JP5201466B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine, and more particularly to an image forming apparatus having a function of adjusting a reference exposure amount used by an exposure unit during image formation.

  Conventionally, in process control, a toner pattern is formed on a photosensitive member under the same conditions as in normal image formation under predetermined toner pattern formation conditions, and the amount of toner attached to this toner pattern is detected by a sensor. An image forming apparatus that adjusts a charging bias, a developing bias, a reference exposure amount (hereinafter referred to as “charging bias etc.”) or the like based on a sensor detection result so as to conform to the current situation is widely known (Patent Document 1, etc.). ). In this type of image forming apparatus, the developing potential is obtained from the sensor detection result, a suitable charging bias corresponding to the obtained developing potential is specified, and the charging bias is adjusted. This makes it possible to maintain a constant image density even if the development γ (gamma) or the like fluctuates due to environmental fluctuations or changes over time.

  A conventional image forming apparatus that performs process control generally uses a background potential as a fixed value, and adjusts a charging bias or the like so as to obtain a target development potential. In this way, the background potential can be set to a fixed value because the general photosensitive member used in the conventional image forming apparatus can be further reduced even when the maximum exposure amount by the exposure unit is exposed. One of the reasons is that the potential on the surface of the photoreceptor (residual exposed portion potential) that remains without changing does not change much. With such a photoconductor, by setting a suitable background potential in advance, the above-described image quality degradation such as edge shading or background smearing of the halftone portion can be achieved without adjusting the background potential thereafter. It doesn't happen very much.

  Further, in Patent Document 2, a halftone toner pattern is formed and imaged by an image imaging device, and an edge blur or background stain of the halftone part is detected from the imaging result, and according to the detection result. An image forming apparatus that adjusts the background potential is disclosed. According to this image forming apparatus, it is possible to directly grasp the occurrence of edge blurring of the halftone portion caused by the background potential being too high and the occurrence of background contamination caused by the background potential being too low using the image pickup unit. As a result, it is possible to stably set an optimum background potential that does not cause end edge blurring or background contamination of the halftone portion.

Japanese Patent Laid-Open No. 5-14729 JP 2005-308833 A

However, the present inventor has a suitable background potential that does not cause problems caused by the background potential being too high (such as edge shading of the halftone portion) or problems caused by the background potential being too low (such as background dirt). Even if it is set, it was confirmed that the following problems occur.
That is, as will be described in detail later, as can be seen from FIGS. 8A and 9A, the development potential is adjusted so that a desired toner adhesion amount can be obtained, and the background potential is also the above-mentioned problem. Even when it is set within a suitable range (for example, 200 [V]) in which no occurrence occurs, it has been confirmed that when the charging potential Vd is different, the line width of the thin line is different, resulting in a change in image quality.

  As described above, a general photoreceptor used in a conventional image forming apparatus does not change the residual exposure portion potential so much, and therefore, it is hardly necessary to largely change the charging potential Vd when adjusting the development potential. However, in recent years, a photoconductor (high hardness photoconductor) has been proposed in which the surface hardness of the photoconductor is increased by adding a filler or the like to the surface layer of the photoconductor to improve the resistance to abrasion. Some of the hardness photoconductors have a characteristic that the residual exposed portion potential gradually increases with time. Although not limited to a high-hardness photoconductor, in a photoconductor whose residual exposed portion potential gradually increases with time, an appropriate development potential is set in order to ensure the same toner adhesion amount (constant image density) over time. In order to ensure, it is necessary to gradually increase the developing bias with time. In this case, as the developing bias increases, the charging potential Vd is adjusted to gradually increase with time so as to maintain a suitable background potential. For this reason, when using a photoconductor in which the residual exposed portion potential gradually increases with time, the charging potential Vd gradually increases with time. The image quality deterioration that the line width becomes thick may occur.

  In addition, the problem that the image quality change in which the line width of the thin line changes occurs is not limited to the above example, and may occur in the same way as long as the image forming apparatus changes the charging potential greatly when adjusting the development potential. It is.

  The present invention has been made in view of the above background, and an object of the present invention is to provide an image quality in which the line width of a fine line changes even in an image forming apparatus in which the charging potential is greatly changed when adjusting the development potential. An object of the present invention is to provide an image forming apparatus capable of suppressing the occurrence of a change.

In order to achieve the above object, the invention of claim 1 comprises a photoconductor and a charging means for uniformly charging the surface of the photoconductor with a charging bias such that the surface of the photoconductor has a target charging potential; An exposure unit that forms an electrostatic latent image by exposing the surface of the photosensitive member charged by the charging unit, and a developer carrying that has a developing bias applied to the electrostatic latent image formed on the surface of the photosensitive member Development means for forming a toner image on the surface of the photosensitive member by attaching toner on the surface of the photosensitive member, and finally transferring the toner image formed on the surface of the photosensitive member onto the recording material. In an image forming apparatus for forming an image on the surface, a toner adhesion amount detecting means for detecting the toner adhesion amount, and a predetermined toner pattern is formed on the surface of the photoconductor by a normal image forming operation at a predetermined timing. The toner pattern The toner adhesion amount is detected by the toner adhesion amount detection means, and based on the detection result, the electrostatic latent image portion potential and development such that the toner adhesion amount with respect to a predetermined electrostatic latent image becomes the target toner adhesion amount. In order to obtain a developing potential that is a difference from the bias, the image forming apparatus includes a control unit that performs process control for adjusting a charging bias and at least one of an exposure amount and a developing bias, and the control unit includes a non-electrostatic latent image with respect to the developing potential. The above process control is performed so that the ratio of the background potential, which is the difference between the potential of the portion and the development bias, becomes a predetermined target ratio, and the toner adhesion amount with respect to a predetermined electrostatic latent image is the target toner. When the background potential obtained by multiplying the development potential that gives the adhesion amount by the above ratio is within a predetermined range, the development potential The process control is performed so that the ratio of the background potential to the target becomes the target ratio. If the background potential is out of the specified range, the background potential is determined to be a value within the specified range; and The process control is performed such that the ratio of the background potential after determination to the development potential becomes the target ratio .
Also, the invention of claim 2, the image forming apparatus according to claim 1, wherein said control means, in the process control, such as toner adhesion amount for a given electrostatic latent image becomes a toner adhesion amount of target developing When the target charging bias determined from the potential and the background potential obtained by multiplying the development potential by the above ratio is out of the predetermined range, the charging bias is adjusted to a value within the predetermined range; and It is characterized in that at least one of the reference exposure amount and the development bias is adjusted so that the ratio becomes the target ratio.
According to a third aspect of the present invention, in the image forming apparatus according to the first aspect, the control means sets the development potential such that the toner adhesion amount with respect to a predetermined electrostatic latent image becomes a target toner adhesion amount and the development potential. If the target charging bias determined from the background potential obtained by multiplying the ratio is within a predetermined range, the process control is performed so that the ratio becomes the target ratio, and the target charging is performed. If the bias is not within a predetermined range, the charging bias is adjusted to a value within the specified range, and the difference between the adjusted charging bias and the target charging bias is subtracted from the ground potential. The above process control is performed so that at least one of the reference exposure amount and the development bias is adjusted according to the background potential after subtraction and the development potential. It is characterized in.
According to a fourth aspect of the present invention, in the image forming apparatus according to any one of the first to third aspects, the ratio is 0.4 or more and 0.8 or less.
According to a fifth aspect of the present invention, in the image forming apparatus according to the fourth aspect , the ratio is 0.4 or more and 0.45 or less.

The optimum development potential (target development potential) that causes the toner adhesion amount to a predetermined electrostatic latent image to be the target toner adhesion amount changes due to environmental changes and changes with time. In the process control, the charging bias and the like are appropriately adjusted according to the target development potential that changes in this way. In this case, the charge potential is changed by adjusting the charging bias or the like, and as described above, the image quality change in which the line width of the thin line is changed may occur.
As will be described in detail later, the present inventor, as shown in FIGS. 8 (b) and 9 (b), as long as the ratio of the background potential to the developing potential is constant, the thin line is not affected even if the charging potential Vd is different. I found that the line width did not change.
Therefore, in the present invention, process control is performed to adjust the charging bias or the like so that the ratio of the background potential to the development potential becomes a predetermined target ratio. As a result, even if the target development potential changes according to environmental changes or changes over time, the ratio of the background potential to the development potential can be maintained at the target ratio, so that it is possible to suppress the change in image quality that the line width of the thin line changes.

  As described above, according to the present invention, it is possible to suppress an image quality change in which the line width of a thin line is changed even in an image forming apparatus that greatly changes a charging potential when adjusting a development potential. There is.

Hereinafter, an embodiment in which the present invention is applied to a printer which is an electrophotographic image forming apparatus will be described.
FIG. 1 is an explanatory diagram showing a schematic configuration of a main part of the printer according to the present embodiment.
As shown in FIG. 1, the printer forms image forming units 102Y (yellow), 102M (magenta), 102C (cyan), and 102K (black) along an intermediate transfer belt 101 stretched around a plurality of stretching rollers. Is provided. The toner images formed by the image forming units 102Y, 102M, 102C, and 102K are transferred onto the intermediate transfer belt 101 by the primary transfer devices 106Y, 106M, 106C, and 106K. Further, an image detection device 110 as a toner adhesion amount detection unit that detects a toner adhesion amount of a toner image transferred onto an intermediate transfer belt, which will be described later, is provided to face the intermediate transfer belt 101. The toner image on the intermediate transfer belt 101 is transferred to a transfer paper 112 as a recording material by a secondary transfer device 111.

FIG. 2 is an explanatory diagram showing a schematic configuration of the image forming units 102Y, 102M, 102C, and 102K. Since the image forming units 102Y, 102M, 102C, and 102K have the same configuration, the following description will be made without distinguishing each other.
Around the photoconductor 202, a charging device 201 as a charging means for charging the surface of the photoconductor, a writing device 203 as an exposure means for writing an electrostatic latent image on the surface of the photoconductor with writing light L, and an electrostatic latent image A developing device 205 as a developing unit that develops with toner, a photosensitive member cleaner 206 as a cleaning unit that cleans transfer residual toner and the like on the photosensitive member, and an erase (static eliminating device) 207 as a discharging unit that neutralizes the surface of the photosensitive member. A potential sensor 210 is provided as a potential detecting means.

  The photoreceptor of this embodiment is a high-hardness photoreceptor in which a filler is included in the photoreceptor surface layer. This photoconductor is similar to a general photoconductor that does not contain a filler in the surface layer of the photoconductor, as shown in FIGS. 14A and 14B, that is, the exposed portion potential with respect to the change in exposure amount. Has a photosensitive characteristic that the change rate gradually decreases as the exposure amount increases. Further, as illustrated in FIG. 15, the photoconductor of the present embodiment has a characteristic that the residual exposure portion potential Vr gradually increases with time. Therefore, in the photoconductor of the present embodiment, the correspondence relationship between the exposure power and the exposure portion potential VL within the range of the exposure power used at the time of image formation changes greatly with time.

  The charging device 201 of the present embodiment is a non-contact charger made of a scorotron charger, and by setting the grid voltage (charging bias) Vg of the scorotron charger to a target charging potential (in this embodiment, a negative potential). The photosensitive member surface potential is set to the target charging potential. Note that the charging device 201 is not limited to this, and other non-contact chargers or contact chargers can also be used.

  The writing device 203 of the present embodiment uses a laser diode (LD) as a light source, and irradiates intermittent writing light, that is, repetitive pulsed writing light L, so that electrostatic charges for each dot are formed on the surface of the photoreceptor. A latent image (1-dot electrostatic latent image) is formed. In this embodiment, gradation control is performed by changing the exposure time (unit exposure time) when forming a 1-dot electrostatic latent image to control the amount of toner attached to the 1-dot electrostatic latent image. It is possible. In the present embodiment, the maximum unit exposure time is divided into 15 (each unit exposure time is hereinafter referred to as “exposure duty”), and gradation control of 16 gradations is possible. Therefore, in the present embodiment, the exposure duty can be adjusted in 16 steps from 0 (not exposed) to 15 (maximum unit exposure time).

  The developing device 205 according to the present embodiment includes a developing roller as a developer carrying member disposed to face the surface of the photosensitive member, and includes a toner charged with a predetermined polarity (in this embodiment, a negative polarity) and a magnetic carrier. A two-component developer is carried on the developing roller, and toner is supplied to the surface of the photoreceptor. A developing bias Vb whose absolute value is sufficiently larger than the exposed portion potential VL and sufficiently smaller than the charging potential Vd is applied to the developing roller. As a result, the toner is moved toward the electrostatic latent image (exposure portion) on the surface of the photoconductor in the developing area where the surface of the photoconductor and the developing roller face each other, and the non-electrostatic latent image on the surface of the photoconductor An electric field that does not move the toner can be formed in the (non-exposed portion), and the electrostatic latent image can be developed with the toner.

  When image formation is performed, first, the surface of the photosensitive member 202 is charged by the charging device 201 so that the surface of the photosensitive member 202 is uniformly at a target charging potential (negative potential). Next, writing light L corresponding to the image data is exposed to the photosensitive member 202Y from the light source (LD) of the writing device 203 to the charged photosensitive member surface portion, whereby the potential of the exposed portion on the photosensitive member surface ( As the absolute value decreases, an electrostatic latent image is formed on the surface of the photoreceptor. Thereafter, the electrostatic latent image (in this embodiment, the exposure unit) formed on the photoconductor 202 is developed into a toner image by toner carried on a developing roller that is a developer carrying member of the developing device 205. . Specifically, a developing bias Vb having an absolute value larger than the exposure portion potential VL and smaller than the charging potential Vd is applied to the developing roller, and the toner charged to a predetermined polarity (negative polarity in this embodiment) is applied. Development is performed by electrostatically attaching to the electrostatic latent image.

  The toner image formed on the photoreceptor 202 is transferred onto the intermediate transfer belt 101 by the primary transfer device 106. Untransferred toner remaining on the photoconductor 202 without being transferred to the intermediate transfer belt 101 is collected by the photoconductor cleaner 206. Further, the surface of the photoconductor after the toner image is transferred onto the intermediate transfer belt 101 is uniformly discharged with an erasing light by an eraser 207, so that a non-electrostatic latent image portion is discharged and the charge is uniformly discharged. It will be in the state.

  The toner images of the respective colors formed by the image forming units 102Y, 102M, 102C, and 102K in this way are primarily transferred so as to overlap each other on the intermediate transfer belt 101. Thereafter, each color toner image transferred onto the intermediate transfer belt 101 is transferred from the intermediate transfer belt 101 to the transfer paper 112 by the secondary transfer device 111, and the toner image is fixed to the transfer paper 112 by a fixing device (not shown) and a series of printing is performed. Terminate the process.

Next, in order to stabilize the output image, the process control for stabilizing the toner adhesion amount on the specified one-dot electrostatic latent image will be described.
In addition, here, for the sake of simplicity, the description will focus on control for adjusting the charging bias Vg, the developing bias Vb, and the exposure power (hereinafter referred to as “LD power”).
In this embodiment, the process control includes exposure adjustment control for adjusting the reference exposure used by the writing device 203 during image formation. However, the exposure adjustment control may be performed separately from the process control. Good.

FIG. 3 is a block diagram showing a control system related to process control in the present embodiment.
In the process control of this embodiment, first, a density patch 113 that is a toner pattern (toner image) is formed on the intermediate transfer belt 101 by a normal image forming operation under predetermined conditions, and the toner adhesion amount of the density patch 113 is optically determined. Detection is performed by an image detection device 110 configured by optical sensors 301 and 302 (to be described later) that are optical reflection density sensors. The control unit 41 adjusts the grid voltage (charging bias) Vg of the charging device 201, the developing bias Vb of the developing device 205, and the LD power of the writing device 203 based on the detection result of the image detecting device 110.

FIG. 4A is an explanatory diagram showing a schematic configuration of the optical sensor 301 constituting the black image detection device 110, and FIG. 4B shows a configuration of the image detection device 110 for other colors. It is explanatory drawing which shows schematic structure of the optical sensor 302 to do.
The optical sensor 301 includes a light emitting element 303 and a regular reflection light receiving element 304 that receives regular reflection light from the surface of the density patch 113 and the intermediate transfer belt 101. On the other hand, the optical sensor 302 includes the light emitting element 303, the density patch 113, and the regular reflection light receiving element 304 that receives regular reflection light from the surface of the intermediate transfer belt 101, and further the surface of the density patch 113 and the intermediate transfer belt 101. It is comprised from the diffuse reflected light light receiving element 305 which receives the diffuse reflected light from. As shown in FIG. 5, the optical sensor 301 and the optical sensor 302 are respectively disposed at positions that can face the density patch 113 formed on the intermediate transfer belt 101. After starting writing of the writing light L, the control unit 41 starts from the specular reflection light receiving element 304 and the diffuse reflection light receiving element 305 in accordance with the timing when the density patch 113 reaches the position facing the optical sensor 301 and the optical sensor 302. The toner adhesion amount of each density patch 113 is derived by performing an adhesion amount conversion process on the detection result (sensor detection result). Specifically, for example, a conversion table describing the correspondence between the output voltage and the toner adhesion amount is stored in the ROM 44 in advance, and the toner adhesion amount is derived using this conversion table. Alternatively, for example, the toner adhesion amount may be derived by calculating a conversion formula for converting the output voltage into the toner adhesion amount.

FIG. 6 is a flowchart showing a main processing flow of process control in the present embodiment.
In this embodiment, the target toner adhesion of the toner gradation pattern when performing process control so that the adhesion amount conversion processing can be appropriately performed on an image from low density to high density formed on the transfer paper 112. The case where the amount range is in the range from around 0 [mg / cm ² ] to 0.5 [mg / cm ² ] will be described.

  In the process control, after finishing pre-processing steps such as calibration and abnormality inspection of the image detection apparatus 110, first, image forming conditions such as the currently set charging bias Vg0, developing bias Vb0, exposure power LDP (the previous time) A density patch of 10 gradations is formed on the surface of the photoreceptor (image forming conditions set by process control) (S1). The charging potential (non-exposed portion potential) Vd0 at this time is detected by the potential sensor 210 (S2). Further, the amount of toner attached to these 10-gradation density patches is detected by the image detection device 110 (S3). Then, development γ (gamma) at the present time is calculated from the charging potential Vd0 detected in S2 and the toner adhesion amount detected in S3 for 10 gradations (S4).

  FIG. 7 shows the development potential when a toner gradation pattern is formed in a high temperature and high humidity environment (32 [° C.], 54 [%]) and a low temperature and low humidity environment (10 [° C.], 15 [%]). 6 is a graph showing results of actual measurement of toner adhesion amount. In this graph, the horizontal axis represents the development potential, and the vertical axis represents the toner adhesion amount. The development γ is a parameter indicating the slope of this graph, and is a parameter indicating the correspondence between the development potential and the toner adhesion amount. Here, the development potential indicates a potential difference between the exposed portion potential VL on the photosensitive member and the development bias Vb. If the development potential is large, the amount of toner adhering to the one-dot electrostatic latent image increases. The concentration will increase. The background potential described later indicates a potential difference between the non-exposed portion potential on the photosensitive member, that is, the charging potential Vd and the developing bias Vb. If the background potential is too small, the toner adheres to the non-exposed portion. If background staining occurs and the background potential is too large, carrier adhesion occurs in which the magnetic carrier in the developer adheres to the surface of the photoreceptor.

In the case of a high temperature and high humidity environment, in order to form a density patch of 0.5 [mg / cm ² ], which is the maximum toner adhesion amount (target maximum toner adhesion amount) in the target toner adhesion amount range in this embodiment, FIG. As shown in FIG. 7, a development potential of 360 [V] is required. On the other hand, in order to form a density patch of 0.5 [mg / cm ² ] in a low-temperature and low-humidity environment, a development potential of 500 [V] is required. Thus, the development potential required to form a density patch with the same toner adhesion amount of 0.5 [mg / cm ² ] varies depending on the temperature and humidity environment. The reason why the development potential varies depending on the temperature and humidity environment is that the charge amount of the toner varies depending on the temperature and humidity environment. In general, since the toner charge amount becomes small in a high temperature and high humidity environment, the toner adhesion amount increases even at the same development potential. On the other hand, in the low temperature and low humidity environment, the toner charge amount increases and the toner adhesion amount decreases.

  As described above, the development potential for obtaining the target image density (target toner adhesion amount) varies depending on the fluctuation of the temperature and humidity environment. Further, the development potential for obtaining the target toner adhesion amount varies depending on factors other than the temperature and humidity environment. Accordingly, the current development γ is confirmed at an appropriate timing, and a development potential for obtaining a target toner adhesion amount is obtained from the development γ, and various image forming conditions (charging bias Vg, development bias Vb, reference exposure amount ( It is necessary to determine the reference exposure power and the reference exposure duty)).

Therefore, in the present embodiment, the development potential VbL for obtaining the toner adhesion amount of 0.5 [mg / cm ² ], which is the target maximum toner adhesion amount, is calculated from the development γ calculated in S4 (S5). Then, various image forming conditions are adjusted so that the development potential when forming an image so as to obtain the target maximum toner adhesion amount is the development potential VbL calculated in S5. Hereinafter, this adjustment method will be specifically described.

  In the present embodiment, with the currently set charging bias Vg0 and developing bias Vb0 applied, the exposure power LDP ′ is 1.5 times (150%) the basic exposure power LDP0 and the exposure duty is maximized. The surface of the photoconductor is exposed with the value (15). Then, the potential of the electrostatic latent image (exposed portion) formed thereby is detected by the potential sensor 210 as the residual exposed portion potential Vr ′ (S6). This residual exposed portion potential Vr 'is used to obtain a developing bias Vb' and a target charging potential Vd 'used when detecting the final residual exposed portion potential Vr.

Next, in the present embodiment, a temporary reference exposure portion potential VL0 ′ at this time is calculated from the residual exposure portion potential Vr ′ detected in S6 by the following formula (1) (S7). The reference exposure portion potential is an exposure portion potential when exposure is performed with a reference exposure amount (reference exposure power LDP, reference exposure duty).
VL0 ′ = Vr′−50 (1)
Here, the value obtained by adding −50 [V] to the residual exposure portion potential Vr ′ is set as the reference exposure portion potential VL0 ′. Generally, the reference exposure portion potential is − This is because it is empirically recognized that it exists in the vicinity of the value obtained by adding 50 [V]. An error between the provisional reference exposure portion potential VL0 ′ and the actual reference exposure portion potential VL0 is corrected by a correction process described later.

Next, from the provisional reference exposure portion potential VL0 ′ thus obtained, first, a development bias Vb ′ for Vr detection used when detecting the final residual exposure portion potential Vr is expressed by the following equation (2). ).
Vb ′ = VbL + VL0 ′ (2)
Subsequently, the target charging potential Vd ′ for Vr detection is calculated by the following equation (3) from the development bias Vb ′ for Vr detection calculated by the equation (2).
Vd ′ = Vb ′ + Vbg (3)

Here, the background potential Vbg in the above formula (3) has conventionally been a constant value (for example, 200 [V]). However, in the present embodiment, the background potential Vbg is changed according to the development potential VbL for the reason described later. Variable value. Specifically, the background potential Vbg is calculated from the following mathematical formula (4) (S8).
Vbg = VbL × α (4)
Α in the equation (4) is a parameter indicating a suitable ratio of the background potential Vbg to the development potential VbL, and is hereinafter referred to as a background potential determination coefficient. The background potential determination coefficient α is a value obtained experimentally from the following viewpoints.

Table 1 below is a table showing experimental conditions and experimental results for obtaining the background potential determination coefficient α.

  In this experiment, as a premise, toner replenishment is not performed, and various image forming conditions are not changed during the experiment. First, the charging potential Vd is adjusted to about 900 [V]. Further, the developing bias Vb and the exposure power are set in accordance with the experimental conditions shown in Table 1 in the state where the ground potential is varied as in the experimental conditions shown in Table 1 above. Thereafter, while printing, the toner is forcibly replenished until the image density ID of the solid image becomes 1.6, and an image for measuring the line width of a 1-dot thin line under the condition that the image density ID becomes 1.6. Is printed. Further, a toner image on the surface of the photoconductor for an image for measuring the line width of a 1-dot thin line is collected, and the toner adhesion amount is measured. Also, a halftone image is printed and the halftone density is measured. This experiment is similarly performed when the charging potential Vd is about 700 [V] and about 500 [V].

FIGS. 8A and 8B show vertical lines of one dot width (photosensitive member surface) by changing the background potential when the charging potential Vd is 900 [V], 700 [V], and 500 [V]. It is a graph of the said experimental result which shows the correspondence of the ground potential and line width when image-forming the line extended in the direction corresponding to a moving direction). In FIG. 8A, the horizontal axis indicates the background potential, and in FIG. 8B, the horizontal axis indicates the ratio of the background potential to the development potential.
FIGS. 9A and 9B show horizontal lines of one dot width (photoconductor surface movement) when the ground potential is changed when the charging potential Vd is 900 [V], 700 [V], and 500 [V]. It is the graph of the said experimental result which shows the correspondence of the ground potential and line | wire width when image-forming the line extended in the direction corresponding to the direction orthogonal to a direction). In FIG. 9A, the horizontal axis represents the background potential, and in FIG. 9B, the horizontal axis represents the ratio of the background potential to the development potential.
These graphs are obtained by changing the background potential while adjusting the development γ and the development potential so that the toner adhesion amount (image density) is all the target maximum adhesion amount of 0.5 [mg / cm ² ]. It is.

  As can be seen from FIG. 8A and FIG. 9A, even if the development potential is adjusted so that the toner adhesion amount is constant, the fine line The image quality changes that the line width is different. This corresponds to the electric field between the non-exposed portion and the developing roller (hereinafter referred to as “background electric field”) for the toner adhering to the boundary portion between the exposed portion and the non-exposed portion in accordance with the difference in the background potential. It is presumed that the impact will be different. More specifically, when the background electric field for moving the toner to the developing roller side becomes stronger, the effect of removing the toner from the boundary portion with the non-exposed portion in the exposed portion or preventing the toner from adhering to the boundary portion is increased. The toner adhesion area with respect to the area of the portion is reduced. This result is presumed to be manifested as image quality deterioration that the line width of the thin line becomes narrow. On the contrary, when the background electric field for moving the toner to the developing roller side becomes weak, the toner adhesion area with respect to the area of the exposed portion becomes large, and the image quality deterioration becomes apparent as the line width of the fine line becomes wide.

  Here, FIG. 8A and FIG. 9A are obtained by adjusting the development potential so that the toner adhesion amount is constant. When such adjustment is performed, the background potential is the same as in the conventional case. When the value is fixed (for example, 200 [V]), it can be seen that the line width of the thin line varies depending on the difference in the charging potential Vd. Even in the process control of the present embodiment, the development potential is adjusted so that the toner adhesion amount is constant. Therefore, if the background potential is a fixed value, a change in image quality in which the line width of the thin line changes occurs. In particular, in this embodiment, as described above, a photoconductor having a characteristic that the residual exposure portion potential Vr gradually increases with time is used. Therefore, in order to secure the same toner adhesion amount over time, it is necessary to gradually increase the development bias with time in order to ensure an appropriate development potential. As the developing bias increases, the charging potential Vd is adjusted so as to gradually increase with time in order to maintain a fixed background potential. Therefore, when the background potential is a fixed value (for example, 200 [V]), the image quality is deteriorated such that the line width of the thin line becomes thicker with time.

  On the other hand, when FIG. 8B and FIG. 9B are viewed, even when the development potential is adjusted so that the toner adhesion amount is constant, if the ratio of the background potential to the development potential is constant, the charging potential It can be understood that the line width of the thin line does not change even when Vd is different. If this ratio is constant, the effect of the development electric field between the exposure unit and the developing roller on the toner adhering to the boundary portion between the exposure unit and the non-exposure unit, and the non-exposure unit and the development roller It is assumed that the effect of the electric field in the background is stable, and as a result, even if the development potential and the background potential change, the toner adhesion area with respect to the area of the exposed part hardly changes.

  As described above, a constant image density can be obtained by adjusting the background potential so that the ratio of the background potential to the development potential (background potential determination coefficient) is constant while securing the development potential so that the toner adhesion amount is constant. It is possible to suppress a change in image quality that the line width of the thin line changes while maintaining the above.

FIG. 10A is a graph of the experimental results showing the correspondence between the background potential and the halftone density when the charging potential Vd is 900 [V], 700 [V], and 500 [V]. . FIG. 10B shows the above experimental results showing the correspondence between the ratio of the background potential to the development potential and the halftone density when the charging potential Vd is 900 [V], 700 [V], and 500 [V]. It is a graph of.
FIG. 10A illustrates a case where the development potential is adjusted so that the toner adhesion amount of the solid image is constant, and the charging potential Vd is obtained when the background potential is a fixed value (for example, 200 [V]) as in the past. It is shown that the halftone density varies depending on the difference. Even in the process control of the present embodiment, the development potential is adjusted so that the toner adhesion amount of the solid image is constant. Therefore, if the background potential is a fixed value, a change in image quality in which the halftone density changes occurs. In particular, in the present embodiment, since the photosensitive member having the characteristic that the residual exposed portion potential Vr gradually increases with time is used, the charging potential Vd is adjusted to gradually increase with time as described above. The Therefore, when the background potential is a fixed value (for example, 200 [V]), the image quality is deteriorated such that the halftone density decreases with time.

  On the other hand, as shown in FIG. 10B, when the development potential is adjusted so that the toner adhesion amount of the solid image is constant, the charging potential Vd is different if the ratio of the background potential to the development potential is constant. However, it can be understood that the halftone density does not change. This is considered to be due to the same reason as in the case of the thin line width described above.

  As described above, a constant image density can be obtained by adjusting the background potential so that the ratio of the background potential to the development potential (background potential determination coefficient) is constant while securing the development potential so that the toner adhesion amount is constant. It is possible to suppress a change in image quality in which the halftone density changes while maintaining the image quality.

  From the experimental results described above, the ratio of the background potential to the development potential, that is, the background potential determination coefficient α is within the range of 0.40 to 0.80, preferably within the range of 0.40 to 0.45. Thus, the above-described image quality change can be suppressed satisfactorily. In the present embodiment, the background potential determination coefficient α is set to 0.4.

  In this way, the background potential Vbg is calculated by multiplying the development potential VbL calculated in S5 by the background potential determination coefficient α according to the above equation (4). However, as described above, if the background potential Vbg is too small, background contamination occurs, and if the background potential Vbg is too large, carrier adhesion occurs. Therefore, if the background potential Vbg deviating from the range in which background contamination and carrier adhesion do not occur is set, a more serious problem than the above-described line width change or halftone density change occurs.

Therefore, in the present embodiment, the following processing is performed so that the background potential Vbg deviating from the specified range in which background contamination and carrier adhesion do not occur is not set. That is, when the background potential Vbg calculated by the above equation (4) is higher than the upper limit value (Vbg _MAX ) of the specified range, the upper limit value Vbg _MAX is calculated as the background potential Vbg and is used for the subsequent processing. use. When the background potential Vbg calculated by the above equation (4) is lower than the lower limit value (Vbg _MIN ) of the specified range, the lower limit value Vbg _MIN is calculated as the background potential Vbg, and the subsequent processing is performed. use.

  Next, the development bias Vb ′ for Vr detection used when detecting the final residual exposure portion potential Vr is calculated from the provisional reference exposure portion potential VL0 ′ calculated in S7 by the above formula (2) ( S9). Further, by using the development bias Vb ′ for Vr detection calculated by the above equation (2) and the background potential Vbg calculated at S8, the target charging potential Vd ′ for Vr detection by the above equation (3) is obtained. Calculate (S9).

Then, the charging bias Vg ′ for detecting Vr is set so that the charging potential becomes the target charging potential Vd ′ for detecting Vr (S10).
Specifically, first, the charging bias is set to a predetermined fixed value (-550 [V] in the present embodiment), and the developing bias is also set to a predetermined fixed value (-350 [in the present embodiment). V]), the surface of the photosensitive member is charged, and the charged potential at this time is detected by the potential sensor 210. If the detection result is within the target range centered on the target charging potential Vd ′ calculated in S9 (in this embodiment, Vd ′ ± 5 [V]), the fixed value (−550 [−5 [V]) used for this measurement is used. V]) is set to the charging bias Vg ′ for Vr detection.
On the other hand, when the detection result is out of the target range, the charging bias fixed value (−550 [V]) and the detection result (charging potential) and the charging bias (pre-process control process) In the present embodiment, −700 [V]) and the charging potential detected by the potential sensor 210 at that time are used to approximate the relationship between the charging bias and the charging potential at the present time by a first-order approximation using the least square method, and an approximate relational expression (Primary approximation formula) is obtained. Then, the charging bias for Vr detection corresponding to the target charging potential Vd ′ for Vr detection is specified from this linear approximation formula. Thereafter, the surface of the photosensitive member is charged again using the Vr detection charging bias specified here, and the charged potential at this time is detected by the potential sensor 210. If this detection result is within the target range, the charging bias for Vr detection specified above is determined as the charging bias Vg ′ for Vr detection. If the detection result is out of the target range, the measurement result at this time is also added to obtain a first-order approximation expression indicating the relationship between the charging bias and the charging potential, and the detection result is within the target range. Repeat the same process until entering.

Here, the range of the charging bias that can be set is often limited depending on the specifications of the charging device 201 used. In the present embodiment, the settable range of the charging bias is limited to a range of −450 [V] or more and −900 [V] or less. Therefore, in this embodiment, when the charging bias Vg ′ for Vr detection determined as described above exceeds the upper limit value (Vg _MAX = −900 [V]) of the setting range of the charging bias, the upper limit value is set. Vg _MAX is set as the charging bias Vg ′. On the other hand, when the charging bias Vg ′ for Vr detection determined as described above is below the lower limit value (Vg _MIN = −450 [V]) of the setting range of the charging bias, the lower limit value Vg _MIN is set as the charging bias. Set as Vg '.

Further, the development bias Vb ′ for Vr detection is corrected and set so that the background potential becomes the background potential Vbg calculated in S8 according to the charging bias Vg ′ for Vr detection set as described above ( S10).
FIG. 11 is a flowchart showing a flow of processing for correcting the developing bias Vb ′ for detecting Vr when the charging bias Vg ′ is set to the charging bias upper limit value Vg _MAX .
FIG. 12 is a flowchart showing a flow of processing for correcting the developing bias Vb ′ for detecting Vr when the charging bias Vg ′ is set to the charging bias lower limit value Vg _MIN .
FIG. 13 shows a flow of processing for correcting the developing bias Vb ′ for detecting Vr when the charging bias Vg ′ is set between the charging bias upper limit value Vg _MAX and the charging bias lower limit value Vg _MIN. It is a flowchart.

When the charging bias Vg ′ is set to the charging bias upper limit value Vg _MAX , as shown in FIG. 11, if the background potential Vbg is set to the upper limit value Vbg _MAX (Yes in S21), the background potential Vbg is set as follows. The value is corrected to the value obtained by the equation (5) (S22).
_{Vbg = Vbg1 = Vbg MAX - (} Vd '[ calculated _{value] -Vg MAX) × β1 ··· (} 5)
The Vd ′ [calculated value] in the equation (5) is the target charging potential Vd ′ for Vr detection calculated in S9 and is distinguished from the charging potential Vd ′ [detected value] detected in S10. It is. Further, β1 in the above formula (5) is a coefficient for making the ratio of the background potential to the development potential constant within the setting range of the charging bias, and is usually set to the same value as the background potential determination coefficient α. Is done.
On the other hand, if the background potential Vbg is set to the lower limit value Vbg _MIN (Yes in S23), the background potential Vbg is not corrected (S24), and the lower limit value Vbg _MIN is set as it is.
On the other hand, if the background potential Vbg is set to the upper limit value Vbg _MAX and the lower limit value Vbg _MIN (No in S23), the background potential Vbg is corrected to a value obtained by the following equation (6) (S25).
Vbg = Vbg2 = Vbg− (Vd ′ [calculated value] −Vg _MAX ) × β1 (6)

Subsequently, when the background potential Vbg is equal to or lower than the lower limit value Vbg _MIN (Yes in S26), the background potential Vbg is re-corrected to the lower limit value Vbg _MIN (S27), and then the development bias Vb ′ for detecting Vr is expressed by the following formula. The value obtained by (7) is set (S28).
Vb ′ = Vg _MAX −Vbg _MIN (7)
On the other hand, when the background potential Vbg is between the upper limit value Vbg _MAX and the lower limit value Vbg _MIN (No in S26), the developing bias Vb ′ for detecting Vr is set to a value obtained by the following equation (8) (S29). ).
Vb ′ = Vg _MAX −Vbg (8)

When the charging bias Vg ′ is set to the charging bias lower limit value Vg _MIN , as shown in FIG. 12, if the background potential Vbg is set to the upper limit value Vbg _MAX (Yes in S31), the background potential Vbg No correction is made (S32), and the upper limit value Vbg _MAX is used as it is.
On the other hand, if the background potential Vbg is set to the lower limit value Vbg _MIN (Yes in S33), the background potential Vbg is corrected to a value obtained by the following equation (9) (S34).
_{Vbg = Vbg3 = Vbg MIN - (} Vd '[ calculated _{value] -Vg MIN) × β2 ··· (} 9)
Β2 in the above formula (5) is a coefficient for making the ratio of the background potential to the development potential constant within the setting range of the charging bias like the above β1, and is usually the same as the background potential determination coefficient α. Set to a value.
On the other hand, if the background potential Vbg is set to the upper limit value Vbg _MAX and the lower limit value Vbg _MIN (No in S33), the background potential Vbg is corrected to a value obtained by the following equation (10) (S35).
Vbg = Vbg4 = Vbg− (Vd ′ [calculated value] −Vg _MIN ) × β2 (10)

Subsequently, when the background potential Vbg is equal to or higher than the upper limit value Vbg _MAX (Yes in S36), the background potential Vbg is re-corrected to the upper limit value Vbg _MAX (S37), and then the development bias Vb ′ for detecting Vr is expressed by the following formula. The value obtained by (11) is set (S38).
Vb ′ = Vg _MIN −Vbg _MAX (11)
On the other hand, when the background potential Vbg is between the upper limit value Vbg _MAX and the lower limit value Vbg _MIN (No in S36), the developing bias Vb ′ for detecting Vr is set to a value obtained by the following equation (12) (S39). ).
Vb ′ = Vg _MIN −Vbg (12)

When the charging bias Vg ′ is set between the upper limit value Vg _MAX and the lower limit value Vg _MIN of the charging bias, as shown in FIG. 13, if the background potential Vbg is set to the upper limit value Vbg _MAX ( (Yes in S41), the background potential Vbg is corrected to a value obtained by the following equation (13) (S42).
Vbg = Vbg5 = Vbg _MAX − (Vd ′ [calculated value] −Vd ′ [detected value]) (13)
On the other hand, if the background potential Vbg is set to the lower limit value Vbg _MIN (Yes in S43), the background potential Vbg is corrected to a value obtained by the following equation (14) (S44).
_{Vbg = Vbg6 = Vbg MIN - (} Vd '[ calculated value] -Vd' [Detection Value) (14)
On the other hand, if the background potential Vbg is set to the upper limit value Vbg _MAX and the lower limit value Vbg _MIN (No in S43), the background potential Vbg is corrected to a value obtained by the following equation (15) (S45).
Vbg = Vbg7 = Vbg− (Vd ′ [calculated value] −Vd ′ [detected value]) (15)
Thereafter, the developing bias Vb ′ for detecting Vr is set to a value obtained by the following equation (16) (S47).
Vb ′ = Vd ′ [detection value] −Vbg (16)

  Next, using the provisional charging bias Vg ′ and development bias Vb ′ for Vr detection set as described above, the same method as in S6, specifically, 1.5 times the basic exposure power LDP0. The photosensitive member surface is exposed with an exposure power LDP ′ of (150%) and the exposure duty set to the maximum value (15). Then, the potential of the electrostatic latent image (exposed portion) formed thereby is detected by the potential sensor 210 as the final residual exposed portion potential (detected residual potential) Vr (S11).

Thereafter, in the present embodiment, from the target charging potential Vd ′ and the residual exposure portion potential Vr, a low exposure amount region in which the change rate of the exposure portion potential on the surface of the photoreceptor with respect to the change in exposure amount is large, FIG. In the graph shown in b), the adjustment exposure portion potential Vpl belonging to the region extending approximately from the center of the graph to its left side is calculated by the following equation (17) (S12).
Vpl = (Vd′−Vr) ÷ 3 + Vr (17)
Then, the provisional charging bias Vg ″ and the developing bias Vb ″ are reset by performing the same processing as the processing from S7 to S10 using the newly detected residual exposure portion potential Vr (13). .

Next, the exposure power for Vpl (pre-reference exposure amount) for obtaining the exposure part potential Vpl for adjustment is specified (S14). However, the adjustment exposure portion potential Vpl of the present embodiment is approximately in the vicinity of 1/3 of the reference exposure portion potential. Therefore, in order to search for the optimum Vpl exposure power in this vicinity, an exposure duty of 5/15, which is 1/3 of the reference exposure amount (exposure duty = 15/15), is used at this time.
In specifying the exposure power for Vpl for obtaining the exposure part potential Vpl for adjustment, the exposure power is 60%, 80%, 100%, 120% of the basic exposure power LDP0, with the exposure duty fixed at 5/15. The electrostatic latent image (exposure portion) is created by sequentially switching to 150%. The charging bias and the developing bias at this time are the provisional charging bias Vg ″ and the developing bias Vb ″ set in S13. The potential of each exposure unit is detected by the potential sensor 210, and the charging potential Vd at this time is also detected by the potential sensor 210. Then, five data sets showing the correspondence relationship between the exposure power corresponding to each exposure portion, the charging potential Vd at that time, and the residual exposure portion potential Vr and each adjustment exposure portion potential Vpl obtained by the above equation (17). Is calculated. Then, from each data set, the relation between the exposure power and the adjustment exposure portion potential Vpl is first-order approximated by the least square method to obtain an approximate relational expression (first-order approximation expression). The exposure power for Vpl for obtaining the adjustment exposure part potential Vpl calculated in the above is specified.

  Thereafter, the surface of the photosensitive member is exposed using the exposure power for Vpl specified here (exposure duty = 5/15), and the potential of the exposed portion at this time is detected by the potential sensor 210. If this detection result is within the target range (within ± 3 [V] of the adjustment exposure portion potential Vpl calculated in S12), the specified Vpl exposure power specified above is used as it is. On the other hand, when the detection result is out of the target range, the specified Vpl exposure power specified above is further adjusted with a predetermined adjustment value, and the photoconductor is used using the adjusted Vpl exposure power. The process of exposing the surface again and detecting the potential of the exposed portion by the potential sensor 210 is repeated until the detection result falls within the target range.

  When the exposure power for Vpl for obtaining the adjustment exposure part potential Vpl is specified in this way, the exposure power for Vpl is then set to the exposure power of 15/15 exposure duty which is the exposure duty of the reference exposure amount. Conversion is performed (S15). In the present embodiment, since the exposure duty used to specify the Vpl exposure power is 1/3 of the exposure duty (15/15) of the reference exposure amount, the exposure power for Vpl specified in S14 is 3 Doubled and converted to exposure power of 15/15 exposure duty.

  Next, the reference exposure power is determined from the converted exposure power obtained by conversion in this way (S16). Here, under the conditions of the present embodiment, it has been previously known by experiments and the like that the relationship between the converted exposure power and the reference exposure power is about 2/3. Therefore, in the present embodiment, a value obtained by multiplying the converted exposure power by 2/3 is determined as the reference exposure power. Note that this converted value (2/3 in the present embodiment) is appropriately set by experiment or the like.

After obtaining the reference exposure power as described above, finally, a correction process for correcting an error between the reference exposure part potential VL0 ′ provisionally determined in S7 and the actual reference exposure part potential VL0 is performed. Do. Specifically, first, an electrostatic latent image (exposure portion) is created with the reference exposure amount (reference exposure power determined in S16, 15/15 exposure duty), and the potential of the exposure portion (reference exposure portion potential VL0). ) Is detected by the potential sensor 210 (S17). The charging bias and the developing bias at this time are the provisional charging bias Vg ″ and the developing bias Vb ″ set in S13. A difference ΔVL between the reference exposure portion potential VL0 detected in this way and the reference exposure portion potential VL0 ′ provisionally determined in S7 is calculated (S18). Then, using the difference ΔVL as a correction value, the provisional charging bias Vg ″ and the developing bias Vb ″ set in S13 are corrected, and the final charging bias Vg and the developing bias Vb are determined (S19). Therefore, the final charging bias Vg is expressed by the following mathematical formula (18), and the final developing bias Vb is expressed by the following mathematical formula (19). However, when the corrected charging bias Vg and developing bias Vb exceed the preset upper and lower limit values, the charging bias Vg and developing bias Vb before correction are used as final values.
Vg = Vg "-[Delta] VL (18)
Vb = Vb ″ −ΔVL (19)

In this embodiment, both the development potential and the background potential are adjusted so that the charging bias Vg is not set to exceed the upper limit value Vg _MAX . Specifically, the ratio of the background potential to the development potential is adjusted to be maintained at the background potential determination coefficient α. By such adjustment, it is possible to suppress changes in image quality such as changes in the line width of thin lines and changes in halftone density while preventing the charging bias Vg from being set exceeding the upper limit value Vg _MAX . However, in this case, since the development potential is set slightly lower, the image density is slightly lowered, and there is a possibility that some image quality changes occur. Therefore, in the case of priority to the maintenance of the image density, the charging bias Vg exceeds the upper limit value Vg _MAX min may be adjusted only background potential. In this case, since the ratio of the background potential to the development potential is slightly changed, there is a possibility that slight changes in image quality such as a change in line width of a thin line and a change in halftone density may occur, but a change in image density can be prevented.

As described above, the printer according to the present embodiment includes the photosensitive member 202 and the charging device 201 as a charging unit that uniformly charges the surface of the photosensitive member 202 with a charging bias such that the surface of the photosensitive member 202 has a target charging potential. A writing device 203 as an exposure unit that forms an electrostatic latent image by exposing the surface of the photosensitive member 202 charged by the charging device 201 with an exposure amount corresponding to the reference exposure amount, and formed on the surface of the photosensitive member 202. A developing device 205 as a developing unit that forms a toner image on the surface of the photosensitive member 202 by attaching toner on a developing roller as a developer carrying member to which a developing bias is applied to the electrostatic latent image formed; And an image forming apparatus that forms an image on the transfer paper 112 by finally transferring the toner image formed on the surface of the photoconductor 202 onto the transfer paper 112 as a recording material. That. This printer includes an image detection device 110 as a toner adhesion amount detection unit for detecting the toner adhesion amount, and a density patch 113 as a predetermined toner pattern on the surface of the photosensitive member 202 by a normal image forming operation at a predetermined timing. Then, the toner adhesion amount of the density patch 113 is detected by the image detection device 110, and based on the detection result, the development potential VbL such that the toner adhesion amount with respect to a predetermined electrostatic latent image becomes the target toner adhesion amount. In order to obtain the above, a control unit 41 is provided as control means for performing process control for adjusting at least one of the charging bias, the reference exposure amount, and the developing bias. Then, the control unit 41 performs process control so that the background potential determination coefficient α, which is the ratio of the background potential Vbg to the development potential VbL, becomes a predetermined target ratio (0.4 in the present embodiment). As a result, as described above, even if the target development potential VbL changes according to environmental changes or changes with time, the ratio of the background potential Vbg to the development potential (background potential determination coefficient α) is set to the target ratio (0.4). Therefore, it is possible to suppress the change in image quality that the line width of the thin line changes.
Further, in the present embodiment, the control unit 41 develops when the background potential Vbg obtained by multiplying the target development potential VbL by the ratio (background potential determination coefficient α) is within a predetermined range. When the process control is performed so that the ratio of the background potential Vbg to the potential VbL becomes the target ratio, and the background potential Vbg is out of the specified range, the background potential is set to a value within the specified range (upper limit value Vbg _MAX or lower limit value). Vbg _MIN ) and process control is performed so that the ratio of the determined background potential Vbg to the development potential VbL becomes the target ratio. As a result, in order to suppress the image quality change in which the line width of the thin line changes, the background potential is out of the specified range, and the problem caused by the background potential being too high (carrier adhesion, half-end edge blurring, etc.) It is possible to prevent the occurrence of a more serious situation in which a problem (soil stain or the like) occurs due to the background potential being too low.
In the present embodiment, the control unit 41 determines in advance the target charging bias determined from the target development potential VbL and the background potential Vbg obtained by multiplying the target development potential VbL by the background potential determination coefficient α. If the charging bias is outside the specified range, the charging bias is adjusted to a value within the specified range (upper limit value Vg _MAX or lower limit value Vg _MIN ), and the ratio of the background potential Vbg after determination to the development potential VbL becomes the target ratio. In this manner, at least one of the reference exposure amount and the development bias is adjusted. Thereby, it is possible to suppress a change in image quality in which the line width of the thin line changes within a setting range of the charging bias.
As described above, when the target charging bias determined from the target development potential VbL and the background potential Vbg obtained by multiplying the target development potential VbL by the background potential determination coefficient α is within a predetermined specified range, Process control is performed so that the ratio of the determined background potential Vbg to the development potential VbL becomes a target ratio. If the target charging bias is not within a predetermined specified range, the charging bias is set to a value within the specified range. And adjusting at least one of the reference exposure amount and the development bias according to the background potential after subtraction after subtracting the difference between the adjusted charging bias and the target charging bias from the background potential and the development potential. Alternatively, process control may be performed. In this case, within the settable range of the charging bias, it is possible to make an adjustment giving priority to maintaining the image density rather than suppressing the image quality change in which the line width of the thin line changes.

FIG. 2 is an explanatory diagram illustrating a schematic configuration of a main part of the printer according to the embodiment. FIG. 2 is an explanatory diagram illustrating a schematic configuration of an image forming unit of the printer. It is a block diagram which shows the control system in connection with process control in embodiment. (A) is explanatory drawing which shows schematic structure of the optical sensor which comprises the image detection apparatus for black, (b) is schematic structure of the optical sensor which comprises the image detection apparatus for other colors (color). It is explanatory drawing shown. It is explanatory drawing which shows the example of arrangement | positioning of the optical sensor 301 and the optical sensor 302. FIG. It is a flowchart which shows the flow of the main processes of the process control in embodiment. 6 is a graph showing a result of actual measurement of toner adhesion amount with respect to development potential when a toner gradation pattern is formed in a high temperature and high humidity environment and a low temperature and low humidity environment. (A) and (b) show that when the charging potential Vd is 900 [V], 700 [V], 500 [V], the background potential is changed to change the vertical line of 1 dot width (the surface movement of the photoconductor 202). It is a graph of the experimental result which shows the correspondence of the ground potential and line width when image-forming the line extended in the direction corresponding to a direction). (A) and (b) show that when the charging potential Vd is 900 [V], 700 [V], and 500 [V], the background potential is changed to change the horizontal potential of 1 dot width (the surface movement direction of the photosensitive member 202). FIG. 6 is a graph of experimental results showing a correspondence relationship between the ground potential and the line width when an image of a line extending in a direction corresponding to a direction perpendicular to the line is formed. (A) is a graph of experimental results showing the correspondence between the background potential and the halftone density when the charging potential Vd is 900 [V], 700 [V], and 500 [V], and (b) 10 is a graph of experimental results showing the correspondence between the ratio of the background potential to the development potential and the halftone density when the charging potential Vd is 900 [V], 700 [V], and 500 [V]. 10 is a flowchart showing a flow of processing for correcting a developing bias Vb ′ for detecting Vr when the charging bias Vg ′ is set to the charging bias upper limit value Vg _MAX . 10 is a flowchart showing a flow of processing for correcting a developing bias Vb ′ for detecting Vr when the charging bias Vg ′ is set to the charging bias lower limit value Vg _MIN . 6 is a flowchart showing a flow of processing for correcting a developing bias Vb ′ for detecting Vr when the charging bias Vg ′ is set between the charging bias upper limit value Vg _MAX and the charging bias lower limit value Vg _MIN . (A) is a graph which shows the relationship between the exposure power of the laser diode (LD) after image formation of a predetermined number of times and each exposure part potential VL in a high temperature and high humidity environment, and (b) is a low temperature and low humidity environment. Below, it is a graph which shows the relationship between the exposure power of LD after each image formation of the same frequency, and each exposure part electric potential VL. 6 is a graph showing the relationship between the number of sheets passing through and the residual exposed portion potential Vr in an image forming apparatus using a specific photoconductor 202. (A)-(c) is a graph which shows the correspondence of the exposure amount of the initial stage with respect to the initial stage photoconductor 202, and exposure part electric potential in 3 environment (normal environment, low temperature low humidity environment, high temperature high humidity environment), ( d) to (f) are graphs showing a correspondence relationship between the exposure amount after printing 5000 sheets on the initial photosensitive body 202 and the exposure portion potential in the three environments, and (g) to (i) are 2000 k in the three environments. 6 is a graph showing a correspondence relationship between an initial exposure amount and an exposed portion potential with respect to the photosensitive member 202 after printing, and (j) to (l) after printing 5000 sheets on the photosensitive member 202 after 2000k printing in three environments. It is a graph which shows the correspondence of the exposure amount and exposure part electric potential.

Explanation of symbols

41 Control Unit 101 Intermediate Transfer Belt 102Y, 102M, 102C, 102K Image Forming Unit 110 Image Detection Device 113 Density Patch 201 Charging Device 202 Photoconductor 202
203 Writing Device 205 Developing Device 210 Potential Sensor 301, 302 Optical Sensor Vbg Background Potential VbL Development Potential Vpl Adjustment Exposure Portion Vr Residual Exposure Portion α α Background Potential Determination Coefficient

Claims (5)

A photoreceptor,
Charging means for uniformly charging the surface of the photoconductor with a charging bias such that the surface of the photoconductor has a target charging potential;
Exposure means for forming an electrostatic latent image by exposing the surface of the photoreceptor charged by the charging means;
A developing means for forming a toner image on the surface of the photosensitive member by attaching the toner on the developer carrying member to which a developing bias is applied to the electrostatic latent image formed on the surface of the photosensitive member;
In an image forming apparatus for forming an image on a recording material by finally transferring the toner image formed on the surface of the photoreceptor onto the recording material,
A toner adhesion amount detecting means for detecting the toner adhesion amount;
At a predetermined timing, a predetermined toner pattern is formed on the surface of the photoreceptor by a normal image forming operation, and the toner adhesion amount of the toner pattern is detected by the toner adhesion amount detection means, and based on the detection result In order to obtain a development potential that is the difference between the potential of the electrostatic latent image portion and the development bias so that the toner adhesion amount with respect to a predetermined electrostatic latent image becomes the target toner adhesion amount, the charging bias, the exposure amount, and the development bias Control means for performing process control to adjust at least one of
It said control means, so that the ratio of the background potential is the difference between the developing bias and the potential of the non-electrostatic latent image portion for development potential is predetermined target ratio, which performs the process control, a predetermined When the background potential obtained by multiplying the development potential by which the toner adhesion amount with respect to the electrostatic latent image becomes the target toner adhesion amount within the predetermined range is obtained, The process control is performed so that the ratio of the background potential becomes the target ratio. When the background potential is out of the specified range, the background potential is determined to be a value within the specified range, and the development potential is determined. the ratio of the background potential after determination and performing the process control such that the target ratio Image forming apparatus. The image forming apparatus according to claim 1 .
The control means is determined from a development potential such that the toner adhesion amount with respect to a predetermined electrostatic latent image becomes a target toner adhesion amount and a background potential obtained by multiplying the development potential by the ratio in the process control. If the target charging bias deviates from a predetermined range, the charging bias is adjusted to a value within the predetermined range, and at least one of the reference exposure amount and the development bias so that the ratio becomes the target ratio. An image forming apparatus characterized by adjusting the angle. The image forming apparatus according to claim 1 .
The control means has a target charging bias determined from a development potential at which a toner adhesion amount with respect to a predetermined electrostatic latent image becomes a target toner adhesion amount and a background potential obtained by multiplying the development potential by the ratio. If the target charge bias is not within the predetermined specified range, the process control is performed so that the ratio is the target ratio. The reference exposure amount and the development bias are adjusted according to the background potential after subtraction after the difference between the adjusted charging bias and the target charging bias is subtracted from the background potential and the development potential. An image forming apparatus that performs the process control so as to adjust at least one of the above. The image forming apparatus according to any one of claims 1 to 3 ,
The ratio is 0.4 or more and 0.8 or less. The image forming apparatus according to claim 4 .
The ratio is 0.4 or more and 0.45 or less.

Images