JPH09244424A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent the fluctuation of transfer efficiency and to output a stable image where the reproducibility of color and density is good by providing a control means controlling output voltage for transfer based on toner adhesive amount and the resistance value of a transfer member. SOLUTION: In order to always obtain the same image density in the case of forming the image, image forming conditions such as the surface potential VO of a photoreceptor 1 and developing bias potential VB impressed on the surface of a developing sleeve 15 must be controlled. Then, the resistance value of an intermediate transfer member 5 is measured by a current detector 13. Furthermore, a solid reference image and a dot reference image are formed on the photoreceptor 1 and the area rate of the dot reference image and the toner adhesive amount of the solid reference image are detected by an image sensor 10 and stored in a memory 16. A printer control part 11 controls the values of the surface potential VO of the photoreceptor 1 and the developing bias VB based on the detected values and the various look-up tables stored in the memory 16.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an image forming apparatus, and more specifically, to an image of a copying machine or the like which employs an electrophotographic system that expresses gradation by increasing or decreasing the printing area ratio of dots and lines. The present invention relates to image density control of a forming apparatus.

[0002]

2. Description of the Related Art Most of the images created by an image forming apparatus are solid areas or halftone areas, and these images can be output with the same color and density with good reproducibility for the same input data. Is required. However, color and density change due to changes in the photoconductor characteristics, developing characteristics, and charging characteristics in the electrophotographic process, and image stability is impaired. Therefore, before the image forming operation, a reference toner image is formed in an area (hereinafter referred to as a non-image area) on the photoconductor that is not involved in the image forming operation under the reference image forming condition, and the image of the formed reference toner image is formed. It is known that the image is stabilized by automatically detecting the density to adjust the image forming conditions such as the developing bias potential, the photosensitive member surface potential, and the laser exposure amount.

[0003]

In order to stabilize the image in this manner, the process of transferring the image cannot be ignored.
Even if the image is constant on the photoconductor, if the transfer efficiency changes, the image transferred on the paper becomes unstable in the end. The transfer efficiency varies depending on the variation in the resistance value of the copy member and the charge amount of the toner, and the optimum value of the transfer voltage also deviates. The optimum value of the transfer voltage requires a higher transfer voltage as the resistance value of the transfer member increases, and also requires a higher transfer voltage due to the higher charge amount of the toner.

An object of the present invention is to provide an image forming apparatus capable of outputting an image in which color and density are reproducible and stable without changing transfer efficiency.

[0005]

A first image forming apparatus of the present invention comprises first detecting means for detecting a resistance value of a transfer member,
Reference image forming means for forming a reference image on the photoconductor before the image forming operation, second detecting means for detecting the toner adhesion amount of the reference image formed by the reference image forming means, toner adhesion amount and transfer member. Control means for controlling the output voltage of the transfer based on the resistance value of. The second image forming apparatus of the present invention is the first image forming apparatus that detects the resistance value of the transfer member.
Detecting means; reference image forming means for forming a reference image on the photosensitive member before the image forming operation; second detecting means for detecting the toner adhesion amount of the reference image formed by the reference image forming means; Adjusting means for adjusting the developing bias potential according to the toner adhesion amount detected by the detecting means, and control for controlling the transfer output voltage based on the developing bias potential and the resistance value of the transfer member adjusted by the adjusting means. And means

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of an image forming apparatus according to the present invention will be described with reference to the accompanying drawings. (1) Configuration of Copying Machine FIG. 1 is a so-called area gradation in which an electrophotographic system, which is an embodiment of the image forming apparatus of the present invention, is used to express the gradation of an image in terms of density of dots and lines. It is a sectional view of a copying machine which adopts the method. A photoconductor 1 as an image carrier having a surface coated with an organic photoconductive material (OPC) is rotatably provided in the direction of arrow A. Around the photoconductor 1, along the rotation direction thereof, the charging brush 2, the surface potential detection sensor 12, the laser exposure device 3, the developing device 4 having the developing sleeve 15, the image sensor 10, the intermediate transfer member 5, Also, a cleaner unit 6 is provided. The surface of the photoconductor 1 is charged to a uniform potential by using the charging brush 2 to which a voltage is applied by the charging power supply 7 as the photoconductor 1 rotates. Then, the surface potential detection sensor 12 detects the surface potential V ₀ of the charged photoconductor. The laser exposure device 3 is turned on / off based on the image data, and exposes the uniformly charged surface of the photoconductor 1. An electrostatic latent image is formed on the exposed surface of the photoconductor 1. The developing device 4 includes developing units for four colors of cyan, magenta, yellow, and black. Under the control of the printer controller 11, first, the cyan developing unit is selected and the electrostatic latent image formed on the photoconductor 1 is selected. Develop the image. The intermediate transfer member 5 is made of a conductive resin belt, and a transfer voltage V _{T having a} polarity opposite to that of the toner is transferred from the transfer power source 14 via the current detector 13.
Is applied. Therefore, the toner image formed on the photoconductor 1 is conveyed to the transfer portion and transferred to the intermediate transfer member 5. The toner remaining on the photoconductor 1 without being transferred to the intermediate transfer member 5 is collected by the cleaner unit 6. In addition,
The current detector 13 is used when measuring the resistance value of the intermediate transfer member 5. The steps of charging and exposing the photoconductor 1 and developing in the developing device 4 are repeatedly executed in the order of cyan, magenta, yellow, and black.
Toner images of four colors are overlaid on. The toner image formed as a multicolor image on the intermediate transfer member 5 is electrostatically transferred onto a transfer material by a final transfer member (not shown) and is conveyed to a fixing device (not shown), where the multicolor image is transferred. The toner image is fixed on the transfer material. An image is formed by the above-described structure. When forming an image, in order to always obtain the same image density for the same data, the photoconductor 1
It is necessary to control the image forming conditions such as the surface potential V _{0 of the} toner and the developing bias potential V _B applied to the surface of the developing sleeve 15. Therefore, in the present case, the solid reference image 91 and the halftone dot reference image 92 are formed on the photoconductor before the image forming operation, and the area ratio of the halftone dot reference image (the ratio of dots per unit area) is determined by the image sensor 10. Also, the toner adhesion amount (thickness) of the solid reference image is detected. The memory 16
In addition to storing a plurality of look-up tables, the detection value by the image sensor 10 and the developing bias potential V _B
The setting values such as are stored. The printer control unit 11 determines the surface potential V of the photoconductor 1 based on the detected values and various look-up tables stored in the memory 16.
_{The value of 0} and the developing bias potential V _B is controlled. The configuration of the image sensor 10 and the control of image forming conditions based on the detection value of the image sensor 10 will be described later.

(2) Configuration of Image Sensor FIG. 2 is a configuration diagram of the image sensor 10. The image sensor 10 is an LED 101 that is a light emitting element that illuminates a reference image formed on the photoconductor 1 at a predetermined angle.
And a photo sensor 102 that is a light receiving element that receives specularly reflected light from the LED 101, and a photo sensor 103 that receives scattered light. Printer control unit 11
Forms the halftone dot reference image 91 shown in FIG. 3 and the solid reference image 92 shown in FIG. 4 in the non-image area of the photoconductor in order to control the density of the image forming apparatus. The halftone dot reference image 91 shown in FIG. 3 is a predetermined halftone dot image formed by switching the laser exposure device 3 to the on / off state at a predetermined cycle. The solid reference image 92 shown in FIG. 4 is a solid image formed by keeping the laser exposure device 3 always on. First, in order to detect the thickness of the toner attached on the photoconductor 1, a solid reference image 92 is formed, and the photosensor 103 detects the scattered light from the LED 101. Then, a halftone dot reference image 91 is formed on the photoconductor 1 in order to detect the area ratio of the halftone dot image, which is the ratio of the dots per unit area.
The photo sensor 102 detects the specularly reflected light from the LED 101. That is, the solid reference image 9 is obtained by the first rotation of the photoconductor.
2 is formed and the scattered light is detected by the photo sensor 103, thereby detecting the toner adhesion amount with respect to the solid reference image. The halftone dot reference image 91 is formed by the second rotation of the photoconductor, and the area ratio of the halftone dot reference image 91 is detected by detecting the specular reflection light with the photosensor 102.

The detection of the area ratio of the halftone dot reference image 91 will be described below. FIG. 5 is a diagram for explaining that the intensity of specularly reflected light generated by irradiation with the LED 101 changes depending on the size of the dots forming the halftone dot reference image 91. As the dot size increases in the order of (a), (b) and (c), the amount of specular reflection light decreases as indicated by the width of the arrow in (d), (e) and (f). This is because the light incident from the LED 101 is hardly scattered on the surface of the photoconductor on which toner is not adhered, and most of the light is specularly reflected, whereas most of the toner image is scattered and toner adheres. This is based on the characteristic that the amount of light in the specular reflection direction is smaller than that of the surface of the photoconductor that is not provided.
That is, most of the light detected by the photo sensor 102 is
This is specular reflection light from the surface of the photoconductor 1 on which the toner of the halftone dot reference image 91 is not attached. Therefore, the photo sensor 10
It is possible to check the area ratio of the halftone dot reference image 91 based on the detected value of 2. Note that if the measurement range of the photosensor 102 is limited, the detected value greatly varies depending on the position of the measurement range. In order to stably detect specularly reflected light for more dots, the LED 101 and the photo sensor 102 do not have much directivity, and
It is preferable to widen the incident angle of 101 with respect to the normal to the photoconductor 1.

Next, the detection of the thickness (adhesion amount) of the toner adhering to the photosensitive member 1 will be described. FIGS. 6A and 6B are views for explaining that the intensity of scattered light generated by irradiation with the LED 101 changes depending on the thickness of the toner. The directions and lengths of a plurality of arrows shown in the figure indicate the direction and intensity of the reflected light. (A) shows that a large amount of light is diffusely and uniformly reflected when the toner adhesion amount is large, and (b) shows that a large amount of light is reflected in the regular reflection direction when the toner adhesion amount is small. It indicates that the remaining slight amount of light is diffusely reflected. The amount of specularly reflected light tends to decrease and the amount of scattered light tends to increase as the toner adhesion amount increases. Therefore, it is considered that the thickness of the toner of the solid image can be detected based on the amount of regular reflection light detected by the photo sensor 102. However, the light actually detected by the photosensor 102 is the sum of the specularly reflected light and the scattered light. As described above, the amount of specular reflection light decreases as the toner adhesion amount increases, but the amount of scattered light increases conversely. Unlike the halftone dot reference image, in the solid image, the value of these sums changes only slightly with an increase in the toner adhesion amount. Therefore, it is conceivable to give the photosensor 102 directivity and detect only the amount of specular reflection light, but this is against the condition required for the photosensor 102 when detecting the area ratio of the halftone dot reference image. Is. Therefore, the image sensor 10
For the purpose of accurately detecting only the scattered light, the photosensor 103 is provided, and the thickness of the toner is obtained based on the detection value of the scattered light of the solid reference image 92. The photo sensor 1
In order to detect only scattered light and eliminate the influence of specularly reflected light as much as possible, 03 is disposed at a position closer to the LED 101 inside the angle formed by the LED 101 and the normal line of the photoconductor 1.

(3) Control of image forming conditions This copying machine adopts an area gradation method. The laser exposure device 3 uses the image data that has been subjected to the area gradation processing to perform
Value exposure is performed. Here, the size (diameter) of each dot forming the halftone dot reference image formed on the photoconductor may become larger or smaller than a desired value depending on changes in temperature and humidity. When the dot size is large, the ratio of halftone dots per unit area, that is, the area ratio increases and the image becomes dark. The density of the halftone dot reference image also changes depending on the thickness of the dots, that is, the amount of toner adhered per unit area. If the dot size is the same,
The thicker the image on which the toner adheres, the higher the density. Figure 7
FIG. 3 is a diagram showing a potential distribution generated on the surface of the photoconductor 1 by exposure by the laser exposure device 3, and illustrates the size and thickness of dots formed on the photoconductor 1 by exposure. The size of the dot and its thickness are
Surface potential V _{0 of the} photoconductor 1 charged by the charging brush 2.
The developing bias power source 8 controls the developing bias potential V _B applied to the surface of the developing sleeve 15. Before the exposure by the laser exposure device 3, the photoreceptor 1 has a negative surface potential V ₀ , and the surface of the developing sleeve 15 of the developing device 4 has a low potential negative bias voltage V _B (however, | V _B | < │V ₀
Is satisfied). When the portion charged with the surface potential V ₀ reaches the portion facing the laser exposure device 3 as the photosensitive member rotates and is exposed by the laser exposure device 3, the surface potential V ₀ reaches the potential V _I. Decay. Figure 7
As shown in (a) of, the exposure amount of the laser exposure device 3 is
The surface potential of the photoreceptor 1 is adjusted to a value that attenuates it to a predetermined maximum attenuation potential. The surface potential V ₀ is detected by the surface potential detection sensor 12. The toner adhesion amount increases in proportion to the developing voltage ΔV = | V _B −V _I |. For example,
The toner adhesion amount can be increased by changing the value of the developing bias potential V _B to V ′ _B. As shown in FIG. 7A, the slope of potential change due to exposure becomes steeper as the surface potential V ₀ increases. When the value of the developing voltage ΔV is constant, the size of the dots formed on the photoconductor 1 changes depending on the value of the surface potential V ₀ . As shown in FIG. 7B, the diameter of the dot 202 formed when the surface potential is set to V ′ ₀ is smaller than the diameter of the dot 201 formed when the surface potential is V ₀ . That is, the toner adhesion amount can be controlled by the developing bias potential V _B , and the dot size can be controlled by the surface potential V ₀ . Based on the above characteristics, the printer control unit 11 detects, with the image sensor 10, the area ratio of the halftone dot reference image 91 developed under the reference image forming condition and the toner adhesion amount of the solid reference image 92. The developing bias V _B and the surface potential V ₀ are adjusted according to the value to stabilize the image density.

FIG. 8 is a diagram showing the potential distribution generated on the surface of the photoconductor 1 by the exposure by the laser exposure device 3, and illustrates the control of the size of the dots formed on the photoconductor 1. As described with reference to FIG. 7, the size of the dots formed on the photoconductor 1 changes depending on the value of the surface potential V ₀ . In FIG. 8, the diameter of the dot 301 is set to 2 L without changing the developing bias potential V _B.
The surface potential V ₀ may be set to V ′ ₀ in order to make it smaller. Further, in the case of the surface potential V ′ ₀ , the dot 30
1 is formed on the surface of the photoconductor 1 by setting the developing bias potential to V ′ _B. In this case, the surface potential V ′ ₀ may be set to V ″ ₀ in order to reduce the diameter of the dot 301 by 2L without changing the developing bias potential V ′ _B.
As will be understood from the above, when the surface potential V ₀ is changed to change the size of the dot, the higher the value of the surface potential V ₀ , the more rapidly the change amount of the potential required for the change of the size. To do. The surface potential V ₀ and the developing bias potential V _B
If the potential difference is large, fogging occurs. Further, when the above potential difference is small, unevenness of the surface potential is picked up, and image unevenness occurs. Therefore, it is necessary that the potential difference be within a certain range. Therefore, when the surface potential V ₀ is large to some extent, the developing bias V is set within a range in which the toner adhesion amount (thickness) does not fluctuate significantly.
_By adjusting _B , the dot size is controlled to prevent the above image noise from occurring.

FIG. 9 is a diagram showing a potential distribution generated on the surface of the photoconductor 1 by the exposure by the laser exposure device 3. The exposure amount of the laser exposure device 3 is adjusted to a value that attenuates the surface of the photoconductor 1 to the maximum attenuation potential V _I. When the exposure amount is further increased, the area of the maximum attenuation potential V _I is in the direction indicated by the dotted line in the direction in which the dot size is increased (in the direction in which the potential is expanded to the developing bias potential V _B or less). spread. Therefore, when the value of the surface potential V ₀ is large to some extent, the developing bias potential is adjusted, or instead of adjusting the developing bias potential, the light emission amount of the laser exposure device 3 is increased above the normal value. It is also possible to control the size of the dots.

FIG. 10 is a flowchart of the control processing of the image forming conditions executed by the printer control unit 11. Hereinafter, the control of the image forming conditions will be described in detail according to this flowchart. First, in order to detect a desired toner adhesion amount, a solid reference image 92 is formed in a non-image area on the photoconductor 1 with a predetermined developing bias potential V _B and surface potential V ₀ (step S1). The toner adhesion amount is detected based on the output value of the image sensor 10 and stored in the memory 16 (step S2). By referring to Table 1 which is a look-up table stored in advance in the memory 16, the developing bias potential V _B which is the desired toner adhesion amount is set based on the detected toner adhesion amount, and the development bias potential V is set. _The surface potential V ₀ corresponding to _B is provisionally set (step S3). Note that each set value is stored in the memory 16.

[Table 1] Generally, the measurement range of a high-sensitivity sensor is narrower than that of a low-sensitivity sensor. The solid line shown in FIG. 11 is a graph showing the relationship between the developing bias potential V _B and the surface potential V ₀ , and the hatched region shows the measurement range of the image sensor 10 that measures the area ratio. In step S3, in order to set the area ratio of the halftone dot reference image formed to detect the desired dot size within the measurement range of the image sensor 10 indicated by the diagonal lines, the developing bias potential V is determined based on the graph indicated by the solid line. _The surface potential V ₀ is temporarily set to the potential corresponding to the value of _B. The upper limits of the developing bias potential V _B and the surface potential V ₀ are −300v and −785v, respectively, so that the potential difference does not exceed 485v. This is to prevent image noise such as fog from occurring when the potential difference is out of the predetermined range, as described above. Then, a halftone dot reference image is formed in the non-image area on the photoconductor 1 with the set developing bias potential V _B and surface potential V ₀ (step S).
4). The area ratio of the halftone dot reference image formed by the image sensor 10 is detected (step S5). When the temporarily set absolute value of the surface potential V ₀ is less than 785 v (YES in step S6), the detected halftone dot reference image is referenced with reference to Table 2 which is a lookup table stored in advance in the memory 16. Area ratio and the temporarily set surface potential V
_The surface potential V ₀ is adjusted based on the value of ₀ (step S
7).

[Table 2] The absolute value of the temporarily set surface potential V ₀ is 785v.
When the above is the case (NO in step S6), further change of the surface potential V ₀ is stopped in order to prevent the occurrence of image noise such as fogging. Then, referring to Table 3, which is a lookup table stored in advance in the memory 16,
The developing bias V _B is adjusted within a range in which the amount of adhered toner (thickness) does not fluctuate significantly to control the dot size (step S8). The amount of change in the development bias potential V _B required to change the dot size is smaller than that when the surface potential V ₀ is used. As a result, the change in the potential difference between the developing bias potential V _B and the surface potential V ₀ is suppressed to a small level, and the occurrence of image noise such as fogging is prevented.

[Table 3] In step S8, the dot size may be controlled by adjusting the developing bias potential, or by increasing the light emission amount of the laser exposure device 3 above a normal value, instead of adjusting the developing bias potential. . in this case,
The spread of the potential difference between the developing bias potential V _B and the surface potential V ₀ can be effectively suppressed. Also, the developing bias potential V _B
If the dot size is controlled only by the amount of light emitted from the laser exposure device 3 instead of adjusting, the fluctuation in the toner adhesion amount (thickness) can be eliminated.

(4) Control of Transfer Potential Hereinafter, control of the transfer potential performed after the image forming condition control process and before the actual image forming process will be described. To stabilize the finally formed image, the transfer efficiency must also be stabilized. The toner image formed on the photoconductor 1 is conveyed to the transfer portion and transferred to the intermediate transfer member 5 to which the transfer voltage V _T having the polarity opposite to that of the toner is applied from the transfer power source 14 via the current detector 13. Here, the transfer voltage V
_{If T} is insufficient, a toner image cannot be sufficiently transferred from the photoconductor 1 and a transfer failure occurs. On the other hand, when the transfer voltage V _T is excessive, electrification is injected into the toner image on the photoconductor 1 and the polarity of the toner is reversed, and the transfer fails because the toner cannot be transferred. The transfer efficiency varies depending on the variation of the resistance value R of the intermediate transfer member 5 and the toner charge amount Q / M, and the optimum value of the transfer voltage V _T deviates with the variation of the transfer efficiency. FIG.
Indicates the relationship between the transfer voltage V _T and the transfer current I. In order to transfer a toner layer having a certain amount of adhesion and a charge amount Q / M, a transfer current equal to the total charge amount of the toner layer is required. Here, the required transfer current I is constant regardless of the resistance value R of the intermediate transfer member 5. However, when the resistance value R of the intermediate transfer member 5 is different, the optimum transfer voltage V _T for obtaining the required transfer current I is changed. Therefore, it is necessary to adjust the transfer voltage V _T based on the resistance value R. The resistance value R of the intermediate transfer member 5 is detected by the following procedure. First, the uniformly charged photoreceptor 1 is exposed by the laser exposure device 3, and a reverse bias is applied to the developing sleeve 15 so that the toner does not adhere to the exposed photoreceptor 1, and the exposed toner does not adhere. A predetermined voltage is applied to the intermediate transfer member 5 by the transfer power supply 14 with respect to the photoconductor 1, and the current value flowing at that time is measured by the current detector 13. Then, the resistance value R is detected from the applied voltage and the value detected by the current detector 13. Alternatively, the resistance value R may be detected by applying a predetermined current value to the photoconductor 1 to which no toner adheres after exposure and detecting the voltage value at that time.
The transfer voltage V _T is adjusted based on the resistance value R of the intermediate transfer member 5 thus detected. However, since the total charge amount of the toner layer changes depending on the toner charge amount Q / M, the optimum transfer current value also changes. FIG. 13 shows the transfer voltage V
The relationship between _T and transcription efficiency is shown. As the toner charge amount Q / M increases, the transfer voltage value required to obtain sufficient transfer efficiency changes. Therefore, it is necessary to adjust the transfer voltage V _T according to the toner charge amount Q / M. Therefore, the transfer voltage V _T is adjusted by both the resistance value R of the intermediate transfer member 5 and the toner charge amount Q / M. As described above, the toner adhesion amount changes depending on the toner charge amount Q / M. In other words, the toner charge amount Q / M can be predicted based on the amount of the solid reference image attached. Therefore,
The transfer voltage V _T may be adjusted based on the resistance value R of the intermediate transfer member 5 and the toner adhesion amount of the solid reference image 92. Further, since it predicted also Q / M by the developing bias potential V _B after being adjusted in accordance with the toner adhesion amount of the solid reference image 92, checks the value of the development bias potential V _B stored in the memory 16, This value and the resistance value R of the intermediate transfer member 5
The transfer voltage V _T may be adjusted based on The developing bias potential V _B , the predicted value of the toner charge amount Q / M, the resistance value R of the intermediate transfer member 5, and the resistance value R of the intermediate transfer member 5 which are set in the control process of the image forming conditions with respect to the toner adhesion amount of the solid reference image Table 4 shows the relationship between the transfer voltages V _T.

[Table 4] However, since the transfer voltage V _T is set based on the information (toner adhesion amount, developing bias potential V _B ) obtained during the control process described with reference to FIG. 10, it is necessary to perform the setting after the process. . FIG. 14 shows the relationship between the transfer voltage V _T and the photoreceptor surface potential V ₀ when a constant voltage V _G is applied to the charging brush 2 from the transfer power supply 7. As shown in the figure, when the voltage V _G applied to the charging brush 2 that charges the photoconductor 1 is constant, the surface potential V ₀ of the photoconductor 1 varies depending on the transfer voltage V _T. Therefore, in the actual image forming process executed after the control process of the transfer voltage, the photoconductor 1
The voltage V _G applied by the charging power source 7 to the charging brush 2 is corrected so that the surface potential V ₀ of the charging power source becomes a value set by the control of the image forming conditions. For example, the output voltage V _G of the charging power source 7 is corrected based on the variation of the transfer voltage V _T set in the transfer voltage control process.

FIG. 15 is a flowchart relating to the setting of the transfer voltage V _T , which is executed by the printer control section 11, following the control processing of the image forming conditions shown in FIG. First, the resistance value R of the intermediate transfer member 5 is obtained (step S1).
0). Previous toner adhesion amount of the reference toner image detected in the control process of the image forming conditions, or read from the printer control unit 11 of the development bias potential V _B set (step S11). Obtains the predicted value of the toner charge amount Q / M (step S12), the value and development bias potential V _B, the resistance value R and the toner adhesion amount of the resistance value R obtained in step S10, or the resistance value R and the toner charging The transfer potential V _T is set according to the value of the amount (step S13). Based on the set V _T variate, in the next image forming process, the charging brush 2 is charged by the charging power source 7 so that the surface potential V ₀ of the photoconductor 1 becomes the value set in the control process of the image forming conditions. The voltage V _G applied to is corrected (step S14).

[0016]

In the first image forming apparatus of the present invention, the transfer efficiency can be stabilized by controlling the transfer voltage in consideration of the resistance value of the transfer member and the toner charge amount, and the color and density can be improved. However, a stable output image can be obtained with good reproducibility. Further, in the second image forming apparatus of the present invention, considering the resistance value of the transfer member and the developing bias potential,
By controlling the transfer voltage, the transfer efficiency can be stabilized and an output image with stable color and density with good reproducibility can be obtained.

[Brief description of drawings]

FIG. 1 is a cross-sectional view of a copying machine according to this embodiment.

FIG. 2 is a diagram showing a configuration of an image sensor.

FIG. 3 is a diagram showing a halftone dot reference image.

FIG. 4 is a diagram showing a solid reference image.

FIG. 5 is a diagram for explaining a change in the amount of regular reflection light with a change in the area ratio of halftone dots.

FIG. 6 is a diagram for explaining a change in light amount of a scattering term due to a change in toner thickness.

FIG. 7 is a diagram showing the relationship between the surface potential V _{0 of} the photoconductor, the developing bias potential V _B , and the size of dots formed on the photoconductor.

FIG. 8 is a diagram for explaining the amount of change in surface potential required to change the size of dots formed on the photoconductor.

FIG. 9 is a diagram showing regions in which the potential is attenuated when exposed with a normal exposure amount and when exposed with a larger exposure amount.

FIG. 10 is a flowchart of control processing of image forming conditions.

FIG. 11 is a graph showing the relationship between the developing bias potential V _B and the temporarily set photoconductor surface potential V ₀ .

FIG. 12 is a graph showing the relationship between the transfer potential V _T and the transfer current.

FIG. 13 is a graph showing the relationship between the transfer potential V _T and the transfer efficiency.

FIG. 14 is a graph showing the relationship between the transfer potential V _T and the photoreceptor surface potential.

FIG. 15 is a flowchart of a control process of a transfer potential V _T.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Photosensitive member 2 ... Charging brush 3 ... Laser exposure device 4 ... Developing device 5 ... Intermediate transfer member 6 ... Cleaner unit 7 ... Charging power source 8 ... Development bias power source 9 ... Reference image 10 ... Image sensor 11 ... Printer control unit 12 ... Surface potential detection sensor 13 ... Current detector 14 ... Transfer power supply 15 ... Development sleeve 16 ... Memory 91 ... Halftone dot reference image 92 ... Solid reference image 101 ... LED 102, 103 ... Photo sensor

Claims (2)

[Claims] 1. A first detecting means for detecting a resistance value of a transfer member, a reference image forming means for forming a reference image on a photosensitive member before an image forming operation, and a reference image formed by the reference image forming means. An image forming apparatus, comprising: a second detection unit that detects the toner adhesion amount of the above; and a control unit that controls the transfer output voltage based on the toner adhesion amount and the resistance value of the transfer member. 2. A first detecting means for detecting a resistance value of a transfer member, a reference image forming means for forming a reference image on a photosensitive member before an image forming operation, and a reference image formed by the reference image forming means. Second detection means for detecting the toner adhesion amount of the toner, and, according to the toner adhesion amount detected by the second detection means,
An image forming apparatus comprising: an adjusting unit that adjusts a developing bias potential; and a control unit that controls an output voltage of transfer based on the developing bias potential adjusted by the adjusting unit and a resistance value of a transfer member.