JP7027822B2 - A program executed by the image forming apparatus and the computer of the image forming apparatus. - Google Patents

Description

This disclosure relates to an image forming apparatus, and more specifically to a technique for improving image quality in an electrophotographic image forming apparatus.

In recent years, there has been an increasing demand for higher image quality for image forming devices. In order to achieve high image quality, technologies such as improvement of resolution, improvement of contrast, and uniformity of image density are required.

As a technique for making the image density uniform, for example, Japanese Patent Application Laid-Open No. 2008-039864 (Patent Document 1) states, "The developed γ characteristic of a developing device is obtained, and the target developed γ characteristic value is set based on the developed γ characteristic. , The measured development γ value is compared with the target development γ value, and correction is made so that the toner concentration in the developing device detected by the sensor matches the toner concentration of the target development γ characteristic value according to the difference. It discloses an image forming apparatus that "controls the amount of toner supplied to the developing apparatus" (see "Summary").

Japanese Unexamined Patent Publication No. 2008-039864

In an electrophotographic image forming apparatus, there is known a "transfer memory" in which the non-uniformity of the surface potential of the image carrier due to the previous printing affects the printing this time. Transfer memory is a phenomenon that hinders the uniformity of image density. The degree of this transfer memory varies depending on the state of the image carrier.

However, since the image forming apparatus disclosed in Patent Document 1 does not control the amount of toner supplied in consideration of the state of the image carrier, the transfer memory cannot be sufficiently suppressed depending on the state of the image carrier. There is. Therefore, there is a need for an image forming apparatus capable of suppressing the transfer memory regardless of the state of the image carrier.

The present disclosure has been made to solve the above-mentioned problems, and an object in a certain aspect is to provide a technique capable of suppressing a transfer memory regardless of the state of an image carrier.

An image forming apparatus according to an embodiment includes an image carrier configured to be capable of carrying and transporting a latent image, a developing apparatus for supplying toner to the latent image and developing a toner image on the image carrier, and a developing apparatus. A power supply for applying a development bias voltage, a density sensor for measuring the density of a toner image, a ratio sensor for measuring the ratio of toner to a carrier in a developing device, and a development efficiency target in the developing device. It is provided with a storage device for storing the correspondence between the image carrier and the amount of the image carrier used, and a control device for adjusting the ratio. The control device is developed by a different development bias voltage, a usage amount acquisition unit for acquiring the usage amount of the image carrier, a target identification unit for specifying a target corresponding to the usage amount acquired from the correspondence relationship, and a development bias voltage. An efficiency calculation unit for calculating the development efficiency based on the measurement results of the density sensor for a plurality of toner images, and an adjustment unit for adjusting the ratio based on the difference between the calculated development efficiency and the specified target. And a stabilization control unit for controlling the development bias voltage based on the ratio measured by the ratio sensor.

Preferably, the adjuster reduces the ratio when the calculated development efficiency is greater than the specified target.

Preferably, the adjuster increases the ratio when the calculated development efficiency is less than the specified target.

Preferably, the usage amount acquisition unit initializes the usage amount based on the replacement of the image carrier.

Preferably, the adjuster replenishes the developer with toner if the ratio is increased based on the replacement of the image carrier.

More preferably, the control device prohibits the image forming process while the process of replenishing the developing device with toner is being performed with the replacement of the image carrier.

Preferably, the adjusting unit consumes the toner of the developing device when the ratio is reduced based on the replacement of the image carrier.

More preferably, the control device prohibits the image forming process while the developing device performs the process of consuming the toner due to the replacement of the image carrier.

Preferably, the adjusting unit gradually brings the ratio closer to a value determined from the difference as the image forming process is performed.

Preferably, the adjusting unit calculates the toner charge amount corresponding to the difference, and calculates the difference ratio for correcting the ratio based on the calculated toner charge amount. The adjusting unit further changes the ratio to a value obtained by adding or subtracting the difference ratio to the ratio measured by the ratio sensor.

Preferably, the image forming apparatus further comprises an environment sensor for measuring the surrounding environment of the image forming apparatus. The adjusting unit adjusts the ratio based on the surrounding environment and the difference.

Preferably, the film thickness variation of the image carrier is 10 μm or more.
Preferably, the toner is 4 . It has 0 or more parts of pigment.

According to other aspects, a program executed by the computer of the image forming apparatus is provided. The image forming apparatus includes an image carrier configured to be capable of carrying and transporting a latent image, a developing apparatus for supplying toner to the latent image to develop a toner image on the image carrier, and a developing bias voltage to the developing apparatus. A power supply for applying, a density sensor for measuring the density of the toner image, a ratio sensor for measuring the ratio of toner to the carrier in the developing device, and a target of development efficiency and an image carrier in the developing device. It is provided with a storage device for storing the correspondence with the usage amount of. The program tells the computer a step to obtain the usage of the image carrier, a step to identify the target corresponding to the usage obtained from the correspondence, and a density sensor for multiple toner images developed with different development bias voltages. The step of calculating the development efficiency based on the measurement result of, the step of adjusting the ratio based on the difference between the calculated development efficiency and the specified target, and the development bias voltage based on the ratio measured by the ratio sensor. And to execute the steps to control.

An image forming apparatus according to an embodiment can suppress the transfer memory depending on the state of the image carrier.

The above and other objectives, features, aspects and advantages of the disclosed technical features will become apparent from the following detailed description of the invention as understood in connection with the accompanying drawings.

It is a figure explaining the technical idea of this disclosure. It is a figure explaining the photoconductor film thickness dependence of a transfer memory. It is a figure explaining an example of the appearance structure of the image forming apparatus according to Embodiment 1. FIG. It is a figure explaining an example of the electric structure of the image forming apparatus according to Embodiment 1. FIG. An example of the functional configuration of the CPU is shown. It shows the correspondence between the development bias voltage and the toner density with respect to the reference image. An example of the data structure of the Vi determination table is shown. It shows the relationship between the developing potential gap and the amount of toner adhered. An example of the data structure of the target table is shown. The correspondence between the development efficiency of the photoconductor and the charge amount of the C color toner is shown. It is a figure explaining the relational expression which expresses the correspondence relation with the toner charge amount of C color, and a toner ratio. It is a flowchart which shows the process for suppressing the transfer memory. An example of the data structure of the correction table used for correcting the difference ratio of C color is shown. It is a figure which shows the transition of the difference ratio and the development potential gap in the image forming apparatus according to Embodiment 2. FIG. It is a flowchart which shows the process of the image forming apparatus according to Embodiment 3.

Hereinafter, embodiments of this technical idea will be described in detail with reference to the drawings. In the following description, the same parts are designated by the same reference numerals. Their names and functions are the same. Therefore, the detailed description of them will not be repeated. In addition, each embodiment and each modification described below may be selectively combined as appropriate.

[Technical Thought]
FIG. 1 is a diagram illustrating the technical idea of the present disclosure. With reference to FIG. 1, the image forming apparatus 100 has a photoconductor 110. A charging roller 120, an exposure device 130, a developing device 140, an intermediate transfer roller 160, and a primary transfer roller 170 are arranged around the photoconductor 110.

The developing device 140 has a developing roller 142. The carrier and toner are stored in the developing device 140. The power supply 150 applies a development bias voltage to the development roller 142. As a result, the toner conveyed to the developing region on the developing roller 142 by the carrier adheres to the latent image on the photoconductor 110.

The ratio sensor 144 measures the ratio of toner to the carrier (toner concentration) in the developing device 140. The control device 180 calculates the development bias voltage based on the measurement result input from the ratio sensor 144, and outputs the calculation result to the power supply 150. More specifically, when the toner ratio is low, the control device 180 sets the development bias voltage high in order to satisfy the target toner supply amount for the latent image. On the other hand, when the toner ratio is high, the control device 180 sets the development bias voltage low.

(Transfer memory)
Next, the transfer memory will be described. First, the charging roller 120 uniformly charges the photoconductor 110 to the potential Vo (negative potential) after charging (state (a)). Next, the charging device 130 irradiates the photoconductor 110 with light. As a result, the potential of the exposed portion of the photoconductor 110 approaches the ground potential and becomes the post-exposure potential Vi (state (b)). Next, the power supply 150 applies the development bias voltage Vd to the developing roller 142 (state (c)). The development bias voltage Vd is set between the post-charge potential Vo and the post-exposure potential Vi. As a result, the toner is supplied to the latent image according to the potential difference between the development bias voltage Vd and the post-exposure potential Vi (hereinafter, also referred to as “development potential gap ΔVd”).

Next, the primary transfer roller 170 applies a positive primary transfer current to the photoconductor 110 via the intermediate transfer belt 160. Current does not easily flow in the portion of the photoconductor 110 to which the toner adheres (exposed portion), and current tends to flow in the portion of the photoconductor 110 to which the toner does not adhere (non-exposed portion). Therefore, the potential of the non-exposed portion of the photoconductor 110 can change from a negative potential (post-charged potential Vo) to a positive potential (state (d)). In such a case, it is difficult for the static elimination device (not shown) to completely eliminate the surface charge of the photoconductor 110, particularly the positive charge. This is because the static eliminator is configured to generate a positive charge inside the photoconductor 110 by irradiating the photoconductor 110 with light to cancel the negative charge on the surface of the photoconductor 110.

As a result, the surface potential of the photoconductor 110 becomes non-uniform. This non-uniformity of the surface potential is also reflected in the next printing. As a result, a toner image having a non-uniform image density is formed. The "transfer memory" represents the non-uniformity of the surface potential of the photoconductor 110.

In order to suppress the transfer memory, it is necessary to make the absolute value of the potential Vo after charging larger. However, if the post-charge potential Vo is increased, the potential difference between the development bias voltage Vd and the post-charge potential Vo (hereinafter, also referred to as “fog margin potential ΔVm”) becomes large. If the fog margin potential ΔVm is too large, there arises a problem that carriers adhere to the photoconductor 110. On the other hand, if the fog margin potential ΔVm is too small, there arises a problem that the toner adheres to the non-exposed portion of the photoconductor 110. Therefore, it is required to increase the developing potential gap ΔVd while keeping the fog margin potential ΔVm within a predetermined range.

The development potential gap ΔVd is set to a potential at which a toner image having a target density can be obtained. More specifically, the development potential gap ΔVd is set by the development efficiency and the target density. The development efficiency represents the amount of toner adhered per unit area (g / V · m ^ 2) with respect to the unit applied voltage.

That is, the control device 180 can control the development potential gap ΔVd by changing the development efficiency. For example, the control device 180 reduces the development efficiency when it is desired to increase the development potential gap ΔVd. As a parameter for changing the development efficiency, the toner ratio Tc in the developing apparatus 140 can be mentioned. Other parameters that change the development efficiency include the peripheral speed ratio between the photoconductor 110 and the developing roller 142, and when the development bias voltage includes an AC voltage, the amplitude and frequency of the AC voltage, etc., but these parameters are It is not suitable as a parameter to control because it may affect the image quality.

In a certain aspect, the control device 180 lowers the toner ratio Tc to lower the development efficiency. As a result, the control device 180 increases the development potential gap ΔVd in order to secure the target concentration.

(Dependence on photoconductor film thickness of transfer memory)
FIG. 2 is a diagram illustrating the photoconductor film thickness dependence of the transfer memory. The thicker the photoconductor 110, the easier it is for transfer memory to occur. The reason is that the primary transfer is controlled by a constant current (that is, the amount of charge Q supplied is constant), and the thicker the photoconductor 110, the larger the positive voltage applied to the photoconductor 110. Further, the film thickness of the photoconductor 110 gradually decreases with the use of the photoconductor 110.

Therefore, as shown by the straight line 210, the thicker the photoconductor 110, the higher the post-charge potential Vo required to suppress the transfer memory. Along with this, as shown by the straight line 220, the thicker the photoconductor 110, the higher the development potential gap ΔVd required to suppress the transfer memory. Therefore, the control device 180 secures the development potential gap ΔVd necessary for suppressing the transfer memory by controlling the toner ratio Tc to be smaller as the photoconductor 110 is thicker.

According to the above, the image forming apparatus 100 can secure an appropriate development potential gap ΔVd according to the state (film thickness) of the photoconductor 110. As a result, the image forming apparatus 100 can suppress the transfer memory regardless of the state of the photoconductor 110. Hereinafter, the configuration and processing required to realize such an image forming apparatus will be described in detail.

[Embodiment 1]
(Appearance configuration of image forming apparatus)
FIG. 3 is a diagram illustrating an example of the appearance configuration of the image forming apparatus 300 according to the first embodiment. The image forming apparatus 300 is an electrophotographic image forming apparatus such as a laser printer or an LED printer, and forms an image on a medium such as paper based on an input image signal. As shown in FIG. 3, the image forming apparatus 300 includes an intermediate transfer belt 1 as a belt member in a substantially central portion inside. Below the lower horizontal part of the intermediate transfer belt 1, four image forming units 2Y, 2M, 2C, and 2K corresponding to each color of yellow (Y), magenta (M), cyan (C), and black (K), respectively. Are arranged side by side along the intermediate transfer belt 1. The image forming units 2Y, 2M, 2C, and 2K each have photoconductors 3Y, 3M, 3C, and 3K as an image carrier configured to be able to carry and transport a latent image. Each image forming unit 2Y, 2M, 2C, and 2K is configured to be interchangeable from the image forming apparatus 300. The photoconductors 3Y, 3M, 3C, and 3K for supporting and transporting the latent image develop a toner image transferred to a medium such as paper on the photoconductor film formed on the outer peripheral surface.

Around each photoconductor 3Y, 3M, 3C, 3K, charging rollers 21Y, 21M, 21C, 21K, exposure devices 22Y, 22M, 22C, 22K, and developing devices 24Y, 24M are arranged in order along the rotation direction. , 24C, 24K, the primary transfer rollers 28Y, 28M, 28C, 28K facing each photoconductor 3Y, 3M, 3C, 3K with the intermediate transfer belt 1 sandwiched between them, and the cleaning blades 29Y, 29M, 29C, 29K. Each is arranged.

The developing devices 24Y, 24M, 24C, 24K include developing rollers 23Y, 23M, 23C, 23K and ratio sensors 27Y, 27M, 27C, 27K, respectively. The ratio sensors 27Y, 27M, 27C, and 27K are mounted on the bottom surfaces of the developing devices 24Y, 24M, 24C, and 24K, respectively. Each power supply 25Y, 25M, 25C, 25K applies a development bias voltage to the developing rollers 23Y, 23M, 23C, 23K, respectively. Further, the toner bottles 26Y, 26M, 26C and 26K are connected to the developing devices 24Y, 24M, 24C and 24K, respectively. The developing devices 24Y, 24M, 24C, 24K can supply the required amount of toner from the corresponding toner bottles 26Y, 26M, 26C, 26K.

The cleaning blades 29Y, 29M, 29C, and 29K are pressed against the corresponding photoconductors 3Y, 3M, 3C, and 3K by a pressing mechanism (not shown), respectively. A density sensor 4 is installed between the image forming unit 2K on the most downstream side of the intermediate transfer belt 1 and the secondary transfer region.

The secondary transfer roller 2 is pressure-welded to the intermediate transfer belt 1, and the secondary transfer is performed in the region. A fixing device 30 including a fixing roller 32 and a pressure roller 34 is arranged at a position downstream of the transport path behind the secondary transfer region.

A paper cassette 40 is detachably arranged at the bottom of the image forming apparatus 300. The paper loaded and stored in the paper feed cassette 40 is sent out one by one from the uppermost paper to the transport path by the rotation of the transport roller 42a. A transport roller pair 42b, 42c, 42d is arranged in the transport path. A paper output tray 50 is arranged downstream of the transport roller pair 42d. Further, an operation panel 44 is arranged on the upper part of the image forming apparatus 300.

In the present embodiment, the image forming apparatus 300 employs, but is not limited to, a tandem type intermediate transfer method as an example. The image forming apparatus may adopt a cycle method. Further, the image forming apparatus may be a multifunction device having a combination of functions such as a copying machine, a printer, and a fax machine.

(Approximate operation of image forming apparatus)
Next, the schematic operation of the image forming apparatus 300 having the above configuration will be described. When an image signal is input to the image forming apparatus 300 from an external device (for example, a personal computer or the like), the image forming apparatus 300 creates each digital image signal obtained by color-converting the image signal into yellow, magenta, cyan, and black. At the same time, based on the digital image signal, the exposure devices 22Y, 22M, 22C, and 22K are made to emit light to perform exposure.

As a result, the electrostatic latent image formed on each of the photoconductors 3Y, 3M, 3C, and 3K is developed by the toner supplied from each of the developing devices 24Y, 24M, 24C, and 24K, and becomes a toner image of each color. .. The toner images of each color are sequentially superposed on the intermediate transfer belt 1 by the action of the primary transfer rollers 28Y, 28M, 28C, and 28K, and are primary transferred. After the primary transfer, the toner remaining on each photoconductor 3Y, 3M, 3C, 3K is recovered by the cleaning blades 29Y, 29M, 29C, 29K.

The toner image thus formed on the intermediate transfer belt 1 is collectively secondarily transferred to the paper by the action of the secondary transfer roller 2. The toner image secondarily transferred to the paper reaches the fixing device 30. The toner image is fixed on the paper by the action of the heated fixing roller 32 and the pressure roller 34. The paper on which the toner image is fixed is discharged to the paper output tray 50 via the transport roller pair 42d.

In the following, the symbols yellow “Y”, magenta “M”, cyan “C”, and black “K” may be omitted from the components provided for each of the above-mentioned colors. Such components represent a generic term for each of the four color components. For example, the photoconductor 3 is a general term for the photoconductors 3Y, 3M, 3C, and 3K.

(Electrical configuration of image forming apparatus)
FIG. 4 is a diagram illustrating an example of an electrical configuration of the image forming apparatus 300 according to the first embodiment. The image forming apparatus 300 has a CPU (Central Processing Unit) 410 that functions as a control device for the image forming apparatus 300. The CPU 410 includes a RAM (Random Access Memory) 420, a ROM (Read Only Memory) 430, a non-volatile memory 440, a density sensor 4, an exposure device 22, a power supply 25, a ratio sensor 27, and an operation panel 44. , The environment sensor 450 and the communication interface (I / F) 460 are electrically connected to each other. The CPU 410 controls the operation of each connected device by reading and executing the control program 432 stored in the ROM 430.

The RAM 420 functions as a working memory for the CPU 410 to execute the control program 432. The non-volatile memory 440 stores the photoconductor rotation speed 441, the Vi determination table 442, the target table 443, and the relational expression 444,445.

The photoconductor rotation speed 441 represents the cumulative rotation speed of each photoconductor 3Y, 3M, 3C, and 3K. The photoconductor rotation speed 441 is updated by the CPU 410 every time the photoconductor 3 rotates. The Vi determination table 442 stores the post-exposure potential of the photoconductor 3 according to the cumulative rotation speed of the photoconductor 3. The target table 443 stores a target range of development efficiency according to the cumulative rotation speed of the photoconductor 3. The relational expression 444 expresses the relationship between the development efficiency and the toner charge amount. The relational expression 445 expresses the relationship between the toner charge amount and the toner ratio Tc. Details of the Vi determination table 442, the target table 443, and the relational expressions 444 and 445 will be described later.

The density sensor 4 detects the density of a reference image (for example, a halftone image) formed on the intermediate transfer belt 1. As an example, the density sensor 4 includes a light emitting element (not shown) that irradiates light and a light receiving element (not shown) that receives reflected light that is emitted and reflected from the light emitting element. When the intermediate transfer belt 1 is irradiated with light from the light emitting element, the light receiving element detects the reflected light reflected by the toner image on the intermediate transfer belt 1. The density sensor 4 outputs the amount of photocurrent (detection voltage) generated in the light receiving element to the CPU 410.

The power supply 25 applies the development bias voltage set by the CPU 410 to the development roller 23. The ratio sensor 27 detects the toner ratio Tc of the two-component developer in the developing device 24, and outputs the detection result to the CPU 410. The toner ratio Tc means (toner weight) / (toner weight + carrier weight). As an example, the operation panel 44 is composed of a display and a button for receiving input from the user, and outputs the operation content received from the user to the CPU 410.

The environment sensor 450 measures the surrounding environment of the image forming apparatus 300. More specifically, the environment sensor 450 measures the temperature and humidity around the image forming apparatus 300 (including the inside of the machine). The environment sensor 450 outputs the measurement result to the CPU 410. The temperature sensor may be a contact type or a non-contact type. Further, the humidity sensor may be a polymer electrostatic type or a polymer resistance type.

The communication I / F 460 is realized by a wireless LAN (Local Area Network) card as an example. The image forming apparatus 300 is configured to be able to communicate with an external device (personal computer, smartphone, tablet, server, etc.) connected to a LAN or WAN (Wide Area Network) via a communication interface 460.

(Control structure)
FIG. 5 shows an example of the functional configuration of the CPU 410. By reading and executing the control program 432, the CPU 410 functions as a usage amount acquisition unit 510, an efficiency calculation unit 520, a target identification unit 530, an adjustment unit 540, and a stabilization control unit 550. These functions will be described in detail with reference to FIGS. 5 to 11.

<Usage amount acquisition unit 510>
The usage amount acquisition unit 510 acquires the cumulative rotation speed of the photoconductor 3 with reference to the photoconductor rotation speed 441. The usage amount acquisition unit 510 outputs the acquired cumulative rotation speed of the photoconductor 3 to the efficiency calculation unit 520 and the target identification unit 530. In another embodiment, the image forming apparatus 300 uses the photoconductor 3 for the cumulative mileage of the photoconductor 3 and the paper printed using the photoconductor 3 instead of the cumulative rotation speed of the photoconductor 3. It may be configured to store the cumulative number of sheets and the like.

<Efficiency calculation unit 520>
The efficiency calculation unit 520 calculates the development efficiency α of the photoconductor 3. As described above, the development efficiency α represents the amount of toner adhered per unit area (g / V · m ^ 2) with respect to the unit applied voltage.

FIG. 6 shows the correspondence between the development bias voltage Vd and the toner density with respect to the reference image. In one aspect, the CPU 410 develops a reference image with different development bias voltages Vd1 to Vd4. As a result, the four reference images are transferred onto the intermediate transfer belt 1. The density sensor 4 outputs the toner adhesion amounts (g / m ^ 2) M1 to M4 of the reference image corresponding to the development bias voltages Vd1 to Vd4 to the CPU 410. As shown in FIG. 6, the larger the absolute value of the development bias voltage Vd, the larger the amount of toner adhered to the reference image.

The efficiency calculation unit 520 calculates the development potential gaps ΔVd1 to ΔVd4 by subtracting the post-exposure potential Vi from each of the development bias voltages Vd1 to Vd4. The efficiency calculation unit 520 refers to the Vi determination table 442 in order to determine the post-exposure potential Vi.

FIG. 7 represents an example of the data structure of the Vi determination table 442. The Vi determination table 442 includes a table 442F, a table 442M, and a table 442S corresponding to the rotation speeds of the different photoconductors 3. As an example, the table 442F has a rotation speed of the photoconductor 3 of 290 mm / sec, the table 442M has a rotation speed of the photoconductor 3 of 250 mm / sec, and the table 442S has a rotation speed of the photoconductor 3 of 166 mm / sec. Corresponds to each case. As the rotation speed of the photoconductor 3 is slower, the exposure amount of the photoconductor 3 per unit time increases, so that the post-exposure potential Vi of the photoconductor 3 approaches the ground potential.

Each table 442F, 442M, 442S holds the post-exposure potential Vi according to the cumulative rotation speed of the photoconductor 3 and the average environment of the image forming apparatus 300. The cumulative rotation speed of the photoconductor 3 corresponds to the film thickness of the photoconductor 3. That is, the higher the cumulative rotation speed of the photoconductor 3, the thinner the film thickness of the photoconductor 3. In each table, the post-exposure potential Vi of the photoconductor 3 is set so that the thicker the photoconductor 3, the closer to the ground potential.

As an example, the average environment of the image forming apparatus 300 is LL environment when the average temperature after replacement of the photoconductor 3 is less than 18 ° C, NN environment when the average temperature is 18 ° C or more and less than 25 ° C, and HH when the average temperature is 25 ° C or more. Defined as environment. The CPU 410 periodically updates the average temperature of the image forming apparatus 300 based on the output of the environment sensor 450. In each table, the post-exposure potential Vi of the photoconductor 3 is set so that the higher the average temperature, the closer to the ground potential.

The efficiency calculation unit 520 includes the rotation speed (process speed) of the photoconductor 3 set in the image forming apparatus 300, the average environment of the image forming apparatus 300, and the cumulative rotation of the photoconductor 3 input from the usage amount acquisition unit 510. The post-exposure potential Vi of the photoconductor 3 is determined based on the number.

The efficiency calculation unit 520 calculates the development potential gaps ΔVd1 to ΔVd4 by subtracting the post-exposure potential Vi determined above from each of the development bias voltages Vd1 to Vd4.

FIG. 8 shows the relationship between the developing potential gap ΔVd and the amount of toner adhered. With reference to FIG. 8, the efficiency calculation unit 520 changes the toner adhesion amount with respect to the change amount of the development potential gap (that is, the inclination) from the correspondence relationship between the development potential gaps ΔVd1 to ΔVd4 and the toner adhesion amounts M1 to M4. ), The development efficiency α is calculated. With reference to FIG. 5 again, the efficiency calculation unit 520 outputs the calculated current development efficiency α to the adjustment unit 540.

<Target identification unit 530>
Next, the processing realized by the target specifying unit 530 will be described. The target specifying unit 530 specifies a target of development efficiency according to the current state (film thickness) of the photoconductor 3. This process will be specifically described with reference to FIG.

FIG. 9 shows an example of the data structure of the target table 443. The target table 443 holds the cumulative rotation speed of the photoconductor 3 and the target range of development efficiency in association with each other. In the target table 443, the smaller the cumulative rotation speed of the photoconductor 3, in other words, the thicker the photoconductor 3, the lower the target upper limit of the development efficiency is set. The reason is that the thicker the photoconductor 3, the more likely it is that a transfer memory is generated. Therefore, it is necessary to secure a large development potential gap ΔVd by setting the development efficiency low. In the example shown in FIG. 9, the target table 443 is configured to maintain the target range of the development efficiency for the C color, but actually, the development efficiency for the other Y, M, and K colors. Also keeps the target range of. Further, in another aspect, the target table 443 may be configured to hold a target value instead of a target range for each color.

The target specifying unit 530 specifies a target range of development efficiency corresponding to the cumulative rotation speed of the photoconductor 3 input from the usage amount acquisition unit 510 based on the target table 443. The target specifying unit 530 outputs the specified target range of development efficiency to the adjusting unit 540.

<Adjustment unit 540>
With reference to FIG. 5 again, the adjusting unit 540 accepts the input of the calculated current development efficiency α and the target range of the development efficiency. The adjusting unit 540 determines whether or not the current development efficiency α is included in the target range. When the current development efficiency α is included in the target range, the adjusting unit 540 determines that the transfer memory will not occur with the current settings, and does not execute any special processing. On the other hand, when the current development efficiency α is not included in the target range, the adjustment unit 540 bases the toner ratio Tc based on the difference between the current development efficiency α and the target range (hereinafter, also referred to as “difference efficiency”). To correct. Hereinafter, the process of correcting the toner ratio Tc will be described.

The adjusting unit 540 includes a charge amount calculation unit 542 and a difference ratio calculation unit 544. The charge amount calculation unit 542 calculates the toner charge amount (hereinafter, also referred to as “differential charge amount”) corresponding to the difference efficiency. The difference ratio calculation unit 544 calculates the toner ratio (hereinafter, also referred to as “difference ratio”) corresponding to the difference charge amount calculated by the charge amount calculation unit 542. Hereinafter, these processes will be specifically described with reference to FIGS. 10 and 11.

FIG. 10 shows the correspondence between the development efficiency α of the photoconductor 3C and the toner charge amount Qb of the C color. Each point shown in FIG. 10 is data calculated in advance by an experiment. For example, the development efficiency α is calculated by the above method, and the toner charge amount Qb is measured in advance by a blow-off method, a suction method, a DC electric field method, or any other method of measuring the charge amount of a known powder. From these experimental data acquired in advance, the relational expression 444C representing the correspondence between the development efficiency α and the toner charge amount Qb of the C color is derived. The relational expression 444 holds not only the relational expression 444C but also the correspondence relationship between the development efficiency α and the toner charge amount Qb for the Y, M, and K colors.

The charge amount calculation unit 542 converts the difference efficiency into the difference charge amount ΔQb. As an example, the development efficiency α of the current photoconductor 3C is 1.60 (corresponding to the star mark in FIG. 10), the cumulative rotation speed of the photoconductor 3C is less than 100 k, and the relational expression 444C is “Y = −45.979X + 95. 603 (X = development efficiency α, Y = toner charge amount Qb) ”. In this case, the target of development efficiency is 0.62 to 1.36 (corresponding to the range surrounded by the alternate long and short dash line in FIG. 10). The charge amount calculation unit 542 calculates the difference efficiency 0.24 by subtracting the target upper limit value 1.36 of the development efficiency from the current development efficiency 1.60. Subsequently, the charge amount calculation unit 542 converts the differential efficiency 0.24 into the differential charge amount -11.0 using the relational expression 444C.

FIG. 11 is a diagram illustrating a relational expression 445C showing a correspondence relationship between the toner charge amount Qb of color C and the toner ratio Tc. As shown in FIG. 11, the larger the toner ratio Tc, the smaller the toner charge amount Qb. The reason is that as the toner ratio Tc increases, the chance of contact friction between the toner and the carrier decreases. The relational expression 445C is calculated based on the data calculated in advance by the experimental data. More specifically, while increasing the toner ratio Tc of C color, the charge amount of the toner is measured at a plurality of points by a method of measuring the charge amount of a known powder, and the relational expression is based on these plurality of experimental data. 445C is derived. The relational expression 445 holds not only the relational expression 445C but also the correspondence between the toner charge amount Qb and the toner ratio Tc for the Y, M, and K colors.

The difference ratio calculation unit 544 calculates the difference ratio ΔTc from the relational expression 445 of the color corresponding to the difference charge amount ΔQb based on the difference charge amount ΔQb input from the charge amount calculation unit 542. This difference ratio ΔTc represents the difference between the target toner ratio required for the current development efficiency α to be included in the target range and the current toner ratio Tc (value measured by the ratio sensor 27). For example, when the current development efficiency α is larger than the target (that is, when the difference efficiency is a positive value), the difference ratio ΔTc becomes a negative value. On the other hand, when the current development efficiency α is smaller than the target (that is, when the difference efficiency is a negative value), the difference ratio ΔTc becomes a positive value.

With reference to FIG. 5 again, the difference ratio calculation unit 544 outputs a control signal for adjusting the toner ratio Tc to the developing device 24 based on the calculated difference ratio ΔTc. When the difference ratio ΔTc is a positive value, the developing device 24 increases the toner ratio Tc by the difference ratio ΔTc by replenishing the toner from the toner bottle 26. On the other hand, when the difference ratio ΔTc is a negative value, the developing device 24 lowers the toner ratio Tc by the difference ratio ΔTc by consuming the toner. More specifically, the image forming apparatus 300 consumes the toner in the developing apparatus 24 by forming a predetermined image (for example, a solid image) on the photoconductor 3. As a result, the current toner ratio Tc measured by the ratio sensor 27 is changed.

<Stabilization control unit 550>
The stabilization control unit 550 determines the development bias voltage for satisfying the target toner supply amount based on the toner ratio Tc (toner ratio Tc changed by the above series of processes) input from the ratio sensor 27. do. The stabilization control unit 550 outputs information indicating the determined value to the power supply 25. The power supply 25 applies a development bias voltage determined based on the information to the development roller 23.

According to the above, the image forming apparatus 300 according to the embodiment can set an appropriate development efficiency target according to the state (film thickness) of the photoconductor 3 by the action of the target specifying unit 530. As a result, the development potential gap ΔVd required to suppress the transfer memory can be secured regardless of the state of the photoconductor 3.

In addition, in the target table 443, the target upper limit value of the development efficiency is set larger as the cumulative rotation speed (usage amount) of the photoconductor 3 increases. As a result, the image forming apparatus 300 sets the developing potential gap ΔVd smaller as the cumulative rotation speed of the photoconductor 3 increases. As a result, the image forming apparatus 300 can reduce the power consumption required for the charging bias voltage applied to the charging roller 21 and the development bias voltage applied to the developing roller 23 as the cumulative rotation speed of the photoconductor 3 increases. ..

FIG. 12 is a flowchart showing a process for suppressing the transfer memory by changing the series of toner ratios Tc. Each process shown in FIG. 12 is realized by the CPU 410 executing the control program 432 stored in the ROM 430.

In step S1310, the CPU 410 determines whether or not the timing is predetermined. The predetermined timing includes, for example, the timing when the power of the image forming apparatus 300 is turned on, the timing when the cumulative number of printed sheets reaches a predetermined number, the timing when the photoconductor 3 is replaced, and the like. When the CPU 410 determines that the timing is predetermined (YES in step S1310), the CPU 410 recommends the process to step S1320.

In step S1320, the CPU 410 forms a plurality of reference images on the intermediate transfer belt 1 with different development bias voltages Vd. The CPU 410 further acquires the toner densities of these plurality of reference images by the density sensor 4.

In step S1330, the CPU 410 calculates the current development efficiency α based on the correspondence between the plurality of development bias voltages Vd and the plurality of toner concentrations.

In step S1340, the CPU 410 specifies a target range of development efficiency corresponding to the cumulative rotation speed of the photoconductor 3 based on the photoconductor rotation speed 441 and the target table 443. The CPU 410 further determines whether or not the development efficiency α calculated in step S1330 is included in the specified target range. When the CPU 410 determines that the development efficiency α is included in the target range (YES in step S1340), the CPU 410 ends a series of processes. On the other hand, when the CPU 410 determines that the development efficiency α is not included in the target range (NO in step S1340), the CPU 410 executes the process of step S1350.

In step S1350, the CPU 410 calculates the difference efficiency between the development efficiency α and the target range, and calculates the difference charge amount ΔQb corresponding to the difference efficiency based on the relational expression 444.

In step S1360, the CPU 410 calculates the difference ratio ΔTc corresponding to the difference charge amount ΔQb based on the relational expression 445.

In step S1370, the CPU 410 determines the final toner ratio correction amount so that the corrected toner ratio Tc does not exceed a predetermined range. As an example, the CPU 410 determines the toner ratio correction amount so that the corrected toner ratio Tc is within the range of 5.0% to 8.0%. If the current toner ratio Tc is 7.5% and the difference ratio ΔTc is 0.6%, the CPU 410 sets the toner ratio correction amount to 0.5%. The reason is that if the toner ratio Tc is too high, the amount of charge of the toner becomes too small, and the electrostatic force acting between the carrier and the toner is less than the centrifugal force accompanying the rotation of the developing roller 23, and the toner scatters. This is because it will be stored. On the other hand, if the toner ratio Tc is too low, the amount of charge of the toner becomes too large, the force acting on the toner from the electric field exceeds the magnetic force acting between the carrier and the developing roller 23, and the carrier easily adheres to the photoconductor 3. This is to become.

In step S1380, the CPU 410 outputs a control signal based on the toner ratio correction amount determined in step S1370 to the developing device 24. The developing device 24 replenishes or consumes toner from the toner bottle 26 according to the input control signal.

When the ratio of the positive difference ratio ΔTc to the toner ratio Tc exceeds a predetermined ratio (for example, 1.0%), the CPU 410 simultaneously applies the toner corresponding to the difference ratio ΔTc to the developing device 24. Instead of supplying the toner, the toner may be controlled to be gradually supplied to the developing device 24 (for example, 0.5% / time). As a result, the image forming apparatus 300 can suppress the possibility of the above-mentioned toner scattering problem.

[Embodiment 2]
The image forming apparatus 300 according to the first embodiment is configured to convert the difference efficiency into the difference ratio ΔTc based on the relational expression 444,445. The image forming apparatus 300 according to the second embodiment calculates the difference efficiency ΔTc based on the environment around the image forming apparatus 300 and the difference efficiency.

More specifically, in the first embodiment, the relational expression 445 is configured to include the corresponding relationship between the toner charge amount Qb and the toner ratio Tc for each color, but in the second embodiment, the relational expression 445 is for each color. And, it is configured to include the correspondence between the toner charge amount Qb and the toner ratio Tc for each environment of the image forming apparatus 300. The reason is that the toner charge amount Qb changes depending on the environment (particularly, humidity). More specifically, the toner charge amount Qb in the low temperature and low humidity environment is larger than the toner charge amount Qb in the high-pitched imperial environment.

Further, the CPU 410 can correct the difference ratio ΔTc according to the environment by using the correction table 1300 as shown in FIG. 13 even if the relational expression 445 does not include the correspondence relationship for each environment.

FIG. 13 shows an example of the data structure of the correction table 1300 used for correcting the difference ratio ΔTc of C color. The correction table 1300 includes two tables 1310 and 1320 in which the amounts of the C color developer (toner, carrier) used are different. The correction table 1300 is stored in the non-volatile memory 440. The non-volatile memory 440 stores not only the correction table 1300 but also a correction table used for correcting the difference ratio ΔTc for the Y, M, and K colors.

As an example, the table 1310 is used when the cumulative number of prints using the same toner bottle 26 is less than 30 k, and the table 1320 is used when the cumulative number of prints using the same toner bottle 26 is 30 k or more. Used. The correction amount of the difference ratio ΔTc held in the table 1320 is set larger than the correction amount (%) of the difference ratio ΔTc held in the table 1310. This is because the toner charge amount Qb becomes smaller as the cumulative number of prints (use period) using the same toner bottle 26 becomes longer, so that the rate (%) of the change due to the environment with respect to the toner charge amount Qb becomes relatively large. Is.

The correction tables 1310 and 1320 hold a correction amount of the difference ratio ΔTc according to the relative humidity and the difference charge amount ΔQb. As described above, the higher the relative humidity, the smaller the toner charge amount Qb. Therefore, in the correction tables 1310 and 1320, the correction amount (%) of the difference ratio ΔTc is set to be relatively large as the relative humidity increases.

As an example, the differential charge amount ΔQb (-μC / g) of C color is 20, the difference ratio ΔTc is 0.3%, the relative humidity measured by the environmental sensor 450 is 30%, and the same toner bottle 26C is used. It is assumed that the cumulative number of printed sheets used is 20 k. In such a case, the CPU 410 refers to the correction table 1310 and specifies that the correction amount of the difference ratio ΔTc is −0.6%. The CPU 410 can calculate 0.2982% as the final correction amount of the toner ratio, which is obtained by subtracting the correction amount 0.0018% (= 0.3 × 0.006) from the difference ratio of 0.3%.

FIG. 14 is a diagram showing changes in the difference ratio ΔTc and the developing potential gap ΔVd in the image forming apparatus 300 according to the second embodiment. The horizontal axis of FIG. 14 represents the cumulative number of prints, the vertical axis on the left side represents the developing potential gap ΔVd (V), and the vertical axis on the right side represents the toner ratio Tc.

In the example shown in FIG. 14, the environment (humidity) of the image forming apparatus 300 is significantly changed at the timing shown by the alternate long and short dash line. Even in such a case, since the image forming apparatus 300 determines the toner ratio Tc in consideration of the environment as described above, the potential required for the development potential gap ΔVd to suppress the transfer memory (broken line). ) It can be maintained by the above.

As an example, the CPU 410 forms an image having a uniform density on paper by controlling the developing apparatus 24 so that the toner ratio Tc reaches a target value before the image forming process (printing process) is executed.

From the above, the image forming apparatus 300 according to the second embodiment converts the difference efficiency into the difference ratio ΔTc in consideration of the environment around the image forming apparatus 300, so that the development potential gap ΔVd necessary for suppressing the transfer memory is obtained. Can be secured more reliably.

[Embodiment 3]
The image forming apparatus 300 according to the third embodiment performs control for suppressing a defect including a transfer memory that may occur when the photoconductor 3 is replaced.

FIG. 15 is a flowchart showing the processing of the image forming apparatus 300 according to the third embodiment. In step S1510, the CPU 410 determines whether or not the photoconductor 3 has been replaced. For example, the CPU 410 determines that the photoconductor 3 has been replaced based on the output of the operation panel 44. As another example, the CPU 410 determines that the photoconductor 3 has been replaced by referring to the non-volatile memory included in the replacement unit including the photoconductor 3. When the CPU 410 determines that the photoconductor 3 has been replaced (YES in step S1510), the CPU 410 executes the process of step S1520.

In step S1520, the CPU 410 resets (initializes) the photoconductor rotation speed 441 stored in the non-volatile memory 440. More specifically, the CPU 410 resets the cumulative rotation speed corresponding to the color of the exchanged photoconductor 3 among the cumulative rotation speeds of each color held in the photoconductor rotation speed 441. In another aspect, the unit including the photoconductor 3 may include a storage medium for storing the cumulative rotation speed (usage history) of the photoconductor 3. In such a case, the CPU 410 may be configured to overwrite the photoconductor rotation speed 441 by using the cumulative rotation speed stored in the storage device of the replaced unit.

In step S1530, the CPU 410 calculates the difference ratio ΔTc for the replaced photoconductor 3. Since this process is the same as the above process, it will not be described repeatedly.

In step S1540, the CPU 410 determines whether the calculated difference ratio ΔTc is a positive value or a negative value. When the CPU 410 determines that the difference ratio ΔTc is a positive value (YES in step S1540), the CPU 410 instructs the developing device 24 to replenish the toner from the toner bottle 26 (step S1550). On the other hand, when the CPU 410 determines that the difference ratio ΔTc is a negative value (NO in step S1540), the CPU 410 consumes the toner of the developing device 24 (step S1560). Since the method of consuming toner is the same as the above method, it will not be described repeatedly.

For example, when the photoconductor 3 is replaced with one older than the one currently used, the development potential gap ΔVd required to suppress the transfer memory becomes smaller. As a result, the difference ratio ΔTc becomes a positive value. On the other hand, when the photoconductor 3 is replaced with a newer one than the one currently used, the development potential gap ΔVd required to suppress the transfer memory becomes large. As a result, the difference ratio ΔTc becomes a negative value.

The CPU 410 prohibits the image forming process in steps S1550 and S1560 while the developing device 24 replenishes or consumes the toner. The reason is to avoid that the image forming process (for example, development) is performed in a situation where the toner ratio Tc has not reached the target value, and the density of the toner image becomes non-uniform.

In another aspect, the CPU 410 does not change the toner ratio Tc to the target value before the image forming process is performed in steps S1550 and S1560, but sets the toner ratio Tc to the target value in accordance with the image forming process. It may be configured to gradually change to.

The developing device 24 consumes a predetermined amount of toner determined by the image to be formed and replenishes the predetermined amount of toner from the toner bottle 26 in association with the image forming process (printing). On the other hand, in step S1550, the CPU 410 causes the developing apparatus 24 to supply a toner amount larger than a predetermined amount with the image forming process. On the other hand, in step S1560, the CPU 410 causes the developing apparatus 24 to consume a toner amount larger than a predetermined amount in accordance with the image forming process.

According to the above, since the image forming apparatus 300 can gradually bring the toner ratio Tc closer to the target value in the image forming process, downtime due to the process of replenishing or consuming the toner can be suppressed.

[Structure of Photoconductor 3 and Toner]
As described above, the thicker the film thickness of the photoconductor 3, the higher the development efficiency and the more likely the transfer memory is to occur. Therefore, the above-mentioned treatment is more effective when a thick photoconductor 3 having a film thickness variation of 10 μm or more is used. The film thickness of the photoconductor 3 referred to here means, for example, the thickness of a layer obtained by adding the carrier generation layer (CGL layer) and the carrier transport layer (CTL layer) of the photoconductor 3.

Further, in recent years, the number of copies of pigments (colored particles) contained in toner has been increasing from the viewpoint of energy saving and environmental consideration. On the other hand, as the number of pigment copies contained in the toner increases, the development efficiency increases and the transfer memory tends to occur. Therefore, the above-mentioned treatment is more effective when a highly filled toner having a pigment contained in the toner of 4.0 parts or more is used.

[Other configurations]
Each of the above-mentioned processes is supposed to be realized by one CPU 410, but is not limited to this. Each process is a semiconductor integrated circuit such as at least one processor, at least one application specific integrated circuit (ASIC), at least one DSP (Digital Signal Processor), and at least one FPGA (Field Programmable Gate Array). ), And / or can be realized by a circuit having other arithmetic functions.

These circuits may perform the various processes described above by reading one or more instructions from at least one tangible readable medium.

Such media take the form of magnetic media (eg, hard disks), optical media (eg, compact discs (CDs), DVDs), volatile memory, and any type of memory, such as non-volatile memory. It is not limited to the form.

Volatile memory may include DRAM (Dynamic Random Access Memory) and SRAM (Static Random Access Memory). The non-volatile memory may include ROM, NVRAM.

It should be considered that the embodiments disclosed this time are exemplary in all respects and not restrictive. The scope of the present invention is shown by the scope of claims rather than the above description, and is intended to include all modifications within the meaning and scope equivalent to the scope of claims.

1,160 Intermediate transfer belt, 2 Secondary transfer roller, 3,110 Toner, 4 Density sensor, 21,120 Charging roller, 22,130 Exposure device, 23,142 Develop roller, 24,140 Develop device, 25,150 Power supply, 26 toner bottle, 27,144 ratio sensor, 44 operation panel, 100,300 image forming device, 180 control device, 420 RAM, 430 ROM, 432 control program, 440 non-volatile memory, 441 photoconductor rotation speed, 442 determination Table, 443 target table, 444,445 relational expression, 450 environmental sensor, 510 usage amount acquisition unit, 520 efficiency calculation unit, 530 target identification unit, 540 adjustment unit, 542 charge amount calculation unit, 544 difference ratio calculation unit, 550 stable Control unit, 1300 correction table, Qb toner charge amount, Tc toner ratio, Vd development bias voltage, Vi post-exposure potential, Vo post-charge potential.

Claims (14)

An image carrier configured to support and transport a latent image,
A developing device for supplying toner to the latent image and developing the toner image on the image carrier.
A power supply for applying a development bias voltage to the developing device, and
A density sensor for measuring the density of the toner image and
A ratio sensor for measuring the ratio of toner to carriers in the developing device, and
A storage device for storing the correspondence between the development efficiency target in the developing device and the amount of the image carrier used, and a storage device.
It is equipped with a control device for adjusting the ratio.
The control device is
A usage amount acquisition unit for acquiring the usage amount of the image carrier, and
A target specifying unit for specifying a target corresponding to the acquired usage amount from the corresponding relationship, and
An efficiency calculation unit for calculating the development efficiency based on the measurement results of the density sensor for a plurality of toner images developed with different development bias voltages.
An adjustment unit for adjusting the ratio based on the difference between the calculated development efficiency and the specified target, and
An image forming apparatus including a stabilization control unit for controlling the development bias voltage based on a ratio adjusted by the adjustment unit. The image forming apparatus according to claim 1, wherein the adjusting unit lowers the ratio when the calculated development efficiency is larger than the specified target. The image forming apparatus according to claim 1 or 2, wherein the adjusting unit increases the ratio when the calculated development efficiency is smaller than the specified target. The image forming apparatus according to any one of claims 1 to 3, wherein the usage amount acquisition unit initializes the usage amount based on the replacement of the image carrier. The image forming apparatus according to any one of claims 1 to 4, wherein the adjusting unit supplies toner to the developing device when the ratio is increased based on the replacement of the image carrier. The image forming apparatus according to claim 5, wherein the control device prohibits an image forming process while a process of supplying toner to the developing apparatus is being performed with the replacement of the image carrier. The image forming apparatus according to any one of claims 1 to 6, wherein the adjusting unit consumes the toner of the developing device when the ratio is lowered based on the replacement of the image carrier. The image forming apparatus according to claim 7, wherein the control device prohibits an image forming process while the developing apparatus performs a process of consuming toner due to replacement of the image carrier. The image forming apparatus according to any one of claims 1 to 4, wherein the adjusting unit gradually brings the ratio closer to a value determined from the difference as the image forming process is performed. The adjustment unit
The toner charge amount corresponding to the difference is calculated, and the toner charge amount is calculated.
A difference ratio for correcting the ratio is calculated based on the calculated toner charge amount, and the difference ratio is calculated.
The image forming apparatus according to any one of claims 1 to 9, wherein the ratio is changed to a value obtained by adding or subtracting the difference ratio to the ratio measured by the ratio sensor. The image forming apparatus further includes an environment sensor for measuring the surrounding environment of the image forming apparatus.
The image forming apparatus according to any one of claims 1 to 10, wherein the adjusting unit adjusts the ratio based on the ambient environment and the difference. The image forming apparatus according to any one of claims 1 to 11, wherein the amount of variation in the film thickness of the image carrier is 10 μm or more. The toner is 4 . The image forming apparatus according to any one of claims 1 to 12, which has 0 or more parts of pigment. A program executed by the computer of the image forming apparatus.
The image forming apparatus is
An image carrier configured to support and transport a latent image,
A developing device for supplying toner to the latent image and developing the toner image on the image carrier.
A power supply for applying a development bias voltage to the developing device, and
A density sensor for measuring the density of the toner image and
A ratio sensor for measuring the ratio of toner to carriers in the developing device, and
A storage device for storing a correspondence relationship between a development efficiency target in the developing device and the amount of the image carrier used is provided.
The program is on the computer
The step of acquiring the amount of the image carrier used, and
The step of identifying the target corresponding to the obtained usage amount from the correspondence relationship, and
A step of calculating the development efficiency based on the measurement result of the density sensor for a plurality of toner images developed with different development bias voltages, and a step of calculating the development efficiency.
A step of adjusting the ratio based on the difference between the calculated development efficiency and the specified target, and
A program that executes a step of controlling the development bias voltage based on the ratio adjusted by the adjusting step .

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