JP2006276703A - Image density control method and image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correct the fluctuation of image density due to environmental change and secular change without needing any dedicated sensor. <P>SOLUTION: A density checking developer image of prescribed density (command value) is formed on an image carrier at a timing other than an image forming operation (S14), and data V<SB>0</SB>equivalent to the resistance value of a transfer member when the density checking developer image does not exist in a transfer nip part is measured (S15). Besides, data V<SB>1</SB>equivalent to the resistance value of the transfer member when the density checking developer image exists in the transfer nip part is measured. The toner density decision reference data V<SB>2</SB>previously prepared corresponding to the data V<SB>0</SB>is compared with the data V<SB>1</SB>(S17), and an image forming condition which has an effect on the image density at a printing operation is corrected based on the comparison result (S18). <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a copying machine, a laser printer, and a facsimile machine, and more particularly to an image density control method for controlling an image density using a developer (toner).

  Conventionally, in the image forming apparatus as described above, in order to stabilize the density of the output image, a sensor for detecting the surface potential on the image carrier of the electrophotographic photosensitive member as described in Patent Document 1 is used. A method has been proposed in which a reference latent image pattern is formed separately from the image forming sequence, the area is detected, and the voltage applied to the charging unit and the developing unit is controlled based on the information.

  In addition, as described in Patent Document 2, there is also a proposal for correcting the toner density by estimating the toner density based on a change in an electrical signal of a toner density detection sensor disposed in the developing device.

Furthermore, as described in Patent Document 3, a method is proposed in which a specific pattern image is formed on an image carrier, the optical density thereof is read, and feedback control is performed on the image forming conditions. For example, a specific pattern image (toner image) formed on a photosensitive drum is irradiated by a light emitting element, reflected light from the pattern image of the irradiated light is received by a light receiving element, and an output signal of the light receiving element is received. Thus, the control signal is fed back to the contrast potential or the like, thereby obtaining an appropriate image density. This density correction control is performed every several hours or in order to stabilize the output image density by correcting fluctuations in the output image density due to changes in the surrounding environment, deterioration of the photosensitive drum, developer density (toner density), etc. It is executed every hundreds to thousands of prints.
JP 61-117572 A Japanese Patent Laid-Open No. 5-100573 Japanese Patent Laid-Open No. 5-80622

  However, in the conventional example as described above, a potential sensor that detects the surface potential on the image carrier, a density detection sensor that detects the image pattern density on the image carrier, a sensor that detects the toner adhesion amount on the developing sleeve, etc. There is a problem that the cost of the apparatus is increased.

  Accordingly, the present invention provides an image density control method and an image forming apparatus using the image density control method that can correct image density without requiring a dedicated sensor for fluctuations in image density due to environmental changes or changes over time. For the purpose.

  An image density control method according to the present invention is an image density control method in an image forming apparatus provided with a transfer member for transferring a developer image formed on the surface of an image carrier onto a recording material, and developing for density check A step of forming an agent image on the image carrier, and a resistance value of the transfer member when the density check developer image does not exist in a transfer nip portion between the image carrier and the transfer member. Measuring the data to be measured, measuring the data corresponding to the resistance value of the transfer member when the density check developer image is present in the transfer nip, and the printing operation based on both measurement results And a step of correcting an image forming condition that affects the image density at the time.

When the developer is present in the transfer nip portion between the image carrier and the transfer member, the resistance value of the transfer member changes. At that time, the resistance value also changes depending on the density (distribution density) of the developer image. That is, the resistance value increases as the concentration increases. Therefore, the resistance value of the transfer member when the developer image is present in the transfer nip portion is proportional to the density. However, since the resistance value of the transfer member itself also changes due to environmental changes or the like, not only the data corresponding to this resistance value (data V ₁ in the embodiment) but also the transfer when the developer image is not present in the transfer nip portion. By using the data corresponding to the resistance value of the member (data V _{0 and} data V ₂ in the embodiment), the influence of factors such as environmental changes can be offset.

  In the step of measuring data corresponding to the resistance value of the transfer member, a constant current is supplied to the transfer member, and the developer image for density check is transferred to the transfer nip portion between the image carrier and the transfer member. The data corresponding to the resistance value of the transfer member when it does not exist and when it exists can be measured as the first and second voltage values at both ends of the transfer member. More specifically, the step of measuring data corresponding to the resistance value of the transfer member includes obtaining density determination reference data based on the first voltage value, the density determination reference data, and the first And the step of performing the correction includes correcting the image forming conditions that affect the image density during the printing operation based on the comparison result.

  When the polarity of the constant current is reversed to the charging polarity of the developer, a step of cleaning the developer attached to the transfer member is provided. When the constant current has the same polarity as the charging polarity of the developer, the cleaning step is unnecessary.

  The step of performing the correction can be realized by changing at least one image forming condition among a charging unit, a latent image forming unit, and a developing unit of the image forming apparatus.

  The transfer member is, for example, an ion conductive transfer roller.

  An image forming apparatus according to the present invention is an apparatus for performing the image density control method, and includes an image forming apparatus including a transfer member that transfers a developer image formed on the surface of the image carrier onto a recording material. The image forming means for forming a density check developer image on the image carrier, and when the density check developer image does not exist in the transfer nip portion between the image carrier and the transfer member. Measuring means for measuring data corresponding to resistance values of the respective transfer members when present, and correcting means for correcting image forming conditions that affect image density during a printing operation based on the measurement results; It is provided with.

  According to the present invention, there is a case where a density check developer image is formed on the image carrier, and the density check developer image is not present in the transfer nip portion between the image carrier and the transfer member. The data corresponding to the resistance value of the transfer member at the time is measured, and based on the measurement result, the image forming conditions that affect the image density during the printing operation are corrected, so that it has been necessary for the conventional toner density correction. It is possible to correct the toner density that varies depending on the environmental state and the durability state without requiring a potential sensor or a density sensor. As a result, the apparatus cost can be reduced.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

<First Embodiment>
FIG. 1 shows a schematic configuration of an image forming apparatus according to the first embodiment of the present invention. In the present embodiment, a laser printer will be described as an example of the image forming apparatus according to the present invention. However, the present invention is not limited to application to a laser printer.

  First, the configuration of the laser printer will be described with reference to FIG.

  This laser printer includes a photosensitive drum 1 as an image carrier. The photosensitive drum 1 is rotatably supported by the apparatus main body M, and is rotationally driven at a predetermined speed (107 mm / sec process speed in the present embodiment) in the direction of arrow A by a driving means (not shown). Around the photosensitive drum 1, a charging roller 2 as a charging device that uniformly charges the photosensitive drum 1 in almost the order along the rotation direction, a laser scanner 3 as an exposure unit for forming an electrostatic latent image, A developing device 4 that visualizes the electrostatic latent image with toner, a transfer roller 5 that is a transfer device for transferring the toner image on the photosensitive drum 1 to a sheet-like recording material P such as paper, and the photosensitive drum 1 A cleaning device 6 for collecting untransferred toner remaining on the top is disposed. A sheet feeding cassette 7 containing a recording material P is disposed at the lower part of the apparatus main body M, and a fixing roller (or fixing film) 26 to be heated and a pressure roller 25 are disposed above the photosensitive drum 1. A fixing device 8 is provided.

  Further, a control board 9 for controlling an image forming operation and the like is disposed on the back surface of the apparatus main body M. On the control board 9, a CPU 9a that issues a command to execute an image forming operation and the like, and a memory 9b that stores a program and the like are mounted. In the memory 9b, an optimum transfer voltage data table for determining by execution of ATVC described later, a data table of toner density determination reference data for determining whether or not toner density correction is necessary, and the like are stored. Yes. The operations of these printers are realized by the CPU 9a reading out and executing a necessary program from the memory 9b (the same applies to the processing according to the flowchart described in detail later).

  Next, the operation of the laser printer configured as described above will be described.

The photosensitive drum 1 rotated in the direction of arrow A by a driving means (not shown) is uniformly charged to a predetermined polarity and a predetermined potential (for example, −585 V) by the charging roller 2. After completion of the charging operation, the CPU 9a applies a constant current (for example, +5 μA) to the transfer roller 5 with a predetermined polarity, and measures the voltage V ₀ across the transfer roller 5. In this example, the polarity of the current flowing toward the transfer roller 5 is positive (+). The charging polarity of the toner is negative (−). Based on this measured value, the optimum transfer output Vt is obtained. Specifically, an optimum transfer output Vt for the transfer roller measurement voltage V ₀ is set in advance in a data table (or calculation formula) in the memory 9b, and this data table (or calculation formula) is set based on the measured value. ) To determine the transfer voltage Vt to be output during the image forming operation.

  That is, since the impedance of the transfer roller 5 can be calculated by applying a constant current to the transfer roller 5 and measuring the voltage at both ends, the optimum transfer voltage Vt corresponding to the resistance change of the transfer roller 5 in the external environment, durability, or the like is set. Can be sought. The “transfer roller measurement voltage” is a value determined in advance so as to obtain a good transfer image corresponding to the impedance obtained by calculation. (Hereinafter, this optimum transfer voltage determination method is called ATVC (Auto Transfer Voltage Control).)

  The operation until the photosensitive drum 1 is uniformly charged to determine the optimum transfer voltage during the image forming operation, the operation of accelerating a polygon motor (not shown) of the laser scanner 3 to a predetermined number of revolutions, and the fixing device 8 is melted with toner. The operation until all the operations for raising the temperature to a predetermined temperature are completed is called initial rotation.

  After completion of the initial rotation operation, the surface of the photosensitive drum 1 is subjected to image exposure based on image information by the laser scanner 3 serving as an exposure unit, and the charge of the exposed portion is removed to form an electrostatic latent image. The electrostatic latent image is developed by the developing device 4. The developing device 4 has a developing sleeve 4a whose surface is coated with carbon on an aluminum roller. A predetermined developing bias (for example, AC: 2400 Hz, 1.6 KVpp / DC: -455V) is applied to the developing sleeve 4a. A toner is attached to the electrostatic latent image on the photosensitive drum 1 and developed (visualized) as a toner image.

  The toner image is transferred to the recording material P such as paper by the transfer roller 5. The recording material P is stored in a paper feed cassette 7, and is conveyed by a paper feed roller and a conveyance roller (not shown), and is conveyed to a transfer nip portion N between the photosensitive drum 1 and the transfer roller 5.

  The transfer roller 5 transfers the toner image formed on the photosensitive drum 1 to the recording material P by applying the optimum transfer voltage determined by the ATVC of the initial rotation operation. The recording material P is conveyed to the fixing device 8 along a conveyance guide (not shown). In the fixing device 8, the unfixed toner image is heated and pressed to melt the toner, and is fixed on the surface of the recording material P.

  On the other hand, after the toner image is transferred, the toner remaining on the surface without being transferred to the recording material P is removed by the cleaning blade 6a of the cleaning device 6 and used for the next image formation.

  By repeating the above operation, image formation can be performed one after another.

  Next, the detailed operation of the printer in this embodiment will be described based on the flowchart of FIG.

  When the printer receives a print signal from a host computer (not shown), the initial rotation operation described above is started (S11). In this initial rotation operation, first, the photosensitive drum 1 is uniformly charged. At the same time, an operation for accelerating a polygon motor (not shown) to a predetermined number of revolutions (25230 rpm in this embodiment) and energizing a halogen lamp (not shown) until the fixing device 8 reaches a predetermined temperature (150 ° C. in this embodiment). The heating operation is executed.

After the photosensitive drum 1 is charged, transfer ATVC is started, and a constant current (+5 μA) is applied to the transfer roller 5 as shown in FIG. 3A (S12). The voltage applied by the transfer high-voltage power supply 19 varies depending on the resistance value of the transfer roller 5 (including the effect of the presence or absence of a black toner band at the transfer nip portion). This voltage corresponds to the voltage V ₀ across the transfer roller 5. Therefore, the voltage V ₀ across the transfer roller 5 is measured to determine the optimum transfer voltage Vt to be applied to the transfer roller 5 for the printing operation (S13). At this point, ATVC ends.

Subsequently, with the +5 μA constant current applied to the transfer roller 5, the uniformly charged photosensitive drum 1 is irradiated with laser light to have a predetermined size (for example, main scanning width 200 mm × sub-scanning width 5 mm). A belt-like latent image is formed, and the same developing bias (AC: 2400 Hz / 1.6 KVpp, DC: −440 V) as that during printing is applied to form a toner black belt 51 on the photosensitive drum 1 (S14). As shown in FIG. 3 (b), the toner black band 51 this formation is measured as a voltage Toner black band voltages V ₁ and at both ends of the transfer roller 5 when passing through the transfer roller 5 (S15).

FIG. 4 is a graph showing the change of the voltage V across the transfer roller 5 with time. The value of the voltage V during the period when the toner black belt 51 is not interposed in the nip portion between the photosensitive drum 1 and the transfer roller 5 is V ₀ , but during the period when the toner black belt 51 is interposed in the nip portion, the voltage V It can be seen that the value of varies from V ₀ to V ₁ .

Thereafter, CPU 9a, the toner concentration reading the judgment reference data _{V 2} from the memory 9b (S16) corresponding to _{V 0} detected by the ATVC, toner black band voltages _{V 1} was measured with a toner concentration determination reference data _{V 2} Are compared (S17). If more toner black band voltage V ₁ is small, it is determined that no longer out concentration decreased the amount of applied toner on the photosensitive drum 1.

In the present embodiment, an ion conductive transfer roller 5 mainly composed of NBR rubber having a resistance value of about 8 × 10 ⁷ Ω is used. Such a resistance value of the transfer roller 5 varies due to environmental variations such as temperature and humidity. Therefore, when determining the toner black band voltages V ₁ in a fixed threshold can not properly determine. Therefore, in the present embodiment, in view of the fact that environmental fluctuations are reflected in V ₀ detected by ATVC, as an appropriate threshold for determining the toner black belt voltage V ₁ based on the value of V ₀ . determining a toner concentration determination reference data V _2.

  In this embodiment, the CPU 9a that determines that the toner density needs to be corrected changes the development DC bias so as to widen the development contrast in order to increase the density in the printing operation, and the development contrast is increased by a predetermined value as the density increases. A control to shift (here, -400V to -450V to 50V) is executed (S18).

In step S17, when it is determined that the direction of the toner black band voltage V ₁ is greater, the toner density correction is not performed.

  Since the toner black belt passes through the transfer roller 5 and the transfer roller 5 is contaminated with toner, the CPU 9a transfers a cleaning bias (-3 KV in the present embodiment) having a polarity opposite to that of the toner to the transfer roller 5. It is applied for a time longer than three rotations of the roller (S19).

  In this way, after executing the necessary toner density correction according to the environmental change, the normal printing operation is executed, and the printing operation on the paper P as the recording material is performed (S20). When the toner image is transferred from the photosensitive drum 1 to the paper P in this printing operation, the optimum transfer voltage Vt determined in step S13 is used. Note that constant voltage control of the transfer high-voltage power supply 19 is performed when the optimum transfer voltage Vt is applied.

The execution timing of the processing for obtaining the toner density data V _1, (1) each print job, (2) when the apparatus power is turned on, when returning from the (3) energy-saving mode, (4) when an instruction of the operator, considered equal It is done. Once the value of the toner density data V ₁ obtained is then to be nonvolatile manner in the memory 9b to update.

Figure 5 is a graph showing the experimentally proper toner concentration determination reference data V ₂ obtained by passing the transfer roller to form a toner black band of the reflection density of 1.3 while changing the V ₀ . Toner concentration determination reference data V ₂ functions as whether threshold performing the toner density correction. From the result of this graph, a data table or a calculation formula for obtaining V ₂ can be created based on the value of V ₀ . Such a data table or calculation formula is stored in the memory 9b in a nonvolatile manner. In this embodiment, the toner density at which the toner density correction is started is set to the reflection density 1.3. However, the present invention is not limited to this and can be arbitrarily set.

For example, in an environment of 23 ° C./50%, V _{0 at} ATVC applied with +5 μA is about +1 KV. In this state, when a toner black band having a reflection density of 1.3 is passed over the transfer roller 5, the voltage across the transfer roller 5 increases to, for example, +1.2 KV because the resistance value of the transfer roller 5 increases due to the influence of the toner black band. To rise. This value changes due to environmental fluctuations. The changed voltage value becomes the toner concentration determination reference data V _2.

Reflection density is thinner than 1.3 (i.e., toner adhesion is reduced to the transfer roller 5), the output value of the toner black band voltages V ₁ decreases. As a result, when the output value of the toner black band voltages V ₁ is smaller than the toner concentration determination reference data V _2, it is determined that the toner density becomes thin, to perform the correction of the toner density.

  There are several methods for correcting the toner density. For example, (1) changing the charging DC bias of the charging means of the photosensitive drum 1, (2) changing the laser power of the latent image forming means, (3) changing the developing bias of the developing means, (4) Any combination, etc.

  By changing the development DC bias from −400 V to −450 V and executing a control to shift the development contrast by 50 V toward a higher density, the toner density printed on the paper P in the printing operation is reflected in this embodiment. It is possible to increase the density from 1.28 to 1.43, and to reduce density fluctuations in environmental conditions and durability with a simple configuration that does not require a dedicated detection member such as a potential sensor or a density sensor. Became possible.

<Second Embodiment>
The detailed operation of the printer according to the second embodiment of the present invention will be described with reference to the flowchart of FIG. The apparatus configuration is the same as that of the first embodiment, and redundant description is omitted.

  When the printer receives a print signal from a host computer (not shown), the process from the initial rotation operation described above to the determination of the optimum transfer voltage Vt at ATVC is the same as that in the flowchart of FIG. 2 (S11 to S13).

Thereafter, as shown in FIG. 7 (a), CPU 9a measures the voltage _{V 3} of the transfer roller 5 across by applying a -5μA constant current of the same polarity as the toner to the transfer roller 5 (S21).

Next, the uniformly charged photosensitive drum 1 is irradiated with laser light to form a belt-like latent image of a predetermined size (for example, main scanning width 200 mm × sub-scanning width 5 mm), and the same developing bias (AC) as during printing. : 2400 Hz / 1.6 KVpp, DC: -440 V) is applied to form a black toner band on the photosensitive drum 1 (S22). When the toner black band was the formation passes through the transfer roller 5, as shown in FIG. 7 (b), the voltage across the transfer roller 5 with a bias of the same polarity as the toner as toner black band voltage V ₄ Measure (S23).

Thereafter, CPU 9a reads a toner concentration determination reference data _{V 5} corresponding to the transfer roller 5 across the voltage _{V 3} of the time the same polarity as the toner of the constant current (-5 .mu.A) applied from the memory 9b (S24). Then, comparing the toner black band voltage V ₄ were measured and the toner concentration determination reference data V ₅ (S25). If more toner black band voltage V ₄ is small, it is determined that no longer out concentration decreased the amount of applied toner on the photosensitive drum 1.

In this embodiment, as described above, the resistance value of the transfer roller 5 varies due to the environmental variation. For example, the voltage V ₃ across the transfer roller 5 when −5 μA is applied in an environment of 23 ° C./50% is − It is about 1 KV. In this state, when a toner black belt having a reflection density of 1.3 is passed over the transfer roller 5, the resistance value (absolute value) of the transfer roller 5 increases as the voltage across the transfer roller 5 increases by the amount of the toner black belt. For example rose to -1.2 kV, this value is the toner concentration determination reference data _{V 5.} Reflection density becomes thinner than 1.3, the toner adhesion decreases the output value of the toner black band voltage V ₄ is numerically than the toner concentration determination reference data V ₅ decreases so small to the transfer roller 5. As a result, it is determined that the toner density has decreased, and correction is executed. If is larger toner black band voltage V _4, the toner density correction is determined to be unnecessary, the toner density correction is not executed.

  When the CPU 9a determines that the toner density needs to be corrected, the development DC bias is changed from -400V to -450V, for example, so as to widen the development contrast in order to increase the density in the printing operation, and the development contrast is shifted by 50V toward the higher density. The control to perform is executed (S26).

  In this way, after executing the necessary toner density correction according to the environmental change, the normal printing operation is executed to perform the printing operation on the paper P (S27).

The toner concentration determination reference data V ₄ stored in the memory 9b changes the transfer roller 5 across the voltage V ₃ at the time of applying a constant current of -5μA to the transfer roller 5, the toner in each V ₃ A toner black belt having a toner density (in this embodiment, a reflection density of 1.3) serving as a threshold value for starting density correction is formed, and the voltage across the transfer roller 5 when passing through the transfer roller 5 is measured in advance by experiments. This value is expressed as a data table (or calculation formula).

  According to the present embodiment, as in the first embodiment, the toner density printed on the paper P by the printing operation can increase the reflection density from 1.28 to 1.43 in the present embodiment, for example. Therefore, it has become possible to reduce concentration fluctuations in environmental conditions and in a durable state with a simple configuration that does not require a dedicated detection member such as a potential sensor or a concentration sensor.

  Furthermore, since the bias having the same polarity as the toner is applied to the transfer roller 5 when the toner black belt passes the transfer roller 5, the amount of toner adhering to the transfer roller 5 is described in the first embodiment. Thus, the time required for the initial rotation operation can be shortened because the cleaning time of the transfer roller 5 can be shortened.

  The preferred embodiments of the present invention have been described above, but various modifications and changes other than those mentioned above can be made. For example, in the correction of image density, only the presence or absence of correction is determined using one threshold value (reference data for toner density determination). However, correction may be performed in a plurality of stages using a plurality of threshold values. Further, as described with reference to FIGS. 3 and 7, the constant current control is used when measuring the toner density data, but it is also possible to use constant voltage control. In this case, the value of the current flowing through the transfer roller can be measured, for example, as a voltage drop amount of the reference resistance, and this can be used as toner density data.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to a first embodiment of the present invention. 3 is a flowchart illustrating a detailed operation of the printer according to the first embodiment of the present invention. It is explanatory drawing of operation | movement of the 1st Embodiment of this invention. 6 is a graph showing a change according to time of a voltage V across the transfer roller 5 in the first embodiment of the present invention. In the first embodiment of the present invention, it is a graph showing the relationship between the detection voltage V ₀ and the toner concentration determination reference data V _2. 10 is a flowchart illustrating a detailed operation of the printer according to the second embodiment of the present invention. It is explanatory drawing of operation | movement of the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Photosensitive drum 2 ... Charging roller 3 ... Laser scanner 4 ... Developing apparatus 4a ... Developing sleeve 5 ... Transfer roller 6 ... Cleaning apparatus 6a ... Cleaning blade
7 ... Paper cassette
8 ... Fixing device 9 ... Control board 9a ... CPU
9b ... Memory 25 ... Pressure roller 26 ... Fixing roller M ... Device main body L ... Laser beam path P ... Recording material N ... Transfer nip part

Claims (15)

An image density control method in an image forming apparatus comprising a transfer member for transferring a developer image formed on the surface of an image carrier onto a recording material,
Forming a density check developer image on the image carrier;
Measuring data corresponding to a resistance value of the transfer member when the developer image for density check is not present in a transfer nip portion between the image carrier and the transfer member;
Measuring data corresponding to a resistance value of the transfer member when the density check developer image is present in the transfer nip; and
An image density control method comprising: a step of correcting an image forming condition that affects the image density during a printing operation based on both measurement results.   In the step of measuring data corresponding to the resistance value of the transfer member, a constant current is supplied to the transfer member, and the developer image for density check is transferred to the transfer nip portion between the image carrier and the transfer member. 2. The data corresponding to the resistance value of each of the transfer members when it does not exist and when it exists is measured as first and second voltage values at both ends of the transfer member. Image density control method. Measuring data corresponding to the resistance value of the transfer member,
Obtaining density determination reference data based on the first voltage value;
A step of comparing the reference data for density determination with the second voltage value,
The image density control method according to claim 2, wherein in the correcting step, an image forming condition that affects an image density during a printing operation is corrected based on the comparison result.   3. The image density control method according to claim 2, further comprising the step of cleaning the developer adhering to the transfer member by reversing the polarity of the constant current from the charging polarity of the developer.   3. The image density control method according to claim 2, wherein the polarity of the constant current is the same as the charging polarity of the developer. The image forming apparatus includes a charging unit that uniformly charges the image carrier, a latent image forming unit that forms an electrostatic latent image on the charged image carrier, and the formed electrostatic latent image. Development means for supplying and developing a developer,
The image density control method according to claim 1, wherein in the correcting step, at least one image forming condition is changed among the charging unit, the latent image forming unit, and the developing unit.   The image density control method according to claim 1, wherein the transfer member is an ion conductive transfer roller. In an image forming apparatus comprising a transfer member for transferring a developer image formed on the surface of an image carrier onto a recording material,
An image forming means for forming a density check developer image on the image carrier;
Measuring means for measuring data corresponding to resistance values of the transfer member when the density check developer image is not present in the transfer nip portion between the image carrier and the transfer member; ,
An image forming apparatus comprising: a correcting unit that corrects an image forming condition that affects an image density during a printing operation based on the measurement result.   The measuring means applies a constant current to the transfer member, and the density check developer image is present in the transfer nip portion between the image carrier and the transfer member, and when it exists. 9. The image forming apparatus according to claim 8, wherein data corresponding to a resistance value of the transfer member is measured as first and second voltage values at both ends of the transfer member. The measuring means obtains density determination reference data based on the first voltage value, compares the density determination reference data with the second voltage value,
The image forming apparatus according to claim 9, wherein the correcting unit corrects an image forming condition that affects an image density during a printing operation based on a comparison result of the comparing unit.   10. The image forming apparatus according to claim 9, further comprising a developer cleaning unit that reverses the polarity of the constant current to the charging polarity of the developer and adheres to the transfer member.   The image forming apparatus according to claim 9, wherein the polarity of the constant current is the same as the charging polarity of the developer. Charging means for uniformly charging the image carrier, latent image forming means for forming an electrostatic latent image on the charged image carrier, and supplying a developer to the formed electrostatic latent image Development means for developing,
The image forming apparatus according to claim 8, wherein the correction by the correcting unit is to change at least one image forming condition among the charging unit, the latent image forming unit, and the developing unit.   The image forming apparatus according to claim 8, wherein the transfer member is an ion conductive transfer roller. In an image forming apparatus comprising a transfer member for transferring a developer image formed on the surface of an image carrier onto a recording material,
Measuring means for measuring data corresponding to the resistance value of the transfer member that changes depending on the presence or absence of the developer at a transfer nip portion between the image carrier and the transfer member;
An image forming apparatus comprising: a correcting unit that corrects an image forming condition that affects an image density during a printing operation based on the measurement result.

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