JP7389964B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming apparatus.

2. Description of the Related Art Conventionally, image forming apparatuses are known in which a latent image on a latent image carrier is developed by a developing means using a developer containing toner and carrier.

For example, Patent Document 1 discloses that toner is replenished to the developer in the developing means by controlling the drive of the replenishing means so that the detection result of the toner concentration of the developer in the developing means becomes a predetermined toner concentration target value. An image forming apparatus that controls the image forming apparatus is disclosed. In this image forming apparatus, the developer is in one of two states: a first carrier deterioration state where the carrier film is scraped and carrier adhesion occurs, and a second carrier deterioration state where toner components adhere to the carrier and cause toner scattering. In order to extend the replacement period (developer lifespan), the toner density target value is continuously corrected to avoid any of these conditions.

However, in conventional image forming apparatuses, depending on the type of developer and usage conditions, the rate of progress of carrier deterioration between the two types may differ greatly, and in such cases, the method of correcting the target toner concentration value may It may not be possible to extend the time for agent replacement sufficiently.

In order to solve the above-mentioned problems, the present invention provides an image forming apparatus in which a latent image on a latent image carrier is developed by a developing means using a developer containing toner and a carrier. It has a toner forced consumption control means that performs toner forced consumption control for forcibly consuming the toner in the developing means, and the toner forced consumption control means is configured such that the amount of toner consumed per unit drive amount of the developing means is equal to or less than that of the carrier film. When the toner consumption amount is less than a predetermined toner consumption increase threshold, which is a criterion for determining a scraped state , the toner consumption amount to be forcibly consumed is set such that the toner consumption per unit driving amount of the developing means is less than the predetermined toner consumption increase threshold. The toner forced consumption amount changing process is performed to change the forced toner consumption amount to be larger than the forced toner consumption amount when the amount is large.

According to the present invention, it is possible to postpone the time for replacing the developer even under conditions where the first carrier deterioration state (carrier film scraping state) progresses depending on the type of developer, usage conditions, etc. Become.

FIG. 1 is an explanatory diagram showing a schematic configuration of a printer according to an embodiment. FIG. 3 is an enlarged configuration diagram showing a process cartridge for K in the same printer. 7 is a graph showing the relationship between the number of printed sheets and carrier resistance due to differences in toner consumption per cumulative drive amount of the developing device. A graph showing the relationship between carrier adhesion quality and development potential (development Pot) for each carrier resistance. A graph showing the relationship between carrier adhesion quality and toner concentration for each carrier resistance. (a) shows the usable range of toner concentration and development potential that can satisfy the carrier adhesion quality in a developer with high image area deterioration that is used under conditions where the amount of toner consumed per unit driving amount of the developing device is large. This is a graph showing. (b) shows the usable range of toner concentration and development potential that can satisfy the carrier adhesion quality in a standard deteriorated developer used under conditions where the amount of toner consumed per unit driving amount of the developing device is standard. This is a graph showing. (c) shows the usable range of toner concentration and development potential that can satisfy the carrier adhesion quality in a developer with low image area deterioration that is used under conditions where the amount of toner consumed per unit driving amount of the developing device is small. This is a graph showing. 7 is a graph showing the relationship between the number of printed sheets and toner charging ability due to differences in toner consumption per cumulative drive amount of the developing device. A graph showing the relationship between toner scattering quality and toner concentration for each toner charging capacity. A graph showing the relationship between toner scattering quality and toner charge amount. A graph showing the relationship between toner concentration and toner charge amount for each usage environment (temperature, humidity). (a) is a toner concentration that satisfies not only carrier adhesion quality but also toner scattering quality in a developer with high image area deterioration that is used under conditions where the amount of toner consumed per unit driving amount of the developing device is large. It is a graph showing the usable range of development potential. (b) is the toner concentration that satisfies not only the carrier adhesion quality but also the toner scattering quality in a standard deteriorated developer used under conditions where the toner consumption per unit driving amount of the developing device is standard. It is a graph showing the usable range of development potential. (c) is a toner concentration that satisfies not only the carrier adhesion quality but also the toner scattering quality in a developer with low image area deterioration that is used under conditions where the amount of toner consumed per unit driving amount of the developing device is small. It is a graph showing the usable range of development potential. A graph showing the relationship between development potential and toner adhesion amount. (a) to (c) are graphs showing a straight line (dashed line) showing the relationship between the toner concentration and the development potential to obtain the desired amount of toner adhesion on the graphs shown in FIGS. 11(a) to (c). . (a) to (c) are graphs showing the relationship between the control range of toner density and the number of printed sheets based on the graphs shown in FIGS. 13(a) to (c). 7 is a graph showing a toner density control range when forced toner consumption control of the embodiment is executed when the amount of toner consumption per cumulative drive amount of the developing device is small. 7 is a graph showing a toner density control range when forced toner consumption control of the embodiment is executed when the amount of toner consumed per cumulative drive amount of the developing device is large. 5 is a flowchart showing the flow of image forming condition correction processing in the embodiment.

An embodiment of an image forming apparatus according to the present invention will be described below.
First, the basic configuration of the printer 100, which is the image forming apparatus of this embodiment, will be explained.
FIG. 1 is an explanatory diagram showing a schematic configuration of a printer 100 of this embodiment.
As shown in FIG. 1, the printer 100 of this embodiment uses toners of yellow, magenta, cyan, and black (hereinafter, the respective colors are referred to as "Y", "M", "C", and "K"). It is equipped with four process cartridges 1Y, 1M, 1C, and 1K for generating images. These use Y, M, C, and K toners of different colors as image forming substances, but otherwise have the same configuration and are replaced when their lifespans are reached.

The optical writing unit 20 irradiates the photoreceptors 3Y, 3M, 3C, and 3K of the process cartridges 1Y, 1M, 1C, and 1K with laser light L based on the image information. The configuration of the optical writing unit 20 is such that a laser beam L emitted from a light source is deflected by a polygon mirror 21 rotationally driven by a motor and irradiated onto each photoreceptor 3Y, 3M, 3C, and 3K via a plurality of lenses and mirrors. It is something. However, other than this polygon scanning method, other configurations such as an LED array method can also be adopted.

Above the process cartridges 1Y, 1M, 1C, and 1K, an intermediate transfer unit 40 is disposed that moves an intermediate transfer belt 41, which is an intermediate transfer member, endlessly while being stretched. The intermediate transfer unit 40 includes an intermediate transfer belt 41, four primary transfer bias rollers 45Y, 45M, 45C, and 45K, a cleaning device 42, and the like. It also includes a secondary transfer backup roller 46, a cleaning backup roller 47, a tension roller 49, and the like. The intermediate transfer belt 41 is stretched around these rollers and is endlessly moved counterclockwise in the figure by the rotational drive of at least one of the rollers.

The primary transfer bias rollers 45Y, 45M, 45C, and 45K sandwich the endlessly moving intermediate transfer belt 41 between the photoreceptors 3Y, 3M, 3C, and 3K to form primary transfer nips, respectively. These systems apply a primary transfer bias of polarity opposite to that of the toner (for example, positive polarity) to the back surface (inner peripheral surface) of the intermediate transfer belt 41. All rollers except the primary transfer bias rollers 45Y, 45M, 45C, and 45K are electrically grounded.

As the intermediate transfer belt 41 moves endlessly, it sequentially passes through primary transfer nips for Y, M, C, and K. The K toner images are superimposed and primary transferred. As a result, a four-color superimposed toner image (hereinafter referred to as a "four-color toner image") is formed on the intermediate transfer belt 41. The four-color toner image formed on the intermediate transfer belt 41 is conveyed to a secondary transfer nip facing the secondary transfer roller 50 as the intermediate transfer belt 41 moves endlessly.

On the other hand, a paper feed roller 32a feeds transfer paper P as a recording material from a paper feed device 32 disposed below the printer 100. The sent-out transfer paper P is conveyed through the paper feed path 33 by a pair of conveyance rollers 34 and then conveyed to a pair of registration rollers 35 . The registration roller pair 35 feeds the transfer paper P into the secondary transfer nip in synchronization with the timing at which the four-color toner image is fed into the secondary transfer nip. Then, the four-color toner image on the intermediate transfer belt 41 is secondarily transferred onto the transfer paper P by the second transfer bias applied to the second transfer nip.

The transfer paper P onto which the four-color toner image has been transferred is then sent to the fixing device 60. The fixing device 60 includes a fixing belt 64 stretched between a fixing roller 63, a heating roller 66, and a tension roller 65, and a pressure roller 61. A fusing nip is formed. When the transfer paper P passes through the fixing nip, the four-color toner image is fixed onto the transfer paper P by heat and pressure. After the fixing, the transfer paper P is discharged to a paper discharge tray 68 by a paper discharge roller 67.

FIG. 2 is an enlarged configuration diagram showing the process cartridge 1K for K in this embodiment.
The process cartridge 1K includes a charging device 23K, a developing device 7K, a drum cleaning device 15K, etc. around the photoreceptor 3K. The photoreceptor 3K has an organic photosensitive layer and a surface layer laminated in sequence on the circumferential surface of a drum-shaped conductive support. Further, the organic photosensitive layer is composed of a charge generation layer, a charge transport layer, and the like. The thickness of the charge transport layer may be appropriately selected from a range of 10 [μm] to 40 [μm] depending on desired photoreceptor characteristics. Further, an undercoat layer may be formed between the conductive support and the organic photosensitive layer in the photoreceptor 3K, if necessary.

The charging device 23K is composed of a charging roller and includes a cleaning brush roller 236K and the like. The charging roller of the charging device 23K consists of a core metal that is a conductive support, a roller portion coated on the circumferential surface of the central part in the longitudinal direction, and abutment rollers fixed to both ends of the core metal in the longitudinal direction. It is configured. A charging bias is applied to the core metal by a power source. Discharge occurs between the conductive roller portion and the photoreceptor through the charging gap, thereby uniformly charging the surface of the photoreceptor 3K.

The cleaning brush roller 236K includes a metal core and a brush roller portion made of a plurality of conductive fibers electrostatically flocked on the circumferential surface of the metal core. Then, while contacting the roller portion of the charging roller with its own weight, the toner is scraped off from the roller portion of the charging roller by rotating along with the rotation of the charging roller. In addition to the charging roller method, the charging device 23K may employ a method in which a charging brush roller is brought into contact with the image forming area of the photoreceptor.

An electrostatic latent image is formed on the surface of the photoreceptor 3K, which is uniformly charged by the charging device 23K, by optical scanning with the laser beam L, and enters a developing area which is a position facing the developing device 7K. The developing device 7K is configured to develop the electrostatic latent image using a two-component developer (hereinafter simply referred to as "developer") containing a magnetic carrier and a non-magnetic toner.

The developing device 7K includes an agitating section 8K that transports new toner and developer while stirring them, which are replenished by a toner replenishing device 4K serving as a replenishing means from a toner bottle 5K that accommodates replenishing toner, and a stirring section 8K that transfers new toner and developer from the agitating section 8K. The supply section 9K transports the developed developer while stirring and supplies it to the cylindrical developing sleeve 12K. The control unit 101 of the printer 100 causes the toner concentration sensor 6K provided in the developing device 7K to detect the toner concentration in the developer in the developing device 7K, and controls the toner replenishing device 4K so that the detection result approaches the toner concentration target value. control to adjust the amount of toner replenishment.

The developing sleeve 12K faces the photoreceptor 3K through an opening provided in the casing, and has a magnet inside. The developing device 7K performs a developing process by transferring the toner in the developer carried on the surface of the developing sleeve 12K to the photoreceptor 3K. The developing device 7K includes a doctor blade 14K, etc., which is arranged so that its tip approaches the developing sleeve 12K. The magnet roller inside the developing sleeve 12K has a plurality of magnetic poles that are sequentially arranged along the sleeve rotation direction from a position facing the doctor blade 14K. These magnetic poles each apply a magnetic force to the developer on the sleeve at a predetermined position in the rotational direction. As a result, the developer sent from the supply section 9K is attracted to and carried on the surface of the developing sleeve 12K, and a magnetic brush is formed along the lines of magnetic force on the sleeve surface.

The developer carried on the developing sleeve 12K is regulated to an appropriate height (layer thickness) when passing through a position facing the doctor blade 14K as the developing sleeve 12K rotates, and then is applied to the photoreceptor 3K. It is transported to the opposing development area. Then, by the action of the developing electric field formed by the potential difference between the developing bias applied to the developing sleeve 12K and the electrostatic latent image on the photoreceptor 3K, toner is transferred onto the electrostatic latent image and contributes to development.

The K toner image formed on the surface of the photoreceptor 3K by development by the developing device 7K enters the primary transfer nip for K as the photoreceptor 3K rotates. In this primary transfer nip, the K toner image on the photoreceptor 3K is primarily transferred onto the intermediate transfer belt 41. Further, after passing through the primary transfer nip, the photoreceptor 3K is cleaned of transfer residual toner by the cleaning brush 19K and cleaning blade 18K of the drum cleaning device 15K, and is neutralized by the static elimination light L' of the static elimination lamp.

Further, in the present embodiment, the control unit 101 of the printer 100 functions as a toner forced consumption control unit, and forcibly consumes the toner in the developing device 7 during a non-image forming period such as after the end of a print job. Performs forced toner consumption control. Forced toner consumption control is also called toner refresh. The toner that stays in the developing device 7 for a long time is subjected to a lot of friction due to the transport and stirring of the developer in the developing device 7, and as a result, it deteriorates and causes image defects such as scumming.

Such long-staying toner is present in large quantities when the amount of toner consumed per unit driving amount of the developing device 7 is small, such as when images with a low image area ratio are continuously formed, resulting in image defects such as background smearing. is more likely to occur. Therefore, if the amount of toner consumed per unit driving amount of the developing device 7 is below a predetermined value, the amount of developer in the developing device 7 will be reduced during the image forming period, such as after the end of the print job. Forced toner consumption control is performed in which toner is forcibly discharged (developed) onto the photoreceptor 3 and collected by the drum cleaning device 15. By performing such forced toner consumption control, deteriorated toner that has been staying in the developing device 7 for a long period of time can be removed from the developing device 7, and that amount is replaced with new toner from the toner replenishing device 4, so that the developing device The amount of deteriorated toner in the image forming apparatus 7 can be reduced, and image defects such as background stains can be suppressed.

Whether the amount of toner consumed per unit driving amount of the developing device 7 is below a predetermined value is determined, for example, if the average image area ratio of images printed during a print job is large enough to cause background smudges. The determination can be made based on whether or not the image area ratio is lower than the minimum image area ratio (specified value) at which no deteriorated toner remains in the developing device 7. If the average image area ratio during the print job is lower than the specified value, forced toner consumption control is performed after the print job ends to forcibly consume the toner in the developing device 7.

The basic idea of forced toner consumption control in this embodiment is that, for example, if the minimum image area ratio (specified value) is 5%, and the average image area ratio during the print job is 0.5%, The forced toner consumption amount during forced toner consumption control is set so that the remaining 4.5% of toner is forcibly consumed. However, if the forced consumption of toner per unit time is too large, the drum cleaning device 15 will not be able to clean the toner discharged onto the photoreceptor 3. Further, since there is a limit to the time period during which forced toner consumption control can be performed, there is an upper limit to the amount of forced toner consumption that can be set in one forced toner consumption control. Therefore, the amount of toner that could not be consumed in one forced toner consumption control is additionally performed in subsequent forced toner consumption controls.

Note that the forced toner consumption control may be performed at any time during the non-image forming operation period, so for example, it is also possible to perform the forced toner consumption control every time the image forming operation for one sheet is completed. However, in this case, there is a risk of a decrease in productivity due to a decrease in image formation speed, so after the print job is finished, the toner for the number of sheets printed in the print job is collected and the amount of toner that is insufficient to meet the minimum image area ratio is It is preferable to forcefully consume it.

Next, the timing of replacing the developer (developer lifespan) will be explained. In addition, in the following description, the color codes Y, C, M, and K will be omitted as appropriate.
In general, there is a first carrier deterioration state (hereinafter referred to as "carrier film scraping state") in which the carrier film is scraped and carrier adhesion, and a second carrier deterioration state (carrier spent) in which toner components adhere to the carrier and toner scattering. When one of the following conditions occurs and the condition progresses to the point where it cannot be resolved even by adjusting the image forming conditions, etc., the time for developer replacement (the life of the developer) arrives.

In the carrier film scraped state, the carrier film is worn away due to use over time (such as stirring of the developer), and the electrical resistance value of the carrier (hereinafter referred to as "carrier resistance") decreases, making it easier for carrier adhesion to occur. The carrier is in a deteriorated state. When the carrier resistance decreases, reverse polarity charge is more likely to be injected into the carrier by the developing electric field, and carrier adhesion, in which the carrier adheres to the photoreceptor 3, becomes more likely to occur. Normally, when the toner concentration of the developer is low or when the development potential is high, opposite polarity charges are more likely to be injected into the carrier, and carrier adhesion tends to deteriorate. However, even if the carrier film wears out, the charging ability of the carrier does not change much, so toner scattering does not worsen. When the carrier film wears off to such an extent that it becomes difficult to suppress carrier adhesion even if image forming conditions are adjusted, it is time to replace the developer (the life of the developer is reached).

The carrier spent state is a carrier deterioration state in which toner components adhere to the carrier, reducing the toner charging ability of the carrier and causing toner scattering. When toner components adhere to the surface of the carrier, the opportunity for the carrier to come into contact with the toner and triboelectrically charge the toner decreases, and the charging ability to charge the toner to a desired amount of charge decreases. When the toner charging ability decreases, the amount of charging of the toner becomes insufficient, and toner scattering becomes more likely to occur. Normally, when the environment is high temperature and high humidity, or when the toner concentration of the developer is high, the amount of charge on the toner tends to be insufficient, and toner scattering tends to worsen. However, as the carrier spent state progresses, carrier resistance increases, so carrier adhesion is rather improved. When the carrier spent state progresses to such an extent that it becomes difficult to suppress toner scattering even if image forming conditions are adjusted, it is time to replace the developer (the life of the developer is reached).

Table 1 below summarizes the above.

First, the carrier film scraped state will be explained.
The degree of progress of the carrier film scraping state can be ascertained from the cumulative amount of drive of the developing device 7 as a developing means and the cumulative amount of toner consumption.
The cumulative drive amount of the developing device 7 mainly indicates the amount (time) by which the developer is stirred inside the developing device 7, which has a correlation with the amount of carrier film scraping. Specifically, the information that can be used as this index value includes the travel distance (rotational drive amount) of the developing sleeve 12 of the developing device 7 from the time when the new developer was started to be used. As long as the information has a correlation with the cumulative drive amount of the device 7, for example, the travel distance of the photoreceptor or the number of sheets printed (number of sheets formed with images) may be used.
Further, the cumulative toner consumption amount mainly indicates the amount of new toner that is replenished from the toner replenishing device 4 to the developer of the developing device 7 . Specifically, information that can be used as this index value includes the average image area ratio of images formed after the start of developer use mentioned above, but if the information is correlated with cumulative toner consumption, for example, The amount of toner replenishment or the like may also be used.

The greater the cumulative driving amount of the developing device 7, the greater the degree of progress of the carrier film scraping state. On the other hand, as the cumulative amount of toner consumed increases, the amount of new toner increases, and the amount of toner components adhering to the carrier surface increases, resulting in an increase in carrier resistance. Therefore, carrier adhesion due to carrier film scraping is less likely to occur, and the degree of progress of the carrier film scraping is reduced. Considering these relationships, the amount of toner consumption per unit driving amount of the developing device 7 can be suitably used as an index value indicating the degree of progress of the carrier film scraping state. That is, the smaller the amount of toner consumed per unit driving amount of the developing device 7, the more the carrier film is worn away, the carrier resistance decreases, and the more likely carrier adhesion occurs.

FIG. 3 is a graph showing the relationship between the number of printed sheets and carrier resistance depending on the difference in toner consumption per cumulative drive amount of the developing device 7.
As shown by symbol A in FIG. 3, when the amount of toner consumed per cumulative drive amount of the developing device 7 is large (when the image area ratio of the images that have been formed so far is high), the carrier resistance increases. Further, as shown by the symbol B in FIG. 3, when the amount of toner consumption per cumulative drive amount of the developing device 7 is standard (when the image area ratio of the images formed so far is standard), the number of printed sheets is The carrier resistance tends to decrease slightly as . On the other hand, as shown by symbol C in FIG. 3, when the amount of toner consumed per cumulative drive amount of the developing device 7 is small (when the image area ratio of the images formed so far is low), the number of printed sheets increases. Accordingly, carrier resistance decreases. In this way, carrier resistance can be predicted based on the toner consumption amount per cumulative drive amount of the developing device 7.

FIG. 4 is a graph showing the relationship between carrier adhesion quality and development potential (development Pot) for each carrier resistance.
FIG. 5 is a graph showing the relationship between carrier adhesion quality and toner concentration for each carrier resistance.
As shown in FIG. 4, in the case of a developer with reduced carrier resistance, the reduction in carrier resistance tends to cause opposite polarity charge to be injected into the carrier by the developing electric field, and as a result, carrier adhesion tends to deteriorate. That is, as shown in FIG. 4, it is possible to suppress carrier adhesion by setting the developing potential low, but in the case of a developer with reduced carrier resistance, that is, per unit drive amount of the developing device 7. In the case of a developer used in a situation where toner consumption is low (hereinafter referred to as "deteriorated developer with low image area") (symbol C' in Figure 4), the toner adhesion should not exceed the allowable limit value. The range of development potential that can be adjusted is narrow, and the life of the developer comes to an end early. Similarly, as shown in Figure 5, it is possible to suppress carrier adhesion by setting a high toner concentration, but in the case of a developer with reduced carrier resistance, that is, with a developer with low image area deterioration. In the case (symbol C' in FIG. 4), the toner concentration range that can be adjusted so as not to exceed the allowable limit value of carrier adhesion is narrow, and the life of the developer comes to an early end.

Further, as shown in FIG. 4, the higher the development potential is, the more likely it is that charges of opposite polarity will be injected into carriers by the development electric field, and as a result, carrier adhesion will be more likely to deteriorate.
Furthermore, as shown in Figure 5, the lower the toner concentration, the less likely it is that toner component adhesion, which causes an increase in carrier resistance, will occur, and the more likely it will be that reverse polarity charge will be injected into the carrier by the developing electric field, resulting in worse carrier adhesion. It's easy to do.

From the above, for each toner consumption amount per unit driving amount of the developing device 7 (high image area deterioration developer, standard deterioration developer, low image area deterioration developer), toner concentration and development that can satisfy the carrier adhesion quality are determined. The usable potential range is summarized as shown in FIGS. 6(a) to 6(c).
As shown in FIGS. 6(a) to 6(c), a developer with low carrier resistance, that is, a developer used in a situation where the amount of toner consumed per unit driving amount of the developing device 7 is small (low image area deterioration) The further the developer), the narrower the range of development potential and range of toner concentration that can suppress carrier adhesion, so the life of the developer comes to an end sooner.

Next, the carrier spent state will be explained.
The degree of progress of the carrier spent state can also be ascertained from the cumulative drive amount of the developing device 7 and the cumulative amount of toner consumption, similar to the carrier film scraped state described above. As described above, the cumulative driving amount of the developing device 7 indicates the amount of time (time) that the developer is stirred inside the developing device 7, so that the toner components separated from the toner due to stirring adhere to the carrier surface. There is a correlation with quantity. Further, since the cumulative toner consumption mainly indicates the amount of new toner that is replenished from the toner replenishing device 4 to the developer of the developing device 7, it is correlated with the amount of toner components that can adhere to the carrier surface. When using the above-mentioned toner consumption per unit driving amount of the developing device 7 as an index value indicating the degree of progress of the carrier spent state, the larger this index value is, the more opportunity there is for new toner components to adhere to the carrier surface. As a result, adhesion of toner components to the carrier progresses, resulting in a decrease in toner charging ability, and toner scattering becomes more likely to occur.

FIG. 7 is a graph showing the relationship between the number of printed sheets and the toner charging ability depending on the difference in toner consumption per cumulative drive amount of the developing device 7.
As shown in FIG. 7, the larger the amount of toner consumed per cumulative drive amount of the developing device 7 (the higher the image area ratio of the images that have been formed), the more likely the toner charging ability is reduced. This is because as the amount of toner consumed per cumulative drive amount of the developing device 7 increases, the amount of new toner replenished from the toner replenishing device 4 to the developer of the developing device 7 increases. This is because as the supply amount increases, the carrier spent state tends to progress and the toner charging ability tends to decrease.

FIG. 8 is a graph showing the relationship between toner scattering quality and toner concentration for each toner charging capacity.
FIG. 9 is a graph showing the relationship between toner scattering quality and toner charge amount.
FIG. 10 is a graph showing the relationship between toner concentration and toner charge amount for each usage environment (temperature, humidity).
As shown in FIGS. 8 and 9, as the carrier spent state progresses and the carrier charging ability decreases, the toner charging amount decreases, and as a result, the toner scattering quality deteriorates. That is, as shown in FIG. 8, it is possible to suppress toner scattering by setting the toner concentration low, but in the case of a developer with a reduced toner charging ability, that is, the unit drive amount of the developing device 7 In the case of a developer used under conditions where the amount of toner consumed per unit is high (hereinafter referred to as "high image area deterioration developer") (symbol A' in FIG. 8), the toner scattering tolerance limit value is not exceeded. Therefore, the range of toner concentration that can be adjusted is narrow, and the life of the developer comes to an end quickly.

Further, as shown in FIG. 10, the toner charge amount varies depending on the usage environment (temperature, humidity), and as shown in FIG. 9, the smaller the toner charge amount, the worse the toner scattering becomes. The higher the temperature and humidity, the lower the toner charge amount and the more likely toner scattering will occur.

From the above, for each toner consumption amount per unit driving amount of the developing device 7 (high image area deterioration developer, standard deterioration developer, low image area deterioration developer), not only the carrier adhesion quality but also the toner scattering quality is satisfied. The usable ranges of toner density and development potential that can be used are summarized as shown in FIGS. 11(a) to 11(c).

FIG. 12 is a graph showing the relationship between development potential and toner adhesion amount.
FIG. 12 shows three graphs γ1, γ2, and γ3 with different development γ. Development γ is a parameter (image forming condition) corresponding to the slope of toner adhesion amount with respect to development potential. Generally, the higher the toner charge amount, the lower the development γ, and the lower the toner charge amount, the higher the development γ.

13(a) to 13(c) show straight lines (broken lines) on the graphs shown in FIGS. 11(a) to 11(c) showing the relationship between the toner concentration and the development potential for obtaining the desired amount of toner adhesion. This is a graph.
As shown in FIGS. 13(a) to (c), by adjusting the target value of development γ, the desired toner can be obtained within the usable range of toner concentration and development potential that can suppress both carrier adhesion and toner scattering. The amount of adhesion can be obtained. Then, in accordance with the adjustment of the target value of development γ, the toner concentration control range (target toner concentration range) also changes.

14(a) to 14(c) are graphs showing the relationship between the control range of toner density and the number of printed sheets based on the graphs shown in FIGS. 13(a) to 13(c).
The control range of toner density corresponding to each amount of toner consumption per unit driving amount of the developing device 7 (high image area deteriorated developer, standard deteriorated developer, low image area deteriorated developer) is shown in FIGS. c). As shown in FIGS. 14(a) to 14(c), as the number of printed sheets increases (as the unit driving amount of the developing device 7 increases), the carrier deterioration state (carrier film scraped state, carrier spent state) progresses. As a result, carrier adhesion and toner scattering become more likely to occur, resulting in a narrower adjustment range for the target value of development γ and a narrower toner density control range.

In this embodiment, the developer reaches the end of its lifespan when the narrowing toner concentration control range (difference between the upper and lower limits of the toner concentration control range) becomes equal to or less than a predetermined lifespan threshold. The system determines this and prompts the user to replace the developer. This is because when the toner concentration control range narrows to the extent that the difference between the upper and lower limits of the toner concentration control range becomes less than the life threshold, the actual toner concentration easily deviates from the toner concentration control range, causing toner scattering and carrier adhesion. This is because it can lead to a situation where this occurs.

In this embodiment, the toner concentration control range is appropriately changed as shown in FIGS. 14(a) to (c) according to the carrier deterioration state, and the toner concentration target value (for example, By adjusting the toner density control range (set to the median value of This extends the lifespan of the developer.

However, when the progress of carrier film wear is progressing, it is difficult to sufficiently slow down the progress just by appropriately changing the toner concentration control range and adjusting the toner concentration target value as described above. . Specifically, as shown in FIG. 14(c), when the degree of carrier film abrasion is progressing, the toner concentration of the developer is increased by adjusting the toner concentration target value to be higher. The occurrence of carrier adhesion can be suppressed by increasing the amount of new toner that is replenished and increasing the amount of toner components adhering to the carrier film to increase carrier resistance and suppressing carrier adhesion. However, there are limits to increasing the toner concentration of the developer from the viewpoint of ensuring a desired amount of toner adhesion and from toner scattering. Moreover, in situations where images with low image area ratios are being formed, the amount of new toner that can be replenished is limited even if the target toner density is increased, so the amount of toner that adheres to the carrier film is increased to reduce carrier resistance. There is a limit to suppressing carrier adhesion by increasing the temperature.

Therefore, in this embodiment, the above-described forced toner consumption control is used to increase the forced toner consumption amount when the degree of carrier film wear is progressing, thereby suppressing carrier adhesion and developing. We are trying to further extend the life of the agent.

As shown in FIG. 14(c), FIG. 12 is a graph showing a toner concentration control range when forced toner consumption control of the present invention is executed.
In the forced toner consumption control of this embodiment, when the amount of toner consumption per cumulative drive amount of the developing device 7 is small, the forced toner consumption amount is increased so that more new toner can be replenished to the developer. . Thereby, the toner component adhering to the carrier film can be increased to compensate for the decrease in carrier resistance due to the scraping of the carrier film, and carrier adhesion can be suppressed. As a result, as shown in FIG. 15, it becomes possible to set the lower limit value of the toner concentration control range to a lower value.

At this time, by increasing the toner forced consumption amount so that more new toner can be replenished to the developer and increasing the toner component adhering to the carrier film, the toner charging ability of the carrier is reduced. Therefore, as shown in FIG. 15, the upper limit value of the toner concentration control range is slightly lowered. However, the extent to which the lower limit of the toner concentration control range can be lowered by suppressing carrier adhesion by increasing the forced toner consumption is the same as the upper limit of the toner concentration control range due to worsening of toner scattering by increasing the forced toner consumption. is larger than the width by which it falls. Therefore, the difference between the upper and lower limits of the toner concentration control range increases, and as shown in FIG. The timing of reaching this point can be delayed.

Furthermore, even if the progress of carrier spent is progressing, it is difficult to slow down the progress sufficiently by simply changing the toner density control range appropriately and adjusting the toner density target value as described above. . Specifically, as shown in FIG. 14(a), when the carrier spent progresses, the toner concentration of the developer is reduced by adjusting the toner concentration target value to be low. By reducing the amount of new toner that is applied and reducing the amount of toner components that adhere to the carrier film, it is possible to suppress a decrease in the toner charging ability by the carrier, thereby suppressing a decrease in the toner charge amount and suppressing the occurrence of toner scattering.

However, there is a limit to reducing the toner concentration of the developer from the viewpoint of ensuring a desired amount of toner adhesion, carrier adhesion, and the like. Moreover, when an image with a high image area ratio is being formed, even if the target toner concentration value is lowered, the amount of new toner that is replenished cannot be sufficiently restricted, so the amount of toner components adhering to the carrier film can be reduced. However, there are limits to the ability to suppress the decline in toner charging ability and suppress the occurrence of toner scattering.

Therefore, in this embodiment, the above-described forced toner consumption control is used to reduce the forced toner consumption amount (including setting it to zero) when the degree of progress of carrier spent is progressing. This suppresses toner scattering and further extends the life of the developer.

As shown in FIG. 14(a), FIG. 12 is a graph showing a toner concentration control range when forced toner consumption control of the present invention is executed.
In the forced toner consumption control of this embodiment, when the amount of toner consumption per cumulative drive amount of the developing device 7 is large, the forced toner consumption amount is reduced (or zeroed) and new toner is replenished to the developer. so that the amount of Thereby, it is possible to suppress the amount of toner components adhering to the carrier film, delay the progress of deterioration of toner charging ability, and suppress toner scattering. As a result, as shown in FIG. 16, it becomes possible to set the upper limit of the toner concentration control range to a higher value.

At this time, as a result of reducing the forced consumption of toner and suppressing the amount of new toner replenished to the developer, the toner component adhering to the carrier film decreases, resulting in an increase in carrier resistance. As shown in , the lower limit of the toner density control range will rise slightly. However, the range in which the upper limit of the toner concentration control range can be raised by suppressing toner scattering by reducing the forced toner consumption is the lower limit of the toner concentration control range due to the deterioration of carrier adhesion caused by reducing the forced toner consumption. is larger than the width of the rise. Therefore, the difference between the upper and lower limits of the toner concentration control range increases, and as shown in FIG. The timing of reaching this point can be delayed.

FIG. 17 is a flowchart showing the flow of image forming condition correction processing in this embodiment.
When the distance traveled since the previous correction process (cumulative drive amount of the developing device 7) has exceeded a predetermined distance (Yes in S1), the control unit 101 of the printer 100 first controls the current environmental information ( temperature and humidity information) is acquired (S2). In addition, the toner consumption amount from the previous correction processing to the present (cumulative toner consumption) is calculated from the information on the average image area ratio of images formed from the previous correction processing to the present, and the calculated toner consumption is The amount of toner consumed per mileage is calculated by dividing by the distance traveled from the correction process to the present time (S3). Further, the control unit 101 causes the toner concentration sensor 6 provided in the developing device 7 to detect and acquire the current toner concentration in the developer in the developing device 7 (S4).

Next, the control unit 101 operates as shown in FIGS. 11A to 11C based on the toner consumption amount per mileage calculated in processing step S3 and the current toner concentration obtained in processing step S4. Next, the usable range (upper limit value and lower limit value) of the development potential and the toner density control range (upper limit value and lower limit value) are determined (S5).

After that, the control unit 101 determines whether the difference between the upper limit and the lower limit of the toner concentration control range determined in processing step S5 (the width of the upper and lower limits of toner concentration) is larger than the first threshold (S6). . If it is determined that it is larger than the first threshold (Yes in S6), the toner density target value and development potential are determined as usual, and the development γ is corrected (S7).

On the other hand, when the control unit 101 determines that it is equal to or less than the first threshold value in processing step S6 (No in S6), the control unit 101 next determines that the difference between the upper limit value and the lower limit value of the toner concentration control range determined in processing step S5 ( It is determined whether the width of the upper and lower limits of toner concentration) is larger than the lifespan threshold (S8). If it is determined that it is below the lifespan threshold (No in S8), it is determined that the developer has reached its lifespan, and a process of displaying an error message is executed (S9).

When it is determined in processing step S8 that the toner consumption amount per mileage calculated in processing step S3 is greater than the lifespan threshold (Yes in S6), the control unit 101 next determines whether the toner consumption amount per mileage calculated in processing step S3 is greater than the lifespan threshold (Yes in S6). It is determined whether or not it is less than or equal to the second threshold (S10). In this determination, if the toner consumption amount per traveling distance is equal to or less than the second threshold value (Yes in S10), it is determined that the carrier film wear-off state is progressing. On the other hand, if the toner consumption amount per mileage is greater than the second threshold (No in S10), the control unit 101 controls the amount of toner consumed per mileage in order to check whether the carrier spent state is progressing. It is further determined whether the consumption amount is below a third threshold (S11), and if it is larger than the third threshold (No in S11), it is determined that the carrier spent state is progressing.

If the control unit 101 determines that the toner consumption per mileage is larger than the second threshold and even larger than the third threshold (No in S10, No in S11), the controller 101 determines that the carrier spent state is progressing. Therefore, the amount of forced toner consumption during forced toner consumption control is reduced to zero. That is, the forced toner consumption control (toner refresh) is turned off (S12), so that the forced toner consumption control is not performed even when the timing for implementing the forced toner consumption control arrives.

As a result, as mentioned above, the forced consumption of toner is reduced and the amount of new toner replenished to the developer can be kept low, which reduces the amount of toner components adhering to the carrier film and slows down the progress of carrier spent. Can be done. As a result, as shown in FIG. 16, the difference between the upper and lower limits of the toner concentration control range widens, and the time when the difference between the upper and lower limits of the toner concentration control range reaches the lifespan threshold (developer lifespan increases). (the timing of reaching the target) can be delayed.

On the other hand, if the control unit 101 determines that the toner consumption amount per mileage is greater than the second threshold and less than or equal to the third threshold (No in S10, Yes in S11), the carrier deterioration state is normal. Therefore, the forced toner consumption amount of the forced toner consumption control is not changed (S13).

On the other hand, if the control unit 101 determines that the toner consumption amount per mileage is equal to or less than the second threshold (Yes in S10), the carrier film wear-off state is progressing, so the toner forced consumption control during forced toner consumption control is performed. The consumption amount is increased by a predetermined amount (desired amount) (S14). As a result, as mentioned above, the amount of forced toner consumption increases and the amount of new toner replenished to the developer can be increased, which increases the amount of toner components adhering to the carrier film, increases the carrier resistance, and causes the carrier film to be scraped. It is possible to suppress the occurrence of carrier adhesion due to As a result, as shown in FIG. 15, the difference between the upper and lower limits of the toner concentration control range widens, and the time when the difference between the upper and lower limits of the toner concentration control range reaches the lifespan threshold (developer lifespan increases). (the timing of reaching the target) can be delayed.

Here, regarding the forced toner consumption amount of the forced toner consumption control, it is preferable that the forced toner consumption amount per unit time is larger because this leads to a reduction in the time of the forced toner consumption control. However, if the forced consumption of toner per unit time is too large, the drum cleaning device 15 will not be able to clean the toner discharged onto the photoreceptor 3. Therefore, there is an upper limit to the forced consumption amount of toner per unit time in relation to cleaning performance. On the other hand, since there is a limit to the time that can be applied to the forced toner consumption control, there is an upper limit to the amount of forced toner consumption that can be set in one forced toner consumption control.

On the other hand, the basic operation of forced toner consumption control in this embodiment is that after a print job is finished, if the average image area ratio of images printed during the print job is lower than the minimum image area ratio (specified value), , the toner is forcibly consumed by the difference. Therefore, as the number of images formed in one print job increases, the amount of forced toner consumption in forced toner consumption control after the end of the print job increases.

Therefore, when increasing the forced toner consumption amount during forced toner consumption control (S14), when the number of images formed in a print job is large, it is difficult to simply increase it by a predetermined amount (desired amount) once. There is a risk that the maximum value of the forced toner consumption amount that can be set using the forced toner consumption control may be exceeded.

Therefore, in the present embodiment, when increasing the forced toner consumption amount during forced toner consumption control (S14), the average number of images formed (average Page/Job) in past print jobs is calculated, and the average Page/Job is It is determined whether or not it is equal to or greater than four threshold values (S15). If it is determined in this judgment that the average Page/Job is equal to or higher than the fourth threshold (Yes in S15), if the forced toner consumption amount is increased by a predetermined amount (desired amount), the There is a possibility that the forced toner consumption amount in the forced toner consumption control after the print job exceeds the above-mentioned maximum value. Therefore, in this case, the forced toner consumption amount is increased to the maximum value (S16). On the other hand, if it is determined that the average Page/Job is smaller than the fourth threshold in the determination at processing step S15 (No at S15), the amount is increased by an amount (desired amount) corresponding to the average Page/Job (S17). .

What has been described above is just an example, and each of the following aspects has its own unique effects.
[First aspect]
A first aspect is an image forming apparatus (e.g. printer 100) that develops a latent image on a latent image carrier (e.g. photoreceptor 3) by a developing means (e.g. developing device 7) using a developer containing toner and carrier. includes a forced toner consumption control means (for example, a control unit 101) that performs forced toner consumption control to forcibly consume the toner in the developing means during a non-image forming period (after the end of a print job); The consumption control means is configured to forcibly control the carrier according to a carrier deterioration state (for example, a carrier film scraped state or a carrier spent state) that is specified based on the cumulative driving amount (for example, traveling distance) and the cumulative toner consumption amount of the developing means. This method is characterized by changing the forced consumption amount of toner to be consumed.
Generally, either of the first carrier deterioration state, in which the carrier film is scraped and carrier adhesion occurs, and the second carrier deterioration state, in which toner components adhere to the carrier and toner scattering, occurs when adjusting the image forming conditions, etc. If the situation progresses to the point where it cannot be resolved, it will be time to replace the developer (the life of the developer).
The first carrier deterioration state (carrier film scraped state) is a state in which the carrier film is scraped off due to use over time, the electrical resistance value of the carrier (carrier resistance) decreases, and carrier adhesion is likely to occur. When the carrier resistance decreases to such an extent that it becomes difficult to suppress carrier adhesion even if the developer is adjusted, it is time to replace the developer (the life of the developer is reached). However, even if the first carrier deterioration state progresses, the charging ability of the carrier does not change much, so toner scattering does not worsen.
The second carrier deterioration state (carrier spent state) is a state in which toner components adhere to the carrier, reducing the toner charging ability of the carrier and causing toner scattering. Adjust the image forming conditions etc. When toner component adhesion to the carrier progresses to such an extent that it becomes difficult to suppress toner scattering, it is time to replace the developer (the life of the developer is reached). However, as the second carrier deterioration state progresses, the carrier resistance increases, so the first carrier deterioration state that causes carrier adhesion is rather improved.
Here, the degree of progress of the first carrier deterioration state (carrier film scraped state) can be grasped from the cumulative driving amount of the developing means and the cumulative toner consumption amount. For example, when the amount of toner consumption per unit driving amount of the developing means is used as an index value, the smaller the index value is, the lower the carrier resistance is. Further, the degree of progress of the second carrier deterioration state (carrier spent state) can also be ascertained from the cumulative drive amount of the developing means and the cumulative toner consumption amount. For example, as described above, when the amount of toner consumed per unit driving amount of the developing means is used as an index value, the larger this index value is, the larger the amount of toner replenishment is, and the greater the chance that new toner components will adhere to the carrier surface. As a result, adhesion of toner components to the carrier progresses, and the toner charging ability decreases. In this way, it is possible to grasp the degree of progress of the carrier deterioration state (carrier film scraped state and carrier spent state) from the cumulative driving amount of the developing means and the cumulative toner consumption amount.
However, when the degree of progress of the first carrier deterioration state (carrier film scraping state) is progressing, it is difficult to sufficiently slow down the progress with the conventional method of correcting the toner concentration target value. To explain in detail, conventionally, the toner concentration of the developer is increased by correcting the toner concentration target value to increase the amount of new toner to be replenished, and the carrier resistance is increased. Slow down the progress of deterioration. However, in addition to there being a limit to increasing the toner concentration of the developer, there is also a limit to the amount of new toner that can be replenished under conditions where an image with a low image area ratio is being formed. Therefore, even if the toner concentration target value is increased, it is difficult to sufficiently increase the amount of new toner that causes toner components to adhere to the carrier, and it is difficult to sufficiently slow down the progress of the first carrier deterioration state.
In this aspect, the toner forced consumption control means is provided to forcibly consume the toner in the developing means, and according to the carrier deterioration state specified based on the cumulative drive amount of the developing means and the cumulative toner consumption amount. Now you can change the forced toner consumption amount. According to this, when the degree of progress of the first carrier deterioration state (carrier film scraping state) is progressing, by increasing the forced toner consumption amount, more new toner can be replenished (replaced) to the developer. This makes it possible to sufficiently delay the progress of the first carrier deterioration state. Therefore, even if the first carrier deterioration state (carrier film scraping state) progresses depending on the type of developer and usage conditions, the progress of the first carrier deterioration state can be sufficiently delayed. It becomes possible to extend the time for replacing the developer.

[Second aspect]
In a second aspect, in the first aspect, the carrier deterioration state is specified based on the amount of toner consumed per unit driving amount of the developing means.
As described in the above embodiment, the carrier deterioration state (carrier film scraped state and carrier spent state) can be identified from the toner consumption amount per unit driving amount of the developing means.

[Third aspect]
In a third aspect, in the second aspect, when the amount of toner consumption per unit driving amount of the developing device is equal to or less than a predetermined toner consumption increase threshold (for example, a second threshold) (for example, during processing Step S10 (Yes) is characterized in that the forced toner consumption amount is increased.
When the amount of toner consumption per unit driving amount of the developing means is less than or equal to a predetermined toner consumption increase threshold, it can be determined that the type of carrier deterioration state is a carrier film scraping state. Therefore, in this case, by increasing the forced consumption of toner, the amount of toner components adhering to the carrier increases, the carrier resistance increases, carrier adhesion is suppressed, and the progress of carrier film scraping can be delayed. .

[Fourth aspect]
In a fourth aspect, in the second or third aspect, when the toner consumption amount per unit driving amount of the developing device is larger than a predetermined toner consumption increase threshold (for example, a second threshold), , the toner forced consumption amount is not changed.
When the toner consumption amount per unit driving amount of the developing means is larger than the predetermined toner consumption increase threshold, the carrier film wear-off state has not progressed much, so the toner forced consumption amount is adjusted according to the carrier film wear-off state. By not changing (increasing) , unnecessary control can be avoided.

[Fifth aspect]
In a fifth aspect, in the fourth aspect, when the amount of toner consumption per unit driving amount of the developing device is larger than a predetermined toner consumption reduction threshold (for example, a third threshold) (processing step No) in S11 is characterized by reducing the forced toner consumption amount or not performing the forced toner consumption control.
When the amount of toner consumption per unit driving amount of the developing means is larger than a predetermined toner consumption reduction threshold, it can be determined that the type of carrier deterioration state is a carrier spent state. Therefore, in this case, by reducing or eliminating the toner forced consumption amount, it is possible to reduce the amount of toner components adhering to the carrier, and it is possible to delay the progress of the carrier spent state.

[Sixth aspect]
In a sixth aspect, in any one of the first to fifth aspects, a toner concentration detection means (for example, a toner concentration sensor 6) for detecting the toner concentration of the developer in the developing means; a replenishing means (for example, toner replenishing device 4) for replenishing toner, and a toner concentration control means for controlling the driving of the replenishing means so that the detection result by the toner concentration detecting means falls within a predetermined toner concentration control range. an upper limit value and a lower limit value of the toner concentration control range are determined based on the cumulative driving amount and cumulative toner consumption amount of the developing means, and the forced toner consumption control means is configured to control the toner concentration control range. The toner forced consumption amount is changed when the difference between the upper limit value and the lower limit value is less than or equal to a predetermined upper and lower limit difference threshold (for example, a first threshold value) (for example, No in processing step S6). be.
If the difference between the upper and lower limits of the toner concentration control range is larger than the predetermined upper and lower limit difference threshold, it means that the carrier deterioration state has not progressed much, so in this case, the carrier deterioration state is By not changing the forced toner consumption amount, unnecessary control can be avoided.

[Seventh aspect]
In a seventh aspect, in any one of the first to sixth aspects, the forced toner consumption control means performs the forced toner consumption control after the end of the continuous image forming operation (for example, after the end of the print job), and When increasing the toner forced consumption amount, the toner forced consumption amount is determined in accordance with the number of image formations (average Page/Job) per the continuous image forming operation.
According to this, a necessary and sufficient amount of forced toner consumption can be achieved without excessively increasing the amount of forced toner consumption.

[Eighth aspect]
In an eighth aspect, in any one of the first to seventh aspects, the forced toner consumption control means performs the forced toner consumption control after the end of the continuous image forming operation (for example, after the end of the print job), and When increasing the toner forced consumption amount, the number of image formations per continuous image forming operation (average Page/Job) is equal to or greater than a predetermined image formation number threshold (for example, the fourth threshold) (for example, Yes in processing step S15). The toner forced consumption amount is set to a maximum value within an allowable range.
According to this, it is possible to prevent the forced toner consumption amount from exceeding the maximum value of the allowable range.

1: Process cartridge 3: Photoconductor 4: Toner supply device 5: Toner bottle 6: Toner density sensor 7: Developing device 12: Developing sleeve 14: Doctor blade 15: Drum cleaning device 20: Optical writing unit 23: Charging device 40: Intermediate transfer unit 41 : Intermediate transfer belt 45 : Primary transfer bias roller 50 : Secondary transfer roller 60 : Fixing device 100 : Printer 101 : Control section

JP2016-057423A

Claims (6)

In an image forming apparatus that develops a latent image on a latent image carrier by a developing means using a developer containing toner and carrier,
a toner forced consumption control means for performing toner forced consumption control for forcibly consuming the toner in the developing means during a non-image forming period;
The toner forced consumption control means is configured to forcibly cause toner consumption when the amount of toner consumed per unit driving amount of the developing means is less than or equal to a predetermined toner consumption increase threshold that is a criterion for determining the state of carrier film scraping. A toner forced consumption amount changing process is performed to change the amount so that the toner consumption amount per unit drive amount of the developing means is greater than the toner forced consumption amount when the toner consumption amount per unit driving amount of the developing means is larger than a predetermined toner consumption increase threshold value. image forming apparatus. The image forming apparatus according to claim 1,
In the forced toner consumption changing process, when the toner consumption per unit driving amount of the developing means is larger than a predetermined toner consumption increase threshold, the forced toner consumption to be forcibly consumed is changed from the predetermined forced toner consumption. An image forming apparatus characterized by not being changed. The image forming apparatus according to claim 1 or 2,
In the toner forced consumption amount changing process, the toner consumption amount per unit driving amount of the developing means is larger than the predetermined toner consumption increase threshold , and the toner consumption amount per unit drive amount of the developing means is larger than the predetermined toner consumption increase threshold , and the toner consumption amount is a predetermined value that is a criterion for determining a carrier spent state. When the toner consumption reduction threshold is larger than the toner consumption reduction threshold, the forced toner consumption amount is changed to be lower than a predetermined forced toner consumption amount, or the forced toner consumption control is turned off. image forming device. The image forming apparatus according to any one of claims 1 to 3,
toner concentration detection means for detecting the toner concentration of the developer in the development means;
replenishing means for replenishing toner to the developer in the developing means;
toner concentration control means for controlling the driving of the replenishing means so that the detection result by the toner concentration detection means falls within a predetermined toner concentration control range;
The upper and lower limits of the toner density control range are determined based on the cumulative driving amount and cumulative toner consumption of the developing means,
The image forming apparatus is characterized in that the forced toner consumption control means performs the forced toner consumption amount changing process when the difference between the upper limit and the lower limit of the toner density control range is less than or equal to a predetermined upper and lower limit difference threshold. Device. The image forming apparatus according to any one of claims 1 to 4,
The forced toner consumption control means performs the forced toner consumption control after the end of the continuous image forming operation, and when increasing the forced consumption amount of toner to be forcibly consumed, the forced toner consumption control means increases the forced toner consumption amount to be forcibly consumed. An image forming apparatus characterized in that the determination is made according to the number of times of image formation per continuous image forming operation. The image forming apparatus according to any one of claims 1 to 5,
When the forced toner consumption control means performs the forced toner consumption control after the end of the continuous image forming operation and increases the amount of forced toner consumption that is forced to be consumed, the forced toner consumption control means controls the number of times of image formation per the continuous image forming operation. An image forming apparatus characterized in that when the number of times of image formation is equal to or greater than a predetermined image forming frequency threshold, a forced consumption amount of toner to be forcibly consumed is set to a maximum value within an allowable range.

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