JP4422844B2 - Color image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a color image forming apparatus that includes a plurality of image forming units including an image carrier, an image carrier charging member, a developing unit, and the like and forms a color image by an electrophotographic method.
[0002]
[Prior art]
In recent years, image forming apparatuses using an electrophotographic method have been reduced in size, increased in functionality, and in color, but on the other hand, demands for improved reliability, networking, environmental support, etc. are increasing. Various image output apparatuses have been proposed to satisfy these requirements. In particular, with regard to colorization, it is predicted that the frequency of use will increase in the future due to the appearance of various color applications. Furthermore, since the networking in the office is rapidly spreading, there has been a demand for the appearance of a color image forming apparatus capable of outputting at a higher speed.
[0003]
By the way, as a technique for increasing the speed of color image output devices, recently, a plurality of image forming units or cartridges including a photoconductor, a charger, a developing device, etc. are provided, and a transfer material is electrostatically conveyed by a belt-like conveying means. A device (4-drum system / tandem drum system) that sequentially transfers toner images from each color image forming unit or cartridge while adsorbing and transporting them has been proposed. It has been thrown.
[0004]
Such a four-drum type image forming apparatus can eliminate the difference in output speed between a full-color image and a monochrome image as seen in a conventional color image forming apparatus using an electrophotographic method. High-speed color image output is possible.
[0005]
Here, FIG. 13 shows an example of the configuration of a four-drum type color image forming apparatus using a belt for electrostatically attracting and conveying a transfer material (hereinafter referred to as a transfer and conveyance belt). Each image forming unit and cartridge U ′ _Y , Y ' _M , U ' _C , U ' _Bk Are all the same, U ′ here _Y Will be described as a representative example.
[0006]
In FIG. 13, 101y is a cylindrical photoconductor as an electrostatic latent image carrier, and this photoconductor 101y is driven to rotate in the direction of arrow a '. Reference numeral 102y denotes a contact-type charger, which uniformly charges the surface of the photoreceptor 101y.
[0007]
Reference numeral 103y denotes an image exposure apparatus that exposes the photosensitive member 101y to form an electrostatic latent image. Reference numeral 104y denotes a two-component developer, which includes, for example, a two-component developer composed of a mixture of about 50 μm magnetic carrier particles and about 8 μm non-magnetic toner. By applying a bias, non-magnetic toner is caused to fly onto the photoreceptor 101y, and the electrostatic latent image is developed and visualized as a toner image. The toner image on the photosensitive member 101y visualized by the developing unit 104y is conveyed to a transfer portion formed between the transfer conveying belt 105 and the photosensitive member 101y as the photosensitive member 101y rotates.
[0008]
In the transfer section, a transfer roller 109 y is disposed in pressure contact with the transfer conveyance belt 105 in the direction of the photosensitive member 101 y, and the transfer roller 109 y is driven to rotate as the transfer conveyance belt 105 is conveyed. Then, the transfer material P ′ is conveyed by a transfer material conveying means (not shown) to the nip portion N ′ composed of the driving roller 106 and the suction roller 120 via the transfer conveyance belt 105, and a bias is applied to the adsorption roller 120. As a result, the toner is electrostatically attracted onto the transfer conveyance belt 105. The transfer conveyance belt 105 is stretched around the drive roller 106, the support rollers 107-1, 107-2, and the tension roller 108, and the arrow f while holding the transfer material P ′ as the drive roller 106 rotates. Driven in the direction.
[0009]
Thereafter, the transfer material P ′ is conveyed to the transfer unit by the transfer conveyance belt 105 in accordance with the timing at which the toner image of each color reaches the transfer unit, and a predetermined bias set in advance from the high voltage power source 114 is applied to the transfer roller 109y. As a result, the toner images are sequentially transferred onto the transfer material P ′, and finally a full-color toner image is formed. The transfer roller 109y includes a conductive elastic roller (10 ^Four Ω: when 100 V is applied).
[0010]
The transfer conveyance belt 105 is stretched and driven by a driving roller 106, support rollers 107-1 and 107-2, and a tension roller 108, and rotates along with the rotation of the driving roller 106. In order to maintain the transportability of the transport belt 105, an appropriate tension is applied to the transfer transport belt 105.
[0011]
Thereafter, when the transfer material P ′ reaches the transfer material separating portion adjacent to the transfer material belt 105 and the transfer material material guide 110, it is separated from the transfer material belt 105 by the curvature of the support roller 107-1. Then, the transfer material P ′ separated from the transfer conveyance belt 105 is fed to the fixing device 111 while holding the toner image, and the toner is melted and fixed by the action of heat and pressure to be fixed on the transfer material P ′. .
[0012]
On the other hand, after the toner is removed by the photoconductor cleaners 113y, 113m, 113c, and 113bk, the surface potential of the photoconductors 101y, 101m, 101c, and 101bk after transfer is uniform by the pre-exposure lamps 124y, 124m, 124c, and 124bk. Is discharged and used again for image formation. In addition, the transfer conveyance belt 105 that has finished supplying the transfer material P ′ to the fixing device 111 is used again after its surface is cleaned by the belt cleaner 112.
[0013]
By adopting the apparatus configuration as described above, it is possible to achieve high-speed color image output, which is the greatest feature of the 4-drum system, and is therefore very promising as a future apparatus configuration. .
[0014]
[Problems to be solved by the invention]
However, in such an apparatus, when the resistance value of the transfer / conveying belt to be used fluctuates, the transfer efficiency and the retransfer rate change, causing a change in hue and various image defects. For this reason, it is necessary to sequentially adjust and set the transfer control voltage value in accordance with the resistance value of each transfer / conveying belt. However, this is very inefficient in manufacturing the apparatus.
[0015]
On the other hand, when the standard is set so that the volume resistance value is within one digit from the manufacturing side of the transfer transfer belt, electrical characteristics (volume resistance value rate, surface resistance value, dielectric constant, etc.) There are many factors such as thickness, and in particular, it is very difficult to accurately produce an outer diameter (about φ100 mm) and thickness (about 100 μm) as used in this apparatus, and the manufacturing yield is high. It will be very bad.
[0016]
Furthermore, since the transfer conveyance belt and the transfer member itself also change the electrical characteristics due to environmental fluctuations and wear / energization, even if the transfer bias adjustment and the belt volume resistance value are made during the manufacturing described above. Therefore, an image defect is generated while the apparatus is used for a long time. In particular, the change in transfer characteristics due to environmental changes is very large, and the transfer voltage-current characteristics (transfer VI characteristics) are shown in FIG.
[0017]
As shown in FIG. 14, in a low temperature / low humidity environment (16 ° C./10%: hereinafter referred to as L / L environment) and a high temperature / high humidity environment (32 ° C./50%: hereinafter referred to as H / H environment), transfer V is performed. -I characteristics are greatly different. For example, when an appropriate bias is applied in the L / L environment in the H / H environment, the transfer voltage is too strong and deviates from the current region optimum for transfer.
[0018]
On the other hand, when an appropriate bias is applied in an H / H environment in an L / L environment, a bias necessary for transfer is not applied, and a transfer failure occurs.
[0019]
Here, from the above, the transfer bias was carried out with constant current control. However, when a small-size transfer material such as a postcard is passed, the non-image area and the non-paper pass area on the photosensitive member at the transfer area. Since the current density flowing through the photoconductor varies greatly, a positive memory is generated on the photosensitive member due to the transfer bias, and this positive memory appears on the image as a density difference at the next printing.
[0020]
Therefore, an attempt has been made to adopt an ATVC control method, which has been conventionally used to improve environmental stability of transfer in a monochrome image forming apparatus or the like, in an image forming apparatus having a four-drum configuration.
[0021]
Here, the ATVC control method is a method in which a transfer portion is set in advance for a non-image portion on a photosensitive member in a multi-rotation before the start-up warm-up of the apparatus in the morning or a pre-rotation performed before image formation. The constant current control is performed by the value, the resistance variation of the transfer member is detected by the variation of the generated voltage value at this time (hereinafter referred to as ATVC control 1), and the constant voltage control is performed based on the calculation result of the previous generated voltage at the time of image formation. (Hereinafter referred to as ATVC control 2). By doing so, it is possible to prevent an overcurrent flowing from the transfer unit to the photosensitive member via the transfer conveyance belt, eliminate the memory of the photosensitive member, and apply an appropriate bias at the time of image formation. Therefore, it is possible to stably output a good transfer image. FIG. 15 shows an example of a basic transfer bias sequence of the ATVC control method.
[0022]
However, when the conventional ATVC control method is employed in an image forming apparatus having a four-drum configuration, the following problems occur.
[0023]
As an example, the volume resistance value is about 10 ⁶ A case where a transfer conveyance belt of Ω (JISK-661; when 100 V is applied; resistance values shown in the future will be the same measurement method) is used will be described.
[0024]
In this case, when ATVC control 1 is performed at the transfer unit, not only the transfer current flows into the photoconductor, but also the transfer current flows into another transfer unit, the photoconductor, the driving roller, the tension roller, etc. that are adjacent through the transfer conveyance belt. For this reason, it is impossible to accurately detect a change in resistance value of the transfer portion (change in voltage generated during control). As a result, even if ATVC control 2 is performed with a bias detected during ATVC control 1 during image formation, transfer efficiency is significantly reduced. In particular, if the size of the apparatus main body is further reduced, the transfer portions of the respective colors are brought close to each other, so that the mutual interference of the transfer biases of the respective colors during the ATVC control 1 becomes very large.
[0025]
The present invention has been made in view of the above problems, and the object of the present invention is to always stably output a high-quality color image regardless of fluctuations or fluctuations in the resistance value of the transfer conveying member or transfer means. An object of the present invention is to provide a color image forming apparatus capable of ensuring high transfer efficiency and maintaining a low retransfer rate.
[0026]
[Means for Solving the Problems]
In order to achieve the above object, the present invention provides: A plurality of image carriers on which toner images are formed; a transfer conveyor belt that is rotatable and conveys a transfer material; and a plurality of transfer units that respectively face the plurality of image carriers via the transfer conveyor belt; A voltage supply means for applying a voltage to the plurality of transfer means; a high-voltage power supply having a circuit for detecting a current value flowing through the plurality of transfer means; and a transfer material provided at a position in contact with the transfer / conveyance belt. A transfer roller formed by the image carrier and the transfer unit via the transfer conveyance belt. An image is transferred from the plurality of image carriers onto a transfer material conveyed by the transfer conveyance belt. In the image forming apparatus,
The application means applies a voltage to the plurality of transfer means so that a predetermined current flows through the circuit for at least a period until the transfer conveyance belt rotates at least once before the transfer material is conveyed to the transfer portion, In addition, a voltage having the same polarity as the voltage applied by the applying unit is applied to the suction roller and the plurality of stretching rollers, the transfer material is conveyed to the transfer unit, and the plurality of transfer units use the toner image as a transfer material. The voltage applied by the applying unit during transfer is a constant voltage calculated using an average value of the voltages applied by the applying unit during the period as a reference voltage. It is characterized by that.
[0027]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the accompanying drawings.
[0028]
<Embodiment 1>
FIG. 1 is a schematic cross-sectional view of a color image forming apparatus according to the present invention that employs an electrophotographic method, and will be described in order according to a process for forming a color image. However, each image forming unit U shown in FIG. _Y , U _M , U _C , U _Bk Since all the basic configurations are the same, the image forming unit U is referred to thereafter. _Y We will only talk about.
[0029]
Image forming unit U _Y 1y is a photoreceptor as an electrostatic latent image carrier, and this photoreceptor 1y forms a photosensitive layer made of an organic photoconductor (OPC) on the outer peripheral surface of a grounded conductor such as aluminum. The diameter is 30 mm, and it is rotationally driven at a peripheral speed of 100 mm / sec in the direction of arrow a in the figure.
[0030]
A charging roller 2y is pressed against the surface of the photosensitive member 1y, and the charging roller 2y rotates following the rotation of the photosensitive member 1y. The charging roller 2y is composed of a conductive metal core made of iron or the like, a conductive rubber layer concentrically and integrally formed on the outer periphery thereof, and a coating film provided on the outer periphery for resistance value control. I used something. An AC and DC bias is applied to the conductive core of the charging roller 2y from a high voltage power supply (not shown), and the surface of the photoreceptor 1y is uniformly charged to a potential of -500V.
[0031]
Thereafter, when the photosensitive member 1y is rotated to reach the exposure unit, the surface of the photosensitive member 1y is irradiated with laser light modulated in accordance with an image information signal output from the image exposure device 3y, and the potential of the irradiated portion is attenuated. As a result, an electrostatic latent image is formed on the surface of the photoreceptor 1y. In addition to the laser, an LED or the like may be used as the light source of the image exposure apparatus 3y.
[0032]
The electrostatic latent image formed on the surface of the photoreceptor 1y is visualized as a toner image when negatively charged toner is supplied (reverse development) from the developing device 4y. The developing device 4y is a one-component non-magnetic contact developing device, and a developing roller 4y-1 for transporting the toner to the surface of the photoreceptor 1y and a developer supply roller 4y for re-applying the toner to the surface of the developing roller 4y-1. -2 and a developer regulating blade 4y-3 for regulating the toner coating amount on the developing roller 4y-1. In the developing process, the developing roller 4y-1 whose surface is uniformly coated with toner by the developer regulating blade 4y-3 is lightly pressed against the photoreceptor 1y, and the developing roller 4y-1 rotates with a speed difference in the forward direction. By applying a predetermined DC voltage from a power source (not shown) to the toner, the toner flies onto the surface of the photoreceptor 1y and the electrostatic latent image is developed as a toner image. In this embodiment, the one-component nonmagnetic contact development method is used, but a two-component development method may be used. Further, by adopting a spherical S toner produced by a polymerization method as a toner, an improvement in transfer rate and an oil-less operation at the fixing portion are simultaneously achieved.
[0033]
Next, the toner image on the photoreceptor 1y visualized by the developing device 4y is conveyed to a transfer section in the next process according to the rotation of the photoreceptor 1y.
[0034]
The transfer unit is each image forming unit U. _Y , U _M , U _C , U _Bk 1 comprises photoconductors 1y, 1m, 1c and 1bk, a transfer conveying belt 5 and transfer rollers 9y, 9m, 9c and 9bk. The conveyance belt 5 is sandwiched. The transfer / conveying belt 5 has an endless belt shape with a thickness of about 100 μm, and is stretched by four rollers including a driving roller 6, support rollers 7-1 and 7-2, and a tension roller 8. It is driven and conveyed in the direction of arrow c in the figure by the rotation of the roller 6.
[0035]
The transfer conveyance belt 5 adsorbs and conveys the transfer material P on its surface, and each image forming unit U _Y , U _M , U _C , U _Bk The transfer process of the transfer material P in the transfer and transport belt 5 will be described below.
[0036]
First, the transfer material P conveyed by a paper feeding device (not shown) is mainly conveyed to a nip portion N formed by the suction roller 10 and the drive roller 6 and simultaneously, the power is supplied to the suction roller 10 from a power source (not shown). The bias is applied and is attracted onto the transfer conveyance belt 5 by the electrostatic force of the charge supplied to the surface of the transfer material P.
[0037]
Thereafter, the transfer material P is transferred to each image forming unit U. _Y , U _M , U _C , U _Bk The toner images formed in (1) are sequentially conveyed while being attracted onto the transfer / conveyance belt 5 in accordance with the timing at which the toner images reach the respective transfer portions, and finally a full-color toner image is formed.
[0038]
The transfer rollers 9y, 9m, 9c, and 9bk are made conductive by dispersing carbon in EPDM rubber (volume resistance value: 10). ^Five Ω or less), and a foamed product is used in the form of a roller. Its hardness is about 25 ° in Asker-C and the outer diameter is φ18 mm. However, as the transfer member, a blade or a brush can be used as long as the resistance value is approximately the same.
[0039]
In addition, 500 g springs are provided at both end bearings of the transfer rollers 9y, 9m, 9c, and 9bk, and the transfer rollers 9y, 9m, 9c, and 9bk are pressed against the photoreceptors 1y, 1m, 1c, and 1bk. And is driven to rotate as the transfer / conveying belt 5 is driven.
[0040]
The illustrated high-voltage power supply (HV) 15 for transfer includes a circuit for outputting a bias controlled by the CPU 16 and a circuit for detecting a current flowing through each of the transfer rollers 9y, 9m, 9c, and 9bk. In ATVC control 1, the current flowing here is detected.
[0041]
Here, the transfer conveyance belt 5 has a volume resistance value of 10 ^Five -10 ⁸ The thing of about Ω is used. The belt may be a single layer whose resistance is adjusted by dispersing conductive particles in a resin or rubber material. ^Four A resin having a resistance value of about Ω or a surface layer of a rubber belt may be used which has a multi-layer structure in which a fluororesin such as PTFE, PFA, ETFE or the like is coated in order to improve releasability.
[0042]
Thus, the transfer material P on which the full color toner image is formed is separated from the transfer conveyance belt 5 by the curvature of the support roller 7-2 at the separation portion where the transfer material conveyance guide 11 and the transfer conveyance belt 5 are close to each other. It is conveyed on the material conveyance guide 11 and conveyed to the fixing device 12. In the fixing device 12, the toner image on the transfer material P is fixed by the action of heat and pressure, and the transfer material P on which the toner image is fixed is discharged outside the apparatus. After the transfer, the residual toner on the photoreceptors 1y, 1m, 1c, and 1bk is removed by the photoreceptor cleaners 13y, 13m, 13c, and 13bk, and the residual toner on the transfer conveyance belt 5 is removed by the belt cleaner 14. Is done.
[0043]
Next, ATVC control performed in the above-described four-drum type image forming apparatus will be described based on the transfer bias control flowchart shown in FIG.
[0044]
First, when a print signal is input to the apparatus, each color image forming unit U _Y , U _M , U _C , U _Bk Each of the photoconductors 1y, 1m, 1c, 1bk and the transfer / conveying belt 5 are driven to start pre-rotation. Simultaneously with the start of the pre-rotation, a predetermined bias is applied to the charging rollers 2y, 2m, 2c, 2bk, and the surfaces of the photoreceptors 1y, 1m, 1c, 1bk are charged to -500V. When the surfaces of the charged photoconductors 1y, 1m, 1c, and 1bk reach the transfer portion, the transfer rollers 9y, 9m, 9c, and 9bk for each color are subjected to constant current control with a bias (positive polarity) opposite to the toner. The The constant current control value at this time is controlled by a current (4 μA) that does not cause a memory by charging the photoreceptors 1y, 1m, 1c, and 1bk to positive polarity. The high voltage power supply 15 detects the voltage generated in each of the color transfer rollers 9y, 9m, 9c, 9bk during the constant current control and records it in the CPU 16. The CPU 16 averages the generated voltages of the respective transfer rollers 9y, 9m, 9c, and 9bk that are detected as needed, and the control is continued from the time when the constant current control is started until the transfer conveyance belt 5 rotates one or more times. The average value (transfer bias 1) at the time when the control is finally finished is recorded and finished (ATVC control 1). At that time, the drive roller 6, the support rollers 7-1 and 7-2, and the tension are prevented so that the control current does not flow from the transfer portions of the respective colors to the portions other than the photoconductors 1y, 1m, 1c and 1bk along the transfer conveyance belt 5. A similar bias is applied to the roller 8 from a power source (not shown). In the present embodiment, the transfer current can be prevented from flowing by applying a voltage of about +200 to +300 V to each of the rollers 6, 7-1, 7-2, and 8. The suction roller 10 is applied with a voltage (about -200 to -500 V) for sucking the transfer material P during actual printing, and the ATVC control 1 is performed in the same state as during printing.
[0045]
As described above, the transfer bias of each color interferes with each other, and the transfer roller 9y, 9m, 9c, 9bk is added to the drive roller 6, the support rollers 7-1, 7-2, the tension roller 8, and the suction roller 10. Therefore, it is possible to reliably detect a change in current in the transfer portion due to an environmental change or the like.
[0046]
Next, each image forming unit U _Y , U _M , U _C , U _Bk When image signals are sequentially sent to the image exposure apparatuses 3y, 3m, 3c, and 3bk, the timings on the photoreceptors 1y, 1m, 1c, and 1bk are adjusted to the respective image forming units U. _Y , U _M , U _C , U _Bk A developing bias is applied every time, and the electrostatic latent images on the photoreceptors 1y, 1m, 1c, and 1bk are visualized as toner images with toner. When this toner image reaches the transfer portion as the photoconductors 1y, 1m, 1c, and 1bk rotate, the transfer material P is sent to the transfer portion of the first color and is transferred to the transfer rollers 9y, 9m, 9c, and 9bk for the respective colors. At the same time, a predetermined bias is applied at a constant voltage (ATVC control 2). The transfer bias setting (transfer bias 2) at this time is obtained by applying a pre-estimated voltage partial pressure (approximately 250 V) bias to the transfer bias 1 recorded in the CPU 16. The reason why the constant voltage control is performed by the ATVC control 2 is to obtain an optimum transfer property even if the image printing ratio changes.
[0047]
Thereafter, the transfer material P is sequentially supplied to each color image forming unit U. _Y , U _M , U _C , U _Bk In the same manner, the toner passes through the transfer portion P, and the toner is transferred onto the transfer material P in an overlapping manner. The timing of bias application at each part in such control is shown in FIG.
[0048]
By performing the control as described above, even if a resistance change due to an environmental change or a change in resistance value due to a change in friction or electrical characteristics of a member occurs in each transfer portion, the transfer conveyance belt 5 and the transfer roller 9y, An appropriate transfer bias commensurate with the resistance value fluctuations of 9 m, 9 c, and 9 bk can be applied at the time of image formation, and a stable image can always be output.
[0049]
Actually, it can be seen from the VI characteristics of the transfer portion with respect to the environmental change shown in FIG. 4 that the control voltage is controlled in the optimum region in both the H / H and L / L environments.
[0050]
Further, when the transfer efficiency and retransfer rate of each color were measured, it was confirmed that the transfer efficiency of each color was 95% or more and the retransfer rate was 5% or less. At the same time, it was confirmed that a high-quality image without defects was obtained, and that the stability of the color variation was very high.
[0051]
Next, an example of another sequence that can achieve the same effect by using the same image forming apparatus as described above will be described. The timing of the bias applied to each part is shown in the timing chart of FIG.
[0052]
In this example, as in the example described above, detection of the generated voltage for determining the transfer bias 1 is performed only at a plurality of points at a specific timing, and the transfer bias 2 is determined from the generated voltage detected at each transfer unit at that time. I decided to decide. However, since it is not necessary to simultaneously detect the voltage generation timing at each transfer portion as shown in FIG. 5, resistance unevenness in the conveyance direction of the transfer conveyance belt 5 can be detected and averaged as much as possible. It is desirable to set.
[0053]
The purpose of carrying out such a sequence is to reduce the processing load on the CPU 16 during ATVC control 1 and simplify the control as much as possible so that a dedicated CPU for high-pressure transfer control can be avoided. The purpose is to suppress the cost increase by making it possible to adopt an inexpensive one.
[0054]
In the bias control sequence described above, the image forming process speed is slower than that for printing on normal plain paper because of the high fixing property when printing on special media such as OHT and cardboard. The same control is performed during this control. In this case, since the transfer bias 1 when the process speed is reduced is clearly different from the transfer bias 1 when the process speed is reduced, the ATVC control 1 is used when entering the mode for decreasing the process speed. The constant current control value at the time and the value for the virtual partial pressure of the transfer material P when the transfer bias 2 ′ is calculated inside the CPU 16 must be set in advance. In addition, it is desirable to reduce the process speed to 1/2 when printing on OHT or thick paper. In this case, the constant current control value in the ATVC control 1 is 2 μA, and the virtual voltage of the transfer material P is +500 V. . Here, when printing on OHT cardboard is performed alternately and continuously, it is desirable to perform ATVC control 1 at the time of pre-rotation each time.
[0055]
As described above, by performing ATVC control for the transfer bias control of the 4-drum system, the transfer efficiency of each image forming unit can be optimized stably even if the resistance value of the transfer conveyance belt or transfer member fluctuates. Therefore, a good image can always be output.
[0056]
Further, by implementing such control, it is possible to cope with fluctuations in the volume resistance value of the transfer transfer belt that can be used, so that the yield in manufacturing can be improved and the cost of the transfer transfer belt can be kept low. Can do.
[0057]
<Embodiment 2>
Next, a second embodiment of the present invention will be described.
[0058]
FIG. 6 is a schematic cross-sectional view of an electrophotographic color image forming apparatus according to Embodiment 2 of the present invention, and the configuration of the color image forming apparatus is substantially the same as that of Embodiment 1, but a transfer conveyance belt. 17 has a volume resistance of 10 ⁷ -10 ¹² Another difference is that a neutralizing brush 18 for neutralizing the surface of the transfer conveyance belt 17 is provided.
[0059]
The volume resistance value used in this embodiment is 10 ⁷ -10 ¹² The transfer conveyance belt 17 of about Ω is used for each image forming unit U shown in FIG. _Y , U _M , U _C , U _Bk As can be seen from the transfer VI characteristics in FIG. 3, the current values are different from each other even though the same voltage is applied, and the current hardly flows in the downstream transfer portion. This is a decrease caused by the influence of the charge because the transfer conveyance belt 17 is charged at the transfer portion of the previous color and the charge is not attenuated until reaching the transfer portion of the next color. In other words, there is a large difference in transfer current between when the transfer conveyance belt 17 is charged and when it is not charged.
[0060]
Further, according to the study by the present inventor, in particular, the volume resistance value 10 ^Ten -10 ¹² In the case of a transfer conveyance belt of about Ω, the charged charge on the transfer conveyance belt 17 is not attenuated after the transfer material P is separated from the transfer conveyance belt 17 and is again used for image formation. For this reason, the neutralizing brush 18 is disposed at a position facing the tension roller 8, and the transfer conveyance belt 17 is decharged once, and then the image forming process is started again. In this static elimination process, the static elimination brush 18 has V _PP An AC bias of 1 kV and 750 Hz is applied.
[0061]
Hereinafter, an ATVC control method in an apparatus using the transfer conveyance belt 17 having such a resistance value will be described based on a bias application timing chart shown in FIG.
[0062]
First, in the pre-multi rotation at the time of starting up the apparatus and the pre-rotation of image formation, the image forming unit U _Y , U _M , U _C , U _Bk At the same time as the driving of the transfer / conveying belt 17, the charging process of the surfaces of the photoreceptors 1y, 1m, 1c, and 1bk and the charge removal of the transfer / conveying belt 17 by the charge eliminating brush 18 are started. The charged surfaces of the photoconductors 1y, 1m, 1c, and 1bk and the removed portions of the transfer conveyance belt 17 are the first color image forming unit U. _Y 4 μA of constant current control (ATVC control 1) is performed on the first color transfer roller 9y.
[0063]
Next, constant current control (ATVC control 1) of 4 μA is performed on the transfer roller 9m for the second color at the timing when the control start position on the transfer conveyance belt 17 is synchronized. Similarly, ATVC control 1 is performed at the transfer portion of the fourth color. This eliminates the current detection error during ATVC control 1 caused by the difference in transfer current between the charged portion of the transfer conveyance belt 17 and the uncharged portion as described above, and control during actual image formation. This is because the transfer control bias is set in a form corresponding to.
[0064]
In the subsequent control, as in the first embodiment, the transfer bias 1 and the transfer bias 2 are set by the CPU 16 and the ATVC control 2 is performed at the time of image formation.
[0065]
By carrying out the control in this way, the volume resistance value becomes 10 ⁷ -10 ¹² Even in the case where the transfer / conveyance belt 17 and the transfer rollers 9y, 9m, 9c, and 9bk for each color fluctuate in the transfer / conveyance belt 17 of about Ω, an optimum transfer control bias can be set. As in the first mode, it is possible to always stably output a good image with little image defect and less color variation over a long period of time.
[0066]
Here, the volume resistance value of the transfer conveyance belt 17 is 10 ⁷ -10 ¹² In this apparatus configuration using a device of about Ω, the transfer portion that performs ATVC control is designated as the first color image forming unit U. _Y A control method in the case of being limited to the above will be described below in accordance with the transfer bias control flowchart shown in FIG.
[0067]
First, in the same manner as in the above-described example, the pre-rotation before the image formation is performed, and the first color image forming unit U _Y Only the ATVC control 1 is performed until the transfer / conveying belt 17 rotates once. Thereafter, the transfer bias of each color is determined as needed from the relationship between the transfer bias 1 determined by the ATVC control 1 and the color bias correspondence table as shown in FIG.
[0068]
By performing such ATVC control, a good image could be obtained as in the first embodiment. That is, by adopting the configuration and control as in the present embodiment, 10 ⁷ -10 ¹² Even when the transfer / conveying belt 17 having a volume resistance value of about Ω is used, very stable transfer can be performed, and the image can be stabilized.
[0069]
<Embodiment 3>
Next, a third embodiment of the present invention will be described.
[0070]
Although the configuration of the color image forming apparatus according to the present embodiment is shown in FIG. 11, the configuration of the color image forming apparatus according to the present embodiment is substantially the same as that of the second embodiment, and the description thereof is omitted. To do. However, the volume resistance value of the transfer conveyance belt 19 is 10 here. ¹¹ -10 ¹⁵ The neutralizing brush 20 not only neutralizes the transfer / conveying belt 19 but also uniformly charges it. The first color transfer high-voltage power supply (HV.2) 21 outputs a negative bias.
[0071]
Here, the control in the present embodiment will be described based on the bias application timing chart shown in FIG.
[0072]
First, as in the first and second embodiments, when the pre-rotation before image formation is started, the photosensitive members 1y, 1m, 1c, 1bk and the transfer conveying belt 19 are driven and the photosensitive members 1y, 1m, 1c, Charging of the 1bk surface is started. At this time, the transfer / conveying belt 19 is supplied with AC: V to DC: +750 from a high voltage power source (not shown) to the neutralizing brush 20. _PP 2kV _PP By applying a bias superimposed with / 750 Hz, the surface potential is uniformly charged to about + 750V.
[0073]
Thus, the transfer material P is attracted to the uniformly charged transfer transport belt 19 at the transfer material suction portion (nip portion) N and then transported to the first color transfer portion. Similar ATVC control 1 is performed. The bias applied to the suction roller 10 when the transfer material P is sucked is +1.5 kV.
[0074]
Here, in the transfer ATVC control 1 for the first color, optimum transfer efficiency is obtained by controlling with the bias having the same polarity as the toner due to the influence of the bias applied to the static elimination brush 20 and the bias applied to the suction roller 10. It will be obtained. However, in the transfer portion for the second and subsequent colors, it is desirable to perform ATVC control 1 with a bias having a polarity opposite to that of the toner, as in the above embodiment.
[0075]
The transfer resistance belt 19 actually has a volume resistance value of 10 ¹³ As a result, the optimum transfer bias (transfer bias 2) of the first color was −300V, the second color was DC + 300V, the third color was + 700V, and the fourth color was + 1000V.
[0076]
On the other hand, when the transfer conveyance belt 19 is not charged by the charge eliminating brush 20, the optimum bias for the fourth color is required to be 5 kV or more, and an expensive transformer is required for the high voltage power supply 21 for transfer. Also, since the charged potential of the transfer / conveying belt 19 becomes high, discharge / leak to an unexpected part occurs, thereby causing malfunction of the apparatus and image disturbance.
[0077]
However, the volume resistance value is 10 by controlling as in the present embodiment. ¹¹ -10 ¹⁵ Even when a transfer conveyance belt 19 of about Ω is used, the transfer bias of the final color is about +1 kV, so that the above problems can be solved and a stable image can be output over a long period of time. It is also possible to avoid an increase in the cost of the transfer high-voltage power supply 21.
[0078]
【The invention's effect】
As is apparent from the above description, according to the present invention, a plurality of image forming units for forming a latent image on the image carrier by the image forming unit and developing the latent image by the developing unit are provided. In the color image forming apparatus for forming a color image by sequentially transferring the toner images formed by the image forming units onto the transfer material, the toner images are electrostatically adsorbed on the transfer material conveying member from the plurality of image forming units. At least one of transfer means for transferring a toner image onto a transfer material, current control means for performing constant current control on the transfer means, and output voltage for detecting an output voltage value during constant current control by the current control means Since the detection means and the output voltage detection means are configured to include a means for determining the output voltage to the transfer material based on the calculation result of the empty input, the fluctuation of the resistance value of the transfer material conveying member and the transfer means Can be output constantly stable and high-quality color images regardless of variations, ensuring high transfer efficiency, there is an advantage that it is possible to maintain a low back-transfer rate.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a main part showing a schematic configuration of a color image forming apparatus according to Embodiment 1 of the present invention.
FIG. 2 is a flowchart showing an ATVC control procedure in the color image forming apparatus according to Embodiment 1 of the present invention.
FIG. 3 is a control timing chart of bias application in the color image forming apparatus according to Embodiment 1 of the present invention.
FIG. 4 is a transfer VI characteristic diagram in the color image forming apparatus according to the first embodiment of the present invention;
FIG. 5 is a bias application control timing chart showing another sequence in the color image forming apparatus according to Embodiment 1 of the present invention;
FIG. 6 is a cross-sectional view of a main part showing a schematic configuration of a color image forming apparatus according to Embodiment 2 of the present invention.
FIG. 7 is a transfer VI characteristic diagram in the color image forming apparatus according to Embodiment 2 of the present invention;
FIG. 8 is a control timing chart of bias application in the color image forming apparatus according to Embodiment 2 of the present invention;
FIG. 9 is a flowchart showing an ATVC control procedure in the color image forming apparatus according to Embodiment 2 of the present invention.
FIG. 10 is a diagram showing a color bias correspondence table of transfer biases in a color image forming apparatus according to Embodiment 2 of the present invention.
FIG. 11 is a cross-sectional view of an essential part showing a schematic configuration of a color image forming apparatus according to Embodiment 3 of the present invention.
12 is a control timing chart of bias application in the color image forming apparatus according to Embodiment 3 of the present invention. FIG.
FIG. 13 is a cross-sectional view of a main part showing a schematic configuration of a conventional color image forming apparatus.
FIG. 14 is a transfer VI characteristic diagram in a conventional color image forming apparatus.
FIG. 15 is a flowchart showing an ATVC control procedure in a conventional monochrome image forming apparatus.
[Explanation of symbols]
1y, 1m, 1c, 1bk photoconductor (image carrier)
2y, 2m, 2c, 2bk charging roller
3y, 3m, 3c, 3bk Image exposure device (image forming means)
4y, 4m, 4c, 4bk Developer (Developing means)
5, 17, 19 Transfer conveyor belt (transfer material conveying means)
9y, 9m, 9c, 9bk transfer roller (transfer means)
15, 21 High voltage power supply (output voltage detection means)
16 CPU (current control means)
18, 20 Static elimination brush (static elimination / charging device)
P transfer material
U _Y , U _M , U _C , U _Bk Image forming unit

Claims (3)

A plurality of image carriers on which toner images are formed; a transfer conveyor belt that is rotatable and conveys a transfer material; and a plurality of transfer units that respectively face the plurality of image carriers via the transfer conveyor belt; A voltage supply means for applying a voltage to the plurality of transfer means; a high-voltage power supply having a circuit for detecting a current value flowing through the plurality of transfer means; and a transfer material provided at a position in contact with the transfer / conveyance belt. A transfer roller formed by the image carrier and the transfer unit via the transfer conveyance belt. In an image forming apparatus in which an image is transferred from the plurality of image carriers to a transfer material conveyed by the transfer conveyance belt ,
The application means applies a voltage to the plurality of transfer means so that a predetermined current flows through the circuit for at least a period until the transfer conveyance belt rotates at least once before the transfer material is conveyed to the transfer portion, In addition, a voltage having the same polarity as the voltage applied by the applying unit is applied to the suction roller and the plurality of stretching rollers, the transfer material is conveyed to the transfer unit, and the plurality of transfer units use the toner image as a transfer material. The image forming apparatus according to claim 1, wherein the voltage applied by the applying unit during transfer is a constant voltage calculated using an average value of the voltages applied by the applying unit during the period as a reference voltage . 2. The image forming apparatus according to claim 1 , wherein when the applying unit applies a voltage to the plurality of transfer units so that the predetermined current flows, the high-voltage power source performs constant current control . 3. The method according to claim 1, wherein a plurality of process speeds, which are rotational speeds of the image carrier at the time of image formation, are provided, and the value of the predetermined current is set according to the plurality of process speeds. The image forming apparatus described in 1 .

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