JP2016066042A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus that can reduce unevenness in image density.SOLUTION: There is provided an image forming apparatus 1 including a rotatable image carrier 122, a rotatable charing member 23 that charges the surface of the image carrier, latent image forming means 124, and developing means 125 for developing a latent image on the image carrier with a developer on a rotatable developer carrier 125a, the image forming apparatus 1 including: first image density variation detection means 69 for detecting a variation in image density in the direction of image carrier surface movement that occurs in one rotation cycle of the image carrier or the developer carrier; second image density variation detection means 128 for detecting a variation in image density in the direction of image carrier surface movement that occurs in one rotation cycle of the charging member; and control means 10 for controlling the rotation of the charging member, on the basis of results of the detection by the first image density variation detection means and second image density variation detection means, so that the cycle and phase of the variation in image density occurring in one rotation cycle of the charging member become the same as the cycle and reverse to the phase of the variation in image density occurring in one rotation cycle of the image carrier or the developer carrier.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image forming apparatus such as a printer, a facsimile machine, and a copying machine.

  Conventionally, as this type of image forming apparatus, the one described in Patent Document 1 is known. The image forming apparatus includes a drum-shaped photoconductor as an image carrier, a charging roller that rotates while contacting the photoconductor, and a developing roller that rotates while facing the photoconductor through a predetermined gap. ing. Then, the surface of the photoreceptor is uniformly charged by a charging roller to which a charging bias is applied, and then the charged surface is exposed by an exposure device to form a latent image. Thereafter, the latent image is developed with a developer carried on the surface of the developing roller to obtain a toner image. The toner image on the photoconductor is finally transferred to a sheet as a recording medium to form an image on the sheet.

  In such a configuration, when the charging roller is eccentric, uneven charging is generated on the surface of the photoreceptor in synchronization with the rotation period of the charging roller. Such charging unevenness causes periodic image density unevenness that increases or decreases the image density in the same cycle as the rotation period of the charging roller. Further, when the photosensitive member and the developing roller are eccentric, the gap between the photosensitive member and the developing roller (hereinafter referred to as a developing gap) varies with the rotation of the photosensitive member and the developing roller. The intensity of the developing electric field formed between the rollers varies. Such fluctuations in the intensity of the developing electric field cause periodic image density unevenness that increases or decreases the image density in the same cycle as the rotation cycle of the photosensitive member or the developing roller. Then, when periodic image density unevenness cycles that occur at the same period as the rotation cycle of the charging roller, the photoconductor, and the developing roller overlap, there arises a problem that the image density unevenness deteriorates.

  The present invention has been made in view of the above problems, and an object thereof is to provide an image forming apparatus capable of reducing image density unevenness.

  In order to achieve the above-mentioned object, the invention of claim 1 includes a rotatable image carrier, a rotatable charging member for charging the surface of the image carrier, and the image carrier. An image forming apparatus comprising: a latent image forming unit that forms a latent image on a surface; and a developing unit that develops the latent image on the image carrier with a developer carried on a developer carrier provided rotatably. A first image density fluctuation detecting means for detecting an image density fluctuation in a moving direction of the image carrier surface that occurs in one rotation cycle of the image carrier or the developer carrier, and an image carrier generated in one rotation cycle of the charging member. A second image density fluctuation detecting means for detecting an image density fluctuation in a body surface moving direction; and the image carrier or the development based on detection results of the first image density fluctuation detecting means and the second image density fluctuation detecting means. Rotation cycle of the agent carrier Control means for controlling the rotation of the charging member such that the period of the image density fluctuation generated in one rotation period of the charging member is the same and the phase is opposite to the period and phase of the generated image density fluctuation. It is characterized by this.

  As described above, according to the present invention, there is an excellent effect that unevenness in image density can be reduced.

The graph which shows the relationship between each sensor output after rotary body phase adjustment, and the image density nonuniformity on a transfer paper. 1 is a schematic configuration diagram of an image forming apparatus according to an embodiment. The hardware block diagram of the control part of an image forming apparatus. Explanatory drawing which shows an example of the image pattern used for correction control of image density nonuniformity. FIG. 3 is a cross-sectional view illustrating a schematic configuration of a toner image detection sensor. The schematic block diagram of the phase and rotation speed detection apparatus of a rotary body. The graph which showed the relationship between an encoder output and a toner image detection sensor output. The graph which shows the relationship between each sensor output before rotary body phase adjustment, and the image density non-uniformity on a transfer paper. The flowchart which concerns on control of a phase adjustment operation | movement. (A) The graph which shows the relationship between the speed difference between a photoreceptor drum and a charging roller, and a friction coefficient. (B) A graph showing the relationship between the coefficient of friction between the photosensitive drum and the charging roller and the wear amount of the photosensitive drum. The graph which shows the relationship between charging roller rotation speed and charging roller cleaning property. The figure which shows the output of the toner image detection sensor at the time of performing phase detection with the rotation speed at the time of printing. The figure which shows the output of a toner image detection sensor at the time of performing phase detection at the rotation speed lower than the time of printing. FIG. 3 is a schematic configuration diagram of another image forming apparatus according to the embodiment.

  FIG. 2 is a hardware configuration diagram of the image forming apparatus 1. FIG. 3 is a hardware configuration diagram of the control unit 10 of the image forming apparatus 1. The image forming apparatus 1 forms an image by fixing a toner image on a sheet as an example of a recording medium. 2, the image forming apparatus 1 includes a control unit 10, an image reading unit 11, an image forming unit 12, a paper feeding unit 13, a transfer unit 14, a fixing unit 15, a paper discharge unit 16, and a display / operation unit. 17 etc.

  As shown in FIG. 3, the control unit 10 includes a CPU (Central Processing Unit) 1011, a main memory (MEM-P) 1012, a North Bridge (NB) 1013, a South Bridge (SB) 1014, and an AGP (Accelerated Graphics Port) bus 1015. , An ASIC (Application Specific Integrated Circuit) 1016, a local memory (MEM-C) 1017, an HD (Hard Disk) 1018, an HDD (Hard Disk Drive) 1019, and a network I / F 102.

  The CPU 1011 processes and calculates data in accordance with a program stored in the main memory 1012, and the image reading unit 11, image forming unit 12, paper feeding unit 13, transfer unit 14, fixing unit 15, and paper discharge unit 16. It controls the operation of. The main memory 1012 is a storage area of the control unit 10, and includes a ROM (Read Only Memory) 1012a and a RAM (Random Access Memory) 1012b. The ROM 1012a is a memory for storing programs and data for realizing the functions of the control unit 10. The program stored in the ROM 1012a is configured to be recorded and provided in a computer-readable recording medium such as a CD-ROM, FD, CD-R, or DVD as a file in an installable or executable format. May be.

  The RAM 1012b is used as a memory for drawing when developing programs and data and printing memory. The NB 1013 is a bridge for connecting the CPU 1011, the MEM-P 1012, the SB 1014, and the AGP bus 1015. The SB 1014 is a bridge for connecting the NB 1013 to a PCI device and peripheral devices. The AGP bus 1015 is a bus interface for a graphics accelerator card that has been proposed to speed up graphic processing.

  The ASIC 1016 includes a PCI target and an AGP master, an arbiter (ARB) that forms the core of the ASIC 1016, a memory controller that controls the MEM-C 1017, and a plurality of DMACs (Direct Memory Access Controllers) that perform image data rotation using hardware logic. Become. The ASIC 1016 is connected to an interface of USB (Universal Serial Bus) and an interface of IEEE 1394 (Institut of Electrical and Electronics Engineers 1394) via a PCI bus.

  The MEM-C 1017 is a local memory used as a copy image buffer and a code buffer. The HD 1018 is a storage for accumulating image data, accumulating font data used during printing, and accumulating forms. The HDD 1019 controls reading or writing of data with respect to the HD 1018 according to the control of the CPU 1011. The network I / F 102 transmits / receives information to / from an external device such as an information processing apparatus via a communication network.

  The control unit 10 is electrically connected to image forming units 120C, 120M, 120Y, 120K, 120T, a toner image detection sensor 69, and the like. And the control part 10 controls these various apparatuses based on the control program memorize | stored in ROM1012a. The ROM 1012a and RAM 1012b store output conversion information used when calculating the toner density (toner adhesion amount) from the detection value of the toner image detection sensor 69. Examples of the output conversion information include output conversion data (conversion table), output conversion formula (algorithm), and the like.

  The image reading unit 11 generates image information by optically reading an image written on a sheet. Specifically, the image information is read by applying light to a sheet and receiving the reflected light by a reading sensor such as a CCD (Charge Coupled Devices) or a CIS (Contact Image Sensor). The image information is information representing an image to be formed on a recording medium such as paper, and uses electrical color separation image signals indicating red (R), green (G), and blue (B) colors. It is shown.

  The image reading unit 11 includes a contact glass 111, a reading sensor 112, and the like as shown in FIG. The contact glass 111 is for placing a sheet on which an image is written. The reading sensor 112 reads image information of an image described on a sheet placed on the contact glass 111.

  The image forming unit 12 attaches toner to the surface of the intermediate transfer belt 143 of the transfer unit 14 based on the image information read by the image reading unit 11 or the image information received by the network I / F 102. (Toner image) is formed.

  The image forming unit 12 includes an image forming unit 120C, an image forming unit 120M, an image forming unit 120Y, an image forming unit 120K, and an image forming unit 120T. The image forming unit 120 </ b> C forms a toner image using a developer having cyan (C) color toner. The image forming unit 120M forms a toner image using magenta (M) toner. The image forming unit 120Y forms a toner image using yellow (Y) toner. The image forming unit 120K forms a toner image using black (K) toner. The image forming unit 120T forms a toner image using clear (T) toner.

  Hereinafter, one or more of the C color toner, the M color toner, the Y color toner, and the K color toner is referred to as a colored toner. Each colored toner is a resin particle having a charging property containing a coloring material such as a pigment or a dye.

Further, the clear toner is a colorless and transparent toner, and is a resin particle configured so that the colored toner can be visually recognized when attached to the colored toner attached to the recording medium. The clear toner is resin particles that can be visually recognized when attached to the recording medium. The clear toner is produced, for example, by externally adding silicon dioxide (SiO ₂ ) or titanium dioxide (TiO ₂ ) to a low molecular weight polyester resin. Note that the clear toner may contain a coloring material as long as the amount is such that the recording medium or the colored toner attached on the recording medium can be visually recognized.

  Hereinafter, of the image forming unit 120C, the image forming unit 120M, the image forming unit 120Y, the image forming unit 120K, and the image forming unit 120T, an arbitrary image forming unit is represented as an “image forming unit 120”.

  The image forming unit 120C includes a developer container 121C, a photosensitive drum 122C, a charging unit 123C, an exposure unit 124C, a developing unit 125C, a charge removal unit 126C, a cleaning unit 127C, and a potential detection unit 128C.

  The developer storage unit 121C stores C-color toner, and supplies the C-color toner to the development unit 125C. The toner accommodated in the developer accommodating portion 121C is supplied to the developing portion 125C by a predetermined amount by driving the conveying screw in the developer accommodating portion 121C.

  The developing unit 125C is provided with a cylindrical developing roller 125aC that is rotationally driven by a drive motor. The developing roller 125aC is configured to remove a part of its peripheral surface from an opening provided in the casing of the developing unit 125C. It is exposed outside the casing. The exposed portion of the developing roller 125aC is opposed to the photosensitive drum 122C with a developing gap of a predetermined interval.

  The surface of the photosensitive drum 122C is uniformly charged by the charging unit 123C, and an electrostatic latent image is formed on the surface by the exposure unit 124C based on the image information received from the control unit 10. On the surface of the photosensitive drum 122C, a toner image is formed by the developing unit 125C attaching toner to the surface on which the electrostatic latent image is formed. The photosensitive drum 122C is provided so as to be in contact with the intermediate transfer belt 143, and is provided to rotate in the same direction as the moving direction of the intermediate transfer belt 143 at a contact point with the intermediate transfer belt 143.

  The charging unit 123C has a charging roller 23C disposed in contact with the surface of the photosensitive drum 122C. Then, by applying a voltage to the charging roller 23C, a discharge is generated between the charging roller 23C and the photosensitive drum 122C, and the surface of the photosensitive drum 122C is uniformly charged. The charging unit 123C is provided with a charging cleaning roller as a charging cleaning member that rotates in contact with the surface of the charging roller 23C and cleans the surface of the charging roller. The charging roller 23C may be disposed close to the photosensitive drum 122C with a minute gap between the surface of the photosensitive drum 122C and the charging roller 23C.

  The exposure unit 124C irradiates the surface of the photosensitive drum 122C charged by the charging unit 123C with light based on the C halftone dot area ratio determined by the control unit 10 to form an electrostatic latent image. The developing unit 125C develops the toner image by attaching the C-color toner stored in the developer storage unit 121C to the electrostatic latent image formed on the surface of the photosensitive drum 122C by the exposure unit 124C. Form.

  The neutralization unit 126C neutralizes the surface of the photosensitive drum 122C after the image is transferred to the intermediate transfer belt 143. The cleaning unit 127C removes the transfer residual toner remaining on the surface of the photosensitive drum 122C that has been neutralized by the neutralization unit 126C. The potential detector 128C detects the potential of the photosensitive drum 122C.

  The image forming unit 120M includes a developer storage unit 121M, a photosensitive drum 122M, a charging unit 123M, an exposure unit 124M, a developing unit 125M, a charge removal unit 126M, a cleaning unit 127M, and a potential detection unit 128M. The developer storage unit 121M stores M-color toner.

  The image forming unit 120Y includes a developer storage unit 121Y, a photosensitive drum 122Y, a charging unit 123Y, an exposure unit 124Y, a developing unit 125Y, a charge removal unit 126Y, a cleaning unit 127Y, and a potential detection unit 128Y. The developer storage unit 121Y stores Y toner.

  The image forming unit 120K includes a developer storage unit 121K, a photosensitive drum 122K, a charging unit 123K, an exposure unit 124K, a development unit 125K, a charge removal unit 126K, a cleaning unit 127K, and a potential detection unit 128K. The developer storage unit 121K stores K-color toner.

  The image forming unit 120T includes a developer storage unit 121T, a photosensitive drum 122T, a charging unit 123T, an exposure unit 124T, a developing unit 125T, a charge removal unit 126T, a cleaning unit 127T, and a potential detection unit 128T. The developer storage unit 121T stores clear toner.

  In the following description, any developer accommodating portion among the developer accommodating portion 121C, the developer accommodating portion 121M, the developer accommodating portion 121Y, the developer accommodating portion 121K, and the developer accommodating portion 121T will be referred to as the “developer accommodating portion 121”. ". Further, among the photosensitive drum 122C, the photosensitive drum 122M, the photosensitive drum 122Y, the photosensitive drum 122K, and the photosensitive drum 122T, an arbitrary photosensitive drum is represented as “photosensitive drum 122”. Further, among the charging unit 123C, the charging unit 123M, the charging unit 123Y, the charging unit 123K, and the charging unit 123T, an arbitrary charging unit is referred to as a “charging unit 123”.

  Further, among the exposure unit 124C, the exposure unit 124M, the exposure unit 124Y, the exposure unit 124K, and the exposure unit 124T, an arbitrary exposure unit is represented as an “exposure unit 124”. Further, among the developing unit 125C, the developing unit 125M, the developing unit 125Y, the developing unit 125K, and the developing unit 125T, an arbitrary developing unit is represented as “developing unit 125”. Further, among the static elimination unit 126C, the static elimination unit 126M, the static elimination unit 126Y, the static elimination unit 126K, and the static elimination unit 126T, an arbitrary static elimination unit is referred to as a “static elimination unit 126”. Further, among the cleaning unit 127C, the cleaning unit 127M, the cleaning unit 127Y, the cleaning unit 127K, and the cleaning unit 127T, an arbitrary cleaning unit is represented as a “cleaning unit 127”. In addition, among the potential detection unit 128C, the potential detection unit 128M, the potential detection unit 128Y, the potential detection unit 128K, and the potential detection unit 128T, an arbitrary potential sensor is represented as a “potential detection unit 128”.

  The paper supply unit 13 supplies paper to the transfer unit 14. The paper feed unit 13 includes a paper storage unit 131, a paper feed roller 132, and a registration roller 134. The paper storage unit 131 stores paper that is an example of a recording medium. The paper feed roller 132 is provided to rotate in order to move the paper stored in the paper storage unit 131 toward the paper transport path 133. The paper feed roller 132 provided in this manner feeds the uppermost paper among the stored paper one by one and feeds it to the paper transport path 133.

  The sheet fed to the sheet conveyance path 133 by the sheet feeding roller 132 is conveyed to the transfer unit 14 through the sheet conveyance path 133 by a plurality of conveyance roller pairs 135a and 135b. The registration roller 134 feeds the sheet conveyed through the sheet conveyance path 133 at a timing when a portion where a toner image is formed on the intermediate transfer belt 143 to be described later reaches the transfer unit 14.

  The transfer unit 14 primarily transfers the image formed on the photosensitive drum 122 by the image forming unit 12 to the intermediate transfer belt 143 and secondarily transfers the image transferred to the intermediate transfer belt 143 to a sheet. The transfer unit 14 includes a drive roller 141, a driven roller 142, an intermediate transfer belt 143, primary transfer rollers 144 </ b> C, 144 </ b> M, 144 </ b> Y, 144 </ b> K, 144 </ b> T, a secondary transfer counter roller 145, and a secondary transfer roller 146.

  The intermediate transfer belt 143 is stretched around the driving roller 141 and the driven roller 142, and moves while being in contact with the photosensitive drum 122 as the driving roller 141 rotates. The driven roller 142 rotates as the intermediate transfer belt 143 moves. As the intermediate transfer belt 143 moves while being in contact with the photosensitive drum 122, the image formed on the photosensitive drum 122 is transferred to the surface of the intermediate transfer belt 143.

  The primary transfer rollers 144C, 144M, 144Y, 144K, and 144T are provided to face the photosensitive drums 122C, 122M, 122Y, 122K, and 122T, respectively, with the intermediate transfer belt 143 interposed therebetween, and move the intermediate transfer belt 143. Rotate to let The secondary transfer roller 146 rotates with the intermediate transfer belt 143 and the paper sandwiched between the secondary transfer counter roller 145.

  The fixing unit 15 fixes the toner transferred to the sheet by the transfer unit 14. Fixing refers to fusing the resin component of the toner to the paper by simultaneously applying heat and pressure to the toner. By fixing the toner transferred to the paper by the transfer unit 14, the state of the toner on the paper becomes stable.

  The fixing unit 15 includes a fixing belt 152, a fixing roller 153, a fixing belt conveying roller 154, a fixing counter roller 155, and a heat generating unit 156. The sheet on which the toner is transferred by the transfer unit 14 is conveyed toward the fixing unit 15 through the sheet conveyance path 151. The fixing belt 152 is stretched around a fixing roller 153 and a fixing belt conveying roller 154, and moves as these rollers rotate. A heat generating unit 156 is installed inside the fixing roller 153, and the sheet is heated via the fixing roller 153 by generating heat. The fixing roller 153 sandwiches the sheet transported through the sheet transport path 151 between the fixing facing roller 155 that is disposed opposite to the fixing belt 152, and heats and pressurizes the sheet and the toner on the sheet. To fix the toner on the paper.

  The paper discharge unit 16 discharges the paper on which the toner is fixed by the fixing unit 15 from the image forming apparatus, and includes a paper discharge roller 162, a paper discharge port 163, and a paper discharge tray 164. The sheet fixed by the fixing unit 15 is conveyed toward the sheet discharge outlet 163 through the sheet discharge conveyance path 161. The paper discharge roller 162 discharges the paper conveyed through the paper discharge conveyance path 161 from the paper discharge port 163 and stores it in the paper discharge tray 164.

  The display / operation unit 17 includes a panel display unit 171 and an operation unit 172. The panel display unit 171 displays setting values and selection screens. The panel display unit 171 is a touch panel or the like that receives input from the user. The operation unit 172 is operated by a user for input such as a numeric keypad for receiving various conditions for image formation and a start key for receiving a copy start instruction.

  Here, in the image forming apparatus, it is desired that the image density change is small. Cylindrical parts are frequently used in the image forming process, but periodic image density unevenness occurs due to the shake of the rotating body parts. This is because the gap between the photosensitive drum and the charging roller or the gap between the photosensitive drum and the developing roller is caused by the eccentricity of the rotating body (photosensitive drum, developing roller, charging roller) or not being a perfect circle. And fluctuates in one rotation cycle of the rotating body. This is because charging unevenness and development unevenness occur. From the viewpoint of image quality such as periodic image density unevenness, the rotating bodies (photosensitive drum, developing roller, charging roller) are required to have high shake accuracy. However, since the required runout accuracy is several [μm] or less, it is the limit of machining accuracy, and cost is increased when quality is obtained only by accuracy. Therefore, it is necessary to reduce the change in image density by another approach.

  In addition, when the image density unevenness is generated in the rotation cycle of the rotating body, dividing the linear velocity V [mm / s] of the rotating body by the circumference X [mm] of the rotating body ( Therefore, the image density unevenness occurs at the image density unevenness occurrence frequency of (V / X) [Hz]. For example, when the linear velocity V of the developing roller 125a is 560 [mm / s] and the circumference X of the developing roller 125a is 80 [mm], the developing roller 125a rotates 7 times per second, so 7 [Hz] Image density unevenness occurs at the image density unevenness occurrence frequency.

  The image forming apparatus 1 illustrated in FIG. 2 includes a toner image detection sensor 69 configured by an optical sensor or the like as a density detection unit that detects the density of the toner image formed on the surface of the intermediate transfer belt 143. The toner image detection sensor 69 is disposed at a position facing the portion of the intermediate transfer belt 143 that is wound around the drive roller 141. The toner image detection sensor 69 can detect the density of the toner image of the image pattern formed on the surface of the intermediate transfer belt 143 so as to be used for the correction control of the image density unevenness.

  FIG. 4 is an explanatory diagram illustrating an example of an image pattern used for image density unevenness correction control (detection). In this example, a belt-like image pattern 900 that is long in the intermediate transfer belt moving direction X is formed on the surface of the intermediate transfer belt 143 facing the toner image detection sensor 69. This image pattern 900 has a length of at least one rotation period of the rotating body to be phase detected in order to detect the phase of each rotating body such as the photosensitive drum 122 and the developing roller 125a. For example, when detecting image density unevenness in one rotation cycle of the photosensitive drum, the length of the image pattern 900 is set to be at least the circumferential length Lp of the photosensitive drum. In addition, when detecting the image density unevenness in one rotation cycle of the developing roller, the length of the image pattern 900 is set to be at least the developing roller circumferential length Lq.

  FIG. 5 is a cross-sectional view showing a schematic configuration of the toner image detection sensor 69. As shown in FIG. 5, the toner image detection sensor 69 mainly receives a light emitting element 311 composed of an LED as a light emitting means, a regular reflection light receiving element 312 for receiving regular reflection light, and diffuse reflection light. And a diffuse reflection light receiving element 313.

  The toner image detection sensor 69 emits light from the light emitting element 311 toward the surface of the intermediate transfer belt 143. Then, the regular reflection light that is regularly reflected by the surface of the intermediate transfer belt 143 and the toner image on the surface is received by the regular reflection light receiving element 312 and a voltage corresponding to the amount of received light is output. Further, the diffuse reflection light diffusely reflected by the surface of the intermediate transfer belt 143 and the toner image on the surface is received by the diffuse reflection light receiving element 313, and a voltage corresponding to the amount of received light is output. The image density (toner adhesion amount) of the toner image on the intermediate transfer belt 143 is determined based on the detected voltage and the voltage corresponding to the amount of specularly reflected light and the amount of diffusely reflected light. Calculated.

  As described above, in the image forming apparatus 1 of the present embodiment, the image density fluctuation in the sub-scanning direction, which is the surface movement direction of the photosensitive drum 122 and the intermediate transfer belt 143, is detected based on the detection result of the toner image detection sensor 69. Then, the phase and amplitude of the image density fluctuation are calculated from the detected value.

  FIG. 6 is an explanatory diagram of an encoder 70 which is a charging roller phase / rotation number detection device as a phase / rotation number detection means for detecting the phase and rotation speed of the charging roller 23.

  The encoder 70 is provided separately for each of the charging rollers 23Y, 23M, 23C, 23K, and 23T, but has the same configuration as that shown in FIG. Further, as shown in FIG. 6, the charging roller 23 is configured such that a roller shaft 76 that forms a rotation center axis is connected to a drive transmission shaft 79 that is an output shaft of a drive motor 78 via a coupling 77. Yes. The drive motor 78 is driven to rotate.

  The encoder 70 includes a light shielding member 72 that is provided integrally with the drive transmission shaft 79 and that rotates as the drive transmission shaft 79 rotates, and a photointerrupter 71 provided with a light emitting portion 71a and a light receiving portion 71b. Yes. A slit 72a is formed in the light shielding member 72, and light from the light emitting portion 71a of the photo interrupter 71 is sequentially transmitted and blocked by the light shielding member 72 and the slit 72a according to the rotation of the charging roller 23, and light is received accordingly. The unit 71b sequentially receives the light.

  Thereby, a pulse-like ON / OFF signal is obtained according to the rotation amount of the light shielding member 72. By using this pulse-like ON / OFF signal, the movement angle (hereinafter referred to as angular displacement) of the charging roller 23 is obtained to detect the phase (rotational position) of the charging roller 23 or to rotate the charging roller 23. (Linear velocity) is detected.

  As a configuration for detecting the phase (rotation position) and the number of rotations (linear velocity), a photoconductor home position sensor that detects the phase (rotation position) of the photoconductor drum 122 is also the same as the encoder 70 of the photoconductor drum 122. The rotational position is detected.

  In the example shown in FIG. 6, a direct drive system directly connected to the drive motor is used for driving the charging roller 23, but a speed reduction mechanism may be included between the power transmissions from the drive motor 78. However, when the speed reduction mechanism is employed, it is desirable that the light shielding member 72 is installed on the roller shaft 76 so as to have the same rotational speed as the charging roller 23. The same applies to the case where the phase (rotational position) of the photosensitive drum 122 is detected.

  The rotating body phase / rotation number detecting device is also attached to the developing roller 125a and the photosensitive drum 122 which are rotating bodies other than the charging roller 23, but the configuration is the same.

  By calculating the density unevenness of the rotating body cycle of the encoder output and toner image detection sensor output of each rotating body, the correlation between the phase of the corresponding rotating body and the phase of the density unevenness can be obtained. Then, density unevenness in the radial scanning direction can be suppressed by adjusting the phase and controlling the phase opposite to the density unevenness due to the other rotating body.

  FIG. 7 is a graph showing the relationship between the sensor output of the toner image detection sensor 69 that detects the image pattern 900 formed on the intermediate transfer belt 143 and the sensor output of the encoder 70. As shown in FIG. 7, every time the charging roller 23 rotates, the output of the encoder 70 rises once in a rectangular shape. The rising timing is the timing when the charging roller 23 assumes a predetermined rotation angle posture. As can be seen from FIG. 7, the sensor output of the toner image detection sensor 69, that is, the image density of the image pattern 900 formed on the intermediate transfer belt 143 varies with the rotation period of the charging roller.

  In this way, striped image density unevenness may occur in the image at the charging roller cycle. In the configuration in which the charging roller 23 is provided in contact with the photosensitive drum 122, the photosensitive drum 122 and the charging roller 23 are rotated. Due to the eccentricity of the charging roller 23, the photosensitive drum 122 and The contact width with the charging roller 23 varies. For this reason, the time for which the photosensitive drum 122 passes through the contact position between the photosensitive drum 122 and the charging roller 23 varies, and the photosensitive drum 122 cannot be charged to a uniform potential, resulting in uneven charging. . Then, even if the exposure unit 124 exposes the photosensitive drum 122 with the same intensity, the potential of the latent image varies, and finally, image density unevenness corresponding to charging unevenness occurs in the image.

  The surface potential of the photosensitive drum 122 charged by the charging roller 23 is measured in synchronism with the rotational position detecting means for detecting the rotational position of the charging roller 23, and the charging roller cycle is determined from the measured surface potential of the photosensitive drum 122. Charge unevenness (potential unevenness) is detected.

  As shown in FIG. 8, the image density unevenness of the image formed on the paper is deteriorated by overlapping the image density unevenness periods due to the flare of each rotating body such as the charging roller 23 and the developing roller 125a. Therefore, the surface potential of the photosensitive drum 122 is detected by the potential detection unit 128, and the phase of charging unevenness (potential unevenness) generated in one rotation cycle of the charging roller of the photosensitive drum 122 is detected. Further, the image density of the image pattern 900 formed on the intermediate transfer belt 143 is detected by the toner image detection sensor 69, and the phase of the image density unevenness generated in one rotation cycle of the developing roller of the image pattern 900 is detected.

  In the image forming apparatus 1 of the present embodiment, the charging roller 23 can be rotated by the drive motor 78 independently of the photosensitive drum 122 and the developing roller 125a. Therefore, the charging roller is set so that the period and phase of the image density fluctuation generated in one rotation cycle of the developing roller 125a are the same and the phase of the image density fluctuation generated in one rotation cycle of the charging roller 23 is opposite to each other. Control the rotation of

  Specifically, by controlling the drive motor 78 to change the rotation speed of the charging roller 23, one rotation cycle of the charging roller 23 is made the same as one rotation cycle of the developing roller 125a. Further, the phase of the image density fluctuation generated in one rotation cycle of the charging roller 23 is detected in advance in correspondence with the rotation position of the charging roller 23 detected by the encoder 70. The charging roller is positioned so that the phase of the image density fluctuation generated in one rotation period of the charging roller 23 is opposite to the phase of the image density fluctuation generated in one rotation period of the developing roller 125a. The rotation of 23 is controlled.

  As a result, as shown in FIG. 1, the image density fluctuation generated in one rotation cycle of the developing roller 125a and the image density fluctuation generated in one rotation cycle of the charging roller 23 cancel each other on the image, and the photosensitive drum surface movement direction The image density unevenness in the sub-scanning direction is reduced and becomes inconspicuous.

  Control of the phase adjustment operation of each rotating body (photosensitive drum 122, developing roller 125a, charging roller 23) can be performed as follows. First, an image pattern of one or more cycles of each rotating body is formed on the intermediate transfer belt 143, and the toner image detection sensor 69 reads fluctuation data of the toner adhesion amount of the image pattern on the intermediate transfer belt 143. Then, the amplitude / phase of the toner adhesion amount at each frequency (cycle) is calculated by performing Fourier transform on the read fluctuation data of the toner adhesion amount on the intermediate transfer belt 143. The correlation between the amplitude / phase of the toner adhesion amount in the period of each rotating body (photosensitive drum 122, developing roller 125a, charging roller 23) calculated in this way and the phase of the corresponding rotating body is acquired.

  Then, if the amplitude of the toner adhesion amount at each frequency calculated above is the developing roller 125a> the photosensitive drum 122, the charging roller 23 is driven so as to have the same period with respect to the density unevenness of the developing roller period. Change the motor speed. Further, the phase is adjusted so that the density unevenness in the charging roller cycle is opposite to the density unevenness in the developing roller cycle. On the other hand, if the amplitude of the toner adhesion amount at each frequency is the developing roller 125a <photosensitive drum 122, the charging roller cycle / phase is adjusted with respect to the photosensitive drum cycle. Further, if the amplitude of the toner adhesion amount at each frequency is the developing roller 125a <charging roller 23 and the photosensitive drum 122 <charging roller 23, the charging roller 23 is not rotated.

  FIG. 9 is a flowchart relating to the control of the phase adjustment operation performed in the image forming apparatus 1 of the present embodiment. First, an image pattern is formed (S1), and unevenness of image density (potential) in one rotation period of each of the developing roller 125a and the charging roller 23 is detected (S2). Based on the detection result, the control unit 10 calculates the image density unevenness period / phase / amplitude of the developing roller 125a and the charging roller 23 (S3). The charging roller is positioned so that the phase of the image density fluctuation generated in one rotation period of the charging roller 23 is opposite to the phase of the image density fluctuation generated in one rotation period of the developing roller 125a. The rotation of 23 is controlled to adjust the phase (S4).

  In the above description, the developing roller 125a may be the photosensitive drum 122. That is, the periodic fluctuation of the developing gap is caused not only by the eccentricity of the developing roller 125a but also by the eccentricity of the photosensitive drum 122. Therefore, in the image forming apparatus 1 of the present embodiment, the phase (rotational position) of the developing roller 125a and the phase (rotational position) of the photosensitive drum 122 are detected. Then, density fluctuation caused by the rotation period of the developing roller 125a and density fluctuation caused by the rotation period of the photosensitive drum 122 can be extracted from density fluctuation data as a detection result of the toner image detection sensor 69, respectively. . Accordingly, it is possible to perform correction control so as to suppress the density fluctuation in consideration of the density fluctuation caused by the developing roller 125a and the photosensitive drum 122, respectively.

  In addition, the adjustment of the phase of the image density fluctuation occurring in one rotation cycle of the charging roller 23 with respect to the phase of the image density fluctuation occurring in one rotation cycle of the developing roller 125a or the photosensitive drum 122 is performed at a lower rotation speed than in printing. By doing so, the accuracy of phase adjustment can be improved.

  A configuration is also employed in which image density fluctuations that occur in each rotation cycle of the developing roller 125a and the photosensitive drum 122 are detected based on the detection result of the toner image detection sensor 69 from the image pattern 900 on the intermediate transfer belt 143. can do. In this case, when the image density fluctuation generated in one rotation cycle of the photosensitive drum 122 is not detected, the rotation control of the charging roller 23 is performed as follows. That is, the charging roller is set so that the period and phase of the image density fluctuation generated in one rotation cycle of the developing roller 125a are the same and the phase is opposite to that of the image density fluctuation generated in one rotation cycle of the charging roller 23. The rotation of 23 is controlled. Thereby, it is possible to reduce image density unevenness that occurs in one rotation cycle of the developing roller 125a.

  On the other hand, when the image density fluctuation generated in one rotation cycle of the developing roller 125a is not detected, the rotation control of the charging roller 23 is performed as follows. That is, charging is performed so that the period and phase of the image density fluctuation generated in one rotation period of the charging roller 23 are the same and the phase is opposite to the period and phase of the image density fluctuation generated in one rotation period of the photosensitive drum 122. The rotation of the roller 23 is controlled. Thereby, it is possible to reduce image density unevenness that occurs in one rotation cycle of the photosensitive drum 122.

  Further, when the image density fluctuation generated in one rotation period of each of the photosensitive drum 122 and the developing roller 125a is not detected, the charging roller 23 is not rotated during image formation. Thereby, it is possible to suppress the occurrence of image density unevenness that occurs in one rotation cycle of the charging roller 23. At this time, the charging roller 23 is rotated between the corresponding papers between the trailing edge of the preceding paper and the leading edge of the succeeding paper when performing continuous image formation. As a result, the amount of wear between the photosensitive drum 122 and the charging roller 23 is reduced, and the life can be extended.

  FIG. 10A shows the relationship between the speed difference between the photosensitive drum 122 and the charging roller 23 and the friction coefficient. FIG. 10B shows the relationship between the friction coefficient between the photosensitive drum 122 and the charging roller 23 and the wear amount of the photosensitive drum. As shown in FIG. 10A, when a speed difference is generated between the photosensitive drum 122 and the charging roller 23, the friction coefficient between the photosensitive drum 122 and the charging roller 23 increases. As shown in FIG. 10B, when the coefficient of friction between the photosensitive drum 122 and the charging roller 23 increases, the photosensitive drum wear amount per travel distance increases. Therefore, considering the life of the photosensitive drum 122, it is desirable not to create a speed difference between the photosensitive drum 122 and the charging roller 23.

  FIG. 11 shows the relationship between the charging roller rotation speed and the charging roller cleaning property. As can be seen from FIG. 11, the time required for ensuring sufficient cleaning differs by changing the rotation speed of the charging roller during charging roller cleaning. Also, the time required to ensure sufficient cleaning properties varies depending on the cleaning time. Therefore, by increasing the number of rotations of the charging roller at the time of cleaning the charging roller, it is possible to shorten the time required to ensure sufficient cleaning properties and reduce downtime.

  Further, when the surface of the charging roller 23 is cleaned by the charging cleaning roller other than during printing such as before the start of the image forming operation or after the end of the image forming operation, it is preferable to increase the rotational speed of the charging roller 23 than during printing. Thereby, the cleaning property of the charging roller 23 by the charging cleaning roller can be improved.

  FIG. 12 shows the output of the toner image detection sensor 69 when phase detection is performed at the number of rotations during printing. FIG. 13 shows the output of the toner image detection sensor 69 when phase detection is performed at a lower rotational speed than during printing. If the phase is detected and adjusted at the number of rotations during printing, it is strongly influenced by other noises as shown in FIG. 12, and therefore there is a possibility that a deviation between the phase of density unevenness and the phase of the rotating body occurs. Becomes higher. Therefore, when detecting or adjusting the phase, the effect of noise can be reduced as shown in FIG. 13 by performing the rotation at a lower rotation speed than at the time of printing, and the density unevenness phase and the rotator phase are accurately detected. It can be detected well.

  FIG. 14 is a schematic configuration diagram of a copying machine 100 which is another image forming apparatus according to the embodiment. A copying machine 100 shown in FIG. 14 shows a configuration example of a full-color machine of a quadruple tandem type intermediate transfer system.

  In FIG. 14, image forming units 120 </ b> C, 120 </ b> M, 120 </ b> Y, and 120 </ b> K are arranged in parallel along the stretched surface (stretched surface) of the intermediate transfer belt 143. The yellow image forming unit 120Y will be described as a representative. Around the photosensitive drum 122Y provided in the image forming unit 120Y, there are a charging unit 123Y, an exposure unit 124Y, and a developing unit 125Y as a developing unit in the order of rotation. Has been placed. Further, a primary transfer roller 144Y, a cleaning unit 127Y, and a charge removal unit 126Y are arranged.

  The charging unit 123Y is provided with a charging roller 23Y at a predetermined gap from the surface of the photosensitive drum 122Y. The developing unit 125Y is provided with a cylindrical developing roller 125a that is rotationally driven by a driving motor so as to face the photosensitive drum 122Y with a developing gap of a predetermined interval. Above the exposure unit 124, an image reading unit 11 as an image reading unit, an automatic document feeder (ADF) 40, and the like are provided.

  The intermediate transfer belt 143 is rotatably stretched by stretching rollers such as a driving roller 141, a driven roller 142, and a secondary transfer counter roller 145, and a belt cleaning unit 50 is provided at a portion facing the driven roller 142. It has been. A secondary transfer roller 146 as a transfer unit is provided at a portion facing the secondary transfer counter roller 145.

  Two paper feeders 13a and 13b are provided at the lower part of the apparatus main body. The paper supply units 13a and 13b are provided with paper storage units 131a and 131b for storing paper as a recording medium. The paper stored in the paper storage portions 131a and 131b is fed to the paper transport path 133 by the paper feed rollers 132a and 132b, and then transported by the transport roller pairs 135a, 135b, and 135c. It is sent to the secondary transfer unit at the timing.

  A fixing unit 15 as a fixing unit is provided downstream of the secondary transfer unit in the sheet conveyance direction. The fixing unit 15 includes a fixing roller 153, a fixing counter roller 155, and a heat generating unit 156. The sheet on which the toner is transferred in the secondary transfer unit is conveyed toward the fixing unit 15 through the sheet conveyance path 151. A heat generating unit 156 is installed inside the fixing roller 153, and the sheet is heated via the fixing roller 153 by generating heat. The fixing roller 153 sandwiches the sheet transported through the sheet transport path 151 between the fixing facing roller 155 that is disposed opposite to the fixing belt 152, and heats and pressurizes the sheet and the toner on the sheet. To fix the toner on the paper.

  The paper discharge unit 16 discharges the paper on which the toner is fixed by the fixing unit 15 from the image forming apparatus, and includes a paper discharge roller 162, a paper discharge port 163, and a paper discharge tray 164. In the paper discharge unit 16, the paper fixed by the fixing unit 15 and conveyed through the paper discharge conveyance path 161 toward the paper discharge port 163 is discharged from the paper discharge port 163 by the paper discharge roller 162, and the paper discharge tray 164. To house.

  Further, the copying machine 100 includes a toner image detection sensor 69 configured by an optical sensor or the like as density detection means for detecting the density of the toner image formed on the outer peripheral surface of the intermediate transfer belt 143. The toner image detection sensor 69 can detect the density of the toner image of the image pattern formed on the surface of the intermediate transfer belt 143 so as to be used for the correction control of the image density unevenness. In the example of FIG. 14, the toner image detection sensor 69 is disposed at a position facing the portion of the intermediate transfer belt 143 that is wound around the drive roller 141.

  In the configuration shown in FIG. 14, an image forming operation will be described. When a print start command is input, the rollers around the photosensitive drum 122, the intermediate transfer belt 143, the paper feed conveyance path, and the like start to rotate at a predetermined timing, and the sheet is loaded from the lower sheet storage unit 131. Paper feeding starts.

  On the other hand, the surface of the photosensitive drum 122 is charged to a uniform potential by the charging unit 123, and the surface is exposed according to the image data by the writing light emitted from the exposure unit 124. The potential pattern after exposure is called an electrostatic latent image. The toner is supplied from the developing unit 125 to the surface of the photosensitive drum 122 carrying the electrostatic latent image, so that the photosensitive drum 122 carries the electrostatic latent image. The electrostatic latent image is developed to a specific color. In the configuration of FIG. 14, since there are four photosensitive drums 122, yellow, magenta, cyan, and black toner images are developed on the photosensitive drums 122Y, 122M, 122C, and 122K, respectively.

  The toner images on the respective photoconductive drums 122Y, 122M, 122C, and 122K are transferred onto the intermediate transfer belt 143 by the primary transfer roller 144 that is disposed opposite to the photoconductive drum 122 at the contact point with the intermediate transfer belt 143. The By repeating this primary transfer operation for four colors at the same timing, a full-color toner image is formed on the intermediate transfer belt 143.

  The full-color toner image formed on the intermediate transfer belt 143 is transferred onto the sheet conveyed at the timing by the registration roller 134 in the secondary transfer unit. At this time, the secondary transfer is performed by the secondary transfer bias and the pressing force applied to the secondary transfer roller 146. The sheet on which the full color toner image has been transferred passes through the fixing unit 15, whereby the toner image carried on the surface of the sheet is heated and fixed.

  If it is single-sided printing, it is straightly conveyed and conveyed to the paper discharge tray 164. If it is double-sided printing, the conveying direction is changed downward and conveyed to the paper reversing unit 30. The paper that has reached the paper reversing unit 30 is reversed in the conveying direction by the switchback roller pair 27 and exits the paper reversing unit 30 from the rear end of the paper. This is called a switchback operation, and the front and back of the paper can be reversed by this operation. The sheet that has been turned upside down does not return to the fixing unit direction, but passes through the refeed conveyance path 31 and joins the original sheet feed path. Thereafter, the toner image is transferred in the same manner as in the front surface printing, and is discharged through the fixing unit 15. This is a double-sided printing operation.

  Further, the primary transfer residual toner is carried on the surface of the photosensitive drum 122 that has passed through the primary transfer portion, and this is removed by a cleaning portion 127 constituted by a blade and a brush. Thereafter, the surface is uniformly discharged by the charge removing unit 126 to prepare for charging for the next image. The intermediate transfer belt 143 that has passed through the secondary transfer portion also carries secondary transfer residual toner on its surface, which is also removed by the belt cleaning unit 50 composed of blades and brushes. In preparation for the transfer of the next toner image. By repeating such an operation, single-sided printing or double-sided printing is performed.

  14 also executes various controls such as the phase adjustment operation control shown in FIG. 9 as described using the image forming apparatus 1 shown in FIG. Image density unevenness can be reduced.

What has been described above is merely an example, and the present invention has a specific effect for each of the following modes.
(Aspect A)
A latent image is formed on the surface of the image carrier, such as an image carrier such as a photosensitive drum 122 provided rotatably, a charging member such as a charging roller 23 provided rotatably to charge the surface of the image carrier. A latent image forming unit such as an exposure unit 124, and a developing unit such as a developing unit 125 that develops a latent image on the image carrier with a developer carried on a developer carrier such as a developing roller 125a provided rotatably. In the image forming apparatus such as the image forming apparatus 1 including the toner image detecting sensor 69 for detecting the image density fluctuation in the moving direction of the surface of the image carrier that occurs in one rotation cycle of the image carrier or the developer carrier. One image density fluctuation detecting means, a second image density fluctuation detecting means such as a potential detector 128 for detecting an image density fluctuation in the moving direction of the image carrier surface generated in one rotation cycle of the charging member, and a first image density fluctuation detecting Based on the detection result of the stage and the second image density fluctuation detecting means, the image density generated in one rotation cycle of the charging member with respect to the cycle and phase of the image density fluctuation generated in one rotation cycle of the image carrier or developer carrier. Control means such as the control unit 10 for controlling the rotation of the charging member is provided so that the fluctuation period is the same and the phase is opposite.
In (Aspect A), by controlling the rotation of the charging member, the image density generated in one rotation cycle of the charging member with respect to the cycle and phase of the image density fluctuation generated in one rotation cycle of the image carrier or developer carrier. The period of variation is the same and the phase is reversed. Thus, after such rotation control of the charging member is performed, when an image is formed on the image carrier, image density fluctuations that occur in one rotation cycle of the image carrier or developer carrier, and the charging member Image density fluctuations that occur in one rotation cycle cancel each other on the image. Therefore, the image density fluctuation can be reduced correspondingly, and the image density unevenness in the moving direction of the image carrier surface can be reduced.
(Aspect B)
In (Aspect A), the second image density fluctuation detecting means includes a surface potential detecting means such as a potential detecting unit 128 that detects the surface potential of the image carrier and an encoder 70 that detects the rotational position of the charging member. Second rotational position detecting means. According to this, as described in the above embodiment, it is possible to detect image density fluctuations that occur in one rotation cycle of the charging member in correspondence with the rotation position of the charging member.
(Aspect C)
In (Aspect A) or (Aspect B), the first image density fluctuation detection means includes a toner adhesion amount detection means such as a toner image detection sensor 69 for detecting a toner adhesion amount of an image, and the image carrier or the development. And a first rotation position detection means such as a phase / rotation number detection device for detecting the rotation position of the agent carrier. According to this, as described in the above embodiment, an image density variation that occurs in one rotation cycle of the image carrier or developer carrier is detected in correspondence with the rotational position of the image carrier or developer carrier. be able to.
(Aspect D)
In (Aspect A), (Aspect B), or (Aspect C), a charging cleaning unit such as a charging cleaning roller that cleans the charging member is provided. When the charging member is cleaned by the charging cleaning unit, printing is performed. Rather than increasing the number of rotations of the charging member. According to this, as described in the above embodiment, the cleaning property of the charging member by the charging cleaning unit can be improved.
(Aspect E)
In (Aspect A), (Aspect B), (Aspect C) or (Aspect D), one rotation of the charging member with respect to the phase of the image density fluctuation occurring in one rotation period of the image carrier or the developer carrier. The adjustment of the phase of the image density fluctuation occurring in the cycle is performed at a lower rotation speed than during printing. According to this, as described in the above embodiment, the accuracy of phase adjustment can be improved.
(Aspect F)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D) or (Aspect E), when the variation in image density occurring in one rotation cycle of the image carrier is not detected, the developer carrier The control means controls the charging member so that the period and phase of the image density fluctuation generated in one rotation period of the charging member are the same and the phase is opposite to the period and phase of the image density fluctuation generated in one rotation period. Control the rotation. According to this, as described in the above embodiment, it is possible to reduce image density unevenness that occurs in one rotation cycle of the developer carrier.
(Aspect G)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D), or (Aspect E), when no variation in image density that occurs in one rotation period of the developer carrier is detected, the image carrier The control means controls the charging member so that the period and phase of the image density fluctuation generated in one rotation period of the charging member are the same and the phase is opposite to the period and phase of the image density fluctuation generated in one rotation period. Control the rotation. According to this, as described in the above embodiment, it is possible to reduce image density unevenness that occurs in one rotation cycle of the image carrier.
(Aspect H)
In (Aspect A), (Aspect B), (Aspect C), (Aspect D) or (Aspect E), when image density fluctuations occurring in one rotation period of each of the image carrier and the developer carrier are not detected Does not rotate the charging member during image formation. According to this, as described in the above embodiment, it is possible to suppress the occurrence of uneven image density that occurs in one rotation cycle of the charging member.
(Aspect I)
In (Aspect H), the charging member is rotated between the corresponding papers between the trailing edge of the preceding paper and the leading edge of the succeeding paper when performing continuous image formation. According to this, as described in the above embodiment, the wear amount between the image carrier and the charging member is reduced, and the life can be extended.
(Aspect J)
In (Aspect I), the rotational speed of the image carrier and the rotational speed of the charging member between the papers are the same. According to this, as described in the above embodiment, the amount of wear between the image carrier and the charging member can be further reduced, and the life of the image carrier and the charging member can be extended.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 10 Control part 11 Image reading part 12 Image forming part 13 Paper feed part 14 Transfer part 15 Fixing part 16 Paper discharge part 17 Display and operation part 23 Charging roller 27 Switchback roller pair 30 Paper reversing part 31 Refeed Conveying path 40 Automatic document feeder 50 Belt cleaning unit 69 Toner image detection sensor 70 Encoder 71 Photo interrupter 71a Light emitting part 71b Light receiving part 72 Light shielding member 72a Slit 76 Roller shaft 77 Coupling 78 Drive motor 79 Drive transmission shaft 100 Copying machine 111 Contact Glass 112 Reading sensor 120 Image forming unit 121 Developer accommodating part 122 Photosensitive drum 123 Charging part 124 Exposure part 125 Developing part 126 Static eliminating part 127 Cleaning part 128 Potential detecting part 131 Paper accommodating part 132 Paper feed roller 133 Conveying path 134 Registration roller 135 Conveying roller pair 141 Driving roller 142 Driven roller 143 Intermediate transfer belt 144 Primary transfer roller 145 Secondary transfer counter roller 146 Secondary transfer roller 151 Paper conveying path 152 Fixing belt 153 Fixing roller 154 Fixing belt conveying roller 155 Fixing opposing roller 156 Heat generating part 161 Paper discharge conveyance path 162 Paper discharge roller 163 Paper discharge port 164 Paper discharge tray 171 Panel display part 172 Operation part 311 Light emitting element 312 Regular reflection light receiving element 313 Diffuse reflection light receiving element 900 Image pattern 1012 Main memory 1015 AGP bus

Japanese Patent No. 5288233

Claims (10)

An image carrier provided rotatably;
A rotatable charging member for charging the surface of the image carrier;
Latent image forming means for forming a latent image on the surface of the image carrier;
In an image forming apparatus comprising: a developing unit that develops a latent image on the image carrier with a developer carried on a developer carrier that is rotatably provided;
First image density fluctuation detecting means for detecting an image density fluctuation in the moving direction of the image carrier generated in one rotation period of the image carrier or the developer carrier;
Second image density fluctuation detecting means for detecting an image density fluctuation in the moving direction of the image carrier surface generated in one rotation cycle of the charging member;
Based on the detection results of the first image density fluctuation detection means and the second image density fluctuation detection means, with respect to the period and phase of the image density fluctuation that occurs in one rotation period of the image carrier or the developer carrier, An image forming apparatus comprising control means for controlling the rotation of the charging member so that the period of image density fluctuations generated in one rotation period of the charging member is the same and the phase is opposite. The image forming apparatus according to claim 1.
The second image density variation detecting means includes a surface potential detecting means for detecting a surface potential of the image carrier and a second rotational position detecting means for detecting a rotational position of the charging member. Forming equipment. The image forming apparatus according to claim 1, wherein
The first image density fluctuation detecting means includes a toner adhesion amount detecting means for detecting a toner adhesion amount of an image, and a first rotational position detecting means for detecting a rotational position of the image carrier or the developer carrier. An image forming apparatus. The image forming apparatus according to claim 1, 2 or 3.
A charging cleaning means for cleaning the charging member;
An image forming apparatus characterized in that when the charging member is cleaned by the charging cleaning means, the number of rotations of the charging member is higher than that during printing. The image forming apparatus according to claim 1, 2, 3, or 4.
The adjustment of the phase of the image density fluctuation occurring in one rotation cycle of the charging member with respect to the phase of the image density fluctuation occurring in one rotation cycle of the image carrier or the developer carrier is performed at a lower rotation speed than in printing. An image forming apparatus. The image forming apparatus according to claim 1, 2, 3, 4 or 5.
When an image density variation that occurs in one rotation cycle of the image carrier is not detected, it occurs in one rotation cycle of the charging member with respect to the cycle and phase of the image density variation that occurs in one rotation cycle of the developer carrier. An image forming apparatus, wherein the control means controls the rotation of the charging member so that the period of image density fluctuation is the same and the phase is opposite. The image forming apparatus according to claim 1, 2, 3, 4 or 5.
When an image density variation occurring in one rotation cycle of the developer carrier is not detected, it occurs in one rotation cycle of the charging member with respect to a cycle and phase of image density variation occurring in one rotation cycle of the image carrier. An image forming apparatus, wherein the control means controls the rotation of the charging member so that the period of image density fluctuation is the same and the phase is opposite. The image forming apparatus according to claim 1, 2, 3, 4 or 5.
An image forming apparatus, wherein the charging member is not rotated during image formation when an image density variation occurring in one rotation period of each of the image carrier and the developer carrier is not detected. The image forming apparatus according to claim 8.
An image forming apparatus, wherein the charging member is rotated between corresponding papers between a trailing edge of a preceding sheet and a leading edge of a succeeding sheet when performing continuous image formation. The image forming apparatus according to claim 9.
An image forming apparatus characterized in that the rotation speed of the image carrier between the sheets is the same as the rotation speed of the charging member.

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