JP4882674B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an electrophotographic image forming apparatus and an image forming method, and more particularly, to an image forming apparatus such as a copying machine, a printer, a facsimile, or a multifunction machine having these functions combined, and these image forming apparatuses. The present invention relates to an image forming method for forming an image using the image forming method.

  The tandem color image forming apparatus includes four image forming units for forming yellow (Y), magenta (M), cyan (C), and black (K) toner images. The imaged toner images are transferred onto the endless intermediate transfer belt (primary transfer), and a full-color toner image superimposed on the intermediate transfer belt is transferred between the intermediate transfer belt and the secondary transfer roller. Transfer (secondary transfer) to a medium such as paper at the nip portion.

  Each image forming unit includes an electrostatic latent image carrier disposed in contact with the intermediate transfer belt, a developer carrier that forms a toner image by supplying toner to the electrostatic latent image carrier, and an intermediate transfer A primary transfer roller disposed opposite to the electrostatic latent image carrier with the belt interposed therebetween. A predetermined voltage is applied to the primary transfer roller, whereby a current flows between the primary transfer roller and the electrostatic latent image carrier, so that the toner image formed on the surface of the electrostatic latent image carrier is The image is transferred (primary transfer) to the intermediate transfer belt at a portion facing the primary transfer roller.

  A power source is connected to the primary transfer roller of the image forming unit for each color, but in recent years, an image forming apparatus that reduces costs by connecting a common power source to the primary transfer rollers of yellow, magenta, and cyan. It has increased.

  In recent years, ion conductive rollers having excellent uniformity of electrical resistance are often used as primary transfer rollers. When an ion conductive roller is used as a primary transfer roller, transfer performance is improved, so that image quality can be improved.

  However, since the ion conductive roller has a property that its electric resistance value is likely to change due to a change in the temperature and humidity environment inside the apparatus, when an ion conductive primary transfer roller is used, the transfer voltage applied to the primary transfer roller is large. It is necessary to control the length according to the change in the electrical resistance value of the roller.

As one method for controlling the transfer voltage, ATVC (Auto Transfer Voltage Control) control has been proposed. ATVC control detects the voltage when a constant current flows through the primary transfer roller as a substitute value for the electrical resistance value, and determines the optimum transfer voltage based on the detected voltage and a preset table and arithmetic expression. To do. A specific configuration of ATVC control is disclosed in, for example, Patent Document 1.
JP 2003-156916 A

  By the way, as a tandem color image forming apparatus, an apparatus that performs image density correction at a preset timing (for example, when a power is input or when a predetermined durable sheet has elapsed) has been proposed. By performing image density correction at a predetermined timing, it is possible to prevent changes in image quality due to toner deterioration, consumption of constituent members such as a photoconductor, or changes in the temperature and humidity environment.

  Since the image density correction is performed by transferring the toner image of each color onto the intermediate transfer belt, it is necessary to appropriately control the transfer voltage applied to the primary transfer roller before the image density correction operation, and the ATVC control is performed. In the image forming apparatus set to, image density correction is performed after performing ATVC control.

  In the image density correction, the developing bias voltage applied to the developing roller is controlled to an appropriate voltage, and the surface potential of the electrostatic latent image carrier is controlled to an appropriate potential corresponding to the developing bias voltage. Therefore, when the image forming operation is performed after the image density correction, an image having a good density can be formed.

  However, after the image density correction is performed, the surface potential of the electrostatic latent image carrier may differ significantly depending on the color. Therefore, when a common power source is connected to the primary transfer rollers for yellow, magenta, and cyan as described above, the magnitude of the current flowing between the primary transfer roller and the electrostatic latent image carrier varies significantly depending on the color. There is a risk of insufficient transfer or excessive transfer of any color.

  In addition, when image density correction is performed, the surface potential of the electrostatic latent image carrier may change significantly before and after the image density correction in the image forming unit of any color. The magnitude of the current flowing between the toner and the electrostatic latent image carrier greatly changes, which may result in insufficient transfer and excessive transfer.

  In both the former and the latter cases, if ATVC control is performed again after image density correction, the optimum voltage is applied to the primary transfer roller, so that insufficient transfer and excessive transfer can be prevented. However, if ATVC control is frequently performed, Print productivity is greatly impaired.

  SUMMARY An advantage of some aspects of the invention is that it provides an image forming apparatus and an image forming method capable of preventing occurrence of insufficient transfer or excessive transfer after image density correction while maintaining good print productivity.

In order to solve the above problems, an image forming apparatus according to the present invention provides:
A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means is an image forming apparatus configured to control the surface potential by adjusting an adjustment factor represented by a variable value corresponding to the surface potential,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, when the absolute value of the difference between the maximum variable value and the minimum variable value among the variable values of the plurality of surface potential control means is larger than a predetermined value, the ATVC control is performed again. It is characterized by comprising control means for controlling as described above.

Another aspect of the image forming apparatus according to the present invention is:
A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means is an image forming apparatus configured to control the surface potential by adjusting an adjustment factor represented by a variable value corresponding to the surface potential,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, the largest value among the absolute values of the difference between the variable value before the density correction operation and the variable value after the density correction operation in each surface potential control unit is larger than a predetermined size. Control means for controlling to perform the ATVC control again.

An image forming method according to the present invention includes:
A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means is a method of forming an image using an image forming apparatus configured to control the surface potential by adjusting an adjustment factor represented by a variable value corresponding to the surface potential. There,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, when the absolute value of the difference between the maximum variable value and the minimum variable value among the variable values of the plurality of surface potential control means is larger than a predetermined value, the ATVC control is performed again. It is characterized by that.

An image forming method according to another aspect of the present invention includes:
A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means is a method of forming an image using an image forming apparatus configured to control the surface potential by adjusting an adjustment factor represented by a variable value corresponding to the surface potential. There,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, the largest value among the absolute values of the difference between the variable value before the density correction operation and the variable value after the density correction operation in each surface potential control unit is larger than a predetermined size. The ATVC control is performed again.

  According to the present invention, after performing the image density correction operation, the variable value such as the grid voltage of the surface potential control means for controlling the surface potential of the electrostatic latent image carrier satisfies a predetermined condition that can cause a transfer defect. In this case, since the ATVC control is performed again, an appropriate voltage is applied to the primary transfer roller when an image is formed after the image density correction operation. Therefore, for any color toner image, primary transfer is performed well in a state where an appropriate current flows through the primary transfer roller, so that an image with good image quality can be formed. Further, since the ATVC control after the image density correction operation is performed only when a predetermined condition is satisfied, it is possible to maintain good print productivity.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the following description, terms indicating a specific direction and position (for example, “up”, “down”, “right”, “left” and other terms including those terms) are used as necessary. These terms are used for easy understanding of the invention with reference to the drawings, and the technical scope of the present invention is not limited by the meaning of these terms.

  FIG. 1 shows a schematic configuration of an image forming apparatus 2 according to an embodiment of the present invention.

  The image forming apparatus 2 is an electrophotographic image forming apparatus such as a copying machine, a printer, a facsimile machine, or a multi-function machine having a combination of these functions. Currently, various types of electrophotographic image forming apparatuses have been proposed. The illustrated image forming apparatus is a so-called tandem color image forming apparatus.

  The image forming apparatus 2 includes an endless intermediate transfer belt 30. The intermediate transfer belt 30 is made of a conductive material.

  In the present embodiment, the intermediate transfer belt 30 is wound around a pair of rollers 32 and 34 disposed on the right and left sides of the drawing, respectively. The roller 32 on the right side of the drawing is drivingly connected to a motor (not shown). The roller 32 connected to the motor rotates based on the driving of the motor, and the belt 30 and the other roller 34 in contact with the roller 30 are opposite to each other in the figure. It rotates in the clockwise direction.

  A secondary transfer roller 40 is provided outside the belt portion supported by the roller 32 disposed on the right side in the drawing. The secondary transfer roller 40 is in contact with the outer peripheral surface of the belt, and the contact portion (nip portion) forms a secondary transfer region 41.

  An intermediate transfer belt cleaning member 42 is provided outside the belt portion supported by the roller 34 arranged on the left side in the drawing. The cleaning member 42 is in pressure contact with the roller 34 via the belt 30, and the contact portion forms a collection region 62 for collecting untransferred toner.

  Below the belt portion moving from the roller 34 on the left side to the roller 32 on the right side in the drawing, yellow (Y), magenta (M), cyan (C), black ( Four image forming units 3 (3Y, 3M, 3C, and 3K) that respectively create toner images of corresponding colors using the developer K) are arranged along the intermediate transfer belt 30.

  Each image forming unit 3 includes a cylindrical photosensitive member 4 as an electrostatic latent image carrier. Around the photosensitive member 4, a charger 8, an exposure device 10, a developing device 18, a primary transfer roller 14, and a photosensitive member cleaning member 16 are arranged in this order along the rotation direction (clockwise direction in the drawing). Yes. The primary transfer roller 14 is disposed inside the endless intermediate transfer belt 30. The configuration of the charger 8 will be described later.

  The developing device 18 includes a developing roller 36 that carries the developer in its housing. For example, a two-component toner is used as the developer. As shown in FIG. 2, a power source 70 (70Y, 70M, 70C, 70K) is supplied to the developing roller 36 (36Y, 36M, 36C, 36K) via a control circuit 72 (72Y, 72M, 72C, 72K) (patented). Corresponding to the developing bias applying means in the claims).

  The primary transfer roller 14 (14Y, 14M, 14C, 14) is connected to power supplies 64, 65 (corresponding to the primary transfer voltage applying means in the claims) via control circuits 66, 67. Specifically, a common power supply 64 and a control circuit 66 are connected to the primary transfer rollers 14Y, 14M, and 14C, and another power supply 65 and a control circuit 67 are connected to the primary transfer roller 14K. The power supplies 64 and 65 and the photoconductor 4 are grounded.

  Under the intermediate transfer belt 30, density sensors 61 are provided on the downstream side of the four image forming units 3.

  Returning to FIG. 1, in the embodiment, a plate-like blade is used as the photosensitive member cleaning member 16, and one end side thereof is in contact with the outer peripheral surface of the photosensitive member 4. However, the photosensitive member cleaning member 16 is not limited to a blade, and other cleaning members (for example, a fixed brush, a rotating brush, a roller, or a combination of these members) can also be used. Further, the photoconductor cleaning member 16 is not necessarily provided, and a cleanerless system in which the untransferred toner on the photoconductor 4 is collected by the developing device 18 may be employed.

  A paper feed cassette 44 as a paper feed device is detachably disposed below the image forming apparatus 2. The sheets (recording media) 36 stacked and accommodated in the sheet feeding cassette 44 are sent out one by one from the uppermost one to the transport path 50 by the rotation of the sheet feeding roller 52 disposed in the vicinity of the sheet feeding cassette 44. It has become. A registration roller 54 for sending the paper 36 to the secondary transfer area 41 at a predetermined timing is provided near the paper feed roller 52.

  The conveyance path 50 extends from the paper feed cassette 44 to the paper discharge unit 58 through the nip portion of the registration roller pair 54, the secondary transfer region 41, and the fixing device 22.

  A control unit 60 (corresponding to control means in claims) that controls ATVC control and image density correction operation, which will be described later, is provided on the upper part of the image forming apparatus 2. However, the position where the control part 60 is arrange | positioned is not specifically limited.

  The image forming apparatus 2 can be switched between a monochrome mode in which a monochrome image is formed using one color toner (for example, black) and a color mode in which a color image is formed using four color toners. .

  An example of an image forming operation in the color mode will be briefly described.

  First, in each image forming unit 3, the outer peripheral surface of the photosensitive member 4 that is rotationally driven at a predetermined peripheral speed is uniformly charged by the charger 8. Next, light corresponding to the image information is projected from the exposure device 10 on the outer peripheral surface of the charged photoconductor 4 to form an electrostatic latent image. Subsequently, the electrostatic latent image is made visible by the developer toner supplied from the developing roller 36 of the developing device 18. More specifically, the electrostatic latent image portion formed on the outer peripheral surface of the photosensitive member 4 when the toner carried on the developing roller 36 reaches the developing region facing the photosensitive member 4 by the rotation of the developing roller 36. As a result, a toner image is formed.

  When the toner image of each color formed on the photoconductor 4 in this way reaches the primary transfer region by the rotation of the photoconductor 4, yellow, magenta, cyan, and black are sequentially transferred from the photoconductor 4 to the intermediate transfer belt 30. Transferred (primary transfer) and overlaid.

  Untransferred toner remaining on the photosensitive member 4 without being transferred to the intermediate transfer belt 30 reaches the contact portion between the photosensitive member 4 and the cleaning member 16 and is scraped off by the cleaning member 16. It is removed from the outer peripheral surface.

  The superimposed four color toner images are conveyed to the secondary transfer region 41 by the intermediate transfer belt 30. On the other hand, the paper 36 accommodated in the paper feed cassette 44 is conveyed to the secondary transfer area 41 in accordance with the timing. Then, the four color toner images are transferred (secondary transfer) from the intermediate transfer belt 30 to the paper 36 in the secondary transfer region 41. The paper 36 to which the four color toner images have been transferred is transported further downstream in the transport path 50, and the toner image is fixed on the paper 36 by the fixing device 22, and then sent to the paper discharge unit 58.

  The intermediate transfer belt 30 that has passed through the secondary transfer region 41 is cleaned by the cleaning blade 42. Thereafter, the rotational drive of each photoreceptor 4 and the intermediate transfer belt 30 is stopped.

  Next, the charger 8 will be described. As the charger 8, for example, a scorotron charger is used.

  As shown in FIG. 3, the scorotron charger 8 includes a discharge electrode 80 having a plurality of discharge points 82 disposed opposite to the outer peripheral surface of the photoconductor 4, and a shield case 84 having an inverted U-shaped cross section surrounding the discharge electrode 80. And a grid electrode 86 disposed so as to be interposed between the outer peripheral surface of the photoreceptor 4 and the discharge electrode 80. The discharge points 82 are arranged at intervals along the axial direction of the photoconductor 4.

  In the embodiment, a needle electrode is used as the discharge electrode 80, but a discharge electrode other than the needle electrode may be used. For example, a wire type electrode may be used.

  As the material of the discharge electrode 30, a material having conductivity is used, and specifically, for example, stainless steel is used. As a material of the shield case 84, a conductive material is used, and specifically, for example, stainless steel is used.

  The grid electrode 80 is configured by forming a plurality of openings side by side along the longitudinal direction in a strip-shaped conductive member extending along the axial direction of the photoreceptor 4. As the material of the grid electrode 80, a material having conductivity is used, and specifically, for example, stainless steel is used.

  The discharge electrode 80 is connected to a power source 88 as discharge voltage application means for applying a voltage to the discharge electrode 80. It is preferable to use a constant current power source as the power source 88, so that a constant current can flow through the discharge electrode 80 even if foreign matter such as a discharge product adheres to the discharge electrode 80.

  The shield case 84 is connected to a power supply 90 as case voltage application means for applying the voltage Vs to the shield case 84. As the absolute value of the voltage Vs increases, the charge of ions emitted from the discharge point 82 becomes less likely to flow into the shield case 84.

  The grid electrode 86 is connected to a power source 92 as grid voltage application means for applying a grid voltage Vg to the grid electrode 86 via a control circuit 94 as grid voltage control means for controlling the grid voltage Vg. As the absolute value of the grid voltage Vg increases, the charge of ions emitted from the discharge point 82 hardly flows into the grid electrode 86.

  A part of the charge of ions emitted from the discharge point 82 flows into the shield case 84 according to the magnitude of the absolute value of the voltage Vs applied to the shield case 84. When the amount of charge flowing into the shield case 84 increases, the amount of charge reaching the outer peripheral surface of the photoconductor 4 decreases, so that the voltage Vs is set to a magnitude such that the amount of charge flowing into the shield case 84 is less than or equal to a predetermined value. The Specifically, the voltage Vs is preferably set to 1 kV or more and 5 kV or less, for example.

  Similarly, part of the charge of ions emitted from the discharge point 82 flows into the grid electrode 86 according to the magnitude of the absolute value of the grid voltage Vg applied to the grid electrode 86. When the amount of charge flowing into the grid electrode 86 increases, the amount of charge reaching the outer peripheral surface of the photoconductor 4 decreases, and therefore the grid voltage Vg is set to a magnitude such that the amount of charge flowing into the grid electrode 42 is not more than a predetermined value. Is done. Specifically, the grid voltage Vg is preferably set to 0.2 kV or more and 1 kV or less.

  According to the charger 8 configured as described above, a current supplied from the power supply 88 flows to the discharge electrode 80, thereby generating a corona discharge at the discharge point 82, and from the discharge point 82 to the outer peripheral surface of the photoreceptor 4. Ions are released toward the target. A part of the charge of the ions emitted from the discharge point 82 depends on the magnitude of the grid voltage Vg applied to the grid electrode 86 and the voltage Vs applied to the shield case 84, or the shield electrode 84. Flow into.

  The electric charges that have passed through the grid electrode 86 without flowing into the grid electrode 86 or the shield case 84 reach the outer peripheral surface of the photoconductor 4, thereby charging the outer peripheral surface of the photoconductor 4.

  The amount of charge reaching the outer peripheral surface of the photoconductor 4, that is, the charging potential of the outer peripheral surface of the photoconductor 4 is determined by the magnitude of the current flowing through the discharge electrode 80, the magnitude of the voltage Vs applied to the shield case 84 and the grid electrode 86. It is determined by the magnitude of the grid voltage Vg applied to.

  In the embodiment, the surface potential control means 91 for controlling the surface potential of the photosensitive member 4 includes a grid electrode 86, a power source 92, and a control circuit 94, and the control circuit 94 controls the magnitude of the grid voltage Vg. Thus, the surface potential of the outer peripheral surface of the photoconductor 4 can be controlled.

  Returning to FIG. 2, the ATVC control will be described. In the ATVC control, transfer voltages Vt (Vt (Y), Vt (M), Vt (C), Vt (K)) applied to the primary transfer roller 14 in order to appropriately perform primary transfer of each color toner image appropriately. This is control for determining the size, and is performed by the control unit 60.

  ATVC control is performed, for example, when a power input to the image forming apparatus 2 is started, when a printing operation is started, when a predetermined number of continuous prints has elapsed, when the ambient temperature inside the image forming apparatus 2 has increased by a predetermined temperature, This is performed when the photosensitive drum unit or the toner bottle is replaced.

  In the ATVC control, the primary transfer rollers 14Y, 14M, and 14C are connected to the common power source 64, and thus the common control is performed. The primary transfer roller 14K is connected to another power source 65, and thus individually controlled. Is controlled.

  The ATVC control of the primary transfer rollers 14Y, 14M, and 14C will be described.

  First, the magnitude of the voltage (constant current voltage) applied by the power source 64 to the primary transfer rollers 14Y, 14M, 14C is controlled so that a constant current is supplied from the power source 64 to the primary transfer rollers 14Y, 14M, 14C. 66.

  The magnitude of the constant current voltage at this time is detected by a voltmeter (not shown) or the like, and the control unit 60 transfers the voltage derived from the detected constant current voltage information and a preset table and arithmetic expression. The voltages Vt (Y), Vt (M), and Vt (C) are determined. However, the voltage derived from the detected constant current voltage information and one of a preset table or an arithmetic expression may be determined as the transfer voltage Vt.

  The ATVC control of the primary transfer roller 14K is performed in the same manner, and the control unit 60 determines the transfer voltage Vt (K) based on the information, table, and arithmetic expression of the constant current voltage applied to the primary transfer roller 14K.

  Next, the image density correction operation will be described. The image density correction operation is an operation performed to correct the image density to a predetermined density. For example, when the power of the image forming apparatus 2 is input, when a predetermined number of durable sheets has elapsed, the intermediate transfer unit, the developing device, the photosensitive device This is performed when the body drum unit or the toner bottle is replaced.

  FIG. 4 is a flowchart showing the flow before and after the image density correction operation according to the first embodiment.

  As shown in FIG. 4, first, at step 1, the above-described ATVC control is performed for each primary transfer roller 14, and thereby, at step 2, the magnitude of the transfer voltage Vt applied to the primary transfer roller 14 is determined. The

  Subsequently, in step 3, an image density correction operation is performed. In the image density correction operation, the toner image of each color is developed in each image forming unit 3, and then the toner image of each color is applied with the transfer voltage Vt determined by the ATVC control applied to the primary transfer roller 14. Transfer (primary transfer) is performed on the intermediate transfer belt 30. At this time, a plurality of solid images having different densities are formed as the toner images of the respective colors. The density of these solid images is adjusted by controlling the magnitude of the developing bias voltage Vd applied to the developing roller 36.

  The density of the toner image thus transferred to the intermediate transfer belt 30 is detected by the density sensor 61. For each color, the control unit 60 compares the detected density information of the plurality of solid images with a predetermined density set in advance, and is the same as or substantially the same as the predetermined density from the plurality of solid images. Those having the same density are selected, and the development bias voltage Vd when the selected solid image is developed is determined as the development bias voltage Vd at the time of image formation after the image density correction.

  Further, the control unit 60 controls the grid voltage Vg of the charger 8 together with the control of the developing bias voltage Vd, so that the surface potential Vp of the photoconductor 4 becomes a predetermined potential corresponding to the developing bias voltage Vd. Control to be. Thus, it is possible to prevent the developer carrier from adhering to the surface of the photoconductor 4 and the toner from adhering to the non-latent image portion on the surface of the photoconductor 4 to cause fogging.

  Thus, in the image density correction operation in step 3, the developing bias voltage Vd and the grid voltage Vg are determined in the image forming unit 3 for each color.

In the subsequent step 4, the largest value (maximum value) of the grid voltages Vg (Y), Vg (M), and Vg (C) of yellow, magenta, and cyan determined by the image density correction operation, and the grid voltages thereof. It is determined whether or not the absolute value of the difference from the smallest value (minimum value) among Vg (Y), Vg (M), and Vg (C) is greater than a predetermined voltage V _A (eg, 300 V). .

If it is determined in step 4 that the absolute value of the difference between the maximum value and the minimum value of the grid voltages Vg (Y), Vg (M), Vg (C) is greater than the predetermined voltage V _A , the process proceeds to step 5. If it is determined that the voltage is smaller than the predetermined voltage V _{A, the} process ends.

  In step 5, the second ATVC control is performed on the primary transfer rollers 14Y, 14M, and 14C of yellow, magenta, and cyan, whereby the transfer voltage Vt applied to the primary transfer rollers 14Y, 14M, and 14C in step 6 is performed. The sizes of (Y), Vt (M), and Vt (C) are determined again, and the process ends.

  Thus, in the present embodiment, after the image density correction operation, the ATVC control is performed again for the primary transfer rollers 14Y, 14M, and 14C of yellow, magenta, and cyan only when the above condition is satisfied. As a result, the following problems can be avoided while maintaining good print productivity.

  If image formation is performed with the transfer voltage Vt determined by the first ATVC control applied to the primary transfer roller 14 after the image density correction operation in step 3 is completed, the surface potential Vp of the photoreceptor 4 is the image. Since this is different from that before the density correction operation, a current having a magnitude different from that before the image density correction flows through the primary transfer roller 14.

  At this time, since the primary transfer rollers 14Y, 14M, and 14C of yellow, magenta, and cyan are connected to the common power supply 64, the transfer voltage Vt of the same magnitude is applied, but is determined by image density correction. Since the grid potential Vg is different for each color, the surface potentials Vp of the photoconductors 4Y, 4M, and 4C are also different. Therefore, the potential difference between the primary transfer rollers 14Y, 14M, and 14C and the photoconductors 4Y, 4M, and 4C may be different for each color, and the currents flowing through the primary transfer rollers 14Y, 14M, and 14C may be significantly different from each other. Therefore, excessive transfer or insufficient transfer may occur in the primary transfer of one of the yellow, magenta, and cyan toner images, and image quality may be impaired.

In contrast, in the present embodiment, after the image density correction operation, the absolute value of the difference between the maximum value and the minimum value of the grid voltages Vg (Y), Vg (M), and Vg (C) is a predetermined voltage V _A. If the value is larger than that, the ATVC control is performed again, so that image formation is performed with an appropriate transfer voltage Vt applied to the primary transfer rollers 14Y, 14M, and 14C. Therefore, the primary transfer of the toner images of the respective colors is favorably performed in a state where an appropriate current flows through the primary transfer roller 14, so that an image with good image quality can be formed.

  FIG. 5 is a flowchart showing the flow before and after the image density correction operation according to the second embodiment.

  As shown in FIG. 5, as in the first embodiment, first, at step 21, ATVC control is performed for each primary transfer roller 14, whereby the transfer voltage Vt applied to the primary transfer roller 14 at step 22. Is determined.

  Subsequently, in step 23, the same image density correction operation as in the first embodiment is performed, and the developing bias voltage Vd and the grid voltage Vg are determined in the image forming unit 3 for each color.

In the subsequent step 24, the absolute value of the difference between the black grid voltage Vg (K) determined by the image density correction operation and the black grid voltage preVg (K) before the image density correction | Vg (K) −preVg ( It is determined whether or not K) | is greater than a predetermined voltage V _B (for example, 300 V).

If it is determined in step 24 that the absolute value | Vg (K) −preVg (K) | of the difference is smaller than the predetermined voltage V _B , the process proceeds to step 25 and is determined to be larger than the predetermined voltage V _B. If yes, go to Step 28.

  In step 28, the second ATVC control is performed for the black primary transfer roller 14K, whereby the transfer voltage Vt (K) applied to the primary transfer roller 14K is determined again in step 29, and then step 25 is performed. Proceed to

In step 25, grid voltages Vg (Y), Vg (M), Vg (C) determined by the image density correction operation for yellow, magenta, and cyan, and grid voltages preVg (Y), preVg (before image density correction) are determined. M), absolute value of difference from preVg (C) | Vg-preVg | (| Vg (Y) -preVg (Y) |, | Vg (M) -preVg (M) |, | Vg (C) -preVg It is determined whether or not the largest value (maximum value) of (C) |) is larger than a predetermined voltage V _B.

In step 25, the absolute value of the difference | If the maximum value of the process if it is determined to be smaller than the predetermined voltage V _B is completed, it is determined to be greater than the predetermined voltage V _B | Vg-preVg Proceeds to step 26.

  In step 26, the second ATVC control is performed for the primary transfer rollers 14Y, 14M, and 14C of yellow, magenta, and cyan, whereby the transfer voltage Vt that is applied to the primary transfer rollers 14Y, 14M, and 14C in step 27 is performed. The sizes of (Y), Vt (M), and Vt (C) are determined again, and the process ends.

As described above, in the present embodiment, after the image density correction operation, the ATVC control is performed again only when the grid voltage Vg changes by a predetermined magnitude V _B or more before and after the image density correction operation. Accordingly, an image can be formed in a state where an appropriate transfer voltage Vt is applied to each primary transfer roller 14 at the time of image formation after the image density correction operation while maintaining good print productivity. Therefore, the primary transfer of the toner images of the respective colors can be performed satisfactorily with an appropriate current flowing through the primary transfer roller 14, and an image with good image quality can be formed.

  While the present invention has been described with reference to the above-described embodiments, the present invention is not limited to the above-described embodiments.

  For example, in the above-described embodiment, the adjustment factor represented by a variable value corresponding to the surface potential of the photoconductor 4 is the grid voltage of the scorotron charger 8, and the surface potential of the photoconductor 4 is controlled by controlling the grid voltage. However, in the present invention, it is not always necessary to use a scorotron charger, and the surface potential of the photoreceptor 4 may be controlled by controlling an adjustment factor other than the grid voltage.

  Referring to FIG. 6, a specific example of the magnitude of the transfer current It flowing in the primary transfer roller 14 when image formation is performed after image density correction is performed after the processing according to the first embodiment is performed. The case of forming (Example) and the case of forming an image after performing a conventional process (Conventional Example) will be compared.

  As shown in FIG. 8, the processing of the conventional example is completed by performing an image density correction operation in step 103 after the transfer voltage Vt is determined in step 102 by performing ATVC control in step 101. Regardless of the state after the image density correction operation, the second ATVC control is not executed.

  The processing of the conventional example has the same configuration as the processing from the first ATVC control (step 1 in FIG. 4) to the image density correction operation (step 3 in FIG. 4) in the embodiment. Accordingly, the processing until the image density correction operation is completed will be considered together with the embodiment and the conventional example.

  As for the black toner image, since the same processing is performed in the embodiment and the conventional example, only the yellow, magenta, and cyan toner images are considered.

  As shown in FIG. 6A, when the first ATVC control is performed, the grid voltage Vg of the charger 8 is -200V, and the surface potential Vp of the photoconductor 4 is -200V. Assume. Further, it is assumed that the electrical resistance value R of the primary transfer roller 14 and the intermediate transfer belt 30 is the same for all of yellow, magenta, and cyan.

  Assuming that a constant current of 30 μA is supplied from the power source 64 in the first ATVC control, a current of 10 μA flows through each primary transfer roller 14Y, 14M, 14C.

  At this time, assuming that the detected constant current voltage Vi is 1000V, the potential difference ΔV between the primary transfer roller 14 and the photosensitive member 4 is 1200V. From this, it can be seen that the electric resistance value R is 120 MΩ.

  Assuming that the voltage derived from the detection voltage 1000V and a preset table and arithmetic expression is 1000V, the transfer voltage Vt determined by the first ATVC control is 1000V.

  As shown in FIG. 6B, the image density correction operation is performed in a state where the transfer voltage 1000V determined by the first ATVC control is applied to the primary transfer roller 14, and the grid voltage Vg (Y) determined thereby is determined. Is -200V, Vg (M) is -1000V, and Vg (C) is -200V. At this time, the surface potential Vp (Y) of the photoreceptor 4 is -200V, and Vp (M) is -1000V. , Vp (C) is assumed to be −200V.

  In the conventional example, the image forming operation is performed in a state where the grid voltage Vg is applied to the grid electrode 86 of the charger 8. At this time, the potential difference ΔV (Y) between the primary transfer roller 14 and the photosensitive member 4 is 1200V, ΔV (M) is 2000V, ΔV (C) is 1200V, and the electric resistance value R is as described above. Since it is 120 MΩ, the transfer current It (Y) in the conventional example is 10 μA, It (M) is about 17 μA, and It (C) is 10 μA.

  In the embodiment, when the second ATVC control is performed, it is assumed that a constant current of 30 μA is supplied from the power source 64 as in the first ATVC control, as shown in FIG.

  When a voltage of 1000 V was applied to the primary transfer roller 14, the currents flowing through the three primary transfer rollers 14Y, 14M, and 14C were about 37 μA in total (see FIG. 6B). When current is passed through the three primary transfer rollers 14Y, 14M, and 14C, the voltage applied to the primary transfer roller 14 is about 818V. That is, the detection voltage Vi in the second ATVC control is about 818V.

  Assuming that the voltage derived from the detection voltage 818V and a preset table and arithmetic expression is 818V, the transfer voltage Vt determined by the second ATVC control is 818V.

  In the embodiment, the image forming operation is performed in a state where the transfer voltage 818 V determined by the second ATVC control is applied to the primary transfer roller 14 in this way. At this time, the surface potential Vp (Y) of the photoconductor 4 is −200 V, Vp (M) is −1000 V, and Vp (C) is −200 V. Therefore, the potential difference ΔV between the primary transfer roller 14 and the photoconductor 4. (Y) is 1018V, ΔV (M) is 1818V, and ΔV (C) is 1018V. As described above, since the electric resistance value R is 120 MΩ as described above, the transfer current It (Y) of the embodiment is about 8 μA, It (M) is about 15 μA, and It (C) is about 8 μA.

  FIG. 7 shows the magnitude of the transfer current It of the embodiment studied as described above and the conventional example.

  As shown in FIG. 7, in the conventional example, since the magenta transfer current It (M) is remarkably large, it can be confirmed that the primary transfer of the magenta toner image becomes excessively transferred and a transfer memory may be generated. On the other hand, in the embodiment, all the transfer currents It (Y), It (M), It (C) have appropriate sizes, so that the primary transfer is performed well and an image with good image quality is formed. I can confirm that I can do it.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the structure of a primary transfer voltage application means and a development bias application means. It is a figure which shows the structure of a scorotron charger. 6 is a flowchart showing an image density correction operation according to the first embodiment and a flow of processing before and after the operation. It is a flowchart which shows the image density correction | amendment operation | movement which concerns on 2nd Embodiment, and the flow of the process before and behind that. It is a table | surface which shows the examination result of the specific example of the transfer current of an Example and a prior art example. It is a graph showing the examination result shown in FIG. It is a flowchart which shows the flow of a process of the image density correction operation | movement of a prior art example.

Explanation of symbols

2: Image forming apparatus,
4: Electrostatic latent image carrier (photoconductor),
8: Scorotron charger,
14: Primary transfer roller,
18: Developing device
30: Intermediate transfer belt,
36: developer carrier (developing roller),
60: Control means (control unit),
64: primary transfer voltage application means (power supply),
70: Development bias applying means (power supply),
80: discharge electrode,
82: discharge point,
86: Grid electrode,
91: Surface potential control means,
92: Grid voltage application means (power supply),
94: Grid voltage control means (control circuit).

Claims (6)

A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means is an image forming apparatus configured to control the surface potential by adjusting an adjustment factor represented by a variable value corresponding to the surface potential,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, when the absolute value of the difference between the maximum variable value and the minimum variable value among the variable values of the plurality of surface potential control means is larger than a predetermined value, the ATVC control is performed again. An image forming apparatus comprising control means for controlling in such a manner. A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means is an image forming apparatus configured to control the surface potential by adjusting an adjustment factor represented by a variable value corresponding to the surface potential,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, the largest value among the absolute values of the difference between the variable value before the density correction operation and the variable value after the density correction operation in each surface potential control unit is larger than a predetermined size. An image forming apparatus comprising control means for performing control so as to perform the ATVC control again. A scorotron charger for uniformly charging the surface of the electrostatic latent image carrier,
The scorotron charger includes a discharge electrode having a plurality of discharge points facing the surface of the electrostatic latent image carrier, and a grid electrode interposed between the discharge electrode and the surface of the electrostatic latent image carrier. Grid voltage application means for applying a grid voltage to the grid electrode, and grid voltage control means for controlling the grid voltage,
The surface potential control means includes the grid electrode, the grid voltage application means, and the grid voltage control means, and controls the grid voltage as the adjustment factor by the grid voltage control means, thereby controlling the static voltage. 3. The image forming apparatus according to claim 1, wherein the surface potential of the electrostatic latent image carrier is controlled. A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means adjusts an adjustment factor represented by a variable value corresponding to the surface potential, thereby forming an image using an image forming apparatus configured to control the surface potential. A method,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, when the absolute value of the difference between the maximum variable value and the minimum variable value among the variable values of the plurality of surface potential control means is larger than a predetermined value, the ATVC control is performed again. An image forming method. A rotatable endless intermediate transfer belt;
A plurality of electrostatic latent image carriers disposed along the intermediate transfer belt;
A plurality of surface potential control means for controlling the surface potential of the electrostatic latent image carrier;
A plurality of developer carriers that carry a toner of a predetermined color and attach the toner to the surface of the electrostatic latent image carrier to form a toner image of a predetermined color;
Developing bias applying means for applying a developing bias voltage to the developer carrying member;
A plurality of primary transfer rollers arranged to face the electrostatic latent image carrier with the intermediate transfer belt interposed therebetween;
Primary transfer voltage application means for applying a transfer voltage to the plurality of primary transfer rollers,
The surface potential control means adjusts an adjustment factor represented by a variable value corresponding to the surface potential, thereby forming an image using an image forming apparatus configured to control the surface potential. A method,
After performing an ATVC control for determining a voltage derived from a voltage when a constant current voltage is applied to the primary transfer roller and a preset table and / or an arithmetic expression as the transfer voltage, the density of each color image Image density correction operation to correct the image to a predetermined density,
In the image density correction operation, the developing bias voltage applied to the developer carrier of each color is controlled to a magnitude that can correct the image density to a predetermined density, and the surface potential of the electrostatic latent image carrier is Controlling the variable value of the plurality of surface potential control means so as to have a predetermined potential corresponding to the developing bias voltage;
After the image density correction operation, the largest value among the absolute values of the difference between the variable value before the density correction operation and the variable value after the density correction operation in each surface potential control unit is larger than a predetermined size. And performing the ATVC control again. The image forming apparatus includes a scorotron charger for uniformly charging the surface of the electrostatic latent image carrier.
The scorotron charger includes a discharge electrode having a plurality of discharge points facing the surface of the electrostatic latent image carrier, and a grid electrode interposed between the discharge electrode and the surface of the electrostatic latent image carrier. Grid voltage application means for applying a grid voltage to the grid electrode, and grid voltage control means for controlling the grid voltage,
The surface potential control means includes the grid electrode, the grid voltage application means, and the grid voltage control means,
6. The image according to claim 4, wherein a surface potential of the electrostatic latent image carrier is controlled by controlling the grid voltage as the adjustment factor by the grid voltage control means. Forming method.

Images