JP4333056B2 - Image forming apparatus - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an image forming apparatus used for a copying machine, a printer, or the like. More specifically, the present invention relates to an image forming apparatus capable of always obtaining an appropriate transfer capability when transferring an image carried on an image carrier onto a transfer material.
[0002]
[Prior art]
2. Description of the Related Art Conventionally, image forming apparatuses that obtain an output image by transferring an image formed on an image carrier onto a transfer material and fixing the transfer material on which the image has been transferred by a fixing unit have been widely used. In this type of image forming apparatus, in order to obtain a good output image, it is necessary to ensure stable transfer ability. Therefore, ATVC (Active Transfer Voltage Control) is performed to appropriately control the voltage applied to the transfer member for transferring to the transfer material. By performing this ATVC, a transfer voltage corresponding to the resistance of the transfer member is applied, and as a result, an appropriate transfer current flows through the transfer member. Therefore, stable transfer capability is ensured.
[0003]
[Problems to be solved by the invention]
However, the above-described conventional technique has a problem that an appropriate transfer ability may not be ensured. This is because the current-voltage characteristics of the transfer member cannot be detected by the conventional technique. Here, consider the case where the current-voltage characteristic of the transfer member changes from L1 to L2, as shown in FIG. Note that the current-voltage characteristics of the transfer member change due to changes in durability of the transfer member, lot variations, humidity, and the like.
[0004]
The constant current value Ir used for detecting the resistance of the transfer member during ATVC is a current value slightly larger than the optimum current value under the most frequently used paper passing conditions (usually plain paper). Is common. This is because ATVC is normally performed in a non-sheet passing state. That is, a larger amount of current flows through the transfer member during transfer, that is, when paper is not passed than when paper is passed. Then, based on the voltage Vr measured at the time of ATVC measurement, an optimum transfer voltage at the time of passing paper such as plain paper, cardboard, and postcard is determined using a preset transfer voltage table. For example, when the transfer voltage V is set for plain paper, the transfer current I flows through the transfer member. This transfer voltage table is determined based on the current-voltage characteristics of the transfer member at the time of product development.
[0005]
Therefore, even if the current-voltage characteristics of the transfer member at the time of product development change (current-voltage characteristics change from L1 to L2) according to the endurance change of the transfer member and environmental changes such as humidity, the above-described transfer A transfer voltage is set using a voltage table. Therefore, in order to obtain a proper transfer current I to the plain paper as described above, despite the need to apply a transfer voltage V _2, the transfer voltage V is applied to the transfer member. As a result, a current I ₂ smaller than the appropriate current I flows through the transfer member. That is, an appropriate transfer current does not flow through the transfer member. For this reason, the conventional technique has not been able to ensure an appropriate transfer capability.
[0006]
Accordingly, the present invention has been made to solve the above-described problems, and an image forming apparatus capable of always supplying an appropriate transfer current during transfer and thereby obtaining a good image with little image deterioration. It is an issue to provide.
[0007]
[Means for Solving the Problems]
An image forming apparatus according to the present invention, which has been made to solve the above-described problems, calculates a transfer member that electrostatically transfers an image carried on an image carrier to a transfer material, and current-voltage characteristics of the transfer member. And a voltage applying unit that determines and applies an applied voltage to the transfer member based on the current-voltage characteristic calculated by the calculating unit. Here, calculation means, the constant current of a plurality of different sizes is applied to the transfer member during the non-sheet passing, calculates a current-voltage characteristic of the transfer member on the basis of the result of measurement obtained by measuring the voltage value at different times You just have to do it. Alternatively, the current-voltage characteristics of the transfer member may be calculated based on a measurement result obtained by applying a plurality of different constant voltages to the transfer member when paper is not passed and measuring the current value at that time. Good.
[0008]
In this image forming apparatus, the calculating means, the current-voltage characteristic of the transfer member is calculated. Specifically, by calculating means, a plurality of different magnitude of the constant current to the transfer member during the non-sheet passing is marked pressurized, the voltage value at that time to time is measured. Based on the measurement results, the current-voltage characteristics of the transfer member are calculated . Or by calculating means, the magnitude of the constant voltage different to the transfer member at the non-sheet passing is marked pressurized, each current value in the times is measured, current-voltage characteristics of the transfer member on the basis of their measurement results Is calculated .
[0009]
Thus the current-voltage characteristic of the transfer member by the calculating means in the are calculated by the voltage applying means, the voltage applied to the transfer member on the basis of the current-voltage characteristic calculated by the calculation means is applied is determined. When determining the applied voltage in the voltage applying unit, other conditions such as a paper passing condition may be considered in addition to the current-voltage characteristics calculated by the calculating unit. This is because the applied voltage can be determined with higher accuracy. Since the current-voltage characteristics of the transfer member are calculated in this way, even if the current-voltage characteristics of the transfer member change due to endurance changes of the transfer member, lot variations, humidity, etc., the necessary transfer current is transferred to the transfer member. applied voltage that can be flowed in is marked addition to the transfer member. As a result, an appropriate transfer current can always be applied during transfer, so that a good image with little image deterioration can be obtained.
[0010]
In the image forming apparatus according to the present invention, when applying a constant current to the transfer member, the calculating unit calculates an average value by measuring a voltage value with respect to the applied current a plurality of times, and calculates the average value. It is desirable to set the voltage value at the time. Alternatively, when applying a constant voltage to the transfer member, the calculation means calculates an average value by measuring a current value with respect to the applied voltage a plurality of times, and sets the average value as the current value at that time. desirable. This is because the current-voltage characteristics of the transfer member can be calculated with high accuracy.
[0011]
Further, in the image forming apparatus according to the present invention, the calculation means outputs a switching signal for controlling the switching operation of the high-voltage transformer, the transistor connected to the primary side of the high-voltage transformer and performing switching , Signal control means to which the current value and voltage value on the secondary side of the high-voltage transformer are fed back , based on either the current value or voltage value on the secondary side of the high-voltage transformer fed back to the signal control means, by outputting a constant current or constant voltage of several different sizes by changing the control of the switching signal by the signal control unit, and to calculate the current-voltage characteristic of the transfer member.
[0012]
In this image forming apparatus, in the calculation means, a switching signal output from the signal control means is input to the base of a transistor connected to the primary side of the high-voltage transformer. The switching operation of the transistor is controlled based on this switching signal. In addition, the current value and the voltage value on the secondary side of the high-voltage transformer are fed back to the signal control means. Therefore, the output from the calculation means is controlled by controlling the switching signal based on this feedback signal.
[0013]
Specifically, when the current value on the secondary side of the high-voltage transformer is fed back to the signal control means, the switching signal is controlled based on the current feedback signal, and the output control of the calculation means becomes constant current control. On the other hand, when the voltage value on the secondary side of the high-voltage transformer is fed back to the signal control means, the switching signal is controlled based on this voltage feedback signal, and the output control of the calculation means becomes constant current control. Further, by changing the output of the switching signal, the constant current value or the constant voltage value output from the calculating means is changed. Accordingly, a plurality of different constant current values or constant voltage values can be output as the output of the calculating means. As a result, the relationship between the current value and the voltage value in the transfer member can be measured under a plurality of conditions. For this reason, the current-voltage characteristic of the transfer member can be calculated with high accuracy.
[0014]
In the image forming apparatus according to the present invention, calculation detecting means, by changing the control of the switching signal based on these feedback signals, it is more desirable to change the constant current control and the constant voltage control to each other .
[0015]
Thus, by feeding back both the current value and the voltage value on the secondary side of the high-voltage transformer to the signal control means, the calculation means can perform either constant voltage control or constant current control. That is, when the voltage value is selected after selecting the current value as the feedback signal, the output control in the calculating means can be changed from the constant current control to the constant voltage control. Further, when the current value is selected after the voltage value is selected as the feedback signal, the output control in the calculating means can be changed from the constant voltage control to the constant current control. For this reason, it is not necessary to provide a constant current circuit and a constant voltage circuit separately.
[0016]
Therefore, in the image forming apparatus according to the present invention, the calculation unit can also serve as the voltage application unit. Thereby, the apparatus configuration is simplified.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, a most preferred embodiment embodying an image forming apparatus according to the invention will be described in detail with reference to the drawings. In the present embodiment, the present invention is embodied as an electrophotographic copying machine.
[0018]
The main part of the copier according to the present embodiment is shown in FIG. The copying machine is provided with a cylindrical photosensitive drum 14 that is driven to rotate in the direction of arrow A. Around the photosensitive drum 14, in order along the rotation direction, a charging device 17 for uniformly charging the surface of the photosensitive drum 14, and the surface of the uniformly charged photosensitive drum 14 are exposed to each color. The electrostatic latent image for each color formed on the surface of the photosensitive drum 14 and the exposure device 16 that forms the electrostatic latent image is developed with yellow toner, magenta toner, cyan toner, and black toner to form a toner image. Developing devices 15Y, 15M, 15C, and 15K and a cleaner 9 that removes toner remaining on the photosensitive drum 14 after transfer are provided.
[0019]
An endless intermediate transfer belt 12 wound around a plurality of rollers and driven to rotate in the direction of arrow B is disposed below the photosensitive drum 14. The intermediate transfer belt 12 is formed of a resin sheet material such as polycarbonate, and carbon black is dispersed so that the surface electrical resistance thereof is 10 ⁵ to 10 ¹² (Ω / cm ² ). A part of the intermediate transfer belt 12 comes into contact with the photosensitive drum 14 to form a primary transfer portion 18. In the primary transfer portion 18, each color toner image formed on the surface of the photosensitive drum 14 is sequentially primary transferred onto the intermediate transfer belt 14 to form a superimposed toner image. The intermediate transfer member is not limited to a belt shape, and may be another shape such as a drum or a roller.
[0020]
Further, the transfer roller 11 is disposed so as to sandwich the intermediate transfer belt 12 between the roller 13 that supports the intermediate transfer belt 12 and a secondary transfer portion 19 is formed. Therefore, an enlarged view of the secondary transfer portion 19 is shown in FIG. The transfer roller 11 is a semiconductive member having a resistance of 10 ⁵ to 10 ¹² (Ω / cm ² ), and a voltage having a polarity opposite to that of the toner is applied by the high voltage power source 20 at the time of secondary transfer. ing. As a result, a surface potential having a polarity opposite to that of the toner is generated on the copy sheet 10 conveyed along the direction of arrow C from the sheet feeding unit of the copying machine, and the superimposed toner image formed on the intermediate transfer belt 12 is formed. Can be transferred.
[0021]
Next, the high-voltage power supply 20 connected to the transfer roller 11 will be described with reference to FIG. As shown in FIG. 3, the high-voltage power supply 20 includes a high-voltage transformer 21 connected to a 24V power supply, a transistor 22 connected to the primary side of the high-voltage transformer 21, a plurality of resistors, an amplifier, a Zener diode, and the like. ing. The high-voltage power supply 20 is connected to a CPU 23 that controls the copy machine. A switching signal SW is output from the CPU 23 to the high-voltage power supply 20 and is input to the base of the transistor 22. On the other hand, the current value and voltage value of the secondary side of the high voltage transformer 21 are detected from the high voltage power supply 20 to the CPU 23, and the current feedback signal Ifb and the voltage feedback signal Vfb are respectively input to the A / D conversion input. As a result, the CPU 23 can measure the current and voltage in the transfer roller 11.
[0022]
The CPU 23 controls the output of the switching signal SW based on the current feedback signal Ifb and the voltage feedback signal Vfb, so that the voltage or current applied from the high-voltage power supply 20 to the transfer roller 11 is adjusted. ing. Here, the CPU 23 controls the switching signal SW based on the current feedback signal Ifb, thereby performing output control of the high-voltage power supply 20 by constant current control. On the other hand, the CPU 23 controls the switching signal SW based on the voltage feedback signal Vfb, thereby performing output control of the high-voltage power supply 20 by constant voltage control. That is, by configuring the circuit shown in FIG. 3, it is not necessary to have both a constant current circuit and a constant voltage circuit as in the prior art. Further, by controlling the output of the switching signal SW by the CPU 23, a plurality of different constant currents or constant voltages can be output.
[0023]
Next, the operation of the copying machine configured as described above will be described. When copying is started, image information of the original is read by a scanner or the like, and an image signal for image formation is generated. Further, the surface of the photosensitive drum 14 is uniformly charged by the charging device 17. Then, an electrostatic latent image for each color is written on the photosensitive drum 14 by the exposure device 16 based on the image signal for each color. These electrostatic latent images are developed by developing devices 15Y, 15M, 15C, and 15K, respectively, to form toner images of respective colors. The formation of the toner images of the respective colors on the photosensitive drum 14 is performed in the order of Y, M, C, and K.
[0024]
The toner images of the respective colors are conveyed to the primary transfer unit 18 where they are sequentially superimposed and transferred onto the intermediate transfer belt 12. Thus, a superimposed toner image is formed on the intermediate transfer belt 12. The superimposed toner image is conveyed to the secondary transfer unit 19 where it is transferred onto the copy paper supplied from the paper supply unit by the transfer roller 11. Thereafter, the toner image transferred onto the copy sheet is fixed on the print sheet by heating and pressing. Then, the fixed copy paper is discharged out of the apparatus, and the copy for one sheet is completed.
[0025]
Here, the setting control of the transfer voltage applied to the transfer roller 11, which is a feature of the present invention, will be described with reference to FIG. First, when the power of the copier is turned on, preliminary rotation of each device is started (S1). During this preliminary rotation, in addition to stabilization control of the secondary transfer unit 19, residual heat of the fixing device, density control of the developing devices 15Y, 15M, 15C, and 15K, and application voltage control of the intermediate transfer belt 12 are performed. .
[0026]
Next, a first constant current I _r1 is applied to the transfer roller 11 in order to estimate the current-voltage characteristics of the transfer roller 11. That is, the CPU 23 performs constant current control on the high voltage power source 20 and applies the first constant current I _r1 to the transfer roller 11. Then, the voltage V _r1 of the transfer roller 11 at this time is measured by the CPU 23 using the voltage feedback signal Vfb (S2). The current I _r1 may be set to a value near the minimum value of the current flowing through the transfer roller 11 during actual paper _feeding . Specifically, it may be about 10 ± 5 μA. The measurement of the voltage V _r1 of the transfer roller 11 is performed a plurality of times while the transfer roller 11 is rotated. Then, the CPU 23 calculates the average of those measured values and sets the average value as the first measured voltage V _r1 .
[0027]
Further, the second current I _r2 is applied to the transfer roller 11. That is, the CPU 23 controls the high-voltage power supply 20 at a constant current, and the second constant current I _r2 is applied to the transfer roller 11. Then, the voltage V _r2 of the transfer roller 11 at this time is measured by the CPU 23 using the voltage feedback signal Vfb (S3). Note that the current I _r2 may be set to a value near the maximum value of the current flowing through the transfer roller 11 during actual paper _feeding . Specifically, it may be about 25 ± 5 μA. The measurement of the voltage V _r2 of the transfer roller 11 is also performed a plurality of times in a state where the transfer roller 11 is rotated, as described above. Then, the CPU 23 calculates the average of those measured values and sets the average value as the second measured voltage V _r2 .
[0028]
Next, based on the measurement results obtained in S2 and S3, the current-voltage characteristic (slope a) of the transfer roller 11 is calculated (S4). In the present embodiment, the current-voltage characteristics of the transfer roller 11 are calculated by measuring only two points of the relationship between current and voltage. However, the current-voltage characteristics can be calculated more accurately by increasing the number of measurement points. can do. Further, in the present embodiment, calculates the current-voltage characteristic by measuring the voltage at that time a constant current to sign addition to the transfer roller 11, then a constant voltage to sign addition to the transfer roller 11 May be measured using the current feedback signal Ifb to calculate the current-voltage characteristics.
[0029]
When the current-voltage characteristic (inclination a) of the transfer roller 11 is calculated, one transfer table that determines the transfer voltage based on the detection voltage and the sheet passing condition is selected according to the magnitude of the inclination a. Specifically, when the inclination a is a> 150, the transfer table T1 shown in FIG. 5 is selected (S5). When the inclination a is a = 100, the transfer table T2 shown in FIG. 6 is selected (S6). If the inclination a is 100 <a ≦ 150, the transfer table T3 shown in FIG. 7 is selected (S7). When the transfer table is selected in this way, the transfer voltage is determined for each sheet passing condition based on the selected transfer table (S8).
[0030]
5 to 7 show only paper types as typical paper passing conditions, the transfer table may be subdivided according to temperature, humidity, paper size, and the like. This is because the transfer voltage can be set in more detail by subdividing the transfer table. In addition, the transfer voltage setting control described above is performed when there is a possibility that the current-voltage characteristics of the transfer roller may change in addition to when the power of the copier is turned on. Is executed when the temperature reaches a predetermined value or when the temperature / humidity changes by a predetermined value or more.
[0031]
Therefore, as shown in FIG. 8, when the current-voltage characteristic of the transfer roller 11 changes from L1 to L2, the subroutine shown in FIG. 4 is executed. That is, the first constant current I _r1 is applied to the transfer roller 11, and the voltage V _r12 of the transfer roller 11 at this time is measured (S2). Further, the second current I _r2 is applied to the transfer roller 11, and the voltage V _r22 of the transfer roller 11 at this time is measured (S3). Then, based on the measurement results obtained in S2 and S3, the slope a of the current-voltage characteristic L2 of the transfer roller 11 is calculated (S4). Next, according to the magnitude of the calculated inclination a, one that matches the current-voltage characteristic L2 is selected from the transfer tables T1 to T3 (S5 to S7). Then, the transfer voltage applied to the transfer roller 11 is determined according to the sheet passing condition by the transfer table selected based on the detection voltage V _r1 (S8).
[0032]
As described above, in the copying machine according to the present embodiment, the current-voltage characteristic (slope a) of the transfer roller 11 is calculated, and a transfer table that matches the characteristic is selected. Then, a transfer voltage to be applied to the transfer roller 11 is determined based on the selected transfer table. For example, as shown in FIG. 8, the current-voltage characteristics of the transfer roller 11 and it is necessary to flow a transfer current I to the transfer roller 11 in the case of changes from L1 L2, the V ₁ is the voltage applied to the transfer roller 11 been changed to V ₂ is marked pressure. For this reason, even when the current-voltage characteristic of the transfer roller 11 changes, an appropriate transfer current can be passed through the transfer roller 11. Therefore, a good image with little image deterioration can be obtained.
[0033]
In the above description, the transfer table is used when setting the transfer voltage. Instead of using the transfer table (stored in advance), the transfer voltage is calculated using an arithmetic expression. May be. Specifically, the transfer voltage may be calculated and set according to the following equation based on the current-voltage characteristics (slope a) of the transfer roller 11, the detection voltage, and the sheet passing condition.
(Transfer voltage) [V] = (Slope a) × (Detection current) [μA]
+ (B x 100 / a) + C [V]
Here, the slope a is the slope of the current-voltage characteristics, B is a correction value for each sheet passing condition, and C is an intercept. A typical value of the transfer voltage calculated by this equation is shown in FIG.
[0034]
As described above, according to the copying machine according to the present embodiment, the current-voltage characteristic of the transfer roller 11 is detected, and a transfer table that matches the characteristic is selected. That is, when the change in the current-voltage characteristic changes, a transfer table that matches the characteristic after the change is selected. Then, an optimum transfer voltage is set for each sheet passing condition according to the selected transfer table. For this reason, even when the current-voltage characteristics of the transfer roller 11 change, an appropriate transfer voltage is always set and secondary transfer is performed. As a result, an appropriate transfer current always flows through the transfer roller 11, and a good image can be obtained.
[0035]
In addition, this Embodiment is only a mere illustration and does not limit this invention at all. Accordingly, the present invention can be variously improved and modified without departing from the scope of the invention. For example, in the above-described embodiment, the case where the present invention is applied to a copying machine has been described. Further, although the transfer voltage setting control of the present invention is performed on the secondary transfer unit 19, it can of course be performed on the primary transfer unit 18. Furthermore, although the transfer roller 11 is used as the transfer member, the transfer roller 11 is not limited to the roller, and a contact-type conductive member such as a belt, a drum, a blade, or a brush can be used.
[0036]
【The invention's effect】
As described above, according to the image forming apparatus according to the present invention, an appropriate transfer current can always flow at the time of transfer, whereby a good image with little image deterioration can be obtained.
[Brief description of the drawings]
FIG. 1 is a diagram illustrating a schematic configuration of a main part of a copier according to an embodiment.
FIG. 2 is an enlarged view of a secondary transfer portion.
FIG. 3 is a diagram for explaining a configuration of a high-voltage power supply.
FIG. 4 is a flowchart showing control details of transfer voltage setting.
FIG. 5 is a diagram illustrating an example of a transfer table.
FIG. 6 is a diagram similarly showing an example of a transfer table.
FIG. 7 is a diagram similarly showing an example of a transfer table.
FIG. 8 is a diagram for explaining the effect of transfer voltage setting control according to the present invention.
FIG. 9 is a diagram illustrating a representative value of a transfer voltage calculated by an arithmetic expression.
FIG. 10 is a diagram for explaining a problem of conventional transfer voltage setting control.
[Explanation of symbols]
10 Copy Paper 11 Transfer Roller 14 Photosensitive Drum 20 High Voltage Power Supply 21 High Voltage Transformer 22 Transistor 23 CPU
SW switching signal Ifb current feedback signal Vfb voltage feedback signal

Claims (4)

A transfer member for electrostatically transferring an image carried on the image carrier to a transfer material;
Calculating means for calculating a current-voltage characteristic of the transfer member;
Voltage application means for determining and applying an applied voltage to the transfer member based on the current-voltage characteristics calculated by the calculation means,
The calculating means includes
A high-voltage transformer,
A transistor connected to a primary side of the high-voltage transformer and performing switching;
A signal control means for outputting a switching signal for controlling the switching operation of the transistor, and for feeding back a current value and a voltage value on the secondary side of the high-voltage transformer;
When the paper is not passed ,
Based on the current value on the secondary side of the high-voltage transformer fed back to the signal control means, the control of the switching signal by the signal control means is changed to apply a plurality of different constant currents and from time to time Measuring a voltage value, calculating a current-voltage characteristic of the transfer member based on a voltage value as a result of the measurement and an applied current value at that time ;
Based on the voltage value on the secondary side of the high-voltage transformer fed back to the signal control means, the control of the switching signal by the signal control means is changed to apply a plurality of constant voltages of different magnitudes and from time to time An image forming apparatus, comprising: measuring a current value and calculating a current-voltage characteristic of the transfer member based on a current value as a measurement result and an applied voltage value at that time . The image forming apparatus according to claim 1,
Before SL calculating means, these by changing the control of the switching signal based on the feedback signal, an image forming apparatus, characterized in that the switching between the constant current control and the constant voltage control to each other. The image forming apparatus according to claim 1 or 2 ,
The image forming apparatus, wherein the calculating unit also serves as the voltage applying unit. In the image forming apparatus according to any one of claims 1 to 3 ,
When the constant current or the constant voltage is applied to the transfer member, the calculation means calculates the average value by measuring the voltage value or the current value for the applied current a plurality of times, and calculates the average value at that time An image forming apparatus having a voltage value or a current value .

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