JP6173280B2 - Image forming apparatus and image forming method - Google Patents

Description

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

  Conventionally, in a touch-down development type image forming apparatus, toner remaining on a solid image at the time when development of the electrostatic latent image on the surface of the image carrier is completed is accumulated at the rear end of the solid image, and the rear end. As the density increases, the density gradually increases, so-called poor development of rear end accumulation occurs. In the touch-down development method, a toner thin layer is formed on the developing sleeve by transferring only the toner from a magnetic roller carrying a two-component developer containing toner and carrier, and an electrostatic latent image is formed. This is a system for developing an electrostatic latent image as a toner image by flying toner from the thin toner layer on the surface of the photoreceptor.

  If this rear end accumulation occurs, there is a problem that the image quality of the printed matter is likely to deteriorate. In response to such a problem, for example, Japanese Patent Laid-Open No. 10-39654 (Patent Document 1) discloses that the toner adhesion amount at the edge (rear end) of a solid patch (solid image) is different from that at the center of the solid patch. An image forming apparatus that suppresses the edge effect (rear end accumulation) of the solid patch by reducing the number of the patches is disclosed. In this image forming apparatus, an edge portion in image data is detected by image processing, and a laser writing area of the detected edge portion is reduced to form a shallow latent image of the edge portion, thereby reducing a toner adhesion amount. Let

Japanese Patent Laid-Open No. 10-39654

  However, the technique described in Patent Document 1 has a problem that it is difficult to improve the accuracy of edge detection because the accuracy of edge detection is determined by the detection limit of the sensor. Further, when the writing area of the detected edge portion is adjusted, there is a problem that the image processing time required for the adjustment becomes long.

  In addition, in the image forming apparatus using the amorphous silicon photoconductor, the rear end accumulation occurs remarkably. However, in order to suppress this rear end accumulation, if the writing area at the rear end portion is thinned out, the trailing edge is immediately before the thinned area. There is a problem in that edge accumulation occurs, and the rear edge accumulation cannot be suppressed as the entire image.

  Accordingly, the present invention has been made to solve the above-described problems, and an object of the present invention is to provide an image forming apparatus and an image forming method capable of suppressing rear end accumulation without adding complicated means. And

  An image forming apparatus according to one aspect of the present invention includes an area ratio determining unit, a half patch forming unit, a control value determining unit, and a control value registering unit. When the calibration is performed, the area ratio determination unit determines an initial area ratio of a half patch obtained by thinning a printing portion from a solid patch having an area ratio of 100% for the calibration. The half patch forming unit changes the control value stepwise within a range within the upper limit of the development bias or laser power control value, thereby converting the half patch of the determined initial area ratio into the amorphous silicon photosensitive drum. And a plurality of intermediate transfer members are formed. The control value determination unit creates a table indicating the relationship between the toner density of the plurality of half patches detected by the density detection sensor and the control value used for forming each half patch, and is set in advance in the table. It is determined whether there is a control value corresponding to the target toner density. When there is a control value corresponding to the target toner density, the control value registration unit registers the existing control value and the initial area ratio of the half patch as control values used for printing a solid image.

  Further, when there is no control value corresponding to the target toner density, the control value used for forming the half patch is determined as the upper limit value of the control value, and the range is equal to or lower than the upper limit value of the area ratio of the half patch. An area ratio changing unit that changes the area ratio stepwise from the initial area ratio in the previous period. The half patch forming unit forms a plurality of half patches that are increased in stages from the initial area ratio at the upper limit value of the control value. The control value determination unit creates a table indicating a relationship between the toner density of the plurality of half patches and the area ratio used for forming each half patch, and the area corresponding to the target toner density in the table Determine whether a rate exists. When the area ratio corresponding to the target toner density exists, the control value registration unit registers the upper limit value of the control value and the existing area ratio as control values used for printing a solid image.

  An image forming apparatus according to one aspect of the present invention includes an area ratio determining unit, an upper / lower value determining unit, a half patch forming unit, a control value determining unit, and a control value registering unit. When the calibration is performed, the area ratio determination unit corresponds to the measured value of the environment of the image forming apparatus detected by a predetermined environment sensor, and the area ratio for the calibration is from a solid patch with a 100% area ratio. Determine the area ratio of the half patch with the printed part thinned out. The upper / lower value determination unit determines an upper limit value and a lower limit value of a control value of the developing bias or laser power used for forming the half patch in accordance with the measured value of the environment. The half patch forming unit changes the control value in a stepwise manner within a range of the upper limit value and the lower limit value of the determined control value, so that the half patch of the determined area ratio is passed through the amorphous silicon photosensitive drum. Thus, a plurality of intermediate transfer members are formed. The control value determination unit creates a table indicating the relationship between the toner density of the plurality of half patches detected by the density detection sensor and the control value used for forming each half patch, and is set in advance in the table. A control value corresponding to the target toner density is determined. The control value registration unit registers the determined area ratio and the determined control value as control values used for printing a solid image.

  Further, when a control value corresponding to the target toner density is determined, the image processing apparatus further includes a gradation correction unit that performs I / O calibration and corrects the toner gradation before the registration of the control value. .

  An image forming method according to an aspect of the present invention includes an area ratio determining step, a half patch forming step, a control value determining step, and a control value registering step. In the area ratio determination step, when calibration is performed, an initial area ratio of a half patch obtained by thinning a printing portion from a solid patch having a 100% area ratio for the calibration is determined. In the half patch forming step, the control value is changed stepwise within a range within the upper limit value of the development bias or the laser power, so that the half patch of the determined initial area ratio is changed to the amorphous silicon photosensitive drum. And a plurality of intermediate transfer members are formed. The control value determination step creates a table indicating the relationship between the toner density of the plurality of half patches detected by the density detection sensor and the control value used for forming each half patch, and is set in advance in the table. It is determined whether there is a control value corresponding to the target toner density. In the control value registration step, when there is a control value corresponding to the target toner density, the existing control value and the initial area ratio of the half patch are registered as control values used for printing a solid image.

  An image forming method according to an aspect of the present invention includes an area ratio determining step, an upper / lower value determining step, a half patch forming step, a control value determining step, and a control value registering step. In the area ratio determination step, when calibration is performed, the area ratio for the calibration is determined from a solid patch having a 100% area ratio corresponding to the measured value of the environment of the image forming apparatus detected by a predetermined environment sensor. Determine the area ratio of the half patch with the printed part thinned out. The upper / lower value determination step determines an upper limit value and a lower limit value of a control value of the developing bias or laser power used for forming the half patch in accordance with the measured value of the environment. The half patch forming step changes the control value stepwise within the range of the upper limit value and the lower limit value of the determined control value, so that the half patch of the determined area ratio is passed through the amorphous silicon photosensitive drum. Thus, a plurality of intermediate transfer members are formed. The control value determination step creates a table indicating the relationship between the toner density of the plurality of half patches detected by the density detection sensor and the control value used for forming each half patch, and is set in advance in the table. A control value corresponding to the target toner density is determined. The control value registration step registers the determined area ratio and the determined control value as control values used for printing a solid image.

  According to the image forming apparatus and the image forming method of the present invention, it is possible to suppress rear end accumulation without adding complicated means.

1 is a schematic configuration diagram of an image forming apparatus according to an exemplary embodiment. FIG. 3 is a detailed view of one of the image forming units FY, FM, FC, and FB of the present embodiment. 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 according to a first embodiment of the present invention. It is a flowchart for showing the execution procedure which concerns on 1st embodiment of this invention. It is the figure (FIG. 6 (A)) which shows the example of generation | occurrence | production of the rear end accumulation of a solid patch, a half patch, and the figure (FIG. 6 (B)) which shows the example of another half patch. FIG. 7A is a graph showing the relationship between the toner density of a plurality of half patches when a developing bias corresponding to the target toner density exists and the developing bias used to form each half patch (FIG. 7A); FIG. 7B is a graph showing the relationship between the toner density of a plurality of half patches when there is no development bias corresponding to the target toner density and the development bias used to form each half patch (FIG. 7B). It is. It is a figure which shows the graph which shows the relationship between the toner density of the some half patch when the developing bias corresponding to target toner density does not exist, and the area ratio used for formation of each half patch. FIG. 6 is a functional block diagram of an image forming apparatus according to a second embodiment of the present invention. It is a flowchart for showing the execution procedure which concerns on 2nd embodiment of this invention. FIG. 11A shows an example of a table according to the second embodiment of the present invention (FIG. 11A), the toner density of a plurality of half patches in the case of normal temperature and humidity, and the developing bias used for forming each half patch. It is a figure (FIG. 11 (B)) which shows the graph which shows the relationship between these. FIG. 12A is a graph showing the relationship between the toner density of a plurality of half patches in the case of high temperature and high humidity and the developing bias used to form each half patch, and the plurality of cases in the case of low temperature and low humidity. FIG. 12 is a diagram (FIG. 12B) showing a graph showing the relationship between the toner density of each half patch and the developing bias used for forming each half patch.

  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. Further, a fixing unit 4 for fixing the transferred toner image on the paper, a paper discharge device 5 for discharging the paper on which the fixing has been completed, and a paper discharge tray 7 for receiving the discharged paper are provided. 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.

  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. Each image forming unit FY, FM, FC, FB has an equivalent 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 application unit) 20, and a cleaning for cleaning the photosensitive drum 10. A blade 35 and a static elimination device 13 are provided.

  The photoconductor drum 10 is an amorphous silicon photoconductor and is in contact with the surface of the intermediate transfer belt B1 at a predetermined primary transfer position 10S. 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 that the surface of the photosensitive drum 10 is statically exposed. 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. 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 on the back surface of the intermediate transfer belt B1 so as to be opposed to the primary transfer position 10S in the moving direction of the intermediate transfer belt B1 at the voltage application position 20S. A voltage having a polarity opposite to that of the toner in the toner image is applied to the primary transfer roller 20 from a power source (not shown). 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.

  The cleaning unit 31 is provided in the image forming unit FY. In addition to the cleaning blade 35, a developer (including toner and carrier) removed from the surface of the photosensitive drum 10 by the cleaning blade 35 is used as the cleaning unit 31. A conveying member 31c for conveying to the outside.

  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, stirring spirals 40c and 40d, and a magnetic roller doctor blade 40e.

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

  The magnetic roller 40b is provided with a magnetic roller doctor blade 40e that rotates in the counter direction of the developing roller 40a and simultaneously peels off the developer and places the developer near the nip. The 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. The developing roller 40a is in contact with the photosensitive drum 10, and responds to an image instructed to be formed by 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).

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

  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 synchronization 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 is 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 (optical sensors) for detecting the patch density of the patch formed on the intermediate transfer belt B1 at the predetermined timing and the background density of the intermediate transfer belt B1 are black image forming units. It is provided at a predetermined position between the FB and the secondary transfer unit 3. Two density detection sensors 605 and 606 are provided in the vicinity of both ends of the intermediate transfer belt B1. 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.

  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.

<First embodiment of the present invention>
Next, the configuration and execution procedure according to the first embodiment of the present invention will be described with reference to FIGS. 4 and 5.

  Usually, in the image forming apparatus 1, the toner density of the solid image (solid image, solid patch) and the toner density of the half image in the image data are appropriate values based on correction of the development bias and the control value of the laser power by calibration. Controlled.

  Here, when the photosensitive drum 10 of the image forming apparatus 1 uses an amorphous silicon photosensitive drum, the following problem occurs at the rear end portion of the solid image. That is, the relative dielectric constant of the amorphous silicon photoconductor drum is about three times higher than that of the organic photoconductor drum (OPC), and the amorphous silicon photoconductor drum has a predetermined development bias (development contrast voltage). The amount of toner that can be held is large. For this reason, the toner density of the solid image formed using the amorphous silicon photosensitive drum is in a non-saturated state at the developing bias that is normally used, and can be further increased by increasing the developing bias.

  Here, at the time of developing a solid image, almost all of the toner formed on the developing roller 40a is transferred to the amorphous silicon photosensitive drum 10, whereby the toner density of the solid image is determined. When developing the rear end portion of the toner, untransferred (not consumed) toner exists on the surface of the developing roller 40a and faces the amorphous silicon photosensitive drum 10.

  Here, as described above, in the amorphous silicon photoconductor drum 10, since the donor density of the solid image is not saturated, the toner existing on the developing roller 40 a is transferred to the amorphous silicon photoconductor drum 10. The toner accumulates only at the trailing edge of the solid image, and the toner density at the trailing edge of the solid image becomes higher than the toner density at the other part of the solid image (front edge, center, etc.) (rear edge) (Accumulation) occurs.

  The occurrence of such rear end accumulation causes deterioration of image quality and wasteful toner consumption when an image including a solid image is printed on paper. Therefore, in the present invention, the following procedure is adopted to suppress the rear end accumulation without adding complicated means.

  First, the calibration execution unit 401 of the image forming apparatus 1 performs calibration at a predetermined timing such as when the power is turned on or when a predetermined number of printed sheets is output (FIG. 5: S101).

  Here, although there is no particular limitation on the calibration, for example, halftone adjustment, layer thickness calibration, light amount calibration, and I / O calibration are applicable. Halftone adjustment is usually performed at the time of shipment or unit maintenance, and is a calibration that corrects the tone characteristics (gamma characteristics) of the image forming unit to approximate a straight line (creates a color table). .

  In the layer thickness calibration, the developing bias of the developing device HY is changed, the toner density of the solid patch drawn on the intermediate transfer belt B1 is detected by the density detection sensors 605 and 606, and the developing bias that becomes the target toner density is detected. decide. Here, the potential difference between the developing roller 40a and the magnetic roller 40b is determined with the determined developing bias, and a toner layer is formed on the developing roller 40a by the determined potential difference. Since the formed toner layer is developed on the photosensitive drum 10, the toner density of the solid patch (solid image) is determined by the developing bias.

  In the light quantity calibration, the laser power of the exposure device 12 is changed to draw a half patch having an area ratio of 25% with respect to the solid patch on the intermediate transfer belt B1, and the toner density of the half patch is detected to detect the target density. The laser power for the toner density is determined. In the I / O calibration, the color table prepared by the halftone adjustment is readjusted in response to the change in the characteristics of the image forming unit.

  Here, the layer thickness calibration will be specifically described. First, the calibration execution unit 401 notifies the area ratio determination unit 402 when performing layer thickness calibration. Upon receiving the notification, the area ratio determining unit 402 determines the initial area ratio of the half patch obtained by thinning out the printed portion from the solid patch having the area ratio (image printing ratio) for the layer thickness calibration of 100% (FIG. 5). : S102).

  Here, there is no limitation in particular in the method which the area ratio determination part 402 determines. For example, the area ratio determination unit 402 refers to the initial area ratio stored in advance in a predetermined memory, and determines this initial area ratio as the area ratio of the half patch. If the area ratio of the half patch is low, the rear end accumulation of the half patch becomes inconspicuous, but it is easy to visually recognize that the half patch is a half patch, and it is difficult to increase the toner density to the target toner density of the solid patch. On the other hand, when the area ratio of the half patch is high, the rear end accumulation of the half patch becomes conspicuous and approaches the solid patch, so that the toner density is easily increased. For this reason, the area ratio of the half patch is in the range of 60% to 90% in consideration of the visibility of the rear end reservoir and the toner density, and the initial area ratio is stored as 75%, for example.

  Here, as shown in FIG. 6A, the half patch means a patch in which the printing area ratio is reduced by thinning out the printing portion with respect to the solid patch having an area ratio of 100%. For example, a plurality of diagonal lines (screen lines) can be printed as a half patch by thinning out a plurality of diagonal lines printed at predetermined intervals from the solid patch. The print pattern of the half patch is not particularly limited. For example, as shown in FIG. 6B, a vertical line (screen line) print pattern parallel to the traveling direction is also perpendicular to the traveling direction. A horizontal line (screen line) printing pattern may be used. A dot printing pattern may also be used. Also, by combining these print patterns, changing the size of the unit print pattern constituting the print pattern in units of dots, or changing the interval between print patterns per unit area in units of dots Also good.

  Now, when the area ratio determination unit 402 completes the determination, the half patch formation unit 403 is notified to that effect, and the half patch formation unit 403 that has received the notification steps the development bias within a range within the upper limit of the development bias. Thus, a plurality of (for example, four) half patches with the determined initial area ratio are formed on the intermediate transfer belt B1 via the amorphous silicon photosensitive drum 10 (FIG. 5: S103).

  Here, the method for forming the half patch by the half patch forming unit 403 is not particularly limited. For example, in the development bias of the control value to be changed, an upper limit value (for example, 350 V) is provided in advance due to an output limit or an adverse effect (fogging etc.) on the printed image. For this reason, when changing the developing bias, the half patch forming unit 403 subtracts a predetermined value (33V) from the upper limit stepwise to obtain a plurality of developing biases (for example, 350V, 317V, 284V). 251V). Then, the half patch forming unit 403 forms half patches at an initial area ratio (75%) in order from the lowest developing bias among the calculated developing biases. The diameter of the amorphous silicon photosensitive drum 10 when the half patch is formed is 30 mm, and the linear velocity is 180 mm / s. The linear velocity of the developing roller 40a corresponding to the amorphous silicon photosensitive drum 10 is set to 1.6 times the linear velocity of the amorphous silicon photosensitive drum 10.

  Here, conventionally, a solid patch is used in the layer thickness calibration to determine a developing bias that becomes a target toner density. In the present invention, the solid patch is not used, but a half patch that may have a toner density equivalent to that of the solid patch is used. For this reason, it is possible to prevent consumption of toner required for forming a solid patch. Further, in the layer thickness calibration, the entire calibration can be simplified by performing the calibration using the half patch from the beginning.

  When the half patch forming unit 403 completes the formation of the half patch, the control value determining unit 404 is notified of this, and the control value determining unit 404 that has received the notification is detected by the density detection sensors 605 and 606. Create a table showing the relationship between the toner density of multiple half patches and the development bias used to form each half patch, and whether there is a development bias corresponding to a preset target toner density in the table Determine whether or not.

  Here, there is no limitation in particular in the method which the control value determination part 404 determines. For example, the control value determination unit 404 communicates with density detection sensors 605 and 606 installed in advance on the intermediate transfer belt B1, and a plurality of density detection sensors 605 and 606 detect according to the rotation of the intermediate transfer belt B1. The toner density of the half patch is acquired (FIG. 5: S104).

  Next, in response to the acquisition of the toner density of the half patch, the control value determination unit 404 acquires the development bias used for forming the half patch from the half patch forming unit 403. When the control value determination unit 404 acquires the toner density of all the half patches, as shown in FIG. 7A, the development bias ΔV (V) used for forming the half patch is set on the horizontal axis. A table (here, the relationship between the toner density D (−) of a plurality of half patches and the development bias ΔV (V) of each half patch with the acquired toner density D (−) of the half patch as the vertical axis. , Graph). Here, the developing bias is, for example, 251 V, 284 V, 317 V, and 350 V, and is within the range of the upper limit value of the developing bias.

  Then, the control value determination unit 404 refers to a target toner density D0 (for example, ID “1.4”) stored in advance in a predetermined memory, and in the graph, the referenced target toner density D0. It is determined whether or not the developing bias V0 (V) corresponding to (-) exists (FIG. 5: S105).

  As a result of the determination, if the development bias exists, for example, as shown in FIG. 7A, it corresponds to the target toner density D0 (−) within the range of the development bias upper limit value Vmax (V) or less. When the developing bias V0 (V) to be present exists (FIG. 5: S105 YES), the control value determination unit 404 notifies the control value registration unit 405 to that effect. Upon receiving the notification, the control value registration unit 405 registers the existing development bias V0 (V) and the initial area ratio (75%) of the half patch as control values used for printing a solid image (FIG. 5: S106).

  Here, there is no limitation in particular in the method which the control value registration part 405 registers. For example, the control value registration unit 405 stores the development bias V0 (V) and the initial area ratio (75%) in a predetermined memory. The control value stored in the memory is used when the printing unit 406 of the image forming apparatus 1 prints a solid image. A half patch print pattern may be registered together with the initial area ratio (75%).

  For example, the layer thickness calibration is completed, and the printing unit 406 of the image forming apparatus 1 prints based on the image data to be printed in response to a printing instruction from the user. At this time, if a solid image exists in the image data, the printing unit 406 uses the control value to print the solid image with the initial area when performing printing corresponding to the solid image. A half image with a rate (75%) is printed with the developing bias V0 (V). As a result, even a half image can be printed with a toner density equivalent to that of a solid image.

  It should be noted that more toner is attached to each print pattern (screen line) forming a half image than in the conventional image formation. If the toner amount is a saturated toner amount that can be held on the amorphous silicon photoconductor drum 10, toner exceeding the saturated toner amount does not adhere even at the rear end portion of the print pattern of the half image. For this reason, it is possible to make the half image free from edge effects and trailing edge accumulation equal to the toner density of the solid image.

  On the other hand, in S105, if the development bias does not exist as shown in FIG. 7B, the development bias is changed as shown in FIG. When the developing bias V0 (V) corresponding to the target toner density D0 (−) does not exist within the upper limit value Vmax (V) (FIG. 5: S105 NO), the following is performed. That is, when the developing bias does not exist (FIG. 5: S105 NO), the control value determination unit 404 notifies the area ratio changing unit 407 to that effect. Upon receiving the notification, the area ratio changing unit 407 determines the developing bias used for forming the half patch as the upper limit value of the developing bias, and then the area ratio is within a range equal to or lower than the upper limit value of the area ratio of the half patch. Is gradually changed from the initial area ratio (75%) in the previous period (FIG. 5: S107).

  Here, there is no limitation in particular in the method which the area ratio change part 407 changes. For example, as shown in FIG. 8, the area ratio changing unit 407 subtracts a predetermined value (3.75%) stepwise from the upper limit value (for example, 90%) of the area ratio, and the initial area A plurality of area ratios (86.25%, 82.50%, 78.75%, 75.00%) greater than or equal to the ratio (75%) are calculated. Then, the area ratio changing unit 407 notifies the half patch forming unit 403 in order from the lowest area ratio among the plurality of (four) calculated area ratios.

  Then, the area ratio changing unit 407 causes the half patch forming unit 403 to form a plurality of half patches that are increased stepwise from the initial area ratio (75%) at the upper limit value of the developing bias (see FIG. 5: S108). This makes it possible to form a half patch whose area ratio increases stepwise with the developing bias fixed at the upper limit, and to set the toner density of the half patch to the target toner density D0 (−) or more. .

  In particular, in the above description, when the toner density of the half patch does not reach the target toner density D0 (−) even though the developing bias is increased to the upper limit value Vmax (V), the cause is, for example, the image It can be assumed that the toner charge amount is increased due to the environmental fluctuation of the forming apparatus 1. In such a state, the amount of toner that can be held on the amorphous silicon photosensitive drum 10 decreases, and the toner amount on the amorphous silicon photosensitive drum 10 is likely to be saturated. Therefore, even if the area ratio of the half patch is increased, each half patch print pattern (screen line) can be saturated with toner. Therefore, it is possible to form a half patch having no edge effect or trailing edge accumulation. Even if the toner charge amount is high and the toner density of the half patch is difficult to increase, by increasing the area ratio, there is no edge effect or trailing edge accumulation, and the half patch has a toner density equivalent to the solid patch toner density Can be formed.

  In S108, when the half patch forming unit 403 forms a plurality of half patches having different area ratios, in S109, the control value determining unit 404 acquires the toner density of the plurality of half patches (FIG. 5: FIG. 5). S109). Then, as shown in FIG. 8, the control value determination unit 404 uses the area ratio S (%) used for forming the half patch as the horizontal axis and sets the acquired toner density D (−) of the half patch as the vertical axis. A table (here, a graph) showing the relationship between the toner density D (−) of the plurality of half patches and the area ratio S (%) used for forming each half patch is created on the axis. Here, the area ratio is, for example, 75.00%, 78.75%, 82.50%, 86.25%, and is within the range of the upper limit (90%) or less.

  Then, the control value determination unit 404 determines whether or not there is an area ratio S0 (%) corresponding to the target toner density D0 (−) in the graph (FIG. 5: S110).

  Here, in S110, if the area ratio S0 (%) exists as a result of the determination, for example, as shown in FIG. 8, the target toner is within a range equal to or less than the upper limit value (90%) of the area ratio. When the area ratio S0 (%) corresponding to the density D0 (−) exists (FIG. 5: S110 YES), the control value determination unit 404 notifies the control value registration unit 405 to that effect. Upon receiving the notification, the control value registration unit 405 uses the upper limit value Vmax (V) of the developing bias and the existing area ratio S0 (%) (for example, 78.75%) for printing a solid image. It registers as a control value (FIG. 5: S106). As a result, it is possible to print using a half image instead of a solid image with the upper limit value Vmax (V) of the developing bias and the area ratio S0 (%).

  On the other hand, in S110, when the area ratio S0 (%) does not exist as a result of the determination (FIG. 5: S110 NO), the control value determination unit 404 notifies the control value registration unit 405 to that effect. Upon receipt of the notification, the control value registration unit 405 selects a half-image control value (for example, the upper limit value Vmax (V) of the developing bias and the upper limit value (90%) of the area ratio) that can be selected at the present time ( FIG. 5: S111), the selected control value is registered as a control value used for printing a solid image (FIG. 5: S106). Thereby, a half image having a toner density as high as possible can be output.

  In the above description, the control value to be changed is set as the development bias corresponding to the layer thickness calibration. However, the laser power of the exposure apparatus 12 that affects the toner density is controlled in accordance with the light amount calibration. It does not matter as a value.

<Second embodiment of the present invention>
Next, the configuration and execution procedure according to the second embodiment of the present invention will be described with reference to FIGS.

  The second embodiment is different from the first embodiment in that the range of the developing bias and the initial area ratio are changed in response to a change in the environment of the image forming apparatus 1. First, the calibration execution unit 401 of the image forming apparatus 1 performs calibration at the above-described predetermined timing (FIG. 10: S201).

  Here, the calibration execution unit 901 notifies the area rate determination unit 902 when performing the above-described layer thickness calibration. In response to the notification, the area ratio determination unit 902 corresponds to the measured values (temperature, humidity) of the environment of the image forming apparatus 1 detected by the predetermined environment sensor 903, and is a half patch obtained by thinning the print portion from the solid patch. Determine the area ratio.

  Here, there is no limitation in particular in the method which the area ratio determination part 902 determines. For example, the area ratio determination unit 902 communicates with an environmental sensor 903 provided in advance inside the image forming apparatus 1 and acquires measurement values (temperature, humidity) of the environment detected by the environmental sensor 903 (FIG. 10: S202).

  Next, the area ratio determining unit 902 refers to a table stored in advance in a predetermined memory. In the table 1100, as shown in FIG. 11A, the measured value item 1101 of the environment, the area ratio 1102 in the measured value item 1101 of the environment, and the development bias in the measured value item 1101 of the environment. Are stored in association with each other. For example, “normal temperature, normal humidity”, “high temperature, high humidity”, and “low temperature, low humidity” are stored in the measurement value item 1101 of the environment. “Normal humidity” means, for example, a humidity range of 45% to 55%. “High temperature” means a range where the temperature exceeds 25 degrees, “High humidity” means a range where the humidity exceeds 55%, and “Low temperature” means a range where the temperature is less than 21 degrees. “Low humidity” means a range where the humidity is less than 45%. In the case of “high temperature and humidity” or “normal temperature and high humidity”, it is “high temperature and high humidity”, and in the case of “low temperature and normal humidity” or “normal temperature and low humidity”, “low temperature and low humidity”. Is done.

  Here, in a high-temperature and high-humidity environment, the toner charge amount decreases, so even if the developing bias is low, the toner concentration increases, but the developability to the rear end portion also increases, and rear end accumulation occurs. easy. On the other hand, in a low-temperature and low-humidity environment, the toner charge amount increases, so the toner developability deteriorates.If the development bias is not increased, the desired toner concentration cannot be obtained, but the developability at the rear end is also low. Therefore, the occurrence of rear end accumulation is reduced.

  Therefore, in order to optimally adjust the degree of toner density of the image and the degree of occurrence of the trailing edge accumulation, it is necessary to change the area ratio of the half patch due to environmental fluctuations. For example, in a high-temperature and high-humidity environment, by reducing the area ratio of the half patch compared to the area ratio of a normal temperature and normal humidity environment, it is possible to suppress the occurrence of rear end accumulation while maintaining the toner density of the image. I can do it. For example, the area ratio “high temperature, high humidity” is associated with “65%”, which is lower than the area ratio “75%” of “normal temperature, normal humidity”. In a low-temperature and low-humidity environment, by increasing the area ratio of the half patch compared with the area ratio of a normal temperature and normal humidity environment, the toner density of the image can be increased while suppressing the occurrence of rear end accumulation. . For example, the area ratio “low temperature and low humidity” is associated with “85%”, which is higher than the area ratio “75%” of “normal temperature and normal humidity”.

  Now, the area ratio determining unit 902 identifies an environment measurement value item 1101 corresponding to the environment measurement value of the environment sensor 903 in the referenced table 1100 and corresponds to the identified environment measurement value item 1101. The area ratio 1102 to be acquired is acquired (FIG. 10: S203). Thereby, the area ratio of the half patch corresponding to the measured value of the environment is determined.

  Next, when the area ratio determination unit 902 completes the determination, the upper / lower value determination unit 904 notifies the upper / lower value determination unit 904 to that effect, and the upper / lower value determination unit 904 receives the notification in response to the measured value of the environment. The upper limit value and the lower limit value of the developing bias used for forming the patch are determined (FIG. 10: S204).

  Here, there is no limitation in particular in the method which the up-and-down value determination part 904 determines. For example, the upper / lower value determination unit 904 refers to the table 1100. Here, it is necessary to change the upper limit value and the lower limit value of the developing bias in accordance with the environmental variation. For example, since the area ratio of the half patch is low in a high-temperature and high-humidity environment, the upper and lower limits of the development bias are set lower than the upper and lower limits of the development bias in a normal temperature and normal humidity environment. Thereby, in a high temperature and high humidity environment, it is possible to prevent the toner density of the image from becoming excessively high and thus causing fogging. For example, the upper and lower limits of the “high temperature, high humidity” development bias are “200 V” and “300 V”, which are lower than the upper limits “250 V” and “350 V” of the “normal temperature, normal humidity” development bias. Is associated. On the other hand, since the area ratio of the half patch is high in a low temperature and low humidity environment, the upper and lower limits of the development bias are made higher than the upper and lower limits of the development bias in a normal temperature and normal humidity environment. This can prevent the toner density of the image from becoming too low in a low temperature and low humidity environment. For example, the upper and lower limits of the “low temperature, low humidity” development bias are “300 V” and “400 V”, which are higher than the upper limits “250 V” and “350 V” of the “normal temperature, normal humidity” development bias. Are associated.

  Now, the upper / lower value determination unit 904 identifies an environment measurement value item 1101 corresponding to the environment measurement value of the environment sensor 903 in the referenced table 1100, and corresponds to the identified environment measurement value item 1101. An upper limit value and a lower limit value 1103 of the developing bias to be acquired are acquired (FIG. 10: S204). Thus, the upper and lower limits of the developing bias corresponding to the measured value of the environment are determined, and the toner density of the half patch is changed by changing the area ratio of the half patch and the variable range of the developing bias corresponding to the environment. And the degree of occurrence of rear end accumulation can be controlled to be constant.

  When the upper / lower value determination unit 904 completes the determination, the half patch forming unit 905 notifies the fact, and the half patch forming unit 905 that has received the notification notifies the upper limit value and lower limit value of the determined development bias. By changing the developing bias stepwise within the range, a plurality of (for example, four) half patches having the determined area ratio are formed on the intermediate transfer belt B1 via the amorphous silicon photosensitive drum 10 (see FIG. 10: S205). The half patch formation method is the same as in the first embodiment.

  Next, when the half patch forming unit 905 completes the formation of the half patch, the control value determining unit 906 is notified to that effect, and the control value determining unit 906 that has received the notification is detected by the density detection sensors 605 and 606. A table showing the relationship between the toner density of a plurality of half patches and the development bias used to form each half patch is created, and a development bias corresponding to a preset target toner density is determined in the table. (FIG. 10: S206). The table forming method is the same as in the first embodiment.

  Here, the control value determination unit 906 acquires toner densities of a plurality of half patches detected by the density detection sensors 605 and 606 according to the rotation of the intermediate transfer belt B1. Then, the control value determination unit 906 acquires the developing bias used for forming the half patch from the half patch forming unit 905 in response to the acquisition of the toner density of the half patch. Then, as shown in FIG. 11B, the control value determination unit 906 sets the developing bias ΔV (V) used for forming the half patch as the horizontal axis, and acquires the toner density D (− of the acquired half patch. ) On the vertical axis, a table (graph) showing the relationship between the toner density D (−) of a plurality of half patches and the development bias ΔV (V) of each half patch is created. Here, in the case of normal temperature and humidity, the area ratio is 75%, the lower limit value Vmin of the developing bias is 250V, and the upper limit value Vmax is 350V. In the case of high temperature and high humidity, as shown in FIG. 12A, the area ratio is 65%, the lower limit value Vmin of the developing bias is 200V, and the upper limit value Vmax is 300V. In the case of low temperature and low humidity, as shown in FIG. 12B, the area ratio is 85%, the lower limit value Vmin of the developing bias is 300V, and the upper limit value Vmax is 400V. As shown in FIGS. 11B, 12A, and 12B, in the half-patch print pattern, the diagonal lines (screen lines) constituting the print pattern are changed to a multi-line screen. Therefore, the rear end accumulation can be reduced as compared with the halftone screen. This is because each screen line is independent and a rear end accumulation (edge effect) occurs in each screen line until the saturation region on the amorphous silicon photosensitive drum 10 is reached. This is because the toner is loaded. The amount of toner is the same at the rear end portion and the other portions of the screen line. In addition, since the toner density of each screen line tends to increase, the toner density of the half patch is brought close to the toner density of the solid patch by appropriately increasing the thinned area.

  As described above, in the graph created for each environment, the control value determination unit 906 determines the development bias V0 (V) corresponding to the target toner density D0 (−). Thus, since the area ratio and the upper and lower ranges of the developing bias are determined according to the environment, the developing bias V0 (V) corresponding to the target toner density D0 (−) can be determined reliably.

  Then, when the determination is completed, the control value determination unit 906 notifies the control value registration unit 907 to that effect. Upon receiving the notification, the control value registration unit 907 registers the determined area ratio and the determined development bias V0 (V) as control values used for printing a solid image (FIG. 10: S207). This makes it possible to print using a half image instead of a solid image with the area ratio and the development bias V0 (V).

  After the control value determination unit 906 completes the determination, the tone correction unit 908 notifies the tone correction unit 908 to that effect, and the tone correction unit 908 that has received the notification performs I / O calibration and performs toner calibration. The gradation (level of color shading) is corrected (FIG. 10: S207). Thereafter, the gradation correction unit 908 may notify the control value registration unit 907 to that effect, and the control value registration unit 907 that has received the notification may register the control value (FIG. 10: S207). The printing unit 909 of the image forming apparatus 1 uses the registered control value when printing a solid image, as described above.

  In the embodiment of the present invention, a solid image of a predetermined color (magenta) has been described. However, the present invention may be applied to a solid image for each color. Here, in a black solid image, it is difficult to visually recognize the trailing edge accumulation, and since there is little color mixing with other colors in the solid image, for example, it is applied only to a solid image of color (magenta, cyan, yellow). You may comprise so that it may carry out.

  In the embodiment of the present invention, a solid image in normal image formation has been described. However, whether or not to use a half patch to replace a solid image may be determined according to the type of image formation. For example, when there is a high image quality mode and a normal image quality mode with an image quality inferior to the image quality of the high image quality mode in image formation, if the high image quality mode is set, the printing unit 406 (909) Then, control is performed so as to form a half patch having a predetermined area ratio instead of the solid image. When the normal image quality mode is set, the printing unit 406 (909) may be configured to control to form the solid image with a normal developing bias.

  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 made 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 copiers, printers, and the like, and can prevent rear end accumulation without adding complicated means. This is effective as an image forming apparatus and an image forming method.

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 401 Calibration execution part 402 Area ratio determination part 403 Half patch formation part 404 Control value determination part 405 Control value registration part 406 Printing part 407 Area ratio change part 901 Calibration execution part 902 Area ratio determination part 903 Environmental sensor 904 Upper / lower value determination unit 905 Half patch formation unit 906 Control value determination unit 907 Control value registration unit 908 Tone correction unit 909 Printing unit

Claims (6)

An area ratio determining unit that determines an initial area ratio of a half patch obtained by thinning a printing portion from a solid patch having an area ratio of 100% for calibration when the calibration is performed;
By changing the control value stepwise within a range within the upper limit of the developing bias or laser power control value, the half patch of the determined initial area ratio is transferred to the intermediate transfer member via the amorphous silicon photosensitive drum. A plurality of half-patch forming portions to be formed,
Create a table showing the relationship between the toner density of multiple half patches detected by the density detection sensor and the control value used to form each half patch, and correspond to the preset target toner density in the table A control value determination unit that determines whether there is a control value to be
A control value registration unit for registering the existing control value and the initial area ratio of the half patch as a control value used for printing a solid image when a control value corresponding to the target toner density exists;
An image forming apparatus comprising: When there is no control value corresponding to the target toner density, the control value used for forming the half patch is determined as the upper limit value of the control value, and is within a range equal to or less than the upper limit value of the area ratio of the half patch. It further comprises an area ratio changing unit that changes the area ratio in stages from the initial area ratio in the previous period,
The half patch forming unit is configured to form a plurality of half patches that are increased stepwise from the initial area ratio at the upper limit value of the control value,
The control value determination unit creates a table indicating a relationship between the toner density of the plurality of half patches and the area ratio used for forming each half patch, and the area corresponding to the target toner density in the table Determine if the rate exists,
The control value registration unit registers an upper limit value of the control value and the existing area ratio as control values used for printing a solid image when an area ratio corresponding to the target toner density exists. The image forming apparatus according to 1. When calibration is performed, corresponding to the measured value of the environment of the image forming apparatus detected by a predetermined environmental sensor, the half of the print patch is thinned out from a solid patch with an area ratio of 100% for the calibration An area ratio determining unit for determining the area ratio of the patch;
Corresponding to the measured value of the environment, an upper and lower value determination unit for determining an upper limit value and a lower limit value of a development bias or laser power control value used for forming the half patch,
By gradually changing the control value in the range of the upper limit value and the lower limit value of the determined control value, the half patch having the determined area ratio is transferred to the intermediate transfer member via the amorphous silicon photosensitive drum. A plurality of half patch forming portions to be formed;
Create a table showing the relationship between the toner density of multiple half patches detected by the density detection sensor and the control value used to form each half patch, and correspond to the preset target toner density in the table A control value determination unit for determining a control value to be performed;
A control value registration unit for registering the determined area ratio and the determined control value as a control value used for printing a solid image;
An image forming apparatus comprising: The apparatus further includes a gradation correction unit that, when a control value corresponding to the target toner density is determined, performs I / O calibration and corrects the toner gradation before the registration of the control value. The image forming apparatus according to 3. An area ratio determining step for determining an initial area ratio of a half patch obtained by thinning out a printing portion from a solid patch having an area ratio of 100% for calibration when the calibration is performed;
By changing the control value stepwise within a range within the upper limit of the developing bias or laser power control value, the half patch of the determined initial area ratio is transferred to the intermediate transfer member via the amorphous silicon photosensitive drum. A half patch forming step to form a plurality of
Create a table showing the relationship between the toner density of multiple half patches detected by the density detection sensor and the control value used to form each half patch, and correspond to the preset target toner density in the table A control value determination step for determining whether or not there is a control value to be performed;
A control value registration step of registering the existing control value and the initial area ratio of the half patch as a control value used for printing a solid image when a control value corresponding to the target toner density exists;
An image forming method comprising: When calibration is performed, corresponding to the measured value of the environment of the image forming apparatus detected by a predetermined environmental sensor, the half of the print patch is thinned out from a solid patch with an area ratio of 100% for the calibration An area ratio determining step for determining an area ratio of the patch;
In accordance with the measured value of the environment, an upper and lower value determining step for determining an upper limit value and a lower limit value of a development bias or laser power control value used for forming the half patch;
By gradually changing the control value in the range of the upper limit value and the lower limit value of the determined control value, the half patch having the determined area ratio is transferred to the intermediate transfer member via the amorphous silicon photosensitive drum. A half patch forming step of forming a plurality of; and
Create a table showing the relationship between the toner density of multiple half patches detected by the density detection sensor and the control value used to form each half patch, and correspond to the preset target toner density in the table A control value determination step for determining a control value to be performed;
A control value registration step of registering the determined area ratio and the determined control value as a control value used for printing a solid image;
An image forming method comprising: