JP2014132318A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of suppressing deviation of image density over the entire gradation area.SOLUTION: An image forming apparatus main scanning direction image density adjusting means such as a control unit that forms adjustment patterns on an image carrier such as an intermediate transfer belt 7, detects the image density of the adjustment patterns at positions different from one another with optical sensors 160f, 160c, and 160r, and adjusts the intensity of light of an exposing device that exposes photoreceptors to light on the basis of a detection result to adjust the deviation of the image density in the main scanning direction. The control unit forms adjustment patterns having image density equal to or lower than a half tone.

Description

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

  Conventionally, in this type of image forming apparatus, due to the characteristics of the latent image writing means for writing a latent image on the latent image carrier, density unevenness in the main scanning direction may be caused in the image. For example, in a light beam scanning optical system serving as a latent image writing means, the light beam intensity on the surface of the photosensitive member as a latent image carrier varies in the main scanning direction, so that the image density varies in the main scanning direction. Sometimes. This variation in light beam intensity is a so-called shading characteristic in which the light transmittance and light reflectivity vary depending on the incident angle of the light beam in the lens and mirror through which the light beam passes from the light emitting element to the surface of the photoreceptor. Caused by. Further, in a light beam scanning optical system using a light emitting element array in which a plurality of light emitting elements are arranged in the main scanning direction, it is also caused by variations in the amount of light beam emitted from each light emitting element.

  Japanese Patent Laid-Open No. 2004-133867 discloses image formation in which the light beam intensity from the light source in the light beam scanning optical system is increased or decreased in the main scanning direction so that the light beam intensity on the surface of the photosensitive member is made uniform in the main scanning direction. A device has been proposed. In this image forming apparatus, first, adjustment patches having the same image density are respectively formed at the center and both ends of an image carrier such as an intermediate transfer belt. These adjustment patches are detected by optical sensors respectively disposed at both ends and the center of the intermediate transfer belt, and the toner adhesion amount of each adjustment patch is calculated. The light amount is increased or decreased according to the calculated adhesion amount of each adjustment patch. According to this, density unevenness in the main scanning direction of the toner image due to the shading characteristics of the light beam scanning optical system can be suppressed.

  However, the following problems have been discovered in the image forming apparatus disclosed in Patent Document 1. In other words, depending on the image density of the adjustment patch to be formed, density unevenness in the main scanning direction cannot be sufficiently suppressed over the entire gradation.

  As a result of intensive studies by the present inventors on the above problems, the following has been found. That is, as shown in FIG. 10, the change in the photoreceptor potential with respect to the change in the light amount is not linear. This will be specifically described below. As described above, as a factor of the image density deviation in the main scanning direction, the main factors of light transmittance and light reflectance are transmitted to the lens and mirror through which the light beam is emitted from the light emitting element and reaches the surface of the photoreceptor. There is a deviation in the scanning direction. The density deviation in the main scanning direction due to the deviation in the light transmittance and the light reflectance can be brought about by the deviation in the main scanning direction of the amount of light applied to the latent image carrier.

  The intermediate gradation and the highlight image are formed by changing the latent image potential by reducing the light amount of the light source of the latent image writing means as compared with the solid image (100% image). As shown in FIG. 10, even if the deviation ΔL in the main scanning direction of the amount of light applied to the latent image carrier is the same, the latent image potential deviation ΔV2 in the halftone image and the latent image potential deviation ΔV1 in the solid image are The former is larger than the latter (ΔV2> ΔV1). As a result, the image density deviation in the main scanning direction in the solid image and the image density deviation in the main scanning direction in the halftone image are greatly different, and the former is smaller.

  Therefore, when each adjustment patch is a solid image, the image density deviation in the main scanning direction of the halftone image cannot be sufficiently suppressed.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an image forming apparatus capable of suppressing an image density deviation over the entire gradation.

  In order to achieve the above object, the invention of claim 1 is characterized in that an adjustment pattern is formed on an image carrier, and an image in the main scanning direction is based on the image density of the adjustment pattern at different positions in the main scanning direction. In the image forming apparatus including the main scanning direction image density adjusting means for adjusting the density deviation, the image density of the adjustment pattern is set to a halftone or less.

  According to the present invention, by adjusting the image density of the adjustment pattern to a halftone or less, compared to the case where the image density of the adjustment pattern is a solid image, the density deviation is large and the halftone or highlight that is easily noticeable. The density deviation of the part can be suppressed. On the other hand, when the image density of the adjustment pattern is equal to or lower than the halftone, the density deviation in the main scanning direction of the solid image cannot be adjusted more accurately than when the adjustment pattern is a solid image. As shown in FIG. 10, the image density deviation in the main scanning direction in the solid image is smaller than the image density deviation in the main scanning direction in the halftone image. For this reason, when the image density of the adjustment pattern is set to a halftone or less, the adjustment amount in the solid image is larger than the adjustment amount necessary to eliminate the density deviation in the main scanning direction of the solid image. Therefore, by setting the image density of the adjustment pattern to a halftone or less, the density deviation in the main scanning direction of the solid image cannot be adjusted with higher accuracy than when the image density of the adjustment pattern is a solid image. However, as shown in FIG. 10, even if there is some adjustment error, the density error due to the adjustment error is slight. Therefore, it is possible to suppress the image density deviation in the main scanning direction over the entire gradation compared to the case where the image density of the adjustment pattern is a solid image.

1 is a schematic configuration diagram of a printer according to an embodiment. FIG. 3 is a schematic configuration diagram of an image forming unit. The perspective view which shows the example of 1 structure of a laser exposure apparatus. FIG. 4 is a diagram illustrating a gradation pattern row on an intermediate transfer belt. The expansion block diagram which expands and shows a 1st optical sensor. FIG. 2 is a block diagram showing a part of an electric circuit in the printer according to the embodiment. The graph which plotted the relationship between development potential and toner adhesion amount to xy coordinates. FIG. 4 is a diagram illustrating an adjustment pattern on an intermediate transfer belt. The figure explaining the effect of the main scanning direction image density adjustment of this embodiment. The figure which shows the relationship between a latent image electric potential and exposure light quantity.

Hereinafter, an embodiment in which the present invention is applied to a full-color printer (hereinafter referred to as a printer) 100 as an image forming apparatus will be described.
FIG. 1 is a configuration diagram showing a schematic configuration of the printer 100. As shown in FIG. 1, the printer 100 includes an apparatus main body that is fixed in position for storing each component as an image forming unit, and a drawable sheet cassette 21 that stores a transfer material S. An image forming unit 1Y, 1C, 1M, 1K for forming toner images of each color of yellow (Y), cyan (C), magenta (M), and black (K) is provided at the center of the apparatus main body. Yes. Hereinafter, the subscripts Y, C, M, and K of the respective symbols indicate members for yellow, cyan, magenta, and black, respectively.

  FIG. 2 is a configuration diagram showing a schematic configuration of the image forming means. As shown in FIGS. 1 and 2, in the present embodiment, drum-shaped photoconductors 2Y, 2C, 2M, and 3K as latent image carriers, charging rollers 3Y, 3C, 3M, and 3K as charging means, and latent images. A laser exposure device 20 is provided as writing means (exposure means). Further, developing devices 4Y, 4C, 4M, and 4K as developing means, and cleaning devices 6Y, 6C, 6M, and 6K for removing transfer residual toner on the surface of the photoreceptor are provided. The image forming units 1Y, 1C, 1M, and 1K for each color include photoconductors 2Y, C, M, and K, charging rollers 3Y, C, M, and K, developing devices 4Y, C, M, and K, and cleaning devices 6Y, C, and K, respectively. M and K are provided. The image forming units 1Y, 1C, 1M, and 1K for each color of yellow (Y), magenta (M), cyan (C), and black (K) are provided on an intermediate transfer belt 7 as an image carrier that runs in a loop. Opposite the horizontal tension surface. Further, the image forming units 1Y, 1C, 1M, and 1K for the respective colors are arranged in the order of Y, C, M, and K from the left under the intermediate transfer belt 7. Further, the four image forming units 1Y, 1C, 1M, and 1K for each color have the same configuration.

  The charging rollers 3Y, 3C, 3M, and 3K charge the photoconductors 2Y, 2C, 2M, and 3K by charging with the same polarity as that of the toner held at a predetermined potential (in this embodiment, negative charging). The uniform potential is applied to the photoreceptors 2Y, 2C, 2M, and 2K. The charging means is not limited to the charging roller, and various devices such as a charging brush and a charging charger can be used as appropriate.

  The laser exposure device 20 exposes the upstream sides of the developing devices 4Y, C, M, and K to the charging rollers 3Y, C, M, and K on the downstream side in the rotation direction of the photoreceptors 2Y, C, M, and K. Further, the laser exposure device 20 is arranged so as to perform exposure scanning in the main scanning direction in parallel with the rotation axes of the photoreceptors 2Y, 2C, 2M, and 2K.

  FIG. 3 is a perspective view showing one configuration of the laser exposure apparatus 20. The laser exposure apparatus 20 includes, for example, a light source 1200 made of a semiconductor laser (LD), a rotary deflector 1201 made of a rotating polygon mirror, an fθ lens 1202, a folding mirror 1203, and the like. The light source 1200 emits laser light whose intensity is modulated according to each color image data. The image data is image data of each color read by an image reading device (not shown) provided in another configuration and recorded in a memory, or image data of each color input from an external device such as a personal computer. The laser light whose intensity is modulated in accordance with the image data of each color in this way is reflected by the mirror surface of the rotating deflector 1201 that rotates in the direction of the arrow in the drawing, and is scanned in the main scanning direction. The laser light from the light source 1200 is reflected by the reflecting surface of the rotary deflector 1201 and then scans the photosensitive member 2 in the direction of the arrow through the fθ lens 1202 and the folding mirror 1203. The fθ lens 1202 is an optical component for causing the beam to scan on the photosensitive member 2 at a constant speed. A beam detector (hereinafter abbreviated as “BD”) 1204 serving as a light detection means is an element that detects a light beam and performs light-voltage conversion. The beam reflected from the mirror 1205 provided on the beam scanning path enters the BD 1204 at a predetermined timing. The BD 1204 generates a BD signal based on the voltage generated by the incident light, and the control unit 500 performs intensity modulation of the light source based on the image data in synchronization with the BD signal.

  The laser exposure device 20 has the configuration shown in FIG. 3 for each color, and image-exposes the photosensitive layers of the photoreceptors 2Y, 2C, 2M, and 2K for each color to form an electrostatic latent image for each color. As the latent image writing means (exposure means), in addition to the laser exposure apparatus 20 described above, an LED writing apparatus combining a light emitting diode array (LED array) and a lens array can be used.

  The photoreceptors 2Y, 2C, 2M, and 2K are formed in the order of a charge generation layer (lower layer) and a charge transport layer (upper layer) as the photosensitive layer on the undercoat layer formed on the surface of the conductive cylindrical support, or These photosensitive layers are laminated in the reverse order. Further, a known surface protective layer such as an overcoat layer mainly composed of a thermoplastic or thermosetting polymer may be formed on the surface of the charge transport layer or the charge generation layer. In the present embodiment, the conductive cylindrical supports of the photoreceptors 2Y, 2C, 2M, and 2K are grounded.

  The developing devices 4Y, 4C, 4M, and 4K are formed of a cylindrical nonmagnetic stainless steel or aluminum material that maintains a predetermined gap with respect to the peripheral surface of the photoconductor 2 and rotates in the forward direction and the rotation direction of the photoconductor 2. The developing sleeves 41Y, 41C, 41M, and 41K are provided. In addition, the developing device 4 accommodates a one-component or two-component developer of yellow (Y), magenta (M), cyan (C), and black (K) according to the development color of each color. In the present embodiment, as an example, a two-component developer composed of toner and a magnetic carrier (in the present embodiment, the toner is negatively charged) is accommodated in the developing device 4. In this case, a magnet roll having a plurality of fixed magnets or a plurality of magnetic poles magnetized therein is disposed in the developing sleeve 41. The developing devices 4Y, 4C, 4M, and 4K for each color are provided with a stirring / conveying member 42 that transports the developer in the container while stirring the developer. In addition, a replenishing unit 43 that replenishes toner from the toner bottles 37 for each color is provided. Furthermore, the developing devices 4Y, 4C, 4M, and 4K for the respective colors are provided with toner concentration sensors 44Y, 44C, 44M, and 44K that detect the toner concentration of the developer in the container as necessary.

  The developing sleeves 41Y, C, M, and K of the developing devices 4Y, 4C, 4M, and 4K of the respective colors are not spaced apart from the drum surfaces of the photoreceptors 2Y, 2C, 2M, and 2K by an abutment roller (not shown). Kept in contact. In the present embodiment, the developing sleeves 41Y, 41C, 41M, and 41K are arranged to face the photoconductor with a gap of 100 [μm] to 500 [μm]. The developer carried on the developing sleeves 41Y, 41C, 41M, and 41K passes through a gap (doctor gap) between the doctor blades 42Y, 42C, 42M, and 42K and the surface of the developing sleeves 41Y, 41C, 41M, and 41K. This regulates the layer thickness. A developing bias in which a DC voltage and an AC voltage are superimposed is applied to the developing sleeves 41Y, 41C, 41M, and 41K. Contact or non-contact reversal development is performed by the developing bias applied to the developing sleeves 41Y, 41C, 41M, and 41K, and toner images are formed on the surfaces of the photoreceptors 2Y, 2C, 2M, and 2K.

  The cleaning devices 6Y, 6C, 6M, and 6K include, for example, a cleaning blade 61 and a cleaning roller (or cleaning brush) 62, and the cleaning blade 61 is provided in contact with the counter surface of the photoreceptor surface.

The intermediate transfer belt 7 that is an image carrier is stretched in contact with a drive roller 8 that also serves as a secondary transfer backup roller, a support roller 9, tension rollers 10 a and 10 b, and a backup roller 11. The intermediate transfer belt 7 rotates counterclockwise as indicated by an arrow in the figure.
Further, a secondary transfer roller 14 is provided through the intermediate transfer belt 7 so as to face the driving roller 8. A cleaning blade 12 a of the belt cleaning device 12 is provided in contact with the intermediate transfer belt 7 at the position of the support roller 9 in the counter direction. Similarly, primary transfer rollers 5Y, 5C, 5M, and 5K for each color are provided to face the photoreceptors 2Y, 2C, 2M, and 2K with the intermediate transfer belt 7 interposed therebetween.

The intermediate transfer belt 7 is an endless belt having a volume resistance of 10 ⁶ [Ω · cm] to 10 ¹² [Ω · cm]. For example, resin materials such as polycarbonate (PC), polyimide (PI), polyamideimide (PAI), polyvinylidene fluoride (PVDF), and tetrafluoroethylene-ethylene copolymer (ETFE) can be used. Further, a material obtained by dispersing a conductive filler such as carbon in a rubber material such as EPDM, NBR, CR, or polyurethane, or containing an ionic conductive material can also be used. The thickness of the intermediate transfer belt 7 is preferably set to about 50 [μm] to 200 [μm] in the case of a resin material and about 300 [μm] to 700 [μm] in the case of a rubber material. A rubber layer may be provided on the resin belt, and a coating layer may be provided on the surface layer. Further, in order to prevent the toner from adhering to the surface of the intermediate transfer belt 7 or to improve the cleaning property, a means for applying a release agent such as a fluorine-based resin or a lubricant may be provided on the belt surface. .

  The intermediate transfer belt 7 is driven by rotation of the drive roller 8 by a drive motor (not shown). The drive roller 8 is a conductive or semi-conductive material in which a conductive filler such as carbon is dispersed in a circumferential surface of a conductive metal bar (not shown) such as stainless steel, or a rubber or resin material such as polyurethane, EPDM, or silicon. A material coated with a conductive material is used.

  The primary transfer rollers 5Y, 5C, 5M, and 5K are provided to face the photoreceptors 2Y, 2C, 2M, and 2K across the intermediate transfer belt 7, and the intermediate transfer belt 7 and the photoreceptors 2Y, 2C, 2M, and 2K are provided. A transfer zone is formed between the two. To the primary transfer rollers 5Y, 5C, 5M, and 5K, a DC voltage having a polarity opposite to that of the toner (in the present embodiment, a positive polarity) is applied from a DC power source (not shown). As a result, a transfer electric field is formed in the transfer area, and the toner images of the respective colors formed on the photoreceptors 2Y, 2C, 2M, and 2K are transferred onto the intermediate transfer belt 7.

The primary transfer rollers 5Y, 5C, 5M, 5K, which are the first transfer means for each color, have a volume on the peripheral surface of a conductive metal core (not shown) such as stainless steel having an outer diameter of 8 [mm], for example. A semiconductor rubber material having a resistance of about 10 ⁵ [Ω · cm] to 10 ⁹ [Ω · cm] is coated. As the rubber material, polyurethane, EPDM, silicon or the like can be used. By dispersing a conductive filler such as carbon or containing an ionic conductive material in these rubber materials, the volume resistance can be changed from 10 ⁵ [Ω · cm] to 10 ⁹ [Ω · cm]. it can. The rubber material is in a solid state or a foamed sponge state, and has a thickness of 5 [mm] and a rubber hardness of about 20 [°] to 70 [°] (Asker-C).

  The secondary transfer roller 14 that performs transfer onto the surface of the transfer material S is provided to face the drive roller 8 that is grounded with the intermediate transfer belt 7 interposed therebetween. A DC voltage having a polarity opposite to that of the toner (plus polarity in this embodiment) is applied to the secondary transfer roller 14 by a DC power source. As a result, the superimposed toner image carried on the intermediate transfer belt 7 is transferred onto the surface of the transfer material S via the secondary transfer roller 14.

The secondary transfer roller 14 serving as a second transfer unit that re-transfers the color toner image on the intermediate transfer belt 7 onto the transfer material S includes a conductive metal core such as stainless steel having an outer diameter of 16 [mm]. ing. A semiconductive elastic rubber (not shown) such as polyurethane, EPDM, or silicon is coated on the peripheral surface of the core metal. The volume resistance is set to about 10 ⁵ [Ω · cm] to about 10 ⁹ [Ω · cm] by dispersing a conductive filler such as carbon or containing an ionic conductive material in the rubber material. The rubber material is in a solid state or a foamed sponge state, and has a thickness of 7 [mm] and a rubber hardness of about 20 [°] to 70 [°] (Asker-C). Unlike the primary transfer rollers 5Y, 5C, 5M, and 5K, the secondary transfer roller 14 may come in contact with toner and may cover the surface with a good releasability such as semiconductive fluorine resin or urethane resin. Further, as described above, the drive roller 8 includes a conductive metal core such as stainless steel. The core metal is covered with a rubber or resin material such as polyurethane, EPDM, or silicon so as to have a thickness of about 0.05 [mm] to 0.5 [mm]. The rubber or resin material has a semiconductive property in which a conductive filler such as carbon is dispersed or an ionic conductive material is contained.

  The cleaning blades 61 and 12a in contact with the photoreceptors 2Y, 2C, 2M, and 2K and the surface of the intermediate transfer belt 7 include a sheet metal holder. A plate-like urethane rubber having a thickness of 1 [mm] to 3 [mm] and a JIS-A hardness of 60 [°] to 80 [°] is bonded onto the sheet metal holder. Urethane rubber is bonded to the sheet metal holder so that the free length is about 5 [mm] to 12 [mm]. The urethane rubber is in contact with the photoreceptors 2Y, 2C, 2M, 2K and the intermediate transfer belt 7 with a load of about 5 [gf] to 50 [gf]. In addition, a fluorine coating may be applied to the blade tip so that the blade does not roll up. Moreover, you may use electroconductive urethane rubber so that the other party may not be charged.

  The transfer material S such as transfer paper is conveyed one by one from the paper feed cassette 21 by the paper feed roller 27. Next, the sheet is conveyed so as to overlap the intermediate transfer belt 7 sandwiched between the secondary transfer roller 14 and the driving roller 8 through the registration roller 13. The toner image is transferred from the intermediate transfer belt 7 at the secondary transfer portion and sent to the fixing device 15 as fixing means. Then, fixing is performed by heat welding by the fixing roller 15 a and the pressure roller 15 b of the attaching device 15, and the paper is discharged to the paper discharge unit 18.

  In this embodiment, charging rollers 3Y, C, M, and K are used as charging means for the photoreceptors 2Y, 2C, 2M, and 2K, and primary transfer rollers 5Y, 5C, 5M, and 5K are used as primary transfer members. From the viewpoint of suppressing the generation of harmful ozone. However, the present invention is not limited to this, and the corotron discharger can be used as a charging means or a primary transfer means in a non-contact state.

  In addition, a plurality of optical sensors 160 as optical detection means that face the downstream side of the secondary transfer portion in the rotation direction of the intermediate transfer belt 7 from the front surface side of the intermediate transfer belt 7 with a predetermined gap. The provided optical sensor unit 16 is disposed. Specifically, as shown in FIG. 4, the first optical sensor 160f disposed near one end in the belt width direction, the second optical sensor 160c disposed in the center of the belt width direction, and the other in the belt width direction. A third optical sensor 160r is provided in the vicinity of the end. These optical sensors 160f, 160c, and 160r are disposed with an interval of 160 mm. The optical sensors 160f, 160c, and 160r detect the test toner image formed on the surface of the intermediate transfer belt 7 and the toner adhesion amount per unit area with respect to the test toner image. It is.

  FIG. 5 is an enlarged configuration diagram showing the first optical sensor 160f in an enlarged manner. In the figure, the first optical sensor 160f includes an LED 161 as a light emitting element, a regular reflection type light receiving element 162, a diffuse reflection type light receiving element 163, a glass cap 164, a casing 165, and the like. In addition, you may use a laser light emitting element etc. instead of LED as a light emitting element. In addition, as the regular reflection type light receiving element 162 and the diffuse reflection type light receiving element 163, phototransistors are used, but it is also possible to use a photodiode or an amplifier circuit.

  Infrared light emitted from the LED 161 passes through the glass cap 164 and then reaches a test toner image formed on the intermediate transfer belt 7. Part of the infrared light is specularly reflected on the surface of the test toner image to become specularly reflected light, and then retransmits through the glass cap 164 and is received by the specular reflection type light receiving element 162. The regular reflection type light receiving element 162 outputs a voltage corresponding to the amount of received light. This output value is converted into digital data by an A / D converter (not shown) and then input to a control unit described later. Further, another part of the infrared light is diffusely reflected on the surface of the test toner image to become diffusely reflected light, and then retransmits through the glass cap 164 and is received by the diffuse reflection type light receiving element 163. . The diffuse reflection type light receiving element 163 outputs a voltage corresponding to the amount of received light. This output value is converted into digital data by an A / D converter (not shown) and then input to a control unit described later. Based on the output voltage from the regular reflection type light receiving element 162 and the output voltage from the diffuse reflection type light receiving element 163, the control unit converts the test toner image formed on the surface of the intermediate transfer belt 7 to the first optical sensor. It grasps the timing when it entered just below 160f. In addition, the toner adhesion amount per unit area in the test toner image is grasped.

  Although the first optical sensor 160f has been described, the second optical sensor (160c in FIG. 4) and the third optical sensor (160r in FIG. 4) have the same configuration as the first optical sensor 160f. The explanation is omitted.

  FIG. 6 is a block diagram illustrating a part of an electric circuit in the printer according to the embodiment. In the figure, a control unit 500 as image forming condition adjusting means has a CPU (Central Processing Unit) 500a. Further, a ROM (Read Only Memory) 500c storing a control program and various data is provided. Further, a RAM (Random Access Memory) 500b for temporarily storing various data and a flash memory 500d for storing various data in a nonvolatile manner are also provided. The controller 500 is connected to various peripheral devices via an I / O unit 510 that relays signal transmission and reception with various peripheral devices. Various peripheral devices are connected to the control unit 500 via the I / O unit 510. In the figure, only the main ones are shown. The optical writing control unit 505 controls driving of the laser exposure apparatus 20. The toner replenishment control circuit 506 is a toner replenishing device (not shown) that individually replenishes the toner in each color toner bottle (37Y, C, M, K) to each color developing device (4Y, C, M, K). The drive is controlled. The various power supply circuits 507 output the above-described primary transfer bias for each color, secondary transfer bias, a developing bias for applying to the developing sleeve of the developing device for each color, and the like. Further, the toner density sensors (44Y, C, M, K) for Y, C, M, K are used for the developer in the developing devices (4Y, C, M, K) for Y, C, M, K. The toner density is measured. The first A / D converter 501 converts the output voltage value from the first optical sensor 160f into digital data. The second A / D converter 502 converts an output voltage value from the second optical sensor 160c into digital data. The third A / D converter 503 converts the output voltage value from the third optical sensor 160r into digital data. The belt drive motor 508 is a motor that is a drive source for the drive roller 8 and the intermediate transfer belt 7. The operation display unit 504 includes a display for displaying an image, various keys for receiving input information from the operator, and the like.

  The optical writing control circuit 505 controls driving of the laser exposure apparatus 20 based on a control signal input from the control unit 500 via the I / O unit 510. The various power supply circuits 507 control bias output values from the various power supply circuits based on control signals input from the control unit 500 via the I / O unit 510.

  The control unit 500 performs the following image density stabilization processing at a predetermined timing such as every elapse of a predetermined time or every predetermined number of prints. That is, first, gradation patterns composed of a plurality of toner images having different toner adhesion amounts per unit area are formed on the Y, C, M, and K photoconductors (2Y, M, C, and K). . About each toner image, the toner adhesion amount is made different from each other by forming the photoconductor background portion potential (uniform charging potential) and the developing bias different from each other. In FIG. 4 described above, the reference numeral GPk indicates a K gradation pattern formed by K toner. The K gradation pattern GPk is composed of ten K toner images arranged at a predetermined pitch in the belt moving direction. Reference numerals GPm, GPc, and GPy indicate M gradation patterns, C gradation patterns, and Y gradation patterns that are formed by M toner, C toner, and Y toner. These gradation patterns (GPm, GPc, GPy) are also composed of ten toner images arranged at a predetermined pitch in the belt moving direction. The K gradation pattern GPk, the M gradation pattern GPm, the C gradation pattern GPc, and the Y gradation pattern GPy are successively formed in this order from the downstream side to the upstream side in the belt moving direction. Constitutes a column. A gradation pattern sequence composed of such gradation patterns of four colors is formed at one end, the center, and the other end of the intermediate transfer belt 7 in the belt width direction.

  Each toner image in the gradation pattern row formed at one end of the intermediate transfer belt 7 in the belt width direction sequentially passes directly below the first optical sensor 160f as the belt moves. Then, the toner adhesion amount per unit area is grasped by the control unit 500 during the passage. Similarly, each toner image of the gradation pattern row formed in the central portion of the intermediate transfer belt 7 in the belt width direction has a toner adhesion amount per unit area when passing directly below the second optical sensor 160c. Be grasped. Further, each toner image of the gradation pattern row formed on the other end portion of the intermediate transfer belt 7 in the belt width direction grasps the toner adhesion amount per unit area when passing directly below the third optical sensor 160r. Is done.

  In the printer according to the embodiment, the arrangement pitch (hereinafter referred to as primary transfer nip pitch) of the four photoconductors (2Y, C, M, K) shown in FIG. 1 is set to 110 [mm]. . On the other hand, each toner image in the gradation pattern row is formed in a size of length in the belt moving direction = 7 [mm] × length in the belt width direction = 5 [mm], and the trailing edge of the preceding toner image The distance from the leading edge of the subsequent toner image is set to 4 [mm]. The length of the K gradation pattern GPk in the belt moving direction is (7 + 4) × 9 + 7 = 106 [mm], which is shorter than the primary transfer nip pitch described above. For this reason, even if the formation of gradation patterns is started simultaneously in two image forming units adjacent to each other, the gradation patterns are not overlapped. For example, it is assumed that gradation pattern formation is started simultaneously in the K image forming unit and the M image forming unit. Then, at the moment when the rear end of the K gradation pattern GPk is primarily transferred from the K photosensitive member 2K to the intermediate transfer belt 7 by the K image forming unit, the M photosensitive member 2M in the M image forming unit. The tip of the M gradation pattern GPm transferred from the intermediate transfer belt 7 to the intermediate transfer belt 7 is at the following position. That is, it is located upstream (4 mm) from the rear end of the K gradation pattern GPk. For this reason, the trailing edge of the K gradation pattern GPk does not overlap the leading edge of the M gradation pattern GPm. Similarly, the trailing edge of the M gradation pattern GPm and the leading edge of the C gradation pattern GPc are not overlapped. Further, the trailing edge of the C gradation pattern GPc and the leading edge of the Y gradation pattern GPy are not overlapped. Therefore, the formation of the gradation pattern for each color can be started simultaneously. Then, as shown in FIG. 4, it is possible to form a gradation pattern row in which the gradation patterns of the respective colors are arranged with a slight gap.

  In the gradation pattern, as already described, the distance between the trailing edge of the preceding toner image and the leading edge of the subsequent toner image is 4 [mm]. Since the printer according to the embodiment performs the density stabilization process at a process linear velocity of 250 [mm / sec] (belt or photosensitive member linear velocity), the time required for the movement of 4 [mm] is 4/250 = 0.016 [second]. The time required for movement of 7.5 [mm], which is the sum of 4 [mm] and the distance (3.5 mm) from the edge to the center of the toner image, is 7.5 / 250 = 0.03 seconds. It is. As described above, each toner image in the gradation pattern is formed under different bias conditions (development bias). It takes longer than 0.016 [seconds] until the bias stabilizes after changing the bias condition, but is shorter than 0.03 [seconds]. By setting the length and interval of the toner image so as to have such a magnitude relationship, the length of the gradation pattern is efficiently shortened. Specifically, the edge of the toner image has a larger amount of toner adhesion than the original due to the so-called edge effect, and therefore the edge portion is inappropriate as a detection target area of the toner adhesion amount. Even if the edge portion is formed under a condition where the bias condition is stabilized, it cannot be a detection target region of the toner adhesion amount, so it is inefficient to start forming after waiting for the stabilization. It is. Therefore, the edge portion is formed before stabilization, so that the length of the toner image is shortened.

  When the controller 500 grasps the toner adhesion amount in all the toner images, the controller 500 obtains a linear function expression of the development characteristics for each of Y, C, M, and K colors. Specifically, based on the respective toner adhesion amounts in the ten toner images of the gradation pattern, and the development potentials at the time of image formation (difference between the development bias and the latent image potential) individually corresponding to the toner images. Thus, the relationship between the toner adhesion amount and the development potential is obtained. The relationship between the toner adhesion amount and the development potential is a linear function expression y = ax + b as shown in FIG. Such a linear function formula is obtained individually for each of the gradation pattern formed at one end in the belt width direction, the gradation pattern formed at the center, and the gradation pattern formed at the other end. Then, the average value of each inclination a in the obtained three linear function equations is calculated, and the image forming conditions such as the developing potential and the charging bias are adjusted based on the calculation result. Details thereof are described in Japanese Patent Application Laid-Open No. 9-2111911 and the like, and thus description thereof is omitted. Adjustment of the image forming conditions as described above is performed individually for each of the colors Y, C, M, and K.

The controller 500 adjusts the image density deviation in the main scanning direction following the image density stabilization process described above.
The following factors can be cited as factors that cause image density deviation in the main scanning direction.
・ Eccentricity of photoconductor and deflection of photoconductor ・ Deviation of gap between developing sleeve and photoconductor ・ Deviation of doctor gap ・ Deviation of laser exposure device (deviation of transmittance of lens such as fθ lens, folding mirror and rotation Deviation of reflectivity such as deflector)
Due to the above factors, a deviation occurs in the developing potential (difference between the developing bias and the latent image potential), thereby causing a density deviation. In such adjustment of the density deviation in the main scanning direction, it is necessary to be able to set conditions by dividing in the main scanning direction. Therefore, in the present embodiment, the amount of light from the light source 1200 of the laser exposure apparatus 20 that is conditionally set by dividing in the main scanning direction is controlled relatively easily.

  Among the above factors, the image density deviation in the main scanning direction due to the eccentricity of the photosensitive member, the deflection of the photosensitive member, the deviation of the gap between the developing sleeve and the photosensitive member, and the deviation of the doctor gap is the same for all gradations. It is. However, the deviation of the laser exposure apparatus is not the same for all gradations, and the density deviation in the main scanning direction varies greatly depending on the gradations.

  Therefore, in the present embodiment, a plurality of adjustment patches having different image densities are formed at one end, the center, and the other end of the intermediate transfer belt 7, and image density deviation in the main scanning direction at the plurality of image densities. Based on the above, the image density deviation in the main scanning direction is adjusted. This will be specifically described below.

  As shown in FIG. 8, adjustment patterns S1 to S6 having different image densities (toner adhesion amounts per unit area) of six colors are formed in the surface movement direction (sub-scanning direction) of the intermediate transfer belt 7 (100). % To any 6 gradations). Each of the adjustment patterns S1 to S6 includes three adjustment patches having the same image density formed at one end, the center, and the other end of the intermediate transfer belt 7 in the width direction (main scanning direction). Each of the adjustment patterns S <b> 1 to S <b> 6 may be composed of one adjustment patch that covers the entire width direction of the intermediate transfer belt 7. Each adjustment pattern was formed by changing the amount of exposure light using the developing bias and the charging bias obtained in the image density stabilization process. For a solid image (100% density), the detection result of a solid toner image in the gradation pattern row formed by the above-described image density stabilization processing may be used.

  The adjustment patches of the adjustment patterns S1 to S6 are formed in a size of length in the belt moving direction = 10 [mm] × length in the belt width direction = 5 [mm]. The distance between the rear end of the preceding adjustment pattern and the front end of the subsequent adjustment pattern is set to 7.88 [mm]. The six adjustment patterns S1 to S6 for each color are shorter than the primary transfer nip pitch 110 [mm] described above. Therefore, also in this case, the formation of the six adjustment patterns S1 to S6 for each color can be started simultaneously.

  In the same manner as described above, the adjustment patch in each adjustment pattern formed on one end of the intermediate transfer belt 7 in the belt width direction passes directly under the first optical sensor 160f as the belt moves. Then, the toner adhesion amount per unit area is grasped by the control unit 500 during the passage. Similarly, the adjustment patch of each of the adjustment patterns S1 to S6 formed in the central portion of the intermediate transfer belt 7 in the belt width direction passes toner directly below the second optical sensor 160c, and the toner per unit area. The amount of adhesion is grasped. Further, the adjustment patches of the adjustment patterns S1 to S6 formed on the other end portion of the intermediate transfer belt 7 in the belt width direction adhere toner per unit area when passing directly below the third optical sensor 160r. The amount is grasped.

  Next, based on the adhesion amount of each adjustment patch formed on one end side of the intermediate transfer belt 7 of each of the adjustment patterns S1 to S6, the development potential at the time of image formation of each adjustment patch is calculated. First, based on the toner adhesion amount detected by the first optical sensor 160f and the linear function expression y = ax + b of the development characteristics shown in FIG. 7 obtained in the previous image density stabilization processing, the development potentials V1f to V6f are obtained. calculate. The linear function formula at this time is obtained from the gradation pattern formed at one end in the belt width direction. Moreover, you may use the average value of each inclination a and the average value of intercept b in three linear function formulas respectively obtained by the gradation pattern formed in the one end part, the center part, and the other end part. Similarly, the development potentials V1c to V6c at the time of image formation of each adjustment patch are calculated based on the adhesion amount of each adjustment patch at the center of the intermediate transfer belt 7. Further, based on the adhesion amount of each adjustment patch on the other end of the intermediate transfer belt 7, development potentials V1r to V6r at the time of each adjustment patch image formation are calculated.

  Next, difference values ΔV1f to ΔV6f between the calculated potentials V1f to V6f on one end side of the intermediate transfer belt 7 and the target development potential at the time of image formation for each adjustment patch are calculated. Similarly, ΔV1c to ΔV6c and ΔV1r to ΔV6r are calculated.

  Next, an average value ΔVaf of difference values ΔV1f to ΔV6f from the calculated development potential on one end side of the intermediate transfer belt is calculated. Similarly, the average value ΔVac of the difference value at the center of the intermediate transfer belt and the average value ΔVar of the difference value at the other end side of the intermediate transfer belt are calculated.

  Then, the light quantity of the light source 1200 of the laser exposure apparatus 20 is adjusted based on the calculated ΔVaf, ΔVac, ΔVar. The difference values ΔVaf, ΔVac, ΔVar of the development potential are equal to the difference value with respect to the target latent image potential because the development bias is a specified value. Therefore, the light amount adjustment amount (voltage adjustment amount applied to the light source 1200) for each gradation is calculated from the relationship between the latent image potential and the exposure light amount shown in FIG. The flash memory 500d of the control unit 500 stores a table in which each gradation is associated with the corresponding light amount profile (light source applied voltage) of the light source in the main scanning direction. Based on the calculated light intensity adjustment amount for each gradation and the light intensity at one end, the center, and the other end of each gradation of the table, the light intensity at one end, the center, and the other end of each new gradation is calculated. To do. The light intensity profile in the main scanning direction of the light source in each gradation is obtained by complementing the light intensity between one end and the center and between the center and the other end from the light intensity at one end, the center, and the other end of each gradation. Create and update the table based on the created light intensity profile. For example, when the light intensity profile stored in the flash memory is divided into 16, the light intensity profiles in the entire 16 locations are calculated based on the light intensity at one end, the center, and the other end. And it memorize | stores in the flash memory 500d as a new light quantity profile. Such light quantity adjustment is performed for each of Y, M, C, and K.

  In the present embodiment, as described above, a plurality of adjustment patterns having different image densities are formed, and the image density deviation in the main scanning direction is adjusted based on the detection results of these adjustment patterns. Thereby, it is possible to suppress the density deviation in the main scanning direction over all gradations, compared to the case where the adjustment pattern is a solid image. Hereinafter, this will be specifically described with reference to FIG.

For example, as shown in FIG. 9, the difference value with respect to the target latent image potential of the solid image (100% image) at the center in the main scanning direction is ΔV1, and the difference value with respect to the target latent image potential of the halftone (70% image). Consider a case where the value is ΔV2 (ΔV1 <ΔV2).
When only an adjustment pattern for a solid image is formed and the image density deviation is adjusted based on the detection result (hereinafter referred to as a conventional example), the halftone (70% image) is also light based on the difference value ΔV1. Is corrected. As a result, the halftone (70% image) latent image potential after the light amount adjustment is VB. On the other hand, when correction is performed using the difference value ΔV1 of the solid image (100% image) and the average value ΔVa of the difference value ΔV2 of the halftone (70% image) (hereinafter referred to as an example), the halftone (70) % Image) is a VC. As is apparent from VB and VC in FIG. 9, it can be seen that the adjusted latent image potential is closer to the target latent image potential VA in the example than in the conventional example. On the other hand, in the case of a solid image (100% image), the conventional example can be corrected to the target latent image potential after the light amount adjustment. On the other hand, in the embodiment, the solid image after the light amount adjustment cannot be corrected to the target latent image potential. However, as shown in FIG. 9, in the vicinity of the solid image, the latent image potential hardly decreases even when the amount of light is increased (saturated state). Therefore, in a solid image, even if there is some adjustment error, the density error due to the adjustment error is small. Therefore, the embodiment can averagely correct the density deviation over all gradations, and can improve the final image as compared with the conventional example.

  The image density deviation in the main scanning direction is often caused by parts. Therefore, the adjustment of the image density deviation in the main scanning direction is performed when the use of the image forming apparatus is started (at the first use). The timing to implement may be performed in a manufacturing process, and may be performed when installing in a customer. It is also preferable to adjust the image density deviation in the main scanning direction even when parts in the image forming apparatus are replaced. The adjustment of the image density deviation in the main scanning direction at the time of installation at the customer or at the time of parts replacement is performed by the serviceman operating the operation display unit 504 (see FIG. 6).

  Further, the component performance changes due to the environment and aging, and the gap between the developing sleeve and the photosensitive member changes. Even if these changes occur, the image density deviation in the main scanning direction fluctuates, so that the environment in the main scanning direction also changes when the environment changes over a predetermined range from the previous execution environment, or after a predetermined period has elapsed since the previous execution. Adjust the image density deviation. Whether or not the environment has changed from a previously performed environment over a predetermined range is determined based on the detection result of the temperature / humidity sensor provided with a temperature / humidity sensor in the image forming apparatus. It is possible to detect whether or not the environment has changed over a predetermined range. Whether or not a predetermined period has elapsed since the previous execution is measured by, for example, measuring the number of image formations, the travel distance of the photosensitive member, and adjusting the image density deviation in the main scanning direction when the measured value exceeds a threshold value. carry out.

  Further, the user may operate the operation display unit 504 (see FIG. 6) to adjust the image density deviation in the main scanning direction at an arbitrary timing. As a result, when the user views the image and perceives the density deviation in the main scanning direction, the image density deviation can be adjusted and the user's image quality requirement can be met.

  Further, in the above description, the adjustment pattern is formed from 100% to arbitrary six gradations, but one adjustment pattern having an intermediate gradation or less may be formed. By reducing the image density of the adjustment pattern to halftone or less, compared to the case where the image density of the adjustment pattern is a solid image, the density deviation is large and suppresses the grayscale and highlight density deviation that are easily noticeable. can do. In addition, as described above, with respect to a solid image, even if there is an adjustment error, the density error due to the adjustment error is small. Therefore, it is possible to suppress the image density deviation in the main scanning direction over the entire gradation compared to the case where the image density of the adjustment pattern is a solid image.

  In particular, as the adjustment pattern, a halftone is preferable, and an adjustment pattern with an image density of 70% is particularly preferable. This is because the inventors have earnestly studied and found that a change in color tone in a halftone with an image density of about 70% is perceived remarkably. By adopting such a configuration, it is possible to accurately suppress a density deviation in the main scanning direction in a halftone having an image density of about 70% in which color variation is easily perceived. Further, it may be possible to selectively implement whether the adjustment pattern is formed with two or more gradations or a halftone adjustment pattern by an operation.

What has been described above is an example, and the present invention has a specific effect for each of the following aspects.
(Aspect 1)
A control unit 500 that forms an adjustment pattern on an image carrier such as the intermediate transfer belt 7 and adjusts an image density deviation in the main scanning direction based on the image density of the adjustment pattern at different positions in the main scanning direction. In the image forming apparatus provided with the image density adjusting means in the main scanning direction, the image density of the adjustment pattern is set to a halftone or less.
With this configuration, as described in the embodiment, the image density deviation in the main scanning direction can be corrected in a well-balanced manner over all gradations compared to the case where the image density of the adjustment pattern is increased to a solid image. Can do.

(Aspect 2)
In (Aspect 1), the main scanning direction image density adjusting means such as the control unit 500 forms a plurality of adjustment patterns having different image densities, and based on the detection results of these adjustment patterns, Adjust the image density deviation.
With this configuration, as described in the embodiment, each gradation can be adjusted on an average basis, and the main density is increased over all gradations compared to the case where the image density of the adjustment pattern is increased to a solid image. The image density deviation in the scanning direction can be corrected with a good balance.

(Aspect 3)
In the above (Aspect 2), the main scanning direction image density adjusting means such as the control unit 500 uses the average value of the difference values for the target image density calculated based on the detection result of each adjustment pattern. The image density deviation in the main scanning direction is adjusted.
With such a configuration, as described in the embodiment, the image density deviation in the main scanning direction can be corrected in a well-balanced manner over all gradations.

(Aspect 4)
In the above (Aspect 1) or (Aspect 2), the main scanning direction image density adjusting means such as the control unit 500 forms at least a halftone adjustment pattern.
By using the halftone in which the color variation is perceived remarkably as the adjustment pattern, it is possible to make the density deviation in the main scanning direction less noticeable in the adjusted image.

(Aspect 5)
In the above (Aspect 4), the halftone adjustment pattern has a 70% image density.
By using the 70% image density adjustment pattern in which the color variation is easily perceived, the density deviation in the main scanning direction can be made inconspicuous in the adjusted image.

(Aspect 6)
In any one of (Aspect 1) to (Aspect 5), the latent image of the laser exposure apparatus 20 or the like that writes a latent image on a latent image carrier such as the photosensitive member 2 by light from the light source 1200 emitted based on the image information. A main scanning direction image density adjusting unit such as the control unit 500 includes a writing unit and adjusts the light amount of the light source based on the detection result of each adjustment pattern.
With this configuration, the image density deviation in the main scanning direction can be adjusted.

(Aspect 7)
In any one of (Aspect 1) to (Aspect 6), the latent image writing unit such as the laser exposure apparatus 20 includes a rotary deflector 1201 that deflects and scans the light emitted from the light source 1200 in the main scanning direction. The light from the light source 1200 emitted based on the image information is deflected and scanned in the main scanning direction on the latent image carrier such as the photosensitive member 2 by the rotary deflector 1201 to write the latent image on the latent image carrier.
In the latent image writing means such as the laser exposure apparatus 20 having such a configuration, the optical system parts such as the fθ lens and the folding mirror disposed after the rotary deflector are members that are long in the main scanning direction and transmit in the main scanning direction. There is a high possibility of deviations in rate and reflectivity. As a result, deviation tends to occur in the exposure light quantity in the main scanning direction. As a result, when the gradation is obtained by adjusting the exposure amount, the image density deviation in the main scanning direction varies greatly depending on the gradation. Therefore, in the case of the exposure apparatus configured as described above, in which the exposure amount is likely to vary, the image density in the main scanning direction is adjusted over all gradations by adjusting the density deviation in the main scanning direction as described above. The advantage that the deviation can be corrected in a balanced manner can be effectively exhibited.

(Aspect 8)
In any one of (Aspect 1) to (Aspect 7), when the use of the image forming apparatus is started, or when the use period of the image forming apparatus exceeds a predetermined period, the previous image density adjustment in the main scanning direction is executed. The main scanning direction image density adjustment by the main scanning direction image density adjusting means is executed at least one of the timing when the environmental fluctuation exceeds the predetermined range and when the components of the apparatus are replaced.
With this configuration, as described in the embodiment, image density adjustment in the main scanning direction can be performed at the timing when the density deviation in the main scanning direction fluctuates, and deterioration in image quality can be suppressed.

(Aspect 9)
In any one of (Aspect 1) to (Aspect 8), the image density adjustment in the main scanning direction can be arbitrarily performed by the user.
By providing such a configuration, as described in the embodiment, it is possible to meet the image quality desired by the user.

2: Photoconductor (latent image carrier)
7: Intermediate transfer belt (image carrier)
20: Laser exposure device (latent image writing means)
41: Development sleeve (developer carrier)
160: Optical sensor 500: Control unit 504: Operation display unit 1200: Light source 1201: Rotating deflector

JP 2004-29217 A

Claims (9)

A main scanning direction image density adjusting unit is provided that forms an adjustment pattern on the image carrier and adjusts an image density deviation in the main scanning direction based on the image density of the adjustment pattern at different positions in the main scanning direction. In the image forming apparatus,
An image forming apparatus, wherein an image density of the adjustment pattern is set to a halftone or less. The image forming apparatus according to claim 1.
The image density adjusting unit in the main scanning direction forms a plurality of adjustment patterns having different image densities, and adjusts an image density deviation in the main scanning direction based on a detection result of the adjustment patterns. Forming equipment. The image forming apparatus according to claim 2.
The main scanning direction image density adjusting means adjusts an image density deviation in the main scanning direction using an average value of a difference value with respect to a target image density calculated based on a detection result of each adjustment pattern. An image forming apparatus. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the image density adjusting unit in the main scanning direction forms at least a halftone adjustment pattern. The image forming apparatus according to claim 4.
An image forming apparatus, wherein the halftone adjustment pattern has an image density of 70%. The image forming apparatus according to claim 1,
Comprising a latent image writing means for writing a latent image on a latent image carrier by light from a light source emitted based on image information;
The image forming apparatus according to claim 1, wherein the main-scanning-direction image density adjusting unit adjusts the light amount of the light source based on a detection result of each adjustment pattern and each adjustment patch. The image forming apparatus according to claim 1.
The latent image writing unit includes a rotary deflector that deflects and scans light emitted from a light source in a main scanning direction, and the light of the light source emitted based on image information is applied to the latent image carrier by the rotary deflector. An image forming apparatus for writing a latent image on the latent image carrier by performing deflection scanning in the main scanning direction. The image forming apparatus according to claim 1,
At the start of use of the image forming apparatus, when the usage period of the image forming apparatus exceeds a predetermined period, when environmental fluctuations from the previous execution of image density adjustment in the main scanning direction exceed a predetermined range, and the apparatus An image forming apparatus wherein the main scanning direction image density adjustment is performed by the main scanning direction image density adjusting means at least at one timing when the parts are replaced. The image forming apparatus according to claim 1,
An image forming apparatus characterized in that a main scanning direction image density adjustment by the main scanning direction image density adjustment means can be arbitrarily executed by a user.