JP2003195657A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus by which stable image density and image quality are obtained by always applying transfer bias suitable for a resistance value even though a transfer roller, whose resistance value is fluctuated at a manufacturing time or a service time, is used. <P>SOLUTION: The image forming apparatus for possessing an image forming means, an attracting/feeding means to attract and feed a transfer material, a transfer means to transfer a toner image from the image forming means to the transfer material on the attracting/feeding means, a bias means to apply transfer bias to the transfer means, a first detecting means to detect the resistance of the transfer means are provided. The resistance of the transfer means in a state that the transfer material is not fed is detected by the first detecting means, so that the transfer bias applied to the transfer means is corrected based on the resistance value detected. <P>COPYRIGHT: (C)2003,JPO

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 using an electrophotographic system or the like, and more particularly to transfer of a toner image.

[0002]

2. Description of the Related Art Conventionally, various systems such as an electrophotographic system, a thermal transfer system, and an inkjet system have been adopted as an image forming apparatus. Among these, the image forming apparatus using the electrophotographic method has advantages in high speed, high image quality, and quietness.

FIG. 5 shows a schematic structure of an example of a conventional image forming apparatus using an electrophotographic system. The electrophotographic image forming apparatus includes, as image forming means, a photosensitive drum 100 which is an image carrier, a primary charging means 101, a developing device 103, and a cleaning device 108. The photoconductor drum 100 is a drum-shaped electrophotographic photoconductor, and is rotationally driven in the arrow direction, for example. After the surface of the photosensitive drum 100 is uniformly charged by the primary charging means 101, for example, an exposing means such as an LED or a laser.
The 102 exposes according to the image information to form an electrostatic latent image on the surface of the photoconductor drum 100. After that, the developing device 103 electrostatically attaches the developer 104 (including toner) to the electrostatic latent image to form a toner image on the photosensitive drum 100. Then, the toner image on the photoconductor drum 100 is electrostatically transferred onto the transfer material P transported by the transport means 105 to the transfer position facing the photoconductor drum 100 by the action of the transfer roller 106 as the transfer means. Transfer to.

After that, the unfixed toner image transferred onto the transfer material P is fixed on the transfer material P by being heated and pressed by the fixing device 107 to form a permanent image. On the other hand, the transfer residual toner remaining on the photoconductor drum 100 after the transfer is removed by a cleaning blade (not shown), and is collected in the waste toner container of the cleaning device 108. Photoreceptor drum 10 whose surface is thus cleaned
0 is repeatedly used for image formation.

Further, in recent years, color image forming apparatuses using an electrophotographic system have become widespread. The color image forming apparatus using the electrophotographic system is also divided into various systems. For example, in addition to the well-known multiple transfer system and intermediate transfer body system, a multiple development system in which a color image is superposed on the surface of the photoconductor and then collectively transferred to form an image, or an image of a plurality of different colors is formed. There is an in-line method or the like that has a forming unit (process station) and transfers a developer onto a transfer material conveyed by a transfer belt. The color image forming apparatus using the in-line method can achieve high speed,
In addition, since the number of times the toner image is transferred is small, it has many advantages such as being advantageous in image quality. In this in-line method, a configuration has been proposed in which process stations are arranged in a vertical direction and a transfer material is conveyed almost vertically in order to improve usability and reduce an installation area.

FIG. 6 shows a schematic structure of an example of a conventional full-color image forming apparatus using an in-line system. As shown in the figure, a transfer belt 110 as a suction conveyance means is provided with a driving roller 111, a suction facing roller 112, and a tension roller 113.
It is wound around the rollers a and 113b. Along the peripheral surface of the transfer belt 110, a process station 109a that is an image forming unit for each color of yellow, magenta, cyan, and black.
To d are arranged, the transfer belt 110 rotates in the direction of the arrow in the drawing to sequentially convey the transfer material P to each process station 109. Each process station 1
Reference numeral 09 denotes a process cartridge that can be attached to and detached from the apparatus main body, and each includes a photosensitive drum 100a to 100d, primary charging means 101a to 101d, developing devices 103a to 103d, and cleaning devices 108a to 108d.

The photosensitive drums 100a to 100d in the process stations 109a to 109d are in contact with the transfer rollers 106a to 106d which are the transfer means via the transfer belt 110. Power supply 114a ~
A transfer bias is applied from d. In the electrophotographic image forming apparatus, for example, as the photosensitive drum 100,
In the case of developing an exposed portion whose negative charge is attenuated by exposure using a negative polarity organic semiconductor electrophotographic photoreceptor (OPC photoreceptor), a developer containing a negative polarity toner is used.
Therefore, the transfer bias power source 114 applies a positive transfer bias to the transfer roller 106.

When the transfer material is sent from the feeding cassette 115 or the like into the image forming apparatus by the pickup roller 116, the feeding roller 117, and the conveying roller 118, first, the image forming operation and the conveyance of the transfer material are synchronized. For, for example,
Roller-shaped synchronous rotating body, that is, a pair of registration rollers
After being sandwiched by 119, the transfer material P and the transfer belt 110 are guided to a suction portion where the suction is performed. In the suction portion, for example, a suction roller 120 as a suction member faces the suction facing roller 112 via the transfer belt 110, and is configured to sandwich the transfer belt 110 and the transfer material P. Suction roller 12
A voltage is applied to 0 by a pre-transfer bias power source (not shown), which is a high voltage source, so that the transfer material P is charged, and the charged transfer material P polarizes the transfer belt 110. Electrostatically attracted to the transfer belt 110.
The transfer material P thus attracted to the transfer belt 110 sequentially passes through the process stations 109a to 109d, and the toner images of the respective colors on the photosensitive drums 100a to 100d are sequentially transferred.
Thereafter, the color image of the unfixed toner is heated and pressed by the fixing device 107 to become a permanent image.

The transfer belt 110 has a thickness of 50 to 200 μm.
m, volume resistivity 9th to 16th power (LogΩcm), PVDF (vinylidene fluoride resin), ETFE (tetrafluoroethylene-ethylene copolymer resin), polyimide, PET (polyethylene terephthalate), resin film such as polycarbonate, Alternatively, a rubber base layer having a thickness of about 0.5 to 2 mm and made of, for example, EPDM or the like is coated with, for example, urethane rubber and a fluororesin dispersed therein such as PTFE.

The transfer belt 110 does not directly carry a toner image on the surface thereof, so that it is unlikely to be contaminated by the toner image, but at the time of jamming, the adhesion of the background fog toner to the non-image portion, or the transfer belt. Toner adheres when a system is used in which a resist mark or a density detection pattern is directly formed on 110 to detect it. A separate cleaning means 12 is provided to clean this contaminated toner.
1 or by applying a cleaning bias having a reverse polarity to that at the time of transfer to the transfer rollers 106a to 106d.
It is conceivable that the process of collecting the toner on 0 to the cleaning devices 108a to 108d via the photosensitive drum 100 is performed for each of the process stations 109a to 109d.

[0011]

However, since the paper and the transfer belt are unstable elements in terms of resistance value, the transfer may be affected. In particular, as described above, the transfer material is attracted to the transfer belt, and in an in-line device for performing multiple transfer, it is necessary to perform transfer four times.
There is a problem that it is easily affected by the environment in which the device is placed and the paper type.

Here, the transfer belt is a film-shaped member in which an electronic conductive agent such as carbon black or an ionic conductive agent is added to the plastic to adjust the resistance value. Occurs, the amount of water contained in the ionic conductive agent changes depending on the environment, and the resistance also changes.

On the other hand, the main component of paper is cellulose having a high hygroscopic property, and the resistance value greatly changes depending on the dry state. For example, in a high-temperature and high-humidity environment where paper absorbs moisture (hereinafter referred to as H / H environment, 30 ° C x 80% RH), the volume resistance of the paper decreases to the 7th power (LogΩcm) and the charge Leakage is more likely to occur, while under low temperature and low humidity environment (hereinafter L / L
In the environment, represented by 15 ℃ × 10% RH), the volume resistance of paper is 12
It rises to the power of 2 (LogΩcm), making it difficult to inject charges into the paper and making it difficult to apply charges.
Furthermore, in an image forming apparatus having an automatic double-sided mechanism, once the printed paper passes through the fixing device, the moisture in the paper evaporates, and when it is re-fed, the resistance becomes extremely high. Will end up.

When toner transfer is performed on a transfer belt or paper having such resistance fluctuation factors as described above, if the member resistance is high, transfer failure occurs due to difficulty in flowing the transfer bias, and conversely, if it is low. However, there is a problem in that the toner that has been once transferred due to the excessive transfer bias is reversely charged from the photosensitive drum and is reversed, and the transfer efficiency is reduced, and a retransfer phenomenon occurs.

In order to solve such a problem, there has been conventionally devised a means for correcting the resistance variation of the transfer belt or the transfer material by controlling the transfer bias at a constant current and always performing the transfer at a constant current value. ing. However, when the constant current control is executed, the current value also changes depending on the amount of toner to be transferred, so there is a problem that the transfer efficiency changes depending on the image ratio.

Therefore, conventionally, a method has been devised in which the transfer bias is set without being affected by the image ratio by measuring the resistance of the paper at the suction portion upstream of the transfer portion. When the resistance of the paper is measured by the suction unit, if the resistance of the paper is larger than the resistance fluctuation of the member relating to other transfer, the difference in the resistance fluctuation of the member can be ignored. Since the transfer belt is a member that is commonly interposed, the resistance fluctuation can be ignored. The film thickness of the photosensitive drum decreases as printing is repeated, but the resistance fluctuation can be considered to be minute. Although the resistance value of the suction roller fluctuates due to moisture absorption and deterioration due to energization, it is possible to reduce the influence of resistance fluctuation by setting the original resistance low.

However, in the case of the transfer roller, if the resistance is set to be low, a portion that extends beyond the width of the paper will flow a much larger current than the portion where the paper is present, and damage the opposing photosensitive drum. There is a problem to give.

Specifically, as shown in the sectional view of the image forming portion in FIG. 7, the photosensitive drum 100, the transfer material P, the transfer belt 11
0, when the transfer roller 106 faces each other, a transfer bias necessary for transferring toner onto the transfer material P is applied to the transfer roller 106 under the L / L environment where the resistance of the transfer material P becomes high, and When the transfer bias β is applied to the drum 100, an excessive current flows into the photosensitive drum 100 from the transfer roller portion protruding from the width of the transfer material P as indicated by an arrow α. This current works in the direction of eliminating the electric potential on the photoconductor drum 100, and in the worst case, the electric potential is charged to the opposite polarity. After that, the photosensitive drum 100 is charged to the electric potential of the non-image portion by the primary charging means 101. However, the electric charge cannot catch up and the desired electric potential cannot be obtained, and the toner becomes the same electric potential as the halftone image. As a result, the photosensitive drum 100
If the edge of the paper is soiled in the latter half of one round, or if the width of the paper to be fed next is large, the edge of the back surface of the paper is soiled, a so-called paper trace phenomenon occurs.

FIG. 8 shows L / when a conventional image forming apparatus is used.
FIG. 6 is a diagram showing a relationship between an optimum transfer bias and a paper trace limit voltage under an L environment. From FIG. 8, it can be seen that as the resistance of the transfer roller increases, the bias value optimum for transfer indicated by the solid line increases, but at the same time, the limit voltage value of the paper trace indicated by the broken line also increases. As can be seen from the figure, the limit of the paper trace is lower than the optimum transfer value until the volume resistance of the transfer roller is around 8.0th power (LogΩcm), so a sufficient transfer bias is applied to suppress the generation of the paper trace. It will not be possible. On the other hand, when the power exceeds 8.0 (LogΩcm), the paper trace limit voltage value becomes higher than the optimum bias value, so that a sufficient transfer bias can be applied to the paper.

By the way, in the production of a resistance band member such as a transfer roller, it is difficult to strictly control the resistance value, and the resistance value varies from production lot to production lot due to material lots and seasonal variations. It is inevitable that it will end up. Also,
The transfer roller has a characteristic that, by continuing to output an image while applying a voltage, so-called energization deterioration is caused and the resistance value increases. When these resistance fluctuations are summed up, it is necessary to consider a swing of about 0.8 power (LogΩcm) as the volume resistance range of the transfer roller even when measured under the same temperature and humidity.

Here, referring to FIG. 8, for example, when the center of the transfer roller resistance is set to the 7.6th power (LogΩcm), the resistance of the transfer roller is 7.2th power (LogΩcm) to 8.0th power (LogΩc).
You can consider up to m). Within this resistance range, the optimum value of the transfer bias is constant around 2400V, so it can be understood that a constant transfer bias may be selected based on the resistance value of the paper detected by the suction roller.

However, as described above, unless the volume resistance value of the transfer roller is 8.0 power (Log Ωcm) or more, a paper mark is generated, so the center value of the transfer roller volume resistance value before the deterioration of energization is 8.4 power. (LogΩcm) must be set. However, the volume resistance value of the transfer roller is the 8.0th power (LogΩ
cm) or more, the optimum transfer voltage value also increases as the transfer roller resistance increases. This difference in the optimum transfer bias value is from the 8.0th power (LogΩcm) to the 8.8th power (LogΩcm)
It becomes about 400V between 0.8th power (LogΩcm), and if a uniform transfer bias is applied with the paper resistance value detected by the suction roller, the transfer bias deviated from the optimum transfer bias by up to 400V will be applied. There is a problem that improper bias causes transfer failure.

Therefore, according to the present invention, even if a transfer roller whose resistance value changes due to manufacturing or durability is used, a transfer bias suitable for the resistance value is always applied to obtain an image in which stable image density and image quality can be obtained. An object is to provide a forming device.

[0024]

In order to solve the above-mentioned problems, a typical structure of an image forming apparatus according to the present invention includes an image forming unit, a suction conveying unit for sucking and conveying a transfer material, and the suction conveying. An image forming apparatus including: a transfer unit that transfers a toner image from the image forming unit to a transfer material on the unit; and a bias unit that applies a transfer bias to the transfer unit. A detection unit, wherein the first detection unit detects the resistance of the transfer unit in a state where the transfer material is not conveyed, and corrects the transfer bias applied to the transfer unit based on the detected resistance value. Is characterized by.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION A first embodiment of an image forming apparatus according to the present invention will be described with reference to the drawings. FIG. 1 is an overall configuration diagram of an image forming apparatus according to the present embodiment, FIG. 2 is a diagram illustrating an example of a schematic diagram of a power supply circuit, and FIG. 3 is a diagram illustrating a relationship between a resistance of a transfer material and an optimum value of a transfer bias. is there.

The image forming apparatus shown in FIG. 2 is an electrophotographic image forming apparatus using an in-line system, and a plurality of process stations 1a to 1d as image forming means are horizontally arranged. Each of the process stations 1a to 1d serves as a process means and includes a photosensitive drum 2a to an image carrier.
d, primary charging means 3a to 3d, developing devices 4a to 4d, and cleaning devices 6a to 6d are integrated together. Each process station is detachable from the main body of the image forming apparatus as a process cartridge.

The photosensitive drum 2 is a drum-shaped electrophotographic photosensitive member. After the surface of the photosensitive drum 2 is uniformly charged by the primary charging means 3, the exposing means 9a to 9d such as an LED or a laser expose the surface according to image information. By doing so, an electrostatic latent image is formed on the surface of the photoconductor drum 2. After that, the developing device 4 sets the developer 5 for each color of yellow, magenta, cyan, and black.
A to d (including toner) are electrostatically attached to this electrostatic latent image to form a toner image on the photosensitive drum 2.

A transfer belt 10 serving as a suction conveyance means includes a drive roller 11, a suction facing roller 12, and a tension roller 13.
It is wound around rollers a and 13b. This transfer belt 10
The process stations 1 are arranged along the peripheral surface of the transfer belt 10, and the transfer belt 10 rotates in the direction of the arrow in the figure to sequentially convey the transfer material to the process stations 1. Photoconductor drum 2a of process station 1a-d
Through d are in contact with the transfer rollers 14a to 14d, which are transfer means, via the transfer belt 10. A transfer bias is applied to the transfer rollers 14a to 14d from transfer bias power sources 15a to 15d, which is a bias means, whereby the photoconductor drum 2 is driven.
The upper toner image is transferred to the transfer material P on the transfer belt 10.

When the transfer material P is sent out from the feeding cassette 17 or the like into the image forming apparatus by the pickup roller 18, the feeding roller 19 and the conveying roller 20, first, the image forming operation and the conveyance of the transfer material are synchronized. For this purpose, for example, a synchronous rotating body in the form of a roller, that is, after being sandwiched by a pair of registration rollers 21, is guided to a suction portion where the transfer material P and the transfer belt 10 are suctioned. In the suction section, a suction roller 22 as a suction member faces the suction facing roller 12 via the transfer belt 10, and the transfer material P is brought into pressure contact with the transfer belt 10 to be nipped and conveyed.

A voltage is applied to the attraction roller 22 from a pre-transfer bias power source 23, which is a high voltage source, so that the transfer material P is charged, and the charged transfer material P polarizes the transfer belt 10. By doing so, it is electrostatically attracted to the transfer belt 10. The pre-transfer bias power supply 23 is connected to a second detection means 24 for detecting the flowing current value or the applied bias value, and the type and characteristics of the transfer material P are determined by the detected resistance value. .

Further, the suction roller 22 may also have a function as a pre-charging means for pre-charging the transfer material P. Precharging the transfer material P has an effect of lowering the transfer bias particularly for a transfer material having a high electric resistance value such as OHP or thick paper, and is not suitable for the in-line type image forming apparatus described in this embodiment. Is particularly effective. In the present embodiment, the suction roller 22 is applied with a pre-charging bias to pre-charge the transfer material surface. Therefore, the pre-charging bias has a polarity opposite to that of the developer (toner). In the case of the form, since the negatively charged toner is used as the developer, the pre-charging bias becomes positive). In this case, the value of the pre-transfer bias needs to be set to a high value for OHP or the like having a high resistance as described above. Because of this, O
Although it is possible to manually or automatically detect HP and set the value of the pre-transfer bias, when the transfer material P is determined to be a high resistance transfer material by the second detection means 24,
The pre-transfer bias may be set higher than other transfer materials, and the application of this high pre-transfer bias has the effect of reducing the transfer bias.

The transfer material P thus attracted to the transfer belt 10 sequentially passes through each process station 1, and the toner images of the respective colors on the photosensitive drums 2a to 2d are transferred one after another.
Thereafter, the color image of the unfixed toner is heated and pressed by the fixing device 25 to become a permanent image.

According to the study by the applicants, the transfer belt 10
As for the thickness of 100 to 200 μm, the volume resistivity is from the 8th power to 1
The resin film of PVDF, ETFE, polycarbonate, PET, polyimide, etc., whose resistance is adjusted to the square (Log Ωcm), has good adsorption and transferability, and also has a proper self-damping property, which is a means of eliminating static electricity. It is suitable for application to the present embodiment, such as being able to prevent charge-up even without providing.
In this embodiment, the transfer belt 10 has a circumference of 800 mm,
A 100 μm thick ETFE resin film having a volume resistivity of about 11th power (LogΩcm) by dispersing carbon or the like was used.

Further, in the present embodiment, the suction roller 22
Is the 5th volume resistivity (Log
Ωcm) or less EPDM (ethylene-propylene-diene terpolymer) rubber with a diameter of 6 mm and a thickness of 3 mm
The roller formed in 1. According to the study by the present applicants, in order to set the influence of the resistance fluctuation so as not to affect the detection of the transfer material, the volume resistivity of the attraction roller 22 which is the pre-transfer bias applying member is from the fourth power to the sixth power ( LogΩcm). One suction facing roller 12 was a metal roller, and the bearing portion thereof was electrically grounded.

The transfer roller 14 has a conductive base shaft which also serves as a power supply electrode, and at least one elastic layer which surrounds the outer peripheral surface of the conductive base shaft in a cylindrical shape. Here, as the elastic layer, for example, EPDM, urethane rubber, hydrin rubber,
Silicon rubber, NBR, etc. can be used, and a conductive agent for adjusting resistance is dispersed in these. This elastic layer is composed of a foam-vulcanized sponge layer. In addition, one or more coat layers of hydrin rubber, NBR, urethane, water-soluble nylon or the like may be formed on the outer peripheral surface of the elastic layer. Transfer roller 14 of the present embodiment
The volume resistance of is 8.0 power (LogΩc
m), 8.4th power (LogΩcm), and 8.4th power (LogΩcm) were used for the durability test of 100,000 sheets assuming the life of the transfer roller. I used the one.

Here, the volume resistivities of the above various members are measured by ADVANT using a measuring probe in accordance with JIS method K6911.
A value obtained by applying 100 V with a high resistance meter R8340 manufactured by EST, and normalized by the thickness of the transfer belt 10, the suction roller 22, or the transfer roller 14 is a value.

As the driving roller 11, a rubber layer for preventing slippage is formed on the metal core of a metal roller to a thickness of approximately 0.5.
The one provided in the range of up to 3.0 mm was used. As the resistance of this rubber layer, an insulation type of 15th power (Log Ωcm) or more was used as an example, but a low resistance may be used. Regarding the cores of the tension rollers 13a and 13b and the driving roller 11, the transfer belt 10 itself is a self-damping system, and
Since there are no members (electrodes) facing each other with 10 in between, both may be grounded or floated.

An example of the power supply circuit in this embodiment will be described with reference to FIG. The pre-transfer bias power supply 23 for applying a voltage to the attraction roller 22 is connected to the second detection means 24, and when the output of the pre-transfer bias power supply 23 is under constant voltage control, the current amount at the time of bias application, When the constant current control is performed, each output bias of the pre-transfer bias power supply 23 can be detected. Similarly, a transfer bias power source 15a for applying a voltage to the transfer roller 14a of the process station 1a is also connected to the first detecting means 16, and when the transfer bias power source 15a is controlled to a constant bias, the current when the transfer bias is applied. When the constant amount is controlled, the output bias of the transfer bias power source 15a can be detected. The first detection means 16, the second detection means 24, the pre-transfer bias power supply 23, and the transfer bias power supply 15 of each process station 1 are connected to the arithmetic control mechanism 26, and the first detection means 16 and the second detection means 24 are connected. The output bias can be arbitrarily controlled according to the detection result in.

Hereinafter, the pre-transfer bias power supply 23 and the transfer bias power supplies 15a to 15d of the respective process stations 1a to 1d.
The present invention will be described in detail by taking as an example the case where is controlled by a constant voltage.

As described above, the transfer bias value for the transfer material P can be set to the photosensitive drum 2 by controlling the transfer bias value to an optimum value according to the environment and the moisture absorption state of the paper. It will be possible. For that purpose, it is necessary to measure not only the resistance of the member involved in the transfer but also the resistance value of the transfer material P itself. As a method therefor, it is possible to measure the transfer bias flowing at the time of actual transfer. However, since the transfer bias changes depending on the image pattern, that is, the amount of charge of the transferred toner, it is necessary to control the transfer bias in consideration of the influence of the image pattern. It is also possible to execute control within the image margin at the tip of the transfer material so as not to be affected by the image, but in consideration of the fact that the transfer bias waveform is disturbed by the shock of the transfer material entering the transfer nip, Detection must be executed at a momentary timing from when the bias has settled to when the image area is entered. Actually, it is very difficult to secure the reliability of the paper resistance measurement due to the margin of the leading edge of the paper in consideration of the skew of the paper.

Therefore, in the present embodiment, the resistance of the paper is measured by the suction portion. Second detection means on the suction roller 22
The pre-transfer bias voltage is applied while controlling the pre-transfer bias power supply 23 so that the current detected by 24 is a constant current of 18 μA, and the pre-transfer bias voltage value resulting from the control is the paper resistance value that represents the paper resistance. And As the transfer material, office planner paper (A4 size, 64g / m ^ 2) sold by Canon Sales Co., Ltd. was used.

FIG. 3 shows the relationship between the paper resistance value measured as described above and the optimum transfer bias value for each paper resistance value. As shown by the solid line in FIG. 3, when the paper resistance value is low, the transfer bias is weakly controlled, and the transfer bias is strengthened as the paper resistance value becomes higher, whereby it is possible to always achieve optimum image quality.

However, as shown by the three solid lines in the figure, as the resistance of the transfer roller 14 becomes higher, the optimum transfer bias must be strengthened especially in the area where the paper resistance value is high (the area indicated by the arrow A). I won't. In order to detect the difference in the resistance of the transfer roller 14, in the present embodiment, members related to transfer (transfer belt 10, transfer roller 10 and transfer roller 10) are used at the time of powering on the main body and a cleaning sequence executed when returning from the sleep state. It was configured to perform resistance detection in 14). To detect resistance, transfer belt of 1000V transfer belt 1
The current was applied from the transfer bias power supply 15a at the time of steady rotation of 0, and the current flowing out to the photosensitive drum 2a through the transfer roller 14a and the transfer belt 10 at that time was detected by the first detection means 16, and this current value was taken as the member resistance value.

The broken line in FIG. 3 shows the detection result of the member resistance value with respect to the volume resistance of the transfer roller 14 under the environment corresponding to the paper resistance value. As is clear from the figure, as the resistance of the transfer roller 14 increases, the current value of the member resistance value decreases. Therefore, in the region where the paper resistance value is high (the region indicated by arrow A) in which the correction of the transfer bias against the resistance difference of the transfer roller 14 is required, the reference value is set to the current value of the member resistance value and the member resistance value is set. Based on this, it is possible to define a region (hatched portion in the drawing) in which the transfer bias applied to the transfer roller 14 needs to be corrected.

At this time, as indicated by the arrow B in the figure, the optimum transfer bias difference between the upper and lower limits of the member resistance value is about 250V. Therefore, first, the transfer bias determined based on the paper resistance value is determined on the assumption that the resistance is low to the power of 8.0 (LogΩcm), and the member resistance value becomes equal to or lower than the reference value (that is, the transfer roller 14 and the transfer belt 10). If the voltage of 250 V is added to the transfer bias at the point C, the optimum transfer bias can be obtained (for example, point D).

By correcting the transfer bias based on the member resistance value as described above, it becomes possible to always apply the optimum transfer bias regardless of the resistance of the transfer roller 14 due to manufacturing or durability. It is possible to always obtain a high quality image.

[Second Embodiment] A second embodiment of the image forming apparatus according to the present invention will be described with reference to the drawings. Figure 4
FIG. 3 is a diagram showing the relationship between the resistance of the transfer material and the optimum value of the transfer bias, and the same parts as those of the first embodiment described above are designated by the same reference numerals and the description thereof will be omitted.

In the first embodiment, the transfer bias is uniformly increased by 250 V only when the member resistance value satisfies the predetermined reference value. On the other hand, the present embodiment is characterized in that the resistance correction is performed more finely.

As shown in FIG. 4, the resistance value of the transfer roller differs from the area of the paper resistance value as shown by arrow E in the figure, which has a lower resistance than the L / L environment where the resistance of the transfer material is completely increased. The optimum transfer bias is starting to change. However, in such a region where the paper resistance value is low, the member resistance value greatly changes depending on the paper resistance value. Therefore, the correction cannot be performed simply by setting one reference value and comparing the member resistance value. It is possible.

Therefore, in the present embodiment, as shown in Table 1 below, the paper resistance value is divided into seven areas, and a predetermined member resistance value is defined as a reference value in each area. Further, in the present embodiment, in order to perform the fine correction of the transfer bias, a plurality of reference values are further defined in each area so that the transfer bias is not suddenly corrected and the image quality is not suddenly changed. To control. In addition, each correction value is variable from 100V to 400V so that the optimum correction amount can be obtained for each area.
The configuration is such that an optimum transfer bias value can always be applied in accordance with the resistance variation of the above.

[0051]

[Table 1]

By subdividing the cases as described above, it is possible to perform the optimum transfer bias correction even with respect to the resistance value of the transfer roller 14 and environmental changes, and the transfer is always executed in the optimum state. It has become possible to stably obtain high quality images. Further, by performing the transfer bias correction stepwise, the image quality does not suddenly change before and after the correction is introduced, and the user does not notice the existence of the control. .

Although the transfer roller 14 is used as the transfer means in each of the above-described embodiments, a member having a different shape, such as a transfer blade, is used, and the correction is performed according to the member to be used. The present invention can be applied to and the effects of the present invention can be obtained.

Further, in the image forming apparatus as described in the above embodiment, the fixing speed is generally changed to match the thickness of the transfer material and to improve the glossiness of the image. Further, in media such as OHP having a film such as PET as a base material, which is different from paper in properties such as charging characteristics, it is necessary to completely control transfer bias and fixing conditions. Even with respect to these differences in conditions, it is possible to perform optimum transfer bias correction by dividing the paper resistance value and the like as described in the present embodiment, and it is possible to always apply the optimum transfer bias. Become.

[0055]

As described above, according to the present invention, the transfer bias applied to the transfer means is determined based on the resistance value of the transfer material, and is corrected based on the resistance value of the transfer means. Optimal transfer bias correction can be performed regardless of resistance fluctuation during manufacturing of the means and resistance fluctuation due to endurance, and transfer is always performed in the optimum state, and stable high-quality images can be obtained. Become. Further, since it is not necessary to strictly manage the resistance fluctuation of the transfer means,
The yield of the transfer means is improved, and the cost of the apparatus can be reduced.

[Brief description of drawings]

FIG. 1 is an overall configuration diagram of an image forming apparatus according to a first embodiment.

FIG. 2 is a diagram illustrating an example of a schematic diagram of a power supply circuit.

FIG. 3 is a diagram showing a relationship between a resistance of a transfer material and an optimum value of a transfer bias according to the first embodiment.

FIG. 4 is a diagram showing a relationship between a resistance of a transfer material and an optimum value of a transfer bias according to a second embodiment.

FIG. 5 is a diagram showing a schematic configuration of a conventional image forming apparatus using an electrophotographic method.

FIG. 6 is a diagram showing a schematic configuration of a conventional full-color image forming apparatus using an inline system.

FIG. 7 is a cross-sectional view of an image forming unit according to a conventional example.

FIG. 8 is a diagram showing a relationship between a transfer optimum bias and a paper trace limit voltage under an L / L environment when using a conventional image forming apparatus.

[Explanation of symbols]

P ... Transfer material 1 ... Process station 2 ... Photosensitive drum 3 ... Primary charging means 4 ... Developer 5 ... Developer 6 ... Cleaning device 9 ... Exposure means 10… Transfer belt 11… Drive roller 12 ... Suction opposite roller 13… Tension roller 14… Transfer roller 15… Transfer bias power supply 16… First detection means 17… Feed cassette 18… Pickup roller 19… Feeding roller 20… Conveyor roller 21… Registration roller pair 22… Suction roller 23 Bias power supply before transfer 24… Second detection means 25… Fixing device 26 ... Arithmetic control mechanism 100 ... Photosensitive drum 101 ... Primary charging means 102 ... Exposure means 103… Developer 104 ... Developer 105… Transportation means 106… Transfer roller 107… Fixing device 108… Cleaning device 109… Process Station 110… Transfer belt 111… Drive roller 112… Suction opposite roller 113… Tension roller 114… Transfer bias power supply 115… Feed cassette 116… Pickup roller 117… Feeding roller 118… Conveyor rollers 119 ... Registration roller pair 120… Suction roller 121… Cleaning means

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Takaaki Tsurutani             3-30-2 Shimomaruko, Ota-ku, Tokyo             Non non corporation F-term (reference) 2H027 DA01 DA03 DE04 DE07 DE10                       EA03 EC06 EC10 ED24 EE02                       EF09                 2H200 FA18 GA23 GA34 GA47 HA03                       HB12 HB22 JA02 JA28 JA29                       JA30 JB06 JB10 JB25 JB45                       MA03 MA04 MA08 MA14 MA20                       MB04 NA02 PA05 PA18 PA22                       PA30 PB02 PB08 PB12 PB13                       PB38

Claims (6)

[Claims] 1. An image forming unit, a suction conveying unit that sucks and conveys a transfer material, a transfer unit that transfers a toner image from the image forming unit to the transfer material on the suction conveying unit, and a transfer bias to the transfer unit. An image forming apparatus having a bias unit for applying a voltage, a first detection unit for detecting a resistance of the transfer unit, wherein the first detection unit detects the resistance of the transfer unit in a state in which a transfer material is not conveyed. An image forming apparatus which detects resistance and corrects a transfer bias applied to the transfer means based on the detected resistance value of the transfer means. 2. The image forming apparatus according to claim 1, wherein the first detection unit detects resistance including the transfer unit and the suction conveyance unit. 3. A transfer bias applied to the transfer means based on a resistance value of the transfer material detected by the second detection means, the second bias detecting means detecting the resistance of the transfer material prior to the transfer process. The image forming apparatus according to claim 1, wherein the image forming apparatus determines. 4. The transfer bias applied to one or more transfer means is corrected when the resistance value of the transfer means detected by the first detection means exceeds a predetermined reference value. The image forming apparatus according to any one of 1 to 3. 5. The image forming apparatus according to claim 4, wherein a plurality of the predetermined reference values are set according to the resistance value of the transfer material. 6. The predetermined reference value is set in plural according to the resistance value of the transfer material and at a constant resistance value of the transfer material according to the resistance value of the transfer means, and the transfer bias is corrected. The image forming apparatus according to claim 4, wherein the image forming apparatus is implemented in a specific manner.