JP4948241B2 - Image forming apparatus, transfer current setting method, and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus including a transfer device that transfers a toner image formed on an image carrier such as a photoreceptor to a transfer material, a transfer current 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 photosensitive member 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 problem occurs. 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.

  In order to solve the above problem, the present applicant has proposed an image forming apparatus described in Japanese Patent Application No. 2006-278245 (hereinafter referred to as “prior application”). More specifically, in the image forming apparatus described in the prior application, the third correction unit corrects the current value that the first correction unit passes through the transfer unit based on the detection result of the temperature / humidity detection unit. Correction of a predetermined threshold used in the above is performed. 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, since the current value according to the temperature and humidity environment is further corrected by the second correction means, the current value flowing through the transfer means can be set in total, so that the production capacity of the machine is not reduced. In addition, the transfer bias of the transfer means can be optimally corrected.

  However, it is generally known that the current value necessary for obtaining an optimum transfer property varies depending on the size of a transfer material used for image formation. For example, in an image forming apparatus configured to be able to use a transfer material having a size smaller than the maximum size transfer material usable in the apparatus main body, when transferring a toner image onto the transfer material having a small size, Part of the current that should flow through the transfer material due to the application of the transfer bias by the transfer means flows to other than the transfer material due to the influence of the resistance of the transfer material. For this reason, even if the optimized current value is applied to the maximum size transfer paper, the amount of current flowing through the small size transfer material is necessary to obtain the optimum transferability in the small size transfer material. There arises a problem that a transfer defect occurs due to a decrease in current amount.

  The present invention is to improve the above-mentioned prior application in view of the above background. The object of the present invention is to transfer means without reducing the production capacity of the machine and according to the size of the transfer material to be used. The present invention provides an image forming apparatus, a transfer current setting method, and an image forming method that can optimally correct the transfer bias.

In order to achieve the above object, an invention according to claim 1 includes an image carrier that carries a toner image, bias applying means that applies a constant current controlled bias, the image carrier and the image carrier. A transfer means for forming a transfer electric field by the bias applying means in a region facing the transfer medium to which the toner image is transferred, and an electric current 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 and a characteristic detection means, the temperature and humidity detecting means for detecting the temperature and humidity environment in the apparatus main body, a transfer medium width for detecting the width direction of the transfer medium orthogonal to the moving direction of the transfer medium a detecting means, a first correction means for correcting the value of the current flowing to the transfer unit based on the electrical characteristic detecting means a detection result and a predetermined threshold relating to corresponding characteristic values to the resistance value, the transfer medium Detection of width detection means A correction amount correcting means for correcting a correction amount when the first correcting means corrects the current value based on the result, and a second for correcting the current value based on the detection result of the temperature / humidity detecting means. the correcting means, based on a detection result of the temperature and humidity sensing means possess a threshold modifying means for modifying the predetermined threshold value, the correction by the correction means corrects the second by the correction means of the first In the case of simultaneous execution, the current value is corrected by the first correction unit using the threshold value corrected by the threshold value correction unit .
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 second correction unit corrects the current value according to the absolute humidity detected by the temperature / humidity detection unit. It is characterized by being.
According to a fifth aspect of the present invention, in the image forming apparatus according to the first, second, third, or fourth aspect, the threshold correction unit corrects the predetermined threshold according to the absolute humidity detected by the temperature / humidity detection unit. It is what is performed.
According to a sixth aspect of the present invention, in the image forming apparatus of the fifth aspect, the correction of the predetermined threshold value by the threshold value correcting means is performed when the absolute humidity is lower than a reference absolute humidity that is a reference for the correction. , And so as to be higher than the predetermined threshold value at the reference absolute humidity.
According to a seventh aspect of the present invention, in the image forming apparatus according to the fifth aspect, the correction of the predetermined threshold value by the threshold value correcting means is performed when the absolute humidity is higher than a reference absolute humidity serving as a reference for the correction. , And so as to be lower than the predetermined threshold value at the reference absolute humidity.
The invention according to claim 8 is the image forming apparatus according to claim 6 or 7, wherein the image forming apparatus has a plurality of the reference absolute humidity.
According to a ninth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, fifth, sixth, seventh or eighth aspect, the electrical characteristic detecting means detects at least a resistance value of the transfer means. It is characterized by being.
According to a tenth aspect of the present invention, in the image forming apparatus according to the ninth 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 an eleventh aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, or tenth aspect, the image carrier is a belt member, and the transfer means is The toner image on the belt member is transferred onto the transfer medium .
The invention according to claim 12 is the image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11, wherein the electrical property detecting means The characteristic value is detected in the absence of a transfer medium .
The invention according to claim 13 is the image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12, wherein a plurality of the predetermined threshold values are provided. It is what.
According to a fourteenth aspect of the present invention, in the image forming apparatus according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth or thirteenth aspect, the detection operation by the electric characteristic detecting means. Is performed in an alignment operation for correcting a positional deviation of toner images of different colors.
According to a fifteenth aspect of the invention, in the image forming apparatus according to the first, second, third, fourth, fifth, sixth, seventh, eighth, ninth, tenth, eleventh, twelfth or thirteenth aspect, the detection operation by the electric characteristic detecting means. Is characterized in that it is performed in a toner density adjustment operation for adjusting the toner density by detecting the toner adhesion amount.
The invention of claim 16, by the toner image from the image bearing member for bearing a toner image applies a constant current control bias to the transfer medium is transferred, the image carrier and the transfer medium An image forming apparatus that detects a characteristic value according to a resistance value on a path through which a current flowing through a transfer unit that forms a transfer electric field in a facing region flows, and sets a transfer current based on at least the detection result of the characteristic value in the transfer current setting method in the detection of the first correction and, said transfer medium width value of the current flowing to the transfer unit based on a predetermined threshold relating to the characterization in accordance with the detection result and the resistance value of the characteristic value Correction of the correction amount when performing the first correction based on the result, second correction of the current value based on the detection result of the temperature / humidity environment, and the predetermined based on the detection result of the temperature / humidity environment There rows and modifications of thresholds, and the first correction When performing second correction at the same time, it is characterized in row Ukoto a first correction by using a threshold value that has been modified based on a detection result of the temperature and humidity environment.
According to a seventeenth aspect of the present invention, there is provided a step of applying a constant current controlled bias to a transfer medium onto which a toner image is transferred from an image carrier, and a current passed through the transfer unit when the bias is applied. an image forming method for performing the step of detecting a characteristic value corresponding to the resistance value on the path to flow, further comprising the steps of detecting the temperature and humidity environment in the apparatus main body, in a direction perpendicular to the moving direction of the transfer medium performing a step of detecting a width of the transfer medium, a first correction value of the current flowing to the transfer unit based on a predetermined threshold relating to the characterization in accordance with the detection result and the resistance value of the characteristic value , a correction amount of the correction at the time of correcting the first based on a detection result of the transfer medium width, a second correction of the current value based on the detection result of the temperature and humidity environment, the temperature and humidity environment Correction of the predetermined threshold based on the detection result of Row have, in a case where the first correction and the second correction and at the same time, and wherein the row Ukoto a first correction by using a threshold value that has been modified based on a detection result of the temperature and humidity environment To do.

In the present invention, the threshold correction unit corrects the 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. Further, the correction amount correcting unit corrects the correction amount when the first correcting unit corrects the current value based on the detection result of the transfer medium width detecting unit. Accordingly, the first correction unit can correct the current value with the correction amount according to the size of the transfer medium . Therefore, in the correction of the current value by the first correction unit, the current value associated with the resistance of the transfer unit that has changed over time and is not affected by the temperature and humidity environment of the transfer material according to the size of the transfer material to be used. Only the correction can be performed. 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 appropriately corrected so as to obtain optimum transfer efficiency 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 in the substantially center, and the intermediate transfer belt 10 is stretched by a driving roller 14 and driven rollers 15 and 16. 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.
Above the linear intermediate transfer belt 10 spanned between the driving roller 14 and the driven roller 15, four image forming portions of yellow, cyan, magenta, and black are formed 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. In the secondary transfer device 22, the secondary transfer roller 9 and the driven roller 16 are pressed against each other 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. A sheet reversing device 28 for reversing the sheet when images are formed 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 to the paper feed path 48 of the copying machine main body 1 by the conveyance roller 47 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 stopped sheet 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, is 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.

Further, 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 14 are moved so that the yellow, cyan, and magenta photoreceptors 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 and the secondary transfer device 22 is controlled at a constant current.
When the transfer device 20 and the secondary transfer device 22 are controlled at a constant current, even if the electrical resistance of the transfer device 20 and the secondary transfer device 22 fluctuates in the energization or temperature / humidity environment, the applied voltage changes accordingly. The transfer electric field is stable and stable transfer performance can be obtained. However, if the resistance of the transfer device 20 or the secondary transfer device 22 is too low, the influence of the resistance of the toner layer increases, and the voltage applied to the transfer device 20 or the secondary transfer device 22 varies greatly depending on the image area. The transfer efficiency changes depending on whether the image area is small or large. In general, the apparatus main body is configured to be able to use a sheet having a size smaller than the maximum size sheet that can be used. However, when transferring to a sheet by the transfer device 20 or the secondary transfer device 22, the sheet size In particular, the influence of the size in the direction orthogonal to the sheet conveying direction, that is, the sheet width direction becomes large. More specifically, when a toner image is transferred onto the small-sized sheet, a part of the current that should originally flow through the sheet by applying a transfer bias by the transfer device 20 or the secondary transfer device 22 is caused by the sheet itself. It flows outside the sheet due to the influence of resistance. As a result, if the amount of current flowing through the sheet is less than the amount of current required to obtain optimum transferability, transfer failure occurs. That is, even with the same current value, the transfer efficiency is reduced when the size is small compared to when the size in the width direction of the sheet is large. Further, even when the resistance of the transfer device 20 or the secondary transfer device 22 is too high, the applied voltage becomes too high, causing current leakage and disturbing the image, or the voltage increases to the upper limit of the power supply performance. In such a case, there is a problem that there is a risk that current will not flow and transfer will not be performed sufficiently, or that the power supply will be broken. On the other hand, the members constituting the transfer device 20 such as the intermediate transfer belt 10 and the primary transfer roller 62 and the secondary transfer device 22 such as the secondary transfer roller 9 generally have a resistance that gradually changes due to application of a transfer voltage. It can be seen. Therefore, when the resistance of the transfer device 20 or the secondary transfer device 22 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 secondary transfer roller 9 from a power source (not shown) provided in the apparatus main body is controlled at a constant current, and the resistance of the secondary transfer device 22 is detected by detecting the applied voltage. The electric characteristic detecting means 65 for detecting the value is used. The voltage detection of the secondary transfer device 22 is any one of voltage detection of only the secondary transfer roller 9, voltage detection of only the intermediate transfer belt 10, and voltage detection of the secondary transfer roller 9 and the intermediate transfer belt 10. It doesn't matter.

FIG. 3 shows the result of examining the detection voltage when the constant current control value is changed by changing the resistance of the secondary transfer roller 62 (hereinafter referred to as “roller resistance”). When the current used for actual detection is set to, for example, −30 μA, 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 secondary transfer rate (ratio of the toner adhesion amount on the sheet and the toner adhesion amount on the intermediate transfer belt 10) when the constant current control value is changed is examined by changing the roller resistance. FIG. 4 shows the case of the roller resistance 7.0 power (1 × 10 ^7.5 [Ω]) [logΩ], FIG. 5 shows the case of the roller resistance 7.5 power [logΩ], and FIG. 5 shows the roller resistance 8.0 power [logΩ]. This case is shown in FIG. At this time, the transfer efficiency when the sheet size in the sheet width direction was changed was examined using two types of sheets, A4 landscape paper (sheet width 297 mm) and A6 portrait paper (sheet width 105 mm). . Note that the sheet width of the sheet to be used is detected by a sheet width detection unit 67 (not shown) provided in, for example, a sheet feeding cassette of the apparatus main body.
For example, in the case of a roller resistance of 7.0 [logΩ], as can be seen from FIG. 4, the transfer current at which the transfer rate is maximum between A4 landscape paper and A6 portrait paper differs by 20 μA. In the case of .0th power [logΩ], as can be seen from FIG.
As described above, since the influence of the sheet size varies depending on the difference in roller resistance, even if the transfer current is corrected according to only the sheet size, an appropriate transfer current is obtained when the resistance of the secondary transfer roller 9 changes. There is a high possibility that it will not be possible. Therefore, it is necessary to correct the transfer current based on the roller resistance and the sheet size.
That is, when the maximum sheet size in the width direction that can be used in the apparatus is A4 landscape paper, the transfer current when passing a sheet having a sheet width smaller than that of A4 landscape paper is the maximum transfer rate of A4 landscape paper. It may be corrected so as to be larger than the transfer current. For example, as described above, when the roller resistance is 7.0, the transfer current value at which the transfer rate is maximum when A4 landscape paper is -20 μA, and the transfer rate is maximum at A6 portrait paper. Since the current value is −40 μA, 200% (double) correction may be performed with respect to −20 μA which is the optimum value for A4 landscape paper in the case of A6 portrait paper. If this correction amount is called a sheet size correction coefficient, as shown in Table 2, the appropriate sheet size correction coefficient varies depending on the roller resistance.

Therefore, the change of the sheet size correction coefficient according to the roller resistance is 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 3, the voltage is 0.6 kV from Table 1 when the roller resistance is 7.0, so that the second threshold is greater than the first threshold. In the case of less than the threshold value and the power of 8.0, the voltage is 2.8 kV from Table 1, and therefore, is not less than the third threshold value and less than the fourth threshold value.

Table 4 shows the relationship between the threshold value and the correction value for A6 portrait paper. As a result, when the roller resistance that is greater than or equal to the first threshold and less than the second threshold is 7.0, the sheet size correction coefficient is 200%, so the transfer current is corrected to −40 μA, and the maximum transfer efficiency shown in Table 2 is achieved. The transfer current value is set as follows. Further, in the case of a roller resistance of 8.0 to the third threshold and below the fourth threshold, the sheet size correction coefficient is 125% from Table 4, so the transfer current is corrected to −25 μA, and the transfer efficiency shown in Table 2 is maximum. Is set to the transfer current value.

  In this embodiment, only an example of A4 landscape paper and A6 portrait paper is given, but a sheet having a sheet width corresponding to between A4 landscape paper and A6 portrait paper is also corrected by experiment. It has been found that if the sheet width is between these values, the value of the sheet size correction coefficient is also between them. For example, when the sheet size correction coefficient of the transfer current value of A6 longitudinal paper is 200% with respect to the transfer current value that maximizes the transfer efficiency of A4 landscape paper, A5 longitudinal paper (sheet width 148.5 mm). ) Sheet size correction coefficient is between 100% and 200%. Therefore, it is necessary to prepare in advance the sheet size correction coefficient table according to the voltage threshold as shown in Table 4 for the sheet size to be corrected.

  By performing the control as described above, it is possible to select a transfer current value that maximizes the transfer rate according to the sheet size even when the roller resistance changes. Here, the resistance of the secondary transfer roller 9 is changed. However, when the resistance of the intermediate transfer belt 10 is changed, the same change is exhibited. Therefore, the same transfer current value correction is effective. It is done. It should be noted that the correction control of the transfer current value performed based on the electrical characteristic detection means 65 and the predetermined threshold value, and the correction amount when performing the correction control, that is, the correction value shown in Table 4, correspond to the sheet size. The correction to be performed is performed by a control unit (not shown) in the apparatus main body. If the roller resistance is detected when the secondary transfer device 22 is in contact with the sheet, the voltage changes depending on the size of the image transferred to the sheet and the amount of toner during actual printing. The accurate detection cannot be performed. If the detection is performed when printing is not being performed, the sheet is transported through the apparatus main body only for the detection operation, so that the sheet is wasted. In view of these problems, by performing the detection when the secondary transfer device 22 and the sheet are not in contact with each other, it is possible to perform the detection with high accuracy without causing the above-described problem.

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.

A 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. In this embodiment, for example, the at 19 ° C. 30% absolute humidity 4g ^/ m 3, 23 ℃ in 50% absolute humidity 10 g / ^{m 3} and 27 ° C. At 80% absolute humidity 21g / ^{m 3.} The absolute humidity can also be obtained from the temperature and relative humidity by a calculation formula. Next, the current environment (temperature / humidity 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, values and combinations of temperature and humidity are not limited to this. Finally, the transfer current value is corrected with the correction amount corresponding to the current environment obtained above (S5). The correction amount can be determined from Table 6 showing the relationship between the absolute humidity threshold and the correction amount depending on whether the absolute humidity in the current environment is lower or higher than the absolute humidity threshold shown in Table 5. For example, in A6 longitudinal paper, which will be described later, since LL (19 ° C. 30%) and absolute humidity is 4 g / m ³ , it is less than the first threshold from Table 5, and the correction amount is 82% and MM (23 ° C. 50%) from Table 6. Since the absolute humidity is 10 g / m ³ , the second threshold value is less than the third threshold value from Table 5, and the correction amount is 100% from Table 6, and HH (27 ° C. 80%) and the absolute humidity is 21 g / m ^3. From Table 6, the correction amount is 125% or more. The method for determining the correction amount and the relationship between the current environment and the correction amount are not limited to this, and are set in advance for each sheet size to be used.

Since the resistance of the secondary transfer roller 9 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.
If the voltage detection of the secondary transfer device 22 is frequently performed by the electrical characteristic detection means 65 described in the present embodiment, a change in resistance of the secondary transfer device 22 due to temperature and humidity can be detected by the voltage detection. Therefore, such detection by the temperature / humidity sensor 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 23 ° C. and 50%, the roller resistance is 7.5th power [logΩ], the detection voltage is 1.5 kV when the transfer current is −30 μA, and the sheet size is suitable for A6 longitudinal paper. The correction factor was 150%.

Also, when the temperature and humidity environment is 27 ° C. and 80%, the roller resistance is 7.1 [logΩ], and the detection voltage is 0.8 kV when the transfer current is −30 μA, which is suitable for A6 longitudinal paper. The sheet size correction coefficient was 190%.
FIG. 8 shows a case where the transfer current value is corrected without changing the voltage threshold at this time by temperature and humidity. The voltage detection result when the temperature and humidity environment is 27 ° C. and 80%, and the case of A6 longitudinal paper are shown. In addition to correcting the transfer current by 200% (twice) based on the relationship between the voltage threshold value and the correction value, the transfer current correction by the output of the temperature / humidity sensor 66 is also 125% (1.25) as described above. Double) correction. Therefore, the total transfer current is corrected by 250% (2 times × 1.25 times = 2.5 times) when A6 longitudinal paper is fed under the above-described condition of 27 ° C. and 80%. This is significantly different from 190% which is an appropriate sheet size correction coefficient when A6 longitudinal paper is used under the above-described condition of 27 ° C. and 80%. Therefore, if the transfer current is corrected without changing the voltage threshold in the temperature and humidity environment in this way, if the temperature and humidity environment is 27 ° C. and 80%, excessive current will flow, and an appropriate transfer current and Therefore, the transfer efficiency is lowered.
On the other hand, FIG. 1 shows a case where the voltage threshold is changed by temperature and humidity (absolute humidity) at this time. When the temperature / humidity environment is 27 ° C./80% (when the absolute humidity is 21 g / m ³ ), the voltage threshold is set higher than when the temperature / humidity environment is 23 ° C./50% (the absolute humidity is 10 g / m ³ ). Set low. Then, when the temperature and humidity environment is 27 ° C. and 80% (when the absolute humidity is 21 g / m ³ ), the detection voltage of 0.8 kV is the second from the relationship between the voltage threshold value and the correction value when A6 longitudinal paper is fed. It is determined that the threshold value is greater than or equal to the third threshold value, and correction by voltage detection is 150% (1.5 times). If the correction of the transfer current by the output of the temperature / humidity sensor 66 is 125% (1.25 times), the total correction is 188% (1.5 times × 1.25 times≈1.88 times). The value is substantially the same as 190%, which is an appropriate sheet size correction coefficient when using A6 longitudinal paper under the condition of 27 ° C. and 80%.
As a result, it is possible to correct the transfer current to an appropriate transfer current for each sheet size to be used even when the resistance changes due to the temperature and humidity environment, in other words, correct transfer bias correction, and voltage detection operation. The frequency can be reduced as much as possible.

When the temperature and humidity environment is 19 ° C. and 30%, the roller resistance is 7.9 [logΩ], the detection voltage is 2.5 kV when the transfer current is −30 μA, which is suitable for A6 longitudinal paper. The sheet size correction coefficient was 125%.
FIG. 8 shows a case where the transfer current value is corrected without changing the voltage threshold at this time by temperature and humidity. The voltage detection result when the temperature and humidity environment is 19 ° C. and 30% and the case of A6 longitudinal paper are shown. Although the transfer current is corrected by 125% based on the relationship between the voltage threshold and the correction value, the correction of the transfer current by the output of the temperature / humidity sensor 66 results in 82% correction. Therefore, the transfer current is corrected only by a total of 103% (1.25 times × 0.82 times = 1.03 times) when A6 longitudinal paper is fed under the condition of 19 ° C. and 30%. This is greatly different from 125% which is an appropriate sheet size correction coefficient when A6 longitudinal paper is used under the above condition of 19 ° C. and 30%. Therefore, if the transfer current is corrected without changing the voltage threshold value in the temperature and humidity environment in this way, when the temperature and humidity environment is 19 ° C. and 30%, there is not enough current to flow, and an appropriate transfer current is not obtained. Therefore, transfer efficiency is lowered.
On the other hand, FIG. 1 shows a case where the voltage threshold is changed by temperature and humidity (absolute humidity) at this time. When the temperature / humidity environment is 19 ° C. and 30% (when the absolute humidity is 4 g / m ³ ), the voltage threshold is lower than when the temperature and humidity environment is 23 ° C. and 50% (the absolute humidity is 10 g / m ³ ). Set high. Then, when the temperature and humidity environment is 19 ° C. and 30% (when the absolute humidity is 4 g / m ³ ), the detection voltage of 2.5 kV is the second because of the relationship between the voltage threshold value and the correction value for A6 longitudinal paper. It is determined that the threshold value is greater than or equal to the third threshold value, and correction by voltage detection is 150% (1.5 times). If 82% (0.82 times) of the transfer current is corrected by the output of the temperature / humidity sensor 66, the total correction is 123% (1.5 times × 0.82 times = 1.23 times). This is approximately the same value as 125%, which is an appropriate sheet size correction coefficient when A6 longitudinal paper is used under the condition of 30% at 19 ° C.
As a result, it is possible to correct the transfer current to an appropriate transfer current for each sheet size to be used even when the resistance changes due to the temperature and humidity environment, in other words, correct transfer bias correction, and voltage detection operation. The frequency can be reduced as much as possible.

In this embodiment, when the voltage threshold is changed by temperature and humidity (absolute humidity), the reference temperature and humidity (absolute humidity) is set to 23 ° C. and 50% (absolute humidity 10 g / m ³ ). Other temperature / humidity environments (absolute humidity) may be used. Further, by providing a plurality of reference temperature and humidity (absolute humidity), it is possible to finely divide the temperature and humidity environment. In other words, the correction amount can be set finely, so that the transfer current can be corrected more appropriately for each temperature and humidity environment. be able to.

  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. 9 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. 9, 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 secondary transfer device 22 when performing such misregistration correction of each color, it is possible to suppress a decrease in the production capacity of the machine due to the voltage detection alone.

[Example 2]
Next, Example 2 will be described. The correction of the transfer current and the description of the configuration related thereto are the same as in the first embodiment, so that the description thereof will be omitted, and the characteristic part in the second embodiment will be described. Specifically, the timing for performing the voltage detection operation of the secondary transfer device 22 by the electrical characteristic detection means 65 will be described.
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. The detection result by the P sensor is compared with a predetermined target adhesion amount by a control unit (not shown). Based on the comparison result, the control unit functions as an image density control unit, and the laser beam of the optical system. The strength of the toner, the charging bias applied to the charging device 18, the developing bias applied to the developing sleeve, the amount of toner replenished into the developing device 61, and the like are appropriately changed to adjust the image density to a desired density.

  By performing voltage detection of the secondary transfer device 22 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.

As described above, according to the present embodiment, the intermediate transfer belt 10 that is an image carrier that carries a toner image, the power source provided in the apparatus main body that is a bias applying unit that applies a bias controlled by constant current, and the intermediate A secondary transfer device 22 that is a transfer unit that forms a transfer electric field by the power source in a region facing the transfer belt 10 and a sheet that is a transfer medium to which the toner image is transferred from the intermediate transfer belt 10, and a secondary transfer device 22 Temperature / humidity detecting means for detecting a temperature / humidity environment in the apparatus main body in a copying machine which is an image forming apparatus provided with an electrical characteristic detecting means 65 for detecting a characteristic value corresponding to a resistance value on a path through which a current flows a temperature and humidity sensor 66 is, the sheet width detecting means 67 for detecting the width direction of the sheet orthogonal to the moving direction of the sheet, and the detection result of the electric characteristics detecting means 65 resistance A first correction unit device which is a control unit provided in the body to correct the value of the current flowing in the secondary transfer device 22 based on a predetermined threshold relating to the characterization in accordance with the value, the sheet width detecting means 67 Based on the detection result, the control unit as the first correction unit corrects the correction amount when the current value is corrected. The control unit that is also a second correction unit that corrects the current value based on the control unit, and the control unit that is also a threshold correction unit that corrects the predetermined threshold based on the detection result of the temperature / humidity sensor 66. Based on the detection result of the electric characteristic detection means 65 by the control unit and a predetermined threshold value, the current value to be passed through the secondary transfer device 22 is corrected, and the current based on the detection result of the temperature / humidity sensor 66 by the control unit. Simultaneously with value correction When performing, using the threshold value corrected based on the detection result of the temperature / humidity sensor 66 by the control unit, the secondary transfer device 22 is controlled based on the detection result and threshold value of the electrical characteristic detection means 65 by the control unit. The current value to be applied is corrected . As a result, the correction of the current value accompanying the change in resistance of the secondary transfer device 22 with time can be performed based on the detection result of the electrical characteristic detection means 65 and the predetermined threshold value. Further, the control unit corrects the correction amount based on the detection result of the sheet width detecting means 67. Accordingly, the control unit can correct the current value with the correction amount according to the sheet size. Further, the correction of the transfer bias due to the resistance change of the secondary transfer device 22 due to the change in temperature and humidity is performed based on the detection result of the temperature and humidity detection sensor 66, so that the electrical characteristic detection means 65 frequently performs the detection operation. It can suppress that the production capacity of the machine 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 electric characteristic detection means 65 and the changed predetermined threshold value, is not affected by the temperature and humidity environment according to the size of the sheet to be used. Only the correction of the current value associated with the resistance of the secondary transfer device 22 that has been changed to 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 supplied to the secondary transfer device 22 in total. Therefore, the transfer bias applied to the secondary transfer device 22 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, it is set to be higher than the current value applied at the time of detecting the electric characteristics, and when it is higher than the predetermined threshold value, it is set to be lower than the current value applied at the time of detecting the electric characteristics. As a result, even if the resistance of the secondary transfer device 22, for example, the resistance of the secondary transfer roller 9, changes, a transfer bias that maximizes the transfer rate can be selected, and image defects can be prevented.
According to the present embodiment, the control unit corrects the current value according to the absolute humidity detected by the temperature / humidity sensor 66. In general, the resistance of the secondary transfer roller 9, the opposing roller 16, and the intermediate transfer belt 10 often shows a linear dependence on the absolute humidity. Therefore, the current value is corrected according to the absolute humidity as in this embodiment. The configuration to be performed is effective.
According to the present embodiment, the control unit corrects the predetermined threshold according to the absolute humidity detected by the temperature / humidity sensor 66. The detection result (detection voltage) of the electrical characteristic detection means 65 is determined by the resistances of the secondary transfer roller 9, the opposing roller 16, and the intermediate transfer belt 10, and these resistances often show linear dependence on absolute humidity. Therefore, a configuration for correcting the threshold value for current value correction according to the absolute humidity as in the present embodiment is effective.
According to the present embodiment, the predetermined threshold value is corrected by the control unit when the absolute humidity is lower than a reference absolute humidity that is a reference for the correction. This is performed so as to be higher than the threshold value. As a result, it is possible to suppress a decrease in transfer efficiency due to insufficient correction amount in a low temperature and low humidity environment.
According to the present embodiment, the correction of the predetermined threshold by the control unit is performed when the absolute humidity is higher than a reference absolute humidity that is a reference for the correction, and the predetermined threshold at the reference absolute humidity is set. This is performed so as to be lower than the threshold value. As a result, it is possible to suppress a reduction in transfer efficiency due to an excessively large correction amount in a high temperature and high humidity environment.
Further, according to the present embodiment, by having a plurality of the above-mentioned reference absolute humidity, the range of the temperature and humidity environment can be finely divided, in other words, the correction amount can be set finely, so that the transfer more suitable for each temperature and humidity environment Current correction can be performed.
Further, according to the present embodiment, the electrical characteristic detecting means 65 detects at least the resistance value of the secondary transfer device 22. If the resistance of the secondary transfer device 22 is too low, the influence of the resistance of the toner layer becomes large, and the voltage applied to the secondary transfer device 22 varies greatly depending on the image area, and is transferred when the image area is small or large. There is a problem that the efficiency changes. Also, if the resistance of the secondary transfer device 22 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 secondary transfer device 22, and the resistance value is detected based on the voltage value. It is what is done. The electrical characteristic detection means 65 can detect the resistance of the secondary transfer device 22 by measuring current under constant voltage control, but has a constant current power source for forming a transfer electric field. In this case, it is only necessary to measure the voltage under constant current control and detect the resistance of the secondary transfer device 22, so that only one power source is required. Space saving in the main body is possible.
Further, according to the present embodiment, the present invention is applied to the secondary transfer device 22 in such a configuration that when the toner image is carried on the intermediate transfer belt 10, the toner image is secondarily transferred and the toner image is transferred onto a sheet. ing. The present invention is also effective when applied to transfer means for transferring a toner image directly from a photoreceptor 40 onto a sheet, or transfer means for transferring a toner image on the photoreceptor 40 onto an intermediate transfer belt 10. 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.
Further, according to the present embodiment, the electrical characteristic detection means 65 detects the characteristic value in a state where the sheet is not present in the facing area. If resistance detection is performed in a state where the sheet is in the facing region, that is, when the secondary transfer device 22 is in contact with the sheet, the actual transfer may be performed depending on the size of the image transferred onto the sheet and the amount of toner. Since the voltage changes, accurate detection cannot be performed. Therefore, by performing the resistance detection in a state where there is no sheet in the facing region, that is, in a state where the secondary transfer device 22 is not in contact with the sheet, the detection can be performed with high accuracy without causing the above-described problem. Can do.
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 secondary transfer device 22 changes greatly, it is possible to perform current value correction corresponding to the resistance, and transfer can always be performed in an optimum state. . Further, it is possible to simultaneously improve the transfer efficiency when the resistance of the secondary transfer device 22 is low and to 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 misregistration correction of each color is performed, the voltage detection of the secondary transfer device 22 is also performed, thereby suppressing a decrease in the production capacity of the machine due to the voltage detection operation of the electrical characteristic detection unit 65 independently. be able to.
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. As described above, when the toner density adjustment operation is performed, the voltage detection of the secondary transfer device 22 is performed, thereby suppressing the decrease in the production capacity of the machine due to the electric characteristic detection unit 65 performing the voltage detection operation alone. Can do.
Further, according to the present embodiment, the correction of the current value passed through the secondary transfer device 22 based on the detection result of the characteristic value, the detection result of the sheet width, and the predetermined threshold value, and the detection of the temperature and humidity environment a correction of the current value based on the result, by performing the correction of the detection result to the predetermined threshold value depending upon the temperature and humidity environment, by applying the present invention to transfer current setting method for setting a transfer current The optimum transfer current can be set.
Further, according to the present embodiment, the correction of the current value passed through the secondary transfer device 22 based on the detection result of the characteristic value, the detection result of the sheet width, and the predetermined threshold value, and the temperature / humidity environment By applying the present invention to an image forming method for correcting the current value based on the detection result and correcting the predetermined threshold based on the detection result of the temperature / humidity environment, image formation with an optimal transfer bias can be performed. It can be carried out.

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. The graph which showed the relationship between the secondary transfer electric current and the transfer rate of each sheet size in roller resistance 7.0 power. 6 is a graph showing the relationship between the secondary transfer current and the transfer rate for each sheet size when the roller resistance is 7.5. The graph which showed the relationship between the secondary transfer electric current and the transfer rate of each sheet size in roller resistance 8.0th power. The flowchart of the environmental correction control using a temperature / humidity sensor. 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 setting position of P sensor.

Explanation of symbols

9 Secondary transfer roller 10 Intermediate transfer belt 22 Secondary transfer device 40 Photoconductor 65 Electrical characteristic detection means 66 Temperature / humidity sensor 67 Sheet width detection means

Claims (17)

An image carrier for carrying a toner image;
Bias applying means for applying a constant current controlled bias;
Transfer means for forming a transfer electric field by the bias applying means in a region facing the image carrier and a transfer medium to which the toner image is transferred from the image carrier;
In an image forming apparatus comprising: an electrical characteristic detection unit that detects a characteristic value according to a resistance value on a path through which a current passed through the transfer unit flows.
Temperature / humidity detection means for detecting the temperature / humidity environment in the device body;
A transfer medium width detection means for detecting a width direction of the transfer medium orthogonal to the moving direction of the transfer medium,
First correction means for correcting a current value flowing through the transfer means based on a detection result of the electrical characteristic detection means and a predetermined threshold value relating to a characteristic value corresponding to the resistance value ;
A correction amount correction means for correcting a correction amount when the first correction means corrects the current value based on a detection result of the transfer medium width detecting means,
Second correction means for correcting the current value based on the detection result of the temperature and humidity detection means;
Possess a threshold modifying means for modifying the predetermined threshold value based on the detection result of the temperature and humidity detecting means,
When the correction by the first correction unit and the correction by the second correction unit are performed simultaneously, the current value is corrected by the first correction unit using the threshold value corrected by the threshold value correction unit. An image forming apparatus. 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 2, wherein the second correction unit corrects the current value according to the absolute humidity detected by the temperature and humidity detection unit. The image forming apparatus according to claim 1, 2, 3, or 4.
The image forming apparatus, wherein the threshold correction unit corrects the predetermined threshold according to the absolute humidity detected by the temperature / humidity detection unit. The image forming apparatus according to claim 5.
When the absolute humidity is lower than the reference absolute humidity that is the reference for the correction, the correction of the predetermined threshold by the threshold correction means is performed so as to be higher than the predetermined threshold at the reference absolute humidity. What is claimed is: 1. An image forming apparatus comprising: The image forming apparatus according to claim 5.
When the absolute humidity is higher than the reference absolute humidity serving as a reference for the correction, the correction of the predetermined threshold by the threshold correcting means is performed so as to be lower than the predetermined threshold at the reference absolute humidity. What is claimed is: 1. An image forming apparatus comprising: The image forming apparatus according to claim 6 or 7,
An image forming apparatus having a plurality of the reference absolute humidity. 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 electrical characteristic detecting means detects at least a resistance value of the transfer means. The image forming apparatus according to claim 9.
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, 5, 6, 7, 8, 9 or 10.
The image carrier is a belt member,
The image forming apparatus, wherein the transfer means transfers a toner image on the belt member onto the transfer medium . The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10 or 11.
The image forming apparatus according to claim 1, wherein the electrical characteristic detecting means detects the characteristic value in a state where the transfer medium is not present in the facing area. The image forming apparatus according to claim 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11 or 12.
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, 7, 8, 9, 10, 11, 12, or 13.
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, 8, 9, 10, 11, 12, or 13 .
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. By the toner image applies a constant current control bias to the transfer medium is transferred from the image bearing member for bearing a toner image, transferring to form a transfer electric field region opposed to the image carrier and the transfer medium In a transfer current setting method in an image forming apparatus that detects a characteristic value according to a resistance value on a path through which a current flowing through a unit flows, and sets a transfer current based on at least the detection result of the characteristic value.
A first correction value of the current flowing to the transfer unit based on a predetermined threshold value for the detection result and the characteristic value according to the resistance value of the characteristic value, the first based on the detection result of the transfer medium width Correction of the correction amount when performing correction of the current, second correction of the current value based on the detection result of the temperature and humidity environment, and correction of the predetermined threshold based on the detection result of the temperature and humidity environment. Yes,
When performing the first correction and the second correction and at the same time, the transfer current, characterized in row Ukoto correct the first using a threshold that has been modified based on a detection result of the temperature and humidity environment Setting method. A step of applying a constant current controlled bias to a transfer medium on 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 flows when the bias is applied In the image forming method for performing the process of detecting the characteristic value,
Furthermore, it performed the steps of detecting the temperature and humidity environment in the apparatus main body, and a step of detecting a width direction of the transfer medium orthogonal to the moving direction of the transfer medium,
A first correction value of the current flowing to the transfer unit based on a predetermined threshold value for the detection result and the characteristic value according to the resistance value of the characteristic value, the first based on the detection result of the transfer medium width Correction of the correction amount when the correction is performed, a second correction of the current value based on the detection result of the temperature and humidity environment, and correction of the predetermined threshold based on the detection result of the temperature and humidity environment There line,
When performing the first correction and the second correction and at the same time, image formation correction of first and said row Ukoto using a threshold that has been modified based on a detection result of the temperature and humidity environment Method.

Images