JP2013190682A - Image forming apparatus and image forming method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that forms images by using toner and an image forming method in such image forming apparatus capable of adjusting density of images to reduce density unevenness of images due to rotational deflection of image carriers, while avoiding complexity in control and suppressing toner consumption and required time.SOLUTION: Density unevenness of an image is detected by image density detection means 52 when rotational positions of image carriers 40Y, C, M, K may be changed, and unevenness in image density caused by developing gap fluctuation components of the image carrier 40Y, C, M, K is extracted on the basis of potential distribution of surface potential detected by potential detection means 56Y, C, M, K when the image is formed and the density unevenness. Image forming means 42Y, C, M, K are operated to suppress the extracted unevenness according to conditions determined by image forming condition determination means 37.

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, a facsimile machine, a plotter, a multifunction machine having at least one of these functions, which forms an image using toner, and image formation in such an image forming apparatus. The present invention relates to an image forming apparatus and an image forming method capable of adjusting the density of the image.

  A so-called electrophotographic image forming apparatus that forms an image using toner is known (see, for example, [Patent Document 1] to [Patent Document 3]). In such an image forming apparatus, the image carrier is uniformly charged by the charging device, a latent image is formed on the image carrier by the exposure device based on the data input corresponding to the image to be formed, and the developing device Thus, toner is attached to the latent image to form an image.

  In recent years, such image forming apparatuses have begun to spread in the printing industry, and the demand for high-speed output and high image quality is rapidly increasing. Among the requirements related to high image quality, there is a strong demand for uniformity of density within a page, that is, uniformity of the density of an image formed on one sheet of recording medium such as paper, and when a user selects an image forming apparatus, It is a judgment criterion. Therefore, it is important to suppress the density unevenness in the page as much as possible.

  Such density unevenness is known to occur due to various factors. For example, uneven charging due to non-uniform charging, exposure unevenness of an exposure apparatus, rotational shake or sensitivity unevenness of an image carrier such as a photoconductor, uneven resistance of a developer carrier such as a developing roller, uneven charging of a toner, transfer roller Transfer irregularities. Among them, density unevenness due to rotational shake and sensitivity unevenness of the image carrier in particular has a short period, and thus periodically occurs in the page and is easy to visually recognize. Therefore, it is particularly important to suppress density unevenness caused by rotational shake and sensitivity unevenness of the image carrier.

This density unevenness will be described below.
The density unevenness caused by the rotational shake of the image carrier will be described. In an image forming apparatus using an electrophotographic system, an image carrier using an electric field generated by a potential difference between the developer carrier and the image carrier. Since an image is formed by adhering toner on the image, if the development gap, which is an interval between them, fluctuates due to the rotational shake of the image carrier, the electric field fluctuates, resulting in density fluctuations and density unevenness.

  Further, for example, density unevenness caused by sensitivity unevenness of the image carrier is as follows. That is, if the sensitivity of the image carrier to exposure varies due to factors such as environmental fluctuations and deterioration over time, even if the exposure is performed at a constant exposure amount, it differs from the light potential after exposure of the image carrier. Therefore, the electric field fluctuates, density fluctuations occur, and density unevenness occurs. In addition, regarding the sensitivity unevenness of the image carrier, it is desirable to avoid this as much as possible because a high-accuracy manufacturing method is used to reduce the sensitivity change.

  In this regard, as a technology for correcting density unevenness, in order to change process conditions such as charging bias, development bias, and exposure conditions based on the density unevenness profile that varies depending on the rotation period of the image carrier and sensitivity unevenness, A method is conceivable in which a detection pattern is formed and correction data for each process condition is created.

As such a method, for example, a method of modulating the developing bias in accordance with the rotation period of the image carrier will be considered. This method uses a rotational position detection sensor that detects the rotational position of the image carrier and a density detection sensor that detects the density of the image. The rotational position detection sensor detects the density unevenness detected by the density detection sensor by the period of the image carrier, and suppresses the detected density unevenness to cancel the electric field fluctuation caused by rotational shake and make the electric field constant. The development bias is periodically changed using a signal as a trigger.
Further, as such a method, for example, a method of modulating not only the developing bias but also the charging bias can be considered.

  However, according to these methods, if the profile is valid, the density unevenness is reduced, but if the profile changes due to factors over time, the effect of reducing the density unevenness is reduced or the density unevenness is increased. It will be allowed to. Therefore, in order to optimize the profile and update the process conditions in a timely manner, it is necessary to create a density unevenness detection pattern, which increases the toner consumption, and cleaning for cleaning the formed image. There may arise problems that the load on the mechanism increases, the time required for image formation and cleaning increases, and the downtime becomes longer. Further, when a plurality of means are modulated, density unevenness is reduced with higher accuracy, but in this case, control can be complicated.

  In addition, although not intended to form a density unevenness detection pattern, a technique for comprehensively reducing striped density unevenness that periodically occurs in an image is known (for example, [See Patent Document 1]. This technique relates to an image forming apparatus of an electrophotographic system or an electrostatic recording system, and the image forming apparatus includes first fluctuation data storage means for storing periodic density fluctuation data of image density in advance. First control means for controlling the image forming conditions based on the density fluctuation data, and the first fluctuation data storage means stores density fluctuation data corresponding to at least one cycle of the developer carrying member. One control means employs a correction method in which any one of the charging voltage, the exposure light quantity, the development voltage, and the transfer voltage is controlled, and the density is corrected by the control means in accordance with the rotation cycle of the image carrier.

  Considering the problem caused by the above-described method, as described above, this problem is caused by a plurality of factors such as density unevenness caused by rotational shake of the image carrier and sensitivity unevenness. It is considered that one of the causes of such a problem is that correction is not performed focusing on each of the above.

  That is, for example, since a change in rotational shake of the image carrier occurs only in a limited time such as when it is attached or detached, the correction data for the change in rotational shake is updated at such time. That's enough. Further, in the rotational shake and sensitivity unevenness of the image carrier, the former often has a larger influence on the density unevenness, so at least the density unevenness due to the rotational shake needs to be suppressed. When the sensitivity change is also added to the correction data, the density unevenness phase may be reversed when the sensitivity changes, and the density unevenness may increase. In addition, in order to avoid complication of control, it is better that the process conditions to be controlled are small.

  The present invention relates to an image forming apparatus for forming an image using toner, and an image forming method in such an image forming apparatus, and the rotational shake and sensitivity unevenness of an image carrier while suppressing toner consumption and required time. An object of the present invention is to provide an image forming apparatus and an image forming method capable of adjusting the image density while avoiding complicated control so as to reduce at least image density unevenness due to rotational shake.

  In order to achieve the above object, the present invention provides an image density detecting means for detecting the density of an image formed by attaching toner to an image carrier, and a surface potential of the image carrier in a state where the toner is attached. A first image forming unit capable of adjusting the density using a first element for forming the image, and the image carrier detected by the image density detecting unit. A first image forming condition determining means for determining a first condition for the first element in order to adjust the density based on density unevenness of the image for at least one circumference of When the rotational position of the image carrier can change, the image density detection means detects density unevenness of the image, and the potential distribution of the surface potential detected by the potential detection means when forming the image The dark Based on the unevenness, the first condition is determined by the first image forming condition determining means so as to extract the unevenness of the image density due to the development gap fluctuation component of the image carrier and to suppress the extracted unevenness. The image forming apparatus performs image formation by determining and operating the first image forming unit according to the first condition.

  The present invention relates to image density detection means for detecting the density of an image formed by attaching toner to an image carrier, and potential detection means for detecting the surface potential of the image carrier in a state where toner is attached. A first image forming means capable of adjusting the density using a first element for forming the image, and at least one circumference of the image carrier detected by the image density detecting means. A first image forming condition determining means for determining a first condition for the first element in order to adjust the density based on the density unevenness of the image, and a rotational position of the image carrier; Can be changed by the image density detecting means, and based on the potential distribution of the surface potential detected by the potential detecting means when the image is formed and the density unevenness. The above The first condition is determined by the first image forming condition determining means so as to extract the unevenness of the image density due to the developing gap fluctuation component of the carrier, and the extracted unevenness is suppressed. Accordingly, since the image forming apparatus performs image formation by operating the first image forming unit, the toner consumption amount and the required time can be reduced by suppressing the image formation frequency and the number of times for determining the first condition. An image forming apparatus capable of adjusting image density and improving in-page density uniformity so as to reduce unevenness of image density due to rotational shake of the image carrier while suppressing complexity of control. Can be provided.

1 is a schematic configuration diagram of an example of an image forming apparatus to which the present invention is applied. FIG. 2 is an enlarged view of an image forming unit and the like provided in the image forming apparatus illustrated in FIG. 1. FIG. 2 is a schematic front sectional view of a developing unit provided in the image forming apparatus shown in FIG. 1. FIG. 2 is a schematic front sectional view of an image density detection unit provided in the image forming apparatus shown in FIG. 1. FIG. 5 is a schematic plan view illustrating an example of an arrangement mode of the image density detection unit illustrated in FIG. 4 and a configuration mode of an image whose density is detected by the image density detection unit. It is the figure which showed the example of density nonuniformity. It is the figure which showed the sensitivity nonuniformity component of the image carrier contained in the density nonuniformity shown in FIG. FIG. 7 is a diagram showing a rotational shake component of the image carrier included in the density unevenness shown in FIG. 6. It is a figure which shows the example of the relationship of the 1st condition produced based on the rotation position detection signal detected by a rotation position detection means, the toner adhesion amount detection signal by an image density detection means, and these signals. FIG. 4 is a schematic control block diagram showing that an image pattern is created based on signals from an image density detection unit and a rotation position detection unit. It is a timing chart which shows the relationship between the signal of an image density detection means, and the signal of a rotation position detection means. It is a flowchart which shows the outline of the example of control for suppressing density nonuniformity. It is a flowchart which shows the outline of the other example of control for suppressing density nonuniformity.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a schematic diagram of an image forming apparatus according to the present embodiment, and FIG. 2 is a schematic configuration diagram of an image forming unit and the like provided in the image forming apparatus.

  As shown in FIG. 1, the image forming apparatus 10 includes an image forming unit 14 having four process units 36 </ b> Y, 36 </ b> C, 36 </ b> M, and 36 </ b> K for forming an image on a recording paper 12 as a recording medium, and an image forming unit 14. A paper feeding device 16 that supplies recording paper, a scanner 18 that reads a document image, and an automatic document feeder 20 that automatically feeds the document to the scanner 18 are provided.

  The image forming apparatus 10 also includes a transfer unit 26 serving as a transfer unit provided with an endless intermediate transfer belt 24 serving as a transfer body, and an optical writing unit serving as an exposure unit positioned above the image forming unit 14 in the main body 22. 38.

  The image forming apparatus 10 also conveys the recording paper 12 and transfers the toner image carried on the intermediate transfer belt 24 to the recording paper 12 at a secondary transfer position N that is a nip portion with the intermediate transfer belt 24. A transfer belt 46 serving as a transfer transfer belt serving as a secondary transfer unit, and a pair of registration rollers 44 for feeding the recording paper 12 supplied from the paper feeding device 16 to the secondary transfer position N at a predetermined timing.

  The image forming apparatus 10 also passes a fixing unit 48 that fixes the toner image on the recording paper 12 that has been transported by the transport belt 46 that has passed the secondary transfer position N and carries the toner image, and the fixing unit 48. And a pair of paper discharge rollers 50 for discharging the recording paper 12 on which the toner image is fixed to the outside of the main body 22.

  The image forming apparatus 10 also detects image toner density on the intermediate transfer belt 24 and detects density of the toner image, which is an image on the intermediate transfer belt 24, in order to detect density unevenness of the image. The toner adhesion amount detection sensor 52 serving as density unevenness detection means, and a control unit 37 as control means equipped with a CPU (not shown) and a non-volatile memory and a volatile memory.

  As shown in FIG. 2, each of the process units 36Y, 36C, 36M, and 36K includes drum-shaped photoconductors 40Y, 40C, 40M, and 40K as image carriers that rotate counterclockwise in the drawing, and photoconductors 40Y, 40C. , 40M, 40K, and the rotational positions of the charging devices 43Y, 43C, 43M, 43K and the photosensitive members 40Y, 40C, 40M, 40K, which are provided along the rotational direction, in other words, the rotational position detecting means for detecting the phase. Photointerrupters 35Y, 35C, 35M, and 35K as image carrier rotation position detecting means, and surface potential sensors 56Y, 56C, and 56M as potential detecting means for detecting the surface potentials of the photoconductors 40Y, 40C, 40M, and 40K. 56K, developing devices 42Y, 42C, 42M, and 42K as developing means, and the transfer unit 26. The primary transfer roller 34Y as a primary transfer means, 34C, 34M, has a 34K, to form yellow, cyan, magenta, color toner images of black.

  The developing devices 42Y, 42C, 42M, and 42K have the same configuration, although the colors of the toners used are different. Accordingly, the developing devices 42Y, 42C, 42M, and 42K are illustrated as the developing device 42 in FIG. 3, and the configuration thereof will be described with reference to FIG. In the figure, the photoconductors 40Y, 40C, 40M, and 40K are denoted by reference numeral 40.

This figure is a schematic view of the developing device 42.
The developing device 42 includes a developing roller 54 as a single developer carrier, a stirring screw 60 as a developer stirring means, a supply screw 62, three screws as recovery screws 64, and a development on the developing roller 54. A doctor blade (not shown) that regulates the height of the agent, a developer container 58 containing these components and containing a powdery two-component developer 66 containing a magnetic carrier and magnetic or nonmagnetic toner, and a stirring screw A toner replenishing section (not shown) for replenishing toner into the developing container 58 from an opening (not shown) formed in the developing container 58 at the upper portion 60.

  The developing roller 54 is disposed opposite to the photoreceptor 40 with a developing gap g that is a certain distance. The stirring screw 60, the supply screw 62, and the recovery screw 64 are provided in parallel to the developing roller 54.

  The stirring screw 60 moves to the end in the front of the figure while stirring the developer 66 and transports it to the supply screw 62 through an opening (not shown) provided in the developing container 58. The developer 66 is supplied to the developing roller 54 while being agitated and conveyed by the supply screw 62.

  The height of the developer 66 supplied to the developing roller 54, in other words, the layer thickness is regulated by the doctor blade, and the developer 66 comes into contact with the photosensitive member 40 at the developing nip facing the photosensitive member 40 to adhere toner to the latent image portion. Development is performed to form an image on the photoreceptor 40. When the toner concentration in the developer 66 decreases, the toner is replenished into the developing container 58 from the toner replenishing portion and stirred by the stirring screw 60.

  In this embodiment, a forward one-stage developing method in which one developing roller 54 rotates in the same direction as the photoreceptor 40 is used. However, the developing device 42 is not limited to this method, and a plurality of developing rollers 54 are arranged. The multistage developing device may be used. Further, although the two-component developer is used for the developer 66, the developer is not limited to this, and may be a one-component developer.

  The photo interrupters 35Y, 35C, 35M, and 35K shown in FIG. 2 can employ, for example, the configuration disclosed in FIG. In this embodiment, photointerrupters 35Y, 35C, 35M, and 35K are used as the means for detecting the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K. If it detects a rotation position, it will not be restricted to this structure.

  The surface potential sensors 56Y, 56C, 56M, and 56K are supplied with toner by the potentials of the electrostatic latent images on the photoreceptors 40Y, 40C, 40M, and 40K written by the optical writing unit 38, that is, the developing devices 42Y, 42C, 42M, and 42K. The surface potential of the photoreceptors 40Y, 40C, 40M, and 40K before being attached and developed is detected.

  As will be described later, the detected surface potential is used to control the developing bias of the developing devices 42Y, 42C, 42M, and 42K, as well as the charging bias of the charging devices 43Y, 43C, 43M, and 43K, and the optical writing unit 38. It can be fed back to process conditions such as laser power and used to maintain image density stability.

  The transfer unit 26 includes a drive roller 28, a secondary transfer backup roller 30, and a driven roller 32 that are rotationally driven by drive means (not shown) as a plurality of support rollers that support the intermediate transfer belt 24, and a process unit. The primary transfer rollers 34Y, 34C, 34M, and 34K provided in the respective 36Y, 36C, 36M, and 36K are also provided as support rollers around which the intermediate transfer belt 24 is wound.

  The intermediate transfer belt 24 is made of a material in which carbon powder for adjusting electric resistance is dispersed in a polyimide resin with little elongation. The intermediate transfer belt 24 is moved endlessly in the clockwise direction in the drawing by the rotation of the driving roller 28.

  The optical writing unit 38 drives four semiconductor lasers (not shown) by a laser control unit (not shown) based on the image information, and is uniformly charged in the dark by the charging devices 43Y, 43C, 43M, and 43K. Four writing lights for irradiating each of 40Y, 40C, 40M, and 40K are emitted. The optical writing unit 38 scans each of the photoconductors 40Y, 40C, 40M, and 40K in the dark with this writing light, and Y, C, M, and 40K on the surfaces of the photoconductors 40Y, 40C, 40M, and 40K. Write an electrostatic latent image for K. Thus, the optical writing unit 38 functions as an optical writing unit that is a writing unit that exposes the photoreceptors 40Y, 40C, 40M, and 40K to write an electrostatic latent image.

  In the present embodiment, the optical writing unit 38 performs optical scanning by deflecting laser light emitted from a semiconductor laser (not shown) by a polygon mirror (not shown) and reflecting the laser light through a reflection mirror (not shown) or passing through an optical lens. Something is used. The optical writing unit 38 may be replaced with an optical scanning unit that performs optical scanning with an LED array.

The paper feeding device 16 has a paper feeding tray 1 indicated by reference numeral 16a in FIG. 1 and a paper feeding tray 2 indicated by reference numeral 16b.
A conveyance path of the recording paper 12 in the image forming apparatus 10 is indicated by a one-dot chain line in FIG.

The toner adhesion amount detection sensor 52 is disposed on the front side of the secondary transfer position N in the rotation direction of the intermediate transfer belt 24. The toner adhesion amount detection sensor 52 functions as a toner image detection sensor that detects a toner image on the intermediate transfer belt 24.
FIG. 4 shows a schematic diagram of the toner adhesion amount detection sensor 52.

  4A shows a configuration of a black toner adhesion amount detection sensor 52A as the toner adhesion amount detection sensor 52, and FIG. 4B shows a configuration of a color toner adhesion amount detection sensor 52B as the toner adhesion amount detection sensor 52. Is shown. The black toner adhesion amount detection sensor 52A substantially functions as a displacement detection sensor that detects the position of the toner image on the intermediate transfer belt 24, and the color toner adhesion amount detection sensor 52B is a toner on the intermediate transfer belt 24. It functions as a toner adhesion amount detection sensor for detecting the adhesion amount and detecting the image density.

  As shown in FIG. 4A, the black toner adhesion amount detection sensor 52A includes a light emitting element 52A-1 made of a light emitting diode (LED) and the like, and a light receiving element 52A-2 that receives specularly reflected light. Yes. The light emitting element 52A-1 irradiates light onto the intermediate transfer belt 24, and this irradiation light is reflected by the intermediate transfer belt 24 or the toner image surface. The light receiving element 52A-2 receives regular reflected light of the reflected light.

  As shown in FIG. 4B, the color toner adhesion amount detection sensor 52B includes a light emitting element 52B-1 made of a light emitting diode (LED), a light receiving element 52B-2 that receives specularly reflected light, and diffuse reflected light. A light receiving element 52B-3 for receiving the light. As in the case of the black toner adhesion amount detection sensor 52A, the light emitting element 52B-1 irradiates light onto the intermediate transfer belt 24, and this irradiation light is reflected by the surface of the intermediate transfer belt 24 or the toner image surface.

  The regular reflection light receiving element 52B-2 receives regular reflection light of the reflected light, and the diffuse reflection light reception element 52B-3 receives diffuse reflection light of the reflected light. In the present embodiment, a GaAs infrared light emitting diode having a peak wavelength of emitted light of 950 nm is used as the light emitting element 52B-1, and the peak light receiving sensitivity is 800 nm as the light receiving elements 52B-2 and 52B-3. Although the Si phototransistor or the like is used, the peak wavelength and the peak light receiving sensitivity may be different from these.

  The black toner adhesion amount detection sensor 52A and the color toner adhesion amount detection sensor 52B are opposed to each other with a detection distance of about 5 mm between the belt surface of the intermediate transfer belt 24 which is a detection target. It is arranged. In the present embodiment, a toner adhesion amount detection sensor 52 is provided in the vicinity of the intermediate transfer belt 24, and image forming conditions are determined based on the toner adhesion amount on the intermediate transfer belt 24, and based on the toner adhesion position on the intermediate transfer belt 24. However, the toner adhesion amount detection sensor 52 may be disposed so as to face the photoreceptors 40Y, 40C, 40M, and 40K, or may be disposed so as to face the conveyance belt 46 and the like. Then, the recording paper 12 having the image transferred from the intermediate transfer belt 24 may be opposed to the recording paper 12.

  In the case where the toner adhesion amount detection sensor 52 is disposed so as to face the photoconductors 40Y, 40C, 40M, and 40K, in the rotation direction of the photoconductors 40Y, 40C, 40M, and 40K, It faces the photoconductors 40Y, 40C, 40M, and 40K at a position upstream of the transfer position.

  The output from the toner adhesion amount detection sensor 52 is converted into the toner adhesion amount by the adhesion amount conversion algorithm in the control unit 37, the toner adhesion amount is recognized, and the image density is stored in the nonvolatile memory or the volatile memory provided in the control unit 37. Is remembered as In this respect, the control unit 37 functions as an image density storage unit. The control unit 37 functioning as an image density storage unit stores the image density as time series data. Since the adhesion amount conversion algorithm is the same as that of the prior art, a description thereof will be omitted.

  In addition to the non-volatile memory or volatile memory provided in the control unit 37, the output of each sensor such as the surface potential sensors 56Y, 56C, 56M, and 56K, the photo interrupters 35Y, 35C, 35M, and 35K, and correction data, Various information related to the control result is stored. The control unit 37 functions as surface potential storage means in that it stores the surface potential detected by the surface potential sensors 56Y, 56C, 56M, and 56K, and the photoconductor detected by the photo interrupters 35Y, 35C, 35M, and 35K. It functions as a rotational position storage means in that the rotational positions of 40Y, 40C, 40M, and 40K are stored. The control unit 37 functioning as surface potential storage means stores the surface potential as time series data.

  In the image forming apparatus 10 configured as described above, the electrostatic latent images written on the photoreceptors 40Y, 40M, 40C, and 40K after charging by the charging devices 43Y, 43C, 43M, and 43K are developed by the developing devices 42Y, 42C, and 42C, respectively. The toner in the developer existing in 42M and 42K adheres onto the photoreceptors 40Y, 40M, 40C, and 40K by electrostatic adhesion and is developed.

  Thereafter, the primary transfer rollers 34Y, 34C, 34M, and 34K sequentially superimpose toner images on the intermediate transfer belt 24 from the photoreceptors 40Y, 40M, 40C, and 40K. The belt 24 is transported as the belt 24 moves, passes through a detection position by the toner adhesion amount detection sensor 52, and reaches a secondary transfer position N.

  The recording paper 12 is sent to the secondary transfer position N by a registration roller pair 44 at a predetermined timing, and each color component image superimposed on the intermediate transfer belt 24, that is, a toner image of four color components is being transferred collectively. Then, it is conveyed by the conveyor belt 46. Thereafter, the recording paper 12 passes through the fixing unit 48, the toner image is fixed to become a color print image, and is discharged out of the apparatus by the discharge roller pair 50.

  In such an image forming apparatus 10, in order to improve the image quality, a so-called pattern image is formed, and the density of the image to be formed is adjusted by user designation using the image density of the formed pattern image. ing.

  As shown in FIG. 5, the pattern image is formed so as to be a shadow portion where the image density is high for each color of yellow, cyan, magenta, and black, which is a solid image in this embodiment. This is because the higher the density of the pattern image, the easier it is to detect fluctuations in the image density, and the solid image is typical as the pattern image of high density. The pattern image is a solid image in this embodiment, but may be an image having a lower density as long as a change in image density is detected.

  The pattern image is formed so as to be a long band pattern in the sub-scanning direction corresponding to the left-right direction in the drawing, that is, the direction along the rotation direction of the photoconductors 40Y, 40C, 40M, and 40K. The length of the pattern image in the sub-scanning direction is at least one circumference of the photoconductors 40Y, 40C, 40M, and 40K. In this embodiment, the length is 3 circumferences.

  This is performed so that the adjustment of the image density in the image forming apparatus 10 suppresses the unevenness of the image density based on the fluctuation of the development gap that is the distance between the photoconductors 40Y, 40C, 40M, and 40K and the developing roller 54. It is for doing so.

  This point will be described in more detail. One of the causes of the development gap fluctuation is the rotational shake of the photoconductors 40Y, 40C, 40M, and 40K. The cause of this rotational shake is, for example, the rotation center position of the photoconductors 40Y, 40C, 40M, and 40K. Eccentricity is mentioned. Therefore, the unevenness of the image density based on the change in the development gap includes a rotation fluctuation component that is a component generated according to the rotation cycle of the photoconductors 40Y, 40C, 40M, and 40K. In order to detect this component, the length of the pattern image in the sub-scanning direction requires at least one circumference of the photoconductors 40Y, 40C, 40M, and 40K.

  In order to detect image density unevenness based on fluctuations in the development gap, the photoreceptors 40Y, 40C are detected by detecting the surface potential of the photoreceptors 40Y, 40C, 40M, 40K during pattern image formation, as will be described later. , 40M, 40K sensitivity unevenness needs to be detected. For this reason as well, the length of the pattern image in the sub-scanning direction requires at least one circumference of the photoconductors 40Y, 40C, 40M, and 40K.

  In FIG. 6A, the solid band patterns of the respective colors are formed at the same position in the main scanning direction corresponding to the vertical direction in the figure, that is, in the direction orthogonal to the sub-scanning direction. This position coincides with the detection area of the toner adhesion amount detection sensor 52 in the main scanning direction. This position is the central portion in the main scanning direction in FIG. 5A, but is not limited to this and may be an end portion in the main scanning direction.

  In FIG. 5B, the solid band patterns of the respective colors are formed at different positions in the main scanning direction. This position coincides with the detection area of each toner adhesion amount detection sensor 52 in the main scanning direction.

Forming an image pattern as shown in FIG. 5A has an advantage that only one toner adhesion amount detection sensor 52 for detecting the image density of the image pattern is required.
When an image pattern is formed as shown in FIG. 6B, the image pattern of each color is formed so as to overlap in the sub-scanning direction, so that the time required to complete the detection of the image density can be shortened. There is.

  As already described, the toner adhesion amount detection sensor 52 is provided for each of the photoreceptors 40Y, 40C, 40M, and 40K, and the density of the image formed on the photoreceptors 40Y, 40C, 40M, and 40K is determined. The detection may be performed, and in this way, the influence due to the running fluctuation of the intermediate transfer belt 24 is avoided. Further, as described above, the toner adhesion amount detection sensor 52 is provided so as to face the recording paper 12 to which the image is transferred from the intermediate transfer belt 24, and detects the density of the image formed on the recording paper 12. In this case, the influence of the running fluctuation of the recording paper 12 can be avoided.

  In order to detect the above-described components included in the unevenness of the image density, image forming conditions when forming a pattern image, specifically, an element for forming an image, that is, for example, in the charging devices 43Y, 43C, 43M, and 43K Elements such as charging conditions, exposure conditions in the optical writing unit 38, in other words, writing conditions, developing conditions in the developing devices 42Y, 42C, 42M, and 42K, and transfer conditions in the primary transfer rollers 34Y, 34C, 34M, and 34K Is kept constant so that the concentration is high, that is, solid here.

  The charging condition includes a charging bias, the writing condition includes the intensity of writing light, the developing condition includes a developing bias, and the transferring condition includes a transfer bias.

  The charging devices 43Y, 43C, 43M, 43K, the optical writing unit 38, the developing devices 42Y, 42C, 42M, 42K, the primary transfer rollers 34Y, 34C, 34M, 34K, etc. It functions as a pattern forming means (see FIG. 10) as an image pattern creating means responsible for an image forming process of a series of electrophotographic image forming apparatuses such as charging and exposure.

  If there is no change in the development gap, the image density becomes uniform when a solid image is formed with the image forming conditions kept constant. However, even if a solid image is formed while maintaining the image forming conditions constant, as described above, the image density actually fluctuates due to variations in the development gap and the like.

  This variation in image density is detected by detecting the image density of a solid image that is a belt-like pattern long in the sub-scanning direction by the toner adhesion amount detection sensor 52. Specifically, the detection signal of the toner adhesion amount detection sensor 52 is input to the control unit 37 as time series data, and the control unit 37 recognizes the toner adhesion amount in time series, and functions as an image density storage unit. And stored as time-series image density.

  Based on the signals from the photointerrupters 35Y, 35C, 35M, and 35K, the control unit 37 that functions as an image density storage unit associates the image density with the phases of the photoconductors 40Y, 40C, 40M, and 40K. By performing the averaging process at the rotation cycles of 40C, 40M, and 40K, the image density associated with the phases of the photoconductors 40Y, 40C, 40M, and 40K is acquired and stored (corresponding to f (t) described later). ).

  As already described, the image density varies not only due to the variation in the development gap, but also due to the sensitivity unevenness of the photoconductors 40Y, 40C, 40M, and 40K. That is, when the sensitivity of the photoreceptors 40Y, 40C, 40M, and 40K with respect to exposure varies due to factors such as environmental fluctuations and deterioration with time, the photoreceptors 40Y, 40C, 40M, Since there is a difference in the bright potential which is the potential after 40K exposure, the electric field fluctuates, density fluctuations occur, and density unevenness occurs. Regarding the sensitivity unevenness of the photoconductors 40Y, 40C, 40M, and 40K, manufacturing the photoconductors 40Y, 40C, 40M, and 40K using a high-precision manufacturing method in order to reduce the sensitivity change increases the cost. It is desirable to avoid as much as possible.

  Therefore, in the image forming apparatus 10, such sensitivity unevenness is caused by the electrostatic potential images on the photoreceptors 40Y, 40C, 40M, and 40K written by the optical writing unit 38 by the surface potential sensors 56Y, 56C, 56M, and 56K. Detection is performed by detecting the potential, that is, the surface potential of the photoreceptors 40Y, 40C, 40M, and 40K before the toner is attached and developed by the developing devices 42Y, 42C, 42M, and 42K.

  Specifically, the detection signals of the surface potential sensors 56Y, 56C, 56M, and 56K are input to the control unit 37 as time series data, and the control unit 37 recognizes the surface potential in time series, and serves as surface potential storage means. Is stored as a time-series surface potential.

  Based on the signals from the photo interrupters 35Y, 35C, 35M, and 35K, the control unit 37 that functions as a surface potential storage unit associates the surface potential with the phase of the photoconductors 40Y, 40C, 40M, and 40K, and By performing the averaging process at the rotation cycles of 40C, 40M, and 40K, the surface potential associated with the phases of the photoconductors 40Y, 40C, 40M, and 40K is acquired and stored (corresponding to Vout (t) described later) ).

  As described above, the image density depends on the fluctuation of the development gap and the sensitivity unevenness of the photoconductors 40Y, 40C, 40M, and 40K. Therefore, it is considered that the density unevenness of the image can be grasped when formed by superimposing these.

This was confirmed by the following experiment using the average processing described above.
6 to 8 show data acquired by such an experiment.
The diameter of the photoreceptor used in this experiment is φ100 mm, the process linear velocity is 440 mm / s, the charging / developing / LD power is −700 V and −500 V, respectively, and the maximum emission time per dot is 70%. I created a pattern. Under these conditions, density unevenness was measured for different photoreceptors A, B, and C.

FIG. 6 shows that the shape of density unevenness varies depending on the photoconductor.
Using the potential sensor output at the time of image pattern formation for density unevenness measurement shown in FIG. 6, the shape of the density unevenness obtained by the measurement was decomposed into a sensitivity unevenness component and a rotational shake component. The results are as shown in FIGS. 7 and 8, respectively.

  FIG. 7 shows the density unevenness due to the photoreceptor sensitivity unevenness, and an appropriate gain (corresponding to adjustment gain 1: A described later) is superimposed from the potential sensor output at the time of forming a belt-like pattern with an image density of 100%. This is converted to a variation in the density unevenness toner adhesion amount sensor output of the photoconductor cycle.

  FIG. 8 shows density unevenness due to rotational shake of the photoconductor, which is calculated from the measurement data shown in FIG. 6 and the data shown in FIG. 7 (corresponding to fg (t) described later). Since this component is determined by the physical positional relationship between the photoconductor and the developing roller, it has been confirmed by the inventors' experiments that the phase does not vary with the environment and time.

  Comparing FIG. 8 and FIG. 6, it can be seen that the waveforms of the photoconductors A, B, and C are almost the same. That is, it can be seen that the photosensitive member rotational shake is the main factor of density unevenness. Furthermore, although the photosensitive member sensitivity unevenness component shown in FIG. 7 is a factor of density unevenness, it can be said that the influence thereof is small compared with the photosensitive member rotational shake.

In response to this result, the inventors
1. Concentration unevenness due to rotational shake is dominant,
2. A correction technology that reduces density unevenness that occurs in the rotation cycle of the image carrier using the property that the rotation shake component does not change with the environment and time, that is, “Correction data for the photoconductor cycle is calculated from the rotation shake component of the photoconductor. This led to the development of a “control system to generate”.

  In this control method, if the rotational shake component is calculated at the time of arrival, the control effect is maintained unless the state of the photoconductor changes at the time of attachment / detachment / exchange. That is, if a control table that eliminates the influence on the image density due to sensitivity unevenness at the time of such attachment / detachment or the like is generated, there is no need to create a control table other than during such attachment / detachment.

  As described above, elements for forming an image include charging conditions, exposure conditions, development conditions, and transfer conditions. In the present embodiment, the developing condition is the first element that is the object to be controlled by this control method, and the first image forming unit that can adjust the image density using this is used as the developing devices 42Y, 42C, 42M, and 42K. And

  The development condition is selected as the first element because it has higher sensitivity to the adjustment of the image density than the other elements, but the exposure condition is also relatively high, so this is the development condition. Alternatively, it may be selected as a parameter as the first element together with development conditions. In this regard, the first image forming means is the developing devices 42Y, 42C, 42M, 42K and / or the optical writing unit 38.

  In performing such control, the control unit 37 determines the image density based on the density unevenness of the pattern image for at least one circumference of the photoreceptors 40Y, 40C, 40M, and 40K detected by the toner adhesion amount detection sensor 52. Therefore, the image forming condition determining unit functions as a first image forming condition determining unit that determines a specific first condition for the developing condition.

  The control unit 37 functioning as the first image forming condition determining unit detects density unevenness of the pattern image by the toner adhesion amount detection sensor 52 when the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K can be changed. Then, based on the potential distribution of the surface potential detected by the surface potential sensors 56Y, 56C, 56M, and 56K when the pattern image is formed and the density unevenness, the photoreceptors 40Y and 40C included in the density unevenness. , 40M, and 40K, the first condition is determined so as to extract the unevenness of the image density caused by the rotational fluctuation component constituting the development gap fluctuation component, and to suppress the extracted unevenness.

  The potential distribution of the surface potential for at least one circumference of the photoreceptors 40Y, 40C, 40M, and 40K detected by the surface potential sensors 56Y, 56C, 56M, and 56K is detected by the toner adhesion amount detection sensor 52 in the sub-scanning direction. It matches with the area where the pattern image to be formed is formed.

  The control unit 37 functioning as the first image forming condition determining unit acquires the potential distribution for the region exposed to form the pattern image, and determines the first condition by calculation using the potential distribution. To do.

  The development condition that is the first condition is a development bias. It should be noted that if the image density can be adjusted without using the developing bias, this may be used as the developing condition. The first condition when the exposure condition is the first element can be the exposure intensity, in other words, the exposure power.

  The developing devices 42Y, 42C, 42M, and 42K operate according to the first condition determined in this way when forming an image. This operation is controlled by the control unit 37. In this regard, the control unit 37 functions as a first control unit.

  Here, the time when the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K can be changed is at least one of when the photoconductors 40Y, 40C, 40M, and 40K are initially attached, replaced, and detached. When the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K change, the pattern of density unevenness caused by the change in the development gap, such as the waveform shown in FIG. 8, changes. This is because it is necessary to change the profile which is the control table, here, the development conditions.

  In other words, determining the image forming conditions, in other words, creating / updating the control table at the initial setting immediately after the image carrier is set, at the time of replacement, at the time of detachment, etc., is performed by mechanically removing the image carrier. This is because there is a high possibility that the occurrence state of image density unevenness in the photoconductor cycle will change. Another reason is that the positional relationship with the installed photoconductor home position sensor, here the photo interrupters 35Y, 35C, 35M, and 35K, is shifted.

  When an image carrier is initially set for which no control table is originally created, it is necessary to create a control table for performing a series of correction controls. At the time of exchanging the photoconductor, the new photoconductor has a difference in the flare characteristic and the photosensitivity characteristic unevenness with respect to the photoconductor used so far. Therefore, it is necessary to recreate a control table corresponding to the new photoconductor. In addition, even when the photoconductor is simply detached for maintenance, there is a possibility that a change in the attachment state of the photoconductor due to the removal of the photoconductor, for example, a change in the deviation between the photoconductor shaft and the rotation shaft may occur. Since the positional relationship between the position of the photoconductor non-uniformity of the flare characteristic and the photosensitivity characteristic and the photoconductor home position sensor is shifted, it is necessary to re-create the control table. For this reason, it is necessary to determine the image forming conditions immediately after the image carrier is set, in other words, to create / update the control table.

  However, as described above, the density of the image is not limited to the change in the development gap, but the environmental condition in the main body 22 is changed when the image forming apparatus 10 is used when the image is formed a certain number of times. The variation also occurs due to the sensitivity unevenness of the photoconductors 40Y, 40C, 40M, and 40K caused by, for example, when the variation occurs. That is, for example, when the sensitivity of the photoconductors 40Y, 40C, 40M, and 40K with respect to exposure varies due to factors such as deterioration over time and environmental fluctuations, the photoconductors 40Y, 40C, Since there is a difference in the bright potential that is the potential after exposure at 40M and 40K, the electric field fluctuates, density fluctuation occurs, and density unevenness occurs.

  In this regard, when the image formation is performed a predetermined number of times after the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K can be changed, the use environment of the image forming apparatus 10 changes, and so on. The first condition is determined by detecting the surface potential of the photoconductors 40Y, 40C, 40M, and 40K with the surface potential sensors 56Y, 56C, 56M, and 56K at a timing such as when the environmental conditions in the lens 22 fluctuate. By updating, it is possible to suppress density unevenness due to fluctuations in sensitivity unevenness. The detection of the surface potential, etc. should be performed at this appropriate timing, such as when a user-specified image is not being formed, and a pattern image is formed in the same manner as described above. Is possible. Alternatively, the first condition may be updated using an image formed by the user designation when the image includes a uniform high density image equal to or longer than the photosensitive member cycle.

  FIG. 9 shows a rotation position detection signal detected by the photo interrupters 35Y, 35C, 35M, and 35K, a toner adhesion amount detection signal by the toner adhesion amount detection sensor 52, and a control that is an image forming condition created based on these signals. An example of a table relationship is shown. This figure shows signals for two rotations of the photoconductors 40Y, 40C, 40M, and 40K.

The first condition is shown as the determined image forming condition in FIG.
Further, the density unevenness of the pattern image is shown as a toner adhesion amount detection signal in FIG.

  As shown in the figure, the toner adhesion amount detection signal fluctuates at the same cycle as that of the rotational position detection signal. In accordance with this, the calculation and determination of the first condition by the control unit 37 functioning as the first image forming condition determining means, and the operations of the developing devices 42Y, 42C, 42M, and 42K according to the first condition This is performed in synchronization with the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K detected by the photo interrupters 35Y, 35C, 35M, and 35K.

  As can be seen from the figure, the first condition is created as time series data having a waveform that cancels density unevenness, in other words, cancels out the density unevenness. For this reason, the control table, which is an image forming condition, is determined so as to have an opposite phase to the toner adhesion amount detection signal.

  Here, the development bias and the exposure power, which are image density control parameters that can be used as the first condition, may have a negative sign, or the amount of adhesion may decrease as the absolute value increases. It may not be appropriate to express "", but this means that a control table is created in a direction to cancel the adhesion amount fluctuation indicated by the toner adhesion amount detection signal. In this case, it is expressed as “anti-phase”.

  The gain at which the control table is determined, that is, the change amount of the control table with respect to the change amount [V] of the toner adhesion amount detection signal (for example, adjustment gain 2: B described later) Equivalent) is calculated from theoretical values in principle, but when installed on actual machines, it is assumed that there is a high probability that actual machines will be verified based on the theoretical values and ultimately determined from experimental data. .

  A control table (eg, corresponding to VB (t) described later) determined with the gain determined in this manner has a timing relationship shown in FIG. 9, for example, with the rotational position detection signal. In the example shown in the figure, the head of the control table is the time when the rotational position detection signal is generated.

  Here, since this control table is a development bias control table, it is necessary to determine the application timing of the control table in consideration of the distance between the development nip and the toner adhesion amount detection sensor 52, that is, the movement distance of the toner image. If this distance is exactly an integral multiple of the photoreceptor circumference, the control table may be applied from the beginning in accordance with the timing of the rotational position detection signal. When such a distance deviates from an integral multiple of the photoreceptor circumference, the control table may be applied with the timing shifted by the deviation distance. Similarly, in the case of an exposure power control table, the control table is applied in consideration of the distance between the exposure position and the toner adhesion amount detection sensor 52.

  The formation of the image pattern for determining the first condition is performed based on the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K detected by the photo interrupters 35Y, 35C, 35M, and 35K. In the example shown in the figure, the image pattern is formed so that the head position of the image pattern in the sub-scanning direction is synchronized with the rising timing of the rotation position detection signal.

  In order to enable the formation of an image pattern at this timing, as shown in FIG. 10, the control unit 37 rotates the photoconductors 40Y, 40C, 40M, and 40K detected by the photo interrupters 35Y, 35C, 35M, and 35K. A detection signal related to the position is input, and the detection signal is transmitted to the pattern forming unit via the control unit 37. The pattern forming unit forms an image pattern based on the input detection signal.

  As shown in the figure, a detection signal related to the density of the pattern image detected by the toner adhesion amount detection sensor 52 is input to the control unit 37. By inputting these detection signals, the relationship between the density unevenness information detected by the toner adhesion amount detection sensor 52 and the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K detected by the photo interrupters 35Y, 35C, 35M, and 35K is as follows. For example, it is obtained as shown in FIG.

  Note that the CPU of the control unit 37 calculates the image pattern acquired by the toner adhesion amount detection sensor 52, specifically, the above average processing based on the signals of the photo interrupters 35Y, 35C, 35M, and 35K. To be implemented.

  As shown in the figure, in this embodiment, the signals of the photo interrupters 35Y, 35C, 35M, and 35K come to the head part of the image pattern so that the timing relationship shown in FIG. 9 can be obtained. The pattern writing position of the pattern forming means is determined.

  Specifically, the phase relationship between the toner adhesion amount detection sensor 52 and the photo interrupters 35Y, 35C, 35M, and 35K is obtained in advance, and when the toner adhesion amount detection sensor 52 detects, the leading portion of the image pattern comes. In addition, the exposure start position of the pattern creating unit is changed. In this embodiment, the exposure start position by the optical writing unit 38 is determined in accordance with the head of the pattern. However, since the amount of adhesion at the head of the pattern is unstable, the amount of toner adhesion is stabilized from the beginning. The exposure start position by the optical writing unit 38 may be determined so that the detection signals of the photo interrupters 35Y, 35C, 35M, and 35K come at a short predetermined distance.

  In determining the tip position of the image pattern in the direction along the sub-scanning direction, the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K detected by the photo interrupters 35Y, 35C, 35M, and 35K; A layout distance from the electrostatic latent image forming position on the photoreceptors 40Y, 40C, 40M, and 40K written by the optical writing unit 38, that is, the exposure position to the detection position of the toner adhesion amount detection sensor 52; Data on the process linear velocity at this layout distance is required.

  These data are stored in a non-volatile memory or a volatile memory provided in the control unit 37, and the tip position of the image pattern in the direction along the sub-scanning direction is determined according to these data. .

  Here, the layout distance is a section between the writing position on the photoconductors 40Y, 40C, 40M, and 40K written by the optical writing unit 38 and the detection position of the image pattern by the toner adhesion amount detection sensor 52. Means the distance in the direction along the sub-scanning direction.

  Further, the process linear velocity at the layout distance is a moving speed in the direction along the sub-scanning direction of the photoconductors 40Y, 40C, 40M, and 40K that are rotating bodies included in the section.

  The rear end position of the image pattern in the direction along the sub-scanning direction may be determined in the same manner as the front end position determined as described above. In addition, even when the leading end position is arbitrarily determined, the trailing end position may be determined according to the above-described data.

  Such determination of the front end position and / or rear end position according to the above-described data is based on the detection of the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K by the photo interrupters 35Y, 35C, 35M, and 35K. You may perform based on elapsed time. Also in this case, the determination of the front end position and / or the rear end position is performed substantially according to the above-described data. In this case, the pattern image may be arbitrarily written and the exposure end position may be determined to be an integral multiple of the circumferences of the photoconductors 40Y, 40C, 40M, and 40K.

  The elapsed time can be measured by the CPU of the control unit 37, for example. When this measurement is performed, the control unit 37 functions as an elapsed time measuring unit that measures the elapsed time.

  In this way, the timing relationship shown in FIG. 9 is obtained, and the pattern image is formed at the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K detected by the photo interrupters 35Y, 35C, 35M, and 35K. It will be done in synchronization.

  For this reason, since the layout distance is different for each color, the pattern image formation position may be adjusted to be different in the sub-scanning direction for each color image forming station. Therefore, as shown in FIG. 5B, the formation positions of the pattern images of the respective colors in the sub-scanning direction can be different from each other.

  By such timing control, the length of the image pattern in the sub-scanning direction is an integral multiple of the photoreceptor circumferential length, or in addition to a length that allows for a slight margin to stabilize the toner density, for example. It can be set well, and can be set to a length necessary and sufficient to determine the first condition corresponding to the photosensitive member rotation period. As a result, it is not necessary to allow the length of the image pattern in the sub-scanning direction to be large enough to match the circumferential length of the photoconductor, for example, and toner yield and control time are reduced.

  Specifically, the determination of the first condition by the control unit 37 functioning as the first image forming condition determination unit is performed as follows.

First, as shown in the following equation 1, a density unevenness component fg (t) due to rotational shake of the surface of the photoreceptor is extracted from the photoreceptor periodic density unevenness data of the image pattern and the photoreceptor periodic bright portion potential data.
fg (t) = f (t) −A * Vout (t) (Equation 1)
here,
fg (t): density unevenness component due to rotational shake on the surface of the photoconductor f (t): photoconductor periodic density nonuniformity data of the image pattern (created based on the output of the toner adhesion amount detection sensor 52)
A: Adjustment gain 1
Vout (t): Image pattern portion light portion potential (created based on the outputs of the surface potential sensors 56Y, 56C, 56M, 56K)
It is.

Next, the first condition VB (t) is calculated by the following equation 2.
VB (t) = B * fg (t) (Expression 2)
here,
VB (t): First condition B: Adjustment gain 2
It is.

Various adjustment gains are tuned according to the actual waveform.
The various adjustment gains are prepared in advance so as to form a table corresponding to the usage environment of the image forming apparatus 10, for example, temperature and humidity, and are provided in the control unit 37. May be stored in the volatile memory and the volatile memory, and read and used according to the use environment of the image forming apparatus 10.

The outline of the control described above is summarized in a flowchart as shown in FIG.
Referring to FIG. 12A, first, an image pattern is formed for each color and detected (S11). At this time, the bright part potential of the image pattern is also detected at the same time. Next, the photosensitive member periodic component detection of density unevenness and the first image forming condition calculation (creating a control table of image forming conditions) which is a first condition are performed (S12), and functions as a first control unit. The control unit 37 sets the created control table to be used and reflects it in the control of the first condition (S13).

  Referring to FIG. 12 (b), this is a more specific example of step S12 in FIG. 12 (a). First, a photosensitive member periodic component of density unevenness and a photosensitive member periodic component of bright portion potential are represented. Based on the density unevenness due to the rotational shake of the photoconductor (S21), the image forming conditions are calculated based on the calculated density unevenness (S22).

  As described above, the image pattern is a solid image, and the first condition is the developing bias that is the developing condition in the developing devices 42Y, 42C, 42M, and 42K. Therefore, when these are applied to FIG. 12, FIG. As shown.

  That is, first, a solid image pattern, which is a high density single density image pattern, is formed for each color and detected (S31). At this time, the bright part potential of the solid image pattern is also detected at the same time. Next, detection of a photosensitive member periodic component of solid image density unevenness and calculation of developing bias conditions (control table creation of developing devices 42Y, 42C, 42M, and 42K) are performed (S32), and a control functioning as a first control unit is performed. This is reflected in the control of the developing devices 42Y, 42C, 42M, and 42K by the unit 37 (S33).

  The processes shown in FIGS. 12 and 13 may be repeated a plurality of times. That is, image formation is performed by operating the developing devices 42Y, 42C, 42M, and 42K according to the determined first condition, and an image pattern is formed as an image whose density is detected by the toner adhesion amount detection sensor 52. Then, the density may be detected by the toner adhesion amount detection sensor 52, the first condition may be determined again, and the user-specified image formation may be performed according to the first condition.

  When this control is installed in an actual machine, there is a possibility that the gain at the time of creating the control table may be set to be weak in order to prevent overcorrection, so there may be a case where image density unevenness cannot be completely removed by a single correction control. . Therefore, it is possible to further reduce density unevenness by repeating a series of correction control. The image pattern may be repeated once or a plurality of times, but if the image pattern is drawn repeatedly, it is disadvantageous in terms of control time and toner yield. Therefore, it is preferable to set the gain setting so that the control effect appears with one correction, and end the correction control without repeating it a plurality of times.

  The controller 37 detects a toner adhesion amount detection sensor that detects the density of an image formed by adhering the toner to the photoconductors 40Y, 40C, 40M, and 40K in the nonvolatile memory and / or the volatile memory. 52, surface potential sensors 56Y, 56C, 56M, and 56K that detect the surface potential of the photoconductors 40Y, 40C, 40M, and 40K in a state where toner is attached, and development conditions for forming an image. When the rotational positions of the photoconductors 40Y, 40C, 40M, and 40K can be changed using the developing devices 42Y, 42C, 42M, and 42K that can adjust the density, the toner adhesion amount detection sensor 52 causes the photoconductor 40Y to move. , 40C, 40M, and 40K, the surface potential sensors 56Y and 5Y are detected when the density unevenness of the image for at least one circumference is detected and the image is formed. Based on the potential distribution of the surface potential detected by C, 56M, and 56K and the density unevenness, image density unevenness caused by the development gap fluctuation component of the photoconductors 40Y, 40C, 40M, and 40K is extracted. The developing devices 42Y, 42C, 42M, and 42K are operated according to the first condition for the development condition determined by the control unit 37 that functions as the first image forming condition determination unit so as to suppress the unevenness. An image forming program is stored as an image density control program for executing an image density control method that is an image forming method for forming an image. In this regard, the control unit 37 or the nonvolatile memory and / or the volatile memory functions as an image forming program storage unit. Such an image forming program includes not only a non-volatile memory and / or a volatile memory provided in the control unit 37, but also a semiconductor medium (for example, RAM, non-volatile memory), an optical medium (for example, DVD, MO, MD, CD-R, etc.), magnetic media (for example, hard disk, magnetic tape, flexible disk, etc.) and other storage media can be stored. Such memory and other storage media are required when such an image forming program is stored. A computer-readable recording medium storing an image forming program is configured.

  The preferred embodiments of the present invention have been described above. However, the present invention is not limited to the specific embodiments, and the present invention described in the claims is not specifically limited by the above description. Various modifications and changes are possible within the scope of the above.

  For example, the image forming apparatus to which the present invention is applied is a copier, a printer, a facsimile multi-function machine, a color digital multi-function machine capable of performing full-color image formation, and other copiers, printers, facsimiles, plotters. It may be a single machine or another combination of multifunction machines such as a multifunction machine of a copying machine and a printer. In recent years, in response to demands from the market, there are an increasing number of image forming apparatuses capable of forming color images, such as color copiers and color printers. However, image forming apparatuses to which the present invention is applied are limited to monocolor images. It may be formed.

  Such an image forming apparatus forms not only plain paper generally used for copying and the like, but also OHP sheets, cardboard, cardboard and other thick paper, envelopes and the like as sheet-like recording media as recording sheets. It is desirable to be able to perform. Such an image forming apparatus may be a double-sided image forming apparatus capable of forming an image on both sides of a transfer sheet which is a recording sheet as a recording medium as a recording medium. The developer used in such an image forming apparatus is not limited to a two-component developer but may be a one-component developer.

  The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 35Y, 35C, 35M, 35K Rotation position detection means 37 1st image formation condition determination means 38, 1st image formation means, exposure means 40Y, 40C, 40M, 40K Image carrier 42Y, 42C, 42M 42K First image forming means, developing means 52 Image density detecting means 56Y, 56C, 56M, 56K Potential detecting means

JP-A-9-62042 Japanese Patent No. 3825184 JP 2000-98675 A

Claims (8)

Image density detecting means for detecting the density of an image formed by attaching toner to the image carrier;
A potential detecting means for detecting a surface potential of the image carrier in a state where toner is attached;
First image forming means capable of adjusting the density using a first element for forming the image;
A first condition for the first element is determined to adjust the density based on the density unevenness of the image for at least one circumference of the image carrier detected by the image density detection means. First image forming condition determining means for
When the rotational position of the image carrier can change, the image density detection means detects density unevenness of the image, and the potential distribution of the surface potential detected by the potential detection means when forming the image Based on the density unevenness, image density unevenness caused by the development gap fluctuation component of the image carrier is extracted, and the first image forming condition determining means controls the first image forming condition determining means so as to suppress the extracted unevenness. Determine the conditions,
An image forming apparatus that forms an image by operating a first image forming unit according to a first condition. The image forming apparatus according to claim 1.
The first condition is determined by forming an image whose density is detected by the image density detecting means while maintaining a constant image forming condition for increasing the image density. . The image forming apparatus according to any one of claims 1 to 6,
An image forming apparatus, wherein the first image forming means is a developing means and / or an exposure means. The image forming apparatus according to any one of claims 1 to 3,
An image forming apparatus, wherein an image whose density is detected by the image density detecting unit is formed by the image formation, the first condition is determined again, and the image is formed according to the first condition. The image forming apparatus according to any one of claims 1 to 4,
Rotation position detection means for detecting the rotation position of the image carrier,
The determination of the first condition by the first image forming condition determining means and the operation of the first image forming means in accordance with the first condition are synchronized with the rotational position detected by the rotational position detecting means. An image forming apparatus characterized by being performed. The image forming apparatus according to any one of claims 1 to 5,
Rotation position detection means for detecting the rotation position of the image carrier,
An image forming apparatus characterized in that image formation for determining the first condition by the first image forming condition determining means is performed based on the rotational position detected by the rotational position detecting means. The image forming apparatus according to any one of claims 1 to 6,
When the rotational position of the image carrier can be changed, it is at least one of the initial attachment of the image carrier, the replacement of the image carrier, and the attachment / detachment of the image carrier. An image forming apparatus. Image density detecting means for detecting the density of an image formed by attaching toner to the image carrier;
A potential detecting means for detecting a surface potential of the image carrier in a state where toner is attached;
Using a first image forming means capable of adjusting the density using a first element for forming the image,
When the rotational position of the image carrier can change, the image density detection means detects density unevenness of the image for at least one circumference of the image carrier, and the potential when forming the image. Based on the potential distribution of the surface potential detected by the detecting means and the density unevenness, image density unevenness caused by the development gap fluctuation component of the image carrier is extracted, and the extracted unevenness is suppressed. An image forming method for performing image formation by operating the first image forming unit according to the first condition for the first element determined by the first image forming condition determining unit.

Images