JP2008096687A - Image forming apparatus, transferring current setting method, and image forming method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus, a transfer current setting method and an image forming method optimally correcting transfer bias of a transfer means without deteriorating production capacity of a machine. <P>SOLUTION: By having the prescribed threshold value made to correspond to the detection result in the electric characteristic detection means varied according to the detection result by a temperature and humidity sensor, influence of temperature and humidity environment at the time can be eliminated in the image forming apparatus in correction of the current value carried out on the basis of a varied prescribed threshold value and the detection result of an electric characteristic detection means. Consequently, in the correction of the current value carried out on the basis of the detection result of the electric characteristic detection means and the varied prescribed threshold value at that time, only correction of the current value accompanied with resistance of a transfer means varied with time can be carried out without any influence from the temperature and humidity environment. In addition, by carrying out correction of the current value according to the temperature and humidity environment, setting of the current value made to flow into the transfer apparatus in total can be suitably carried out. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile, and more specifically, an image forming apparatus including a transfer device that transfers a toner image formed on an image carrier such as a photoconductor to a transfer material, and a transfer current. The present invention relates to a setting method and an image forming method.

  Conventionally, as an intermediate transfer type image forming apparatus, a photosensitive member, an intermediate transfer member, primary transfer means for transferring a toner image on the photosensitive member onto the intermediate transfer member, and a primary transfer toner image on the intermediate transfer member as a transfer material. A device having a secondary transfer means for transferring the image on the surface is known. The photoreceptor bears a toner image corresponding to image information. As the intermediate transfer member, for example, an endless intermediate transfer belt that is stretched around a plurality of rollers is used. As the primary transfer means, a transfer electric field formed between the photoreceptor and the intermediate transfer belt is used for primary transfer, and the transfer electric field formed between the intermediate transfer belt and the transfer material is used as the secondary transfer means. Used. The primary transfer unit is required to faithfully and stably transfer the toner image formed on the photosensitive member to the intermediate transfer member. Similarly, the secondary transfer unit is required to faithfully and stably transfer the toner image formed on the intermediate transfer member to the recording medium. That is, in order to realize the performance required for the primary transfer unit and the secondary transfer unit, it is necessary to perform stable transfer with high transfer efficiency.

  In such an image forming apparatus, a method is known in which the transfer bias applied to the transfer unit is controlled at a constant current. When this constant current control is used, even if the electrical resistance of the transfer means fluctuates in the energization or temperature / humidity environment, the applied voltage changes accordingly, so that the transfer electric field is stable and stable transfer performance can be obtained. it can. However, if the resistance of the transfer means is too low, the influence of the resistance of the toner layer becomes large, and there arises a problem that the transfer efficiency changes depending on whether the image area is small or large. Further, even when the resistance of the transfer unit is too high, the applied voltage becomes too high, causing current leakage, resulting in a problem that transfer efficiency is lowered. Furthermore, when the voltage is increased to the upper limit of the power supply performance, there is a problem that current may not flow and transfer may not be performed sufficiently, or the power supply may be broken.

  In general, the members of the transfer means such as the intermediate transfer belt and the transfer roller are gradually changed in resistance by applying a transfer voltage. For this reason, when the resistance of the transfer means changes with time, various problems as described above occur.

  In order to solve the above-described problems associated with fluctuations in resistance of the transfer means over time, the image forming apparatus described in Patent Document 1 detects the resistance value (voltage-current characteristics) of the transfer means, and the transfer means according to the detection result. The transfer bias to be applied to is controlled. In this control, since the resistance characteristic of the transfer means is actually detected, it is possible to set the transfer bias with high accuracy.

  Further, the resistance of the transfer means also changes depending on the temperature and humidity as described above. Therefore, by frequently performing the control as described in Patent Document 1, it is possible to detect a change in resistance due to temperature and humidity. However, the above control involves a mechanical operation in which a voltage is read by supplying a transfer current while the image forming operation is stopped. For this reason, if the detection is frequently performed, the number of times of stopping the image forming operation increases, resulting in a problem that the production capacity of the machine is reduced.

Therefore, as in the image forming apparatus described in Patent Document 2, the correction value is selected from the environment correction table using the temperature / humidity detected by the temperature / humidity detecting means capable of detecting the temperature / humidity environment without stopping the image forming operation. Then, by correcting the reference current value with the correction value, the mechanical operation performed by stopping the image forming operation as described above is not accompanied, so that it is possible to suppress the disadvantage that the production capacity is reduced. it can.
However, in the image forming apparatus described in Patent Document 2, since the transfer bias is corrected only in the temperature and humidity state without considering the influence of the temporal change in resistance to the transfer unit, an optimal transfer bias is set. The problem that it cannot be done occurs.

JP 2003-195657 A JP 2005-134415 A

Therefore, it is possible to produce a machine by providing a control unit that detects a resistance that changes over time of the transfer unit and corrects the transfer bias, and a control unit that corrects the transfer bias using a correction table using the detection result of temperature and humidity. It is possible to correct the development bias with respect to environmental changes without reducing the capability, and it is also possible to correct the transfer bias due to a change in resistance to the transfer means over time.
However, when the correction by the two means is performed at substantially the same timing,
The following problems occur. That is, the above correction performed by detecting the resistance of the transfer means that changes over time is always performed based on the resistance value of the transfer means changed according to the temperature and humidity environment at that time. The transferred bias that has already been corrected appropriately in consideration of the temperature and humidity environment at that time. In addition, if the above correction is performed by detecting temperature / humidity, the correction considering the temperature / humidity environment is performed twice, so that the transfer bias is excessively corrected and the transfer bias is corrected. Will not be set optimally.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus and a transfer current setting method capable of optimally correcting the transfer bias of the transfer unit without reducing the production capacity of the machine. And an image forming method.

In order to achieve the above object, the invention of claim 1 is to apply a constant current controlled bias to an image carrier that carries a toner image and a transfer member to which the toner image is transferred from the image carrier. Thus, a transfer means for forming a transfer electric field in a region where the image carrier and the transfer member are opposed to each other, and an electrical characteristic detection means for detecting a characteristic value corresponding to a resistance value on a path through which a current passed through the transfer means flows. And a temperature / humidity detecting means for detecting a temperature / humidity environment in the apparatus main body, the correction of the current value passed through the transfer means based on the detection result of the electrical characteristic detecting means and a predetermined threshold value First correction means for performing the correction, second correction means for correcting the current value based on the detection result of the temperature / humidity detection means, and the predetermined threshold value based on the detection result of the temperature / humidity detection means. Having third correcting means for correcting It is an butterfly.
According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the correction of the current value by the first correction unit is performed when the detection result of the electric characteristic detection unit is lower than the predetermined threshold value. Is characterized in that it is performed so as to be higher than the current value at the time of detecting the electrical characteristics.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the correction of the current value by the first correction unit is performed when the detection result of the electric characteristic detection unit is higher than the predetermined threshold value. Is characterized in that it is performed so as to be lower than the current value at the time of detecting the electrical characteristics.
According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second, or third aspect, the electrical characteristic detecting means detects at least a resistance value of the transfer means. .
According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the characteristic value detected by the electric characteristic detecting means includes a voltage value of the transfer means, and the resistance value is It is detected based on a voltage value.
According to a sixth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth or fifth aspect, the transfer means transfers the toner image on the image carrier to an intermediate transfer member. It is characterized by.
According to a seventh aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, fifth or sixth aspect, the image forming apparatus has a plurality of the predetermined threshold values.
According to an eighth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, sixth, or seventh aspect, the detection operation by the electrical characteristic detection unit is performed to detect a positional deviation between toner images of different colors. It is characterized in that it is performed within the alignment operation to be corrected.
According to a ninth aspect of the present invention, in the image forming apparatus of the first, second, third, fourth, fifth, sixth, seventh or eighth aspect, the detection operation by the electric characteristic detecting means detects the toner adhesion amount and This is characterized in that it is performed within a toner density adjustment operation for density adjustment.
According to a tenth aspect of the present invention, in the image forming apparatus of the ninth aspect, the correction of the current value is performed before the toner density adjustment by the toner density adjustment operation.
According to the eleventh aspect of the present invention, the bias between the image carrier and the transfer member is applied by applying a constant current controlled bias to the transfer member to which the toner image is transferred from the image carrier carrying the toner image. Detect the characteristic value according to the resistance value on the path through which the current flowing through the transfer means that forms the transfer electric field in the opposing area and the temperature / humidity environment in the device body, and at least detect the characteristic value In the transfer current setting method in the image forming apparatus that sets the transfer current based on the result and the detection result of the temperature / humidity environment, the current value that flows to the transfer unit based on the detection result of the characteristic value and a predetermined threshold value Correction of the current value based on the detection result of the temperature / humidity environment, and correction of the predetermined threshold based on the detection result of the temperature / humidity environment.
According to a twelfth aspect of the present invention, there is provided a step of applying a constant current controlled bias to a transfer member to which a toner image is transferred from an image carrier by a transfer means, and a current passed through the transfer means when the bias is applied. In an image forming method that performs a step of detecting a characteristic value corresponding to a resistance value on a path through which a current flows and a step of detecting a temperature / humidity environment in the apparatus main body, the detection result of the characteristic value and a predetermined threshold value Correcting the current value flowing through the transfer means based on the correction value, correcting the current value based on the detection result of the temperature / humidity environment, and correcting the predetermined threshold value based on the detection result of the temperature / humidity environment. It is characterized by.

  In the present invention, the third correction unit corrects a predetermined threshold used when the first correction unit performs correction based on the detection result of the temperature / humidity detection unit. Thereby, in the correction of the current value passed through the transfer unit by the first correction unit performed using the corrected predetermined threshold, the influence of the temperature and humidity environment at that time can be eliminated. Therefore, in the correction of the current value by the first correction unit, it is possible to perform only the correction of the current value associated with the resistance of the transfer unit that has changed with time without being affected by the temperature and humidity environment. In addition, by correcting the current value according to the temperature and humidity environment by the second correction unit, it is possible to appropriately set the current value flowing through the transfer unit in total.

  As described above, according to the present invention, there is an excellent effect that the transfer bias of the transfer unit can be optimally corrected without reducing the production capacity of the machine.

Hereinafter, an embodiment in which the present invention is applied to a color copying machine as an image forming apparatus will be described.
FIG. 2 is an overall configuration diagram showing a color copying machine embodying the present invention. This color copying machine is a tandem type electrophotographic apparatus using an intermediate transfer belt 10, a paper feeding table 2 at the bottom, a copying machine main body 1 above it, and a scanner 3 and automatic document feeding at the top. A device (ADF) 4 is provided.
The copying apparatus main body 1 is provided with a transfer device 20 having an endless intermediate transfer belt 10 at the substantially center. The intermediate transfer belt 10 is stretched by a driving roller 9 and driven rollers 15 and 16, and is shown in the figure. The residual toner remaining on the surface after image transfer is removed by the cleaning device 17 that rotates clockwise and is provided on the left side of the driven roller 15, so that the transfer device 20 can prepare for another image formation.
Four image forming portions of yellow, cyan, magenta, and black are formed above the linear intermediate transfer belt 10 spanned between the driving roller 9 and the driven roller 15 along the moving direction. Drum-shaped photoconductors 40Y, 40C, 40M, and 40K (hereinafter simply referred to as photoconductors 40 unless otherwise specified) are provided so as to be rotatable counterclockwise in the figure, around which are charging devices 18, A developing device 61, a primary transfer roller 62 constituting the primary transfer means 60, a photoconductor cleaning device 63, and a charge eliminating device 64 are provided, and an exposure device 21 is provided above the photoconductor 40.

A secondary transfer device 22 constituting secondary transfer means is provided below the intermediate transfer belt 10. The secondary transfer device 22 is in pressure contact with the driven roller 16 via the intermediate transfer belt 10. Then, the secondary transfer device 22 collectively transfers the toner images on the intermediate transfer belt 10 onto a sheet as a recording medium fed to the intermediate transfer belt 10.
A fixing device 25 for fixing the toner image formed on the sheet is provided downstream of the secondary transfer device 22 in the sheet conveying direction, and a pressure roller 27 is pressed against the endless fixing belt 26. The image-transferred sheet is conveyed to the fixing device 25 by an endless conveyance belt 24 that is stretched between a pair of rollers 23 and 23. The secondary transfer device 22 may be a transfer device using a transfer roller or a non-contact charger. A sheet reversing device 28 for reversing the sheet when forming images on both the front and back sides of the sheet is provided below the secondary transfer device 22.

  When making a color copy with the color copying machine having the above-described configuration, the document is usually set on the document table 30 of the automatic document feeder 4, but when the document is manually set, The automatic feeding device 4 is opened, a document is set on the contact glass 32 of the scanner 3, and the document is pressed against the contact glass 32 by closing the automatic document feeding device 4.

Next, when a start switch (not shown) is pressed, when the document is set on the automatic document feeder 4, the document is automatically fed onto the contact glass 32. When the document is manually set on the contact glass 32, the scanner is immediately scanned. 3 operates, and the first traveling body 33 and the second traveling body 34 start traveling. Thereby, the light from the light source of the first traveling body 33 is emitted toward the document, the reflected light from the document surface is reflected by the mirror of the first traveling body 33 toward the second traveling body 34, and further the second A direction of 180 degrees is changed by a pair of mirrors of the traveling body 34, passes through the imaging lens 35, and enters the reading sensor 36 to read the contents of the document.
Further, when the start switch is pressed, the intermediate transfer belt 10 starts rotating, and at the same time, each of the photoconductors 40Y, 40C, 40M, and 40K also starts rotating and yellow (Y) and cyan on each photoconductor. (C) Monochrome images of magenta (M) and black (K) are formed. Each single-color image formed on each photoconductor in this way is superimposed and sequentially transferred onto the intermediate transfer belt 10 that rotates in the clockwise direction in the drawing to form a full-color composite color image.

The paper feed roller 42 of the selected paper feed stage in the paper feed table 2 rotates, and the sheet is fed out from the selected paper feed cassette 44 in the paper bank 43 and separated into a single sheet by the separation roller 45 and fed. It is conveyed to the paper path 46. The fed sheet is conveyed by the conveying roller 47 to the paper feeding path 48 of the copying machine main body 1 and comes into contact with the registration roller 49 to be temporarily stopped. In the case of manual feeding, the sheet set on the manual feeding tray 51 is fed out by the rotation of the paper feeding roller 50, separated into one sheet by the separation roller 52, and conveyed to the manual paper feeding path 53. The roller 49 comes into contact with the roller 49 and temporarily stops.
In any case, the registration roller 49 starts to rotate at an accurate timing according to the color image on the intermediate transfer belt 10, and the sheet that has been stopped is placed between the intermediate transfer belt 10 and the secondary transfer device 22. The color image is transferred onto the sheet by the secondary transfer device 22 described above. The sheet on which the color image has been transferred is transported to the fixing device 25 by the secondary transfer device 22 having a transport function, heated and pressed to fix the transferred image, and then guided to the discharge side by the switching claw 55. The paper is discharged onto the paper discharge tray 57 by the discharge roller 56 and stacked.
When the double-sided copy mode is selected, the sheet on which the image is formed on the front surface is conveyed to the sheet reversing device 28 side by the switching claw 55, reversed and guided again to the transfer position, and the image is formed on the back surface. Then, the paper is discharged onto a paper discharge tray 57 by a discharge roller 56.

When a black single color image is formed on the intermediate transfer belt 10, the driven rollers 15 and 16 other than the driving roller 9 are moved so that the yellow, cyan, and magenta photoconductors 40 Y, 40 C, and 40 M are transferred to the intermediate transfer belt 10. It is trying to keep away from. In the so-called 1-drum type image forming apparatus having only one photoconductor 40 instead of the tandem type shown in FIG. 2, black image formation is first performed in order to increase the first copy speed. After that, the remaining colors are imaged only when the original is in color.
In such a configuration, the registration roller 49 is usually used while being grounded, but a bias can be applied to remove paper dust from the sheet. For example, when a bias is applied using a conductive rubber roller having a diameter of 18 mm and a surface covered with a conductive NBR rubber having a thickness of 1 mm, the volume resistance of the rubber material is about 10 ⁹ Ωcm, and the toner transfer side (surface Side) and a voltage of about +200 V is applied to the back side of the sheet. In general, in the intermediate transfer method, paper dust is difficult to move to the photoreceptor 40, so there is little need to consider paper dust transfer, and there is no problem even if it is grounded. Although a DC bias is generally applied as the applied voltage, an AC voltage having a DC offset component can be applied to charge the sheet more uniformly.
Since the surface of the sheet after passing through the registration roller to which the bias is applied in this way is slightly charged to the negative side, when voltage is not applied to the registration roller 49 in the transfer from the intermediate transfer belt 10 to the sheet. The transfer conditions may change as compared to the above, and the transfer conditions may be changed.

By the way, in the intermediate transfer type copying machine as described above, there is a method in which the transfer bias applied to the transfer device 20 is controlled at a constant current.
When the transfer device 20 is controlled at a constant current, even if the electrical resistance of the transfer device 20 fluctuates in an energization or temperature / humidity environment, the applied voltage changes accordingly, so that the transfer electric field is stable and stable transfer performance is achieved. Obtainable. However, when the resistance of the transfer device 20 is too low, the influence of the resistance of the toner layer increases, and the voltage applied to the transfer device 20 varies greatly depending on the image area, and the transfer efficiency is high when the image area is small and large. It will change. Further, even when the resistance of the transfer device 20 is too high, if the applied voltage becomes too high, current leakage may occur and the image may be disturbed, or the voltage may increase to the upper limit of the power supply performance. There is a problem in that there is a risk that transfer will not be performed sufficiently due to the loss of flow or the power supply will be broken. On the other hand, the members of the transfer device 20 such as the intermediate transfer belt 10 and the primary transfer roller 62 generally have a resistance that gradually changes due to application of a transfer voltage. Therefore, when the resistance of the transfer device 20 changes with time, the above-described problem may occur. Therefore, a specific configuration for solving these problems will be described below.

[Example 1]
In the present embodiment, the transfer bias applied to the primary transfer roller 62 is controlled at a constant current, and the electrical characteristic detection unit 65 that detects the resistance value of the transfer device 20 by detecting the applied voltage is employed. . The voltage detection of the transfer device 20 may be any of voltage detection of only the primary transfer roller 62, voltage detection of only the intermediate transfer belt 10, and voltage detection of the primary transfer roller 62 and the intermediate transfer belt 10.

FIG. 3 shows the result of examining the detection voltage when the constant current control value is changed by changing the resistance of the primary transfer roller 62 (hereinafter referred to as “roller resistance”). When the current used for actual detection is set to 30 μA, for example, the detection voltage is as shown in Table 1. The transfer voltage varies depending on the roller resistance. The higher the resistance, the higher the voltage.

Next, the results of examining the primary transfer rate (ratio between the toner adhesion amount on the intermediate transfer belt 10 and the toner adhesion amount on the photosensitive member) when the constant current control value is changed by changing the roller resistance are shown in FIG. 4 shows. In this transfer rate measurement, a pattern having a small image area (5% area with respect to the entire width in the width direction) was used.
As described above, since the transfer bias that maximizes the transfer rate varies depending on the change in roller resistance, it is necessary to correct the applied bias. Table 2 shows a summary of the transfer bias that gives the maximum transfer rate.

From Table 2, when the reference roller resistance is 7.5th power (1 × 10 ^7.5 [Ω]), the appropriate transfer bias is 30 μA, and when the roller resistance is 7.0th power, the bias value Is corrected to +5 μA to 35 μA, and when it becomes 8.0 power, the bias value is corrected to −5 μA to 25 μA. On the other hand, when the roller resistance is 9.0, the image is disturbed due to discharge. Table 3 shows a situation in which image disturbance due to discharge occurs when the roller resistance and the transfer bias are changed.

  As shown in Table 3, when the roller resistance is 9.0, the image is disturbed by discharge at 25 μA, but not at 20 μA. Further, FIG. 4 shows that when the roller resistance is 9.0 power, the transfer rate hardly changes even when the transfer bias is 20 μA or 25 μA. Therefore, in this case, it is understood that the bias value is corrected by −10 μA to 20 μA.

These transfer bias corrections are determined based on whether the detection voltage shown in FIG. 3 or Table 1 is lower or higher than the voltage threshold. For example, if the threshold when the current used for actual detection is 30 μA is set as shown in Table 4, when the roller resistance is 7.0, the voltage is 0.82 kV from Table 1 and is less than the first threshold. In the case of the 0th power, since the voltage is 2.6 kV from Table 1, it becomes the third threshold value or more.

Table 5 shows the relationship between the threshold value and the correction. As a result, when the roller resistance that is less than the first threshold is 7.0, the transfer bias 30 μA used for detection is corrected to +5 μA to 35 μA, and the transfer bias that sets the transfer rate to the maximum from Table 2 is set. become. When the roller resistance that is equal to or greater than the third threshold is 9.0, the transfer bias 30 μA used for detection is corrected by −10 μA to 20 μA, and the transfer bias that maximizes the transfer rate is set according to Table 2. .

  The above is summarized as shown in FIG. This makes it possible to select a transfer bias that maximizes the transfer rate even when the roller resistance changes, and to prevent image defects. In addition, here, the resistance of the primary transfer roller 62 is changed. However, when the resistance of the intermediate transfer belt 10 is changed, the same change is exhibited. Therefore, the effect can be obtained by performing the same transfer bias correction. The transfer bias correction control performed based on the electrical characteristic detecting means 65 and a predetermined threshold is performed by a control unit (not shown) in the apparatus main body.

Next, details of the environmental correction control using the temperature / humidity sensor 66 for detecting the temperature / humidity environment will be described. The temperature / humidity sensor 66 used in this embodiment is TDK / CHS-CSC-18, which can detect the temperature from the thermistor output and can detect the humidity from the output of the temperature / humidity sensor 66.
The temperature / humidity detection timing is sampled every 1 minute after the power is turned on. Moreover, the timing which performs environmental correction is performed with the same period as a temperature / humidity detection timing. The installation location of the temperature / humidity sensor 66 is not particularly limited, but is preferably located away from a heat source such as the fixing device 25, and may be provided below the paper feed cassette 44. It is attached in the apparatus main body near the tray 51.

The control flow will be described with reference to FIG. First, the thermistor output in the temperature / humidity sensor 66 is detected, and the temperature is determined from the thermistor output-temperature conversion table based on the correlation between the thermistor output and temperature (S1). Next, the humidity sensor output in the temperature / humidity sensor 66 is detected, and the relative humidity is determined from the temperature obtained above and the humidity sensor output-relative humidity conversion table (S2). In this table, the relative humidity is obtained by setting the temperature to the horizontal and the humidity to the vertical. Next, the absolute humidity is calculated from the relative humidity obtained above and the relative humidity-absolute humidity conversion table (S3). In this table, relative humidity is set horizontally and temperature is set vertically, and absolute humidity is obtained. The absolute humidity can also be obtained from the temperature and relative humidity by a calculation formula. Next, the current environment is determined from the absolute humidity obtained above and the absolute humidity-current environment conversion table (S4). The current environment includes, for example, LL (19 ° C. 30%), ML (23 ° C. 30%), MM (23 ° C. 50%), MH (23 ° C. 80%), HH (27 ° C. 80%), and the like. However, the values and combinations of temperature and humidity are not limited to these. Finally, the transfer current value is corrected with the correction amount corresponding to the current environment obtained above (S5). The correction current value is determined from the relationship shown in Table 6, for example. In this embodiment, α is 5 μA and β is 10 μA. However, the relationship between the current environment and the correction current value is not limited to this.

Since the resistance of the primary transfer roller 62 or the resistance of the intermediate transfer belt 10 changes depending on the temperature and humidity, the appropriate transfer bias also changes. Therefore, the correction of the transfer bias according to the output of the temperature / humidity sensor 66 is effective as a method for obtaining an appropriate transfer bias.
In addition, if the voltage detection of the primary transfer unit 60 described in the present embodiment is frequently performed, a change in resistance of the primary transfer unit 60 due to temperature and humidity can be detected by the voltage detection. Detection by 66 is not necessarily required.

However, the voltage detection of the transfer device 20 by the electrical property detection means 65 needs to be accompanied by a machine operation of passing a transfer current for a certain time and reading the voltage, and if it is frequently performed, the production capacity of the machine is lowered. Leads to. In that respect, the detection by the temperature / humidity sensor 66 does not require any mechanical operation, and therefore can always be monitored.
On the other hand, when the voltage detection and the temperature / humidity detection by the temperature / humidity sensor 66 are performed at the same time, if the voltage detection is performed after the temperature / humidity environment changes, there is a problem that the correction related to the temperature / humidity environment is doubled. Get up. Therefore, as a countermeasure, the voltage threshold value used for the current value correction by the voltage detection is changed according to the detection result of the temperature / humidity sensor 66. The transfer bias correction control based on the detection result of the temperature / humidity sensor 66 and the voltage threshold correction control are performed by a control unit (not shown) in the apparatus main body.

Next, details will be described. When the temperature and humidity environment is 27 ° C. and 80%, the roller resistance changes from 7.5 to 7.0 power, and the appropriate current is changed from 30 μA to 35 μA, compared to the case where the temperature and humidity environment is 23 ° C. and 50%. . FIG. 7 shows a case where the voltage threshold value is not changed by temperature and humidity at this time. However, correction by +5 μA is performed for both correction by voltage detection and output by the temperature / humidity sensor 66, and thus correction of a total of +10 μA is performed. In other words, the corrected current value is 40 μA, and an appropriate transfer bias is deviated from FIG. On the other hand, FIG. 1 shows a case where the voltage threshold is changed by temperature and humidity at this time. When the temperature and humidity environment is 27 ° C. and 80%, the voltage threshold is set lower than when the temperature and humidity environment is 23 ° C. and 50%. Then, with the detection voltage of 900 V, the bias correction is determined to be in the range of 0, and is corrected by +5 μA by the environmental correction, so that an appropriate control value of 35 μA is set.
As a result, it is possible to correct the transfer bias appropriately against a change in resistance due to the temperature and humidity environment, and it is possible to minimize the frequency of the voltage detection operation.

  However, as described above, voltage detection needs to be accompanied by a mechanical operation of passing a transfer current for a certain period of time and reading the voltage, so that the problem that the production capacity of the machine due to the voltage detection operation is reduced is completely solved. Not. On the other hand, in general, in a copying machine that forms a color image as in the present embodiment, a positional deviation correction operation for each color is performed in order to prevent the positional deviation of each color. This misalignment correction operation is often performed with a time dedicated for misalignment operation other than during image formation. For this reason, in the present embodiment, the voltage detection operation is performed when the positional deviation correction operation is performed.

Next, correction of misregistration of each color toner image will be described.
A patch pattern for detecting misalignment as shown in FIG. 8 is formed near both ends and the center of the intermediate transfer belt 10 in the width direction. These three patch patterns respectively formed near both ends and near the center of the intermediate transfer belt 10 are four Y, M, C, K reference toner images Sy, Sm, Sc, which are arranged at predetermined intervals in the sub-scanning direction. The reference toner images of the same color are formed so as to be aligned in the main scanning direction.

  In FIG. 8, each reference toner image in the patch pattern formed near the front side end in the belt width direction is detected by the first end P sensor 151. Each reference toner image in the patch pattern formed near the center in the belt width direction is detected by the center P sensor 152. Further, each reference toner image in the patch pattern formed in the vicinity of the back end in the belt width direction is detected by the second end P sensor 153. If the formation timings of the reference toner images of the respective colors are appropriate, the detection intervals of the reference toner images are equal to each other, but if they are inappropriate, the formation intervals of the reference toner images of the respective colors are not equal. Also, the detection intervals are not equal. If there is no optical writing positional deviation in the optical system, the reference toner images of the same color are detected at the same timing between the three patch patterns. However, if there is a positional deviation, the detection timing is Come different. A control unit (not shown) provided in the apparatus main body adjusts the optical system based on the detection interval and detection timing of each color toner image in the main scanning direction and the sub-scanning direction, and suppresses misregistration of each color.

  By performing voltage detection of the transfer device 20 when performing such misregistration correction of each color, it is possible to suppress a decrease in machine production capacity due to the voltage detection alone.

[Example 2]
Next, Example 2 will be described. The correction of the transfer bias and the description of the configuration related thereto are the same as those in the first embodiment, so that the description thereof will be omitted, and the characteristic part in the second embodiment will be described. In detail, the timing which performs the voltage detection operation | movement of the transfer apparatus 20 by the electrical property detection means 65 is demonstrated.
In general, in a copying machine that forms a color image as in the present embodiment, a toner adhesion amount is detected to stabilize the image density, and a toner density adjustment operation based on the detection result is performed. In many cases, this toner density adjustment operation is performed with a dedicated time for toner density adjustment operation other than during image formation. Therefore, in this embodiment, the voltage detection operation is performed when the toner density adjustment operation is performed.

  Next, detection of the toner adhesion amount on the intermediate transfer belt 10 will be described. In this embodiment, a toner density adjustment operation for optimizing the image density of each color is executed when the power is turned on or whenever a predetermined number of prints are performed. In this toner density adjustment operation, density detection patches (hereinafter referred to as “reference patterns”) are formed on the photosensitive drums 40Y, 40M, 40C, and 40K, respectively. The reference patterns formed on the respective photoconductive drums 40Y, 40M, 40C, and 40K are made to be continuous tone reference patterns by sequentially switching the charging bias and the developing bias. That is, in this embodiment, a linear reference pattern in which the toner adhesion amount changes in gradation is created along the surface movement direction of the photosensitive drum 40. Then, this reference pattern is transferred onto the intermediate transfer bell 10, and the transferred reference pattern is detected by a P sensor provided at a position facing the intermediate transfer belt 10.

  Further, a detection result by the P sensor and a predetermined target adhesion amount are compared by a control unit (not shown). Based on the comparison result, the control unit functions as an image density control unit, and the intensity of the laser beam of the optical system, the charging bias applied to the charging device 18, the developing bias applied to the developing sleeve, and the developing device 61. The toner replenishment amount and the like are appropriately changed to adjust the image density to a desired density.

By performing voltage detection of the transfer device 20 when performing such toner density adjustment operation, it is possible to suppress a decrease in the production capacity of the machine accompanying the voltage detection operation.
Further, in the toner density adjustment operation, as described above, the image forming condition is changed in accordance with the detection result of the toner adhesion amount. Therefore, when the toner adhesion amount detection is performed on the intermediate transfer belt 10 after the primary transfer, the following problems may occur.
The resistance of the transfer device 20 has changed, and the primary transfer efficiency has decreased.
In the toner density adjustment, the toner adhesion amount was adjusted so that the toner density on the intermediate transfer belt 10 became an appropriate value.
・ Image density is no problem.
-The image density becomes excessive because the toner adhesion amount is increased.
Therefore, by executing the voltage detection and current correction of the transfer device 20 within the toner density adjustment operation and before the toner density adjustment, the toner density can be adjusted in a state where the primary transfer is appropriately performed. The above-described problems can be prevented.

As described above, according to the present embodiment, the constant current-controlled bias is applied to the photoreceptor 40 that is an image carrier that carries a toner image and the intermediate transfer belt 10 that is a transfer member to which the toner image is transferred from the photoreceptor 40. Is applied to the transfer device 20, which is a transfer means for forming a transfer electric field in a region where the photoconductor 40 and the intermediate transfer belt 10 face each other, and a characteristic corresponding to a resistance value on a path through which a current flowing through the transfer device 20 flows In a copying machine which is an image forming apparatus provided with an electrical characteristic detection means 65 for detecting a value and a temperature / humidity sensor 66 which is a temperature / humidity detection means for detecting a temperature / humidity environment in the apparatus main body, Based on the detection result of the temperature / humidity sensor 66 and the control unit provided in the apparatus main body, which is a first correction unit that corrects the value of the current flowing through the transfer device 20 based on the detection result and a predetermined threshold. The control unit that is a second correction unit that corrects the current value, and the control unit that is a third correction unit that corrects the predetermined threshold based on the detection result of the temperature and humidity sensor 66. ing. Thereby, the correction of the current value accompanying the change in resistance of the transfer device 20 with time can be performed based on the detection result of the electrical characteristic detection means 65 and the predetermined threshold value. Further, the correction of the transfer bias due to the resistance change of the transfer device 20 due to the change in temperature and humidity is performed based on the detection result of the temperature and humidity detection sensor, so that the electrical characteristic detection means 65 frequently detects the machine. It can suppress that production capacity falls. Furthermore, by changing the predetermined threshold value corresponding to the detection result of the electrical characteristic detection unit 65 according to the detection result of the temperature / humidity sensor 66, the changed predetermined threshold value and the detection result of the electrical characteristic detection unit 65 are changed. In the correction of the current value performed based on this, the influence of the temperature and humidity environment at that time can be eliminated. Therefore, the correction of the current value at this time, which is performed based on the detection result of the electrical characteristic detection means 65 and the changed predetermined threshold value, has no influence on the temperature and humidity environment and the transfer device 20 that has changed over time. Only the correction of the current value associated with the resistance can be performed. In addition, by correcting the current value according to the temperature and humidity environment, it is possible to appropriately set the current value to be passed through the transfer device 20 in total. Therefore, the transfer bias applied to the transfer device 20 can be optimally corrected without reducing the production capacity of the machine.
Further, according to the present embodiment, the correction of the current value performed based on the electrical characteristic detection unit 65 and the predetermined threshold value is such that the detection result detected by the electrical characteristic detection unit 65 is greater than the predetermined threshold value. When it is low, the bias is set higher than the bias applied at the time of detecting the electric characteristics, and when it is higher than the predetermined threshold, the bias is set lower than the bias applied at the time of detecting the electric characteristics. Thereby, even if the resistance of the transfer device 20, for example, the resistance of the primary transfer roller 62 changes, the transfer bias that maximizes the transfer rate can be selected, and image defects can be prevented.
Further, according to the present embodiment, the electrical characteristic detecting means 65 detects at least the resistance value of the transfer device 20. If the resistance of the transfer device 20 is too low, the influence of the resistance of the toner layer increases, and the voltage applied to the transfer device 20 varies greatly depending on the image area, and the transfer efficiency changes depending on whether the image area is small or large. There is a problem. Also, if the resistance of the transfer device 20 is too high, there is a problem that the applied voltage becomes too high, causing current leakage and disturbing the toner image. Therefore, the above problem can be solved by detecting the resistance value of the transfer device 20 and correcting the current value based on the detection result.
Further, according to the present embodiment, the characteristic value detected by the electric characteristic detecting means 65 includes the voltage value of the transfer device 20, and the resistance value is detected based on the voltage value. Is. The electrical characteristic detecting means 65 can detect the resistance of the transfer device 20 by measuring the current under constant voltage control, but in the case of having a constant current power source for forming a transfer electric field. Since it is only necessary to measure the voltage under constant current control and detect the resistance of the transfer device 20, only one power source is required. Space becomes possible.
Further, according to the present embodiment, the present invention performs the primary transfer, that is, the intermediate transfer of the toner image on the photoreceptor 40 to the intermediate transfer belt 10 that is an intermediate transfer body, and finally transfers the toner image onto the sheet. This is applied to the transfer device 20 in the configuration. The present invention is also effective when applied to transfer means for transferring directly from the photoreceptor 40 onto a sheet or transfer means for transferring from the intermediate transfer belt 10 onto a sheet. However, the transfer from the photosensitive member 40 to the intermediate transfer belt 10 is more affected by the resistance of the toner layer than there is a sheet, and the transfer efficiency is higher when the transfer means has a lower resistance. It is easy to cause decline. Therefore, a greater effect can be obtained by applying the present invention to the transfer device 20. In addition, by using the intermediate transfer belt 10, it is possible to prevent a change in transferability and color misregistration due to the thickness and type of the sheet, rather than transferring directly from the photoreceptor 40 to the sheet.
Moreover, according to this embodiment, it has two or more said threshold values. Thus, by having a plurality of the threshold values, even if the resistance of the transfer device 20 changes greatly, it is possible to perform current value correction corresponding to the resistance, and transfer can be always performed in an optimum state. Further, it is possible to simultaneously improve the transfer efficiency when the resistance of the transfer device 20 is low and prevent current leakage when it is high.
Further, according to the present embodiment, the detection operation by the electrical characteristic detection unit 65 is performed within a registration operation for correcting the positional deviation of the toner images of different colors. As described above, when the positional deviation correction of each color is performed, the voltage detection of the transfer device 20 is also performed, so that it is possible to suppress a decrease in the production capacity of the machine due to the voltage detection operation of the electrical characteristic detection unit 65 independently. it can.
Further, according to the present embodiment, the detection operation by the electrical characteristic detection unit 65 is performed within a toner concentration adjustment operation in which the toner adhesion amount is detected by detecting the toner adhesion amount. Thus, by performing voltage detection of the transfer device 20 when performing the toner density adjustment operation, it is possible to suppress a decrease in machine production capacity due to the voltage detection operation of the electrical characteristic detection unit 65 independently. .
According to the present embodiment, the current value is corrected before the toner density adjustment by the toner density adjustment operation. As a result, toner density adjustment can be performed in a state where primary transfer is appropriately performed.
Further, according to the present embodiment, the correction of the current value to be passed through the transfer device 20 based on the detection result of the characteristic value and the predetermined threshold, and the correction of the current value based on the detection result of the temperature and humidity environment, By applying the present invention to the transfer current setting method for setting the transfer current by performing the correction of the predetermined threshold based on the detection result of the temperature and humidity environment, the optimum transfer current is set. Can do.
Further, according to the present embodiment, the correction of the current value to be passed through the transfer device 20 based on the detection result of the characteristic value and the predetermined threshold, and the correction of the current value based on the detection result of the temperature and humidity environment, By applying the present invention to an image forming method for correcting the predetermined threshold based on the detection result of the temperature and humidity environment, it is possible to perform image formation with an optimum transfer bias.

Explanatory drawing at the time of changing a voltage threshold according to temperature / humidity environment. 1 is a schematic configuration diagram of a copier according to an embodiment. The graph which shows the result of having investigated the detection voltage at the time of changing a constant current control value by changing transfer roller resistance. A graph showing the relationship between primary transfer current and transfer rate. An example of the relationship between a threshold value and a correction value in each roller resistance. The flowchart of the environmental correction control using the temperature / humidity sensor 66. Explanatory drawing when not changing a voltage threshold value according to a temperature-humidity environment. . The schematic block diagram which showed the patch pattern formation position and the installation position of P sensor.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Intermediate transfer belt 20 Transfer apparatus 40 Photoconductor 60 Primary transfer means 61 Development apparatus 62 Primary transfer roller 65 Electrical characteristic detection means 66 Temperature / humidity sensor

Claims (12)

An image carrier for carrying a toner image;
A transfer means for forming a transfer electric field in a region facing the image carrier and the transfer member by applying a constant current controlled bias to a transfer member to which the toner image is transferred from the image carrier;
Electrical characteristic detection means for detecting a characteristic value corresponding to a resistance value on a path through which a current passed through the transfer means flows;
In the image forming apparatus provided with the temperature and humidity detection means for detecting the temperature and humidity environment in the apparatus body,
A first correction unit that corrects a current value that flows through the transfer unit based on a detection result of the electrical characteristic detection unit and a predetermined threshold;
Second correction means for correcting the current value based on the detection result of the temperature and humidity detection means;
An image forming apparatus comprising: a third correction unit that corrects the predetermined threshold based on a detection result of the temperature and humidity detection unit. The image forming apparatus according to claim 1.
The correction of the current value by the first correction unit is performed such that when the detection result of the electrical characteristic detection unit is lower than the predetermined threshold, the current value is higher than the current value at the time of electrical characteristic detection. What is claimed is: 1. An image forming apparatus comprising: The image forming apparatus according to claim 1.
The correction of the current value by the first correction unit is performed such that when the detection result of the electrical characteristic detection unit is higher than the predetermined threshold, the current value is lower than that at the time of electrical characteristic detection. What is claimed is: 1. An image forming apparatus comprising: The image forming apparatus according to claim 1, 2 or 3.
The image forming apparatus according to claim 1, wherein the electrical characteristic detecting means detects at least a resistance value of the transfer means. The image forming apparatus according to claim 4.
The characteristic value detected by the electric characteristic detection means includes a voltage value of the transfer means, and the resistance value is detected based on the voltage value. apparatus. The image forming apparatus according to claim 1, 2, 3, 4, or 5.
The image forming apparatus, wherein the transfer means transfers a toner image on the image carrier to an intermediate transfer member. The image forming apparatus according to claim 1, 2, 3, 4, 5 or 6.
An image forming apparatus having a plurality of the predetermined threshold values. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6 or 7.
The image forming apparatus according to claim 1, wherein the detection operation by the electrical characteristic detection unit is performed within a registration operation for correcting a positional deviation between toner images of different colors. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7 or 8.
The image forming apparatus according to claim 1, wherein the detection operation by the electrical characteristic detection means is performed within a toner density adjustment operation for adjusting the toner density by detecting the toner adhesion amount. The image forming apparatus according to claim 9.
The image forming apparatus according to claim 1, wherein the correction of the current value is performed before toner density adjustment by the toner density adjustment operation. A transfer that forms a transfer electric field in a region facing the image carrier and the transfer member by applying a constant current controlled bias to the transfer member to which the toner image is transferred from the image carrier that carries the toner image Detecting a characteristic value corresponding to a resistance value on a path through which a current passed through the means flows and detecting a temperature / humidity environment in the apparatus main body, at least the detection result of the characteristic value and the detection result of the temperature / humidity environment In the transfer current setting method in the image forming apparatus that sets the transfer current based on
Correction of the current value passed through the transfer means based on the detection result of the characteristic value and a predetermined threshold, correction of the current value based on the detection result of the temperature / humidity environment, and detection result of the temperature / humidity environment A transfer current setting method, wherein the predetermined threshold value based on the correction is corrected. A step of applying a constant current controlled bias to a transfer member to which a toner image is transferred from an image carrier by a transfer unit, and a resistance value on a path through which a current passed through the transfer unit when the bias is applied In the image forming method for performing the step of detecting the characteristic value and the step of detecting the temperature and humidity environment in the apparatus body,
Correction of the current value passed through the transfer means based on the detection result of the characteristic value and a predetermined threshold, correction of the current value based on the detection result of the temperature / humidity environment, and detection result of the temperature / humidity environment An image forming method, wherein the predetermined threshold value based on the correction is corrected.

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