JP2014119665A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make it possible to appropriately control the density of a solid image and the density of a halftone image during printing.SOLUTION: An image forming apparatus includes: density detection means 130 for detecting the gradation density of gradation toner patterns formed on an image carrier 206; and control means 500 having a first process of determining imaging conditions for deriving solid density required during printing from the gradation density information detected by the density detection means, and a second process of forming toner patterns in an intermediate density and a solid density respectively on the image carrier 206 in the imaging conditions determined in the first process, detecting the densities of the toner patterns in an intermediate density and a solid density with the density detection means, performing halftone correction on the gradation density information detected in the first process on the basis of intermediate density information, and deriving a target value of control to maintain the density during printing on the basis of solid density information. When the solid density information detected in the second process is different from the target value, the control means changes the imaging conditions determined in the first process, and re-executes the second process after the correction.

Description

  The present invention relates to an image forming apparatus using an electrophotographic system, such as a copying machine, a printer, a facsimile machine, or a multifunction machine thereof.

In an electrophotographic image forming apparatus, the charging bias applied by the charging unit and the amount of exposure light (hereinafter referred to as “exposure output”) irradiated by the exposure unit at a predetermined timing in order to keep the image density at the time of printing constant. A plurality of latent image images having different potentials are formed on the image carrier, and the latent images are developed with toner serving as a developer from the developing means, thereby forming a toner image having a predetermined shape. A plurality of gradation toner patterns are formed. Then, after each gradation toner pattern is formed, the adhesion amount (toner adhesion amount) of the gradation toner pattern is detected by an optical sensor serving as a density detection means, and the image forming conditions are controlled based on the detection result. .
As a method of forming gradation toner patterns having different potentials, there is a method of changing the charging bias while fixing the exposure output. Since this method has linearity, it is possible to determine image forming conditions (image forming conditions) for forming an image from a small number of gradation toner patterns. In this method, the relationship between the development potential (development bias-exposure portion potential VL) and the toner adhesion amount is linearly approximated based on the detection result of the optical sensor, and the development γ, which is the slope of the linear approximation formula, is obtained. The charging bias, the developing bias, and the exposure output (hereinafter “image forming conditions”) are adjusted so that the toner adhesion amount with respect to the image potential becomes the target toner adhesion amount. Such control is hereinafter referred to as “potential control”.
Since the setting range of the charging bias applied to the image carrier is determined within a range that does not affect the image quality, it is necessary to control the development γ within a predetermined range. The development γ generally increases as the toner concentration in the developing device increases. Therefore, in order to keep the development γ within a predetermined range, control is performed such as adjusting the toner density in the developing device when the calculated development γ deviates greatly from the target. From this point of view, it is very important to accurately calculate the development γ. However, due to the characteristics of the image carrier, the latent image potential on the image carrier (hereinafter referred to as “light attenuation characteristics”) with respect to the exposure output varies due to environmental fluctuations and deterioration of the image carrier over time. As a result, the calculation accuracy of the development γ is deteriorated.
For this reason, in Patent Document 1, the latent image potential on the image bearing member is detected by a detecting means such as a potential sensor to detect that the light attenuation characteristic has changed, and the detection result is fed back to set an optimum image forming condition. The contents are disclosed.
Further, as a method not using a detection means such as a potential sensor, a state in which the surface potential of the image carrier after exposure is saturated so that the value of the exposure portion potential VL does not change even if the light attenuation characteristic changes. A system using such an exposure output is known. As a result, the exposure portion potential during potential control is kept constant, so that the development γ can be calculated with high accuracy. On the other hand, when the exposure output is strong, there is a problem that the fine line of the image at the time of printing becomes thick. Since the line width at the time of printing is related to the amount of toner consumption, we want to make it as thin as possible within the range where the image density does not change. Therefore, at the time of image formation, a method is used in which the amount of light at the time of image formation is set low so that the image density does not change. However, in this case, the difference in light attenuation characteristics between printing and potential control (exposure portion potential VL difference ΔVL) increases, and the robustness of the image density with respect to time and environmental fluctuations decreases.
As a countermeasure against this problem, in Japanese Patent Laid-Open No. 2004-260688, printing is performed in two steps: a step of detecting a change in light attenuation characteristics and a determination of an optimal charging bias, development bias, and exposure output using the detection result. Differences in light attenuation characteristics during potential control are corrected without a potential sensor. However, in this method, since time is required for potential control, the time during which printing is stopped (downtime) increases, and there is room for improvement in terms of productivity.
In addition, image forming apparatuses capable of expressing a variety of color tones by reproducing halftones by area tones have become widespread. In this image forming apparatus, even if the image density of the solid image is stabilized, the image density of the halftone image due to the area gradation may be changed. This is an image forming condition (development bias, etc.) for setting the toner adhesion amount per unit area in a solid image to a predetermined value, and an operation for setting the toner adhesion amount per unit area in a halftone image by area gradation to a predetermined value. This is because the image conditions are not always the same.
Therefore, Patent Document 3 proposes an image forming apparatus that performs a halftone density stabilization process for stabilizing the image density of a halftone image by area gradation separately from the solid density stabilization process. ing. In Patent Document 3, a solid image stabilization process is performed to adjust the developing bias to a value at which a target image density can be obtained. Next, the toner adhesion amount in the halftone density area gradation toner image formed under the adjusted development bias condition is detected by the detection sensor, and based on the detection result, the intermediate halftone density is obtained so that the target halftone density is obtained. The image area ratio of the toned toner image is adjusted.
However, in the configuration of Patent Document 3, the target image density can be stably obtained for both the solid image and the halftone image, but the solid density stabilization process is performed after the halftone density stabilization process is performed. For this reason, the image density of the halftone image adjusted to the target density is deviated from the target density by changing the development bias or the like. For this reason, it is necessary to perform the halftone density stabilization process after performing the solid density stabilization process.

  An object of the present invention is to propose an image forming apparatus capable of appropriately controlling the density of a solid image and the density of a halftone image during printing.

  The present invention relates to a density detecting unit for detecting a tone density of a tone toner pattern formed on an image carrier by an image forming unit, and a solid density necessary for printing from the tone density information detected by the density detecting unit. The first image forming condition for deriving the image and the image forming condition determined in the first process are used to form an intermediate density and a solid density toner pattern on the image carrier by the image forming means. Then, the density detection means detects the density of the intermediate density and the solid density toner pattern, respectively, and the gradation density information detected in the first process is halftone corrected by the intermediate density information and printed by the solid density information. In the image forming apparatus including a control unit having a second process for deriving a target value for control of maintaining the density in the medium, the control unit has the solid density information detected in the second process different from the target value. If the determined image forming conditions in the first process to change and is characterized by re-executing the second process after modification.

  According to the present invention, it is possible to appropriately control the solid density and halftone density during printing.

1 is a schematic configuration diagram illustrating a main part of a color printer according to an embodiment of the present invention. FIG. 2 is an enlarged view showing a schematic configuration of a representative example of image forming means in the printer. FIG. 3 is a perspective view illustrating a configuration of a transfer unit in the printer. FIG. 3 is an enlarged view showing a configuration example of density detecting means for detecting a gradation toner pattern. FIG. 2 is a block diagram illustrating a configuration of an embodiment of a control system in the printer. The flowchart which shows the control content of one form of control by a control means. 2A and 2B are diagrams illustrating a gradation toner pattern formed on an intermediate transfer belt, where FIG. 3A is a gradation toner pattern formed by a first process, and FIG. 2B is a gradation toner formed by a second process. The top view which shows a pattern. The figure which showed the image formation conditions and toner adhesion amount detection result of the gradation toner pattern. The figure which shows the relationship between the toner adhesion amount at the time of a solid density, and development bias. The characteristic view which shows the relationship between a charging bias and exposure output. FIG. 10 is a diagram for obtaining a difference ΔM / A between a solid density toner adhesion amount and a detection value of a sixth area gradation toner pattern, and obtaining a development bias deficit ΔVb from the difference ΔM / A and a development γ value. 6 is a block diagram illustrating a configuration of another embodiment of a control system in the printer. The flowchart which shows the control content of another form of control by a control means. The flowchart which shows the control content of another form of control by a control means. The flowchart which shows the control content of another form of control by a control means. FIG. 6 is a characteristic diagram for calculating a target value of a solid toner adhesion amount stored in a control unit. The flowchart which shows the control content of another form of control by a control means. The flowchart which shows the control content of another form of control by a control means.

  Hereinafter, an embodiment of an electrophotographic color printer will be described as an image forming apparatus to which the present invention is applied. FIG. 1 is a schematic configuration diagram illustrating a main part of a color printer according to an embodiment. In addition to the configuration shown in FIG. 1, the color printer includes a control unit 500 that controls the operation of the entire apparatus, a paper feeding device (not shown) that supplies the recording paper P as a recording member, and an image-formed recording paper P. A paper discharge tray or the like (not shown) is provided. In the figure, the suffixes Y, C, M, and K attached to the end of the reference numerals indicate members for yellow, cyan, magenta, and black, and may be omitted as appropriate.

In FIG. 1, reference numeral 200 denotes a transfer unit as transfer means.
The transfer unit 200 includes an intermediate transfer belt, which is an image carrier and an intermediate transfer member, on a driving roller 201, a cleaning backup roller 202, a primary transfer nip entrance roller 203, and a secondary transfer nip entrance roller 205, which are a plurality of roller members. 206 is wound. In the inner loop of the intermediate transfer belt 206, four primary transfer rollers 204Y, 204C, 204M, and 204K serving as primary transfer members are disposed so as to contact the belt. Outside the intermediate transfer belt 206, a belt cleaning device 207 is disposed between the cleaning backup roller 202 and the primary transfer nip entrance roller 203. A secondary transfer roller 208 serving as a secondary transfer member is disposed outside the intermediate transfer belt 206 at a position facing the driving roller 201. In the vicinity of the secondary transfer roller 208, a cleaning roller 209 is disposed in contact with the surface of the secondary transfer roller 208.

  In the transfer unit 200, an endless intermediate transfer belt 206 as a belt member is stretched by a plurality of rollers disposed on the inner side of the belt loop, and endless in a counterclockwise direction in FIG. Move it. The driving roller 201 is rotationally driven by a belt driving motor 220 serving as driving means shown in FIG.

  Below the transfer unit 200, four image forming units for Y, C, M, and K as image forming means are arranged along the lower stretched surface of the intermediate transfer belt 206. These image forming units include drum-shaped photoreceptors 101Y, 101C, 101M101, 101K as image carriers, charging units 102Y, 102C, 102M, 102K, developing units 103Y, 103C, 103M, 103K, and drum cleaning devices 120Y, 120C. , 120M, 120K, etc. In each image forming unit, a photosensitive member, a charging unit, a developing unit, and a drum cleaning device are supported by a casing (not shown) and are detachable from the main body of the image forming device. Each photoconductor is in contact with the lower stretched surface of the intermediate transfer belt 206 facing the primary transfer rollers 204Y, 204C, 204M, and 204K for the Y, C, M, and K use. The primary transfer nip is formed.

  Above the transfer unit 200, toner bottles 90Y, 90C, 90M, and 90K, which respectively contain Y, C, M, and K toners (not shown) that serve as replenishment developers, are provided on the intermediate transfer belt 206. It arrange | positions so that it may rank along with an upper tension surface. The toners of the respective colors accommodated in the toner bottles 90Y, 90C, 90M, and 90K are developed as shown in FIG. 1 by driving the Y, C, M, and K toner supply devices 270Y, 270C, 270M, and 270K shown in FIG. The means 103Y, 103C, 103M, and 103K are replenished respectively. Each toner bottle is individually attachable to and detachable from the main body of the image forming apparatus, and is replaced with a new one when the internal toner runs out.

  An optical writing unit 290 serving as an exposure unit is provided below the four image forming units arranged along the belt lower tension surface. The optical writing unit 290 drives a semiconductor laser (not shown) provided in the optical writing unit 290 based on the image information to correspond to Y, C, M, and K exposure light Lb. The photoconductor is output and irradiated. The optical writing unit 290 optically scans the photoconductors 101Y, 101C, 101M, and 101K with the exposure light Lb, and forms an electrostatic latent image on the circumferential surface of each photoconductor that is driven to rotate counterclockwise in the drawing. Form. In addition, irradiation of exposure light Lb is not restricted to a laser, For example, LED may be sufficient.

  Next, the configuration of the image forming unit will be described. The image forming units of the respective colors have the same configuration except that the color of toner used is different. For this reason, in FIG. 2, the image forming unit for K will be described as a representative example. At the end of the reference numerals indicating the various members and devices constituting the image forming unit for K, a suffix “K” should be added. However, in FIG. In the image forming unit for K, a charging unit 102 for uniformly charging the photosensitive member 101, a developing unit 103, a drum cleaning device 120, and the like are disposed around the drum-shaped photosensitive member 101.

  The charging unit 102 is of a contact charging type in which a charging roller 102 a to which a charging bias is applied by the power supply device 300 is brought into contact with the photosensitive member 101, and discharge is generated between the charging roller 102 a and the photosensitive member 101. The peripheral surface of the photoreceptor 101 is uniformly charged. Instead of the contact charging method using the charging roller 102a, a known contact discharge method using a charging brush or a non-contact charging method using a scorotron charger may be used as the charging unit 102.

The developing unit 103 includes a stirring unit 104 that stirs a two-component developer containing a magnetic carrier (not shown) and a non-magnetic toner, and a developing unit 105 that houses a developing sleeve serving as a developer carrier described later. Has in the casing. In the stirring unit 104, a two-component developer (hereinafter simply referred to as “developer”) is conveyed while being stirred by the first screw member 106 and the second screw member 107. The second screw member 107 is positioned below the developing unit 105, and is rotated by a driving unit (not shown) to supply the developer to the developing sleeve 109 while conveying the developer. A toner concentration sensor 180 is fixed to the casing of the developing unit 103 in the vicinity of the first screw member 106, and detects the toner concentration in the developer conveyed by the first screw member 106. This detection result is sent to the control means 500 as a toner density signal. The toner density sensor 180 also includes developing means for other colors. In FIG. 5, the toner density sensor 180 (Y, C, M, K) is indicated.
Based on the toner density signal from the toner density sensor 180, the control unit 500 appropriately drives a K toner replenishing device (not shown) to replenish an appropriate amount of toner into the stirring unit 104 of the developing unit 103. As a result, the developer whose toner concentration has decreased with the development at the developing unit 105 is circulated and conveyed by the first screw member 106 and the second screw member 107 together with the replenished toner, so that the toner concentration is reduced. Adjusted.

A cylindrical developing sleeve 109 arranged in the developing unit 105 and driven to rotate by a drive motor (not shown) has a part of its peripheral surface exposed outside the casing through an opening provided in the casing of the developing unit 103. The exposed portion is opposed to the photoconductor 101 through a predetermined gap.
The developer conveyed by the second screw member 107 is attracted to the surface of the developing sleeve 109 by the magnetic force generated by the magnet roller disposed inside the developing sleeve 109 and pumped up to the sleeve surface. Then, as the sleeve rotates, the layer thickness on the sleeve is regulated when passing through the gap between the sleeve and the regulating blade 110, and then conveyed to the developing region facing the photoreceptor 101.

  A developing electrode (not shown) is disposed inside the developing sleeve 109 made of a nonmagnetic material, and a developing bias is applied to the developing electrode from the power supply 301. In the developing area, a developing electric field is formed between the electrostatic latent image on the photoconductor 101 and the developing sleeve 109. The developer transported to the developing area is raised by a magnetic force generated by a developing magnetic pole (not shown) of the magnet roller to form a magnetic brush, and the tip of the brush is rubbed against the photoreceptor 101. Then, the toner in the magnetic brush is separated from the magnetic carrier by the action of the above-described developing electric field and transferred to the electrostatic latent image on the photosensitive member 101. By this transfer, the electrostatic latent image on the photoconductor 101 is developed into a toner image as a visible image.

  In this embodiment, the developing unit 103 adopting the two-component developing method using the two-component developer as the developer has been described. However, the one-component developing method using the one-component developer (toner) not including the magnetic carrier is described. Means may be employed.

  The toner image formed on the peripheral surface of the photoconductor 101 enters the primary transfer nip due to the contact between the photoconductor 101 and the intermediate transfer belt 206 as the photoconductor 101 rotates in the clockwise direction in the drawing. Then, primary transfer is performed on the front surface of the intermediate transfer belt 206. The surface of the photoconductor 101 that has passed through the primary transfer nip enters a position facing the drum cleaning device 120.

  The drum cleaning device 120 has a cleaning blade 121 made of polyurethane rubber or the like, for example, and presses the tip of the cleaning blade 121 against the photoreceptor 101. A small amount of untransferred toner that has not been transferred to the intermediate transfer belt 206 adheres to the surface of the photoreceptor 101 that has passed through the primary transfer nip. This transfer residual toner is scraped off from the surface of the photoreceptor 101 by the cleaning blade 121 and collected in the drum cleaning device 120.

  In FIG. 1 described above, the surface of the photoreceptor 101K is uniformly charged to, for example, −700 [V] by the charging means (102 in FIG. 2) during printing, and is exposed by the optical writing unit 290 with a predetermined exposure output. The potential of the electrostatic latent image portion irradiated with laser light as light is, for example, −120 [V]. On the other hand, the developing bias voltage applied from the power supply 301 to the developing sleeve (109 in FIG. 2) is, for example, −470 [V], which generates a developing potential of 350 [V]. Such image forming conditions are appropriately changed according to the result of control by the control means 500 described later.

  The primary transfer rollers 204Y, 204C, 204M, and 204K of the transfer unit 200 are in contact with the back side of the primary transfer nip for Y, C, M, and K of the intermediate transfer belt 206. In this way, a primary transfer bias is applied to the primary transfer roller 204Y in contact with the back surface of the belt by a power source (not shown). As a result, a primary transfer electric field is formed in the primary transfer nips for Y, C, M, and K to electrostatically move the toner image on each photoconductor from the surface of the photoconductor toward the belt. In this color printer, primary transfer rollers 204Y, 204C, 204M, and 204K are used as transfer means for forming a primary transfer electric field. However, a conductive brush shape or a non-contact corona charger is used. May be.

  The intermediate transfer belt 206 sequentially passes through the primary transfer nips for Y, C, M, and K along with the endless movement thereof. Then, Y, C, M, and K toner images are sequentially superimposed on the front surface and primarily transferred. As a result, the Y, C, M, and K toner images are superimposed on the front surface of the intermediate transfer belt 206 after passing through the primary transfer nip for K located on the most downstream side in the belt moving direction. A superposed toner image is formed.

  The secondary transfer roller 208 disposed outside the loop of the intermediate transfer belt 206 is in contact with the front surface of the belt so as to sandwich the belt with the driving roller 201 disposed inside the loop. A secondary transfer nip is formed. While the drive roller 201 is grounded, a secondary transfer bias having a polarity opposite to that of the toner is applied to the secondary transfer roller 208 from a power source (not shown). As a result, a secondary transfer electric field for electrostatically moving the toner from the belt front surface side to the secondary transfer roller 208 side is formed in the secondary transfer nip.

This color printer is housed in a paper bundle in which a plurality of recording papers P are stacked in a thickness direction inside a paper feeding cassette (not shown). The paper feed cassette sends out the uppermost recording paper P in the paper bundle toward the paper feed path at a predetermined timing. As shown in FIG. 1, the fed recording paper P is sandwiched between rollers of a registration roller pair 250 disposed near the end of the paper feed path.
The recording paper P is sent out at a timing at which it can be superimposed on the superimposed toner image on the intermediate transfer belt 206 at the secondary transfer nip by the function of the registration roller pair 250 and is conveyed to the secondary transfer nip. Then, the superimposed toner image on the intermediate transfer belt 206 is secondarily transferred collectively at the secondary transfer nip by the action of the secondary transfer electric field, and the full color image is transferred together with the white color of the recording paper P. In the transfer unit 200, a transfer charger may be used in place of the secondary transfer roller 208 as means for forming a secondary transfer electric field.

  A fixing device 260 is disposed above the secondary transfer nip on the downstream side in the recording paper conveyance direction. In this fixing device 260, a fixing roller 261 containing a heat source such as a halogen lamp and a pressure roller 262 are brought into contact with each other to form a fixing nip, and both rollers are surfaced in the same direction at the fixing nip. Rotate to move. The recording paper P that has passed through the secondary transfer nip enters the fixing device 260 and is then sandwiched by the fixing nip, and a full-color image is fixed by nip pressure or heating.

  Of the entire area in the circumferential direction of the intermediate transfer belt 206, the edge of the cleaning blade 210 that is cantilevered by the belt cleaning device 207 is in contact with the portion around the cleaning backup roller 202. Transfer residual toner adhering to the surface of the intermediate transfer belt 206 after passing through the secondary transfer nip and a gradation toner pattern formed by a toner image described later are removed from the belt surface by the cleaning blade 210.

  When color printing is performed using the color printer, first, image information is transmitted to the color printer from a PC (not shown). The color printer sends the image information to the control unit 500 and an image processing unit (not shown). Upon receiving the image information, the control unit 500 drives various drive motors (not shown) to move the intermediate transfer belt 206 endlessly. At the same time, the photosensitive members of the image forming units are also rotated. Further, the image processing unit sends an optical writing signal generated based on the image information to the optical writing unit 290. The optical writing unit 290 generates exposure light Lb for Y, C, M, and K based on the optical writing signal, and irradiates the photosensitive members 101Y, 101C, 101M, and 101K with predetermined exposure outputs. Light scan. As a result, electrostatic latent images for Y, C, M, and K are formed on each photoconductor, and are visualized by each developing unit. In this way, Y, C, M, and K toner images are formed on the photoreceptors 101Y, 101C, 101M, and 101K. These Y, C, M, and K toner images are superimposed on the intermediate transfer belt 206 at the primary transfer nips for Y, C, M, and K, and are primarily transferred to form a superimposed toner image.

  On the other hand, in a paper feed cassette (not shown), the recording paper P is sent out by the rotation of the paper feed roller. The fed recording paper P is separated into one sheet by a separation roller (not shown) and enters the paper feed path, and is then sandwiched between the registration roller pair 250. The registration roller pair 250 feeds the recording paper P toward the secondary transfer nip at a timing at which it can be superimposed on the superimposed toner image formed on the intermediate transfer belt 206. Note that the registration roller pair 250 is generally used while being grounded, but a bias may be applied to remove paper dust from the recording paper P.

  The superposed toner image on the intermediate transfer belt 206 is secondarily transferred collectively onto the recording paper P fed out by the registration roller pair 250 and sandwiched between the secondary transfer nips. Thereafter, the recording paper P passes through the fixing device 260 and is then discharged out of the image forming apparatus.

  FIG. 3 is a perspective view showing the transfer unit 200. Of the entire area of the intermediate transfer belt 206 in the circumferential direction, a reflection-type optical sensor 130 serving as a density detection unit is disposed oppositely at a place around the drive roller 201. The optical sensor 130 is disposed so as to face the central portion in the belt width direction at the above-mentioned hanging portion.

  FIG. 4 is an enlarged configuration diagram showing the optical sensor 130. In the figure, an optical sensor 130 includes a light emitting element 131, a regular reflection type light receiving element 132, a diffuse reflection type light receiving element 133, a condenser lens 134, a casing 135, and the like. In addition, although LED is used for the light emitting element 131, a laser light emitting element or the like may be used. As the regular reflection type light receiving element 132 and the diffuse reflection type light receiving element 133, phototransistors are used, but a phototransistor or an amplifier circuit may be used.

  Infrared light emitted from the light emitting element 131 passes through the condenser lens 134 and then reaches various toner patterns (described later) formed on the intermediate transfer belt 206. A part of the infrared light is specularly reflected on the surface of each toner pattern to become specularly reflected light, and then retransmits through the condenser lens 134 and is received by the specular reflection type light receiving element 132. The regular reflection type light receiving element 132 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 the control means 500 shown in FIG. Further, another part of the infrared light is diffusely reflected on the surface of each toner pattern to become diffusely reflected light, and then retransmits through the condenser lens 134 and is received by the diffuse reflection type light receiving element 133. The diffuse reflection type light receiving element 133 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 the control means 500 shown in FIG.

  As the light emitting element 131, a GaAs light emitting diode having a peak emission wavelength of 940 [nm] is used. Further, as the regular reflection type light receiving element 132 and the diffuse reflection type light receiving element 133, those having a Si phototransistor having a peak spectral sensitivity wavelength of 850 [nm] are used. That is, the optical sensor 130 detects infrared light of 830 [nm] or more with no significant difference in reflectance due to color. By using such an optical sensor 130, it is possible to detect gradation toner patterns of all colors Y, M, C, and K with a single sensor.

  FIG. 5 is a block diagram of a control system of the color printer according to this embodiment. In the figure, a control means 500 functioning as an image forming condition adjusting means is constituted by a computer including a CPU 500a serving as a processing unit, a ROM 500b storing a control program and various data, a RAM 500c temporarily storing various data, and the like. ing. The control unit 500 is connected to various peripheral devices via a well-known I / O unit that relays signal transmission / reception to / from various peripheral devices. In FIG. Only the main ones related to image forming conditions are shown.

The control unit 500 includes a toner replenishing device 270 (Y, C, M, K) for each color, a belt driving motor 220 for rotating and transferring the intermediate transfer belt 206, an optical writing unit 290, a charging power source 300, and a developing power source 301. Are connected by a signal line. The operation state and output adjustment of these members are performed by a control signal from the control means 500.
To the control means 500, toner density sensors 180 (Y, C, M, K) for each color and an optical sensor 130 are connected via signal lines. The toner density sensor 180 (Y, C, M, K) detects the toner density of each color developing means 103 (Y, C, M, K) and inputs it to the control means 500. When the detection signal from the toner density sensor 180 (Y, C, M, K) falls below a predetermined value, the controller 500 controls the toner replenishing device 270 (Y, C, M, K) is operated to provide a control function for supplying supply toner to the developing means. The control means 500 has a control function for determining that the toner density has been recovered and stopping the operation of the toner replenishing device when the detection signal from the toner density sensor 180 (Y, C, M, K) exceeds a predetermined value. ing.
The optical sensor 130 is formed on the intermediate transfer belt 206 at the time of printing, the density of the toner image at the time of printing, the gradation toner pattern formed at the time of adjusting the image forming conditions described later, and the toner image at the time of the second process. The densities of the intermediate density and solid density toner patterns are detected and input to the control means 500.

The control means 500 has a control function for adjusting image forming conditions by executing the first process and the second process shown in FIG. FIG. 6 shows a flowchart of the control contents at the time of image forming condition adjustment executed by the control means 500. Hereinafter, the image forming condition adjusting operation will be described with reference to this flowchart.
The control unit 500 executes the second process after executing the first process. In the first process, in step ST1, as shown in FIG. 7A, the development potential condition is changed by each image forming unit, so that the floors for Y, C, M, and K are formed on the intermediate transfer belt 206. Toning toner patterns Pk, Pc, Pm, and Py are formed. In step ST2, the optical sensor 130 detects the density of the gradation toner patterns Pk, Pc, Pm, and Py of each color, and derives a solid density necessary for printing from the detected density [gradation density information]. Determine the image conditions.
Here, the relationship between the output value of each of the light receiving elements 132 and 133 obtained by detecting each toner patch constituting the gradation toner pattern of each color with the optical sensor 130, and the relationship between the toner adhesion amount and the output value of the light receiving element. Conversion processing to toner adhesion amount (image density) is performed using a toner adhesion amount calculation algorithm constructed based on the algorithm. In this embodiment, as described in JP-A-2006-139180, the toner adhesion amount is calculated by using the regular reflection light regularly reflected by the toner patch and the diffuse reflection light. From the result, the image forming condition at the time of printing is determined.

Hereinafter, an example of determining the image forming condition in step ST2 will be described.
FIG. 8 is a diagram showing image forming conditions and toner adhesion amount detection results of the gradation toner patterns for each color created in step ST2, and the control unit 500 calculates development γ from the results. FIG. 9 shows an example of the calculation result of development γ. In FIG. 9, the vertical axis represents the toner adhesion amount detection value by the optical sensor 130 and the horizontal axis represents the development bias, and the linear portion where both intersect is the development γ.
More specifically, in the first process, the gradation toner patterns Pk, Pc, Pm, and Py of the respective colors formed in step ST1 are the exposure outputs in which the photosensitive member surface potential VL after exposure is stable regardless of the charging bias. (100% in FIG. 8) is used. For this reason, the photosensitive member surface potential VL that is the exposure portion potential at the time of adjusting the image forming conditions (at the time of potential control) is kept constant, so that the development γ can be calculated with high accuracy in step ST2. That is, by keeping the photoreceptor surface potential VL constant, the development potential can be grasped and the development γ can be accurately calculated. Then, an image forming condition is determined from the calculated development γ.

From FIG. 9, the development potential at which the target toner adhesion amount can be obtained is uniquely determined. Further, the developing potential is the developing bias-the surface potential VL of the photoreceptor after exposure, and the developing bias can be determined from this relationship. Next, the charging bias is determined from the calculated developing bias, and the exposure output is determined from the relationship shown in FIG. FIG. 10 is a diagram showing the characteristics of the exposure output during printing with the vertical axis representing the exposure output and the horizontal axis representing the charging bias.
The characteristic diagrams of FIGS. 9 and 10 are stored in the ROM 500c of the control unit 500, and the control unit 500 determines the charging bias, the developing bias, and the exposure output as the image forming conditions from the output of the optical sensor 130. To do. The contents of steps ST1 and ST2 are already known.

An example of calculation is shown below.
(Development γ = 0.69 [mg / cm ^ 2 / kV] from FIG. 9, expressed as a development γ inclination)
If the solid target adhesion amount = 0.400 [mg / cm ^ 2],
Optimal development potential Vpp = 582 [V]
When the photoreceptor surface potential VL = 50V,
Development bias = Development potential Vpp−Photoreceptor surface potential VL = 532 [V]
Charging bias = Vb + fixed value = 632 [V]
From the relationship of FIG. 10, exposure output = 58 [%].

  In the second process, the control unit 500 uses the image forming unit on the intermediate transfer belt 206 on the intermediate transfer belt 206 using the image forming conditions determined in the first process in step ST3. A toner pattern is created. As these toner patterns, for example, as shown in FIG. 7B, six area gradation toner images are formed. This area gradation toner image includes a first area gradation toner pattern Tp1, a second area gradation toner pattern Tp2, a third area gradation toner pattern Tp3, a fourth area gradation toner pattern Tp4, and a fifth area gradation toner. The pattern Tp5 and the sixth area gradation toner pattern Tp6, and the image density (toner adhesion amount) increases in this order. In FIG. 7B, the first area gradation toner pattern Tp1 to the first area gradation toner pattern Tp5 are intermediate density toner patterns, and the sixth area gradation toner pattern Tp6 is a solid density toner pattern. It is. FIG. 7B illustrates only a toner pattern for intermediate density and solid density of black, and other color patterns are omitted.

The control unit 500 obtains the density of each toner pattern from the toner pattern created in step S3 using the same detection unit and calculation method as in step S2. Thereafter, in step ST4, the control means for each of the first to fifth area gradation toner patterns Tp1 to Tp5, the target adhesion amount of each area gradation toner pattern previously stored in the ROM 500c and each area gradation from the optical sensor 130. The difference between the detected values of the toner pattern is obtained. In step ST5, the difference is used as a correction value, and the correction value is used to correct the image area ratio, which is the image forming condition of the first area gradation toner pattern Tp1. The same correction is performed for the second to fifth area gradation toner patterns. Such image area ratio correction is performed for all of Y, C, M, and K. Thereby, for each of Y, C, M, and K, the first to fifth halftone densities can be set to the target densities.
Further, since the sixth area gradation toner pattern Tp6 formed as the solid density toner pattern is created under the image forming conditions determined in step ST2, the detection value by the optical sensor 130 is usually detected value = It should be the solid density target value. However, as described in the background art, when the solid density image forming condition is determined in step ST2, the exposure output is different between the solid density toner pattern formed in step ST4. For this reason, the difference ΔVL between the photosensitive member surface potential (exposure portion potential) VL after exposure in steps ST2 and ST4 increases depending on the time and environment, and as a result, the detected value and the target value of the solid density deviate. There is.

Therefore, in this embodiment, in step ST5, the detection value of the sixth area gradation toner pattern Tp6, which is a solid image toner pattern, is compared with a preset target value range (target range). If the detected value is within the target range, this control is terminated. If the detected value and the target value are not within the target range, the imaging condition is changed (corrected) in step ST6.
If the image forming conditions are corrected in step ST6, the image density of the halftone image that has been adjusted to the target density is shifted from the target density by changing the development bias or the like. For this reason, after correcting the image forming conditions in step ST6, the process returns from step ST3 to step ST4, and halftone density correction is performed again.
By performing such correction, it is possible to appropriately control the density of the solid image and the density of the halftone image at the time of printing even when the photoreceptor surface potential VL varies due to deterioration with time or environmental variation.
That is, the control unit 500 detects the density of each of the intermediate density and solid density toner patterns with the optical sensor 130, and performs halftone correction on the gradation density information detected in the first process based on the intermediate density information. Further, a target value of control for maintaining the density during printing is derived in the second process based on the solid density information. If the solid density information detected in the second process is different from the target value, the image forming condition determined in the first process is corrected, and the second process is re-executed after the correction.

Next, an example of correcting the image forming conditions in step ST6 will be described.
If the solid density toner adhesion amount detected in step ST5 is not within the target range, the control means 500, as shown in FIG. 11, the difference between the solid density toner adhesion quantity and the detected value of the sixth area gradation toner pattern Tp6. ΔM / A is calculated from the map information shown in FIG. Then, a development bias shortage ΔVb is obtained from the difference ΔM / A and from the development γ value, and ΔVb is added to the image forming condition obtained in step ST2 for correction. In FIG. 11, the vertical axis represents the detected toner amount and the horizontal axis represents the development bias. If the optimum developing bias is determined as described above, the charging bias and the exposure light amount are also determined and corrected accordingly. That is, when changing the image forming condition performed in step ST6, the control unit 500 changes the development bias determined in the first process and the exposure output determined in the first process.

When the image forming conditions are corrected, it is necessary to perform halftone density correction again, which increases the time required for adjustment. Therefore, it may be determined from a parameter that contributes to ΔVL whether there is a variation in the photoreceptor surface potential (exposure portion potential), that is, whether there is a density difference due to ΔVL. What contributes to ΔVL includes the temperature and humidity that are the environment during use, the exposure time of the photosensitive member, and the total driving time of the photosensitive member that causes deterioration of the photosensitive member over time. You may make it judge.
In implementing this control content by the control means 500, the color printer, as shown in FIG. 12, the temperature / humidity detection means 510 for detecting the temperature and humidity in the apparatus, and the leaving time acquisition means 511 for obtaining the leaving time information of the apparatus. And total drive time acquisition means 512 for obtaining total drive time information of the apparatus. The temperature / humidity detection unit 510, the standing time acquisition unit 511, and the total drive time acquisition unit 512 are connected to the control unit 500 through signal lines, and are configured to input each detection information to the control unit 500, respectively.

  The control unit 500 performs control so that the image forming condition is not corrected in accordance with output information from the temperature / humidity detection unit 510, the leaving time acquisition unit 511, and the total drive time acquisition unit 512. That is, the control unit 500 includes a threshold value TH to be compared with the change amount Δth of the temperature / humidity information th from the temperature / humidity detection sensor 510, a threshold value T1 to be compared with the leaving time information t from the leaving time acquisition unit 511, and the total drive. A threshold value T2 to be compared with the total drive time information tm from the time acquisition unit 512 is stored in the ROM 500c in advance. The neglected time acquisition unit 511 and the total driving time acquisition unit 512 are constituted by timers. The leaving time is the time from the end of the previous printing operation to the start of the next printing operation, and the leaving time acquisition unit 511 counts from the end of the printing operation. The total driving time information is the total usage time from the start of use of the color printer to the present time. The total drive time acquisition unit 512 measures the time during which the color printer is activated, and stores it in the ROM 500c when the apparatus activation is stopped. As the total driving time, the number of rotations of the photosensitive member may be measured and regarded as the total sum.

Next, specific control contents will be described with reference to the flowcharts shown in FIGS.
FIG. 13 shows a control mode corresponding to the temperature and humidity information. The control means 500 acquires the temperature / humidity information th from the temperature / humidity detection sensor 510 every time the adjustment operation is performed in step ST11 of FIG. 13 and stores it in the RAM 500b of the control means 500.
In step ST12, the temperature / humidity change amount Δth is calculated from the current temperature / humidity information th acquired in step ST11 and the temperature / humidity information acquired in the previous adjustment operation. Steps ST13 to ST17 are the same as steps ST1 to S5 in FIG.
In step ST17, it is determined whether or not the detected value of the solid image toner pattern is within the target range. If the detected value is not within the target range, the process proceeds to step ST18 where the temperature / humidity change Δth is compared with the threshold value TH. If the temperature / humidity change amount Δth ≧ threshold value TH, the process proceeds to step ST19 to change the image forming condition, but if the temperature / humidity change amount Δth is less than the threshold value TH, the image forming condition is not changed. This control is finished.
As in the control mode shown in FIG. 13, when the temperature / humidity fluctuation in the apparatus is less than the threshold value, the time required for adjustment can be shortened unless the imaging condition is changed.

FIG. 14 shows a control mode corresponding to the leaving time information. The control means 500 acquires the leaving time information t from the leaving time acquisition means 511 each time the adjustment operation is performed in step ST21 of FIG. 14, and stores it in the RAM 500b of the control means 500. And the process from step ST22 to step ST26 is performed. The processing from step ST22 to step ST26 is the same as the processing from step ST1 to step ST5 in FIG.
In step ST26, it is determined whether or not the detected value of the solid image toner pattern is within the target range. If it is not within the target range, the process proceeds to step ST27, where the neglected time information t is compared with the threshold value T1. If the leaving time information t ≧ threshold value T1, the process proceeds to step ST28 and the image forming condition is changed. If the leaving time information t is less than the threshold value T1, the image forming condition is not changed. This control is finished.
As in the control mode illustrated in FIG. 14, when the apparatus is left for a time that is less than the threshold, the time required for adjustment can be shortened unless the image forming condition is changed.

FIG. 15 shows a control mode corresponding to the total driving time of the color printer, which is an indicator of the degree of deterioration of the apparatus.
The control unit 500 acquires the total drive time information tm from the total drive time acquisition unit 512 every time the adjustment operation is performed in step ST31 of FIG. 15 and stores it in the RAM 500b of the control unit 500. And the process from step ST32 to step ST36 is performed. The processing from step ST32 to step ST36 is the same as the processing from step ST1 to step ST5 in FIG.
In step ST36, it is determined whether or not the detected value of the solid image toner pattern is within the target range, and if it is not within the target range, the process proceeds to step ST37 to compare the total drive time information tm with the threshold T2. If the total driving time information tm ≧ threshold value T2, the process proceeds to step ST38 to change the imaging condition. If the total driving time information tm is less than the threshold value T2, the imaging condition is changed. Do not finish this control.
As in the control mode shown in FIG. 15, when the total drive time of the apparatus is less than the threshold value, the time required for adjustment can be shortened unless the image forming conditions are changed.

Next, another control mode by the control means 500 will be described with reference to FIGS.
In the first process, the control unit 500 forms gradation toner patterns Pk, Pc, Pm, and Py for each color, and the toner density of the gradation toner patterns Pk, Pc, Pm, and Py for each color is detected by the optical sensor 130. The image forming conditions are determined accordingly. However, in this embodiment, in the gradation density information detected by the optical sensor 130, the highest density gradation density is compared with a preset target value, and the highest density gradation density is less than the target value. Control is performed so that the gradation density information detected by the optical sensor 130 is not used for determining the image forming condition.

In order to achieve this control, the target value information shown in FIG. FIG. 16 is a diagram showing the relationship between the calculated toner adhesion amount and the development potential, with the vertical axis representing the toner adhesion amount and the horizontal axis representing the development potential, and a target value is set. The target value for each color is the same, but the development potential for obtaining it is different for each color.
Hereinafter, this control content will be described with reference to FIG. This control is executed in the first process, and the second process described above is executed after this processing.
When the adjustment operation is performed, the control unit 500 forms gradation toner patterns Pk, Pc, Pm, and Py for Y, C, M, and K having different densities on the intermediate transfer belt 206 in step ST41. Each color gradation toner pattern is composed of a plurality of toner patches having different toner adhesion amounts. For example, at a patch interval of 5.6 [mm], a gradation toner pattern for K, a gradation toner pattern for C, and a gradation toner pattern for M are used. The toner image is formed on the transfer belt 6 in the order of the gradation toner pattern and the Y gradation toner pattern. Each toner patch has a width in the main scanning line direction of 5 [mm] and a width in the sub scanning line direction of 7 [mm]. The gradation toner pattern is formed by changing the development potential condition for each toner patch.

  In step ST42, the controller 500 optically detects the density of the gradation toner pattern of each color using the optical sensor 130. In step ST43, the control means 500 calculates the output value of the light receiving elements 132 and 133 obtained by detecting each toner patch of the gradation toner pattern of each color, the well-known toner adhesion amount, and the output value of the light receiving element. Conversion processing to toner adhesion amount (image density) is performed using an adhesion amount calculation algorithm constructed based on the relationship. In this embodiment, as described in Japanese Patent Application Laid-Open No. 2006-139180 described above, the toner adhesion amount is calculated by using the regular reflection light regularly reflected by the toner patch and the diffuse reflection light. calculate.

In step ST44, the control unit 500 determines whether the maximum toner density (adhesion amount) of each color is equal to or higher than the target value based on the data shown in FIG. 16 set in advance. Referring to FIG.
Toner density of the highest density toner pattern ≧ target value: M, C
Toner density of the highest density toner pattern <target value: K, Y
It has become.

Therefore, in the present embodiment, the control unit 500 calculates the development γ and the development start voltage Vk for M and C in step ST45, but does not calculate K and Y.
An example of calculation is shown.
M: y = x (development γ = 1.00, Vk = 0)
C: y = 0.75x (development γ = 0.75, Vk = 0)
In step ST46, an image forming condition (development potential) at the time of printing is determined from the calculation results of the development γ and the development start voltage Vk.
In the example of FIG. 16, the target value is set to 0.400 [mg / cm ^ 2], but the target value may be, for example, the maximum adhesion amount necessary for printing (the adhesion amount necessary for the solid image). in this case,
M: Development potential = 0.400 [kV]
C: Development potential = 0.533 [kV].

Next, when it is below the target value (K, Y) from the determination in step ST44, it is determined that there is an error here and this control is finished.
In the control mode shown in FIG. 17, when there is a possibility that there is no linearity in development γ (relationship between development potential and adhesion amount), density control is not performed, so that development γ calculation errors can be suppressed. it can.

  Here, it is possible to prevent the occurrence of an error as much as possible by determining the generation condition of the gradation toner pattern to be generated at the next control from the calculation result of the development γ and the development start voltage Vk at the previous control. . This is because the developing ability does not fluctuate greatly except when the environment is suddenly changed or after being left for a long period of time.

An example of determining the creation conditions for the next control is shown below.
From FIG. 16, the development potential required for the image density of K and Y to be the target values is
K: Development potential = 800 [V]
Y: Development potential = 1600 [V]
Therefore, the conditions for creating the highest toner density pattern at the next execution of control are as follows.
K: Development potential = 800 [V]
Y: Development potential = 1600 [V]

FIG. 18 shows another form of control by the control means.
In the first process, the control unit 500 forms gradation toner patterns Pk, Pc, Pm, and Py for each color, and the toner density of the gradation toner patterns Pk, Pc, Pm, and Py for each color is detected by the optical sensor 130. The image forming conditions are determined accordingly. However, in the present embodiment, when the highest density density is less than the target value among the gradation density information detected by the optical sensor 130, the gradation toner pattern having a density higher than the highest density is displayed on the intermediate transfer belt 206. The image forming unit is controlled so as to be formed.

Hereinafter, this control content will be described with reference to FIG. This control is executed in the first process, and the second process described above is executed after this processing.
In step ST51 to step ST54, the control means 500 executes the same processing as in step ST41 to step ST44 in FIG. Details are omitted. In step ST54, it is assumed that the gradation toner pattern having the highest density of K and Y is equal to or less than the target value, as in step ST44.

In the present embodiment, here, instead of determining this as an error and ending this control, the creation condition of the re-creation pattern is calculated in step ST57. From FIG. 16, the development potential required for the image density of K and Y to be the target values is
K: Development potential = 800 [V]
Y: Development potential = 1600 [V]
Therefore, the conditions for creating the highest toner density pattern at the next execution of control are as follows.
K: Development potential = 800 [V]
Y: Development potential = 1600 [V]

After re-creating the pattern, the process returns to step ST51 again to sequentially execute each step. Therefore, in the first control loop, even in the K and Y tone toner patterns in which the highest density tone toner pattern is equal to or lower than the target value, in the second control loop, the high density tone toner pattern Exceeds the target value. When returning from step ST54 to step ST51, the number of gradation toner patterns may be one determined as described above, and development γ, K, C, M, and Y for all colors of K, C, M, and Y together with the toner density detection result created for the first time. The development start voltage Vk is calculated in step ST55. In step ST56, image forming conditions for printing all colors are calculated, and the first process is terminated.
In the control mode shown in FIG. 18, since the development γ is calculated after a gradation toner pattern having a predetermined density or more is created, the image forming conditions can be calculated with high accuracy.

  In the above-described embodiments, the image forming apparatus is described as a color printer. However, the image forming apparatus to which the present invention is applicable is not limited to this, and can be applied to other image forming apparatuses such as a copying machine, a facsimile machine, and a plotter. .

101 (Y, C, M, K) image carrier 130 density detection means 206 image carrier (intermediate transfer belt)
500 Control means 510 Temperature / humidity detection means 511 Leaving time acquisition means 512 Total drive time acquisition means P (y, c, m, k) Toner toner pattern th Temperature / humidity information Δth Temperature / humidity change amount t Leaving time information tm Total drive time Information T1, T2 threshold

JP 2004-184583 A Japanese Patent Laid-Open No. 10-239924 Japanese Patent Laid-Open No. 03-208681

Claims (8)

Density detecting means for detecting the gradation density of the gradation toner pattern formed on the image carrier by the image forming means;
A first process for determining an image forming condition for deriving a solid density required at the time of printing from gradation density information detected by the density detecting unit; and the image forming condition determined in the first process, The intermediate density and solid density toner patterns are respectively formed on the image carrier by the imaging means, and the density detection means detects the density of the intermediate density and solid density toner patterns, respectively, and the first process. An image provided with a control means having a second process for correcting the halftone of the gradation density information detected in step 1 with the intermediate density information and deriving a target value for controlling the density during printing based on the solid density information. In the forming device,
When the solid density information detected in the second process is different from a target value, the control unit changes the image forming condition determined in the first process, and re-executes the second process after correction. An image forming apparatus. The image forming apparatus according to claim 1.
The image forming apparatus, wherein the control unit changes an image forming condition by changing a developing bias determined in the first process. The image forming apparatus according to claim 1 or 2,
The image forming apparatus, wherein the control unit changes an image forming condition by changing an exposure output determined in the first process. The image forming apparatus according to claim 1, 2 or 3.
Has temperature and humidity detection means to know the temperature and humidity in the device,
The control means does not change the image forming condition when the temperature and humidity information detected by the temperature and humidity detection means is less than a predetermined amount of change in temperature and humidity between the previous time and the current control time. An image forming apparatus. The image forming apparatus according to claim 1, 2 or 3.
It has a neglected time acquisition means for obtaining neglected time information,
The image forming apparatus, wherein the control unit does not change the image forming condition when the leaving time information acquired by the leaving time acquisition unit is less than a predetermined value. The image forming apparatus according to claim 1, 2 or 3.
Having total driving time acquisition means for obtaining total driving time information;
The image forming apparatus, wherein the control unit does not change the image forming condition when the total driving time information acquired by the total driving time acquiring unit is less than a predetermined value. The image forming apparatus according to any one of claims 1 to 6,
The control means, in the gradation density information detected by the density detection means, if the highest density gradation density is less than a target value, the control means uses the gradation density information detected by the density detection means in the first process. An image forming apparatus characterized in that the gradation density information is not used for determining an image forming condition. The image forming apparatus according to any one of claims 1 to 6,
In the gradation density information detected by the density detection means, the control means, when the highest density gradation density is less than a target value, outputs a gradation toner pattern having a density higher than the highest density to the image carrier. An image forming apparatus, wherein the image forming means is controlled so as to be formed on the top.

Images