JP2003316134A - Image forming device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which reduces stirring time to the shortest length while obtaining an image satisfactory for a long period and prevents unnecessary stir even in a case where the charging characteristic and mixed and stirred state of developer in a developing device are ununiform due to recycled toner returned to the developing device. <P>SOLUTION: In the image forming device which recovers residual developer on a photoreceptor drum 1 and returns the developer to the developing device 4, thereby recycling it, an optical sensor 30 for detecting an amount of toner developed on the photoreceptor drum 1 detects an amount of toner developed in at least either a potential part corresponding to a white part on the photoreceptor drum 1 or a potential part on the drum 1 to which toner is attached. A signal indicating the detected amount of toner is transmitted to a stir control means. The stir control means which stirs the developer in the developing device r prior to the image forming operation controls a stir screw 45 based upon the amount of toner detected by the optical sensor 30. <P>COPYRIGHT: (C)2004,JPO

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 or a printer, and more particularly, it is excellent in recovering toner remaining on an image carrier and returning it to a developing device for reuse. The present invention relates to an image forming apparatus having excellent durability and capable of obtaining a stable image.

[0002]

2. Description of the Related Art Conventionally, as an electrophotographic image forming apparatus such as a copying machine or a printer, a charged developer is attracted onto an image carrier by a magnetic force, and the developer is conveyed to a developing area so that the image is formed on the image carrier. It is known to develop a latent image. In order to form a good developer image on the image carrier, the developer is required to be well charged in the developing device.
In particular, when a two-component developer is used, it is required that the toner is uniformly mixed in the developer.
Therefore, conventionally, the developer before being supplied to the image carrier is mixed and stirred with the magnetic carrier and the toner in the developing device. Since the degree of mixing and stirring of the developer performed in this developing device affects the charge amount of the developer and the mixing state of the toner in the developer, it is necessary to stir the developer in order to obtain a good image. Is required to be appropriate. Further, in recent years, when environmental issues have been attracting attention, effective use of resources and suppression or reduction of waste have been emphasized.
In such a situation, as one means for reducing the amount of waste toner discharged from the image forming apparatus, in the image forming process, the toner image is not put on the transfer paper and output as a toner image on the image carrier. Collect the remaining toner,
There is a toner recycling system in which it is returned to the developing device and reused.

However, some of the toner remaining on the image bearing member undergoes physical property changes due to various hazards during a series of image forming operations, and the toner supplied to the developing device by normal replenishment is electrically charged. It contains a part of toner whose developer characteristics such as rising ability are changed or deteriorated. For this reason, in the toner recycling type image forming apparatus, the stirring time, the strength and the frequency in the developing apparatus are increased as compared with the image forming apparatus which does not recycle the toner, so that the developer in the developing apparatus is sufficiently mixed and mixed. It is necessary to disperse them to obtain an appropriate amount of charge. Several methods have been proposed as simple means for this. For example, a technique of mixing recycled toner and normal replenishment toner for replenishment is disclosed (for example,
JP-A-2001-42623). However, these techniques are effective means for supplying recycled toner to the developing device, but it is only to stir the developing device to charge the entire developer to an appropriate level. However, it is not sufficient as a means for eliminating the background stain and the density fluctuation when the toner is recycled.

Further, in order to solve the above-mentioned problems, for example, a technique of executing stirring for a certain period of time when the recycled toner exceeds a certain amount (for example, Japanese Patent Laid-Open No. 2000-2000).
No. 267365, etc.), a technique in which the amount of toner is restricted to a certain amount or less and stirring is performed for a certain time (Japanese Patent Laid-Open No. 7-928)
No. 73 and Japanese Patent Laid-Open No. 8-179668). However, in these technologies, how much stirring of the developer is sufficient depends on the toner concentration in the developer immediately before stirring, the amount (percentage) of recycled toner, and the usage status. However, there is a problem that it is not constant.

[0005]

Here, in the method for carrying out stirring for a certain fixed time as described above,
To set this fixed time, it is necessary to accurately grasp the developer characteristics of the developer containing the recycled toner to be stirred. In addition, how much the developer should be agitated depends on the toner concentration in the developer immediately before agitating, the amount (percentage) of recycled toner, the usage situation, etc. It has to be taken into consideration. It was difficult to accurately grasp such conditions and control the stirring time because advanced technology was required. Therefore, if it is required to surely carry out stirring according to various changes in developer characteristics, it is safe to adopt a method of stirring the developer for a sufficiently long time. It is carried out by setting the stirring time with. From the above, in the conventionally proposed image forming apparatus, in order to stably obtain a good image, the developer stirring operation is set to be long in advance. However, if the stirring time of the developer is increased, not only the deterioration of the developer is accelerated, but also a wasteful non-use period of the image forming apparatus or a delay in the work is caused depending on the control method.

Therefore, the present invention has been made in view of the above problems, and the problem is that the recycled toner is returned to the developing device so that the charging characteristics of the developer in the developing device are improved. In addition, it is to provide an image forming apparatus that performs stirring for a minimum time to stably obtain a good image for a long period of time even when the mixing / stirring property is not uniform, and does not continue stirring unnecessarily. .

[0007]

In order to solve the above-mentioned problems, the invention described in claim 1 collects the developer remaining on the image carrier and returns it to the developing device for reuse. In the image forming apparatus, the image forming apparatus includes a developer stirring unit that stirs the developer in the developing device and a density detecting unit that detects the amount of toner developed on the image carrier, prior to the image forming operation. An agitation control unit that controls the developer agitation unit according to the amount of toner to be detected is provided, and the density detection unit has at least one of a potential part corresponding to a white part and a potential part to which toner adheres on the image carrier. In the image forming apparatus, the amount of toner developed in the potential portion is detected, and the agitation control unit controls the developer agitation unit based on the amount of toner detected by the density detection unit. Here, the potential portion corresponding to the white portion is the potential of the photosensitive member portion where toner adhesion is not intended in the normal image forming process. This is the potential of the photoconductor portion, and the potential of the photoconductor portion charged by uniform charging in reversal development. Further, in particular, when forming a potential portion to which toner adheres as such a potential portion,
It is preferable to repeat the image forming means a plurality of times to detect the density. This is because it is possible to appropriately determine whether or not the toner distribution in the developing device is uniform. Therefore, in the image forming apparatus of the present invention, the potential portion for measurement is formed on the image carrier under a predetermined image forming condition while stirring the developer, and the concentration of the developer on the potential portion for measurement is determined. By substantially detecting the developer characteristic, the developer characteristic is substantially judged. If the developer characteristic is not good, stirring of the developer is continued, and when it is good, the developer is stopped immediately.

According to a second aspect of the present invention, in the image forming apparatus according to the first aspect, the image forming apparatus agitates the developer after the main power is turned on and before the first image forming operation is performed. An image forming apparatus for driving the means. Here, in the image forming apparatus of the present invention, after the power of the image forming apparatus is turned on, the drive of the developer stirring means is started before the first image forming operation is performed, so that the chargeability of the developer while left standing is increased. It becomes possible to cope with the change of. Recycled toner often has less margin than storage toner (depending on storage time) (change in charging characteristics with respect to standing time) than toner that is normally replenished. Even in such a case, appropriate developer agitation can be performed, and good image quality can be provided.

The invention according to claim 3 is the invention according to claim 1 or 2.
In the image forming apparatus described in the paragraph 1,
An environmental condition detecting unit for detecting an environmental condition is provided, and when the environmental condition detecting unit detects that the use environment is outside the range of the environment suitable for use of the image forming apparatus, the driving of the developer stirring unit is started. The image forming apparatus. Here, in the image forming apparatus of the present invention, an environmental condition detecting unit for detecting an environmental condition is provided, and when the use environment is detected by the condition detecting unit to be outside the range of the environment suitable for use of the image forming apparatus. By starting the driving of the developer agitating means, it is possible to cope with a change due to environmental changes. Originally, the developer characteristics are affected by use environmental conditions such as time and environment. For example, in the case of a developer highly dependent on the environment due to humidity, if the temperature inside the device is constant, within a certain range of absolute humidity, the developer will have an appropriate humidity with suitable developer characteristics for image formation. Even if it deviates, there is an image-formable range in a humidity close to the proper humidity. If the humidity deviates from this formable range, the developer characteristics will not be suitable for image formation. The recycled toner often has less margin than the replenished toner because of its dependence on the environment (changes in charging characteristics due to changes in the environment). Even in such a case, appropriate developer agitation can be performed, and good image quality can be provided.

According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the image forming apparatus is an image forming apparatus which sets an upper limit on a drive time of the developer stirring means. . Here, the reason why the charge amount of the developer does not fall within an appropriate range is that the degree of developer deterioration affects the detection result of the density in the potential part corresponding to the white part in addition to insufficient stirring. No matter how much the deteriorated developer is stirred, good developer characteristics cannot be obtained. In this case, the stirring operation may continue and the control unit may run away. Conventionally, various methods for detecting the degree of deterioration of a developer have been proposed. For example, according to Japanese Patent Laid-Open No. 5-80655, the density of a non-image portion of a pattern image formed on an image carrier is detected by an optical sensor, and the result of the detection detects the density of the developer based on the degree of background stain. It determines the life. However, such a developer life detecting means does not consider the influence of background stains and image density fluctuations on the image due to insufficient stirring of the developer, and thus the developer life detected by this detecting means There was a possibility that the timing did not match the actual life of the developer. Therefore, an upper limit is set for the drive time of the developer stirring means.

According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect, in the image forming apparatus, when the driving time of the developer agitating means reaches the upper limit, at the time when the upper limit is reached. The image forming apparatus determines whether or not image formation is prohibited according to the detection result of the potential portion corresponding to the white portion by the density detecting unit. If the developer characteristics do not reach the desired level even after continuing the stirring of the developer, the reason is that the developer is deteriorated. Therefore, even if the stirring is continued, the stirring is unnecessarily continued. Will be done. Furthermore, the agitation accelerates the deterioration of the developer. Therefore, when the driving time of the developer agitating means reaches the upper limit, the density detecting means detects the potential portion to determine whether to inhibit the image formation. This is because a high-quality image cannot be obtained even if an image is formed using the deteriorated developer. The determination may be performed by the control unit or the image processing unit. According to a sixth aspect of the present invention, in the image forming apparatus according to the fourth aspect, when the driving time of the developer stirring means reaches the upper limit, the image forming apparatus collects the remaining developer on the image carrier. The image forming apparatus does not return to the developing device. Further, when it is determined that the developer is deteriorated, the further deterioration of the image quality is suppressed by not returning the cause of deterioration or the supply of recycled toner, which is one of the factors promoting the deterioration, to the developing device. Thus, it is possible to prevent the operation of the image forming apparatus from being stopped. In addition, the provision of this grace period extends the life of the developer until the developer is replaced,
It is possible to prevent a non-use period of the image forming apparatus.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION An embodiment in which the image forming apparatus of the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) will be described below. FIG. 1 is a schematic diagram showing the configuration of a copying machine which is an embodiment of the image forming apparatus of the present invention. This copying machine includes a scanner unit 20 for reading an original.
An image processing section 21 for electrically processing a digital signal output from the scanner section 20, and the image processing section 2
The printer unit 22 forms an image on a transfer sheet based on the digital signal output from the printer 1. In the scanner unit, the image of the document placed on the document table is read by the image reading device via the irradiation lamp, the mirror, and the lens, and the data is sent to the image processing unit 21. In the image processing unit 21, this data is subjected to necessary processing and converted into an image signal, and the printer unit 22
Sent to. In the printer unit 22, the photosensitive drum 1 as an image carrier that is driven to rotate in the direction of arrow A in the drawing.
Surface is uniformly charged by the charger 2. Then, a latent image corresponding to the image of the original is formed on the surface of the photosensitive drum 1 by the exposure device 3 including a semiconductor laser, a polygon mirror, a reflection mirror, etc., based on the image signal from the image processing unit 21. . The latent image on the photoconductor drum 1 is developed with a developer supplied from a developing roller 41 as a developer carrying member of the developing device 4 at a portion facing the developing device 4 to form a visible image.

Then, the visible image is placed on a belt-shaped conveying device 7 from the paper feed tray 5 at a timing by the registration rollers 6 and is conveyed to a portion facing the photosensitive drum 1, for example, transfer paper. And is transferred by the transfer device 8. The transfer sheet onto which the visible image has been transferred is conveyed by the conveying device 7, and when passing through the fixing device 9, the visible image is fixed and discharged onto the paper discharge tray 10. Here, the untransferred toner remaining on the photoconductor drum 1 after the image transfer is cleaned from the photoconductor drum 1 by the cleaning device 11 and collected by the cleaning device 11. The collected toner is returned to the developing device 4 as recycled toner via a recycling path (not shown). The surface of the photoconductor drum 1 after cleaning is subjected to elimination of residual electric charge by the elimination lamp.

FIG. 2 is an enlarged schematic view of a portion of the copying machine of FIG. 1 where the developing device is provided. The developing device 4 performs development using a two-component developer including toner and carrier, and is mainly composed of a developer stirring tank 42 and a toner storage tank 43 provided above the developer stirring tank 42. The toner storage tank 43 is provided between the toner storage tank 43 and the developer stirring tank 42.
A toner replenishing roller 44 for replenishing the developer stirring tank 42 with toner is provided, and the developer stirring tank 42 has a stirring screw 45 as a developer stirring means for stirring the developer at the bottom of the casing and a photosensitive drum of the casing. A developing roller 41 that holds a developer on the surface in the opening facing the body drum 1.
Is provided. The stirring screw 45 supplies the developer consisting of the toner and the carrier onto the developing roller 41 while mixing and stirring the developer composed of the toner and the carrier in the developer stirring tank 42. Developing roller 41
The developer replenished on top is regulated to a predetermined thickness,
It is conveyed to the developing area at the portion facing the photosensitive drum 1.
Then, in the copying machine of the present embodiment, the optical sensor 3 which is the density detecting means for detecting the amount of toner to be developed on the photosensitive member.
0 is provided at a position facing the photoconductor drum 1 on the downstream side of the developing area in the rotation direction of the photoconductor drum 1 to detect the toner adhesion state on the photoconductor. This detection signal is transmitted to the control means 32, and based on this signal, it is determined whether the stirring of the developer is continued or stopped, and the motor for driving the stirring screw 45 (not shown) is controlled. The stirring and mixing of the developer and the toner in the developer stirring tank 42 by the stirring screw 45 uniformly mixes the developer and the toner and properly raises the charge amount of the developer. At the time of warming up immediately after the copying machine is started, the developer in the developer stirring tank 42 is
Since the toner concentration and chargeability are non-uniform, stirring of the developer is started by rotation of the stirring screw 45.

By using the charger 2 and the exposure device 3, a halftone pattern as a potential portion to which toner having sufficient detection sensitivity adheres is formed in parallel with driving the developer agitating means, and the developing device 4 uses the photoreceptor. After visualizing on drum 1,
The image density of this halftone pattern is measured by the optical sensor 30.
Is read in. Then, based on the output value of the optical sensor 30, the voltage applied to the charger grid, the LD voltage applied to the exposure device 3, and the voltage applied to the developing roller 41 are controlled,
Maintain high quality images. The optical sensor 30 not only detects the density of the halftone pattern, but also detects the density of the white potential portion as a potential portion corresponding to the white portion. The detection of the densities of the halftone pattern and the white potential portion is alternately performed, and the halftone pattern image formation cycle is set so that each detection cycle is an integral multiple of the rotation pace of the stirring screw 45.

FIG. 3 is a diagram showing the detection results of the halftone pattern and the white potential portion by the optical sensor (density detecting means), where the horizontal axis shows the stirring time and the vertical axis shows the detection value of the optical sensor. . In FIG. 3A, when the detected value of the halftone pattern falls within the area l surrounded by the broken line, it can be determined that the density of the halftone pattern is stable within the proper range and the developer is uniformly mixed. On the other hand, in FIG. 3B, when the detected value of the white part potential part is stable at a value larger than the value m indicated by the broken line, the density of the white part potential part is stable at an appropriate value or more, and the developer is charged to a desired value. It can be judged that the amount has been reached.
Therefore, after the stirring of the developer is started, the detection result of the halftone pattern is stabilized several times continuously in the region l, and the detection result of the white potential portion is experimentally obtained in advance. When the value is larger than the appropriate value m of the white part, at h1, the density of the halftone pattern is stable within the appropriate range, and
When the density of the white potential part is stable at an appropriate value m or more, it is determined that the image has become good, and the stirring is stopped. Here, the criterion for determining the stability of the density of the halftone and the white potential portion depends on the system of the copying machine, the accuracy and stability of the detection value by the optical sensor 30, the characteristics of the photosensitive drum 1 developer used, and the like. In some cases, it is necessary to change according to the usage history of the developer.

Further, instead of judging whether the stirring of the developer is continued or stopped by using the detection results of the densities of both the halftone and white potential portions, only the detection result of the halftone pattern or the white is detected. It is also possible to make the determination based only on the detection result of the potential section. While stirring the developer, the developer characteristics such as the degree of uniform mixing of the toner in the developer and the charge amount are detected by the image density, so that the state of the image can be accurately detected. Also, if the image density is not good, stirring is continued, and when it becomes good, it stops, so it is possible to accurately grasp the time when the image becomes good, and stop stirring immediately when the image becomes good. Also, it is possible to prevent the developer from being unnecessarily continuously stirred to accelerate the deterioration of the developer.
In addition, it is possible to prevent wasteful time of image formation in the copying machine and delay of image forming work. Furthermore, if the detection result of the halftone pattern is stabilized within a desired range several times in succession, it is determined that the image is good, so that the detection accuracy of the optical sensor 30 is unstable or the image density is temporarily reduced. It is possible to prevent the stirring from being stopped by mistake when it becomes good. Further, according to the configuration that determines whether the stirring is continued or stopped based on the detected values of the densities of both the halftone pattern and the white part potential part, from the detection result of the density of only the halftone pattern or only the white part potential part. It is possible to detect more accurately that the developer characteristics are in a state suitable for image formation, as compared with the configuration that determines whether stirring is continued or stopped.

On the other hand, in the case where the control for continuing and stopping the stirring of the developer is judged only by the detection result of the halftone pattern or only the detection result of the white potential portion, compared to the case where both are detected. The configuration for deciding whether to continue or stop stirring can be simplified. In the copying machine of the present embodiment, when the environment in which the copying machine is used greatly changes and the developer characteristics are affected, and there is a risk that the formed image deteriorates, the occurrence of this problem is predicted, In addition, it has a structure for preventing. As shown in the figure, a humidity sensor 31 is provided above the developing device 4 at a position separated from the developing device 4 as an environmental condition detecting means for detecting use environment information.
When the humidity sensor 31 detects that the environment in which the copying machine is used has changed significantly, and it is expected that the charge amount of the developer in the developing device 4 is partially reduced, the next image By the time the forming work command is issued, in order to make the charge amount of the developer in the developing device 4 uniform and to recover the developer characteristics, the stirring of the developer by the operation of the stirring screw 45 is started. It Also for this stirring work,
In the same manner as during the stirring work described above, in parallel with this, various controls in the formation of the halftone pattern on the photosensitive drum 1, the reading of the halftone pattern density and the white part potential part density by the optical sensor 30, and the continuation of the stirring work. And stop control. Regarding the control of continuation and stop of stirring during this stirring work, as in the above-mentioned stirring work, the judgment control of stirring continuation or stop is performed only by the detection result of the halftone pattern or only the detection result of the white potential section. Is also good.

With this configuration, it is possible to prevent the occurrence of defects in the formed image in a use environment in which the developer characteristics are in an unsuitable state for image formation, with a minimum stirring time, and excessive stirring is performed. It is possible to prevent the deterioration of the developer from being accelerated due to the excessive amount. As described above, the charging characteristics of the developer in the developing device 4 are extremely unevenly distributed due to the ratio of the recycled toner present in the developing device 4 and the installation environment in which the temperature and humidity change significantly after being left for a long time. It is not necessary to continue stirring for a sufficiently long time when the developer characteristics are expected to be in a state suitable for image formation assuming that the developer is agitated while the developer is agitated. Can be obtained. Therefore, it is possible to prevent a defect in the formed image due to insufficient agitation of the developer, and to prevent excessive agitation to accelerate the deterioration of the developer. Further, if the developer characteristics do not reach the desired level even if the developer is continuously stirred, the cause may be deterioration of the developer. In the case of this cause, even if the stirring is continued, the stirring is unnecessarily continued. Therefore, in order to avoid runaway of the driving of the developer stirring means due to the deterioration of the developer, an upper limit is set for the driving time of the developer stirring means. Overall structure of copying machine, formation of halftone pattern on photoconductor drum 1,
Basically, the control of the halftone pattern density and the density of the white potential portion by the optical sensor 30 and the continuation and stop of the stirring operation are the same as those in the first embodiment. Further, similarly to the above-described embodiment, the control for continuing and stopping the stirring may be determined only by the detection result of the halftone pattern or only the detection result of the white potential portion. Here, the upper limit time of the stirring work is set, and when the upper limit time is reached, the stirring is stopped regardless of the reading result by the optical sensor 30.

FIG. 4 shows an example of the detection result of the white potential portion by the optical sensor 30 while driving the developer stirring means when the developer is deteriorated. The vertical axis indicates the detection value of the optical sensor 30. The white circles in the figure are examples of the developer with a relatively small degree of deterioration of the developer, and the circles filled with black are examples of the developer with a relatively large degree of deterioration of the developer. Time h2
Considering various usage conditions of the copying machine, the value detected by the optical sensor in the white area potential portion surely reaches the white area appropriate value m or more unless the developer is deteriorated to the extent that it needs to be replaced. It's time. When the time h2 is reached, if the optical sensor output of the white portion potential portion has not reached the white portion proper value m, it can be determined that the developer has deteriorated. In addition, n in the figure
The output level of the optical sensor 30 indicated by is the optical sensor output level of the white portion on the photoconductor corresponding to the abnormal image in which the white background stain is recognized on the transfer paper. This level n is set as the upper limit of the developer life, and this upper limit is set as the NG line.

During the period from the start of stirring to the above-mentioned upper limit time h2, the control for continuing and stopping the stirring is judged by the detection results of both the halftone pattern and the white potential portion. And
When the upper limit time h2 has elapsed while stirring is continued, the stirring is stopped at that point. Then, the state of deterioration of the developer is determined based on the detection value of the white potential portion by the optical sensor 30 at this time. Upper limit time h2
When the detected value of the white potential portion at the time of reaching is smaller than the NG line which is the level n, it is determined that the image quality cannot be maintained any more due to the deterioration of the developer. Then, let the user recognize that the developer needs to be replaced by turning on a toner replacement warning lamp provided on the operation unit,
Disable the copier.

On the other hand, when the detected value of the white part potential portion at the time when the upper limit time h2 is reached falls within the area p on the NG line or between the NG line and the lower limit line of the appropriate detection value range, the image is displayed. Although the background stain is not remarkable, it is judged that the fatigue deterioration of the developer is advanced. At this time, the developer remaining on the image carrier is not returned to the developing device 4 and the user needs to know that it is necessary to replace the developer by turning on a toner replacement warning lamp provided in the operation unit or the like. To recognize. By not recycling the toner, it is possible to temporarily increase the margin of occurrence of background stains on the image and fluctuations in the image density. Therefore, it is possible to secure a grace period until an abnormal image occurs, and because the operation of the copying machine is not stopped during this time, it is possible to prevent unnecessary stoppage of the operation of the copying machine by replacing the developer during the grace period. can do.
That is, in the normal toner density control, firstly, the optical sensor 30 detects the pattern image formed on the image carrier under the predetermined image forming condition, and the detection result is set in advance in the toner replenishment determination. If it is determined that the toner adhesion amount of the pattern image is smaller than the threshold value, the toner is replenished to increase the toner density. Second, the developing device 4 for the recycled toner from the cleaning device 11
It is a return to. Here, by stopping the toner recycling, it is possible to generate a certain grace period for the deterioration speed of the image quality.

The set value of the upper limit time for driving the developer stirring means is determined by the characteristics of the supply such as the charging ability of the developer being used and the stirring ability of the developing device 4, and depending on the use of the supply, depending on the situation. It depends on the history. Further, as means for discriminating the state of deterioration of the developer in order to avoid runaway of the stirring screw 45, instead of means for using the detection results of the densities of both the halftone and white part potential parts, the white part potential parts are detected. It is also possible to determine based on the result alone. Further, only the halftone potential part is used for the judgment control of the stirring continuation and the stop until the upper limit time h2 comes, and the optical sensor output of the white part potential is used only when the upper limit time is reached while stirring is continued. Alternatively, the degree of developer deterioration may be detected. With such a configuration, by setting an upper limit on the working time for driving the developer stirring means,
When the developer characteristics do not reach the desired level due to the deterioration of the developer, it is possible to avoid the runaway of the control unit in which the stirring of the developer continues unnecessarily.

In order to detect the toner concentration on the measuring potential portion, the optical sensor 30 directly detects the toner concentration on the photoconductor, but instead of this, instead of this, the toner concentration on the measuring potential portion is detected. The optical density may be detected after the toner is transferred onto a transfer paper or a conveyor belt of the transfer device 8. In this case, the output level of the optical sensor on the photoconductor does not match the output level of the optical sensor on the transfer paper due to the transferability when the toner on the photoconductor is transferred to the transfer paper or the like. Therefore,
The optical sensor output level corresponding to each is set.

Although the above-mentioned image forming apparatus has only one developing device 4, it can be provided to an image forming apparatus having a plurality of developing devices 4. FIG. 5 shows a tandem type image forming apparatus used in a high speed color printer or a copying machine which is another embodiment of the image forming apparatus of the present invention.

[0026]

As described above, in the image forming apparatus of the present invention, the potential for measurement is formed on the image bearing member under the predetermined image forming condition while stirring the developer, and the measurement is performed. The developer characteristics are substantially judged by detecting the concentration of the developer on the potential part of the developer. If the developer characteristics are not good, the developer is continuously stirred, and when it is good, stirring is started immediately. By stopping, the deterioration of the developer can be delayed, and a high-quality image can be provided for a long period of time. Further, the developer used in the image forming apparatus is sensitive to usage environment conditions such as time and environment, and when recycled toner is used, the tendency is promoted. By determining whether the developer is deteriorated and not supplying the replenishment of recycled toner, which is one of the causes of deterioration of the developer or accelerating the cause of deterioration, to the developing device, further deterioration of image quality is suppressed.
Further, by providing the grace period for this deterioration, it is possible to extend the life of the developer until the developer is replaced and prevent the non-use period of the image forming apparatus.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a configuration of a copying machine that is an embodiment of an image forming apparatus of the present invention.

FIG. 2 is an enlarged schematic view of a portion of the copying machine of FIG. 1 where a developing device is provided.

FIG. 3 is a diagram showing a detection result of a halftone pattern and a white portion potential portion by an optical sensor, in which a horizontal axis shows a stirring time and a vertical axis shows a detection value of the optical sensor.

FIG. 4 is a diagram showing an example of a detection result of a white potential portion by an optical sensor while driving a developer stirring means when the developer is deteriorated, where the horizontal axis indicates the stirring time and the vertical axis indicates the optical portion. The detection value of the sensor is shown.

FIG. 5 is a tandem type image forming apparatus used in a high speed color printer or a copying machine which is another embodiment of the image forming apparatus of the present invention.

[Explanation of symbols]

1 Photosensitive Drum (Image Carrier) 2 Charging Device 3 Exposure Device 4 Developing Device 5 Paper Tray 6 Registration Roller 7 Conveying Device 8 Transfer Device 9 Fixing Device 10 Paper Ejection Tray 11 Cleaning Device 20 Scanner Unit 21 Image Processing Unit 22 Printer Part 30 Optical sensor (concentration detecting means) 31 Humidity sensor (environmental condition detecting means) 32 Stirring control means 41 Developing roller 42 Developer stirring tank 43 Toner storage tank 44 Toner replenishing roller 45 Stirring screw (developer stirring means) A Photoconductor Drum rotation direction 1 Proper range of detection value of halftone pattern m Lower limit of proper range of detection value of white potential part n Upper limit of developer life p Upper limit of developer life and lower limit line of proper detection value Area to be sandwiched h1 Output timing of stirring end command h2 Upper limit of stirring time

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) G03G 21/10 G03G 21/00 326 F term (reference) 2H027 DA10 DA14 DE02 DE07 DE09 DE10 EA04 EC04 EC06 ED08 EF02 GB03 GB07 GB09 HA02 HB13 2H077 AA15 AA37 AB02 AB15 AC02 AC16 AD06 AD13 AD23 AE06 DA03 DA18 DA20 DA47 DA63 DA82 DB25 EA03 GA02 GA13 2H134 GA01 GB02 HD01 JA11 KG03 KG07 KH01 KH04

Claims (6)

[Claims] 1. A developer remaining on the image carrier is recovered,
In an image forming apparatus that returns the toner to a developing device and reuses the image forming device, the image forming device includes a developer stirring unit that stirs the developer in the developing device and the developer on the image carrier before the image forming operation. A density detecting means for detecting the amount of toner that is detected and a stirring control means for controlling the developer stirring means according to the detected toner amount are provided, and the density detecting means is provided on the image carrier with a potential portion equivalent to a white portion. The amount of toner developed in at least one potential part to which toner adheres is detected, and the stirring control means controls the developer stirring means based on the amount of toner detected by the density detection means. Image forming apparatus. 2. The image forming apparatus according to claim 1, wherein the image forming apparatus drives the developer agitating unit after the main power is turned on and before the first image forming operation is performed. Image forming apparatus. 3. The image forming apparatus according to claim 1, wherein the image forming apparatus is provided with an environmental condition detecting means for detecting an environmental condition, and the environment condition detecting means uses the image forming apparatus as an environment. The image forming apparatus is characterized in that the agitation control means starts driving the developer agitation means when it is detected that the temperature is outside the proper environment range. 4. The image forming apparatus according to claim 1, wherein the image forming apparatus sets an upper limit on a driving time of the developer stirring unit. 5. The image forming apparatus according to claim 4, wherein, when the driving time of the developer agitating unit reaches the upper limit, the image forming apparatus corresponds to a white portion by the density detecting unit at the time when the upper limit is reached. An image forming apparatus, which determines whether or not image formation is prohibited according to the detection result of the potential portion of 6. The image forming apparatus according to claim 4, wherein the image forming apparatus returns the collected developer remaining on the image carrier to the developing device when the driving time of the developer stirring means reaches the upper limit. An image forming apparatus characterized by the absence thereof.