JP2002108087A - Image forming device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To perform stable toner density control and image density control by properly grasping the abnormalities of a toner density detection result. SOLUTION: This image forming device which controls image density uniformly is provided with a toner density detecting means 3 in a developing device 2, and an image density detecting means 5 which controls toner density in the developing device 2 uniformly, and detects directly or indirectly the image density of a toner image G developed by a image carrier 1. The image forming device is further provided with a judging means 7 which judges by comparing the variation tendency of a toner density detection result and the variation tendency of an image density detection result that the abnormalities are generated in the toner density detection result under condition that both variation tendencies are contradictory.

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 to an improvement of an image forming apparatus using a developing device using a two-component developer including a toner and a carrier.

[0002]

2. Description of the Related Art In general, there are various types of image forming apparatuses that develop an electrostatic latent image formed on an image carrier such as a photoreceptor with a developing device and then transfer the developed image onto a transfer material such as paper. Exists. As one of developing devices used in this type of image forming apparatus, a so-called two-component developing device using a two-component developer composed of a toner and a carrier is known. Here, the toner and the carrier are configured to be charged to opposite polarities by friction. These are attracted to each other by electrostatic adhesion, but when they come into contact with or come close to the electrostatic latent image during development, the toner is attracted to the electrostatic latent image by electrostatic force stronger than the electrostatic adhesion. This visualizes the electrostatic latent image. In such a two-component developing device, only toner is consumed at the time of development, so toner replenishment is required. However, when toner replenishment is performed, the toner concentration excessively increases, and the toner charge amount decreases. A so-called fogging phenomenon in which toner adheres to a white background portion occurs. Therefore, conventionally, a toner concentration in a two-component developer in a developing device is detected by a toner concentration sensor, and toner replenishment is controlled in accordance with the detected toner concentration so that the toner concentration is maintained at a constant value. Is known.

In this type of image forming apparatus, it is necessary to keep the image density of an image formed on a transfer material constant. For this purpose, several methods are generally used as an image density control system. ing. As a typical example, a pattern (electrostatic latent image) for image density detection is formed on an image carrier, and the image density detection pattern is developed by a developing device. There is known a method of detecting an image with a density sensor and controlling the image density in accordance with the pattern image density. As a specific mode of the image density control, for example, in the mode in which the toner density sensor is provided, the toner density in the developing device is controlled to be constant, and the image density on the image carrier is controlled. According to the image density signal detected by the sensor, the surface potential (development contrast) of the image carrier, and / or
By adjusting the bias applied to the developing roll,
A device that obtains a desired image density (for example,
175501).

[0004]

In an image forming apparatus employing the above-described toner density control method and image density control method, it is assumed that the toner density in the developing device is maintained at a constant level. The role of the toner density detection sensor is important. However, in this type of image forming apparatus, when the toner density detection sensor fails or when the detection result is significantly different from the true toner density, erroneous toner supply control is performed. Would. Here, in the former case, it may be possible to avoid this kind of problem by detecting the failure of the toner concentration detection sensor, but in the latter case, the two-component developer is circulated and conveyed in the developing device. Therefore, there may be a difference between the toner concentration at the portion where the toner concentration detection sensor is provided and the toner concentration at other portions, and even if the toner concentration detection sensor itself has no problem, Such problems cannot be avoided. If, for example, the toner concentration detection result is detected to be significantly lower than the true toner concentration, a situation in which unnecessary toner is originally replenished may occur, and as a result, the toner in the developing device may be replenished. The bulk of the component developer increases, causing an increase in the torque for stirring the two-component developer,
The fog phenomenon is caused by the decrease in the toner charge amount described above. On the other hand, if the toner concentration detection result is detected to be significantly higher than the true toner concentration, a situation occurs in which the originally required toner is not supplied, and as a result, the resistance value of the two-component developer becomes lower. As a result, the carrier is developed on the image bearing member, and white spots occur at the portions where the carrier is developed.
If the toner density cannot be controlled to be constant, not only the toner density control but also the image density control become unstable for the above-mentioned reason.

SUMMARY OF THE INVENTION The present invention has been made to solve the above technical problems, and it is intended to perform stable toner density control and image density control by accurately grasping an abnormality in a toner density detection result. The present invention provides an image forming apparatus capable of performing the following.

[0006]

That is, according to the present invention, as shown in FIG. 1, an image carrier 1 on which an electrostatic latent image Z is formed and carried, and a two-component developer D comprising a toner T and a carrier C are provided.
A developing device 2 for developing the electrostatic latent image Z on the image carrier 1 with toner, a toner concentration detecting device 3 for detecting the toner concentration in the developing device 2, and a toner concentration detecting device 3. Based on the toner density detection result, the developing device 2
A toner density control unit 4 for controlling the toner density in the image carrier to a preset density, an image density detection unit 5 for directly or indirectly detecting the image density of the toner image G developed on the image carrier 1, An image forming apparatus comprising: an image density controller that controls an image density developed on the image carrier to a predetermined density based on an image density detection result of the image density detector. The fluctuation tendency of the toner density detection result and the fluctuation tendency of the image density detection result are compared, and under the condition where the fluctuation tendency of both of them is inconsistent,
The image forming apparatus further comprises a judging means 7 for judging that an abnormality has occurred in the toner density detection result.

In such technical means, as the image carrier 1, a photoconductor, a dielectric, or the like may be appropriately selected as long as the electrostatic latent image Z is formed and carried thereon. , Drum shape, belt shape, etc., may be selected as appropriate, and the number may be not only one but also plural.

[0008] Further, if the developing device 2 accommodates a two-component developer D composed of a toner T and a carrier C,
As well as a so-called two-component developing device, a so-called hybrid developing device in which only the toner T of the two-component developer D is carried on the donor member to perform development may be used.

Further, the toner density detecting means 3 can detect the toner density in the developing device 2, that is, the ratio of the toner T in the two-component developer D, as long as it can detect the toner density. You can choose from the methods.
Further, the toner density control means 4 is appropriately selected as long as it controls the toner density in the developing device 2 to a preset density based on the toner density detection result of the toner density detection means 3. Usually, the toner T
Is used to maintain the toner concentration at a constant level by replenishing the toner. When the toner T is supplied, the carrier C may be supplied at the same time.

The image density detecting means 5 may be appropriately selected as long as it directly or indirectly detects the image density of the toner image G developed on the image carrier 1. Here, as a mode for directly detecting the image density of the toner image G, for example, the image density of the toner image G on the image carrier 1 or the toner image on the transfer material to which the image on the image carrier 1 is transferred is described. One that detects the image density is exemplified. still,
The transfer material mentioned here is not limited to a final transfer material such as paper, but also includes a temporary transfer material such as an intermediate transfer body. On the other hand, the toner image G
As an aspect of indirectly detecting the image density of, for example,
Information on the electrostatic latent image Z formed on the image carrier 1, for example, information on a print signal is detected. FIG. 1 illustrates an example in which the image density of the toner image G developed on the image carrier 1 is directly detected.

Further, the image density control means 6 controls the image density developed on the image carrier to a preset density based on the image density detection result of the image density detection means 5. As a control method of such an image density, for example, a control factor is applied between the image portion of the electrostatic latent image Z formed on the image carrier 1 and the developing device 2 and the image carrier 1. A method using a potential difference (development contrast) between the developing device and a developing bias is used as a control factor.
And a method utilizing the peak value of the AC component of the developing bias applied between the image bearing member 1 and the image bearing member 1.

Further, the judging means 7 compares the fluctuation tendency of the toner density detection result with the fluctuation tendency of the image density detection result, and under the condition that both of these fluctuation trends contradict each other, Is determined to be abnormal. That is, when the toner density detection result increases (or decreases) with time, while the image density detection result decreases (or increases) with time, the toner It is determined that an abnormality has occurred in the density detection result. However, in a general image forming apparatus, for example, when the toner density in the developing device 2 is increased, this increase affects the increase in the image density, but there is a slight time lag. Then, it is preferable to compare the fluctuation tendency of the toner density detection result and the image density detection result.

As for the fluctuation tendency of the image density detection result, the fluctuation tendency of the image density detection result detected by the image density detection means 5 may be directly monitored. May be substituted by the fluctuation tendency of the control factor controlled by the image density control means 6 based on the above. Examples of the control factors include the potential difference between the image portion of the electrostatic latent image Z formed on the image carrier 1 and the developing bias, the peak value of the AC component of the developing bias, and the like as described above. .

If an abnormality occurs in the toner concentration detection result, the toner concentration of the two-component developer D in the developing device 2 may not be able to be controlled to be constant thereafter. Therefore, the toner density control unit 4 stops the toner density control based on the toner density detection result under the condition that the determination unit 7 determines that the toner density detection result is abnormal. It is preferable to change the toner density control based on the above. Note that the image forming operation itself may be stopped under the condition in which the determination unit 7 determines that the toner density detection result is abnormal. Further, it is preferable to provide a warning unit for warning that an abnormality has occurred in the toner concentration detection result, and to notify the user of the abnormality when the abnormality occurs.

[0015]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail based on an embodiment shown in the accompanying drawings. First Embodiment FIG. 2 is an explanatory view showing a first embodiment of an image forming apparatus (tandem image forming apparatus) to which the present invention is applied. In the figure, the image forming apparatus according to the present embodiment has four colors (yellow,
Magenta, cyan, black) image forming unit 22
(Specifically, 22a to 22d) are arranged in the horizontal direction, and a belt unit (belt conveyance device) 23 above which the intermediate transfer belt 230 circulated and conveyed along the arrangement direction of each image forming unit 22 is included. On the other hand, a recording material supply cassette 24 for accommodating a recording material (not shown) such as paper is disposed below the main body housing 21.
A recording material transport path 25 which is a transport path of the recording material from the recording material supply cassette 24 is vertically arranged.

In this embodiment, the image forming units 22 (22a to 22d) are arranged in order from the upstream side in the circulation direction of the intermediate transfer belt 230, for example, for yellow, magenta, cyan, and black (the arrangement is not limited to this. The toner image is formed in any order (not limited to the order), and includes each photoconductor unit 30, each developing unit 33, and one common exposure unit 40. Here, the photoconductor unit 30 includes, for example, a photoconductor drum 31, a charger (a charging roll in this example) 32 for pre-charging the photoconductor drum 31, and a cleaner 34 for removing residual toner on the photoconductor drum 31. Are integrated into a cartridge.

The developing unit 33 develops the electrostatic latent image formed by exposure on the charged photosensitive drum 31 by the exposure unit 40 with a corresponding color toner (for example, negative polarity in the present embodiment). Is what you do. Further, reference numeral 35
(35a to 35d) are toner cartridges for replenishing the respective developing units 33 with respective color component toners. still,
Details of the developing unit 33 and the toner cartridge 35 will be described later.

On the other hand, the exposure unit 40 includes, for example, four semiconductor lasers (not shown), one polygon mirror 42, an image forming lens (not shown), and each photoconductor unit 30 in a unit case 41. (Not shown), the light from the semiconductor laser for each color component is deflected and scanned by the polygon mirror 42, and the light image is formed at the corresponding exposure point on the photosensitive drum 31 via the imaging lens and the mirror. Is to lead.

In the present embodiment, the belt unit 23 has an intermediate transfer belt 230 stretched between a plurality of stretching rolls 231 to 235, and corresponds to the photosensitive drum 31 of each photosensitive unit 30. A primary transfer device (primary transfer roll in this example) 51 is provided on the back surface of the intermediate transfer belt 230, and a voltage having a polarity opposite to the charging polarity of the toner is applied to the primary transfer roll 51, so that the photosensitive drum is charged. The toner image on the transfer belt 31 is electrostatically transferred to the intermediate transfer belt 230 side.

Further, a secondary transfer device 52 is disposed at a position corresponding to the tension roll 235 on the downstream side of the most downstream image forming unit 22d of the intermediate transfer belt 230, and the primary transfer on the intermediate transfer belt 230 is performed. The image is secondarily transferred (collectively transferred) to a recording material. In the present embodiment, the secondary transfer device 52 includes a secondary transfer roll 521 that is disposed in pressure contact with the toner image bearing surface of the intermediate transfer belt 230.
And a backup roll (also used as a stretching roll 235 in this example) which is disposed on the back side of the intermediate transfer belt 230 and serves as a counter electrode of the secondary transfer roll 521.
For example, the secondary transfer roll 521 is grounded, and a bias having the same polarity as the charged polarity of the toner is applied to the backup roll (stretch roll 235) via a power supply roll (not shown). . Further, a belt cleaner 53 is disposed on the upstream side of the uppermost-stream image forming unit 22a of the intermediate transfer belt 230 so as to remove residual toner on the intermediate transfer belt 230.

The recording material supply cassette 24 is provided with a feed roll (not shown) for picking up the recording material. Immediately after the feed roll, a takeaway roll 62 for feeding the recording material is provided. A registration roll (registration roll) 63 for supplying a recording material to the secondary transfer portion at a predetermined timing is disposed in the recording material transporting path 25 located immediately before the secondary transfer portion. On the other hand, a fixing device 66 is provided in the recording material conveying path 25 located downstream of the secondary transfer portion.
A discharge roll 67 for discharging the recording material is provided on the downstream side, and the discharged recording material is stored in a storage tray 68 formed on the upper part of the main body housing 21.
In FIG. 2, reference numeral 71 denotes an image density detection sensor (hereinafter, referred to as a DC sensor) for detecting the image density of the reference toner patch formed on the intermediate transfer belt 230.
Reference numeral 72 denotes a humidity sensor for detecting humidity in the image forming apparatus.

FIG. 3 shows a developing unit 33 used in the present embodiment. In FIG.
Has a developing housing 11 in which a portion facing the photosensitive drum 31 (image carrier) is open and in which a two-component developer (not shown) composed of toner and carrier is stored. And a pair of agitating and conveying augers 13 and 14 for agitating and transporting the two-component developer are disposed on the back side of the developing roll 12. The trimmer bar 15 is disposed at a position separated from the developing roll 12 by a predetermined distance in front (upstream) of a developing region 12 (a region facing the photosensitive drum 31 where development is effectively performed). The developing roll 12 includes a non-magnetic rotatable developing sleeve 121 and a magnet roll 122 fixed inside the developing sleeve 121, and the developing sleeve is rotationally driven by a drive motor (not shown). It has become. Further, a toner density detecting sensor (hereinafter, referred to as a TC sensor) 16 as a toner density detecting means is provided on the back side of the stirring and conveying auger 14. In the present embodiment, a magnetic permeability sensor is used as the TC sensor 16.

In this embodiment, as shown in FIG. 4, each developing unit 33 and each corresponding toner cartridge 35 are connected to a toner dispenser 80 (80a to 80a).
d). An auger (not shown) inside the toner dispenser 80 is driven by a dispenser motor (not shown) to supply toner. Then, the toner supplied from the toner cartridge 35 is supplied to the agitating / conveying auger 14 shown in FIG.
Is supplied into the developing unit 33 from an opening (not shown) provided on the side surface of the developing unit 33.

FIG. 5 is a block diagram of a density control device 100 for controlling the toner density and the image density. In the present embodiment, the concentration control device 100
, The image density signal from the DC sensor 71, and the humidity detection signal from the humidity sensor 72 are taken into the CPU 102 via the input interface 101,
Next, the CPU 102 includes the ROM 103 and the RAM 104
After performing appropriate data processing between the toner dispensers 80 (80
a to 80d), a drive signal is transmitted to each semiconductor laser (LD) 81 and a warning lamp 82 attached to a display (not shown) of the apparatus main body.

Next, an image forming process of the image forming apparatus according to the present embodiment will be described. Each image forming unit 2
2 (22a to 22d) form the respective color component images (toner images) on the photosensitive drum 31 and sequentially and primarily transfer the respective color component images onto the intermediate transfer belt 230 by the primary transfer roll 51. On the other hand, the recording material is supplied from the recording material supply cassette 24, and is conveyed to the secondary transfer portion via the registration roll 63 at a predetermined timing. Then, the intermediate transfer belt 2
The multi-transferred image primarily transferred onto 30 is conveyed to a secondary transfer portion, and is collectively transferred to a recording material by a secondary transfer device 52. After that, the recording material is fixed to the image transferred collectively through the fixing device 66, and then discharged to the storage tray 68 through the discharge roll 67. Each image forming unit 22
Then, the residual toner on the photosensitive drum 31 is
, The residual toner on the intermediate transfer belt 230 is cleaned by the belt cleaner 53.

Here, in the image forming apparatus according to the present embodiment, in order to maintain a high quality image during the image forming operation, the developing unit 33 is controlled by the density control device 100.
And the image density of the toner image formed on the intermediate transfer belt 230. First, the toner density control will be described. First, in the image forming apparatus according to the present embodiment, the toner concentration in each developing unit 33 is controlled to 10 ± 1 (wt.%). The reason is as follows. FIG. 6A shows the toner density T
The result of investigating the relationship between C and the weight of the developed image (≒ image density, DMA) formed on the photosensitive drum 31 is shown. According to this, it was found that an image density near the target value of 6.9 (g / m ² ) was obtained when the toner density TC was in the range of 9 to 11%. FIG. 6B shows the result of investigating the relationship between the toner concentration TC and the number of carriers transferred onto the photosensitive drum 31. According to this, the toner concentration TC is 5
%, That is, when the toner concentration TC is too low, it has been found that the target value exceeds the target value of 6 (particles / A3 size). FIG. 6C shows the toner density TC and the background fog (BKG-P / R) on the photosensitive drum 31.
The relationship is shown below. According to this, when the toner concentration TC is 13
% Or more, that is, if the toner concentration TC is too large, the target G
6 (grade 6). For the above reason, in the present embodiment, the toner concentration TC is set to 1
Control is performed within the range of 0 ± 1%.

Next, the toner concentration control process in the developing unit 33 will be described with reference to the flowchart shown in FIG. When the image formation is started, the toner concentration TC is measured by the TC sensor 16, and as a result, the toner concentration TC
Is less than 10%, the toner is supplied from the toner dispenser 80 to the developing unit 33. Then, when the toner concentration TC becomes 10% or more, the toner supply is stopped. On the other hand, when the toner concentration TC is 10% or more from the beginning, the toner supply is not performed until the toner concentration TC becomes less than 10%. This process is continued until image formation is completed.

Next, the process of controlling the image density of the toner image formed on the intermediate transfer belt 230 will be described with reference to the flowchart shown in FIG. When the image formation is started, a patch image (reference toner patch) having a predetermined shape is formed in each image forming unit 22, and these are sequentially transferred onto the intermediate transfer belt 230. Thereafter, the reference toner patches transferred onto the intermediate transfer belt 230 sequentially pass through a portion facing the DC sensor 71, and at that time, reflectivity R
Is measured. If the measured reflectance R is less than the reference reflectance Rs, the image density is too low and the image density needs to be increased.
The light amount of D81 is increased to increase the contrast of the electrostatic latent image. On the other hand, the measured reflectance R is equal to the reference reflectance Rs.
If it is larger, the image density is too high and it is necessary to lower the image density. Therefore, the light amount of the LD 81 is reduced according to the reflectance R, and the contrast of the electrostatic latent image is reduced. When the reflectance R is equal to the reference reflectance Rs, L
The light amount of D81 is not changed and is kept as it is. This process is continued until the image formation is completed.

Further, in the present embodiment, simultaneously with the toner density control process and the image density control process described above,
A TC control abnormality determination process for monitoring abnormality of the toner density control is also executed. This will be described with reference to flowcharts shown in FIGS. 9 to 11 and timing charts shown in FIGS.

In FIG. 9, first, the TC sensor 1
6 (magnetic permeability: corresponding to toner density) and an output from DC sensor 71 (reflectivity: corresponding to image density). These are input at predetermined time intervals, and their histories are stored in the RAM 104. Then TC
Sensor output is within the set range (toner density TC: 10 ± 1%
Is determined. Where T
When the C sensor output is out of the set range, FIG.
The abnormality determination processing 1 shown in FIG.

The abnormality determination processing 1 includes the TC sensor output and D
The change tendency of the C sensor output is used as a criterion,
For example, as shown in FIG. 12A, when the TC sensor output and the DC sensor output show the same fluctuation tendency (both decreasing tendency or increasing tendency), it is determined that the TC sensor output is normal. . In addition, TC sensor output and DC
The comparison of the sensor output is based on the delay (Dela) until the toner supplied to the developing unit 33 is actually used for development.
y). In FIG. 12,
Reference numeral Ta indicates a target value, Hi indicates an upper limit value, and Lo indicates a lower limit value. On the other hand, for example, as shown in FIGS.
When the TC sensor output and the DC sensor output show different fluctuation trends, it is determined that an abnormality has occurred in the TC sensor output. In the abnormality determination process 1, the fluctuation tendency of the LD light amount (see FIG. 8) determined based on the TC sensor output and the DC sensor output may be compared. However, in this case, when the TC sensor output and the LD light amount show opposite fluctuation trends (when one is decreasing and the other is increasing), it is determined that the TC sensor output is normal. Become.

In FIG. 9, if the TC sensor output is within the set range, then it is determined whether the DC sensor output is within the set range. Where D
When the C sensor output is within the set range, for example, FIG.
As shown in FIG. 3A, the TC sensor output and the DC sensor output fall within the set ranges, respectively.
Is determined to be operating normally. On the other hand, for example, as shown in FIGS. 13B and 13C, when the TC sensor output falls within the set range but the DC sensor output falls outside the set range, the abnormality determination process 2 shown in FIG. Is performed.

The abnormality determination process 2 is based on the fluctuation tendency of the DC sensor output and the humidity sensor output from the humidity sensor 72 as a criterion. If the DC sensor output and the humidity sensor output show the same fluctuation tendency (both tending to decrease or rise), it is determined that the TC sensor output is normal. This is because, for example, when the humidity decreases over time, even if the toner concentration TC is the same, the charge amount of the toner increases and the image density decreases. On the other hand, if the DC sensor output and the humidity sensor output show different fluctuation trends, it is determined that an abnormality has occurred in the TC sensor output.

In this embodiment, as shown in FIG. 14, when an abnormality is determined, there is a risk that the image density control may become abnormal due to the abnormality of the toner density control. The warning lamp 82 is turned on and the image forming operation is stopped.

In this embodiment, the TC sensor output is checked based on the DC sensor output from the DC sensor 71 and the humidity sensor output from the humidity sensor 72, so that the abnormality in the TC sensor output can be accurately grasped. can do. Also, when an abnormality occurs in the TC sensor output, the user is notified by the warning lamp 82, so that the subsequent treatment can be performed quickly.

In this embodiment, image density control is performed by adjusting the amount of LD light. However, the present invention is not limited to this. For example, as shown in FIG. 31 (see FIG. 3). For the abnormality determination process 1 in this case, the same method as that of the present embodiment may be employed, or the variation tendency of the AC component of the developing bias determined based on the TC sensor output and the DC sensor output may be compared. You may make it. However, in this case, if the TC sensor output and the AC component of the developing bias show opposite fluctuation trends (when one is decreasing and the other is increasing), it is determined that the TC sensor output is normal. Will be done.

Embodiment 2 This embodiment is substantially the same as Embodiment 1 except that FIG.
As shown in FIG. 6, when it is determined that the output of the TC sensor is abnormal, the apparatus is not stopped but switched to another toner density control method. Note that, of the components of the image forming apparatus according to the present embodiment, the same components as those of the image forming apparatus according to the first embodiment are denoted by the same reference numerals as those in the first embodiment, and detailed descriptions thereof will be given here. Description is omitted.

In the present embodiment, the toner density control method is switched to a method corresponding to the image density of the reference toner patch, that is, a method based on the DC sensor output. Hereinafter, the toner concentration control process according to the present embodiment will be described with reference to the flowchart shown in FIG. When image formation is started, a patch image (reference toner patch) having a predetermined shape is formed in each image forming unit 22.
These are sequentially transferred onto the intermediate transfer belt 230. Next, the DC sensor 71 detects the reflectance R of the reference toner patch.
Is measured, and as a result, if the reflectance is less than the reference reflectance Rs, toner is supplied to the developing unit 33 from the toner dispenser 80. Then, when the reflectance R of the reference toner patch becomes equal to or higher than the reference reflectance Rs, the toner supply is stopped. On the other hand, when the reflectance R is equal to or greater than the reference reflectance Rs from the beginning, toner supply is not performed until the reflectance R becomes smaller than the reference reflectance Rs. This process is continued until the image formation is completed.

As described above, in this embodiment, when it is determined that the TC sensor output from the TC sensor 16 is abnormal, the toner density control based on the TC sensor output is stopped, and the reflectance of the reference toner patch is reduced. Since the control is changed to the toner density control based on R (corresponding to the image density), image formation can be performed continuously. Further, as in the first embodiment, when an abnormality occurs in the TC sensor output, the user is notified by the warning lamp 82, so that the subsequent treatment can be performed quickly.

In this embodiment, the method of controlling the toner density is based on the image density of the reference toner patch. However, the present invention is not limited to this. For example, as shown in FIG. , PC or other pointing device 73 (FIG. 5)
), The toner consumption may be estimated from the coverage count of the image of each page, and the toner supply may be controlled based on the obtained estimated value.

[0041]

As described above, according to the present invention,
In an image forming apparatus using a two-component developer, by comparing the fluctuation tendency of the toner density detection result with the fluctuation tendency of the image density detection result, it is possible to accurately grasp the abnormality of the toner density detection result in the developing device. Therefore, stable toner density control and image density control can be performed.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram illustrating an outline of an image forming apparatus according to the present invention.

FIG. 2 is an overall configuration diagram of Embodiment 1 of a tandem-type image forming apparatus to which the present invention has been applied.

FIG. 3 is a sectional view of a developing unit.

FIG. 4 is an explanatory diagram illustrating a toner supply system.

FIG. 5 is a block diagram of a concentration control device.

FIGS. 6A to 6C are graphs showing the relationship between toner density and various characteristics.

FIG. 7 is a flowchart of a normal toner density control process.

FIG. 8 is a flowchart of a normal image density control process.

FIG. 9 is a flowchart of a TC control abnormality determination process.

FIG. 10 is a flowchart of abnormality determination processing 1.

FIG. 11 is a flowchart of abnormality determination processing 2;

12 (a) to 12 (c) show TC sensor output values and D
It is a graph which shows an example of C sensor output value.

13 (a) to 13 (c) show the TC sensor output value and D
It is a graph which shows an example of C sensor output value.

FIG. 14 is a flowchart of post-processing when an abnormality is determined in the first embodiment.

FIG. 15 is a flowchart of another image density control process.

FIG. 16 is a flowchart of post-processing at the time of abnormality determination according to the first embodiment.

FIG. 17 is a flowchart of a toner density control process after abnormality determination.

FIG. 18 is a flowchart of another toner density control process.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Image carrier, 2 ... Developing device, 3 ... Toner density detection means, 4 ... Toner density control means, 5 ... Image density detection means,
6 ... image density control means, 7 ... judgment means, C ... carrier,
D: two-component developer, G: toner image, T: toner, Z: electrostatic latent image

Claims (8)

[Claims] An image carrier on which an electrostatic latent image is formed and carried; a developing device for containing a two-component developer including a toner and a carrier, and developing the electrostatic latent image on the image carrier with toner; Toner density detecting means for detecting the toner density in the developing device; toner density controlling means for controlling the toner density in the developing device to a preset density based on the toner density detection result of the toner density detecting means An image density detection unit that directly or indirectly detects an image density of a toner image developed on the image carrier, based on an image density detection result of the image density detection unit,
An image forming apparatus comprising: an image density control unit configured to control an image density developed on the image carrier to a preset density; wherein a fluctuation tendency of the toner density detection result and a fluctuation tendency of the image density detection result An image forming apparatus comprising: a determination unit configured to determine that an abnormality has occurred in the toner density detection result under a condition in which these two fluctuation trends are inconsistent. 2. The image forming apparatus according to claim 1, wherein the image density detecting unit is configured to detect an image density of the toner image on the image carrier or a toner image on a transfer material onto which the image on the image carrier is transferred. An image forming apparatus for detecting the image density of the image. 3. An image forming apparatus according to claim 1, wherein said image density detecting means detects information on an electrostatic latent image formed on an image carrier. . 4. The image forming apparatus according to claim 1, wherein the toner density control unit controls the toner based on the toner density detection result under a condition in which the determination unit determines that the toner density detection result is abnormal. An image forming apparatus, wherein density control is stopped, and the control is changed to toner density control based on the image density detection result. 5. The image forming apparatus according to claim 1, further comprising a warning unit that warns that an abnormality has occurred in the toner density detection result. 6. The image forming apparatus according to claim 1, wherein a fluctuation tendency of the image density detection result is replaced with a fluctuation tendency of a control factor controlled by the image density control means. apparatus. 7. The image forming apparatus according to claim 7, wherein the control factor is applied between an image portion of an electrostatic latent image formed on an image carrier, the developing device, and the image carrier. And a potential difference between the developing bias and the developing bias. 8. The image forming apparatus according to claim 7, wherein the control factor is a peak value of an AC component of a developing bias applied between the developing device and the image carrier. Image forming apparatus.