JPH06214451A - Image forming device - Google Patents

Abstract

PURPOSE:To always stably obtain a high-quality and excellent developing characteristic without receiving the effect of the secular deterioration of developer or environmental fluctuation by controlling the electric field of a developing bias based on the detected result of the electrostatic charged quantity of the developer. CONSTITUTION:The concentration of toner in a black developing device is detected by a toner concentration sensor 50 and the electrostatic charged quantity is calculated based on a signal outputted by the sensor 50 and the attached quantity of the toner. By a main control part 44, the amplitude (peak-to-peak voltage) and the frequency of the AC, component of a developing bias voltage are decided from the calculated electrostatic charged quantity based on relation between the electrostatic charged quantity previously stored in a memory and the peak-to-peak voltage and the frequency of the AC component of the developing bias voltage. Then, the developing bias voltage and the frequency to a developing sleeve from a power source circuit 49 are controlled so as to become the decided voltage and the decided frequency. Therefore, the image without surface staining or edge emphasis can be always stably obtained by the precise attached quantity of the toner without receiving the effect of the secular deterioration of the developer or the environmental fluctuation in the black developing device.

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 such as a copying machine, a printer or a facsimile which develops with a two-component developer containing a carrier and a toner.

[0002]

2. Description of the Related Art Generally, an image forming apparatus includes an image carrier composed of a photoconductor, a latent image forming means for forming an electrostatic latent image on the image carrier, and a developer composed of the image carrier and a developing sleeve. A two-component developer is conveyed by a developer carrying member to a developing region facing the carrying member, and a developing bias voltage is applied to the developer carrying member from a developing bias power source to form a developing bias electric field in the developing region. And a developing device for developing the electrostatic latent image on the image carrier to visualize it, and the developed image is transferred onto a transfer paper.

The image forming apparatus is monochrome or two-color or three-color.
There are copiers and printers that obtain multi-color and full-color images of more than one color. Further, it is known that a smooth image without edge enhancement can be obtained by using a DC bias voltage with an alternating component superimposed as the DC bias voltage in the image forming apparatus. Further, in the image forming apparatus, a method of variably controlling the amplitude of the direct current component, the amplitude of the alternating current component and the frequency of the alternating current component of the developing bias voltage according to the spatial frequency of the document, and the electric resistance of the developer by an environmental sensor near the developing device There is a method of detecting and controlling the magnitude of the developing alternating bias electric field based on the detection result. Further, in the image forming apparatus, there is a control method for controlling the latent image potential on the image carrier so as to correct the influence of environmental fluctuation.

[0004]

In the above method, the DC component and AC component amplitude of the developing bias voltage and the AC component frequency are variably controlled according to the spatial frequency of the original.
Distortion of the image (edge enhancement) due to the characteristics and deterioration of the developer is not taken into consideration. Further, in the above-mentioned method, the humidity is measured by the environment sensor in the vicinity of the developing device and the magnitude of the developing alternating bias electric field is controlled based on the measurement result, but the disturbance of the image due to the deterioration of the developer over time is not considered. . Further, in the above method, the latent image potential on the image carrier is controlled so that the influence of environmental changes is corrected. However, in the case where full-color image formation is performed using toners of a plurality of colors, subtle color There are limitations in terms of reproduction and reproduction of highlights, and it is not possible to achieve high-quality images to the extent required.

In the image forming apparatus, a change in humidity, which is one of environmental changes, has a great influence on the toner and adversely affects the developing state of the developing device. For example, at low humidity, a sufficient image density cannot be obtained, and at high humidity, background stains and toner scattering occur to deteriorate the image quality. Further, the charge amount of the toner decreases with time, and the image quality is deteriorated due to scumming and toner scattering as in high humidity.

SUMMARY OF THE INVENTION The present invention provides an image forming apparatus which improves the above-mentioned drawbacks and can always obtain stable and high image quality and good developing characteristics without being affected by deterioration of the developer with time and environmental changes. To aim.

[0007]

In order to achieve the above object, the invention according to claim 1 provides an image carrier, latent image forming means for forming an electrostatic latent image on the image carrier, and the image. On the image carrier, a two-component type developer is conveyed by the developer carrier to a developing region where the carrier and the developer carrier face each other, and a developing bias electric field having an alternating electric field is formed in the developing region. In the image forming apparatus having the developing means for developing the electrostatic latent image, the developer charge amount detecting means 1 for detecting the charge amount of the developer in the developing means, as shown in FIG.
The developing bias electric field control unit 2 controls the developing bias electric field based on the detection result of the developer charge amount detecting unit 1.

According to a second aspect of the present invention, an image carrier, a latent image forming means for forming an electrostatic latent image on the image carrier, and a developing area where the image carrier and the developer carrier face each other. A two-component developer is conveyed by the developer carrying member and a developing bias electric field having an alternating electric field is formed in the developing area to develop the electrostatic latent image on the image carrying member to form a visible image. In an image forming apparatus having a developing means, a toner adhesion amount detecting means for detecting a toner adhesion amount of a visible image on the image carrier, and a toner density detecting means for detecting a toner density of a developer in the developing means. And a toner charge amount calculation unit for calculating the charge amount of toner from the detection result of the toner concentration detection unit and the detection result of the toner adhesion amount detection unit.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the image forming apparatus described above, when the charge amount detected by the developer charge amount detection unit or the charge amount calculated by the toner charge amount calculation unit is outside the upper and lower limit values, it is determined that the developer has reached the end of life. The developer life determining means is provided.

According to a fourth aspect of the present invention, in the image forming apparatus according to the first, second or third aspect, a developer electric resistance detecting means for detecting electric resistance of the developer in the developing means,
Development bias electric field control means for controlling the development bias electric field based on the detection result of the developer electric resistance detection means and the charge amount detected by the developer charge amount detection means or the charge amount calculated by the toner charge amount calculation means. It is equipped with and.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the developing means has a regulating member for regulating the amount of the developer carried by the developer carrier, The electric resistance detection means detects a dynamic electric resistance of the developer by applying a voltage to the regulating member and detecting a current flowing through the developer.

The invention according to claim 6 is the invention according to claim 4 or 5.
In the image forming apparatus described above, when the charge amount detected by the developer charge amount detection unit or the charge amount calculated by the toner charge amount calculation unit is outside the upper and lower limit values, or by the developer electric resistance detection unit. The developer life determining means is provided for determining that the developer has reached the end of its life when the detected dynamic electric resistance of the developer is out of the specified value.

According to a seventh aspect of the present invention, an image bearing member, a latent image forming means for forming an electrostatic latent image on the image bearing member, and a developing area where the image bearing member and the developer bearing member face each other. And a developing means for developing a static latent image on the image carrier by forming a developing bias electric field having an alternating electric field in the developing area while conveying a two-component developer by the developer carrier. In the image forming apparatus, a plurality of predetermined patterns of electrostatic latent images having different potentials are formed on the image carrier, and the electrostatic latent images are developed with a predetermined developing potential by the developing means to form a visible image. A development bias electric field setting means for detecting a visible image with an optical sensor, calculating a gradient of the toner adhesion amount based on a detection result of the optical sensor with respect to the development potential, and setting the development bias electric field with the gradient. A.

According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, when the gradient does not fall within the allowable value even when the alternating component of the developing bias electric field reaches the upper limit value, the developer is added. It is equipped with a developer replacement means for indicating that the developer has been replaced when it has reached the end of its life.

[0015]

According to the first aspect of the invention, the developer charge amount detecting means 1 detects the charge amount of the developer in the developing means, and the developing bias electric field control means 2 indicates the detection result of the developer charge amount detecting means 1. Based on this, the developing bias electric field is controlled. Therefore, even if the charge amount of the developer changes with time and the condition of the development bias electric field for obtaining an optimum image changes depending on the charge amount of the developer, the development bias electric field changes depending on the charge amount of the developer. Is controlled so that the optimum image is always obtained.

According to the second aspect of the present invention, the toner adhesion amount detecting means detects the toner adhesion amount of the visible image on the image carrier, and the toner density detecting means detects the toner density of the developer in the developing means. Then, the toner charge amount calculation unit calculates the toner charge amount from the detection result of the toner concentration detection unit and the detection result of the toner adhesion amount detection unit. Therefore, the charge amount of the toner can be easily obtained, and the developing bias electric field can be controlled according to the charge amount of the developer to always obtain an optimum image.

According to a third aspect of the present invention, in the image forming apparatus according to the first or second aspect, the developer life determining unit determines the charge amount detected by the developer charge amount detecting unit or the charge amount calculated by the toner charge amount calculating unit. When the amount is out of the upper and lower limits, it is judged that the developer has reached the end of life. Therefore, the time to replace the developer is automatically known, and the charge amount of the developer is excessively increased, an image density is insufficient, an abnormal image is generated due to a large edge emphasis, or the charge amount of the developer is too low, and toner scatters.
It is possible to prevent the occurrence of abnormal images due to background stains and the like.

According to a fourth aspect of the invention, in the image forming apparatus according to the first, second or third aspect, the developer electric resistance detecting means detects the electric resistance of the developer in the developing means, and the developing bias electric field control means. Controls the developing bias electric field based on the detection result of the developer electric resistance detection means and the charge amount detected by the developer charge amount detection means or the charge amount calculated by the toner charge amount calculation means. Therefore, it is possible to determine the optimum developing conditions of the developing means, and it is possible to always obtain stable and high image quality and good developing characteristics without being affected by deterioration of the developer with time and environmental changes.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, the developer electric resistance detecting means applies a voltage to the regulating member to detect a current flowing through the developer, thereby moving the developer. Electrical resistance is detected. Therefore, the electric resistance of the developer can be easily detected with high accuracy.

According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth or fifth aspect, the developer life determining means determines the charge amount detected by the developer charge amount detecting means or the charge amount calculated by the toner charge amount calculating means. When the amount is outside the upper and lower limit values, or when the dynamic electric resistance of the developer detected by the developer electric resistance detecting means is outside the specified value, it is judged that the developer has reached the end of its life. Therefore, the time to replace the developer is automatically known, and the charge amount of the developer rises too much to cause an image density shortage, an abnormal image due to edge enhancement or the like, and the charge amount of the developer is too low to cause toner scattering and background. It is possible to prevent the occurrence of abnormal images due to dirt, etc.
Further, it is possible to prevent the electric resistance of the developer from becoming too high and causing an abnormal image due to edge enhancement or the like, and preventing the electric resistance of the developer from becoming too low to cause a large image roughness due to a leak of the developing bias. Will be possible.

According to a seventh aspect of the invention, the developing bias electric field setting means forms a plurality of predetermined electrostatic latent images having different potentials on the image carrier, and the electrostatic latent images are developed by the developing means to a predetermined development. The potential is developed to form a visible image, the optical image is detected by an optical sensor, the gradient of the toner adhesion amount is calculated based on the detection result of the optical sensor with respect to the developing potential, and the developing bias electric field is set by this gradient. Therefore, the toner adhesion amount γ is optimized, and at the same time, an optimum image is obtained.

According to an eighth aspect of the present invention, in the image forming apparatus according to the seventh aspect, when the developer exchanging means does not fall within the allowable value even if the alternating component of the developing bias electric field reaches the upper limit value. Indicates that the developer has reached the end of its life, and displays the replacement of the developer. Therefore, if the toner adhesion amount γ does not reach the allowable value even if the condition of the alternating component of the developing bias electric field is changed, the replacement of the developer can be warned.

[0023]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A developing device in an image forming apparatus forms a magnetic brush composed of a two-component developer containing a toner and a carrier on a developing sleeve, and the magnetic brush is brought into contact with an image carrier to form a toner on the image carrier. A two-component developing system for developing an electrostatic latent image has been generally used conventionally. In this two-component developing method, the frequency characteristic of the electrostatic latent image on the image carrier is greatly influenced by the electric characteristic of the carrier. The electrical characteristics of the carrier are as follows: the developer carriers are not electrically connected to each other (in the case of an insulating magnetic brush) and the developer carriers are electrically connected to each other (for the conductive magnetic brush). In some cases), and depends largely on the electric resistance of the carrier.

The electric resistance of the carrier is determined by the resin coating material coated on the surface of the carrier for the purpose of imparting and stabilizing the triboelectric charge of the toner. As the resin coating material, Teflon, silicon, or styrene resin is generally used, and carbon or the like is generally used as a carrier resistance imparting agent.

A method is known in which an AC bias voltage on which a DC component is superimposed is used as the developing bias voltage. In this method, the electrostatic latent image on the image carrier can be easily developed by activating the movement of the toner, and the relative speed between the image carrier and the developing sleeve can be set small. Furthermore, the edge phenomenon of the image can be mitigated,
Uniform development can be performed.

By the way, when developing an electrostatic latent image on an image bearing member with a two-component type developer using a conductive carrier as a carrier, edge emphasis is unlikely to occur, but a high resistance insulating carrier is used as a carrier. It is known that edge enhancement easily occurs when the electrostatic latent image on the image carrier is developed with the used two-component developer. For example, when developing an electrostatic latent image on an image bearing member with a two-component developer using a conductive carrier, the relationship between the frequency of the electrostatic latent image on the image bearing member and the developing density is shown in FIG. In contrast to the characteristic curve a, which shows a flat developing characteristic with respect to the frequency of the electrostatic latent image without emphasizing a specific frequency, an insulating carrier is used.
When the electrostatic latent image on the image bearing member is developed with the component type developer, the relationship between the frequency of the electrostatic latent image on the image bearing member and the developing density is as shown by the characteristic curve b in FIG. The development characteristic of edge enhancement for enhancing a specific frequency is shown.

Further, in general, when a toner is attached to the surface of the carrier with the passage of time and the toner is not separated from the toner as shown by a characteristic curve a in FIG. 3 showing the relation between the time (number of sheets used) and the resistance of the carrier, Are known to increase carrier resistance. From these, it is assumed that the degree of edge enhancement over time is due to the increase in the resistance of the carriers over time, and multiple carriers with different resistances are prepared, and the resistance of these carriers and the degree of edge enhancement are As a result of investigating the relationship of, the higher the carrier resistance, the stronger the degree of edge enhancement as shown in FIG.

On the other hand, it is known that as shown by the characteristic curve b in FIG. 3, the resin coating layer of the insulating carrier is abraded over time, and the resistance of the carrier is lowered. From this, it was speculated that the decrease in the sharpness of the image with time was due to the decrease in the resistance of the carrier with time. Therefore, when various experiments and studies were conducted, there was a correlation between the edge emphasis and sharpness deterioration of the image and the peak-to-peak voltage and frequency of the AC component of the developing bias voltage applied to the developing sleeve. In order to obtain a good image without edge enhancement or sharpness reduction, it was found that there is a proper range for the peak-to-peak voltage and frequency, and that the proper range depends on the carrier resistance. .

For example, in FIG. 5, the horizontal axis indicates the above-mentioned peak-to-peak.
Peak voltage (amplitude Vpp of AC component of developing bias voltage)
Taking the degree of edge enhancement of the image on the vertical axis, the peak-to-peak voltage Vpp and the edge of the image for the initial carrier a, the carrier b whose resistance has decreased due to use, and the carrier c whose resistance has increased due to use It shows the correlation with the degree of emphasis. It can be seen from FIG. 5 that as the resistance of the carrier increases, the peak-to-peak voltage Vpp for obtaining a good image with less edge emphasis increases.

In FIG. 6, the horizontal axis represents the above frequency (the frequency fb of the AC component of the developing bias voltage) and the vertical axis represents the degree of edge enhancement of the image. It shows the correlation between the frequency fb and the degree of edge enhancement of an image for the carrier b and the carrier c whose resistance has increased due to use. It can be seen from FIG. 6 that the frequency fb for obtaining a good image with less edge emphasis increases as the resistance of the carrier increases.

The peak-to-peak voltage Vpp
When the frequency fb is higher than the appropriate range of the peak-to-peak voltage Vpp and the frequency fb which can obtain a good image with less edge enhancement, it is clear that the sharpness of the image is deteriorated. did.

From the above, it is possible to obtain a good image in which the peak-to-peak voltage Vpp or the frequency fb does not cause edge enhancement or sharpness deterioration due to the carrier resistance changing with time. It was found that the image quality was out of the proper range, which resulted in deterioration of image quality due to edge enhancement and deterioration of sharpness over time.

In FIGS. 7 and 8, the horizontal axis represents the peak-to-peak voltage Vpp and the vertical axis represents the toner adhesion amount γ and the development density, respectively, and the initial carrier a, and the resistance was lowered by the use. The correlation between the peak-to-peak voltage Vpp, the toner adhesion amount γ, and the development density is shown for the carrier b and the carrier c whose resistance is increased by use. It can be seen from FIGS. 7 and 8 that the higher the carrier resistance, the larger the peak-to-peak voltage Vpp for obtaining the maximum toner adhesion amount γ and the development density.

Further, in FIGS. 9 and 10, the frequency fb is plotted on the horizontal axis and the toner adhesion amount γ and the development density are plotted on the vertical axis, respectively. The initial carrier a, the carrier b whose resistance is lowered by the use, and the use b The correlation between the frequency fb, the toner adhesion amount γ, and the development density is shown for the carrier c having increased resistance. This FIG. 9 and FIG.
It can be seen from the above that as the carrier resistance increases, the maximum toner adhesion amount γ and the above frequency fb for obtaining the development density increase.

It has been found that such a correlation not only applies to the resistance of the developer but also relates to the charge amount of the developer. There are various kinds of developers, some of which have an increase in the charge amount Q / M over time as shown by the characteristic curve a in FIG. 11 and some of which decrease as shown by the characteristic curve b in FIG.
The cause of the decrease in the charge amount Q / M of the developer over time is spent of the developer, scraping of the resin coating layer of the carrier, and the like. Further, the charge amount Q / M of the developer fluctuates greatly depending on the environment, and rises under low temperature and low humidity and decreases under high temperature and high humidity as shown in FIG.

FIG. 13 shows the relationship between the charge amount Q / M of the developer and the edge enhancement level of the image. As can be seen from FIG. 13, the lower the charge amount Q / M of the developer, the better the edge enhancement level of the image. However, if the charge amount Q / M of the developer is too low, toner scattering and background stain occur, and when the AC component of the developing bias is applied, the charge flows through the developer to the image carrier to cause electrostatic latent image on the image carrier. The phenomenon that the image is destroyed occurs.

It has been found that the relationship between the charge amount Q / M of the toner, the edge enhancement level of the image, and the developing characteristics is as shown in FIGS. 14 to 19 for the toners having different charge amounts Q / M. 14 and 15 show an initial carrier a, a carrier b with a reduced charge amount Q / M, and a charge amount Q / M.
FIG. 16 shows the relationship between the peak-to-peak voltage Vpp, the frequency fb, and the edge enhancement level of the image with respect to the carrier c having an increased carrier. FIGS. FIG. 18 and FIG. 19 show the relationship between the peak-to-peak voltage Vpp, the toner adhesion amount γ, and the developing density for the carrier b in which M is decreased and the carrier c in which the charge amount Q / M is increased. a, carrier b with reduced charge amount Q / M, charge amount Q
The relationship between the frequency fb, the toner adhesion amount γ, and the development density is shown for the carrier c with an increased / M.

From these relationships, it can be seen that the higher the toner charge amount Q / M, the stronger the edge emphasis of the image and the lower the toner adhesion amount γ. Also, the toner charge amount Q
When / M is high, it is necessary to increase the peak-to-peak voltage Vpp in order to enhance the edge of the image and improve the toner adhesion amount γ, and conversely, the toner charge amount Q /
When M becomes low, the above peak-to-peak voltage V
It is better to lower pp.

As described above, since the edge enhancement of the image and the developing characteristic are related to the resistance of the carrier and the charge amount of the developer, the embodiment of the present invention detects the resistance of the carrier and the charge amount of the developer, and the result is detected. By controlling the AC component of the development bias voltage based on, the stable high image quality without background stains and edge enhancement is always stable with an appropriate toner adhesion amount γ without being affected by the deterioration of the developer over time and environmental changes. To get the image of.

Generally, it is difficult and impractical to detect the resistance of the developer in the developing device, but the charge amount of the developer can be detected. The charge quantity of the developer, which is a state quantity, represents all of the fluctuations due to the environment (temperature and humidity) and deterioration over time, and it is preferable to determine the AC component of the developing bias voltage based on the charge quantity. Further, in addition to this, if the resistance of the carrier can also be detected, it is most preferable to determine the developing condition by both the resistance of the carrier and the charge amount of the developer.

In another embodiment of the present invention, a plurality of predetermined electrostatic latent images having different potentials are formed on the image carrier, and the electrostatic latent images are developed with a predetermined developing potential by a developing device. To obtain a development image by detecting the development image with an optical sensor and calculating the gradient of the toner adhesion amount based on the detection result of the development potential of the optical sensor with respect to the development potential. By determining the development bias electric field, the smooth and high-quality image free from background stains and edge enhancement is always obtained without being affected by the deterioration of the developer over time and environmental changes.

Conventionally, the developer was considered to have reached the end of its life when the developing device developed a certain number of sheets, and the developer was replaced. However, the life of the developer is not unique.
It fluctuates due to differences in document area and environmental differences. Therefore, in the embodiment of the present invention, the developer is exchanged by accurately determining that the developer has reached the end of life by determining that the developer has reached the end of life by the resistance of the carrier and the charge amount of the developer. To perform.

Examples of the present invention will be described in detail below. FIG. 20 shows the outline of the first embodiment of the present invention. The first embodiment is an embodiment of the invention described in claims 1, 3 and 4, and is an example of an electrophotographic copying machine, which has a document reading section 10 and a printer section 11. In the printer unit 11, a charging charger 13, a writing device 14, a black developing device 15, color developing devices 16 to 18, an intermediate transfer belt 19, a cleaning device 20, and a charge eliminator are provided around an image carrier 12 made of an organic photosensitive drum. 21 is arranged, and the charger 13 and the writing device 14 form a latent image forming means. The intermediate transfer belt 19 is stretched around the rollers 22 to 26, and a transfer voltage is applied from a power supply circuit via the transfer bias rollers 25 and 26.

The photosensitive drum 12 is rotationally driven by a driving mechanism (not shown) during a copying operation, is uniformly charged by the charging charger 13, and an image is written by image exposure by the writing device 14 to form an electrostatic latent image. here,
The writing device 14 drives the semiconductor laser to be modulated by a driving circuit by, for example, a black image signal, and deflects the output light from the optical deflector to irradiate the photoconductor drum 12.

The black electrostatic latent image on the photosensitive drum 12 is developed by a black developing device 15 with a two-component developer containing black toner and a carrier to form a black visible image, which is transferred from the power supply circuit to the transfer bias roller 25. , 26, a transfer voltage is applied to the intermediate transfer belt 19 so that it is transferred to the intermediate transfer belt 19. After the transfer of the black image on the photoconductor drum 12, the cleaning device 20 removes the residual toner, and the static eliminator 21 removes the residual charge to enable the next image formation.

Further, the formation and transfer of the yellow image is performed in the same manner as the formation and transfer of the black image. in this case,
The writing device 14 drives the semiconductor laser to be modulated by a driving circuit with a yellow image signal, and deflects the output light of the semiconductor laser by the optical deflector to irradiate the photosensitive drum 12 with the yellow electrostatic latent image. Form on top.
The yellow electrostatic latent image on the photoconductor drum 12 contains yellow toner and carrier by the yellow developing device 16.
It is developed with a component type developer to form a yellow visible image, which is transferred to the intermediate transfer belt 19. After the transfer of the yellow image on the photoconductor drum 12, the cleaning device 20 removes the residual toner, and the static eliminator 21 removes the residual charge to enable the next image formation.

Similarly, formation and transfer of a magenta image is performed. In this case, the writing device 14 drives the semiconductor laser to be modulated by a magenta image signal by the drive circuit, and deflects the output light thereof by the optical deflector to irradiate the photoconductor drum 12 to expose the magenta electrostatic latent image. It is formed on the body drum 12. The magenta electrostatic latent image on the photosensitive drum 12 is developed by a magenta developing device 17 with a two-component developer containing magenta toner and a carrier to form a magenta image, which is transferred to the intermediate transfer belt 19. After the transfer of the magenta image on the photoconductor drum 12, the cleaning device 20 removes the residual toner, and the static eliminator 21 removes the residual charge to enable the next image formation.

Further, the formation and transfer of the cyan image are similarly performed. In this case, the writing device 14 drives the semiconductor laser to be modulated by the driving circuit with the cyan image signal, and deflects the output light from the optical deflector to irradiate the photoconductor drum 12 to expose the cyan electrostatic latent image. It is formed on the body drum 12. The electrostatic latent image of cyan on the photosensitive drum 12 is developed by a cyan developing device 18 with a two-component developer containing cyan toner and carrier to become a visible image of cyan, which is transferred to the intermediate transfer belt 19. After the transfer of the cyan image, the photosensitive drum 12 is cleaned by the cleaning device 20.
Thus, the residual toner is removed, and the static eliminator 21 removes the residual charge, so that the next image can be formed.

When a single color copy is made, any one of formation and transfer of a black image, formation and transfer of a yellow image, formation and transfer of a magenta image, and formation and transfer of a cyan image is performed. The transfer paper is fed from the paper feed device 27 to the registration rollers 28. The registration roller 28 sends the transfer paper with its front end aligned with the visible image on the intermediate transfer belt 19, and the transfer paper transfers the visible image on the intermediate transfer belt 19 by the transfer bias roller 29 and separates it from the intermediate transfer belt 19. It Next, the transfer paper is conveyed by the conveyor belt 3.
The image is conveyed by 0, the visible image is fixed by the fixing device 31, and is ejected as a copy to the paper ejection tray 32.

When two-color copying is performed, any one of formation and transfer of a black image, formation and transfer of a yellow image, formation and transfer of a magenta image, and formation and transfer of a cyan image is performed. Two are selectively performed and the intermediate transfer belt 1
Two-color images are superposed and transferred on the sheet 9, and the transfer paper is fed, and the images are transferred and fixed as in the case of monochromatic copying.
The color copy is ejected to the paper ejection tray 32. When performing full-color copying, the formation and transfer of a black image, the formation and transfer of a yellow image, the formation and transfer of a magenta image, and the formation and transfer of a cyan image are performed. Visual images of each color are superimposed and transferred onto the transfer belt 19,
As in the case of single-color copying, the transfer paper is fed, the visible image is transferred and fixed, and a full-color copy is output to the paper output tray 32.
Is discharged to.

In the document reading section 10, the document is placed on the document table 33. The original on the original table 33 is illuminated by the exposure lamp 34, and the reflected light image is imaged on the image sensor 39, which is a charge-coupled device, via the mirrors 35 to 37 and the imaging lens 38, and photoelectrically converted. It Then, the exposure lamp 34 and the mirror 35
The document is scanned by the movement of .about.37, and red, green, and blue image signals are obtained from the image sensor 39. The image signals of the three colors are processed by an image processing device (not shown) and converted into yellow, magenta, cyan, and black image signals, and these image signals are selectively sent to the writing device 14 and the semiconductor laser is driven by the drive circuit. Drive modulation.

FIG. 21 shows the control system of this embodiment. This control system has a main control unit 44 composed of a microcomputer including a CPU 40, a ROM 41, a RAM 42 and an interface (I / O) 43. The main control unit 44 includes an optical sensor 45, an environment sensor 46 and a photoconductor surface potential. The input signal from the sensor 47 is fetched to control the laser optical system control unit 48, the power supply circuit 49, the toner density sensors 50 to 53, and the intermediate transfer belt drive unit 54.

The laser optical system controller 48 is the writing device 1
4, the power supply circuit 49 applies a predetermined high voltage to the charging charger 13 and a developing bias voltage to the developing sleeves of the developing devices 15 to 18, and the transfer bias roller 25, 26, 29
A predetermined transfer voltage is applied to. The optical sensor 45 is an optical sensor composed of a light emitting element and a light receiving element, which is arranged on the downstream side of the transfer position for transferring the visible image on the photosensitive drum 12 and on the upstream side of the cleaning device 20, and is formed on the photosensitive drum 12. The toner adhesion amount of the thus-obtained reference density pattern, so-called P sensor pattern, and the toner adhesion amount of the background portion are measured for each visible image of each color toner.

The toner concentration sensors 50 to 53 detect the toner concentration of the developer in the developing devices 15 to 18, respectively. The toner replenishing circuits 55 to 58 compare the output signals of the toner density sensors 50 to 53 with a reference value, and if the toner density is below the reference value based on this comparison result, the toner having a size corresponding to the amount of the toner density is below the reference value. A replenishment signal is generated, and each of the developing devices 15 to 18 is generated by this toner replenishment signal.
The toner replenishing section in is driven to replenish toner to the developer. The photoconductor surface potential sensor 47 detects the surface potential of the photoconductor drum 12, and the intermediate transfer belt drive unit 5
4 drives the intermediate transfer belt 19 to rotate it.

As shown in FIG. 22, each developing device 15-18
In the above, the developer carrying members 59 to 62 made of a non-magnetic cylindrical developing sleeve are arranged at a predetermined gap from the photosensitive drum 12, for example, 0.6 mm, and are alternately arranged inside the developing sleeves 59 to 62. A developing magnet having a plurality of different magnetic poles (not shown) and a magnetic shield plate made of a magnetic material are provided and are held in a fixed state.

The developing sleeves 59 to 62 are rotationally driven in the directions of arrows during development by a black developing sleeve motor, a yellow developing sleeve motor, a magenta developing sleeve motor, and a cyan developing sleeve motor, which are not shown.
A two-component developer containing black toner and a carrier is accommodated inside the black developing device 15, and the developer is supplied to the developing sleeve 59 by the developer stirring / conveying scooping member 63 and the magnet inside the developing sleeve 59. The magnetic brush is attracted to the surface of the developing sleeve 59, thereby forming a magnetic brush. The magnetic brush is carried and conveyed by the developing sleeve 59, adjusted to a constant amount by the developer regulating member 67, and then supplied to the photosensitive drum 12 in the developing area where the photosensitive drum 12 and the developing sleeve 59 face each other. To develop the electrostatic latent image on the photoconductor drum 12.

Similarly, the yellow developing device 16, the magenta developing device 17, and the cyan developing device 18 are a two-component developer containing yellow toner and carrier, a two-component developer containing magenta toner and carrier, and a cyan toner and carrier, respectively. The two-component type developer containing is contained in the developer agitating and conveying pumping member 64 to 64.
The developing sleeves 60 to 62 are supplied to the developing sleeves 60 to 62 by the magnet 66, and the developing sleeves 60 to 62 are driven by the magnets in the developing sleeves 60 to 62.
By being attracted to the surface of 62, it becomes a magnetic brush. These magnetic brushes are carried and carried by the developing sleeves 60 to 62 and adjusted to a certain amount by the developer regulating members 68 to 70, and then in the developing area where the photosensitive drum 12 and the developing sleeves 60 to 62 face each other. The electrostatic latent image on the photosensitive drum 12 is developed by being supplied to the photosensitive drum 12.

Incidentally, in each of the developing devices 15 to 18, various conventionally known insulating carriers or conductive carriers can be used as the carrier of the developer constituting the magnetic brush. For example, the true specific gravity is 5 to 6 kg / coated with silicon or insulating resin having an average particle size of 10 to 60 μm.
cm ³ Ferrite core material, average particle size 3
A carrier having an iron powder having a true specific gravity of 4 to 6 Kg / cm ³ coated with silicon, styrene-acrylic resin, silicon resin, fluorine-modified acrylic resin or the like of 0 to 100 μm, a carrier having ferrite as a core material, or a granulation carrier is used. be able to. As the toner, various conventionally known toners can be used, for example, negatively charged toner to which hydrophobic silica, titanium oxide, etc. are added can be used. Each of the developing devices 15 to 18 develops the electrostatic latent image on the photosensitive drum 12 by, for example, a reversal developing method.

Next, the image forming conditions of this embodiment will be described. The photosensitive drum 12 has, for example, a peripheral speed of 180 mm / se.
-600V by the charger 13 while rotating at c
Be charged to. Next, an electrostatic latent image is formed on the photosensitive drum 12 by the writing device 14 by exposure with any one of a black image signal, a yellow image signal, a magenta image signal, and a cyan image signal. At this time, the photosensitive drum 1
The potential of the background part on 2 is -30V.

The electrostatic latent image on the photosensitive drum 12 is developed by any of the developing devices 15 to 18 and becomes any one of a black image, a yellow image, a magenta image, and a cyan image. . In this case, the developing devices 15 to 18 are arranged such that the developing sleeves 59 to 62 have a gap of 0.60 mm with respect to the photosensitive drum 12 at the time of developing, and the developing sleeves 59 to 62 receive a developing bias voltage from the power supply circuit 49. For example, a rectangular bias AC voltage having a peak-to-peak voltage of 1.8 KV and a frequency of 2 KHZ on which a DC voltage of -450 V is superimposed is applied to form a developing bias electric field having an alternating electric field in the developing area. Development sleeve 59 ~
The rotation peripheral speed ratio of 62 to the photosensitive drum 12 is about 1.8.
That is, the amount of developer pumped to the developing sleeves 59 to 62 is about 0.10 g / cm ² .

In the first embodiment, as shown in FIG. 23, the charge amount of the developer is measured to control the AC component of the developing bias voltage. That is, the main control unit 44 first causes the writing device 14 to perform the exposure of the black P sensor pattern at a predetermined timing, and the photoconductor drum 12 causes the charger 1 to be exposed.
After being uniformly charged by 3, the writing device 14 exposes the black P sensor pattern to form an electrostatic latent image of the black P sensor pattern. The electrostatic latent image of the black P sensor pattern is developed by the black developing device 15 to become a visible image of the black P sensor pattern, and the toner adhesion amount M / A of the visible image of the black P sensor pattern is an optical sensor (P sensor). 45
Measured by

There is a relationship between the toner adhesion amount M / A of the black P sensor pattern visible image and the output signal voltage Vsp of the optical sensor 45 corresponding thereto, as shown in FIG.
The M / A calculation circuit 71 takes in the output signal voltage Vsp of the optical sensor 45 with respect to the visible image of the black P sensor pattern, and outputs the output signal voltage Vsp of the optical sensor 45 as shown in FIG. Output signal voltage V
The toner adhesion amount M / A of the visible image of the black P sensor pattern is converted based on the relationship of sp.

Further, there is a primary or secondary relationship between the toner concentration TC of the developer in the black developing device 15 and the charge amount Q / M. This relationship changes over time and is generally shown in FIG.
As shown in 5, the charge amount Q / M decreases with time. Figure 25
Characteristic curve A is the toner concentration TC for the new developer.
Shows an example of the relationship between the charge amount Q / M and the characteristic curve B of FIG. 25 shows an example of the relationship between the toner concentration TC and the charge amount Q / M for the developer used. In addition, the relationship between the toner concentration TC of the developer and the charge amount Q / M may be such that the charge amount Q / M increases with time.

From the above relationship, the charge amount Q at each toner concentration TC
When the toner adhesion amount M / A when changing / M, the toner density TC and the charge amount Q /
The relationship between M and toner adhesion amount M / A was obtained. Therefore, the toner concentration TC of the developer in the black developing device 15 is detected by the toner concentration sensor (T sensor) 50, and M / A → Q /
The M calculation circuit 72 calculates the charge amount Q / M from the output signal of the toner concentration sensor 50 and the converted toner adhesion amount M / A. In this case, the M / A → Q / M calculation circuit 72 stores the toner density T as shown in FIG.
The charge amount Q / M is calculated from the output signal of the toner density sensor 50 and the converted toner adhesion amount M / A based on the relationship among C, the charge amount Q / M, and the toner adhesion amount M / A.

Next, the main control unit 44, based on the relationship between the charge amount Q / M and the amplitude (peak-to-peak voltage Vpp) of the AC component of the developing bias voltage and the frequency fb, which are stored in advance in the memory. From the calculated charge amount Q / M to the peak-to-peak voltage V of the AC component of the developing bias voltage
pp and frequency fb are determined, and the peak-to-peak voltage Vpp and frequency fb of the AC component of the developing bias voltage from the power supply circuit 49 to the developing sleeve 59 are controlled to the determined values. Therefore, it is possible to always stably obtain a smooth high-quality black image free from background stains and edge enhancement with an appropriate toner adhesion amount γ without being affected by the deterioration of the developer in the black developing device 15 with time and environmental changes. . The charge amount Q /
The relationship between the reciprocal of M and the toner concentration TC may be a straight line, and this relationship causes the toner concentration TC, the charge amount Q / M,
The relationship of the toner adhesion amount M / A may be obtained and stored in the memory.

Similarly, the main controller 44 causes the writing device 14 to expose the yellow P sensor pattern at a predetermined timing, and the photoconductor drum 12 is uniformly charged by the charging charger 13 and then the writing device 14 causes the yellow P sensor pattern to be exposed. By exposing the pattern, an electrostatic latent image of the yellow P sensor pattern is formed. The electrostatic latent image of the yellow P sensor pattern is developed by the yellow developing device 16 to become a visible image of the yellow P sensor pattern, and the toner adhesion amount M / A of the visible image of the yellow P sensor pattern is measured by the optical sensor 45. It

The Vsp → M / A calculation circuit 71 is yellow P
The output signal voltage Vsp of the optical sensor 45 for the visible image of the sensor pattern is taken in, and the output signal voltage Vsp of the optical sensor 45 is calculated based on the relationship between the yellow toner adhesion amount M / A and the optical sensor 45 output signal voltage Vsp.
The toner adhesion amount M / A of the visible image of the sensor pattern is converted. Toner concentration TC of the developer in the yellow developing device 16
Is detected by the toner concentration sensor 51, and M / A → Q /
The M calculation circuit 72 outputs the output signal of the toner concentration sensor 51 based on the relationship among the toner concentration TC, the charge amount Q / M, and the toner adhesion amount M / A relating to the developer in the yellow developing device 16, which is stored in the memory in advance. Toner adhesion amount M calculated above
The charge amount Q / M is calculated from / A.

Next, the main controller 44 stores the charge amount Q / M of the developer for the yellow developing device 16 and the amplitude (peak-to-peak voltage Vpp) of the AC component of the developing bias voltage, which are stored in the memory in advance. Based on the relationship of the frequency fb, the peak-to-peak voltage Vpp and the frequency f of the AC component of the developing bias voltage are calculated from the charge amount Q / M calculated above.
b is determined, and the peak-to-peak voltage Vpp of the AC component of the developing bias voltage from the power supply circuit 49 to the developing sleeve 60 and the frequency fb are controlled to the determined values.

Similarly, the main control unit 44 causes the writing device 14 to expose the magenta P sensor pattern at a predetermined timing, and the photosensitive drum 12 is uniformly charged by the charging charger 13 and then the magenta by the writing device 14. The exposure of the P sensor pattern forms an electrostatic latent image of the magenta P sensor pattern. The electrostatic latent image of the magenta P sensor pattern is developed by the magenta developing device 17 to become a visible image of the magenta P sensor pattern, and the toner adhesion amount M / A of the visible image of the magenta P sensor pattern.
Is measured by the optical sensor 45.

Vsp → M / A calculation circuit 71 is magenta P
The output signal voltage Vsp of the optical sensor 45 for the visible image of the sensor pattern is taken in, and the output signal voltage Vsp of the optical sensor 45 is calculated based on the relationship between the magenta toner adhesion amount M / A and the output signal voltage Vsp of the optical sensor 45.
The toner adhesion amount M / A of the visible image of the sensor pattern is converted. Toner concentration TC of the developer in the magenta developing device 17
Is detected by the toner concentration sensor 52, and M / A → Q /
The M calculation circuit 72 outputs an output signal of the toner concentration sensor 52 based on the relationship among the toner concentration TC, the charge amount Q / M, and the toner adhesion amount M / A regarding the developer in the magenta developing device 17, which are stored in the memory in advance. Toner adhesion amount M calculated above
The charge amount Q / M is calculated from / A.

Next, the main control unit 44 stores the charge amount Q / M of the developer for the magenta developing device 17 and the amplitude (peak-to-peak voltage Vpp) of the AC component of the developing bias voltage, which are stored in the memory in advance, and Based on the relationship of the frequency fb, the peak-to-peak voltage Vpp and the frequency f of the AC component of the developing bias voltage are calculated from the charge amount Q / M calculated above.
b is determined, and the peak-to-peak voltage Vpp of the AC component of the developing bias voltage from the power supply circuit 49 to the developing sleeve 61 and the frequency fb are controlled to the determined values.

Further, similarly, the main controller 44 causes the writing device 14 to expose the cyan P sensor pattern at a predetermined timing, and the photosensitive drum 12 is uniformly charged by the charging charger 13 and then cyan by the writing device 14. Exposure of the P sensor pattern forms an electrostatic latent image of the cyan P sensor pattern. The electrostatic latent image of the cyan P sensor pattern is developed by the cyan developing device 18 to become a visible image of the cyan P sensor pattern, and the toner adhesion amount M / A of the visible image of the cyan P sensor pattern is measured by the optical sensor 45. It

The Vsp → M / A calculation circuit 71 takes in the output signal voltage Vsp of the optical sensor 45 for the visible image of the cyan P sensor pattern, and outputs the output signal voltage Vsp of the optical sensor 45 to the cyan toner adhesion amount M / A vs. optical. Sensor 4
5 Based on the relationship of the output signal voltage Vsp, the toner adhesion amount M / A of the visible image of the cyan P sensor pattern is converted. The toner concentration TC of the developer in the cyan developing device 18 is detected by the toner concentration sensor 53, and the M / A → Q / M calculating circuit 72 is stored in advance in the memory.
The toner concentration sensor 5 based on the relationship among the toner concentration TC, the charge amount Q / M, and the toner adhesion amount M / A relating to the developer inside
The charge amount Q / M is calculated from the output signal of No. 3 and the converted toner adhesion amount M / A.

Next, the main controller 44 stores the charge amount Q / M of the developer for the cyan developing device 18 and the amplitude (peak-to-peak voltage Vpp) of the AC component of the developing bias voltage, which are stored in the memory in advance. Based on the relationship between the frequencies fb, the peak-to-peak voltage Vpp of the AC component of the developing bias voltage and the frequency fb from the charge amount Q / M calculated above.
And the peak-to-peak voltage V of the AC component of the developing bias voltage from the power supply circuit 49 to the developing sleeve 62.
Control pp and frequency fb to that determined.

Further, the main control section 44 is provided for each developing device 15
When the calculated developer charge amount is out of the upper and lower limit values every 18 to 18, it is determined that the developer has reached the end of life, and the replacement of the developer is displayed on the display unit. For this reason, the time to replace the developer is automatically known, the charge amount of the developer rises too much, an image density is insufficient, an abnormal image is generated due to edge enhancement, and the charge amount of the developer is too low. It is possible to prevent the occurrence of abnormal images due to background stains and the like.

The second embodiment of the present invention is defined in claims 2, 4,
In the first and second embodiments, the electric resistance of the developer is measured, and the developing bias voltage is controlled according to the measurement result. As shown in FIG. 27, in the black developing device 15, the developer regulating member 67 has a variable DC power source 7
3, a predetermined voltage V is applied to the variable DC power source 73
The current measuring unit 74 measures the current I flowing from the developing electrode to the counter electrode side through the magnetic brush on the developing sleeve 59.
The relationship between the voltage V and the current I is as shown in FIG.
The inclination is the dynamic resistance of the developer (dynamic electrical resistance)
Equivalent to.

FIG. 29 shows changes with time of the dynamic resistance DR of the developer. In FIG. 29, the horizontal axis represents the number of running sheets (over time), and the vertical axis represents the dynamic resistance D of the developer.
R is shown. As can be seen from FIG. 29, the dynamic resistance DR of the developer decreases as the number of running sheets increases.
This decrease in the dynamic resistance DR of the developer is mainly due to the abrasion of the resin coating layer of the carrier.
As shown in (1), when the amount of abrasion of the resin coat layer of the carrier increases, the dynamic resistance DR of the developer decreases. When measuring the dynamic resistance DR of the developer, conventionally, the cell method and the pressure resistance measuring method have been used. These measuring methods have a large measurement error and the measured values are different depending on the filled state of the developer, and the reproducibility is not good. However, even in an actual developing device, the dynamic resistance DR of the developer can be measured with a simple mechanism. is there.

The electric resistance of the developer differs depending on the toner concentration of the developer, but depending on the developer, the carrier alone may increase or decrease the electric resistance of the developer.
FIG. 31 shows the toner concentration TC and the dynamic resistance D of the developer.
An example of the relationship with R is shown. Dynamic resistance of developer D
When measuring R, it is preferable to measure the resistance of the carrier alone, but actually the resistance of the developer must be measured. Dynamic life DR of developer
In the case of the determination as described above, the toner concentration T and the dynamic resistance DR of the developer as shown in FIG.
When C = 0 wt%, it corresponds to the resistance of only the carrier. If the relationship between the toner concentration TC and the dynamic resistance DR of the developer is known, the dynamic resistance DR of the developer can be known from the toner concentration TC.

The main control unit 44 uses the above-mentioned current measuring unit 74.
And the electric resistance D of the developer from the voltage I applied to the developer regulating member 67 from the variable DC power source 73.
R is calculated, and the toner concentration of the developer in the black developing device 15 is detected by the toner concentration sensor 50. The main control unit 44 calculates the resistance of the carrier alone from the output signal of the toner density sensor 50 and the calculated electric resistance DR based on the relationship between the toner density TC and the dynamic resistance DR of the developer. When it is out of the specified value, it is judged that the developer has reached the end of its life, and the replacement of the developer is displayed on the display section.

As described above, the optimum value of the AC component of the developing bias voltage that maximizes the edge enhancement of the image, the toner adhesion amount γ, and the toner adhesion amount differs depending on both the charge amount and the electric resistance of the developer. Most preferably, the optimum value of the AC component of the developing bias voltage is determined by both the charge amount and the electric resistance of the developer.

As shown in FIG. 32, the main controller 44 controls the charge amount of the developer in the black developing device 15 measured in the same manner as in the first embodiment and the charge amount of the developer in the black developing device 15 obtained as described above. Development based on the relationship between the charge amount of the developer and the electric resistance, the peak-to-peak voltage Vpp of the AC component of the developing bias voltage, the frequency fb, and the DC component, which are stored in advance in the memory based on both the electric resistance DR. Peak-to-peak voltage Vpp and frequency f of AC component of bias voltage
b, the DC component is determined, and the peak-to-peak voltage Vpp and frequency fb of the AC component of the developing bias voltage applied from the power supply circuit 49 to the developing sleeve 59 and the DC component are controlled to be the calculated ones. . Therefore, it is possible to determine the optimum developing conditions of the developing device, and it is possible to always obtain stable and high image quality and good developing characteristics without being affected by deterioration of the developer with time and environmental changes. Here, the memory stores the combinations of the charge amounts and electric resistances of the developers in various states, the peak-to-peak voltage Vpp of the AC component of the optimum developing bias voltage, the frequency fb, and the DC component of the combination. Therefore, the optimum developing bias voltage can be uniquely determined from the charge amount and electric resistance of the developer.

In each of the other developing devices 16 to 18, similarly, a predetermined voltage is applied to the developer regulating members 68 to 70 from the variable DC power source, and the developer regulating members 68 to 70 develop the developing sleeve 60. The current flowing to the counter electrode side through the magnetic brushes above 62 is measured by the current measuring unit. The main controller 44 calculates the resistance of the developer from the voltage applied from the variable DC power source to the developer regulating members 68 to 70 for each of the developing devices 16 to 18 and the current measured by the current measuring unit. Of the developer and the charge amount of the developer in each of the developing devices 16 to 18 measured in the same manner as in the first embodiment, and the charge amount of the developer and the electric resistance and the development bias stored in advance in the memory. The peak-to-peak voltage Vpp and frequency fb of the AC component of the voltage and the frequency fb and the DC component are used to determine the peak-to-peak voltage Vpp and frequency fb and the DC component of the AC component of the developing bias voltage. The peak-to-peak voltage Vpp of the AC component of the developing bias voltage applied to the developing sleeves 60 to 62, the frequency fb, and the DC component are controlled to be the calculated values. Therefore, it is possible to determine the optimum developing conditions of the developing device, and it is possible to always obtain stable and high image quality and good developing characteristics without being affected by deterioration of the developer with time and environmental changes.

Further, the main controller 44 controls each developing device 16
.About.18, based on the output signals of the toner concentration sensors 51 to 53 and the electric resistance DR of the developer in each of the developing devices 16 to 18 calculated as described above, based on the relationship between the toner concentration TC and the dynamic resistance DR of the developer, the carrier alone is determined. The resistance is calculated, and when the resistance of the carrier alone is out of the specified value, it is determined that the developer has reached the end of its life, and the replacement of the developer is displayed on the display unit. Therefore, it is possible to automatically know when to replace the developer, and the electric resistance of the developer becomes too high, which causes an abnormal image due to edge enhancement or the electric resistance of the developer becomes too low, resulting in leakage of the developing bias. It is possible to prevent the roughness of the image from becoming large.

The third embodiment of the present invention is the embodiment of the invention described in claims 7 and 8, and in the first embodiment, the developing bias voltage of each of the developing devices 15 to 18 is as shown in FIG. Set to an appropriate value. That is, the main control unit 44 first causes the writing device 14 to sequentially expose a plurality of black P sensor patterns at a predetermined timing, and the photoconductor drum 12 is uniformly charged by the charging charger 13 and then the writing device 14 operates. By exposing the plurality of black P sensor patterns, electrostatic latent images of the plurality of black P sensor patterns are formed at predetermined intervals along the circumferential direction (rotational direction). The electrostatic latent images of the plurality of black P sensor patterns are developed by the black developing device 15 and the black P as shown in FIG.
Visual images of the sensor pattern 81, 82, 83 ...
Toner adhesion amount M of these visible images 81, 82, 83, ...
/ A is measured by the optical sensor 45.

Here, the plurality of black P sensor patterns exposed on the photosensitive drum 12 by the writing device 14 have different potentials, and the toner adhesion amounts of the visible images 81, 82, 83, ... Are different from each other. As shown in FIG. 34, when the black developing device 15 develops the electrostatic latent images of a plurality of black P sensor patterns, the main control unit 44 develops the developing potentials (the plurality of developing potentials) for the visible images 81, 82, 83. So that the gradient of the relationship between the electrostatic latent image of the black P sensor pattern-the DC component of the developing bias voltage) and the toner adhesion amount M / A of the visible images 81, 82, 83, becomes the toner adhesion amount γ. From the power supply circuit 44 to the developing sleeve 5 of the black developing device 15.
9 controls the developing bias voltage applied to 9.

The relationship between the toner adhesion amount M / A of the visible image on the photosensitive drum 12 and the output signal voltage Vsp of the optical sensor 45 with respect to the visible image is as shown in FIG. With respect to the visible images 81, 82, 83, ... On the photoconductor drum 12, the relationship between the toner adhesion amount M / A of the visible image stored in the memory and the output signal voltage Vsp of the optical sensor 45 for the visible image. The output signal voltage Vsp of the optical sensor 45 is set to the visible image 81 on the photosensitive drum 12,
The toner adhesion amount M / A of the visible images 81, 82, 83 ... And the development potential for the visible images 81, 82, 83. The toner adhesion amount γ is calculated by obtaining the gradient of the relationship.

Next, the main control unit 44 causes the peak-to-peak of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 59 of the black developing device 15 until the toner adhesion amount γ falls within the allowable value range. By changing the peak voltage Vpp and the frequency fb, the peak-to-peak voltage Vpp and the frequency fb when the toner adhesion amount γ falls within the allowable value range are applied from the power supply circuit 44 to the developing sleeve 59 of the black developing device 15. Peak toe of AC component of development bias voltage
The peak voltage Vpp and the frequency fb are set. For this reason,
An optimum image can be obtained at the same time that the toner adhesion amount γ is optimum.

Further, the main controller 44 causes the peak-to-peak voltage V of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 59 of the black developing device 15.
Even if the pp and the frequency fb reach the upper limit values (the values at which the developing bias voltage leaks to the photosensitive drum 12 side and destroy the visible image or the latent image on the photosensitive drum 12), the peak-to-peak voltage Vpp and the frequency When fb does not fall within the allowable value range and the target toner adhesion amount γ cannot be obtained, it is determined that the developer in the black developing device 15 has reached the end of life, and the replacement of the developer is displayed on the display unit. . Therefore, if the toner adhesion amount γ does not reach the allowable value even if the condition of the alternating component of the developing bias electric field is changed, the replacement of the developer can be warned.

Similarly, the main controller 44 causes the writing device 14 to sequentially expose a plurality of yellow P sensor patterns at a predetermined timing, and the photosensitive drum 12 is written after being uniformly charged by the charging charger 13. By exposing the plurality of yellow P sensor patterns by the device 14, electrostatic latent images of the plurality of yellow P sensor patterns are formed at predetermined intervals along the circumferential direction (rotational direction).
The electrostatic latent images of the plurality of yellow P sensor patterns are developed by the yellow image device 16 to become visible images, and the toner adhesion amount M / A of these visible images is measured by the optical sensor 45.

The photoconductor drum 12 by the writing device 14.
The plurality of yellow P sensor patterns exposed to each other have different potentials from each other, and the main control unit 44 causes the yellow developing device 16 to develop a developing potential () for a visible image when the electrostatic latent images of the plurality of yellow P sensor patterns are developed. From the power supply circuit 44 to the yellow developing device so that the gradient of the relationship between the electrostatic latent images of a plurality of yellow P sensor patterns-the DC component of the developing bias voltage) and the toner adhesion amount M / A of the visible image becomes the toner adhesion amount γ. The developing bias voltage applied to the sixteen developing sleeves 60 is controlled.

The main control section 44 determines a plurality of toner adhesion amounts M / A of the visible image, which are stored in advance in the memory, and a plurality of output signals of the optical sensor 45 corresponding to the developed image, and the output signal voltage Vsp. The output signal voltage Vsp of the optical sensor 45 with respect to the visible images of the yellow P sensor patterns is converted into the toner adhesion amount M / A of the visible images of the plurality of yellow P sensor patterns on the photosensitive drum 12, and the toner adhesion of these visible images is performed. The toner adhesion amount γ is obtained by obtaining the gradient of the relationship between the amount M / A and the development potential for these visible images.
To calculate.

Next, the main controller 44 causes the peak-to-peak of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 60 of the yellow developing device 16 until the toner adhesion amount γ falls within the allowable value range. The peak-to-peak voltage Vpp and the frequency f when the toner adhesion amount γ is within the allowable value range by changing the peak voltage Vpp and the frequency fb.
b is set to the peak-to-peak voltage Vpp and frequency fb of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 60 of the yellow developing device 16.

Further, the main control section 44 causes the peak-to-peak voltage Vpp and frequency fb of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 60 of the yellow developing device 16 to reach the upper limit values. When the peak-to-peak voltage Vpp and the frequency fb do not fall within the allowable range and the target toner adhesion amount γ cannot be obtained, it is determined that the developer in the yellow developing device 16 has reached the end of its life and displayed. Display the replacement of developer on the section.

Similarly, the main control unit 44 causes the writing device 14 to sequentially expose a plurality of magenta P sensor patterns at a predetermined timing, and the photosensitive drum 12 is written after being uniformly charged by the charging charger 13. By exposing the plurality of magenta P sensor patterns by the device 14, electrostatic latent images of the plurality of magenta P sensor patterns are formed at predetermined intervals in the circumferential direction (rotational direction).
The electrostatic latent images of the plurality of magenta P sensor patterns are developed by the magenta image device 17 to become visible images, and the toner adhesion amount M / A of these visible images is measured by the optical sensor 45.

The photoconductor drum 12 by the writing device 14.
The plurality of magenta P sensor patterns exposed to each other have different potentials from each other, and the main control unit 44 causes the magenta developing device 17 to develop the development potential () with respect to the visible image when the magenta developing device 17 develops the electrostatic latent images of the plurality of magenta P sensor patterns. From the power supply circuit 44 to the magenta developing device so that the gradient of the relationship between the electrostatic latent images of a plurality of magenta P sensor patterns-the DC component of the developing bias voltage) and the toner adhesion amount M / A of the visible image becomes the toner adhesion amount γ. The developing bias voltage applied to the developing sleeve 61 of 17 is controlled.

The main control section 44 determines a plurality of toner adhesion amounts M / A of a visible image stored in advance in the memory and a plurality of output signal voltages Vsp of the optical sensor 45 corresponding to the developed image on the photosensitive drum 12. The output signal voltage Vsp of the optical sensor 45 for the visible images of the magenta P sensor pattern is converted into the toner adhesion amount M / A of the visible images of the plurality of magenta P sensor patterns on the photoconductor drum 12, and the toner adhesion of these visible images is performed. The toner adhesion amount γ is obtained by obtaining the gradient of the relationship between the amount M / A and the development potential for these visible images.
To calculate.

Next, the main controller 44 causes the peak-to-peak of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 61 of the magenta developing device 17 until the toner adhesion amount γ falls within the allowable value range. The peak-to-peak voltage Vpp and the frequency f when the toner adhesion amount γ is within the allowable value range by changing the peak voltage Vpp and the frequency fb.
b is set to the peak-to-peak voltage Vpp and frequency fb of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 61 of the magenta developing device 17.

Further, the main control section 44 causes the peak-to-peak voltage Vpp and frequency fb of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 61 of the magenta developing device 17 to reach the upper limit values. When the peak-to-peak voltage Vpp and the frequency fb do not fall within the allowable range and the target toner adhesion amount γ cannot be obtained, it is determined that the developer in the magenta developing device 17 has reached the end of its life and displayed. Display the replacement of developer on the section.

Similarly, the main controller 44 causes the writing device 14 to sequentially expose a plurality of cyan P sensor patterns at a predetermined timing, and the photosensitive drum 12 is written after being uniformly charged by the charging charger 13. By exposing the plurality of cyan P sensor patterns by the device 14, electrostatic latent images of the plurality of cyan P sensor patterns are formed at predetermined intervals along the circumferential direction (rotational direction). The electrostatic latent images of the plurality of cyan P sensor patterns are developed by the cyan image device 18 to be visible images, and the toner adhesion amount M / A of these visible images is measured by the optical sensor 45.

The photoconductor drum 12 by the writing device 14.
The plurality of cyan P sensor patterns that are exposed to have different potentials from each other, and the main control unit 44 causes the cyan developing device 18 to develop the development potential () for the visible image when the electrostatic latent images of the plurality of cyan P sensor patterns are developed. From the power supply circuit 44 to the cyan developing device so that the gradient of the relationship between the electrostatic latent images of a plurality of cyan P sensor patterns-the DC component of the developing bias voltage) and the toner adhesion amount M / A of the visible image becomes the toner adhesion amount γ. The developing bias voltage applied to the eighteen developing sleeve 62 is controlled.

The main controller 44 determines a plurality of toner images on the photoconductor drum 12 according to the relationship between the toner adhesion amount M / A of the visible image stored in advance in the memory and the output signal voltage Vsp of the optical sensor 45 for the visible image. The output signal voltage Vsp of the optical sensor 45 for the visualized images of the cyan P sensor pattern is converted into the toner adhesion amount M / A of the visualized images of the cyan P sensor patterns on the photosensitive drum 12, and the toner adhesion of these visualized images is performed. The toner adhesion amount γ is calculated by obtaining the gradient of the relationship between the amount M / A and the development potential for these visible images.

Next, the main controller 44 causes the peak-to-peak AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 62 of the cyan developing device 18 until the toner adhesion amount γ falls within the allowable range. The peak-to-peak voltage Vpp and the frequency fb when the toner adhesion amount γ is within the allowable value range by changing the peak voltage Vpp and the frequency fb.
Is set to the peak-to-peak voltage Vpp and frequency fb of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 62 of the cyan developing device 18.

Further, the main controller 44 causes the peak-to-peak voltage Vpp and the frequency fb of the AC component of the developing bias voltage applied from the power supply circuit 44 to the developing sleeve 62 of the cyan developing device 18 to reach the upper limit values. If the peak-to-peak voltage Vpp and the frequency fb do not fall within the allowable value range and the target toner adhesion amount γ cannot be obtained,
It is determined that the developer in the cyan developing device 18 has reached the end of life, and the display section displays the replacement of the developer.

In each of the above embodiments, the photosensitive drum 12
And the linear velocity ratio Vs / Vp between the developing sleeves 59 to 62 are 1.
When 0 <Vs / Vp <2.0 and the gap Gp between the photosensitive drum 12 and the developing sleeves 59 to 62 is 0.8 mm or less, it is particularly effective in reducing the edge effect. Further, when changing Gp, the gap Gd between the developing sleeves 59 to 62 and the developer regulating members 67 to 70 should be adjusted to correct the appropriate amount of developer on the developing sleeves 59 to 62 when it is changed. It may be changed, and in that case, Gd <Gp is preferable.

[0105]

As described above, according to the first aspect of the invention, the image carrier, the latent image forming means for forming an electrostatic latent image on the image carrier, the image carrier and the developer. The electrostatic latent image on the image carrier is formed by transporting the two-component developer by the developer carrier to a developing area facing the carrier and forming a developing bias electric field having an alternating electric field in the developing area. In the image forming apparatus having a developing means for developing the developer, a developing agent charge amount detecting means for detecting the charge amount of the developer in the developing means, and the developing bias based on the detection result of the developer charge amount detecting means. Since the developing bias electric field control means for controlling the electric field is provided, the charging amount of the developer changes with time, and the condition of the developing bias electric field for obtaining an optimum image changes depending on the charging amount of the developer. Also depends on the charge amount of the developer. Always controls the electric field it is possible to obtain an image of optimum.

According to the second aspect of the invention, the image carrier, the latent image forming means for forming an electrostatic latent image on the image carrier, the image carrier and the developer carrier face each other. A two-component developer is conveyed to the developing area by the developer carrier, and a developing bias electric field having an alternating electric field is formed in the developing area to develop the electrostatic latent image on the image carrier to develop a visible image. In the image forming apparatus having the developing means, the toner adhesion amount detecting means for detecting the toner adhesion amount of the visible image on the image carrier and the toner density detecting means for detecting the toner density of the developer in the developing means. Since the means and the toner charge amount calculation means for calculating the charge amount of toner from the detection result of the toner concentration detection means and the detection result of the toner adhesion amount detection means are provided, the toner charge amount can be easily obtained. Can be applied to the charge amount of the developer Flip it is possible to always obtain a optimum image by controlling the developing bias electric field.

According to the invention of claim 3, in the image forming apparatus of claim 1 or 2, the charge amount detected by the developer charge amount detection means or the charge amount calculated by the toner charge amount calculation means is Equipped with a developer life judgment means that judges that the developer has reached the end of its life when it is out of the upper and lower limits, the developer replacement time is automatically known, and the charge amount of the developer rises too much and the image It is possible to prevent the occurrence of an abnormal image due to insufficient density, edge enhancement, or the like, and the occurrence of an abnormal image due to toner scattering, scumming, etc. due to an excessively low charge amount of the developer.

According to the invention of claim 4, claim 1,
In the image forming apparatus described in 2 or 3, the developer electric resistance detecting means for detecting the electric resistance of the developer in the developing means, the detection result of the developer electric resistance detecting means and the developer charge amount detecting means are used. Since the developing bias electric field control means for controlling the developing bias electric field based on the detected charge amount or the charge amount calculated by the toner charge amount calculating means is provided, the optimum developing condition of the developing means can be determined. It is possible to always obtain stable, high image quality and good developing characteristics without being affected by deterioration of the developer over time and environmental changes.

According to a fifth aspect of the invention, in the image forming apparatus according to the fourth aspect, the developing means has a regulating member for regulating the amount of the developer conveyed by the developer carrying member, The developer electric resistance detecting means detects a dynamic electric resistance of the developer by applying a voltage to the regulating member and detecting a current flowing through the developer, so that the electric resistance of the developer can be easily detected with high accuracy. It becomes possible.

According to the sixth aspect of the invention, in the image forming apparatus according to the fourth or fifth aspect, the charge amount detected by the developer charge amount detection means or the charge amount calculated by the toner charge amount calculation means is Developer life judging means for judging that the developer has reached the end of life when the value exceeds the upper or lower limit value or when the dynamic electric resistance of the developer detected by the developer electric resistance detecting means exceeds the specified value. Since the time to replace the developer is automatically known, the charge amount of the developer rises too much, the image density is insufficient, an abnormal image due to edge enhancement occurs, or the charge amount of the developer is too low. It is possible to prevent the occurrence of abnormal images due to scattering, background stains, etc. Furthermore, the electrical resistance of the developer becomes too high, and abnormal images due to edge enhancement or the electrical resistance of the developer is generated. Too low Roughness of the image due to leak or the like of the developing bias Te becomes possible to prevent may become large.

According to the invention of claim 7, the image carrier, the latent image forming means for forming an electrostatic latent image on the image carrier, and the image carrier and the developer carrier face each other. A developing unit that conveys a two-component developer to the developing area by the developer carrying member and forms a developing bias electric field having an alternating electric field in the developing area to develop the electrostatic latent image on the image carrying member. In the image forming apparatus having the above, a plurality of predetermined patterns of electrostatic latent images having different potentials are formed on the image carrier, and the electrostatic latent images are developed by the developing means with a predetermined developing potential to form a visible image. A developing bias electric field setting means for detecting the visible image with an optical sensor, calculating a gradient of the toner adhesion amount based on the detection result of the optical sensor with respect to the developing potential, and setting the developing bias electric field with the gradient. Since, at the same time optimum image when the toner adhesion amount γ is optimal is obtained.

According to the eighth aspect of the invention, in the image forming apparatus according to the seventh aspect, when the gradient does not fall within the allowable value even when the alternating component of the developing bias electric field reaches the upper limit value, the developing operation is performed. Since the developer exchange means for displaying the developer exchange when the developer has reached the end of its life is provided, even if the condition of the alternating component of the developing bias electric field is changed, the toner adhesion amount γ does not reach the allowable value. It is possible to warn of replacement of the developer.

[Brief description of drawings]

FIG. 1 is a block diagram showing an invention according to claim 1.

FIG. 2 is a curve characteristic diagram showing the relationship between the frequency of the electrostatic latent image in the image forming apparatus and the developing density of the developing device.

FIG. 3 is a characteristic curve diagram showing a change with time of carrier resistance in the image forming apparatus.

FIG. 4 is a characteristic curve diagram showing a relationship between carrier resistance and an image edge enhancement level in the image forming apparatus.

FIG. 5 is a characteristic curve diagram showing the relationship among the amplitude of the AC component of the developing bias voltage, the edge enhancement level of the image, and the resistance of the developer in the image forming apparatus.

FIG. 6 is a characteristic curve diagram showing the relationship between the frequency of the AC component of the developing bias voltage, the edge enhancement level of the image, and the resistance of the developer in the image forming apparatus.

FIG. 7 is a characteristic curve diagram showing the relationship among the amplitude of the AC component of the developing bias voltage, the toner adhesion amount γ, and the resistance of the developer in the image forming apparatus.

FIG. 8 is a characteristic curve diagram showing the relationship among the amplitude of the AC component of the developing bias voltage, the developing density, and the resistance of the developer in the image forming apparatus.

FIG. 9 is a characteristic curve diagram showing the relationship among the frequency of the AC component of the developing bias voltage, the toner adhesion amount γ, and the resistance of the developer in the image forming apparatus.

FIG. 10 is a characteristic curve diagram showing the relationship between the frequency of the AC component of the developing bias voltage, the developing density, and the resistance of the developer in the image forming apparatus.

FIG. 11 is a characteristic curve diagram showing a change with time of a toner charge amount in the image forming apparatus.

FIG. 12 is a characteristic curve diagram showing the relationship between toner concentration, developer charge amount, and environment in the image forming apparatus.

FIG. 13 is a characteristic curve diagram showing a relationship between a toner charge amount and an image edge enhancement level in the image forming apparatus.

FIG. 14 is a characteristic curve diagram showing the relationship among the amplitude of the AC component of the developing bias voltage, the edge enhancement level of the image, and the toner charge amount in the image forming apparatus.

FIG. 15 is a characteristic curve diagram showing the relationship among the frequency of the AC component of the developing bias voltage, the edge emphasis level of the image, and the toner charge amount in the image forming apparatus.

FIG. 16 is a characteristic curve diagram showing the relationship among the amplitude of the AC component of the developing bias voltage, the toner adhesion amount γ, and the developer charge amount in the image forming apparatus.

FIG. 17 is a characteristic curve diagram showing the relationship among the amplitude of the AC component of the developing bias voltage, the developing density, and the developer charge amount in the image forming apparatus.

FIG. 18 is a characteristic curve diagram showing the relationship between the frequency of the AC component of the developing bias voltage, the toner adhesion amount γ, and the developer charge amount in the image forming apparatus.

FIG. 19 is a characteristic curve diagram showing the relationship among the frequency of the AC component of the developing bias voltage in the image forming apparatus, the developing density, and the developer charge amount.

FIG. 20 is a sectional view showing the outline of the first embodiment of the present invention.

FIG. 21 is a block diagram showing a control system of the first embodiment.

FIG. 22 is a sectional view showing a part of the first embodiment in an enlarged manner.

FIG. 23 is a diagram for explaining the first embodiment.

FIG. 24 is a characteristic curve diagram showing the relationship between the toner adhesion amount and the optical sensor output signal voltage in the first embodiment.

FIG. 25 is a characteristic curve diagram showing the relationship between toner concentration and developer charge amount in the first embodiment.

FIG. 26 is a characteristic curve diagram showing the relationship between the toner adhesion amount, the developer charge amount, and the toner concentration in the first embodiment.

FIG. 27 is a schematic view showing a part of the second embodiment of the present invention.

FIG. 28 is a characteristic curve diagram of the second example.

FIG. 29 is a characteristic curve diagram showing the relationship between the number of running sheets and the dynamic electric resistance of the developer in the second example.

FIG. 30 is a characteristic curve diagram showing the relationship between the thickness of the carrier resin coating layer and the dynamic electric resistance of the developer in the second example.

FIG. 31 is a characteristic curve diagram showing the relationship between the toner concentration and the dynamic electric resistance of the developer in the second embodiment.

FIG. 32 is a flowchart showing a part of the operation flow of the second embodiment.

FIG. 33 is a perspective view showing a part of the third embodiment of the present invention.

FIG. 34 is a characteristic curve diagram showing the relationship between the developing potential and the toner adhesion amount for the P sensor pattern of the third embodiment.

FIG. 35 is a flowchart showing a part of the operation flow of the third embodiment.

[Explanation of symbols]

 1 developer charge amount detecting means 2 developing bias electric field control means

Continuation of front page (51) Int.Cl. ⁵ Identification number Office reference number FI Technical display location G03G 15/09 Z

Claims (8)

[Claims] 1. A two-component developer in an image bearing member, a latent image forming means for forming an electrostatic latent image on the image bearing member, and a developing area where the image bearing member and the developer bearing member face each other. And a developing means for developing an electrostatic latent image on the image carrier by forming a developing bias electric field having an alternating electric field in the developing area while carrying the developer carrier on the image carrier. A developer charge amount detecting means for detecting the charge amount of the developer in the developing means, and a developing bias electric field control means for controlling the developing bias electric field based on the detection result of the developer charge amount detecting means are provided. An image forming apparatus characterized by. 2. A two-component developer in an image carrier, a latent image forming means for forming an electrostatic latent image on the image carrier, and a developing area where the image carrier and the developer carrier face each other. And a developing means for developing an electrostatic latent image on the image carrier to develop it into a visible image by forming a developing bias electric field having an alternating electric field in the developing area. In the forming apparatus, a toner adhesion amount detecting means for detecting the toner adhesion amount of the visible image on the image carrier, a toner concentration detecting means for detecting the toner concentration of the developer in the developing means, and the toner concentration detecting means. And a toner charge amount calculation means for calculating the charge amount of toner from the detection result of the toner adhesion amount detection means and the detection result of the toner adhesion amount detection means. 3. The image forming apparatus according to claim 1, wherein when the charge amount detected by the developer charge amount detection means or the charge amount calculated by the toner charge amount calculation means is outside the upper and lower limit values. An image forming apparatus comprising: a developer life determining unit that determines that a developer has reached the end of life. 4. An image forming apparatus according to claim 1, 2 or 3, wherein a developer electric resistance detecting means for detecting electric resistance of the developer in the developing means, and a detection result of the developer electric resistance detecting means. And an developing bias electric field control means for controlling the developing bias electric field on the basis of the charge amount detected by the developer charge amount detecting means or the charge amount calculated by the toner charge amount calculating means. Forming equipment. 5. The image forming apparatus according to claim 4, wherein the developing means has a regulating member for regulating the amount of the developer carried by the developer carrying member, and the developer electric resistance detecting means is the above-mentioned. An image forming apparatus characterized in that a dynamic electric resistance of a developer is detected by applying a voltage to a regulating member and detecting a current flowing through the developer. 6. The image forming apparatus according to claim 4, wherein the charge amount detected by the developer charge amount detection means or the charge amount calculated by the toner charge amount calculation means is outside the upper and lower limit values. Or a developer life judging means for judging that the developer has reached the life when the dynamic electric resistance of the developer detected by the developer electric resistance detecting means is out of a specified value. Image forming apparatus. 7. A two-component developer in an image bearing member, a latent image forming means for forming an electrostatic latent image on the image bearing member, and a developing area where the image bearing member and the developer bearing member face each other. And a developing means for developing an electrostatic latent image on the image carrier by forming a developing bias electric field having an alternating electric field in the developing area while carrying the developer carrier on the image carrier. A plurality of predetermined patterns of electrostatic latent images having different electric potentials are formed on the image carrier, and the electrostatic latent images are developed by the developing means with a predetermined developing potential to form a visible image. An image forming apparatus comprising: a developing bias electric field setting means for detecting and detecting a gradient of the toner adhesion amount based on the detection result of the optical sensor with respect to the developing potential, and setting the developing bias electric field based on the gradient. . 8. The image forming apparatus according to claim 7, wherein when the gradient of the alternating component of the developing bias electric field reaches the upper limit and the gradient is not within the allowable value, it is determined that the developer has reached the end of its life. An image forming apparatus comprising: a developer exchange unit for displaying a developer exchange.