JP2005010499A - Image forming apparatus and method for controlling transfer bias - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus by which image output is realized without stopping image forming operation even in the case of performing image forming under the environment of low temperature. <P>SOLUTION: The image forming apparatus is provided with an image carrier 10 to carry a toner image, a transfer means 21 to transfer the toner image on the image carrier 10 to a transfer material 25, a transfer bias applying means 100 to apply a specified first transfer bias value T1 to the transfer means 21, an electric current value detecting means 102 and a voltage value detecting means 103 to detect an electric current value made to flow through the transfer means 21 and a voltage value applied to it and a transfer bias value controlling means 101 for controlling a transfer bias value by a specified second transfer bias value T2 in the case that a transfer bias value T0 applied by the transfer bias applying means 100 does not reach the specified first transfer bias value T1. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus using an electrophotographic system such as a copying machine, a printer, and a facsimile machine.
[0002]
[Prior art]
Conventionally, a toner image formed on a first image carrier (hereinafter referred to as a photoconductor) is transferred to a second image carrier (hereinafter referred to as a transfer material) such as paper, and then the toner image on the transfer material is transferred to a fixing device. There is known an image forming apparatus in which fixing is performed by thermocompression bonding.
In addition, as an image forming apparatus that forms full-color images, the transfer material is held on a transfer material carrier such as a transfer drum, and each color of yellow, magenta, cyan, and black developed on the photoconductor is supported on the transfer material. It is known to obtain a full-color image by sequentially transferring to a transfer material on the body and then fixing the transfer material peeled off from the transfer material carrier by thermocompression bonding with a fixing device.
On the other hand, instead of transferring the toner image to the transfer material on the transfer material carrier, for example, as disclosed in Patent Document 1, yellow, magenta, cyan, and black colors developed on the photoconductor are intermediately transferred. The images are sequentially superimposed on the body (hereinafter referred to as primary transfer), and the four color toner images formed on the intermediate transfer body are collectively transferred to the transfer material (hereinafter referred to as secondary transfer) and then fixed by a fixing device. Such image forming apparatuses are already in the market and are well known.
Since the above-described color image forming apparatus does not require the transfer material to be held on the transfer material carrier unlike the conventional image forming apparatus, it is thin paper (40 g / m ² ) And cardboard (200 g / m ² ), Postcards and envelopes can be transferred to various types of transfer materials, and has the advantage of high versatility of transfer materials.
Further, in recent years, in the image forming apparatus as described above, not only a copying function but also a so-called multi-function machine equipped with a printer function, a FAX function, a scanner function and the like has begun to operate in the market. Such multifunction devices are not only multifunctional, but are also being reduced in size.
[0003]
However, the image forming apparatus is in a low temperature environment (for example, an environment of 5 ° C. below freezing) in a state where the main body is turned off or in a power saving state where the main body is turned on but the fixing device is not energized. When the image forming operation is performed for a long time, the transfer bias does not reach a predetermined value during the immediately subsequent image forming operation, and it is determined that the self-diagnostic function may determine that there is an abnormality and stop the machine operation.
This is because if the image forming apparatus is left in an environment of a very low temperature as described above, each member of the transfer bias path (for example, a transfer roller, an intermediate transfer member, etc.) becomes highly resistant and the transfer current does not flow easily. It is because it ends.
When the image forming apparatus becomes in a state where the transfer current hardly flows as described above and reaches the output upper limit value of the high-voltage power supply, for example, when the transfer bias is controlled with a constant current, it cannot be controlled to a predetermined current value. For this reason, it is determined that an abnormal state or a failure avoidance of the high voltage power supply is necessary, and the image forming operation is stopped.
In general, there is almost no possibility that the conventional color image forming apparatus is used in the low temperature environment as described above. However, as described above, as a result of the promotion of multifunction and miniaturization of the image forming apparatus, the image forming apparatus is used in various regions and modes, and it is necessary to perform the image forming operation even in a very low temperature environment. Came out.
In particular, when it is necessary to operate even in an unattended environment where the room temperature is not controlled, such as a FAX reception function, if the image forming operation stops, the operator cannot deal with it, so it is necessary to perform image formation reliably. is there.
In order to eliminate such problems in a low temperature environment, Patent Document 2 proposes a technique for reducing the amount of toner and maintaining transferability in a low temperature and low humidity environment. The technique described in Patent Document 3 corrects a target current from a transfer voltage when transfer is performed with constant current control. Further, Patent Document 4 proposes a technique for providing a sensor for measuring relative humidity or absolute humidity and controlling the transfer bias from the detection result.
[Patent Document 1] Japanese Patent Laid-Open No. 05-323704
[Patent Document 2] Japanese Patent Laid-Open No. 2000-75572
[Patent Document 3] Japanese Patent Application Laid-Open No. 07-146619
[Patent Document 4] Japanese Patent Laid-Open No. 2000-147923
[0004]
[Problems to be solved by the invention]
However, the technique described in Japanese Patent Laid-Open No. 2000-75572 still has a problem that the color tone changes in a full color image. In the technique described in Japanese Patent Application Laid-Open No. 07-146619, the target current cannot be passed when the upper limit voltage of the high voltage power source is reached, so that the transfer bias cannot be controlled, and a defective transfer image is output. End up. Further, the technique described in Japanese Patent Laid-Open No. 2000-147923 also has a problem that the transfer bias cannot be controlled because detection becomes impossible in a very low temperature environment such as 5 ° C. below freezing point.
SUMMARY OF THE INVENTION An object of the present invention is to provide an image forming apparatus capable of solving the above-described problems and realizing image output without stopping an image forming operation even when image formation is performed in a low temperature environment. is there.
[0005]
[Means for Solving the Problems]
In order to achieve the above object, according to the first aspect of the present invention, an image carrier that carries a toner image, a transfer unit that transfers a toner image on the image carrier to a transfer material, First transfer bias T ₁ Transfer bias applying means for applying current, current value detecting means and voltage value detecting means for detecting the current value and voltage value applied to the transfer means, and transfer bias value T applied by the transfer bias applying means. ₀ Is a predetermined first transfer bias value T ₁ Is not reached, the transfer bias value is set to a predetermined second transfer bias value T. ₂ The image forming apparatus provided with the transfer bias value control means to be controlled in the above is the main feature.
According to the second aspect of the present invention, the predetermined second transfer bias value T ₂ A predetermined transfer current threshold I when ₀ The main feature of the image forming apparatus is that the image forming apparatus stops the image forming operation and notifies the user when it does not reach.
According to a third aspect of the present invention, the predetermined first and second transfer bias values and the transfer current threshold value are determined from a transfer material type and a color number mode. And
According to a fourth aspect of the present invention, the image forming apparatus according to any one of the first to third aspects is characterized in that the transfer bias value is constant current controlled.
According to a fifth aspect of the invention, the image forming apparatus according to any one of the first to third aspects is characterized in that the transfer bias value is controlled by switching between a constant current and a constant voltage.
According to a sixth aspect of the present invention, the image carrier is an intermediate transfer member that carries a plurality of color toner images and forms a full-color image. .
According to the seventh aspect of the present invention, an image carrier that carries a toner image, a transfer unit that transfers the toner image on the image carrier to a transfer material, and a predetermined first transfer bias T on the transfer unit. ₁ A transfer bias control method for an image forming apparatus, comprising: a transfer bias applying unit that applies voltage; a current value detecting unit that detects a current value flowing through the transfer unit and a voltage value to be applied; and a voltage value detecting unit. Transfer bias value T applied by the transfer bias applying means ₀ Is a predetermined first transfer bias value T ₁ Is not reached, the transfer bias is a predetermined second transfer bias value T. ₂ And the predetermined second transfer bias value T ₂ A predetermined transfer current threshold I when ₀ The transfer bias control method for stopping the image forming operation and notifying the user when it does not reach is the most important feature.
[0006]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment of the present invention. The photosensitive belt 1 rotating in the direction of the arrow is stretched by a primary transfer counter roller 16, a photosensitive member driving roller 17, and a photosensitive member tension roller 18, and around the photosensitive belt 1, a photosensitive member cleaning unit 2. A charger 4, an exposure unit 5, an intermediate transfer belt 10, and the like are disposed. The developing means includes four developing units, a yellow developing unit 6, a magenta developing unit 7, a cyan developing unit 8, and a black developing unit 9.
When a full color image is formed, a visible image is formed in the order of the yellow developing unit 6, the magenta developing unit 7, the cyan developing unit 8, and the black developing unit 9, and the visible images of the respective colors are sequentially superimposed and transferred onto the intermediate transfer belt 10. Thus, a full color image is formed. The peripheral speed (so-called process speed) of the photosensitive belt 1 is set to 180 mm / sec. Reference numeral 3 denotes a blade of the photoconductor cleaning unit 2.
The intermediate transfer belt 10 is stretched by a primary transfer bias roller 11, a secondary transfer counter roller 12, a drive roller 13, a tension roller 14, and a belt cleaning counter roller 15, and is driven by a drive motor (not shown). ing. The primary transfer bias roller 11 is pressed in the direction of the photoreceptor belt 1 by a pressure contact spring 27. Each roller is supported from both sides of the intermediate transfer belt 10 by an intermediate transfer belt unit side plate (not shown).
The intermediate transfer belt 10 is composed of PVDF (vinylidene fluoride), ETFE (ethylene-tetrafluoroethylene copolymer), PI (polyimide), PC (polycarbonate) or the like in a single layer or a plurality of layers, such as carbon black. Conductive material is dispersed and its volume resistivity is 10 ⁸ -10 ¹² Ωcm and surface resistivity of 10 ⁸ -10 ¹⁵ It is adjusted to be in the range of Ωcm. If necessary, a release layer may be coated on the surface of the intermediate transfer belt 10.
Materials used for the coating include ETFE (ethylene-tetrafluoroethylene copolymer), PTFE (polytetrafluoroethylene), PVDF (vinylidene fluoride), PEA (perfluoroalkoxy fluorocarbon resin), FEP (four-fluorocarbon). Fluorine resin such as ethylene fluoride-propylene hexafluoride copolymer) or PVF (vinyl fluoride) can be used, but is not limited thereto.
[0007]
The method of manufacturing the intermediate transfer belt 10 includes a casting method, a centrifugal molding method, and the like, and the surface thereof may be polished if necessary. If the volume resistivity and surface resistivity of the intermediate transfer belt 10 exceed the above-described ranges, the bias necessary for transfer increases, which increases the power supply cost, which is not preferable. Further, since the charging potential of the intermediate transfer belt 10 becomes high and the self-discharge becomes difficult in the transfer process, the transfer material peeling process, and the like, it is necessary to provide a static eliminating unit.
Also, if the volume resistivity and surface resistivity are below the above ranges, the charge potential decays faster, which is advantageous for static elimination by self-discharge, but toner scattering occurs because the current during transfer flows in the surface direction. End up. Accordingly, the volume resistivity and surface resistivity of the intermediate transfer belt 10 in the present invention must be within the above ranges.
The volume resistivity and surface resistivity were measured by connecting a probe (inner electrode diameter 50 mm, ring electrode inner diameter 60 mm: JIS-K6911 compliant) to a digital ultra-high resistance microammeter (manufactured by Advantest: R8340A). A voltage of 500 V (surface resistivity is 500 V) was applied to the front and back of the transfer belt 10 and measurement was performed at a discharge of 5 sec and a charge of 10 sec. The environment during the measurement was fixed at 22 ° C. and 55% RH. The resistance environment fluctuation of the intermediate transfer belt 10 will be described later.
The belt cleaning unit 19 includes a contact / separation mechanism 26 that can contact and separate from the intermediate transfer belt 10 and that contacts and separates from the intermediate transfer belt 10. While the third and fourth colors are being transferred onto the belt, the contact / separation mechanism 26 separates the belt from the surface of the intermediate transfer belt 10, and when the secondary transfer is performed, it is pressed against the toner at a predetermined timing to clean the remaining toner.
A belt position detection mark 23 is provided at the end of the intermediate transfer belt 10, and an image forming process for each color is started at the timing when the mark is detected by the mark sensor 24, so that each color image is accurately overlaid. It becomes possible.
The secondary transfer unit 20 includes a secondary transfer bias roller 21 and a contact / separation mechanism 22 that contacts and separates the secondary transfer bias roller 21 from the belt 10. The secondary transfer bias roller 21 is made of a conductive material on a metal core such as SUS. ⁶ -10 ¹⁰ It is configured by covering an elastic body such as urethane adjusted to a resistance value of Ω.
[0008]
Here, since the current hardly flows when the resistance value of the secondary transfer bias roller 21 exceeds the above range, it is necessary to apply a higher voltage in order to obtain a required transfer property, which increases the power supply cost. Invite. In addition, since a high voltage is applied, a discharge occurs in the gap before and after the transfer portion nip, and white spots are lost due to the discharge on the halftone image. On the contrary, if the resistance value of the secondary transfer bias roller 21 is below the above range, the transferability between the multi-color image portion (for example, three-color superimposed image) and the single-color image portion existing on the same image cannot be achieved.
This is because the resistance value of the secondary transfer bias roller 21 is low, so that a sufficient current flows to transfer the monochrome image portion at a relatively low voltage. However, it is optimal for the monochrome image portion to transfer the multiple color image portion. This is because a voltage value higher than the required voltage is required, and if the voltage is set to a voltage at which the multi-color image portion can be transferred, the transfer current becomes excessive in the single-color image and the transfer efficiency is reduced.
The resistance of the secondary transfer bias roller 21 is set such that the secondary transfer bias roller 21 is installed on a conductive metal plate, and a load of 4.9 N on one side (total of 9.8 N on both sides) is applied to both ends of the core metal. It calculated from the value of the electric current which flows when a voltage of 1000 V is applied between the cored bar and the metal plate in the applied state. Note that the environment was fixed at 22 ° C. and 55% RH when measuring the resistance of the secondary transfer bias roller 21. Variations in the resistance value environment of the secondary transfer bias roller 21 will be described later.
The secondary transfer bias roller 21 is given a driving force by a driving gear (not shown), and its peripheral speed is adjusted to be substantially the same as the peripheral speed of the intermediate transfer belt 10.
The secondary transfer bias roller 21 is usually separated from the surface of the intermediate transfer belt 10, but when the four color superimposed images formed on the surface of the intermediate transfer belt 10 are collectively transferred to the transfer material 25, the secondary transfer bias roller 21 contacts and separates at a timing. The image is transferred to the transfer material 25 by being pressed by the mechanism 22 and applying a predetermined bias voltage.
The transfer material 25 is fed by a pickup roller 28, a paper feeding / conveying roller 29, and a registration roller 30 at the timing when the leading end of the four-color superimposed image on the surface of the intermediate transfer belt 10 reaches the secondary transfer position. The four-color superimposed image transferred to the transfer material 25 is fixed by the fixing unit 31 and then discharged by a discharge roller 32.
[0009]
Here, full color image formation will be described in detail. First, the photosensitive belt 1 is uniformly charged to a surface potential of -500 V by the charger 4, and then exposed by the exposure means 5 to form an electrostatic latent image, and image writing is performed. The electrostatic latent image on 1 is visualized with a one-component developer made of yellow toner by the yellow developing device 6 to become a yellow image (yellow toner image). At this time, the developing bias applied to the yellow developing device 6 is −300V.
The primary transfer bias roller 11 is applied with a secondary transfer bias from a high-voltage power supply (not shown) to contact the back surface of the intermediate transfer belt 10 and apply a charge to transfer the yellow image on the photosensitive belt 1 to the intermediate transfer belt 10. Let The primary transfer bias at this time was set to 700V. The photoreceptor belt 1 is cleaned of residual toner by a photoreceptor cleaning unit 2 after the yellow image is transferred.
Next, the photosensitive belt 1 is again uniformly charged to a surface potential of -500 V by the charger 4, and then exposed by the exposure means 5 to form an electrostatic latent image, and image writing is performed. The electrostatic latent image on the body belt 1 is visualized with a one-component developer made of magenta toner by a magenta developing device 7 to form a magenta image (magenta toner image). The developing bias applied to the magenta developing device 7 is −300V.
The primary transfer bias roller 11 is applied with a transfer bias from a high-voltage power source and contacts the back surface of the intermediate transfer belt 10 to apply a charge, thereby transferring the magenta image on the photosensitive belt 1 to the intermediate transfer belt 10. The primary transfer bias at this time was set to 800V. The photoreceptor belt 1 is cleaned by the photoreceptor cleaning unit 2 after the magenta image is transferred.
[0010]
Next, the photosensitive belt 1 is again charged uniformly to a surface potential of -500 V by the charger 4, and then exposed by the exposure means 5 to form an electrostatic latent image, whereby an image is written. The electrostatic latent image on the photosensitive belt 1 is visualized with a one-component developer made of cyan toner by a cyan developing device 8 to become a cyan image (cyan toner image). At this time, the developing bias applied to the cyan developing device 8 is −300V.
The primary transfer bias roller 11 is applied with a transfer bias from a high-voltage power supply and is brought into contact with the back surface of the intermediate transfer belt 10 to apply a charge, whereby a cyan image on the photosensitive belt 1 is transferred to the intermediate transfer belt 10 as a yellow image and a magenta image. And superimpose and transfer. The primary transfer bias at this time was set to 900V. The photoreceptor belt 1 is cleaned by the photoreceptor cleaning unit 2 after the cyan image is transferred.
Further, the photoreceptor belt 1 is uniformly charged to a surface potential of -500 V by the charger 4, and thereafter exposed by the exposure means 5 to form an electrostatic latent image, whereby an image is written. The electrostatic latent image on the belt 1 is visualized with a one-component developer made of black toner by the black developing device 9 to become a black image (black toner image). At this time, the developing bias applied to the black developing device 9 is −300V.
The primary transfer bias roller 11 is applied with a transfer bias from a high-voltage power supply and is brought into contact with the back surface of the intermediate transfer belt 10 to apply a charge, thereby transferring a black image on the photoreceptor belt 1 to the intermediate transfer belt 10 as a yellow image and a magenta image. The image is transferred with being superimposed on the cyan image. The primary transfer bias at this time was set to 900V. The photoreceptor belt 1 is cleaned by the photoreceptor cleaning unit 2 after the transfer of the black image.
A full-color image (4-color superimposed image) on the intermediate transfer belt 10 is transferred by the secondary transfer bias roller 21 to the transfer material 25 fed from the sheet feeding device by the pickup roller 28, the sheet feeding / conveying roller 29, and the registration roller 30. After the image is transferred, the transfer material 25 is discharged after the image transferred from the intermediate transfer belt 10 is fixed by the fixing unit 31.
[0011]
In the present embodiment, a single color mode for forming an image of any one color of yellow, magenta, cyan, and black, a two-color mode for forming an image of two colors of yellow, magenta, cyan, and black, and yellow , Magenta, cyan, and black, a three-color mode that forms an image with three colors superimposed, and a full-color mode that forms a four-color superimposed image as described above. These modes can be specified on the operation unit. is there.
When any one of the single color mode, the two color mode, and the three color mode is designated, in the full color mode as described above, images of each color of yellow, magenta, cyan, and black are formed on the photosensitive belt 1 and intermediate transfer is performed. Instead of the operation of transferring to the belt 10, the image is formed on the photoreceptor belt 1 in a single color corresponding to the single color mode and transferred to the intermediate transfer belt 10, or the two color image corresponding to the two color mode is exposed. An operation of forming the image on the body belt 1 and transferring it to the intermediate transfer belt 10, or an operation of forming an image of three colors corresponding to the three-color mode on the photosensitive belt 1 and transferring it to the intermediate transfer belt 10 is performed. After the single-color image, the two-color superimposed image, or the three-color superimposed image on the intermediate transfer belt 10 is transferred to the transfer material 25 by the secondary transfer bias roller 21 and fixed by the fixing unit 31. It is discharged.
[0012]
Here, when an image forming operation for forming a superimposed image of a plurality of colors on the transfer material 25 is continuously performed by the number set by the operation unit, the rear end of the transfer material 25 sufficiently passes through the secondary transfer bias roller 21. In order to prevent the secondary transfer bias voltage from the high-voltage power supply 100, which will be described later, from the high-voltage power source 100, which will be described later, from being turned off, and then prevent the toner image of the next page on the intermediate transfer belt 10 from being attached to the secondary transfer bias roller 21, The secondary transfer bias roller 21 is separated from the intermediate transfer belt 10 by the contact / separation mechanism 22.
Incidentally, it is desirable that the toner particle size is in the range of 4 to 10 μm in terms of volume average particle size. When the particle size is smaller than this, it becomes a cause of background stains during development, fluidity is deteriorated, and further, it tends to agglomerate. On the other hand, when the particle size is larger than this, it is impossible to obtain a high-definition image due to toner scattering or resolution deterioration.
In this embodiment, a toner having a volume average particle diameter of 7.5 μm is used. When copying is performed by the image forming apparatus, reading is performed by the scanner unit 33, and various operations and displays are performed by the operation display unit 34.
[0013]
[Example 1]
Next, examples of the present invention will be described in detail. FIG. 2 is a circuit diagram of the secondary transfer unit. When the transfer material 25 is aligned with the toner image formed on the intermediate transfer belt 10 and conveyed to a secondary transfer unit including the intermediate transfer belt 10 and the secondary transfer bias roller 21, the high-voltage power source 100 and the transfer bias are transferred. A predetermined first transfer bias value is applied by the value control means 101.
In this embodiment, the transfer bias is constant current control. Further, the current value and the voltage value can be detected by the current value detection means 102 and the voltage value detection means 103. Here, the output upper limit value of the high-voltage power supply 100 in the present embodiment is 8 KV. Although an output of 8 KV or more is possible, it is desirable that the output is 8 KV or less in consideration of the occurrence of abnormal images such as white spots due to discharge and safety considerations such as dielectric strength and creepage distance.
The resistance environment fluctuation of the intermediate transfer belt 10 and the secondary transfer bias roller 21 will be described. The intermediate transfer belt 10 used in this example is a material whose resistance is adjusted by adding carbon to PVDF, and the resistance value in an environment of 22 ° C. and 55% RH is measured by the method described above.
Volume resistivity: 11.9 [Log Ω · cm]
Met. The results of examining the volume resistivity temperature fluctuation of the intermediate transfer belt 10 are shown in FIG. As can be seen from FIG. 3, the resistance increases as the temperature decreases.
[0014]
On the other hand, the secondary transfer bias roller 21 used in this example is made of polyurethane foam, and a roller obtained by mixing an electrolyte (a quaternary ammonium salt of alkyl sulfuric acid in this example) to obtain conductivity. When the resistance value of this roller was measured by the method described above in an environment of 22 ° C. and 55% RH,
Volume resistance value: 7.7 [LogΩ]
Met. FIG. 4 shows the results of examining the volume resistance value temperature variation of the secondary transfer bias roller 21. As can be seen from FIG. 4, the resistance increases as the temperature decreases. As described above, since the resistance values of the intermediate transfer belt 10 and the secondary transfer bias roller 21 related to the secondary transfer increase as the temperature becomes lower, the current is less likely to flow. Incidentally, the predetermined first transfer current value is set in advance depending on the type of transfer material, the number of times of transfer to the same transfer material as in double-sided printing, the atmospheric environment, and the like.
As an example, when transfer is performed on plain paper in a four-color mode in an environment of 22 ° C. and 55% RH, a predetermined first transfer current value T ₁ = Constant current control was performed at 26 μA, and the applied voltage value at that time was 2.3 KV. The temperature and humidity are detected by an environment detection sensor (not shown), and the transfer current value is determined from the detected temperature and humidity.
[0015]
On the other hand, the predetermined first transfer current value T under the same image forming conditions as described above under the environment of 10 ° C. and 15% RH. ₁ = Constant current control was performed at 24 μA, and the applied voltage value at that time was 4.1 KV. Further, when image formation is performed in an environment of 0 ° C. under the same image formation conditions described above, a predetermined first transfer current value T ₁ Is 24 μA as in the environment of 10 ° C. and 15% RH, but the applied voltage value at that time reaches the upper limit of 8 KV, and the current value T ₀ However, only 21 μA was flowing.
For this reason, even in the conventional image forming apparatus, the control current value has not been reached and it is determined as an abnormal state, and an error operation such as stopping the operation of the machine has been activated. On the other hand, in this embodiment, when the voltage value detecting means 103 detects that the applied voltage value has reached the upper limit, a predetermined second applied voltage value T ₂ (In this embodiment, the upper limit is 8 KV).
At this time, the current value detecting means 102 detects the transfer current value, and the detected current value T ₀ A predetermined current threshold I ₀ Compared to I ₀ If it is larger, the transfer process is continued. Current threshold I ₀ Is set to almost the lower limit of the usable range of the transfer current value, and in this embodiment, the value is set to 13 μA. This transfer current value is the current threshold I ₀ When it is detected that the temperature is below the threshold value, a transfer failure occurs due to a shortage of the transfer current value, so that the user is notified that the temperature is too low. Specifically, notification display is performed on the operation display unit 34.
In this embodiment, in addition to 0 ° C. as described above, experiments were also performed at 5 ° C. and 10 ° C. below the freezing point. The current values were 21 μA, 16 μA, and 10 μA, respectively. It is possible to output an image even in an environment, and when used under conditions where transfer defects occur, such as −10 ° C., it is possible to prompt the user to improve the room temperature environment by issuing a notification. FIG. 5 is a flowchart showing the above series of operations. The above process is executed in S1 to S7.
[0016]
On the other hand, in the case of a monochrome image or FAX reception, the transfer bias may be low unlike the case of the full color image described above. This is because when the toner on the intermediate transfer belt 10 is transferred to the transfer material 25, a stronger electric field is required for a full-color image in which a plurality of color toners overlap. In this embodiment, the transfer current value for a single color image was set to apply 50% of the full color.
Predetermined transfer current value T in a monochromatic image in a low temperature environment ₁ Is 50% of 24 μA of a full color image, that is, 12 μA. Further, a predetermined current threshold I ₀ Is the lower limit of a monochromatic image, 4 μA in this embodiment. As a result of experiments in such a low temperature environment as described above, it has been confirmed that a monochrome image and FAX reception can be operated without problems even in a -10 ° C environment. In this embodiment, the T for each paper type and color number mode. ₁ , T ₂ , I ₀ Each set value is shown in FIG.
According to the present embodiment, even when the parts involved in the transfer cannot be controlled to a predetermined transfer current value in a low temperature environment where the resistance increases, an image can be output without stopping the image forming operation.
[0017]
[Example 2]
In this embodiment, the control of the transfer bias can be switched between a constant current and a constant voltage. In the first embodiment, when the upper limit voltage of the high-voltage power supply is reached, the upper-limit voltage is always output. However, in this embodiment, the life and failure of the high-voltage power supply are avoided.
Specifically, the transfer bias is set to a predetermined transfer current value T. ₁ When it is detected that the upper limit voltage of the high-voltage power source has been reached during constant current control at, a predetermined second applied voltage value T set lower than the upper limit voltage is detected. ₂ The constant voltage control is performed at. The rest is the same as in the first embodiment.
In the present embodiment, the predetermined second applied voltage value T ₂ Is set to 7 KV, and even when continuous output is performed for a long time, it is possible to prevent a failure of the high-voltage power source and a decrease in service life. In addition, even when the components involved in transfer cannot be controlled to a predetermined transfer current value in a low temperature environment where resistance increases, an image can be output without avoiding a failure of the high voltage power supply and stopping the image forming operation.
FIG. 7 is a configuration diagram of an image forming apparatus according to the second embodiment of the present invention. The second embodiment is a monochromatic image forming apparatus using a photosensitive drum 40. The present invention can also be applied to such a monochrome image forming apparatus.
The embodiments described above are described for easy understanding of the present invention and do not limit the present invention. For example, in the above-described embodiments, the intermediate transfer belt is used as the image carrier. However, the present invention is not limited to this, and the intermediate transfer in which a medium resistance rubber or the like is provided on the surface of a metal cylinder shape. It can be applied to all image carriers such as drums.
Furthermore, the transfer roller was used as the primary transfer means and the secondary transfer means, but not only the rotary contact transfer system such as the rotary transfer brush, but also the contact transfer system such as transfer belt, transfer brush, transfer blade, transfer plate, etc. The present invention can also be applied to an image forming apparatus using the image forming apparatus.
[0018]
【The invention's effect】
According to the first aspect of the present invention, an image carrier that carries a toner image, a transfer unit that transfers the toner image on the image carrier to a transfer material, and a predetermined first transfer bias T on the transfer unit. ₁ Transfer bias applying means for applying current, current value detecting means and voltage value detecting means for detecting the current value and voltage value applied to the transfer means, and transfer bias value T applied by the transfer bias applying means. ₀ Is a predetermined first transfer bias value T ₁ Is not reached, the transfer bias value is set to a predetermined second transfer bias value T. ₂ The image forming operation can be performed without stopping the image forming operation even in a low temperature environment.
According to the second aspect of the present invention, the predetermined second transfer bias value T ₂ A predetermined transfer current threshold I when ₀ In this case, by stopping the image forming operation and notifying the user, the output of a defective transfer image can be prevented, and the operator can be notified to improve the use environment of the image forming apparatus. Can be urged.
According to a third aspect of the invention, the predetermined first and second transfer bias values T ₁ , T ₂ And transfer current threshold I ₀ Is determined from the transfer material type and the color number mode, so that each of the above values can be set to an optimum setting value according to conditions, and a good image can be output even in a low temperature environment.
According to the fourth aspect of the present invention, the transfer bias value is controlled at a constant current, so that a charge amount in an optimum range can be supplied and a good image can be output.
In the invention of claim 5, the transfer bias value is controlled by switching between a constant current and a constant voltage, so that it can be prevented from being applied for a long time at the output upper limit voltage of the high voltage power source, and It is possible to extend the service life and reduce the occurrence of failures.
According to the invention of claim 6, the image carrier is an intermediate transfer member that carries a plurality of color toner images and forms a full color image, so that a good image from a full color image to a single color image can be obtained regardless of the type of transfer material. Output is possible.
According to the seventh aspect of the present invention, an image carrier that carries a toner image, a transfer unit that transfers the toner image on the image carrier to a transfer material, and a predetermined first transfer bias T on the transfer unit. ₁ A transfer bias control method for an image forming apparatus, comprising: a transfer bias applying unit that applies voltage; a current value detecting unit that detects a current value flowing through the transfer unit and a voltage value to be applied; and a voltage value detecting unit. Transfer bias value T applied by the transfer bias applying means ₀ Is a predetermined first transfer bias value T ₁ Is not reached, the transfer bias is a predetermined second transfer bias value T. ₂ And the predetermined second transfer bias value T ₂ A predetermined transfer current threshold I when ₀ If not, the image forming operation is stopped and the user is notified, so that the image can be output without stopping the image forming operation even in a low temperature environment, and a transfer failure occurs. When such transfer conditions are met, the user can be notified to improve the temperature environment.
[Brief description of the drawings]
FIG. 1 is a configuration diagram of an image forming apparatus according to a first embodiment of the present invention.
FIG. 2 is a circuit diagram of a secondary transfer unit.
FIG. 3 is a diagram illustrating temperature characteristics of volume resistivity of an intermediate transfer belt.
FIG. 4 is a diagram illustrating a temperature characteristic of a volume resistance value of a secondary transfer bias roller.
FIG. 5 is a flowchart of the control operation of the present invention.
FIG. 6 is a diagram showing a list of setting values.
FIG. 7 is a configuration diagram of an image forming apparatus according to a second embodiment of the present invention.
[Explanation of symbols]
1 Photoreceptor belt (image carrier)
10 Intermediate transfer belt (image carrier)
21 Secondary transfer roller (transfer means)
25 Transfer material
40 Photosensitive drum (image carrier)
100 High-voltage power supply (transfer bias application means)
101 Transfer bias value control means
102 Current value detection means
103 Voltage value detection means

Claims (7)

An image bearing member for bearing a toner image, a transfer unit that transfers to a transfer material the toner image on the image bearing member, a transfer bias applying means for applying a first transfer bias T ₁ of the predetermined said transfer means, Current value detection means and voltage value detection means for detecting a current value flowing through the transfer means and an applied voltage value, and a transfer bias value T ₀ applied by the transfer bias application means is a predetermined first transfer bias value. If you do not reach T _1, the image forming apparatus is characterized in that a transfer bias value control means for controlling the transfer bias value at a predetermined second transfer bias value T _2. The image forming operation is stopped and notified to the user if the predetermined transfer current threshold value I ₀ is not reached when controlled by the predetermined second transfer bias value T _2. The image forming apparatus according to claim 1. 3. The image forming apparatus according to claim 2, wherein the predetermined first and second transfer bias values and transfer current threshold values are determined from a transfer material type and a color number mode. The image forming apparatus according to claim 1, wherein the transfer bias value is constant-current controlled. The image forming apparatus according to claim 1, wherein the transfer bias value is controlled by switching between a constant current and a constant voltage. 6. The image forming apparatus according to claim 1, wherein the image carrier is an intermediate transfer member that carries a toner image of a plurality of colors and forms a full color image. An image bearing member for bearing a toner image, the transfer means for transferring to a transfer material the toner image on the image bearing member, a transfer bias applying means for applying a first transfer bias T ₁ of the predetermined said transfer means, A transfer bias control method for an image forming apparatus, comprising: a current value detection unit that detects a current value flowing through the transfer unit and a voltage value to be applied; and a voltage value detection unit, wherein the transfer bias is applied by the transfer bias application unit. When the transfer bias value T ₀ does not reach the predetermined first transfer bias value T ₁ , the transfer bias is controlled by the predetermined second transfer bias value T ₂ , and the predetermined second transfer bias value A transfer bias control method characterized by stopping an image forming operation and notifying a user when a predetermined transfer current threshold value I ₀ is not reached when controlled at T ₂ .

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