JP2019066797A - Image formation apparatus and image formation method - Google Patents

Abstract

To solve a problem in which the photoreceptor surface potential necessary for adjusting the electrification bias, the developing bias, LD power and the like cannot be correctly obtained due to correction for suppressing the fluctuation of the image unevenness due to the fluctuation following the rotation of a development gap.SOLUTION: An image formation apparatus includes: a photoreceptor; an electrification member which electrifies the photoreceptor; an exposure member which exposes the photoreceptor electrified by the electrification member; a development member which forms a toner image on the photoreceptor exposed by the exposure member; and a potential detection member which detects the surface potential of the photoreceptor. The image formation apparatus forms the correction surface potential on the photoreceptor by correcting the electrification bias application from the electrification member or the exposure output from the exposure member with control data canceling the fluctuation of the image density generated in the toner image, and calculates the original surface potential by removing the correction potential being the potential for the correction with the control data from the real surface potential obtained by detecting the formed correction surface potential by the potential detection member.SELECTED DRAWING: Figure 16

Description

  The present invention relates to an image forming apparatus and an image forming method.

  In the electrophotographic system, the drum-shaped photosensitive member and the developing roller each have an eccentricity with respect to the rotation axis, so that the development gap changes with each rotation. Uneven density of the photosensitive member and the developing roller pitch caused by this fluctuation has occurred.

  Therefore, Patent Document 1 describes a technique in which correction is performed on the charging bias so as to suppress unevenness in the pitch between the photosensitive member and the developing roller caused by the fluctuation caused by the rotation of the developing gap.

  On the other hand, in the electrophotographic system, it is known that the efficiency of charging, exposure, and development changes depending on the time-dependent change of the photosensitive member and the toner, the environmental change of the apparatus, and the like. In order to respond to that, a sensor called a surface potential sensor, which detects the surface potential of the photosensitive member, detects the potential of the non-exposed portion of the surface of the photosensitive member and the potential of the exposed portion exposed to a predetermined potential. There is known control for adjusting the charging bias, the developing bias, and the LD power based on the fluctuation of the potential and the difference between surface potentials.

  However, in Patent Document 1, the charging bias correction is performed so as to suppress the fluctuation of the image quality due to the rotation of the developing gap, and the correction for adjusting the charging bias, the developing bias, the LD power, etc. is performed before being performed. The surface potential of the photosensitive member due to the original charging bias or the like can not be accurately obtained.

  Even if the image forming conditions are corrected to suppress the image quality fluctuation caused by the rotation of the development gap, the original image forming conditions before the correction can be accurately obtained in order to adjust the image forming conditions. You need to do so.

  In order to solve the above problems, the invention according to claim 1 comprises a photosensitive member, a charging member for charging the photosensitive member, an exposing member for exposing the photosensitive member charged by the charging member, and the exposing member In an image forming apparatus having a developing member for forming a toner image on the photosensitive member exposed by the exposure method, and a potential detection member for detecting the surface potential of the photosensitive member, control for canceling out the fluctuation of image density generated in the toner image Based on data, charging bias application from the charging member or exposure output from the exposure member is corrected to form a correction surface potential on the photosensitive member, and the formed correction surface potential is detected by the potential detection member According to another aspect of the present invention, there is provided an image forming apparatus, wherein an original surface potential is calculated from a surface potential except for a correction potential which is a potential for correction according to the control data.

  According to the present invention, even if the image forming conditions are corrected to suppress the image quality fluctuation caused by the rotation of the developing gap, the original image forming conditions before the correction are performed to adjust the image forming conditions. Can be accurately obtained.

FIG. 2 is a hardware configuration diagram of an image forming apparatus. It is an explanatory view which saw through an optical writing unit from the side. It is an explanatory view which saw through an optical writing unit from the upper surface. It is a fragmentary perspective view which shows an example of the installation condition of an image density detection sensor. FIG. 2 is a functional block diagram of the image forming apparatus. FIG. 6 is an explanatory view showing fluctuation of a development gap due to rotational runout of a photosensitive drum. FIG. 6A is an explanatory view showing an example of a correction toner pattern in which toner patterns of respective colors are formed at the same position in the main scanning direction. FIG. 6B is an explanatory view showing an example of a correction toner pattern in which toner patterns of respective colors are formed at mutually different positions in the main scanning direction. An example of the relationship between the rotational position detection signal output from the photo interrupter, the toner adhesion amount detection signal (photosensitive drum rotation period component) detected by the image density detection sensor, and the correction table generated based on these signals FIG. 5 is a timing chart showing a relationship between a rotational position detection signal of a photosensitive drum input to a control unit and an output signal of an image density detection sensor (toner adhesion amount detection signal). It is a schematic diagram which shows the image development rotation position detection apparatus provided with the photo-interrupter which detects the home position of a development roller. It is a graph which shows an example of the output signal of the same photo-interrupter. 7 is a graph showing an example of the relationship between the fluctuation of the amount of toner adhesion based on the toner adhesion amount detection signal from the image density detection sensor and the output signal of the photo interrupter (development roller rotation position detection signal). It is the graph which accumulated and showed the several signal division obtained by dividing a toner adhesion amount detection signal at the home position detection timing contained in the output signal of the same photo interrupter. It is an example of the image formation processing flow of an image forming apparatus. FIG. 6 is an explanatory view showing a potential relationship among a charging bias, a non-image portion potential of the photosensitive drum, an image portion potential (a low density image portion and a solid image portion), and a developing bias. 7 is an example of a print job execution processing flow of the image forming apparatus. 10 is another example of the image forming process flow of the image forming apparatus. It is an example of the photosensitive body potential characteristic acquisition flow of an image forming apparatus. FIG. 6 is an explanatory view showing an example of a surface potential on a photosensitive drum on which image unevenness correction is superimposed. (A) is an explanatory view showing an example of a photoraptor output signal of a developing roller. (B) is an explanatory view showing an example of a photoraptor output signal of a photosensitive member. (A) is an explanatory view showing an example of a prediction waveform. (B) is an explanatory view showing an example of a waveform obtained by subtracting a predicted waveform in a part of the exposure portion on the photosensitive drum on which the image unevenness correction is superimposed. (A) is explanatory drawing showing another example of a predicted waveform. (B) is an explanatory view showing an example of a waveform obtained by subtracting a predicted waveform in a part of the non-exposed portion on the photosensitive drum on which the image unevenness correction is superimposed.

  Hereinafter, an embodiment of the present invention will be described based on the attached drawings. In each of the drawings for describing the embodiments of the present invention, components such as members having the same function or shape and components such as components are described once by attaching the same reference numerals as much as possible. So I will omit the explanation.

  The image forming apparatus shown in FIG. 1 is a configuration example of a full color machine of four tandem tandem type intermediate transfer system, but a full color machine of quadruple tandem direct transfer system, full color machine of one drum type intermediate transfer system, The present invention is also applicable to an image forming apparatus having another configuration, such as a monochrome machine such as a drum type direct transfer system.

  An image forming apparatus 100 shown in FIG. 1 includes an intermediate transfer belt 1 as an intermediate transfer member as an image carrier and an image carrier as juxtaposed along a stretched surface or a stretched surface of the intermediate transfer belt 1. It has photosensitive drums 2Y, 2M, 2C, and 2K, which are rotary members serving as latent image carriers. The symbols Y, M, C, and K appended to the symbols indicate the colors yellow, magenta, cyan, and black, respectively.

  First, the yellow image forming station will be described representatively. Around the photosensitive drum 2Y, the reference rotating positions of the charging charger 3Y and the photosensitive drum 2Y, which are charging devices as charging members, are sequentially arranged in the rotational direction (home position And a reference rotational position detection unit 18Y that is a phase detection member that detects the The charging member may be a charging roller instead of the charging charger. The reference rotational position detection means 18Y can employ detection using a photo interrupter and a light shielding plate known as an example. However, the configuration is not limited thereto, and any other configuration that can detect a rotational position, such as a rotary encoder, may be adopted. In addition, since a reference | standard rotational position detection means can specify a rotational phase by detecting a reference rotational position, it can also be called a phase detection means. The same applies to the means for detecting the reference rotational position of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka as developing members, as described later.

  Furthermore, an optical writing unit 50, which is an optical writing unit as a latent image forming member as a latent image forming member that exposes the photosensitive drum 2Y to write an electrostatic latent image, and a potential detection member that detects the surface potential of the photosensitive drum 2Y. Surface potential sensor 19Y, developing unit 5Y as a developing device, primary transfer roller 6Y as a primary transfer means, photoreceptor cleaning unit 7Y as a latent image carrier cleaning means comprising a blade and a brush, etc., charge removing member 8Y, which is a quenching lamp (QL), is disposed.

  An image forming station as an image forming member for forming a toner image on the intermediate transfer belt 1 comprises a photosensitive drum 2Y, a charger 3Y, an optical writing unit 50, a developing unit 5Y, a primary transfer roller 6Y, etc. There is. The same is true for the other colors, ie, magenta, cyan and black imaging stations.

  The intermediate transfer belt 1 is rotatably supported by rollers 11, 12, 13 as a plurality of support members. On the opposite side of the intermediate transfer belt 1 from the roller 12, a belt cleaning unit 15 provided with a blade, a brush and the like is provided. The intermediate transfer belt 1, the rollers 11, 12 and 13, and the belt cleaning unit 15 constitute an intermediate transfer unit 33. At a portion facing the roller 13, a secondary transfer roller 16 as a secondary transfer member is provided.

  Above the optical writing unit 50, a scanner unit 9 as an image reading member, an ADF 10 as an automatic document supply member, and the like are provided. At the lower part of the apparatus main body 99, paper feed trays 17 as a plurality of paper feed units are provided. A recording sheet 20 as a recording material stored in each sheet feeding tray 17 is fed by the pickup roller 21 and the sheet feeding roller 22, conveyed by the conveying roller pair 23, and intermediately transferred at a predetermined timing by the registration roller pair 24. The belt 1 and the secondary transfer roller 16 are fed to a secondary transfer nip N2, which is a secondary transfer area in which the belt 1 and the secondary transfer roller 16 face each other. A fixing unit 25 as a fixing member is provided on the downstream side of the secondary transfer nip portion N2 in the sheet conveyance direction.

  The image forming members for forming toner images on the surfaces of the photosensitive drums 2Y, 2M, 2C and 2K and finally transferring the toner images to the recording paper 20 include four imaging stations, an optical writing unit 50, and an intermediate It is comprised by each member in connection with image formation, such as the transfer unit 33 and the secondary transfer roller 16.

  In FIG. 1, reference numeral 26 denotes a paper discharge tray, and reference numeral 27 denotes a switchback roller pair.

  The developing units 5Y, 5C, 5M, 5K are developing rollers 5Ya, 5Ca, 5Ca, 5Ca, 5Ca, which are rotating bodies as developer carrying members disposed close to the surfaces of the photosensitive drums 2Y, 2M, 2C, 2K via developing gaps. It has 5 Ma and 5 Ka. The developing rollers 5Ya, 5Ca, 5Ma, 5Ka carry a two-component developer including toner and carrier in the developing units 5Y, 5C, 5M, 5K, and the toner in the carried two-component developer is a photosensitive drum The photosensitive drums 2Y, 2M, 2C, and 2K are adhered to the photosensitive drums 2Y, 2M, 2C, and 2K in a development region facing the photosensitive drums 2Y, 2M, 2C, and 2K, and an image is formed on the photosensitive drums 2Y, 2M, 2C, and 2K.

  The surface potential sensors 19Y, 19C, 19M, 19K are generated by the potentials of the electrostatic latent images on the photosensitive drums 2Y, 2M, 2C, 2K written by the optical writing unit 50, that is, by the developing units 5Y, 5C, 5M, 5K. The surface potentials of the photosensitive drums 2Y, 2M, 2C, and 2K before the toner is attached and developed are detected. The detected surface potential is fed back to setting information of image forming conditions such as charging biases of the chargers 3Y, 3C, 3M and 3K, the power of optical writing of the optical writing unit 50, and the stability of image density is maintained. Used for Since the performance of charging and exposure may change due to the deterioration of the photosensitive member itself and the environmental change in which the image forming apparatus 100 is placed, the stability of the image density by the feedback of the surface potential sensor detection is maintained even during printing. .

  The optical writing unit 50 writes on the surfaces of the photosensitive drums 2Y, 2M, 2C, 2K uniformly charged in the dark by the chargers 3Y, 3C, 3M, 3K based on the image information. Emit light. The optical writing unit 50 scans each of the photosensitive drums 2Y, 2M, 2C, and 2K in the dark by this writing light, and Y, C, and C on the surface of the photosensitive drums 2Y, 2M, 2C, and 2K. Write electrostatic latent images for M and K. The writing light emitted from the optical writing unit 50 may be light from a semiconductor laser as will be described later as an example, or may be light from an LED array as another example, but is not limited thereto.

  Reference numeral 37 denotes a controller board. A central processing unit (CPU) 38, a random access memory (RAM) 39, a read only memory (ROM) 40, a hard disk drive (HDD) 41, and an I / F (interface) 42 are mounted on the controller board 37. The CPU 38 controls each member in the image forming apparatus 100 by executing an image forming operation program stored in the ROM 40 or the HDD 41 with the RAM 39 as a work area, and performs an image forming operation. The ROM 40 or the HDD 41 can store various settings used for the image forming operation. The CPU 38 can also control the image forming apparatus 100 based on image forming operation programs and various settings stored in various known external recording media.

  The HDD 41 stores, reads, and writes data according to the control of the CPU 38. The I / F 42 performs communication between the image forming apparatus 100 and an external apparatus according to the control of the CPU 38, and exchanges data between members in the image forming apparatus 100.

  In the configuration shown in FIG. 1, the image forming operation will be described in a general way. When a print start command is input to the controller board 37, the rollers around the photosensitive drums 2Y, 2M, 2C, 2K, around the intermediate transfer belt 1, the sheet feeding / conveying path, etc. start to rotate at a predetermined timing. Sheet feeding from the sheet feeding tray 17 is started. On the other hand, each photosensitive drum 2Y, 2M, 2C, 2K is irradiated with light from the optical writing unit 50 after the charging step of charging the surface to a uniform potential by the chargers 3Y, 3M, 3C, 3K. The light is transferred to an exposure step in which the surface is exposed according to the image data. The potential pattern after being exposed is called an electrostatic latent image, but toner is transferred from the developing units 5Y, 5M, 5C, 5K onto the surface of the photosensitive drum 2Y, 2M, 2C, 2K carrying the electrostatic latent image. By being supplied, it becomes a developing step in which electrostatic latent images carried on the photosensitive drums 2Y, 2M, 2C, 2K are developed.

  In the configuration of FIG. 1, since the photosensitive drums 2Y, 2M, 2C, and 2K are for four colors, the toner images of yellow, magenta, cyan, and black (the order of colors differs depending on the system) It will be developed on 2M, 2C, 2K. The toner images developed on the respective photosensitive drums 2Y, 2M, 2C, 2K have a primary transfer nip as a primary transfer area which is an opposing area between the photosensitive drums 2Y, 2M, 2C, 2K and the intermediate transfer belt 1. In N1, the image is transferred onto the intermediate transfer belt 1 by the primary transfer bias and the pressing force applied to the primary transfer rollers 6Y, 6M, 6C, 6K disposed opposite to the photosensitive drums 2Y, 2M, 2C, 2K. Ru. A full color toner image is formed on the intermediate transfer belt 1 by repeating this primary transfer operation for four colors while adjusting the timing.

  The full color toner image formed on the intermediate transfer belt 1 is transferred to the recording paper 20 conveyed at the secondary transfer nip N2 by the registration roller pair 24 at the same timing. At this time, secondary transfer is performed by the secondary transfer bias and the pressing force applied to the secondary transfer roller 16. The recording paper 20 to which the full color toner image has been transferred passes through the fixing unit 25 so that the toner image carried on the surface of the recording paper 20 is heated and fixed.

  In the case of single-sided printing, the sheet is straightly conveyed and conveyed to the sheet discharge tray 26. In the case of double-sided printing, the conveying direction is changed downward and conveyed to the sheet reversing unit. The recording paper 20 that has reached the paper reversing unit is reversely conveyed in the transport direction by the switchback roller pair 27 and leaves the paper reversing unit from the rear end of the paper. This is called a switchback operation, which reverses the front and back of the recording paper 20. The recording paper 20, which has been turned upside down, does not return to the fixing unit 25, but passes through the paper refeeding conveyance path and merges with the original paper feeding path. After that, the toner image is transferred in the same manner as in the case of the front surface printing, and the sheet passes through the fixing unit 25 and is discharged. This is a duplex printing operation.

  Further, to explain the operation of each part to the end, the photosensitive drums 2Y, 2M, 2C, 2K which have passed through the primary transfer nip N1 carry primary transfer residual toner on their surface, and these are taken as the photosensitive member cleaning unit 7Y, It is removed by 7M, 7C, 7K. Thereafter, the surface is uniformly discharged by quenching lamps 8Y, 8M, 8C, 8K to prepare for charging for the next image. The secondary transfer residual toner is also carried on the surface of the intermediate transfer belt 1 which has passed through the secondary transfer nip N2, but this is also removed by the belt cleaning unit 15, and the next toner image is Prepare for transfer. By repeating such an operation, single-sided printing or double-sided printing is performed.

  The image forming apparatus 100 is an optical sensor unit including an optical sensor or the like as an image density detection unit that detects an image density (toner adhesion amount per unit area) of a toner image formed on the outer peripheral surface of the intermediate transfer belt 1 The image density detection sensor 30 is provided. The detection result of the image density detection sensor 30 is used for correction control of image forming condition setting information for reducing image density unevenness (image density unevenness in the sub scanning direction; the same applies hereinafter) to be described later.

  In the configuration example shown in FIG. 1, the image density detection sensor 30 is disposed at a position P1 before secondary transfer, which is a position opposite to the portion of the intermediate transfer belt 1 wound around the roller 11. The image density detection sensor 30 may be disposed at a position P2 after secondary transfer, which is a position on the downstream side of N2, as shown in the figure. When the image density detection sensor 30 is arranged on the downstream side of the secondary transfer nip N2 such as the position P2, as shown in FIG. Preferably, a roller 14 is provided, and an image density detection sensor 30 is provided to face the roller 14.

  Of the above-described two types of arrangement positions of the image density detection sensor 30, the position P1 before secondary transfer is a position for detecting the toner pattern on the intermediate transfer belt 1 before the secondary transfer step, and the machine layout is restricted. Without this, this configuration is often adopted. Further, since the position P1 before secondary transfer can be detected immediately after forming the toner pattern (correction toner pattern) for detecting uneven image density, the waiting time is also small, and the secondary transfer to the correction toner pattern is performed. Since it is not necessary to slip through the nip portion N2, there is also an advantage that the device for that purpose is unnecessary.

  However, in a model where the secondary transfer position such as the secondary transfer nip N2 is immediately after the imaging station for the fourth color (black in the example of FIG. 1), the sensor is installed at the above position P1. It may be difficult in space. In such a case, the image density detection sensor 30 is installed at the position P2 which is the position after the secondary transfer, and the toner image of the image pattern formed on the intermediate transfer belt 1 is made to pass through the secondary transfer nip N2. After that, the density of the toner image is detected by the image density detection sensor 30. As a method of causing the secondary transfer nip portion N2 to pass through, separation of the secondary transfer roller 16 from the intermediate transfer belt 1, application of a reverse bias to the secondary transfer roller 16, and the like can be considered, but it is not particularly limited here.

  In addition to the image forming apparatus shown in FIG. 1, a single drum type intermediate transfer full color machine including a photosensitive drum and a revolver developing unit opposed thereto, and four photosensitive units below four image forming stations. The present invention is also applicable to a full color machine, a monochrome machine, and the like of a four tandem tandem direct transfer system having a transfer unit for transferring a toner image formed on a body drum onto a recording sheet.

  In each configuration example, the correction toner pattern is formed on the photosensitive drum and transferred to the intermediate transfer belt or the transfer conveyance belt which is a downstream belt, so that the image is opposed to the surface of the photosensitive drum. The concentration detection sensor 30 may be installed. In this case, the installation position of the image density detection sensor 30 is from the developing position by the developing unit or the revolver developing unit to the transfer position to the intermediate transfer belt or the transfer conveyance belt.

  Here, the optical writing unit 50 will be described in detail with reference to FIGS. 2 and 3. FIG. 2 is an explanatory view in which the optical writing unit 50 is seen through from the side, and FIG. 3 is an explanatory view in which the optical writing unit 50 is seen through from the top.

  The optical writing unit 50 uses a polygon mirror 51 to deflect and scan light beams of different colors above and below the polygon mirror surface in the main scanning direction, and also to perform an opposite distribution scan around the polygon mirror 51. The light beams of four colors scan on the photosensitive drums 2Y, 2M, 2C, and 2K of the respective colors.

  The optical writing unit 50 includes LD units 64-1 and 64-2, which are light source units as exposure members. The LD units 64-1 and 64-2 each have a laser element, and each laser element is activated and modulated according to image data to selectively emit a light beam. The operation until the surface of each photosensitive drum is exposed by the light beam will be described below.

  The light beam emitted from the LD unit 64-1 passes through the cylinder lens 65-1 and enters the polygon mirror 51 which is rotated by the polygon motor. The LD unit 64-1 has LDs (Laser Diodes) in the upper and lower portions, and the light beam for M color emitted from the LD in the upper portion is incident on the upper surface of the polygon mirror 51. The light beam for the Y color emitted from the LD at the lower portion is made to be incident on the lower surface of the polygon mirror 51.

  The light beam of M color incident on the upper surface of the polygon mirror 51 is deflected by the rotation of the polygon mirror 51, and the deflected light beam of M color passes through the fθ lens 52-1 and is reflected by the mirrors 53 to 55. It is folded back and scans over the photosensitive drum 2M of FIG. In addition, the Y light beam incident on the lower surface of the polygon mirror 51 is deflected by the rotation of the polygon mirror 51, and the deflected Y light beam passes through the fθ lens 52-1 by the mirror 56. It is folded back and scans over the photosensitive drum 2Y of FIG.

  In addition, a synchronization mirror 61-1, a synchronization lens 62-1, and a synchronization sensor 63-1 are provided at the end in the main scanning direction writing side which is ahead of the image writing position in the non-image writing area in the main scanning direction. . The light beam of each of the M and Y colors transmitted through the fθ lens 52-1 is reflected by the synchronous mirror 61-1, condensed by the synchronous lens 62-1, and is incident on the synchronous sensor 63-1. The synchronization sensor 63-1 outputs a synchronization detection signal for determining the write start timing of the main scan of the color when the light beam of each of the M and Y colors is incident.

  The light beam emitted from the LD unit 64-2 which is a light source unit passes through the cylinder lens 65-2 and enters the polygon mirror 51 which is rotated by the polygon motor. The LD unit 64-2 has LDs in the upper and lower portions, and the C-color light beam emitted from the LD in the upper portion is incident on the upper surface of the polygon mirror 51 and emitted from the LD in the lower portion. The K light beam is made to enter the lower surface of the polygon mirror 51.

  The C light beam incident on the upper surface of the polygon mirror 51 is deflected by the rotation of the polygon mirror 51, and the deflected C light beam passes through the fθ lens 52-2 by the mirrors 57 to 59. It is folded back and scans over the photosensitive drum 2C of FIG. The K light beam incident on the lower surface of the polygon mirror 51 is deflected by the rotation of the polygon mirror 51, and the deflected K light beam passes through the fθ lens 52-2 by the mirror 60. It is folded back and scans over the photosensitive drum 2K of FIG.

  In addition, a synchronization mirror 61-2, a synchronization lens 62-2, and a synchronization sensor 63-2 are provided at the end in the main scanning direction writing side which is ahead of the image writing position in the non-image writing area in the main scanning direction. . The light beams of C and K colors transmitted through the fθ lens 52-2 are reflected by the synchronous mirror 61-2, condensed by the synchronous lens 62-2, and are incident on the synchronous sensor 63-2. There is. The synchronization sensor 63-2 outputs a synchronization detection signal for determining the write start timing of the main scan of the color when the light beam of each color of C and K is incident.

  Each member in the optical writing unit 50 operates as described above, scans the surface of the photosensitive drums 2Y, 2M, 2C, and 2K with a light beam to write a latent image. The units made of members for writing the latent image by scanning the surface of the photosensitive drums 2Y, 2M, 2C, 2K with a light beam are respectively referred to as optical writing units 50Y, 50M, 50C, 50K.

  FIG. 4 is a partial perspective view showing an example of the installation state of the image density detection sensor 30 (P1) of FIG. The example shown in FIG. 2 shows an example in which the image density detection sensor 30 is installed at a position P1 before secondary transfer in the image forming apparatus 100. The image density detection sensor 30 is a four-head type image density detection sensor 30 in which four LED (Light Emission Diode) optical sensors are mounted on a sensor substrate 32. Four sensor heads 31 are arranged side by side in the direction (main scanning direction) orthogonal to the intermediate transfer belt rotation direction (sub scanning direction), in other words, in the axial direction of the photosensitive drums 2Y, 2M, 2C, 2K. The LED optical sensor includes, as an example, a light emitting element and two light receiving elements.

  With this configuration, it is possible to simultaneously detect the amount of toner adhesion at four locations in the main scanning direction, and it is possible to use each sensor head 31 exclusively for each color. The number of sensor heads in the image density detection sensor 30 is not limited to four, and may be, for example, the configuration of the image density detection sensor 30 provided with one to three sensor heads. The configuration of the plurality of image density detection sensors 30 may be employed.

  Each sensor head 31 is disposed to face the outer peripheral surface of the intermediate transfer belt 1 at a distance of about 5 mm as a detection distance. In the present embodiment, the image density detection sensor 30 is provided in the vicinity of the intermediate transfer belt 1, and the setting information of the image forming condition is corrected based on the toner adhesion amount on the intermediate transfer belt 1. The image density detection sensor 30 may be disposed to face the photosensitive drums 2Y, 2M, 2C, and 2K, or may face the recording sheet 20 to which the image is transferred from the intermediate transfer belt 1. It may be disposed.

  An output signal from the image density detection sensor 30 is converted into a toner adhesion amount in the CPU 38 and stored as an image density in the RAM 39, the ROM 40 or the HDD 41. In this regard, the RAM 39 or the ROM 40 or the HDD 41, together with the image density detection sensor 30, constitutes an image density detection means. The RAM 39 or the ROM 40 or the HDD 41 stores the image density as time series data of a predetermined sampling interval. The RAM 39 or the ROM 40 or the HDD 41 also stores various information on output data of the sensors such as the surface potential sensors 19Y, 19C, 19M, 19K, correction data, control results, and the like.

  FIG. 5 is a functional block diagram. FIG. 2 is a functional block diagram of the image forming apparatus 100. Image forming apparatus 100 includes an input receiving unit 110, a control unit 120, a storage unit 130, and a read / write processing unit 140.

  The input receiving unit 110 executes a function of receiving various inputs from the operator on the image forming apparatus 100. A communication I / F that receives a print instruction from an external terminal, a known operation panel, or the like may be used.

  The control unit 120 is realized by the CPU 38 executing a program stored in the HDD 41, and executes control of the entire image forming apparatus 100.

  The storage unit 130 is executed by processing of the RAM 39 or the ROM 40 or the HDD 41, and executes a function of storing programs, document data, various setting information necessary for the operation of the image forming apparatus 100, an operation log of the image forming apparatus 100, and the like.

  The read / write processing unit 140 is executed by the processing of the CPU 38, and executes functions of storing various data in the storage unit 130 and reading out various data stored in the storage unit 130. The uneven density correction table storage unit 131 will be described later.

  Here, the fluctuation of the development gap which is one of the causes of the image density unevenness will be described. FIG. 6 is an explanatory view showing the fluctuation of the development gap due to the rotational runout of the photosensitive drum. In the figure, the photosensitive drum is eccentric and the developing gap with the developing roller has a maximum value d1. The rotational position 1 (solid line) of the photosensitive drum and the gap with the developing roller has a minimum value d2. 6 illustrates the case where the rotational shake of the photosensitive drum occurs between the rotational position 2 (dotted line) of FIG. Assuming that the surface potential V of the developing roller is constant due to the applied developing bias, the developing electric field E takes a minimum value when the rotational position of the photosensitive drum is position 1. At this time, the image density becomes relatively thin. On the other hand, when the rotational position of the photosensitive drum is position 2, the development electric field E takes a maximum value, and the image density at this time becomes relatively high.

  Since the photosensitive drum rotates at a constant cycle, the toner image developed so that the image density becomes relatively thin in the rotational cycle of the photosensitive drum, and the toner developed so as to be relatively thick An image portion repeatedly occurs, and image density unevenness occurs on the image. In this embodiment, as an example, even when such a change in the development gap occurs, the detection result of the image density unevenness (toner adhesion amount detection signal for the correction toner pattern) is set so that the development electric field becomes constant. Accordingly, the development bias is modulated and controlled to control the image density unevenness. The rotational shake of the developing roller is the same as that of the photosensitive drum.

  Further, the image density unevenness is caused not only by the fluctuation of the development gap but also by the sensitivity unevenness of the photosensitive drums 2Y, 2M, 2C, 2K. If the sensitivity (photosensitive characteristics) of the photosensitive drums 2Y, 2M, 2C, and 2K to exposure occurs due to factors such as environmental fluctuations and deterioration with time, the photosensitive drums 2Y, 2M, 2C, and 2K have variations in the subscanning direction. Since the light potential (latent image portion potential) which is the potential after exposure of 2Y, 2M, 2C, and 2K is different, the potential difference between the latent image portion and the developing roller surface is different. As a result, even if exposure is performed with the same exposure amount, different latent image portion potentials are obtained, and the toner adhesion amount is different, and image density unevenness is generated with the rotation cycle of the photosensitive drum. Incidentally, regarding sensitivity unevenness of the photosensitive drums 2Y, 2M, 2C, 2K, the cost is increased to reduce sensitivity unevenness, but the photosensitive drums 2Y, 2M, 2C, 2K are manufactured using a highly accurate manufacturing method There is also a way.

  The correction control of the image forming condition setting information in the image forming apparatus 100 in the present embodiment for reducing the image density unevenness as described above will be described. This correction control is to form a correction toner pattern to be described later, detect the image density of the formed correction toner pattern, and reduce the image density unevenness in order to improve the image quality of the image to be formed. .

  As shown in FIGS. 7A and 7B, the correction toner pattern is formed to be a toner pattern with high image density for each color of yellow, cyan, magenta, and black. As the image density of the correction toner pattern is higher, it is easier to detect the fluctuation of the image density. Therefore, in the present embodiment, a solid image is used as the correction toner pattern. The correction toner pattern is a high density solid image in the present embodiment, but may be a low density solid image having a density lower than that as long as a change in image density is detected.

  The correction toner pattern is formed to be a long band pattern in the rotation direction (sub scanning direction) of the intermediate transfer belt 1 for any color. The length in the sub scanning direction of the correction toner pattern is set to at least one circumferential length of a rotating body having the same rotation cycle as that of the periodic component of the image density unevenness or a rotation cycle of an integer fraction. The rotating body here is the photosensitive drum 2Y or the developing roller 5Ya, and in the present embodiment, the rotating body corresponds to three circumferential lengths of the photosensitive drum 2Y with a rotation cycle of an integral fraction.

  In this embodiment, in order to suppress image density unevenness due to periodic fluctuation of the development gap between the photosensitive drums 2Y, 2M, 2C, 2K and the developing rollers 5Ya, 5Ca, 5Ma, 5Ka Execute control. Explaining this point in more detail, one of the factors of fluctuation of the development gap is the rotational shake of the photosensitive drums 2Y, 2M, 2C, 2K, and this rotational shake is, for example, the photosensitive drums 2Y, 2M, 2C. And eccentricity of the rotation center position of 2K. Therefore, in the image density unevenness based on the fluctuation of the development gap, the image density having the rotation cycle of the photosensitive drums 2Y, 2M, 2C, 2K (including a rotation cycle of an integral fraction of the rotation cycle). Uneven component is included. Then, in order to detect this image density unevenness component, it is necessary to have a length of at least one circumferential length of the photosensitive drums 2Y, 2M, 2C, 2K as the sub-scanning direction length of the correction toner pattern.

  The example of the correction toner pattern shown in FIG. 7A is an example in which the toner patterns of the respective colors are formed at the same position in the main scanning direction. This position coincides with the detection area of the image density detection sensor 30 in the main scanning direction, specifically the arrangement position of the sensor head 31. In the example of FIG. 7A, the position in the main scanning direction of the toner pattern for correction is at the central portion of the intermediate transfer belt 1, but the present invention is not limited thereto. For example, the end portion in the main scanning direction of the intermediate transfer belt 1 It may be near. On the other hand, the example of the correction toner pattern shown in FIG. 7B is an example in which the toner patterns of the respective colors are formed at mutually different positions in the main scanning direction. The positions coincide with the detection area of the image density detection sensor 30 in the main scanning direction, specifically, the arrangement position of the sensor head 31.

  Forming the correction toner pattern as shown in FIG. 7A is advantageous in that the number of sensor heads 31 for detecting the image density of each toner pattern is only one. On the other hand, when a correction toner pattern as shown in FIG. 7B is formed, it becomes possible to detect each color toner pattern in parallel, and the image density detection of all color correction toner patterns is completed. There is an advantage that the time until it is short can be done.

  Incidentally, as described above, the image density detection sensor may be provided for each of the photosensitive drums to detect the density of the image formed on the photosensitive drum. The influence of the movement variation of the intermediate transfer belt is avoided. Further, as described above, the image density detection sensor may be provided to face the recording sheet on which the image is transferred from the intermediate transfer belt, and the density of the image formed on the recording sheet may be detected.

  Image forming conditions for forming the correction toner pattern, specifically, for example, charging conditions for the chargers 3Y, 3C, 3M, 3K, exposure conditions for the optical writing units 50Y, 50M, 50C, 50K (writing conditions) The developing conditions in the developing units 5Y, 5M, 5C, 5K and the transfer conditions in the primary transfer rollers 6Y, 6C, 6M, 6K, etc. are maintained constant. The charging condition here is a charging bias, the writing condition is an intensity of writing light, the developing condition is a developing bias, and the transfer condition is a transfer bias. In addition, the chargers 3Y, 3C, 3M, 3K, the optical writing units 50Y, 50M, 50C, 50K, the developing units 5Y, 5M, 5C, 5K, the primary transfer rollers 6Y, 6C, 6M, 6K, etc. In creating a pattern, it takes charge of a series of image forming processes such as development, charging, exposure and the like as in the image forming operation.

  If there are no development gap fluctuations and other image density unevenness generation factors (sensitivity unevenness of photosensitive drums 2Y, 2M, 2C, 2K, etc.), the image forming conditions are maintained constant and the correction toner pattern consisting of a solid image is When formed, the image density is uniform in the sub-scanning direction, and image density unevenness does not occur. However, even if the image forming conditions are maintained constant and the correction toner pattern consisting of a solid image is formed, the image density unevenness occurs due to the image density unevenness generation factor such as the fluctuation of the development gap. The image density unevenness can be obtained by continuously detecting the image density of the correction toner pattern which is a belt-like pattern of a solid image long in the sub scanning direction by the image density detection sensor 30. Specifically, the output signal of the image density detection sensor 30 is input to the control unit 120 as time series data at a predetermined sampling interval, so that the control unit 120 detects each reference rotational position (a phase detection unit). ) Based on the rotational position detection signals from 18Y, 18C, 18M and 18K, the image density is stored as time series image density based on the home position of each photosensitive drum 2Y, 2M, 2C and 2K.

  FIG. 8 shows rotational position detection signals output from reference rotational position detection means (phase detection means) 18Y, 18C, 18M, 18K, and toner adhesion amount detection signal (photosensitive drum rotation period component) by the image density detection sensor 30. And a correction table (correction information) which is control data for canceling the fluctuation of the image density created based on these signals. Note that FIG. 8 shows signals for two revolutions of the photosensitive drums 2Y, 2M, 2C, and 2K.

  In FIG. 8, the image density unevenness of the correction toner pattern is shown as a fluctuation of the sensor output value of the toner adhesion amount detection signal. As shown in FIG. 8, the toner adhesion amount detection signal fluctuates in the same cycle as the cycle of the rotational position detection signal. In the present embodiment, setting information of the image forming conditions of the developing units 5Y, 5M, 5C, 5K and the chargers 3Y, 3C, 3M, 3K so as to generate the image density unevenness having the opposite phase to the image density unevenness. Correction is performed to generate a correction table that cancels the image density unevenness.

  Here, the developing bias, the exposure power (exposure output), the charging bias, etc., which are the image forming condition setting information, may have a negative sign or the adhesion amount may decrease as the absolute value thereof increases. In some cases, it is not appropriate to express as: but a correction table in the direction to cancel the image density unevenness indicated by the toner adhesion amount detection signal is generated, that is, an image density unevenness in reverse phase to the image density unevenness indicated by the toner adhesion amount. Generate a correction table to create.

  The amount of fluctuation of the correction table with respect to the amount of fluctuation [V] of the toner adhesion amount detection signal at the time of determining this correction table can be obtained from a theoretical value. In the present embodiment, using a gain from the theoretical value, a correction table is generated from the toner adhesion amount detection signal to generate an image density unevenness in the opposite phase. At that time, the correction table is generated based on the rotational position detection signals output from the reference rotational position detection means (phase detection means) 18Y, 18C, 18M and 18K, for example, as shown in FIG. Ru. In the example shown in FIG. 8, the top of the correction table is generated so as to be the home position detection timing (rising timing of the rotational position detection signal).

  When generating such a correction table, for example, the development bias correction table in which the correction table corrects the development bias takes into consideration the correction toner pattern movement time from the development region to the image density detection sensor 30. If the movement time is just an integral multiple of the photosensitive drum rotation period, the top of the correction table is adjusted to the timing of the rotational position detection signal. If the movement time deviates from an integral multiple of the photosensitive drum rotation period, the correction table is generated by shifting the timing by the time of the deviation. Similarly, the exposure power correction table applies the correction table in consideration of the toner pattern movement time from the exposure position to the image density detection sensor 30. Similarly, in the case of the charging bias correction table, the correction table is applied in consideration of the toner pattern moving time from the charging position to the image density detection sensor 30. In the present embodiment, a phase shift may occur due to an error in the layout distance due to a delay in output responsiveness of the high voltage power supply, a variation in component accuracy, a variation in assembly accuracy, or the like. Therefore, the correction table is generated by adjusting the phase shift based on the theoretical value. The correction table to be applied is applied to at least the exposure power correction table and the charging bias correction table among the developing bias correction table, the exposure power correction table, and the charging bias correction table. In the present embodiment, a charging bias correction table is used.

  The formation start timing of the correction toner pattern is determined based on the timing at which the home position of the photosensitive drums 2Y, 2M, 2C, 2K is detected by the reference rotational position detection means (phase detection means) 18Y, 18C, 18M, 18K. Be done. In the example shown in FIG. 8, the image density detection sensor 30 synchronizes with the home position detection timing so that the tip position of the correction toner pattern is detected by the image density detection sensor 30 at the home position detection timing (rising timing of the rotational position detection signal). Then, a correction toner pattern is formed.

  In order to enable formation of a correction toner pattern at this timing, rotational position detection signals from reference rotational position detection means (phase detection means) 18Y, 18C, 18M, 18K are input to the control unit 120. Then, the control unit 120 obtains the home position detection timing from the input rotational position detection signal, and controls the image forming unit in synchronization with this timing to form a correction toner pattern.

  An output signal (toner adhesion amount detection signal) from the image density detection sensor 30 is input to the control unit 120. When generating the correction table, the control unit 120 acquires the home position detection timing from the rotational position detection signals from the reference rotational position detection means (phase detection means) 18Y, 18C, 18M and 18K, and synchronizes with this timing. The sampling of the toner adhesion amount detection signal from the image density detection sensor 30 is started to create a correction table. The created correction table is stored in the density unevenness correction table storage unit 131. Although developing bias, exposure power, charging bias and the like have been mentioned as an example of the image forming conditions for canceling the image density unevenness, in addition to this, the developing gap, the width of the developing region in the rotational direction, the developing roller or The rotational speed of the photosensitive member may be used.

  FIG. 9 is a timing chart showing the relationship between the rotational position detection signal of the photosensitive drum input to the control unit 120 and the output signal of the image density detection sensor 30 (toner adhesion amount detection signal). In the present embodiment, the tip position of the correction toner pattern is detected by the image density detection sensor 30 at the home position detection timing (rising timing of the rotational position detection signal) so as to obtain the reverse phase relationship shown in FIG. As described above, the exposure start position of the correction toner pattern is determined in synchronization with the home position detection timing. In this embodiment, sampling of the toner adhesion amount detection signal from the image density detection sensor 30 is started from the tip position of the correction toner pattern, but the toner adhesion amount near the top of the correction toner pattern becomes unstable. Cheap. Therefore, sampling of the toner adhesion amount detection signal from the image density detection sensor 30 is started not from the leading end position of the correction toner pattern but from the position shifted to the rear end side to the extent that the toner adhesion amount is stabilized. The exposure start position of the correction toner pattern by the optical writing units 50Y, 50M, 50C, and 50K may be determined.

  In determining the exposure start position of such a correction toner pattern, the home of the photosensitive drum 2Y, 2M, 2C, 2K detected by the reference rotational position detection means (phase detection means) 18Y, 18C, 18M, 18K. Data on the position detection timing and the time required for the correction toner pattern to move from the exposure position by the optical writing units 50Y, 50M, 50C, and 50K to the detection position of the image density detection sensor 30 are required. These data are stored in the storage unit 130, and the exposure start position of the correction toner pattern is determined according to the data. During the time when the correction toner pattern moves from the exposure position by the optical writing units 50Y, 50M, 50C, 50K to the detection position of the image density detection sensor 30, the exposure position by the optical writing units 50Y, 50M, 50C, 50K It may be calculated from the layout distance from the image density detection sensor 30 to the detection position of the image density detection sensor 30 and the process linear velocity.

  The rear end position of the correction toner pattern is determined by the correction toner pattern length, but the rear end position of the correction toner pattern may be determined in the same manner as the front end position determined as described above. In addition, even when the tip end position is arbitrarily determined, the rear end position may be determined according to the above-mentioned data. Such determination of the front end position and / or the rear end position according to the above data is performed by the reference rotational position detection unit (phase detection unit) 18Y, 18C, 18M, and 18K, and the photosensitive drums 2Y, 2M, and 2C. , 2K may be performed based on the elapsed time from the detection of the home position. Also in this case, the determination of the tip end position and / or the rear end position is performed substantially in accordance with the above-mentioned data. In this case, the writing of the correction toner pattern may be arbitrarily performed, and the exposure end position may be determined to be an integral multiple of the circumferential length of the photosensitive drums 2Y, 2M, 2C, and 2K. The elapsed time can be measured, for example, by the CPU of the control unit 120. When performing this measurement, the control unit 120 functions as an elapsed time measuring unit that measures the elapsed time.

  By controlling the formation timing of such a correction toner pattern, it is not necessary to form an unnecessarily long correction toner pattern, and it is possible to reduce toner yield and control time. Since the time for the correction toner pattern to move to the detection position of the image density detection sensor 30 differs depending on the color, the exposure start position of the correction toner pattern is adjusted for each image forming station of each color. The detection time can be shortened by the same detection timing. On the other hand, as shown in FIG. 7B, the formation positions of the correction toner patterns of the respective colors in the sub scanning direction may be different from each other. By making the difference in this manner, it is possible to prevent the deterioration of the cleaning blade or the like in the belt cleaning unit 15 that cleans the toner on the intermediate transfer belt 1 and achieve the long life.

  The above description is based on the rotation of the photosensitive drums 2Y, 2M, 2C, 2K among the photosensitive drums 2Y, 2M, 2C, 2K and the developing rollers 5Ya, 5Ca, 5Ma, 5Ka, which are rotating members forming the development gap. The case where the development gap fluctuates due to runout was taken as an example. The fluctuation of the development gap due to the runout is also caused by the runout of the development rollers 5Ya, 5Ca, 5Ma, 5Ka. Therefore, the reference rotational position of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka (the home rotation position (home position) is the same as in the case of the photosensitive drums 2Y, 2M, 2C, 2K together with or instead of The position (rotational position) may be detected by the reference rotational position detection means and synchronized with the home position to generate a correction table for reducing the image density unevenness component having a rotational cycle of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka. In the present embodiment, a correction table is generated to reduce the uneven image density component of the photosensitive drum and the developing roller.

  Reference rotational position detection means (phase detection means) 18 for each photosensitive drum shown in FIG. 1 and reference rotational position detection means (phase detection means) for the developing roller similar to this, and reference rotational position detection means to be described later May be used.

  FIG. 10 is a schematic view showing a developing rotational position detecting device 70 as reference rotational position detecting means for detecting home positions of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka. In addition, since the phase of rotation can be specified by detecting the reference rotational position, the development rotational position detection device 70 can also be referred to as phase detection means. The development rotational position detection device 70 includes a photo interrupter 71 as phase detection means. Although provided separately for each of the developing rollers 5 </ b> Ya, 5 </ b> Ca, 5 </ b> Ma, and 5 </ b> Ka, they have the same configuration as each other and have the configuration shown in the same drawing. Further, as shown in the same figure, each of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka has a shaft 76 which is an output shaft of the drive motor 78 through a coupling 77 and a shaft 76 which forms the central axis of rotation thereof. And is rotationally driven by the drive of the drive motor 78.

  In addition to the photo interrupter 71, the rotational position detection device 70 includes a light shielding member 72 which is integrally provided with the shaft 79 and which rotates in accordance with the rotation of the shaft 79. The light blocking member 72 is detected by the photo interrupter 71 when the developing rollers 5Ya, 5Ca, 5Ma, 5Ka occupy a predetermined rotational position as the developing rollers 5Ya, 5Ca, 5Ma, 5Ka rotate. Thus, the photo interrupter 71 detects the reference rotational position (home position) of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka.

  In the example shown in FIG. 10, although the direct drive system directly connected to the drive motor is used to drive the developing rollers 5Ya, 5Ca, 5Ma, 5Ka, the speed reduction mechanism is inserted between the power transmission from the drive motor 78. Also good. However, when the speed reduction mechanism is adopted, it is desirable that the light shielding member 72 be installed on the shaft 76 so as to have the same rotational speed as the developing rollers 5Ya, 5Ca, 5Ma, 5Ka. The same applies to the case where the reference rotational position (home position) of the photosensitive drums 2Y, 2M, 2C, and 2K is detected.

  FIG. 11 is a graph showing an example of the output signal of the photo interrupter 71. As shown in FIG. It can be seen that when the light blocking member 72 rotating integrally with the developing rollers 5Ya, 5Ca, 5Ma, 5Ka blocks the light path of the photo interrupter 71, the output is reduced to almost 0V. By using this edge, home positions of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka can be detected. When generating the correction table for reducing the image density unevenness component having the rotation period of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka, the control unit 120 uses an output signal from the photo interrupter 71 (developing roller rotation position detection signal). Based on this, the toner adhesion amount detection signal of the correction toner pattern described above is sampled in synchronization with the home position of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka.

  12 shows the variation of the toner adhesion amount based on the toner adhesion amount detection signal from the image density detection sensor 30 (P1) of FIG. 1 and the output signal of the photo interrupter 71 of FIG. 10 (development roller rotation position detection signal). It is a graph which shows an example of a relation. In this graph, the abscissa represents time, and the ordinate represents the result of converting the toner adhesion amount detection signal from the image density detection sensor 30 into the toner adhesion amount. As shown in FIG. 1, periodic fluctuation corresponding to the rotation period of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka occurs in the toner adhesion amount detection signal in which the correction toner pattern is detected by the image density detection sensor 30. .

  The toner adhesion amount detection signal from the image density detection sensor 30 also includes, for example, the rotation period components of the photosensitive drums 2Y, 2M, 2C, and 2K, in addition to the rotation period components of the developing rollers 5Ya, 5Ca, 5Ma, and 5Ka. It is done. Therefore, in order to generate a correction table for reducing the image density unevenness having the rotation period of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka, the rotation period of the developing roller is detected from the toner adhesion amount detection signal from the image density detection sensor 30. The process of extracting the components is necessary. Although not described in the description, the photoreceptor adhesion amount detection signal from the image density detection sensor 30 is also used to generate the correction table for reducing the image density unevenness having the rotation cycle of the photoreceptor drum. A process of extracting a rotation period component of the drum is necessary.

  As a processing method of extracting the rotation period component of the developing roller from the toner adhesion amount detection signal from the image density detection sensor 30, for example, the toner adhesion amount detection is performed at the home position detection timing included in the output signal of the photo interrupter 71 of the development roller. The signals are divided, and each divided signal division is averaged to extract the rotation period component of the developing roller.

  FIG. 13 is a graph showing a plurality of signal divisions obtained by dividing the toner adhesion amount detection signal at the home position detection timing included in the output signal of the photo interrupter 71. In the present embodiment, ten signal divisions N1 to N10 for the circumferential length of the developing roller are obtained from the above-described correction toner pattern (for the circumferential length of the photosensitive drum). The waveforms shown by thick lines in the figure show the results Avg of averaging processing of these signal sections. In the present embodiment, the simple averaging process is performed on the ten signal sections N1 to N10, but another process may be performed as long as the rotation cycle component of the developing roller can be extracted.

  The rotational period components of the photosensitive drums 2Y, 2M, 2C, 2K and the developing rollers 5Ya, 5Ca, 5Ma from the toner adhesion amount detection signal from the image density detection sensor 30 which detects the correction toner pattern by such signal processing. , And independently obtain rotation period components of 5 Ka. When these rotation cycle components are acquired from the same correction toner pattern, the length, formation position, etc. of the correction toner pattern are the peripheral length of the photosensitive drums 2Y, 2M, 2C, 2K and the developing rollers 5Ya, 5Ca, 5Ma. , 5Ka, and is set based on the circumferential length of the longer circumferential length, the rotational position, the layout distance, and the process linear velocity. In the present embodiment, the circumferential lengths of the photosensitive drums 2Y, 2M, 2C, and 2K are longer.

  On the other hand, in the case of correcting the image density unevenness having the rotation cycles of the developing rollers 5Ya, 5Ca, 5Ma and 5Ka without correcting the image density unevenness having the rotation cycle of the photosensitive drums 2Y, 2M, 2C and 2K. The length and formation position of the correction toner pattern are set based on the circumferential length, rotational position, layout distance, and process linear velocity of the developing rollers 5Ya, 5Ca, 5Ma, 5Ka. The layout distance here means the distance in the direction along the sub-scanning direction of the section between the development area and the detection position of the correction toner pattern by the image density detection sensor 30.

  The case where both of the reference rotational position detection means (phase detection means) 18Y of the photosensitive drum 2Y in FIG. 1 and the photo interrupter 71 of the development rotational position detection device 70 of the developing roller 5Ya in FIG. When both the rotation period components of the photosensitive drums 2Y, 2M, 2C, and 2K and the rotation period components of the development rollers 5Ya, 5Ca, 5Ma, and 5Ka are obtained from the same correction toner pattern, the formation timing of the correction toner pattern is Home rotational position detection timing of the photosensitive drums 2Y, 2M, 2C, 2K detected by the reference rotational position detection means (phase detection means) 18Y, 18C, 18M, 18K, and developing rollers 5Ya, 5Ca detected by the photo interrupter 71. , 5Ma, and 5Ka are determined based on one of the home position detection timings. Therefore, in terms of determining the formation timing of the correction toner pattern, it is sufficient to detect any home position, and for that purpose, reference rotational position detection means (phase detection means) 18Y, 18C, 18M, 18K and photo Any one of the interrupts 71 may be provided.

  FIG. 14 shows an image forming processing flow for reducing the above-described image density unevenness in the image forming apparatus 100. First, when the power of the image forming apparatus 100 is turned on (S1), the control unit 120 executes pre-printing adjustment (S2). The adjustment before printing includes adjustment of the output of the image density sensor 30, determination of a reference value of development potential required to obtain a target toner adhesion amount, and the like. In the pre-printing adjustment in S2, printing is not executed for several hours after printing, but is not performed for several hours after the power is turned on, or left for printing other than ON of the image forming apparatus 100, or printing ends and there is no next job acceptance. You may carry out also in the case etc.

  After completion of the adjustment before printing, the control unit 120 determines whether the update timing of the eccentricity density unevenness correction table has come (S3). If it has reached, the density unevenness correction table is created as described above, and if the density unevenness correction table already exists, it is updated (S4).

  Here, the update timing is after replacement of the photosensitive member. If the photosensitive members are different, the eccentricity is different, and as a result, the period of the image density unevenness is changed, and the correction table is updated. In addition, conditions in which the eccentricity may change may be set as the update timing, such as after the deterioration with time of the surface of the photosensitive member and the assembly portion and the deviation of the rotational position are detected. Although the description has been made with respect to the correction table of the photosensitive member, in the present embodiment, the description is similarly made in the case of the developing roller, the correction table for the developing roller is created, and the density unevenness correction table is updated if it already exists.

  Thereafter, when the control unit 120 receives a print job for the image forming apparatus 100 (S5), the control unit 120 applies the uneven density correction table and executes the print job (S6). As described above, the image density unevenness can be reduced by applying the correction table for canceling out the image density unevenness to the image forming conditions and correcting the image forming conditions.

  Specifically, in the execution of the print job to which the density unevenness correction table of S6 is applied, the control section 120 synchronizes with the home position detection timing of the photosensitive drum during the image forming operation, and stores the density unevenness correction table storage section. Each time series data of the image density unevenness component is read out sequentially from 131, correction values for correcting the set values of the respective image forming conditions are sequentially calculated so as to cancel out the read out image density unevenness component data, and corrected with the correction values The correction control of sequentially applying the image forming conditions is executed. Although the description has been made in synchronization with the home position detection timing of the photosensitive drum, in the present embodiment, it is also synchronized with the home position detection timing of the developing roller.

  The photoreceptor surface potential detected by the surface potential sensor 19Y (19C, 19M, 19K) will be described with reference to FIG. FIG. 13 is an explanatory view showing a potential relationship among the charging bias, the non-image portion potential of the photosensitive drum, the image portion potential, and the developing bias. The surface of the photosensitive drum is uniformly charged by the charging bias V1 applied by the charging chargers 3Y, 3C, 3M and 3K. As a result, the surface potential of the photosensitive drum is charged to V2. Next, the image area is exposed by light writing. As a result, the potential of the non-image area is V3, the surface potential of the photosensitive drum of the low density image area is V5, and the potential of the surface of the photosensitive drum of the solid image area is V6.

  Next, with the developing bias V4 applied by the developing roller, the toner on the developing roller is moved to the image portion of the photosensitive drum for development processing. The toner has a predetermined charge amount, and in the low density image area and the solid image area (high density image area), an amount of toner corresponding to the difference in development potential according to the potential difference in the hatched area in FIG. Adheres to form a toner image.

  Here, the surface potential of the photosensitive member with respect to the charging bias may change due to the nature of the photosensitive member itself, deterioration with time, and environmental changes. In addition, the charge amount of the toner is changed due to the nature of the toner itself, deterioration with time, and environmental change. If each potential difference shown in FIG. 15 deviates from the appropriate range as a result of such a change, it causes an image defect. Therefore, for example, every predetermined number of prints, a potential pattern is created between the image area (latent image area) on the photosensitive member and the sheet between the image area, and exposure and development of the photosensitive member surface in the rotational direction of the photosensitive member Feedback control is performed to adjust the charging bias, the developing bias, and the LD power so that each potential difference is detected appropriately by the surface potential sensor 19Y opposed to the surface of the photosensitive member between them. This adjustment may adjust all of the charging bias, the developing bias, and the LD power, or adjusting any one of them may maintain each potential difference properly.

  In order to obtain the surface potential of the photosensitive member with the surface potential sensor 19Y, an area which is longer than the effective detection range of the surface potential sensor and longer than the settling time of the surface potential sensor is detected as the photosensitive member rotates. It is known to give an average value of time. Therefore, in order to obtain the surface potential of the non-image area V3 and the solid image area V6 as an example, after charging uniformly on the photosensitive member, partial exposure (solid image) is performed and exposure is performed. A potential pattern is created on the photosensitive member such that the non-placed part and the part exposed to light as a solid image part at least become the above-mentioned area.

  The case where the adjustment performed by detecting the surface potential described in FIG. 15 is performed during a print job will be described as an example using FIG. FIG. 16 is a flow showing the details of step S6 in FIG. The print job referred to here is the content to be printed on a plurality of sheets in succession (hereinafter sometimes referred to as continuous sheet passing).

  The control unit 120 first counts the number of printed sheets (S7). Next, for the image forming condition (for example, charging bias) of the first page among a plurality of sheets, the eccentric density unevenness table is corrected (S8) and printing is performed (S9). That is, in synchronization with the home position detection timing of the photosensitive drum 2Y (2M, 2C, 2K) which has started rotation for printing the first page, the image density due to eccentricity of the photosensitive member from the uneven density correction table storage unit 131 Sequentially read out time series data of unevenness component, sequentially calculate correction values for correcting set values of each image forming condition so as to cancel out the read out image density unevenness component data, and correct each image formation condition corrected by the correction value Execute correction control to apply sequentially. Similarly, correction control is started in synchronization with the home position detection timing of the developing roller also for the image density unevenness due to the developing roller eccentricity.

  Next, the control unit 120 determines whether it is time to execute adjustment during printing (S10). The conditions for executing the print job adjustment may be set as appropriate, for example, when printing a predetermined number of sheets, for example, 10 pages, since the print job adjustment was performed last time. If it is not time to execute the adjustment during print job, the process proceeds to the printing operation of the next page (S16).

  If it is the execution timing of the adjustment during the print job, the control unit 120 sets the potential for adjustment on the surface of the photosensitive member corresponding to the paper between continuous paper (hereinafter sometimes referred to as “paper interval”). Form a pattern. As this potential pattern, for example, one stored in advance in the storage unit 130 can be used. Under the image forming conditions for forming the potential pattern, correction based on the eccentric density unevenness table is sequentially started successively, and a corrected potential pattern is formed on the surface of the photosensitive member as a correction surface potential forming step (S11). . Next, in the predicted potential generation step, generation of the predicted potential (S12), which is the potential obtained by predicting the amount of correction, is performed, and then the surface potential detection (S13) of the photosensitive member is performed by the surface potential sensor as the correction surface potential detection step. . Then, in the original surface potential calculation step, the original surface potential which is the surface potential not corrected is calculated from the potential actually detected by the surface potential sensor and the predicted potential (S14), and the calculated original surface potential Adjustment for maintaining the potential difference appropriately is performed (S15).

  The adjustment referred to here is adjustment of image forming conditions such as charging bias, developing bias, LD power (exposure output), transfer bias and the like based on fluctuations of surface potentials and differences between surface potentials. Besides, a method of adjusting the development gap or the width of the development region in the rotational direction may be used.

  In addition, if the generated predicted potential and the detected surface potential are stored in the storage unit 130, the original surface potential calculation (S14) and the adjustment execution with the original surface potential (S15) can be performed between the following sheets. It is also possible.

  The process by the flow shown in FIG. 16 will be further described. As described above, in the present image forming apparatus 100, in order to correct the image density unevenness due to the eccentricity of the photosensitive member and the developing roller, the image forming conditions are corrected so as to cancel the density unevenness having each rotation cycle. . Therefore, the potentials formed in step S11, which are actually detected by the surface potential sensor in step S13 (hereinafter also referred to as real surface potential), are represented by waveforms having their rotation cycles over the entire potential. The potential of the minute is superimposed. That is, ideally, as shown in FIG. 15, periodic variations (potential fluctuations) occur in each potential which is constant due to the correction. Therefore, if the real surface potential is used as it is for feedback-controlled adjustment, there is a possibility that the adjustment can not be performed accurately.

  Therefore, in the present flow, among the real surface potentials, potentials for control data of image density unevenness correction due to eccentricity, and more specifically, potentials for corrections added to the original surface potential according to the control data, for accurate adjustment. The correction surface potential which is the above is subtracted to calculate the original surface potential originally intended to be acquired.

  That is, in step S12, a predicted potential, which is a potential obtained by predicting the correction potential, is generated as a predicted waveform, and in step S14, the original surface potential is calculated by subtracting the predicted waveform from the real surface potential. Then, in step S15, since the adjustment is performed using the calculated original surface potential, accurate adjustment can be performed.

  Here, comparison with original surface potential acquisition by other methods will be described. Instead of the method of generating the predicted potential (predicted waveform) as described above, it is conceivable to apply a moving average filter having, as a tap length, one period of the combined sine wave superimposed as an example. However, for that purpose, it is necessary to measure at least a pattern of one rotation of the photosensitive member. Also, as another example for acquiring the original surface potential, it may be considered to stop the application of a single sine wave or a synthetic sine wave during that time, but the application stop time for the switching of sine wave application OFF / ON. Is required. Both require special time for acquiring the original surface potential, and in particular, the degree of freedom in control during printing is narrowed, which leads to the decrease in productivity of the image forming apparatus.

  On the other hand, in the present embodiment, since the original surface potential can be calculated by generating a predicted potential (predicted waveform) in a desired range at an arbitrary timing, the photosensitive member necessary for adjustment does not become downtime. The surface potential can be accurately acquired.

Next, an example of calculation of the original surface potential will be described. The periodic waves of the surface potential superimposed for the reduction of eccentricity unevenness are a single sine wave (a single sine wave s1, s2, s3) of the photosensitive body, the developing roller and each periodic wave repeated with each cycle. It can be represented as (Equation 1) as a wave (synthetic sine wave) which is represented by ...) and synthesized them.
S = s1 + s 2 + s3 + ... = A1 * sin (w1 * t + B1) + A2 * sin (w2 * t + B2) + A3 * sin (w3 * t + B3) + ... (Equation 1)

  Thus, since a synthetic sine wave is a superposition of a single sine wave, it explains from single sine wave s. A single sine wave can be expressed by (Equation 2).

s = A * sin (w * t + B) (Equation 2)
A: Amplitude B: Initial phase w: (angular) frequency t: Time

Among these, the amplitude A is obtained by acquiring the potential characteristic of the photosensitive member. Details will be described later. The time t, the (angular) frequency w, and the initial phase B can be analytically derived by the following method. First, the time t can be defined from the timing of applying a sine wave. The frequency w is obtained by the following (Equation 3). Here, in the present embodiment, the rotating body of the rotating body cycle is the photosensitive body and the developing roller, and each single sine wave can be calculated.

  w = photoconductor linear velocity / rotating cycle (Equation 3)

  Also, the initial phase B is expressed by (Expression 4). Among them, the charging bias application time b1 can be obtained at the charging bias application timing. Further, the phase delay b2 due to the layout is expressed by (Equation 5).

Initial phase B = b1 + b2 + b3 (Equation 4)
b1: Phase when charging bias is applied b2: Phase delay due to layout b3: Phase delay due to surface potential sensor detection characteristics b2 = (distance between charging position and surface potential sensor position) / photoconductor linear velocity (Equation 5)

  On the other hand, the detection characteristics of the surface potential sensor can be approximated by a moving average filter because the average surface potential of the photosensitive member in a section where the surface potential sensor is present is determined. The frequency characteristic of the N tap moving average filter is expressed by (Expression 6). At this time, the phase delay due to the sensor detection characteristic is expressed by (Expression 7). The tap length in (Expression 7) is expressed by (Expression 8).

F = Σexp (−m × i × w × T) / N (Equation 6)
b3 = atan (F) (Equation 7)
i: Imaginary unit T: Sampling period N: Tap length
atan (arctangent): inverse tangent function (Σ is the sum of m = 0 to N−1, and w has been derived by (Equation 3))
N = length of section averaged by sensor / photoreceptor linear velocity (Equation 8)

  Next, the amplitude A described above is obtained by (Expression 9). Also, A_org can be acquired at the time of application. Furthermore, a_2 is expressed as (Expression 10), and is obtained by (Expression 6).

A = A_org * a_1 * a_2 (Equation 9)
A_org (input signal amplitude): Applied charging bias amplitude a_1 (gain): Influence of charging bias on photoreceptor surface potential a_2 (gain): Attenuation by detection of surface potential sensor a_2 = | F | (Equation 10)

  a_1 can be determined in advance experimentally. The timing to be determined will be described later. The method of determination varies depending on whether a_1 is an exposed area potential or a non-exposed area potential. As a method of obtaining the non-exposure portion potential, the charge bias DC component is shaken at a plurality of levels, and the slope a of the following (Equation 11) is calculated by the least square method or the like to obtain a_1.

  Δ (surface potential) = a Δ (charging bias DC component) (Equation 11)

  On the other hand, with regard to the exposed portion potential, after the calculation of a, the charging bias and the LDP (LD power) may be calculated by the equation (13) with a non-linear function expressed by the equation (12). If the function of (Equation 13) is made linear with respect to the parameter, the parameter can be calculated by the least squares method.

Δ (surface potential) = f (Δ (charging bias DC component), Δ (LDP)) (Equation 12)
a_1 = f (Δ (charging bias direct current component), Δ (LDP)) (Equation 13)

  If (Equation 2) to (Equation 13) described above are determined for the photosensitive drum and the developing roller, respectively, single sine waves are determined, and a synthesized sine wave obtained by combining them is a predicted waveform. That is, the predicted potential can be expressed by (Equation 14). Then, the original surface potential is calculated by subtracting this predicted potential from the real surface potential.

Predicted waveform S = A1 sin (w1 * t + b1) + A2 sin (w2 * t + b2) (Equation 14)
A1 sin (w1 * t + b1): photosensitive drum single sine wave A2 sin (w2 * t + b2): developing roller single sine wave

  In addition to the photosensitive drum and the developing roller, if there is a factor of uneven density having a rotation cycle, single sine waves may be calculated and added respectively. Moreover, although the method using a synthetic | combination sine wave was demonstrated as a generation method of a prediction waveform, it is not restricted to this.

  Here, FIG. 17 shows another example of the image formation processing flow. 10 shows an image processing flow for reducing the above-described image density unevenness in the image forming apparatus 100. First, when the power of the image forming apparatus 100 is turned on (S17), the control unit 120 executes pre-printing adjustment (S18). The adjustment before printing includes adjustment of the output of the image density sensor 30, determination of a reference value of development potential required to obtain a target toner adhesion amount, and the like. In the pre-printing adjustment in S18, printing is not performed for several hundred pages every few hundred pages after printing, but is not performed for several hours after power ON, or left for printing, and there is no next job acceptance other than ON of the image forming apparatus 100 You may carry out also in the case etc.

  After completion of the adjustment before printing, the control unit 120 determines whether the update timing of the eccentricity unevenness correction table has come (S19). If it has reached, the density unevenness correction table is created as described above, and if the density unevenness correction table already exists, it is updated (S20).

  Here, the update timing is after replacement of the photosensitive member. If the photosensitive members are different, the eccentricity is different, and as a result, the period of the image density unevenness is changed, and the correction table is updated. In addition, conditions in which the eccentricity may change may be set as the update timing, such as after the deterioration with time of the surface of the photosensitive member and the assembly portion and the deviation of the rotational position are detected. Although the description has been made with respect to the correction table of the photosensitive member, in the present embodiment, the description is similarly made in the case of the developing roller, the correction table for the developing roller is created, and the density unevenness correction table is updated if it already exists.

  Next, the photosensitive member potential characteristic necessary to create a predicted waveform is acquired and stored (S21). The above-described (Expression 11) (Expression 12) (Expression 13) is acquired by this photosensitive member potential characteristic acquiring step.

  Thereafter, when the control unit 120 receives a print job for the image forming apparatus 100 (S22), the control unit 120 applies the uneven density correction table to execute the print job (S23). As described above, the image density unevenness can be reduced by applying the correction table for canceling (cancelling) the image density unevenness to the image forming condition and correcting the image forming condition.

  Specifically, in the execution of the print job to which the density unevenness correction table of S23 is applied, the control section 120 synchronizes with the home position detection timing of the photosensitive drum during the image forming operation, and the density unevenness correction table storage section 131. The time series data of the image density unevenness component is sequentially read out from the image, correction values for correcting the set values of the respective image forming conditions are sequentially calculated so as to cancel out the read out image density unevenness component data, and each image corrected with the correction value The correction surface potential is formed on the photosensitive member as correction control in which the formation conditions are sequentially applied. Although the description has been made in synchronization with the home position detection timing of the photosensitive drum, in the present embodiment, it is also synchronized with the home position detection timing of the developing roller.

  A detailed flow of the photosensitive member potential characteristic step (S21) of FIG. 17 is shown using FIG. First, the photosensitive body surface potential is formed by moving the charging bias and the charging bias and the LD power for the exposed portion by a plurality of levels (S24). The formed surface potential is detected by the potential sensor (S25). Based on the measurement results, each constant is calculated by approximating the charging bias and the photosensitive member surface potential change with respect to the LD power change of the exposed portion (S26). The acquired constant is stored for use at the predicted potential generation timing. As an example, it may be stored in the storage unit 130.

  As described above, the photosensitive member potential characteristic, which is data necessary for generating the predicted waveform, is acquired in advance, for example, at the warm-up time before the print job is executed (S23), and the predicted waveform is obtained between sheets in the print job. Since the generation and the calculation of the original surface potential are performed, it is possible to adjust the image forming conditions accurately without any downtime.

  Next, with reference to FIGS. 19 and 20, an example of the surface potential formed on the surface of the photosensitive member when the correction based on the density unevenness correction table is applied to the charging bias will be described.

  First, FIG. 19 shows the elapsed time of rotation of the photosensitive drum on the horizontal axis, and the surface potential of the photosensitive member detected by the surface potential sensor on the vertical axis. The horizontal axis in FIG. 20 corresponds to the horizontal axis in FIG. The vertical axis of FIG. 20 (a) represents the photointerrupter output of the developing roller, and the vertical axis of FIG. 20 (b) represents the photointerrupter output of the photosensitive drum. Each of them has been rotating at a constant speed since the time when the photo interrupter first output.

  As can be seen from the output of FIG. 20 (b), the photosensitive drum is rotating in FIG. A direct current charging bias is applied to the rotating photosensitive drum to uniformly charge the photosensitive member surface potential to about 725V. In this state, from around 500 ms, density unevenness correction is superimposed on the charging bias by the correction table of the charging bias of the single sine wave of the photosensitive member. Further, from around 4500 ms, a surface potential pattern is formed by exposure. That is, as an example of the surface potential pattern, exposure is not performed until about 4500 ms at least in the detection range of the surface potential sensor. This portion is shown as a non-exposed portion in FIG.

  Thereafter, exposure corresponding to the solid image is intermittently performed at four places, and as a result, surface potential pattern formation is formed. The portion where the exposure has been performed is indicated as an exposed portion in FIG. Since a portion between the exposure portion and the exposure portion is not exposed, this portion can also be called a non-exposure portion. Then, as can be seen from the output of FIG. 20A, the developing roller starts rotating at a timing at which development is possible from the first exposed portion among the above-mentioned four locations.

  Here, the density unevenness correction is also performed in synchronization with the HP detection of the photo-interrupter of the photosensitive member in FIG. In the non-exposure portion of FIG. 19, the timing indicated by the arrow indicates the start of image density unevenness correction, that is, the timing at which correction by the correction table of the charging bias of a single sine wave of the photosensitive member for reducing the image unevenness density is reflected. It is. Before the start, a certain point continues at about 725 V, but after the start, there is a periodic increase and decrease of the potential. This periodic increase and decrease of the potential is a waveform due to uneven density correction.

  Furthermore, when rotation of the developing roller in FIG. 20A starts, in addition to the correction synchronized with the HP detection of the photo interrupter of the photosensitive member, a single sine of the developing roller synchronized with the HP detection of the photo interrupter 71 of the developing roller. Uneven density correction is also performed using a correction table for the wave charging bias. That is, in addition to the uneven density correction caused by the eccentricity of the photosensitive member in each exposed portion (and the area between the exposed portions) in FIG. 19, the uneven density correction caused by the eccentricity of the developing roller synchronized with the developing roller HP detection Is also superimposed.

  Thus, the photosensitive member surface potential forms a waveform as shown in FIG. 19, and the surface potential sensor detects this waveform. Note that, in FIG. 19, the entire exposed area is assumed to be a solid image as an example, but the pattern is not limited to a solid image, and may be a pattern including an exposed area consisting of a solid image and a low density image.

  Next, a predicted waveform and an example of a waveform obtained by removing the predicted waveform from the correction surface potential will be described with reference to FIGS. 21 and 22.

  FIG. 21A shows, as an example, a predicted waveform which is cut out from the correction table and reproduced for the section of the exposure part of about 6000 to 7000 ms among the four exposure parts. FIG. 21B is a waveform obtained by removing the predicted waveform of FIG. 21A from the surface potential shown in FIG. 19, that is, the real surface potential detected by the potential sensor. The section indicated by the arrow in FIG. 21B is the original surface potential of the exposed portion, that is, the original surface potential of the exposed portion on which the image density unevenness correction by the charging bias correction table is not superimposed. When the image density unevenness correction by the exposure power correction table is also superimposed, the original surface potential of the exposed portion on which the image density unevenness correction by the exposure power correction table is not superimposed is further obtained by the same method. Further, in the case of only the exposure power correction table, the original surface potential of the exposed portion on which the image density unevenness correction by the exposure power correction table is not superimposed is obtained.

  FIG. 22A shows, as an example, a predicted waveform reproduced in about 1500 to 4500 ms of the non-exposed part. FIG. 22 (b) is a waveform obtained by removing the predicted waveform of FIG. 22 (a) from the surface potential shown in FIG. 19, that is, the real surface potential detected by the potential sensor. The section indicated by the arrow in FIG. 22B is the original surface potential of the non-exposed area, that is, the non-exposed area where the image density unevenness correction is not superimposed by the correction table of the charging bias of the single sine wave of the photosensitive member. The potential (surface potential of the photosensitive member when a direct current charging bias is applied).

  Note that the control unit 120 reads the setting by setting in advance the generation timing of the predicted waveform and the potential pattern to be formed on the photosensitive member surface for the measurement of the original surface potential in the storage unit 130, as shown in FIG. As shown in FIG. 22, the original surface potential of the exposed area can be measured, or the original surface potential of the non-exposed area can be measured as shown in FIG. That is, in FIG. 21 and FIG. 22, the original surface potential can be obtained from the real surface potential for an arbitrary portion and an arbitrary period except for the correction amount by the control data. It is possible to acquire, or to acquire about a part of it.

  When the adjustment pattern is created and performed between sheets of a predetermined number of continuous sheet-passing print jobs as in the flow of FIG. 16, for example, the following program may be stored in the storage unit 130 in advance. That is, HP detection by the photo interrupter in the case of using a photo interrupter as a reference rotational position detection means (phase detection means) of the photosensitive member with generation of adjustment pattern (S11) as a trigger, and HP by photo interrupter of the development roller. At the time of detection, a single sine wave is generated for the exposed portion and the unexposed portion. Then, the timing is adjusted by the exposure signal to the optical writing means, for example, the signal that the image part is Low and the non-image part is High, and the predicted waveform is obtained from the surface potential (S13) detected by the surface sensor for each of the exposed and non-exposed parts. It is a program that performs processing to remove.

2Y, 2C, 2M, 2K Photosensitive drum 3Y, 3C, 3M, 3K Charger 5Ya, 5Ca, 5Ma, 5Ka Developer roller 64-1, 64-2 LD unit 18Y, 18C, 18M, 18K Reference rotational position detection means ( Phase detection means)
19Y, 19C, 19M, 19K Surface potential sensor 70 Developing rotational position detecting device 100 Image forming device 120 Controller

JP 2012-163645

Claims (9)

A photoconductor,
A charging member for charging the photosensitive member;
An exposure member for exposing at least a part of the surface of the photosensitive member charged by the charging member;
A developing member for forming a toner image on the photosensitive member exposed by the exposure member;
An image forming apparatus having a potential detection member for detecting the surface potential of the photosensitive member;
The correction surface potential is formed on the photosensitive member by applying the charging bias from the charging member or the exposure output from the exposing member according to the control data that cancels out the fluctuation of the image density generated in the toner image.
An image forming apparatus, wherein an original surface potential is calculated from the real surface potential detected by the potential detection member by the potential detection member, which is the correction surface potential formed, except for a correction potential which is a correction amount according to the control data. It has a phase detection member for detecting the rotational phase of the photosensitive member or the developing member,
The image forming apparatus according to claim 1, wherein the control data is generated at a predetermined detection timing by the phase detection member. 2. The image forming apparatus according to claim 1, further comprising a phase detection member for detecting a rotational phase of the photosensitive member or the developing member, and removing the potential for correction at a predetermined detection timing by the phase detection member. The image forming apparatus according to any one of claims 1 to 3, wherein the correction potential is generated as a predicted potential from the control data, and the original surface potential is calculated by removing the predicted potential from the real surface potential. The image forming apparatus according to any one of claims 1 to 4, wherein the calculation of the original surface potential is performed at an exposure unit exposed by the exposure member on the surface of the photosensitive member corresponding to a sheet interval. The image forming apparatus according to any one of claims 1 to 5, wherein the calculation of the original surface potential is performed in a non-exposure portion on the surface of the photosensitive member corresponding to the sheet space which is not exposed by the exposure member. The image forming apparatus according to claim 1, wherein the image forming condition is adjusted based on the original surface potential. 8. The image forming apparatus according to claim 7, wherein the adjustment of the image forming condition is an adjustment of a charging condition, an exposure condition, or a developing condition. Charging the photosensitive member;
An exposure step of exposing the charged photosensitive member;
An image forming method comprising the steps of: forming a toner image on the photosensitive member that has been exposed;
A correction surface potential forming step of forming a surface potential on the photosensitive member by correcting the charging bias application in the charging step or the exposure output in the exposure step using control data that cancels out fluctuations in image density generated in the toner image;
A correction surface potential detection step of detecting the correction surface potential formed in the correction surface potential forming step;
An original surface potential calculating step of calculating an original surface potential obtained by removing a potential for correction by the control data from a real surface potential detected in the correcting surface potential detecting step;