JP2002040725A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an image density decrease and an image defect such as character crush or blur which are caused by a great change in developer characteristic, in an image forming device that controls toner supply in order to keep toner concentration of developer in a developing device in an appropriate range. SOLUTION: The image forming device has a toner supply roller 14 which supplies toner to a developing part 4a from a toner supply part 4b, a T sensor 10 which detects concentration of toner in the developing part, and a P sensor 7 which is situated on a photoreceptor 1 and detects image density of a reference image used for image density detection. The device further has a toner supply roller control means 16 which controls drive of the toner supply roller according to the result of comparison of an output value of the P sensor with a control reference value VTref, and a control reference value correction means 17 which corrects the control reference value VTref based on an output value of the P sensor and an output value of the T sensor, thereby controlling toner supply based on the corrected control reference value VTref. In the image forming device, the upper and lower limit values are determined for the corrected control reference value VTref, and a development bias is corrected in accordance with the corrected control reference value VTref.

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 facsimile, a printer, and the like. The present invention relates to an image forming apparatus that performs toner replenishment control in order to keep the toner supply within the range.

[0002]

2. Description of the Related Art In the above-mentioned image forming apparatus, in order to stabilize the image density, it is important to keep the toner concentration of a developer in a developing apparatus within a certain range. There is. As control means for toner replenishment, the present applicant has disclosed an output value of an image density detecting means for detecting an image density of a reference image formed on an image carrier, and an output value of a toner density detecting means for detecting a toner density in a developing device. Based on the above, an image forming apparatus that controls a toner replenishing unit such as a toner replenishing roller (for example, see Japanese Patent Application Laid-Open No. 2-38773) has been proposed.

In controlling the toner replenishing means, the toner density in the developing device is detected by a toner density detecting means during each image forming operation, and an output value VT and a control reference value VTre are provided.
The driving time of the toner replenishing means is calculated according to the result of comparison with f, and control is performed such that the toner replenishing means is driven for the calculated driving time. Then, each time a predetermined number of image forming operations are completed, a reference image is formed on the image carrier, the image density is detected by image density detecting means, and a correction amount ΔVT of the control reference value is calculated based on the output value. I do. And
VTref = VT + Δ based on the correction amount ΔVT and the output value VT of the toner density detecting means at the time of creating the reference image.
A control reference value VTref is determined like VT, and the corrected control reference value VTref is used for toner supply control until the next reference image formation. Further, even when the output value of the image density detected by the image density detecting means changes greatly and the control reference value VTref of the toner density is determined to be largely corrected, the upper and lower limits of the corrected control reference value VTref are set. It is determined that the toner concentration does not deviate from an appropriate range.

The toner replenishment control using both the image density detecting means and the toner density detecting means has a constant toner density as compared with the toner replenishing control using only the toner density detecting means. Nevertheless, there is an advantage that the effect of a change in image density due to a change in the characteristics of the developer or the like is reduced, and the image density during image formation is kept constant.

Further, in the control of the toner replenishing means, the applicant maintains the toner concentration within a certain range even if there is a temporary change in the charging potential during the formation of the reference image and a change in the aging characteristics of the developer. In addition, there has been proposed an improvement on the control of the toner replenishing means so as to obtain an appropriate image density (for example, see JP-A-8-110700, JP-A-8-202137, etc.). Further, improvement of the adjusting means of the toner density sensor (see Japanese Patent Application Laid-Open Nos. 5-134548 and 10-186830) has also been proposed.

[0006]

However, control of the toner replenishing means alone cannot cope with a change in image density due to a remarkable change in developer characteristics. In the above-described image forming apparatus, depending on environmental conditions and copy frequency (hereinafter, referred to as copy duty), the characteristics of the developer significantly change, and there is a possibility that an abnormal image such as crushed characters or bleeding or a decrease in image density may occur. The possibility of causing such a problem will be described based on an experimental example shown in Table 1.

Table 1 shows the change in the amount of charge of the developer depending on the environmental conditions, the copy duty (here, the number of copies per day), the output value of the reference image by the developer, and the reference image creation by the developer. 5 shows an experimental example of a control reference value VTref when a correction amount ΔVT of the control reference value is calculated based on the output value VT of the toner density detecting means at the time and a change in toner density. Here, the upper limit amount and the lower limit amount of the toner density, and the control reference value VTref corresponding thereto are set in advance because their values change depending on the type of the developer used in the developing device. In this experimental example, the control reference value VTref is controlled to be 2.9V or less and 1.1V or more so that the upper and lower limits of the toner concentration fall within a range of about 3.5 wt% to 6.0 wt%.

[0008]

[Table 1]

As shown in Table 1, when 1000 copies are made at a low duty (50 sheets / day) in a high temperature and high humidity environment,
The charge amount (Q / M) of the developer is significantly reduced. When the image density of the reference image is detected by the image density detecting means using such a developer, the output value of the image density detecting means determines that the image density is high. Therefore, the correction works in the direction of lowering the toner density, and the corrected control reference value VTref becomes the upper limit of 2.9 V. Control reference value VTref 2.9V
When the toner replenishment control was performed by using, the toner concentration became 3.3 wt% near the lower limit. In this state, when copying is performed at a further low duty, the charge amount (Q / M) of the developer further decreases even though the toner density is controlled to be near the lower limit, and the image carrier is The amount of toner adhered to the upper portion increased, and abnormal images such as crushed characters and bleeding occurred. In addition, high duty under low temperature and low humidity environment
When copying is performed at (1000 sheets / day), the charge amount (Q / M) of the developer significantly increases. When the image density of the reference image is detected by the image density detecting means with such a developer, the output value of the image density detecting means determines that the image density is low. Therefore, the correction is performed in the direction of increasing the toner density, and the corrected control reference value VTref has a lower limit of 1.
1V. When the toner replenishment control is performed using the control reference value VTref1.1V, the toner concentration becomes 5.7 wt%.
Became. In this state, when copying is performed at a higher duty, the charge amount (Q / M) of the developer further increases even though the toner density is controlled near the upper limit, and the image carrier is The amount of the adhered toner was reduced, resulting in a decrease in image density. Thus, environmental conditions,
Depending on the copy duty, the charge amount of the developer changes remarkably, and controlling the toner density within the range of the set upper and lower limits of the toner density is not enough to cope with the possibility that an abnormal image may be generated.

SUMMARY OF THE INVENTION The present invention has been made in consideration of the above problems, and has as its object to form an image by controlling toner replenishment in order to maintain the toner concentration of a developer in a developing device within an appropriate range. An object of the present invention is to provide an image forming apparatus which prevents the occurrence of an abnormal image such as a decrease in image density due to a remarkable change in the characteristics of a developer, a collapse of characters, and a blur.

[0011]

In order to achieve the above object, according to the first aspect of the present invention, an image carrier, a charging device for charging the image carrier, and a latent image formed on the image carrier are provided. An exposure device, and a developing device that applies a developing bias to a developer carrying member that carries and conveys a two-component developer including a toner and a carrier to visualize a latent image on the image carrier with the two-component developer. A toner replenishing device for replenishing toner in the developing device, a toner density detecting device for detecting a toner density in the developing device, and a reference image for forming a reference image for image density detection on the image carrier. Forming means, image density detecting means for detecting the image density of the reference image, and toner replenishing control for controlling the driving of the toner replenishing means in accordance with a comparison result between the output value of the toner density detecting means and a control reference value Means and an output value of the image density detecting means An image forming apparatus comprising: a control reference value correcting unit that corrects the control reference value based on an output value of the toner density detecting unit; wherein an upper and lower limit value is set for the corrected control reference value; And a developing bias correcting means for correcting the developing bias according to the set control reference value.

In the image forming apparatus according to the present invention, in the toner supply control for supplying toner based on the corrected control reference value, the corrected control reference value is set so as to be within a predetermined upper and lower limit range. Thus, the toner concentration of the developer replenished based on the corrected control reference value is prevented from falling outside an appropriate range. By this toner supply control, the toner density, which is one of the factors affecting the image density, is kept within a certain range. Further, the developing bias is corrected according to the control reference value corrected by the developing bias correcting unit. As described above, in addition to the toner supply density control, the developing bias is corrected based on the output value of the image density detecting means and the control reference value corrected based on the output value of the toner density detecting means. , The influence of the change in image density can be further reduced. By performing the development bias correction, it is possible to cope with a change in the amount of adhesion on the image carrier due to a remarkable change in the characteristics of the developer that cannot be dealt with only in the appropriate range of the toner concentration.
Prevent generation of abnormal images.

According to a second aspect of the present invention, in the image forming apparatus of the first aspect, when the control reference value is higher than a predetermined value, the developing bias correction means sets the image density to a value such that the image density becomes lower. It is characterized in that the developing bias is corrected.

According to a second aspect of the present invention, when the control reference value is higher than a predetermined value, that is, when the image density of the reference image is higher than a predetermined density based on the output value of the image density detection means. When it is determined, by changing the developing bias to a value that reduces the image density,
Decrease toner adhesion. This prevents the occurrence of abnormal images such as crushed characters and bleeding.

According to a third aspect of the present invention, in the image forming apparatus of the first aspect, when the control reference value is lower than a predetermined value, the developing bias correction means sets the image density to a value that increases the image density. It is characterized in that the developing bias is corrected.

In the image forming apparatus according to the third aspect, when the control value is lower than a preset value, that is, based on the output value of the image density detecting means, the image density of the reference image is lower than the predetermined density. When it is determined that the toner density is high, the developing bias is changed to a value that increases the image density, thereby increasing the toner adhesion amount. This prevents a decrease in image density.

According to a fourth aspect of the present invention, in the image forming apparatus of the second or third aspect, a charging potential for correcting the charging potential of the image carrier by the charging device in accordance with the developing bias corrected by the developing bias correcting means. It is characterized in that a correction means is provided.

According to the image forming apparatus of the present invention, by controlling the charging potential of the image bearing member in accordance with the corrected developing bias, the difference between the charging potential and the developing bias changes, thereby causing carrier adhesion and background contamination. Etc. do not occur.

According to a fifth aspect of the present invention, in the image forming apparatus of the fourth aspect, the charging potential correction means corrects the charging potential so that a difference between the developing bias and the charging potential becomes constant. It is assumed that.

In the image forming apparatus according to the present invention, the difference between the developing bias value and the charging potential is fixed, and the difference between the charging potential and the developing bias is changed to prevent carrier adhesion, background contamination, and the like. To prevent.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to an electrophotographic copying machine (hereinafter referred to as a copying machine) using reversal development as an image forming apparatus will be described below. FIG.
FIG. 2 is a diagram illustrating a schematic configuration of an image forming unit and a schematic configuration of a toner supply control unit, a bias control unit, and a charged potential control unit of the copying machine according to the embodiment. In the copying machine shown in FIG. 1, a charger 2, an exposing device 3, a developing device 4, a transferring device 5, a separating device 6, and a cleaning device 8 are provided around a photoreceptor 1 as an image carrier.
Are arranged in order. Also, there are a paper feeder 9 that feeds the transfer body from a paper feed tray (not shown), and a fixing device (not shown) that fixes the toner to the transfer body after the transfer body onto which the toner image has been transferred is separated from the photoconductor 1. Is provided.

In the copying machine constructed as described above, the surface of the photoreceptor 1 rotating in the direction of arrow a is uniformly charged by the charger 2, and then irradiated with a laser beam from the exposure device 3 based on image information. Then, a latent image is formed on the photoconductor 1. In this embodiment, the charged potential VD of the electrostatic latent image formed on the photoconductor 1 is -800 V, and the exposed portion potential VL is -1.
50 V was applied. Then, the developing device 4 forms a toner image by attaching negatively charged toner to such an electrostatic latent image formed on the photoconductor 1. On the other hand, the transfer member is fed from a sheet feed tray by a sheet feeder 9 and then transferred to a transfer unit where the photoconductor 1 and the transfer device 5 face each other. The transfer device 5 applies a charge of a polarity opposite to that of the toner image on the photoreceptor 1 to the transfer body, so that the
The toner image formed thereon is transferred to a transfer body. Then
The transfer member is separated from the photoreceptor 1 by the separation device 6, sent to a fixing device (not shown), and an image is obtained by fixing the toner to the transfer member. On the other hand, the surface of the photoconductor 1 is cleaned by the cleaning device 8.

Next, the developing device 4 employed in the above copying machine
Will be described in detail. The developing device 4 includes the photoconductor 1
A developing unit 4a for developing the upper electrostatic latent image;
And a toner replenishing unit 4b as a toner replenishing means for replenishing the toner with the toner. The developing unit 4a includes stirring members 11 and 12 for stirring a two-component developer including toner and a magnetic carrier housed therein, a developing roller 13 as a developer carrier, and a developer on the developing roller 13. A doctor blade for regulation. Stirring member 1
Numerals 1 and 12 stir the toner of the two-component developer and the magnetic carrier to make the toner concentration uniform and frictionally charge the toner to the negative polarity by the magnetic carrier. The developing roller 13 carries a two-component developer composed of a negatively charged toner and a magnetic carrier, and transports the developer to a developing position facing the photoconductor 1. On the way, the two-component developer on the developing roller 13 is regulated to an appropriate layer pressure by a doctor blade. At the developing position, a predetermined developing potential VB-VL is formed between the photosensitive member 1 and the developing roller 13 by applying a developing bias voltage VB to the developing roller 13 from the developing bias power supply 15. This development potential VB−
By the VL, the negatively charged toner is supplied from the developing roller 13 to an exposed portion on the photoconductor 1 to convert the latent image on the photoconductor 1 into a toner image. The toner replenishing section 4b includes a toner replenishing roller 14 as a toner replenishing member for replenishing the toner contained therein to the developing section 4a. The rotation of the supply roller 14 causes the toner supply unit 4b to rotate.
The toner contained inside is supplied to the developing unit 4a.

Next, from the toner replenishing section 4b to the developing section 4
A description will be given of a toner replenishment control unit for controlling the rotation drive of the replenishment roller 14 for replenishing the toner a. A magnetic permeability sensor (hereinafter, referred to as a T sensor) 10 is provided on the bottom surface of the developing unit 4a as a toner concentration detecting unit for detecting the toner concentration of the developer in the developing unit 4a. Further, a reflection type photosensor (hereinafter, referred to as an image density detection unit) for detecting the image density of the image formed on the photoconductor 1
A P sensor 7 is disposed between the developing device 4 and the transfer device 5 so as to face the photoconductor 1.

The output signal VT of the T sensor 10 is input to the toner supply roller control means 16 and the control reference value correction means 17. Further, the control reference value VTref for toner replenishment is input to the toner replenishment roller control means 16 from the control reference value correction means 17. Toner supply roller control means 16
Are the output value VT of the T sensor 10 and the control reference value VTref.
And the toner replenishing roller 1 according to the comparison result.
4 is calculated, and the supply roller 14 is controlled to be driven for the calculated driving time. Further, a reference image corresponding to a reference pattern having a predetermined reference density is formed on the photoreceptor 1 using a charger 2, an exposure device 3, a developing device 4, and the like as reference image forming means. Is detected by the P sensor 7 and the detected value is input to the control reference value correcting means 17. The control reference value correction means 17
The correction amount ΔV of the control reference value VTref of the T sensor 10 based on the detection value of the sensor 7 and the output value VT of the T sensor 10
Calculate T. Then, based on the correction amount ΔVT and the output value VT of the toner density detecting means at the time of creating the reference image, the control reference value VT is calculated as VTref = VT + ΔVT.
ref is determined, and the corrected control reference value VTref is determined.
Is used for toner supply control until the next reference image formation. By this toner replenishment control, the toner concentration can be kept within a certain range. However, the toner adhesion amount on the photoreceptor 1 is also affected by a remarkable change in developer characteristics due to a use environment of a copying machine, a copy duty, and the like.

Therefore, in the copying machine of the present embodiment, in order to reduce these effects, in addition to the toner supply control, the control reference value corrected by the control reference value correction means 17 by the developing bias correction means 18 is used. The developing bias control according to the value VTref is performed. The value of the control reference value VTref corrected by the control reference value correction means 17 is input to the developing bias correction means 18. The developing bias corrector 18 corrects the developing bias voltage VB based on the control reference value VTref, and applies the corrected developing bias voltage from the developing bias power supply 15 to the developing roller 13.

When the developing bias is controlled by the developing bias means 18, the charge potential VD
And the developing bias VB may change, which may cause a problem. Specifically, as shown in FIG. 3, when the difference VD-VB between the charging potential VD and the developing bias VB increases, carrier adhesion is likely to occur. On the other hand, the charging potential VD
When the difference VD-VB between the bias voltage VB and the developing bias VB is small, background contamination may occur. Therefore, the charging voltage correcting unit 19 corrects the charging potential VD based on the corrected developing bias VB input from the developing bias correcting unit 18 so that the above-described problem does not occur. And the photoconductor 1
Is applied to the charger 2 so that the voltage is charged to the corrected charging potential VD.

FIG. 2 is a flowchart of toner supply control, development bias control and charge potential control using the T sensor 10 and P sensor 7. When the main switch of the copying machine is turned on (step 2), the control unit drives the image forming unit so that a reference image is formed on the photosensitive member 1. In the image forming section, the photosensitive member 1 is uniformly charged by the charger 2 and then exposed by the exposure device 3 to form an electrostatic latent image of the reference image for image density detection. The developing device 4 develops the electrostatic latent image with a predetermined developing potential to form a reference image on the photoconductor 1 (Step 3). At this time, the control reference value correction means 17 supplies the toner supply control reference value Vtr.
The previous reference value VTref is stored in the storage means as ef (step 4). Next, the control reference value correction means 17
The sensor 7 captures the output value Vsp of the reference image on the photoconductor 1 and the output value Vsg for the non-image portion on the photoconductor 1 to calculate the ratio Vsp / Vsg. Developer toner concentration V
T is detected (steps 5 and 6). The control reference value correction unit 17 is configured to store Vsp / Vsg stored in the storage unit in advance.
Table 2 showing the relationship between the correction amount ΔVT of the control reference value VTref based on the detected toner concentration VT of the T sensor 10.
The correction amount ΔVT = f (Vsp / Vsg, VT) of the control reference value VTref is calculated with reference to the correction table (step 7).

[0029]

[Table 2]

In Table 2, T sensor sensitivity S is a value determined by T sensor characteristics, developer characteristics, and the like. In this embodiment, S = 4.0 (wt% / V).

Further, the reference value Vtref stored in the storage means is corrected by the correction amount ΔVt and determined as a new calculation VTref (step 8). Calculation is performed so that the new calculation VTref falls within a preset range (steps 9 to 13), and a new control reference value VTr is calculated.
ef is determined and stored in the storage means (step 14).
In Steps 9 to 13, even when the output value Vsp / Vsg of the image density detected by the P sensor 7 greatly changes and the control reference value VTref of the toner density is determined to greatly change, the control reference value is not changed. The upper and lower limits are determined so that the toner concentration does not fall outside an appropriate range. In the present embodiment, the upper limit of the control target value VTref is set to 2.9 V and the lower limit is set to 1.1 V so that the toner concentration after toner replenishment is in the range of about 3.5 wt% to 6.0 wt%.

Next, the developing bias correcting means 18 outputs VTr
The developing bias voltage to be applied to the developing roller 13 is determined with reference to the correction table in Table 3 showing the relationship between f and the developing bias value stored in the storage means in advance (step 15).

[0033]

[Table 3]

In Table 3, when the control reference value VTref is near the upper limit and the image density is estimated to be lower than the output value of the P sensor 7, the developing bias VB is raised by -100V from the default value of -600V. -700V,
By increasing the development potential VB-VL, the amount of toner adhered to the photoreceptor 1 is increased to prevent a decrease in image density. When the control reference value VTref is near the lower limit and the output value of the image density detecting means is estimated to be high, the developing bias VB is set to the default value of −6.
By lowering the developing potential VB-VL by -100V from -00V to -500V, the amount of toner adhered to the photoreceptor 1 is reduced, and the occurrence of abnormal images such as crushed characters and bleeding is prevented. .

Next, the charging voltage correcting means 19 refers to a correction table (Table 4) in Table 4 showing the relationship between the developing bias voltage VB and the charging potential VD stored in the storage means in advance, and the charging potential of the photosensitive member 1 is determined. Determine VD (Step 1)
6).

[0036]

[Table 4]

Here, the charging potential is determined so that the difference between the charging potential VD and the image bias voltage VB, VD-VB, becomes constant.

Then, the control unit controls the image forming unit so that the developing bias voltage VB and the charging potential VD are determined as described above, and a predetermined number of continuous copying operations (hereinafter, referred to as "hereinafter") set from the operation display unit. 1 Job) (step 17). When the copying operation starts, the toner supply roller control unit 16 takes in the detected value VT of the toner concentration of the developer in the developing unit 4a by the T sensor 10, and
A comparison is made with the reference value VTref, and a toner replenishment time t = f (VTref-VT) is determined based on the comparison result (step 18). The toner supply roller control means 16
By controlling the toner supply clutch (not shown) and rotating the toner supply roller 14 for the toner supply time t, toner is supplied to the developing unit 4a (step 19). Developing unit 4a by T sensor 10 at each copy in one job
Is detected (step 2).
1). The control unit determines whether one job is completed (step 22). If not completed, the process returns to step 18 and repeats steps S18 to S22 until one job is completed.

As described above, according to the copying machine of the embodiment, in addition to the toner replenishment control, the development bias control is performed in accordance with the corrected control reference value VTref, so that environmental conditions, copy duty, and the like are obtained. Thus, even when the characteristics of the developer greatly change, it is possible to prevent the characters from being crushed or blurred, the image density from fluctuating, and the like. Further, it is possible to prevent abnormal images such as carrier adhesion and background contamination, which are caused by the development bias control.

Although the above embodiment has been described using a reversal developing copier, the present invention is also applicable to a regular development copier. An example of a regular development copying machine is as follows. The electrostatic latent image formed on the photoreceptor 1 has a charged potential (image portion) VD = −700 V and an exposed portion potential (non-image portion) VL = −50 V. The default value of the developing bias VB applied to the developing roller 13 is -250V. Then, the toner charged to the positive polarity from the developing roller 13 is supplied to the charging unit on the photoconductor 1 by the developing potential VD-VB formed between the charging unit of the photoconductor 1 and the developing roller 13, and the photosensitive drum is charged. The latent image on the body 1 is converted into a toner image. In the case of such a copying machine using the normal development, the correction table referred to in the development bias control in step 15 is as follows. When the control reference value VTref is near the upper limit,
When it is estimated that the image density is lower than the output value of the P sensor 7, the developing bias VB is set to the default value of -250.
By increasing the developing potential VD-VB by 100V from -V to -150V, the amount of toner adhered to the photoreceptor 1 is increased to prevent a decrease in image density. When the control reference value VTref is near the lower limit and the output value of the image density detecting means is estimated to be high, the developing bias VB is set to 100 from the default value of -250V.
V to -350V, development potential VD-VB
Is reduced, the amount of toner adhered to the photoreceptor 1 is reduced, and the occurrence of abnormal images such as crushed characters and bleeding is prevented. As described above, even in the copier of the normal development, by performing the developing bias control in accordance with the corrected control reference value in addition to the toner replenishment control, it is possible to prevent collapse of characters, bleeding, fluctuation of image density, and the like. be able to.

[0041]

According to the first aspect of the present invention, in the image forming apparatus for controlling the toner replenishment in order to keep the toner concentration of the developer in the developing device within an appropriate range, the characteristics of the developer are remarkably changed. Therefore, there is an excellent effect that it is possible to prevent the occurrence of an abnormal image such as a decrease in image density, crushing of characters, and blurring.

In particular, according to the second aspect of the invention, there is an excellent effect of preventing occurrence of abnormal images such as crushed characters and bleeding.

In particular, according to the third aspect of the invention, there is an excellent effect of preventing a decrease in image density.

In particular, the invention according to claim 4 or 5 has an excellent effect of preventing occurrence of abnormal images such as carrier adhesion and background stain.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating a schematic configuration of an image forming unit and a schematic configuration of a toner supply control unit, a developing bias control unit, and a charging potential control unit of a copying machine according to an embodiment.

FIG. 2 is a flowchart of toner supply control, development bias control, and charging potential control according to the embodiment.

FIG. 3 is a characteristic diagram showing a relationship between a photosensitive member charging potential VD, an exposure portion potential VL, and a developing bias VB.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Photoreceptor 2 Charger 3 Exposure device 4 Developing device 4a Developing unit 4b Toner replenishing unit 5 Transfer device 6 Separation device 7 P sensor 8 Cleaning device 9 Paper feeder 10 T sensor 11, 12 Stirring member 13 Developing roller 14 Replenishing roller Reference Signs List 15 developing bias power supply 16 toner replenishing roller control means 17 control reference value correcting means 18 developing bias correcting means 19 charging potential correcting means

Continued on the front page F term (reference) 2H003 AA02 BB11 DD03 DD11 2H027 DA02 DA10 DE02 DE04 EA01 EA05 EA06 EC03 EC06 ED03 ED09 EF09 2H073 AA02 BA13 BA23 BA25 CA03 2H077 AD06 AD35 DA03 DA10 DA42 DA47 DA52 DA63 DB02 DB08 DB08

Claims (5)

[Claims] An image bearing member, a charging device for charging the image bearing member, an exposure device for forming a latent image on the image bearing member, and carrying and transporting a two-component developer composed of a toner and a carrier. A developing device for applying a developing bias to the developer carrier to visualize a latent image on the image carrier with the two-component developer, a toner replenishing unit for replenishing toner in the developing device, and the developing device Toner density detecting means for detecting the toner density in the image, reference image forming means for forming a reference image for image density detection on the image carrier, image density detecting means for detecting the image density of the reference image, Toner supply control means for controlling the driving of the toner supply means in accordance with the result of comparison between the output value of the toner density detection means and the control reference value, and the output value of the image density detection means and the output value of the toner density detection means Corrects the control reference value based on In the image forming apparatus and a control reference value correcting means sets upper and lower limit values to the corrected control reference value, and,
An image forming apparatus comprising: a developing bias correcting unit configured to correct the developing bias according to the corrected control reference value. 2. The image forming apparatus according to claim 1, wherein said developing bias correcting means corrects said developing bias to a value such that the image density becomes lower when said control reference value is higher than a preset value. An image forming apparatus comprising: 3. The image forming apparatus according to claim 1, wherein said developing bias correcting means corrects said developing bias to a value such that the image density becomes higher when said control reference value is lower than a preset value. An image forming apparatus comprising: 4. An image forming apparatus according to claim 2, further comprising a charging potential correcting means for correcting the charging potential of the image carrier by said charging device in accordance with the developing bias corrected by said developing bias correcting means. An image forming apparatus comprising: 5. An image forming apparatus according to claim 4, wherein said charging potential correcting means corrects said charging potential so that a difference between said developing bias and said charging potential becomes constant. .