JP5965374B2 - Image forming apparatus and image forming method - Google Patents

Description

  The present invention relates to an image forming apparatus and an image forming method, and more particularly, to an image forming apparatus and an image forming method capable of appropriately executing development bias adjustment even when patches are formed between sheets.

  In an image forming apparatus for touchdown development, a predetermined patch is drawn between sheets of printing paper being printed, and the development bias for printing is adjusted by feeding back the density to the development bias. In this case, first, a patch (solid image) is formed between sheets with a developing bias during printing, the density is read by an optical sensor, and the target density is obtained from the relationship between the density and the developing bias during printing. The development bias is calculated by reverse calculation. Thereby, the image quality can be maintained.

  Here, when the color of the patch is black, there is no reflected light component in the black component. Therefore, when the density of the black patch is detected by the optical sensor, the resolution is lowered. In particular, when the density of the black patch is high, the resolution is significantly deteriorated.

  Therefore, in order to solve this problem, the dots are thinned out to draw a black patch (half patch) with a half density between the lowest density and the highest density, or a development bias (lower) than the development bias during printing. A method is employed in which a black patch is drawn with a development bias), and the density of the patch is lowered to increase the resolution.

  Japanese Patent Laid-Open No. 2008-292614 (Patent Document 1) discloses that the actual toner amount obtained by acquiring the density of the inter-sheet patch image formed during continuous printing does not match the reference toner amount. There is disclosed an image density correction method for reconstructing a relational characteristic in which an actual toner amount is associated with each variation of the development bias and resetting the development bias for realizing the reference toner. As a result, when it is determined that the actual toner amount obtained by acquiring the density of the inter-sheet patch image formed during continuous printing and the reference toner amount do not match, the variation of the developing bias The relationship characteristic in which the actual toner amount is associated with each other is reconstructed in consideration of the fact that the actual toner amount and the reference toner amount match, and based on the reconstructed relationship characteristic and the reference toner amount As a result of resetting the development bias for realizing the reference toner amount, even if a large color fluctuation occurs during continuous printing, the color is maintained while maintaining the printing work efficiency at a high level. It is said that high quality images can be obtained while suppressing the taste variation.

JP 2008-292614 A

  Here, by using the technique described in Patent Document 1, the stability of the image density during continuous printing is improved. However, when the actual density cannot be read accurately as in the case of the black density, the above-described case is used. It is necessary to accurately read the patch density by drawing a half patch or drawing a patch with a low development bias.

  However, since the development characteristics of the half patch and the development characteristics of the normal patch are generally different, there is a problem that the adjustment of the development bias using the density of the half patch is not accurate. In addition, a patch formed with a low development bias has a problem that the developing electric field may be unstable because the development electric field is weak, the density of the patch varies, and the development bias cannot be accurately adjusted. . In particular, when a patch is drawn with a low developing bias, the residual toner on the developing roller immediately before becomes a large noise, and the density of the patch may vary greatly.

  Accordingly, the present invention has been made to solve the above problem, and provides an image forming apparatus and an image forming method capable of appropriately executing development bias adjustment even when patches are formed between sheets. The purpose is to provide.

  In order to solve the above-described problems and achieve the object, an image forming apparatus according to the present invention is an image forming apparatus that performs image formation by a touch-down development method, and employs the following configuration.

  That is, the present invention forms a plurality of patches whose development biases are changed in stages, executes a development bias calibration for measuring the density of each patch, and determines a development bias at the time of printing. When adjusting the development bias at the time of printing, two development biases that are changed stepwise by the calibration of the development bias are applied, and a specific patch is applied with a higher development bias of the two development biases. The density of the specific patch is measured in between, and the development bias required for forming the specific patch and the density of the specific patch are adjusted to adjust the development bias at the time of printing. And a developing bias adjusting means.

  Further, the present invention forms a plurality of patches in which the development bias is changed in stages, and a predetermined development bias is set to 0 V in the calibration of the development bias for measuring the density of each patch. A calibration execution means for determining a development bias at the time of printing by adding a bias condition for applying a specific development bias required for forming the development bias, and at the time of adjusting the development bias at the time of printing, Among the bias conditions, the development bias is set to 0 V, and immediately after that, the specific development bias is applied, a specific patch is formed between the papers with the specific development bias, the density of the specific patch is measured, Using the specific development bias required for forming the specific patch and the density of the specific patch, the development bias at the time of printing is set. Characterized in that it comprises a developing bias adjustment means for settling.

  In addition, the present invention can be provided as an image forming method of an image forming apparatus that performs image formation by a touch-down development method.

  That is, the present invention forms a plurality of patches in which the development bias is changed in stages, executes development bias calibration for measuring the density of each patch, and determines the development bias at the time of printing; When adjusting the development bias at the time of printing, two development biases changed stepwise by the development bias calibration are applied, and a specific patch is formed between the two papers with a higher development bias of the two development biases. Measuring the density of the specific patch, and adjusting the development bias at the time of printing using the development bias required for forming the specific patch and the density of the specific patch. It is characterized by providing.

  Further, the present invention forms a plurality of patches in which the development bias is changed in stages, and a predetermined development bias is set to 0 V in the calibration of the development bias for measuring the density of each patch. A bias condition for applying a specific development bias required for forming the development bias, determining the development bias at the time of printing, and adjusting the development bias at the time of printing, Among them, the development bias is set to 0 V, and immediately after that, the specific development bias is applied, a specific patch is formed between the sheets with the specific development bias, the density of the specific patch is measured, and the specific development bias is measured. Adjusting the development bias at the time of printing using the specific development bias required for forming the patch and the density of the specific patch; Characterized in that it comprises. Even with such a configuration, the same effects as described above can be obtained.

  Further, the present invention can be provided as a program for causing a computer to circulate individually via a telecommunication line or the like. In this case, the central processing unit (CPU) realizes the control operation in cooperation with each circuit other than the CPU according to the program of the present invention. Each means realized by using the program and the CPU can also be configured by using dedicated hardware. The program can also be distributed in a state where it is recorded on a computer-readable recording medium such as a CD-ROM.

  According to the image forming apparatus and the image forming method of the present invention, it is possible to appropriately adjust the developing bias even when patches are formed between sheets.

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a detailed view of one image forming unit. 2 is a schematic configuration diagram relating to control of the image forming apparatus 1 in the present embodiment. FIG. 1 is a functional block diagram of an image forming apparatus of the present invention. It is a flowchart for showing the execution procedure of this invention. FIG. 6 is a diagram showing a bias table according to the present invention (FIG. 6A) and a diagram showing a development bias calibration patch according to the present invention (FIG. 6B). FIG. 7 is a diagram showing an approximate straight line for developing bias calibration according to the present invention (FIG. 7A), and a diagram showing bias conditions for forming an inter-sheet patch according to the present invention (FIG. 7B). FIG. 8 is a diagram showing an inter-sheet patch according to the present invention (FIG. 8A) and a diagram showing a new approximate line in consideration of the density of the inter-sheet patch according to the present invention (FIG. 8B). A diagram (FIG. 9A) showing four types of bias conditions showing development bias and unit time to be applied when four patches are continuously formed, and four patches formed under the four types of bias conditions. It is a graph (FIG. 9 (B)) which shows a density | concentration. FIG. 10A shows a bias condition for developing bias calibration with a developing bias of 0 V (FIG. 10A), and FIG. 10B shows a bias condition for adjusting the developing bias during printing (FIG. 10B). is there.

  Hereinafter, an image forming apparatus according to an embodiment of the present invention will be described with reference to the accompanying drawings for understanding of the present invention. In addition, the following embodiment is an example which actualized this invention, Comprising: The thing of the character which limits the technical scope of this invention is not. Moreover, the alphabet S added before the number in a flowchart means a step.

<Image forming apparatus>
The image forming apparatus 1 according to the present invention will be described below. FIG. 1 is a schematic configuration diagram of an image forming apparatus 1 of the present embodiment.

  The image forming apparatus 1 transfers a toner image formed by the tandem-type image forming unit A1 that forms a toner image based on image data, a paper storage unit 2 that stores paper, and the image forming unit A1 onto the paper. A next transfer unit 3 is provided. The image forming apparatus further includes a fixing unit 4 that fixes the transferred toner image on the paper, a paper discharge device 5 that discharges the fixed paper, and a paper discharge tray 7 that receives the discharged paper. Further, the image forming apparatus 1 includes a paper transport unit 6 that transports paper from the paper storage unit 2 to the paper discharge device 5.

  The image forming unit A1 includes an intermediate transfer belt B1 (intermediate transfer member), a cleaning unit B2 for cleaning the intermediate transfer belt B1, and each color of yellow (Y), magenta (M), cyan (C), and black (B). Are provided with image forming units FY, FM, FC, and FB, respectively.

  The intermediate transfer belt B1 is a belt-like member having an endless shape, that is, a loop shape, which is wider than a sheet having the maximum length in the direction perpendicular to the usable sheet conveying direction and having conductivity. Circulated around.

  The image forming units FY, FM, FC, and FB are arranged in this order along the intermediate transfer belt B1 in the moving direction of the intermediate transfer belt B1, downstream from the cleaning unit B2 and upstream from the secondary transfer unit 3. . Note that the order of arrangement of the image forming units FY, FM, FC, and FB is not limited to this, but this arrangement is preferable in consideration of the influence of the color mixture on the completed image. The image forming units FY, FM, FC, and FB are arranged so that the intervals between the image forming units are equal.

  Next, an image forming operation of the image forming apparatus 1 will be described. FIG. 2 is a detailed view of one of the image forming units FY, FM, FC, and FB. The image forming units FY, FM, FC, and FB have almost the same configuration.

  The image forming unit FY includes a photosensitive drum (image carrier) 10, a charger 11, an LED exposure device 12, a yellow developing device HY, a primary transfer roller (voltage applying unit) 20, and a cleaning blade 35 for the photosensitive drum 10. , A static elimination device 13 and a carrier removal roller (carrier removal member) 30.

  The other image forming units FM, FC, and FB include developing devices HM, HC, and HB corresponding to the respective colors. Of the image forming units, the image forming unit FB located on the most downstream side in the moving direction of the intermediate transfer belt B1 is not provided with the carrier removing roller 30 because the image forming unit is not located downstream thereof. Other configurations are the same.

  The photoreceptor drum 10 only needs to be able to carry a toner image including toner charged on its surface (charged positively in this embodiment).

  In the present embodiment, the photosensitive drum 10 is a substantially cylindrical member that is arranged to be rotatable about a rotation axis that is perpendicular to the moving direction of the intermediate transfer belt B1 and parallel to the surface direction of the intermediate transfer belt B1. The photosensitive drum 10 is in contact with the surface of the intermediate transfer belt B1 at a predetermined primary transfer position 10S. The photosensitive drum 10 can rotate so that the moving direction at the primary transfer position 10S is the same as the moving direction of the intermediate transfer belt B1, that is, in FIG.

  The cleaning blade 35, the charge eliminating device 13, the charger 11, the exposure device 12, and the yellow developing device HY are arranged around the photosensitive drum 10 in this order as seen from the primary transfer position along the rotation direction described above. The

  The charger 11 can uniformly charge the surface of the photosensitive drum 10. The exposure device 12 has a light source such as an LED, and irradiates the charged surface of the photosensitive drum 10 with light corresponding to the image data in accordance with the image data from the above-described host device, so An electrostatic latent image can be formed.

  The yellow developing device HY holds a developer containing yellow toner and a carrier so as to face the electrostatic latent image, thereby applying toner to the electrostatic latent image, and converting the electrostatic latent image into a toner image. Can be developed. This toner image is primarily transferred by the primary transfer roller 20 to the intermediate transfer belt B1. Details of the primary transfer roller 20 will be described later.

  The cleaning blade 35 is a blade-like member disposed so as to be in contact with the photosensitive drum 10. The cleaning blade 35 removes the developer remaining on the surface of the photosensitive drum 10 after the primary transfer.

  The neutralization device 13 includes a light source. After the developer is removed by the cleaning blade 35, the surface of the photosensitive drum 10 is neutralized by light from the light source to prepare for the next image formation.

  The primary transfer roller 20 is disposed so as to contact the back surface of the intermediate transfer belt B1 at a voltage application position 20S downstream from the primary transfer position 10S in the moving direction of the intermediate transfer belt B1. A voltage having a polarity opposite to that of the toner in the toner image (minus in this embodiment) is applied to the primary transfer roller 20 from a power source (not shown). That is, the primary transfer roller 20 can apply a voltage having a polarity opposite to that of the toner to the intermediate transfer belt B1 at the voltage application position 20S. Since the intermediate transfer belt B1 has conductivity, the applied voltage attracts toner to the surface side of the intermediate transfer belt B1 at the voltage application position 20S and the periphery thereof.

  Therefore, in the present embodiment, the primary transfer position 10S is disposed within a range in which toner is attracted to the intermediate transfer belt B1 side by the applied voltage. As a result, the toner moves from the photosensitive drum 10 to the surface of the intermediate transfer belt B1, and primary transfer is performed.

  As long as primary transfer is possible in this way, the specific configuration of the primary transfer roller 20 is not particularly limited, and the specific configuration can be changed as appropriate. In the present embodiment, the primary transfer roller 20 can rotate in the opposite direction to the photosensitive drum 10 around a rotation axis parallel to the rotation axis of the photosensitive drum 10, that is, the movement direction at the charge application position 20S is intermediate. It is a substantially cylindrical member that can be rotated in the same direction as the transfer belt B1.

  In this embodiment, the carrier removal roller 30 is a substantially cylindrical member that can rotate in the same direction as the photosensitive drum 10 around a rotational axis parallel to the rotational axis of the photosensitive drum 10. The carrier is not limited, and it is sufficient that the carrier can be removed from the surface of the intermediate transfer belt B1 downstream of the charge application position 20S and upstream of the secondary transfer position in the moving direction of the intermediate transfer belt B1. Specifically, the carrier removing roller 30 only needs to be able to move the carrier on the surface of the intermediate transfer belt B1 to its own surface by contacting the surface of the intermediate transfer belt B1.

  During primary transfer, a small amount of carrier may be transferred from the photosensitive drum 10 to the intermediate transfer belt B1 together with the toner. This carrier transfer may interfere with primary transfer in the downstream image forming unit and cause image defects such as image blurring and blurring. Providing the carrier removal roller 30 can prevent such an image defect.

  In the present embodiment, the carrier removal roller 30 is disposed so as to contact the surface of the intermediate transfer belt B1 downstream of the charge application position 20S in the moving direction of the intermediate transfer belt B1. The carrier removal roller 30 is incorporated in the cleaning unit 31 together with the cleaning blade 35 described above. The cleaning unit 31 is provided in the image forming unit FY. In addition to the cleaning blade 35 and the carrier removing roller 30, the cleaning unit 31 is in contact with the surface of the carrier removing roller 30 to remove the carrier attached to the surface of the carrier removing roller 30. The carrier removal blade 31b, the carrier removed from the carrier removal roller 30, and the developer (including toner and carrier) removed from the surface of the photosensitive drum 10 by the cleaning blade 35 are conveyed to the outside of the cleaning unit 31. A transport member 31c is provided. The image forming unit FY may further include a separation unit that separates the carrier and the toner in order to reuse the carrier and the toner conveyed by the conveyance member 31c.

  Next, the configuration of the developing device HY will be described. The configurations of the developing devices HY, HM, HC, and HB for the respective colors are the same.

  The developing device HY includes a developing container 40, a developing roller 40a, a magnetic roller (mag roller) 40b, a drawing roller 40c, stirring spirals 40d and 40e, a cleaning blade 45, and a magnetic roller doctor blade 40g.

  The developing container 40 stores therein a developer composed of yellow toner (toner particles) and a carrier. The stirring spirals 40d and 40e are provided so as to be entirely immersed in the developer in the developing container 40, and stir the developer. The toner is uniformly dispersed in the carrier by the rotation of the stirring spirals 40d and 40e.

  The drawing-up roller 40c is arranged so that a part of the drawing-up roller 40c is immersed in the developer in the developing container, and the developer is pumped up by adhering to the surface. A magnetic roller 40b is arranged in contact with the pumping roller 40c, and a developer is supplied from the pumping roller 40c. The magnetic roller 40b rotates in the counter direction of the developing roller 40a, and in the vicinity of the nip, a magnetic roller doctor blade 40g is provided that simultaneously peels off the developer and places the developer. The magnetic roller doctor blade 40g regulates the developer layer thickness on the surface of the magnetic roller 40b to a predetermined amount. A developing roller 40a (also referred to as a developing device) is disposed so as to be in contact with the magnetic roller 40b, and a developer is applied to the surface thereof from the magnetic roller 40b. Since the developer layer thickness of the magnetic roller 40b is regulated to a predetermined value, the developer layer thickness formed on the surface of the developing roller 40a is also kept at the predetermined value. The developing roller 40a is in contact with the photosensitive drum 10, and responds to an image instructed to be formed from the host apparatus by the potential difference between the electrostatic latent image potential on the surface of the photosensitive drum 10 and the developing bias value applied to the developing roller 40a. A toner image is formed on the surface of the photosensitive drum 10 (development operation).

  The image forming apparatus of the present invention is characterized in that image density correction of a toner image is performed by adjusting a developing bias value (voltage value, simply referred to as a bias value) applied to the developing roller 40a.

  Further, the developer on the surface of the magnetic roller 40b after the developing operation on the photosensitive drum 10 is removed by the magnetic roller doctor blade 40g, flows down along the surface of the magnetic roller doctor blade 40g, and passes through a flow path (not shown). The developer stored in the developer container 40 is mixed.

  Further, a toner concentration sensor 40h is arranged in the developing container, and detects the toner concentration of the developer in the developing container 40. When it is detected that the toner concentration is lower than a predetermined value, toner (a developer having a toner concentration higher than the predetermined value) is supplied from a toner cartridge (not shown) to the developing container 40, and the toner concentration is higher than the predetermined value. The carrier is supplied to the toner container 40 from a carrier cartridge (not shown). In this specification, the term “toner density” is used for both the meaning of the toner density in the developing container and the meaning of the image density within a range where the meaning is not obscured.

  Under such a configuration, the image forming apparatus 1 that has received an instruction for image formation from a host device such as a personal computer (PC) or the like forms toner images of each color corresponding to the received image data in the image forming units FY, FM. , FC, and FB. The toner image formed in each image forming unit is transferred to the intermediate transfer belt B1, and is superimposed on the intermediate transfer belt B1 to form a color toner image.

  In synchronism with the formation of the color toner image, the paper stored in the paper storage unit 2 is taken out from the paper storage unit 2 one by one by a paper feeding device (not shown) and transported on the paper transport unit 6. Then, the sheet is fed to the secondary transfer unit 3 in synchronization with the primary transfer to the intermediate transfer belt B1, and the color toner image on the intermediate transfer belt B1 is secondarily transferred to the sheet by the secondary transfer unit 3. The sheet on which the color toner image has been transferred is further conveyed to the fixing unit 4 where the color toner image is fixed on the sheet by heat and pressure. Further, the paper is discharged by a paper discharge device 5 to a paper discharge tray section 7 provided on the outer periphery of the image forming apparatus 1. The toner remaining on the intermediate transfer belt B1 after the secondary transfer is removed from the intermediate transfer belt B1 by the cleaning unit B2.

  Further, two density detection sensors 605 and 606 for detecting the patch density of the patch formed on the intermediate transfer belt B1 and the background density of the intermediate transfer belt B1 at a predetermined timing are provided with the black image forming unit FB and the secondary. It is provided at a predetermined position between the transfer unit 3. The black image forming unit FB is located on the most downstream side with respect to the rotation direction of the intermediate transfer belt B1 as compared with the other image forming units FY, FM, and FC. Therefore, the density detection sensors 605 and 606 detect the patch density of any one of the plurality of image forming units FY, FM, FC, and FB even if the patch is formed on the intermediate transfer belt B1. It is configured to be able to.

  Further, the density detection sensors 605 and 606 are provided in advance at positions corresponding to the positions of the intermediate transfer belt B1 where the patches are formed. In the embodiment of the present invention, two density detection sensors 605 and 606 are provided near both ends of the intermediate transfer belt B1. Provided. The density detection sensors 605 and 606 may be in any form as long as they can detect the patch density or background density of the patch for each color. For example, based on the provisions of the ISO 5 series, patches or intermediate transfer Reflection type density detection sensors 605 and 606 that irradiate the background on the belt B1 with light from the light source, detect the reflected light intensity with the light receiving sensor, and convert the light intensity information into the density.

  The density detection sensors 605 and 606 are also used for detecting the toner density of a solid band image to be described later.

  FIG. 3 is a schematic configuration diagram relating to control of the image forming apparatus 1 in the present embodiment.

  The image forming apparatus 1 includes a CPU (Central Processing Unit) 301, a RAM (Random Access Memory) 302, a ROM (Read Only Memory) 303, a HDD (Hard Disk Drive) 304, and a driver 305 corresponding to each driving unit in the printing. They are connected via an internal bus 306. The CPU 301 uses, for example, the RAM 302 as a work area, executes a program stored in the ROM 303, the HDD 304, or the like, and exchanges data and commands with the driver 305 based on the execution result, as shown in FIG. The operation of each driving unit is controlled. Also, each means (shown in FIG. 4) described later other than the drive unit operates as each means when the CPU 301 executes a program.

<Embodiment of the present invention>
Next, the configuration and execution procedure according to the embodiment of the present invention will be described with reference to FIGS. 4 and 5. FIG. 4 is a functional block diagram of the image forming apparatus of the present invention. FIG. 5 is a flowchart for showing the execution procedure of the present invention.

  First, when the user turns on the power to the image forming apparatus 1, the image forming apparatus 1 is activated, and the control unit 401 of the image forming apparatus 1 determines whether or not to execute development bias calibration. (FIG. 5: S101).

  Any method may be used as the method for determining whether or not the control means 401 executes development bias calibration. For example, the control unit 401 determines whether or not the current time point is a specific time point. Specifically, the control unit 401 determines that the current time point is a predetermined time point when the image forming apparatus 1 is turned on. At the time when the number of sheets is printed (when the number of printed sheets exceeds a predetermined threshold) or when the predetermined amount of toner is consumed by the dot count of the printed image (when the toner consumption exceeds a predetermined threshold) A method of determining whether or not there is employed.

  Here, since the image forming apparatus 1 has been started up earlier, the control unit 401 determines to calibrate the developing bias (FIG. 5: S101 YES), and notifies the calibration execution unit 402 to that effect. Upon receipt of the notification, the calibration execution unit 402 forms a plurality of patches with development biases changed in stages, executes development bias calibration for measuring the density of each patch, and sets the development bias at the time of printing. decide.

  The calibration execution unit 402 may execute any development bias calibration to determine the development bias at the time of printing. However, for example, a predetermined color (black) is taken as an example. It is done as follows.

  First, the calibration execution unit 402 forms an electrostatic latent image of a predetermined number (for example, four) of patches on the surface of the photosensitive drum 10 based on patch data stored in advance in a predetermined memory. Here, the positions of the patches are the positions of both ends of the photosensitive drum 10 corresponding to the positions of the two density detection sensors 605 and 606 of the intermediate transfer belt B1.

  The calibration execution unit 402 refers to a bias table (bias condition) stored in advance in a predetermined memory. Here, in the bias table 600, as shown in FIG. 6A, a predetermined number (for example, four) of developing biases V1 (V) to V4 (for example) corresponding to the electrostatic latent image of the patch. V) and a unit time T1 (sec) in which one patch can be formed with each developing bias V (V) are stored in association with each other. The four developing biases V1 (V) to V4 (V) are applied to the developing roller 40a for each unit time T1 (sec). For example, the first developing bias V1 (V) = 40V, the second developing bias V2 ( V) = 80V, third development bias V3 (V) = 120V, last development bias V4 (V) = 160V, and so on, from the first development bias V1 (V) to the last development bias V4 (V) Therefore, the absolute value of the developing bias is stored to be high. Further, the developing bias applied in the calibration of the developing bias is set low so that the image density is halved compared to the developing bias (for example, 300 V) at the time of printing. The time for applying the four developing biases V1 (V) to V4 (V) is 4 * T1 (sec) as a whole.

  The calibration execution unit 402 with reference to the bias table 600 develops in order from the first development bias V1 (V) to the last development bias V4 (V) in each unit time T1 (sec) according to the bias table 600. The electrostatic latent images of the patches on both ends of the surface of the photosensitive drum 10 are made to correspond to the developing roller 40a in accordance with the timing of applying the developing biases V1 (V) to V4 (V). Four patches whose density increases stepwise are formed on both ends of the photosensitive drum 10 respectively.

  Then, as shown in FIG. 6B, the calibration execution unit 402 transfers the four patches 601 and 602 to the intermediate transfer belt B1 (FIG. 5: S102), and is installed on the intermediate transfer belt B1. The two density detection sensors 605 and 606 are activated to measure the densities D1 (−) to D4 (−) of the four patches 601 and 602, respectively (FIG. 5: S103).

  Here, the density of the four patches 601 formed on one end side of the intermediate transfer belt B1 is measured by one density detection sensor 605, and the four patches 602 formed on the other end side of the intermediate transfer belt B1 are The density is measured by the other density detection sensor 606, and the density of each patch 601 and 602 is averaged. For example, the first patch density D1 (−) = 0.52 (−), the second patch density D2 (−) = 0.64 (−), the third patch density D3 (−) = 0. 76 (−) and the density D4 (−) = 0.88 (−) of the last patch.

  The length L1 in the rotational direction of the four patches 601 and 602 formed on the intermediate transfer belt B1 is a value obtained by multiplying 4 * T1 (sec) by the rotational speed R (m / sec) of the intermediate transfer belt B1. It becomes.

  When the densities of the patches 601 and 602 are measured, the calibration execution unit 402 determines the developing biases V1 (V) to V4 (V) required for forming the patches 601 and 602 and the densities of the patches 601 and 602. Based on D1 (−) to D4 (−) and the target image density De (−) as a target, the development bias Ve (V) at the time of printing is determined.

  Specifically, the calibration execution unit 402 is based on the development biases V1 (V) to V4 (V) and the densities D1 (−) to D4 (−) of the patches 601 and 602 based on FIG. As shown in (A), an approximate straight line 700 (approximate straight line passing through zero at the origin) of the patch density D (−) with respect to the developing bias V (V) is generated, and a predetermined line is generated on the generated approximate straight line 700. The target image density De (-) stored in advance in the memory is substituted, and the development bias Ve (V) at the time of printing corresponding to the target image density De (-) is calculated (determined) (FIG. 5: S104). . Here, the target image density De (−) is a high density such as the density of the black solid image, for example, 1.3 (−), and the corresponding developing bias Ve (V) at the time of printing. = 300V. As a result, the development bias calibration is completed, and an image can be formed.

  Now, when a user inputs an instruction for image formation (printing) of predetermined image data to the image forming apparatus 1 connected to the upper apparatus using a predetermined upper apparatus (PC) (FIG. 5: S105 YES). Then, the control unit 401 of the image forming apparatus 1 performs printing using the determined development bias Ve (V) at the time of printing (FIG. 5: S106).

  Specifically, the control unit 401 forms an electrostatic latent image corresponding to the image data on the surface of the photosensitive drum 10, and applies a developing bias Ve (V) during printing to the developing roller 40a. Here, the toner is supplied from the magnetic roller 40b to the developing roller 40a by the developing bias Ve (V) at the time of printing. The control unit 401 supplies toner from the developing roller 40a to the electrostatic latent image on the photosensitive drum 10 to form a toner image, which is transferred to the intermediate transfer belt B1. Further, the control means 401 conveys the sheet from the sheet storage unit 2 corresponding to the transferred toner image, performs the secondary transfer by the secondary transfer unit 3, and then fixes it by the fixing unit 4 and discharges it. The paper is discharged to the paper tray unit 7. By such an operation, one printed matter corresponding to one image data is discharged. When the input image data includes a plurality of sheets, the above-described operation is repeated, so that a plurality of printed materials are discharged.

  Here, when the control unit 401 discharges one printed matter, it determines whether or not to adjust the developing bias Ve (V) at the time of printing required for printing execution (FIG. 5: S107).

  Here, any method may be used as the method for determining whether or not the control means 401 adjusts the developing bias Ve (V) during printing. For example, the control unit 401 determines whether or not the current time is a specific time. Specifically, the control unit 401 counts the number of printed sheets in advance, and the counted printing is performed. When the number of sheets exceeds a predetermined threshold (for example, 1000 sheets), the dot of the print image is counted in advance, and any of the times when the toner consumption corresponding to the counted dot exceeds the predetermined threshold A method of determining whether or not is used.

  If the current time is not a specific time (FIG. 5: S107 NO), the process returns to S105, and the control unit 401 is ready to receive a print instruction from the user (FIG. 5: S105).

  As described above, when the image data related to the print instruction is a plurality of sheets (for example, 100 sheets), when the control unit 401 determines that the current time point is not a specific time point (FIG. 5: S107 NO), Printing is continued (FIG. 5: S105 YES → S106).

  On the other hand, for example, when the counted number of printed sheets exceeds the threshold (1000 sheets) (FIG. 5: S107 YES), the control unit 401 needs to adjust the developing bias Ve (V) during printing. The determination is made and the development bias adjusting means 403 is notified of this. Upon receiving the notification, the development bias adjusting unit 403 applies two development biases Va (V) and Vb (V) that are changed stepwise by the calibration of the development bias, and the higher development bias of the two development biases. A specific patch (referred to as an inter-sheet patch) is formed with Vb (V), and the density Db (−) of the inter-paper patch is measured to determine the developing bias Vb ( The development bias Ve (V) at the time of printing is adjusted using V) and the density Db (−) of the patch between the papers.

  The developing bias adjusting unit 403 may adjust the developing bias Ve (V) at the time of printing, but may be any method, for example.

  First, the developing bias adjusting means 403 is formed on both ends of the surface of the photosensitive drum 10 so that an inter-sheet patch can be formed between sheets of the intermediate transfer belt B1 corresponding to the interval between the toner images of the image data. An electrostatic latent image of each sheet-to-paper patch is formed. Here, the inter-sheet patch is a patch equivalent to the patch used in the calibration of the developing bias.

  Further, the developing bias adjusting means 403 refers to the bias table 600 and specifies two developing biases Va (V) and Vb (V) that are changed in stages by developing bias calibration.

  Here, the two development biases Va (V) and Vb (V) are changed stepwise from, for example, a predetermined number of development biases V1 (V) to V4 (V) stored in the bias table 600. The two developing biases V1 (V) to V4 (V) are used. For example, two development biases Va (V) and Vb (V) are the first development bias V1 (V) and the second development bias V2 (V), the second development bias V2 (V) and the second development bias V2 (V). Two of the three development biases V3 (V), two of the third development bias V3 (V) and the last development bias V4 (V) are used. For example, the density is detected by the two density detection sensors 605 and 606. A pair of development biases that can be reliably measured and that has a high density patch is preferable. The second development bias V2 (V) and the third development bias V3 (V), the third development bias One of V3 (V) and the last development bias V4 (V) is specified. Here, the two development biases Va (V) and Vb (V) are two, that is, the second development bias V2 (V) and the third development bias V3 (V).

  The developing bias adjusting means 403 specifies the second developing bias V2 (V) and the third developing bias V3 (V) as the two developing biases Va (V) and Vb (V). As shown in FIG. 7B, the second developing bias V2 (V) (low developing bias) and the third developing bias V3 are applied from the developing bias Ve applied to the developing roller 40a during printing. (V) (high developing bias) is sequentially applied to the developing roller 40a every unit time T1 (sec). The developing bias adjusting means 403 applies the electrostatic latent image of the inter-sheet patch on both ends of the surface of the photosensitive drum 10 to the developing roller 40a at the timing when the low developing bias V2 (V) is applied to the developing roller 40a. In accordance with the timing at which a high developing bias V3 (V) is applied to the developing roller 40a, the electrostatic latent images of the inter-sheet patches on both ends of the surface of the photosensitive drum 10 are made to correspond to the developing roller 40a and are high. An inter-sheet patch is formed on each end of the photosensitive drum 10 with a developing bias V3 (V).

  Then, as shown in FIG. 8A, the developing bias adjusting unit 403 transfers the inter-sheet patches 800 and 801 formed on the photosensitive drum 10 to the inter-sheet S of the intermediate transfer belt B1 (see FIG. 8A). 5: S108), the two density detection sensors 605, 606 are activated to measure the densities of the inter-sheet patches 800, 801 transferred to both ends (FIG. 5: S109).

  Here, the density of one of the inter-paper patches 800 formed on one end side of the intermediate transfer belt B1 is measured by one density detection sensor 605, and the other inter-paper patch formed on the other end side of the intermediate transfer belt B1. The density of the patch 801 is measured by the other density detection sensor 606, and the densities of the inter-sheet patches 800 and 801 are averaged. Here, the density D3 ′ (−) of the inter-sheet patches 800 and 801 having a high developing bias V3 (V) is set to 0.80 (−), for example.

  Further, the sheet-to-sheet patches 800 and 801 formed on the intermediate transfer belt B1 and the regions 802 and 803 to which the low developing bias V2 (V) is applied immediately before the sheet-to-sheet patches 800 and 801 are formed. The length L2 in the rotational direction is a value obtained by multiplying 2 * T1 (sec) by the rotational speed R (m / sec) of the intermediate transfer belt B1.

  When the density D3` (-) of the inter-sheet patch 800, 801 is measured, the developing bias adjusting unit 403 determines that the high developing bias V3 (V) required for forming the inter-sheet patch 800, 801 and the paper. The development bias Ve (V) at the time of printing is adjusted (corrected) based on the density D3` (-) of the intermediate patch patches 800 and 801, the result of calibration of the development bias, and the target image density De (-). To do.

  Specifically, the developing bias adjusting unit 403 includes the high developing bias V3 (V), the density D3` (-) of the inter-sheet patch patches 800 and 801, and the developing bias V1 (developing bias calibration). V) to V4 (V) and the densities D1 (−) to D4 (−) of the patches 601 and 602, as shown in FIG. 8B, the approximation generated during calibration of the developing bias. The straight line 700 is deleted, and a new approximate straight line 804 is regenerated. Then, the developing bias adjusting unit 403 substitutes the target image density De (−) for the regenerated approximate straight line 804, and develops the developing bias Ve` at the time of printing corresponding to the target image density De (−). (V) is newly calculated backward (determined) (FIG. 5: S110).

  Here, as shown in FIG. 8B, it is understood that the development bias Ve` (V) at the time of new printing is lower than the development bias Ve (V) at the time of old printing. Thereby, even during printing, the development bias Ve` (V) at the time of printing can be appropriately adjusted, and the image quality can be maintained.

  In particular, in the present invention, the low developing bias V2 (V) is applied immediately before forming the inter-sheet patch with the high developing bias V3 (V). Accordingly, it is possible to form the inter-sheet patches 800 and 801 that are hardly affected by the residual toner on the surface of the developing roller 40a, and it is possible to adjust the developing bias Ve` (V) with high accuracy.

  That is, in the touch-down development method, the image density in printing is determined by the amount of toner applied to the developing roller 40a, and this toner amount is determined by the developing roller 40a and the magnetic roller 40b that supplies toner to the developing roller 40a. And the development bias V (V). In the touchdown development method, a toner thin layer is formed on the developing sleeve by transferring only toner from a magnetic roller carrying a two-component developer containing toner and carrier, and an electrostatic latent image is formed. In other words, the electrostatic latent image is developed as a toner image by flying toner from the thin toner layer onto the surface of the photoreceptor.

  Here, in the image forming apparatus 1, the predetermined cleaning blade is not installed on the developing roller 40a, and the predetermined magnetic roller doctor blade 40g peels off the toner only in the nip region between the developing roller 40a and the magnetic roller 40b. And toner are loaded almost simultaneously.

  Therefore, when toner that has not been sufficiently removed by the magnetic roller doctor blade 40g remains on the magnetic roller 40b, the amount of toner supplied from the magnetic roller 40b varies due to the residual toner. The developing roller 40a and the magnetic roller 40b are counters.

  As described above, although the amount of toner supplied to the developing roller 40a is determined by the developing bias V (V), when the residual toner exists in the developing roller 40a via the magnetic roller 40b, It varies greatly depending on the charge amount.

  Here, when the toner does not remain on the developing roller 40a, the toner amount corresponding to the normal developing bias V (V) is supplied to the developing roller 40a, but when the toner remains on the developing roller 40a, Since the residual toner has already been applied to the predetermined developing bias V (V), it has a predetermined charging amount by frictional charging or charge injection, and the charging amount on the surface of the developing bias V (V). Rises. Then, the amount of toner supplied next from the magnetic roller 40b to the developing roller 40a is reduced by the amount of toner corresponding to the charged amount of the remaining toner, and the toner amount of the developing roller 40a is reduced as a whole. .

  Therefore, due to the residual toner on the developing roller 40a, an accurate amount of toner is not supplied to the developing roller 40a, leading to a decrease in image density and image quality.

  In the present invention, a low developing bias V2 (V) is applied immediately before forming the inter-sheet patches 800 and 801 used for adjusting the developing bias Ve` (V) during printing. As a result, the charge amount of the residual toner on the developing roller 40a described above can be reduced, and the toner remaining on the developing roller 40a can be sufficiently peeled off, and development can be performed when the inter-paper patches 800 and 801 are formed. It is possible to stabilize the toner amount of the roller 40a. Therefore, the density of the inter-sheet patches 800 and 801 is also appropriate, and the development bias Ve` (V) at the time of printing can be accurately adjusted.

  In particular, since the developing bias Vb (V) required for forming the inter-sheet patches 800 and 801 is the developing bias V3 (V) used in the calibration of the developing bias, a substantially incompatible approximate line 804 may be generated. In addition, the adjustment (correction) of the developing bias Ve` (V) at the time of printing can be performed with high accuracy. Further, since it is not necessary to newly apply a developing bias necessary for forming the inter-sheet patch in the developing bias calibration, it is not necessary to prolong the time required for the developing bias calibration.

  Here, the influence of the developing bias immediately before the patch is formed will be specifically described. FIG. 9A shows four types of bias conditions indicating the development bias and the unit time to be applied when four patches are formed continuously. FIG. 9B is a graph showing the density of four patches formed under four types of bias conditions.

  Here, as shown in FIG. 9A, in the first bias condition A, the development bias V5 (V) = 320 V close to the development bias at the time of printing is applied to the formation of the three patches, and the last In this case, the development bias V3 (V) = 120 V required for forming the inter-sheet patch is applied. The second bias condition B is a condition in which the development bias V3 (V) = 120 V required for forming the inter-sheet patch is applied to the formation of the four patches. The third bias condition C applies the second development bias V2 (V) (corresponding to a low development bias) = 80 V in the calibration of the development bias for the formation of three patches, and the last patch For the formation, it is assumed that a developing bias V3 (V) = 120 V required for forming the inter-sheet patch is applied. In the fourth bias condition D, the first development bias V1 (V) = 40 V in the development bias calibration is applied to the formation of the three patches, and the inter-sheet patch is applied to the last patch formation. A condition for applying a developing bias V3 (V) = 120 V required for formation is used.

  When the density of the patch corresponding to the four types of bias conditions A to D is confirmed, as shown in FIG. 9B, in the second bias condition B, the last patch density is compared with the previous three patch densities. In the third bias condition C, the density fluctuation of the last patch was the next smallest, and in the fourth bias condition D, the density fluctuation of the last patch was little. On the other hand, in the first bias condition A, that is, the bias condition in the case where the adjustment of the development bias is normally performed with the inter-sheet patch, the density variation of the last patch was remarkable.

  Even if the development bias V3 (V) required for forming the last patch is the same, the higher the previous development bias V (V), the lower the density of the last patch. This is because, as the developing bias required for forming the third patch is higher, the charge amount of the residual toner on the developing roller 40a increases, so even if the developing bias V3 (V) required for forming the last patch is the same, the developing roller This is because the amount of toner supplied to 40a decreases, and the amount of toner transferred to the photosensitive drum 10 decreases.

  Therefore, in the present invention, immediately before the formation of the inter-paper patches 800 and 801, a developing bias V2 (V) lower than the developing bias V3 (V) required for forming the inter-paper patches 800 and 801 is applied in advance. Thus, the charge amount of the residual toner on the developing roller 40a can be reduced, and the toner remaining on the developing roller 40a can be sufficiently peeled off, and the above-described fluctuation in the density of the patch can be suppressed. It is.

  Here, the inter-paper patches 800 and 801 are formed in order to surely reduce the charge amount of the residual toner of the developing roller 40a described above, in other words, to sufficiently remove the toner remaining on the developing roller 40a. The immediately preceding development bias V (V) may be set to 0V. By setting the immediately preceding developing bias V (V) to 0V, the charge amount of the residual toner on the developing roller 40a can be brought close to zero, and the residual toner can be surely peeled off.

  A bias table (bias condition) when the developing bias V (V) immediately before the formation of the inter-sheet patches 800 and 801 is set to 0V has, for example, the following configuration. FIG. 10A shows bias conditions for developing bias calibration with the developing bias set to 0V. FIG. 10B shows bias conditions for adjusting the development bias during printing.

  First, when the calibration execution unit 402 executes calibration of the development bias, as shown in FIG. 10A, the fourth development bias V4 (V) from the first development bias V1 (V) to the last development bias V1 (V). The development bias V1 (V) to V4 (V) is applied to the development roller 40a so that the absolute value of the development bias increases stepwise until the development bias is applied immediately after the last development bias V4 (V) is applied. Is set to 0 V, and immediately after 0 V, the developing bias V3 (V) required for forming the inter-sheet patch is applied. At this time, the calibration execution unit 402 forms four patches corresponding to the first developing bias V1 (V) to the fourth developing bias V4 (V), and is necessary for forming the inter-sheet patch. One patch is formed corresponding to the developing bias V3 (V). The calibration execution unit 402 measures the density of each formed patch and determines the development bias Ve (V) at the time of printing. In this case, the time 6 * T1 (sec) required for calibration of the developing bias is increased by the time 2 * T1 (sec) when the developing bias is 0 V and the developing bias V3 (V) required for forming the inter-sheet patch. .

  Next, as shown in FIG. 10B, the developing bias adjusting unit 403 is required to form the inter-paper patch, 0V among the developing bias for the developing bias calibration, when forming the inter-paper patch. A developing bias V3 (V) is applied as Va (V) and Vb (V), and an inter-sheet patch is formed between sheets with the developing bias V3 (V) required for forming the inter-sheet patch. In this way, by setting the developing bias V (V) immediately before forming the inter-sheet patch to 0 V, it becomes possible to bring the residual toner charge amount of the developing roller 40a close to zero, and the residual toner is peeled off. Can be ensured. As a result, the toner amount of the developing roller 40a can be stabilized during the formation of the inter-sheet patch, and the developing bias Ve` (V) during printing can be accurately adjusted.

  As described above, according to the present invention, the calibration execution means 402 for executing the development bias calibration to determine the development bias at the time of printing, and the adjustment of the development bias Ve (V) at the time of the printing, Two development biases Va (V) and Vb (V), which are changed stepwise by the development bias calibration, are applied, and the patch between papers is placed between the papers with the higher development bias Vb (V) of the two development biases. And the density Db (−) of the inter-paper patch is measured, and the development bias Vb (V) required for forming the inter-paper patch and the density Db (−) of the inter-paper patch are used. And a developing bias adjusting means 403 for adjusting the developing bias Ve (V) at the time of printing.

  In the present invention, the bias condition for applying the specific developing bias V3 (V) required for forming the inter-sheet patch is added to the developing bias calibration immediately after setting the predetermined developing bias to 0 V, and printing is performed. The calibration execution means 402 for determining the development bias Ve (V) at the time of development, and the adjustment of the development bias Ve (V) at the time of printing out of the bias conditions for calibration of the development bias to 0 V Immediately thereafter, the specific development bias V3 (V) is applied, a paper gap patch is formed between the papers with the specific development bias V3 (V), the density of the paper gap patch is measured, A development bar for adjusting the development bias Ve (V) at the time of printing using the development bias V3 (V) required for forming the paper gap patch and the density of the paper gap patch. Characterized in that it comprises a astigmatism adjustment means 403.

  This makes it possible to appropriately adjust the developing bias even if patches are formed between sheets.

  In the present invention, the developing bias of a predetermined color (for example, black) has been described, but the same applies to developing biases of other colors of yellow (Y), magenta (M), and cyan (C).

  In the embodiment of the present invention, the image forming apparatus 1 is configured to include each unit. However, a program that realizes each unit may be stored in a storage medium, and the storage medium may be provided. . In this configuration, the image forming apparatus 1 is caused to read the program, and the image forming apparatus 1 realizes the respective units. In that case, the program itself read from the recording medium exhibits the effects of the present invention. Furthermore, it is possible to provide a method for storing the steps executed by each means in a hard disk.

  As described above, the image forming apparatus and the image forming method according to the present invention are useful not only for complex machines but also for copying machines, printers, and the like. It is effective as an image forming apparatus and an image forming method that can be executed.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 401 Control means 402 Calibration execution means 403 Development bias adjustment means

Claims (6)

An image forming apparatus that performs image formation by a touch-down development method,
A calibration execution unit that forms a plurality of patches in which the development bias is changed in stages, executes calibration of the development bias to measure the density of each patch, and determines the development bias at the time of printing;
When adjusting the development bias at the time of printing, two development biases changed stepwise by the calibration of the development bias are applied, and a specific patch is placed between the two development biases with a higher development bias between the papers. A development bias that is formed, measures the density of the specific patch, and adjusts the development bias at the time of printing using the development bias required for forming the specific patch and the density of the specific patch An image forming apparatus comprising: an adjusting unit. An image forming apparatus that performs image formation by a touch-down development method,
A plurality of patches whose development biases are changed in stages are formed, and a predetermined development bias is set to 0 V in the development bias calibration for measuring the density of each patch. A calibration execution means for determining a development bias at the time of printing by adding a bias condition for applying the development bias;
When adjusting the development bias at the time of printing, among the bias conditions for calibration of the development bias, the development bias is set to 0 V, and immediately after that, the specific development bias is applied. A patch is formed between the papers, the density of the specific patch is measured, and the specific development bias required for forming the specific patch and the density of the specific patch are used to perform the printing. An image forming apparatus comprising: a developing bias adjusting unit that adjusts the developing bias. An image forming method of an image forming apparatus that executes image formation by a touch-down development method,
Forming a plurality of patches with development biases changed in stages, performing development bias calibration to measure the density of each patch, and determining development bias at the time of printing;
When adjusting the development bias at the time of printing, two development biases changed stepwise by the calibration of the development bias are applied, and a specific patch is placed between the two development biases with a higher development bias between the papers. Forming, measuring the density of the specific patch, and using the development bias required to form the specific patch and the density of the specific patch to adjust the development bias at the time of printing; An image forming method comprising: An image forming method of an image forming apparatus that executes image formation by a touch-down development method,
A plurality of patches whose development biases are changed in stages are formed, and a predetermined development bias is set to 0 V in the development bias calibration for measuring the density of each patch. Adding a bias condition for applying a development bias to determine a development bias at the time of printing;
When adjusting the development bias at the time of printing, among the bias conditions for calibration of the development bias, the development bias is set to 0 V, and immediately after that, the specific development bias is applied. A patch is formed between the sheets, the density of the specific patch is measured, and the specific development bias required for forming the specific patch and the density of the specific patch are used to perform the printing. An image forming method comprising: adjusting a developing bias.   A program for causing a computer to execute the image forming method according to claim 3.   A computer-readable storage medium storing the program according to claim 5.

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