. Is also applied, or conversely, the voltage is insufficient and a transfer failure occurs. Therefore, when trying to solve such a problem in the conventional image forming apparatus, very high accuracy is required for detecting the current-voltage characteristics of the transfer device, resulting in a problem that the cost of the apparatus is considerably increased. there were.

Therefore, an object of the present invention is to obtain a stable transfer performance when a transfer member such as a transfer roller is brought into contact with an image carrier to transfer a toner image, regardless of the use environment or the state of the transfer material. An object of the present invention is to provide an image forming apparatus capable of performing the above.

Another object of the present invention is to provide an image forming apparatus capable of correcting the voltage applied to the transfer material when a relatively large change in the use environment or the state of the transfer material is detected.

[0010]

According to a first aspect of the present invention, (a) an image bearing member such as a photoconductor drum which holds charged toner particles on the surface thereof, and (b) a rolling contact with the image bearing member. When a transfer member such as a conductive transfer roller, (c) a voltage applying means for applying a voltage having a polarity opposite to the charge of the toner particles to the transfer member, and (d) when a voltage is applied by the voltage applying means. Current detection means for detecting the current flowing between the image carrier and the transfer member, and (e) Current detection in the presence of a transfer material such as plain paper that receives the transfer of toner particles between the image carrier and the transfer member. When the current detected by the means exceeds a predetermined range, the image forming apparatus is provided with an applied voltage correcting means for correcting the voltage applied by the voltage applying means so as not to exceed the predetermined range.

That is, according to the first aspect of the invention, when the toner particles held on the surface of the image bearing member such as the photosensitive drum are transferred to the transfer material such as plain paper by the transfer member such as the transfer roller, the image bearing is carried. When the transfer material is present between the body and the transfer member, the current detecting means detects the current flowing through the transfer material, and when the current exceeds a predetermined range, the voltage applied to the transfer material is corrected so that the current does not exceed the predetermined range. I did it.
Therefore, the toner particles can be satisfactorily transferred to the transfer material by a simple method as compared with the case where the characteristics such as paper quality and water content of the transfer material are measured one by one and the applied voltage is adjusted. Moreover, since the applied voltage is not adjusted until the current detected by the current detecting means exceeds the predetermined range,
Compared with the case where the applied voltage is adjusted with respect to a minute current change, the reproduction of an image is not adversely affected.

According to the second aspect of the present invention, (a) an image bearing member such as a photosensitive drum which holds charged toner particles on the surface thereof, and (b) a conductive transfer roller which is in contact with the image bearing member. A transfer member, and (c) voltage applying means for applying a voltage having a polarity opposite to the charge of the toner particles to the transfer member,
(D) Current detecting means for detecting a current flowing between the image carrier and the transfer member when voltage is applied by the voltage applying means, and (e) transfer of toner particles between the image carrier and the transfer member. The applied voltage that applies a predetermined voltage to the transfer member by the voltage applying means in the absence of the transfer material such as plain paper, and calculates the voltage applied to the transfer member when the toner particles are transferred to the transfer material based on this. When the current detected by the current detecting means exceeds the predetermined range in the state where the transfer material is present between the arithmetic means and (f) the image carrier and the transfer member, voltage is applied so as not to exceed the predetermined range. The image forming apparatus is provided with an applied voltage correction means for correcting the voltage applied by the means.

That is, according to the second aspect of the invention, a predetermined voltage is applied to the transfer member by the voltage application means in the absence of a transfer material such as plain paper which receives the transfer of toner particles between the image carrier and the transfer member. Based on this, it was decided to set the initial voltage applied to the transfer member when the toner particles were transferred to the transfer material. Therefore, the change of the applied voltage by the applied voltage correction means is likely to be performed when the characteristics of the transfer material are largely different, and for the standard transfer material, the applied voltage is applied in a good state from the beginning, Good image quality can be obtained.

According to a third aspect of the present invention, (a) an image carrier such as a photosensitive drum which holds charged toner particles on the surface thereof, and (b) a conductive transfer roller which is in rolling contact with the image carrier. A transfer member, and (c) voltage applying means for applying a voltage having a polarity opposite to the charge of the toner particles to the transfer member,
(D) Current detecting means for detecting a current flowing between the image carrier and the transfer member when voltage is applied by the voltage applying means, and (e) transfer of toner particles between the image carrier and the transfer member. In the absence of a transfer material such as plain paper, a predetermined voltage is applied to the transfer member by the voltage applying means, and the current applied voltage is set to the current value at which the transfer of the toner particles to the standard transfer material is performed best. The applied voltage calculation means for calculating the voltage applied to the transfer member by multiplying the value by the current value detected by the current detection means, and (f) the transfer material between the image carrier and the transfer member. When the current detected by the current detecting means exceeds the predetermined range in the existing state, the current value at which the transfer of the toner particles to the standard transfer material is best performed is multiplied by the current applied voltage, and the current value is multiplied by that value. Present by detection means The applied voltage recalculating means for recalculating the voltage applied to the transfer member by dividing the current value detected at the point, and (g) Application of the voltage applied to the transfer member recalculated by the applied voltage recalculating means. The image forming apparatus is provided with an applied voltage correction means for correcting the voltage.

That is, according to the third aspect of the invention, a predetermined voltage is applied to the transfer material before the transfer material such as plain paper passes through the transfer member such as the transfer roller, and the current applied to the current actually flowing at this time is applied. The voltage applied to the transfer member is initially set by multiplying the voltage by the current value detected by the current detection means, and the current is detected even when the transfer material is passing through the transfer member. If it exceeds the predetermined range, the current value at which the transfer of the toner particles to the standard transfer material is best performed is multiplied by the current applied voltage, and the current value detected by the current detection means is added to the current value. It was decided to recalculate the voltage applied to the transfer member by removing. Therefore, by making corrections using a standard transfer material as a reference, it is possible to realize good transfer characteristics for all transfer materials without knowing the characteristics of each transfer material.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to embodiments.

FIG. 1 shows the essential parts of the structure of an image forming apparatus according to an embodiment of the present invention. This apparatus is applied to, for example, a printer connected to a host computer (not shown). Around the photosensitive drum 12 of the image forming apparatus 11, the charging roller 13 and the developing roller 1 are provided.
5 and transfer roller 16 are arranged. The charging roller 13 is a roller for uniformly charging the photosensitive drum 12 which rotates in the direction of arrow 18 (clockwise direction). The developing roller 15 is arranged in the developing device 19 and develops the electrostatic latent image with magnetized toner particles. A laser beam 21 modulated by an image signal is repeatedly irradiated in the axial direction (main scanning direction) of the photoconductor drum 12 at a predetermined position between the charging roller 13 and the developing device 19 to generate the electrostatic latent image. The formation is to take place.

A toner image is formed on the surface of the drum that has passed through the developing device 19, and the transfer roller 16 transfers the toner image onto the paper 23. The paper 23 is adapted to be carried from a paper supply source such as a cassette tray (not shown) by paper carrying paths 24 and 25.
The transportation timing is detected by a transmissive optical sensor 26 that detects an object passing between the sheet transportation paths 24 and 25. The paper 23 to which the toner image has been transferred after passing through the transfer roller 16 is sent to a fixing device (not shown), where the toner image is fixed, and the paper 23 is similarly discharged onto a discharge tray (not shown). Also,
The toner particles remaining on the photosensitive drum 12 without being transferred to the paper 23 are scraped off by the cleaning blade 27 pressed against the drum surface between the transfer roller 16 and the charging roller 13 with a predetermined pressure. ing.
After the drum surface is thus cleaned, the charging roller 13 again applies electric charges, and the next image forming operation is started.

In such an image forming apparatus, the high voltage power source 2
Each of the predetermined voltages created by 8 is applied to three types of rollers: the charging roller 13, the developing roller 15, and the transfer roller 16. In addition, the transfer roller 1
6 is also connected to the output current detection circuit 29 to detect the output current. A voltage control circuit 31 is connected to the high-voltage power supply 28, which controls the voltage applied to the transfer roller 16 based on the detection result of the output current detection circuit 29, and also applies the voltage to each roller 13, 15, 16. It is also designed to control the timing of.

FIG. 2 shows an outline of the circuit configuration of this image forming apparatus centering on the voltage control circuit. The image forming apparatus 11 is a CP having a central function of various controls.
It is equipped with U41 (Central Processing Unit). The CPU 41 is connected to each unit in the apparatus through a bus 42 such as a data bus, and controls not only general image formation but also voltage control for the transfer roller 16 in this embodiment.

Of these, the ROM 43 is a read-only memory that stores programs for performing the above-mentioned various controls and fixed data. The work memory 44 is a random access memory that temporarily stores data required for control. The input circuit 45 is connected to the operation panel 46 so that data for various operations can be input. The D / A converter 48 is for converting a digital signal into an analog signal, and the converted analog signal is supplied to the voltage control circuit 31. The detection result of the output current is input to the voltage control circuit 31 from the output current detection circuit 29, and the voltage control circuit 31 controls the voltage of the high voltage power supply. On the contrary, the A / D converter 49 is for converting an analog signal into a digital signal, and the detection result of the voltage control circuit 31 side is input to the CPU 41 side for recognition.

A sensor input circuit 51 is arranged in the image forming apparatus, and the optical sensor 26 detected inside the apparatus main body.
The detection results of various sensors, such as the detection result of 1), are input. The main motor drive circuit 53 drives the main motor 54 for rotating the photosensitive drum 12 shown in FIG. 1 at a constant speed.

FIG. 3 shows the outline of the control from the reception of the print signal to the start of the conveyance of the paper as the first step of the control of the image forming apparatus of the present embodiment at the time of forming the image. When a print start signal arrives from an external device such as the host computer (step S101;
Y), the CPU 41 shown in FIG. 2 receives this and controls the main motor drive circuit 53 to drive the main motor 54 (step S102). As a result, the photosensitive drum 12 (FIG. 1) starts rotating at a constant speed. Also, CPU
41 sends a high voltage application signal to the voltage control circuit 31 to start charging of the photosensitive drum 12 by the charging roller 13 (step S103). That is, when the high voltage application signal is supplied, the voltage control circuit 31 controls the high voltage power supply 28 to apply a negative voltage to the charging roller 13, so that the drum surface is -4.
It is uniformly charged to a voltage V _H of 00V. When the surface of the drum reaches the writing position of the laser beam 21, the CPU 41 causes the laser beam 21 to generate an image signal at that timing.
Modulation is started, and an electrostatic latent image is formed on the photosensitive drum 12. The voltage control circuit 31 also controls the high voltage power supply 28 to apply high voltage to the developing roller 15 and the transfer roller 16. The electrostatic latent image formed on the photoconductor drum 12 is developed by toner particles in the developing device 19 and becomes a visible image.

By the way, the CPU 41 controls the photosensitive drum 12
The voltage applied to the transfer roller 16 when the charging of the
In order to adjust the
Pressure determination voltage V₀Is applied (step S104). So
Then, the transfer current I ₀Is detected (step S1
05), and then this transfer current I₀And transfer voltage determination voltage
V₀Transfer voltage V_TIs calculated and determined (step
S106). However, at this point, the transfer roller 16
Dako transfer voltage V_TIs not applied.

By the way, the transfer roller 16 used in the apparatus of this embodiment is made of urethane rubber mixed with conductive particles such as carbon, and has a volume resistance of 1 at room temperature and normal humidity.
It is adjusted to approximately 10 ⁸ cm · Ω. The process speed of the photoconductor drum 12 is 25 mm / sec. Further, the volume resistance was obtained by measuring the current flowing when a voltage of 1000 V was applied in a state where the transfer roller 16 to be measured was pressed against the ends of the roll shaft with a pressing force of 500 gf / cm on the conductive plate. It is a thing.

FIG. 4 shows the relationship between the volume resistance of the transfer roller and changes in the environment. On the horizontal axis, L / L indicates the low temperature and low humidity environment described above, and N / N indicates the normal temperature and normal humidity environment described above. H / H indicates the high temperature and high humidity environment described above. In this way, when the low temperature and low humidity environment is changed to the high temperature and high humidity environment, the volume resistance is reduced.

FIG. 5 shows L / L, N shown as a representative in FIG.
6 shows voltage-current characteristics of the transfer roller under three environments of / N and H / H. Here, a state in which the transfer roller 16 and the photosensitive drum 12 are in contact with each other, that is, an initial state in which the paper 23 is not sandwiched between them is shown. The current flowing through the transfer roller 16 is 1.0 μA
If it is below (microamperes), transfer failure will occur,
On the other hand, when it becomes 2.0 μA or more, a transfer memory occurs.
The optimum transfer area is in the range of 1.0 to 2.0 μA. As can be seen from this figure, the high temperature and high humidity environment (H /
Since the volume resistance is lower during H), the applied voltage is lower than the normal temperature and normal humidity environment (N / N) indicated by the broken line 62 and the low temperature and low humidity environment (L / L) indicated by the broken line 63. It becomes the optimum transfer area.

In FIG. 5, for example, the transfer roller 16 is used in each environment.
Consider the case where a voltage of +600 V is applied to. The current flowing through the transfer roller 16 is low temperature and low humidity environment (L / L).
It is 0.1 to 0.3 μA under the normal temperature and normal humidity environment (N /
N-) 0.6-0.9 μA. Further, it becomes 1.6 to 1.9 μA in a high temperature and high humidity environment (H / H). Therefore, the transfer failure occurs in the former two cases, and the optimum transfer is performed under the latter high temperature and high humidity environment.

In step S106 of FIG. 3, the transfer voltage V _T is calculated by the following equation (1) in order to obtain a transfer output current of about 1.5 μA that can obtain the optimum transfer performance. Here, it is assumed that the applied voltage is + 600V. V _T = (600V) × (1.5μA) ÷ (detected current value at 600V) (1)

Take the case of a normal temperature and normal humidity environment as an example. 600V
It is assumed that the detection current of 0.75 μA is measured at. In this case, the equation (1) becomes as follows. V _T = (600) × (1.5) ÷ (0.75) = 1200 (V)

That is, in this case, the applied voltage is +120.
It is determined to be 0V. Then, by performing constant voltage control with this determined voltage at the time of paper passing, it is possible to obtain stable transfer characteristics when the use environment is normal temperature and normal humidity. Even if the usage environment is different, since the calculation is performed based on the environment at that time, stable transfer characteristics can be secured regardless of the variation in the volume resistance value of the transfer roller 16. However,
The above calculation does not consider the paper quality, the weight, and the water content of the paper 23 at all.

FIG. 6 shows the relationship between the weight of a sheet as a transfer material and the current flowing through the transfer roller at room temperature and normal humidity. Here, an example is given in which the voltage applied to the transfer roller 16 is + 800V. In this figure, paper 2
Although it has been shown that the current flowing through the transfer roller 16 decreases as the weight of No. 3 increases, the transfer roller may be changed depending on the paper quality of the paper 23 (for example, paper for tracing paper or OHP (overhead projector)) and the water content. The large fluctuations in the current flowing through 16 do not require special explanation.

As described above, the same voltage is temporarily applied to the transfer roller 16
Even if applied as a transfer bias voltage to the paper 23
The current value fluctuates greatly depending on each situation. Therefore, conventionally, it has been impossible to secure an optimum transfer current region assuming all transfer materials. That is, even if the use environment of the image forming apparatus is detected and an optimum transfer voltage is selected assuming a standard transfer material, if the resistance value of the transfer material used is very low, 2 μA The above current flows, and a transfer memory is generated. On the contrary, if the transfer material used has a very high resistance value, only a current of 1.0 μA or less flows, and a sufficient transfer charge cannot be obtained, resulting in a transfer failure. . Therefore, in the image forming apparatus of this embodiment, the current flowing through the transfer roller 16 is monitored even after the transfer onto the paper 23 is actually started, and when the current is out of the optimum transfer current range, the transfer voltage V _T is recalculated. I have decided.

Now, returning to FIG. 3, step S106.
The control after the first calculation is performed will be described. When the initial transfer voltage V _T is obtained without considering the paper 23 (step S106), the CPU 41 starts modulation of the laser beam 21 to start electrostatic writing (step S107). Then, when a predetermined time t ₁ has elapsed from this time (step S108;
Y), the conveyance of the paper 23 stored in the cassette tray (not shown) is started (step S109). Here, the time t ₁ is for adjusting the time required for the portion of the drum surface where the writing of the latent image is started to be sent to the position of the transfer roller 16 and the time for the paper 23 to reach the transfer roller 16. It is a thing.

FIG. 7 shows an outline of control from the start of development to the end of transfer onto a sheet as the second step of control during image formation in the image forming apparatus of this embodiment. When the conveyance of the paper 23 is started in step S109 of FIG. 3, the CPU 41 controls the developing device 19 to start the developing operation (step S110). CPU in this state
41 monitors the time when the optical sensor 26 detects the leading edge of the paper 23 (step S111), and when detected (Y), measures the time t ₂ from this (step S11).
2). At this time t _2, the leading edge of the paper 23 is the transfer roller 16
It is the time until it is sandwiched between the photosensitive drum 12 and the photosensitive drum 12. When the time t ₂ is measured (Y), the transfer voltage V _T determined in step S106 from this time is applied to the transfer roller 16
(Step S113). Then, at the same time, monitoring of whether or not the transfer current flowing through the transfer roller 16 remains within the range of the optimum transfer area shown in FIG. 5 is started (step S114).

That is, until the transfer of the paper 23 is completed
During the period (step S115), the transfer current is 1.0 μA or less.
A situation where the battery is full or exceeds 2.0 μA
Occurs (step S114; Y), the transfer at that time
The transfer current is substituted into the equation (1) to newly generate the transfer voltage V._TCalculate
Yes (step S116). Then, this transfer voltage V _T
To (step S117). Transcription as a result of this
The transfer current flowing through the roller 16 changes, but this is 1.
It will be less than 0 μA or more than 2.0 μA
If such a situation occurs, do the same again until the transfer is completed.
The calculation will be repeated.

However, the recalculation of the transfer voltage V _T is not always performed in small steps so that the transfer current is 1.5 μA, for example, but as described above, the allowable range of 1.0 μA to 2.0 μA is used. When it goes out of the range, it is supposed to be performed exceptionally. This is to prevent the occurrence of adverse effects such as uneven density in the image due to fluctuations in the transfer voltage V _T caused by controlling the transfer current to a constant value. That is, the recalculation of the transfer voltage V _T performed in this embodiment is performed when the paper quality of the paper 23 is largely different from the standard one, or when the water content changes greatly locally. In the case where the image quality is not guaranteed even if the transfer voltage V _T is held and the toner image is transferred, it is a recalculation for maintaining the image quality. Therefore, when the calculated value is largely changed, some shading may occur at the boundary, but it is clear that the image quality is improved as compared with the case where the transfer voltage V _T is not changed.

FIG. 8 shows an outline of the control after the transfer of the toner image onto the paper is completed as the third step of the control at the time of image formation of the image forming apparatus of this embodiment.
When the transfer of the toner image is completed, the CPU 41 controls the voltage control circuit 31 to release the voltage applied to the transfer roller 16 (step S116). Thereafter, the paper 23 is fixed by a fixing device (not shown) (step S11).
7) Similarly, the sheet is discharged onto a discharge tray (not shown) (step S118). At this time, the CPU 41 checks whether or not the reception of the print signal of the subsequent page has started (step S119), and if it has not started (N), the operation of each unit is stopped (step S12).
0), a series of control is ended.

In step S119, the subsequent page is printed.
If the input signal has started receiving (Y),
Proceed to step S107, and print for that page.
Start writing the image. The control after this is the same as before.
is there. However, in step S113, the transfer voltage V_TApplication of
When performing, the initial value calculated in step S106
You may use it, or modify it in step S117.
The transfer voltage V_TYou may make it set as.
However, when performing a series of prints,
Since the use of paper 23 is usually done, the latter correction
Later transfer voltage V _TIs often useful
Conceivable.

In this embodiment, if there is a subsequent page, the process proceeds from step S119 to step S107. However, the process proceeds to step S104, the transfer voltage determining voltage V ₀ is applied, and the transfer voltage V _T is applied. The calculation of may be performed again.

FIG. 9 shows a main part of the voltage control circuit and a peripheral part of the voltage control circuit. The voltage control circuit 31 includes a transfer voltage output ON / OFF circuit 71 for ON / OFF control of the transfer voltage V _T applied to the transfer roller 16 and the transfer voltage determining voltage V ₀ , and is sent from the bus 42. The drive current control circuit is turned on / off by the control signal. Further, the transfer voltage determining voltage V ₀ and the transfer voltage V _T as a calculated value are output from the D / A converter 48 to the output voltage control circuit 73 in the voltage control circuit 31.
The voltage control of the high voltage power supply 28 is performed. The output current detection circuit 29 uses the transfer roller 16
The current flowing between the photosensitive drum 12 and the photosensitive drum 12 is detected, and the result is output to the A / D converter 49 via the voltage control circuit 31, where it is converted into a digital signal and supplied to the bus 42. It has become. Of course, when the CPU 41 has a function as the D / A converter 48 or the A / D converter 49, the bus 42 can be directly connected to the voltage control circuit 31.

In the above-described embodiments, the photoconductor drum is used as the image carrier, but the photoconductor belt, other photoconductors, and the image carrier having a toner image on its surface are also used. It goes without saying that the invention can be applied. In the embodiment, the optimum transfer area of the transfer current is 1.
Although the range is 0 μA to 2.0 μA, it goes without saying that these values vary depending on the characteristics of the photoconductor or the like and the measurement conditions.

[0043]

As described above, according to the first aspect of the present invention, the toner particles held on the surface of the image bearing member such as the photosensitive drum are transferred to a transfer material such as plain paper by a transfer member such as a transfer roller. At the time of transfer, the current detecting means detects the current flowing through the transfer material in the state where the transfer material is present between the image carrier and the transfer member. The voltage applied to the material was adjusted. Therefore, the toner particles can be satisfactorily transferred to the transfer material by a simple method as compared with the case where the characteristics such as paper quality and water content of the transfer material are measured one by one and the applied voltage is adjusted. Moreover, since the applied voltage is not adjusted until the current detected by the current detecting means exceeds the predetermined range, the reproduction of the image is adversely affected as compared with the case where the applied voltage is adjusted for a minute current change. Never give.

According to the second aspect of the invention, the same effect as that of the first aspect of the invention can be obtained, and the applied voltage to the transfer member can be properly set from the beginning of the transfer of the transfer material. The effect is that you can do it. That is, since it is highly likely that the applied voltage is changed by the applied voltage correcting means when the characteristics of the transfer material are largely different, the applied voltage is applied to the standard transfer material in a good condition from the beginning. Therefore, good image quality can be obtained.

Further, according to the third aspect of the invention, a predetermined voltage is applied to the transfer material before the transfer material such as plain paper passes through the transfer member such as the transfer roller. The voltage applied to the transfer member is initially set by multiplying the applied voltage by the current value detected by the current detection unit, and the current is applied even when the transfer material is passing through the transfer member. Is detected, and when it exceeds a predetermined range, the current value at which the transfer of the toner particles to the standard transfer material is best performed is multiplied by the current applied voltage, and the current value is detected by the current detection means at this time. It was decided to recalculate the voltage applied to the transfer member by dividing the current value. Therefore, in addition to being able to obtain the same effect as that of the invention described in claim 1, it is possible to apply it to any transfer material without knowing the characteristics of each transfer material by performing the correction based on the standard transfer material. Also, good transfer characteristics can be realized. That is, the applied voltage is appropriately set even in individual situations such as the pressure of the transfer roller nipped with the photosensitive drum and the nipped area, which cannot be determined only by the environmental change of the volume resistance of the transfer roller. It can be set or modified, and good transfer characteristics without transfer memory can be realized.

[Brief description of drawings]

FIG. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment of the present invention.

FIG. 2 is a block diagram showing an outline of a circuit configuration of this image forming apparatus centering on a voltage control circuit.

FIG. 3 is a flow chart showing a state of control from reception of a print signal to start of conveyance of a sheet in the image forming apparatus according to the present exemplary embodiment.

FIG. 4 is a characteristic diagram showing a relationship between a volume resistance value of a transfer roller and a change in environment.

5 is a characteristic diagram showing voltage-current characteristics of a transfer roller under the three environments of L / L, N / N, and H / H typically shown in FIG.

FIG. 6 is a characteristic diagram showing the relationship between the weight of a sheet as a transfer material and the current flowing through the transfer roller at room temperature and normal humidity.

FIG. 7 is a flow chart showing a state of control from the start of development of the image forming apparatus of the present embodiment to the end of transfer onto a sheet.

FIG. 8 is a flowchart showing a state of control after the transfer of the toner image onto the sheet of the image forming apparatus according to the present exemplary embodiment is completed.

FIG. 9 is a block diagram showing a main part of the voltage control circuit and a peripheral part of the voltage control circuit.

[Explanation of symbols]

11 ... Image forming device, 12 ... Photosensitive drum, 16 ... Transfer roller, 23 ... Paper, 28 ... High-voltage power supply, 29 ... Output current detection circuit, 31 ... Voltage control circuit, 41 ... CPU, 43 ...
ROM, 44 ... Working memory

Claims (3)

[Claims] 1. An image carrier that holds charged toner particles on its surface, a conductive transfer member that contacts the image carrier, and a voltage having a polarity opposite to the charge of the toner particles is applied to the transfer member. Voltage applying means, a current detecting means for detecting a current flowing between the image carrier and the transfer member when a voltage is applied by the voltage applying means, and toner particles between the image carrier and the transfer member. When the current detected by the current detecting means exceeds a predetermined range in the presence of a transfer material which receives the transfer of the applied voltage, the applied voltage correction for correcting the voltage applied by the voltage applying means so as not to exceed the predetermined range. An image forming apparatus comprising: 2. An image carrier that holds charged toner particles on its surface, a conductive transfer member that contacts the image carrier, and a voltage having a polarity opposite to the charge of the toner particles is applied to the transfer member. Voltage applying means, a current detecting means for detecting a current flowing between the image carrier and the transfer member when a voltage is applied by the voltage applying means, and toner particles between the image carrier and the transfer member. Applied voltage calculation for applying a predetermined voltage to the transfer member by the voltage applying means in the absence of the transfer material to be transferred and calculating the voltage applied to the transfer member when the toner particles are transferred to the transfer material based on the voltage. And a voltage so that when the current detected by the current detection means exceeds a predetermined range in a state where the transfer material exists between the image carrier and the transfer member, the voltage does not exceed the predetermined range. To and a voltage applied correction means for correcting the voltage applied by the pressurized unit the image forming apparatus according to claim. 3. An image carrier that holds charged toner particles on its surface, a conductive transfer member that contacts the image carrier, and a voltage having a polarity opposite to the charge of the toner particles is applied to the transfer member. Voltage applying means, a current detecting means for detecting a current flowing between the image carrier and the transfer member when a voltage is applied by the voltage applying means, and toner particles between the image carrier and the transfer member. In the state where there is no transfer material to be transferred, a predetermined voltage is applied to the transfer member by the voltage applying means, and the current applied voltage is set to the current value at which the transfer of the toner particles to the standard transfer material is best performed. An applied voltage calculation unit that calculates the voltage applied to the transfer member by multiplying the obtained value and the current value detected by the current detection unit, and the transfer material exists between the image carrier and the transfer member. You In this state, when the current detected by the current detecting means exceeds the predetermined range, the current value at which the transfer of the toner particles onto the standard transfer material is most favorably performed is multiplied by the current applied voltage, and the value is detected. The applied voltage recalculating means for recalculating the voltage applied to the transfer member by dividing the current value detected by the means, and the application of the voltage applied to the transfer member recalculated by the applied voltage recalculating means. An image forming apparatus comprising: an applied voltage correction unit that corrects the voltage.