JP2004191810A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To correctly measure the density of the reference image and to precisely control the conditions for forming output images. <P>SOLUTION: Forming the first reference images Pa1, Pa2 on the intermediate transfer belt 22 and measuring the density of those reference images PA1, Pa2 by means of a density sensor 30, it is decided whether or not to form the reference image again, depending on the measured results. When it is required to form the reference images again, the second reference images Pa3, Pa4 are formed to be different from the former reference images. When the reference images are not formed again, the conditions for outputting the images are controlled, depending on the measured results of the first reference images Pa1, Pa2. When the reference images are formed again, the conditions are controlled for outputting the images, depending on the measured results of the second reference images Pa3, Pa4. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an image forming apparatus such as a copying machine or a printer, and more particularly, measures a physical quantity related to the image quality of a reference image (mainly, a quantity related to density, color, gradation, etc.) and forms an output image forming condition based on the measurement result. For controlling an image forming apparatus.
[0002]
[Prior art]
At present, the image quality of an output image by an image forming apparatus has been remarkably improved, and as a result, a user's request for image quality fluctuation has become more severe. For example, a color difference of 3 or less, which is close to the limit of human color discrimination ability, has been required.
[0003]
In particular, in an electrophotographic image forming apparatus or the like that uses an electrostatic process, the image quality generally varies greatly. This is mainly because the image quality reproducibility of the electrostatic process is affected by environmental conditions such as temperature and humidity, aging, and the like.
[0004]
Particularly problematic as image quality variations are color reproduction and gradation in the case of a color image, and density and fog in the case of a monochrome image.
[0005]
As an apparatus for solving such image quality fluctuation, for example, a low-density reference image and a high-density reference image are formed as reference images used for controlling image forming conditions, and the densities of these are detected. 2. Description of the Related Art There is known an image forming apparatus which obtains a deviation from a reference value and controls image forming conditions based on a relationship stored in advance (a relationship between each deviation and a development potential Vcont and a cleaning potential Vcln required for correction). (For example, see Patent Document 1). In such an apparatus, an image is actually formed in the form of a reference image, measured by a sensor, and a difference from the reference value is feedback-controlled, so that highly accurate and highly accurate control can be performed.
[0006]
As described above, a method of detecting a reproduction state of image quality using a reference image (hereinafter, this method is abbreviated as an ADC method) has been widely performed conventionally.
[0007]
In addition, generally, the reference image is a rectangular image of usually about 10 to 40 mm, and is formed with a fixed halftone dot coverage.
[0008]
The ADC sensor is provided to face a position where a reference image such as a photoconductor or an intermediate transfer member passes, and is configured to read the detection area when the reference image passes. In particular, an LED or the like is used as an illumination light source to illuminate the reference image, and the amount of specular reflection or the amount of diffuse reflection is received by a photodiode or the like, so that the voltage corresponding to the density of the reference image or the amount of toner forming the image A configuration that outputs a value is widely used.
[0009]
Usually, the irradiation light spot diameter of the LED used in such a sensor is generally about 3 to 10 mm in half width. In addition, the intensity of the irradiation light is high near the center and decreases toward the periphery, and light outside the half width is irradiated with a small amount of light that affects the measured value.
[0010]
Therefore, when the reference image is smaller than the irradiation light spot, when the position where the reference image passes changes due to a registration error or the like, the light passes through the irradiation light portions having different light intensities, and accurate measurement cannot be performed. There is a problem. Therefore, as described above, the size of the reference image is generally a size that can completely cover the irradiation light spot, that is, a size of about 10 to 40 mm.
[0011]
To form such a reference image, a printing toner is generally used. However, since the amount of toner consumed by forming the reference image may be equivalent to one print of the character image, there is a problem that the running cost increases and the burden on the user increases. are doing.
[0012]
Further, some image forming apparatuses that pursue higher image quality use a reference image having various types of gradations in order to accurately detect gradations (for example, see Patent Documents 2 and 3). ), The amount of toner used to form a reference image tends to further increase.
[0013]
Usually, after the reference image is read by the ADC sensor, the reference image is cleaned by a cleaner such as a photoconductor or a transfer belt, and is discarded as waste toner in a waste toner bottle or the like. Therefore, in the image forming apparatus using the image quality control technology of the ADC system, the load of each cleaner increases, image quality defects (ghosts, dirt, etc.) due to poor cleaning occur, and a waste toner bottle having a large capacity is required. Problems such as an increase in machine size and cost, an increase in the frequency of replacing waste toner bottles (an increase in maintenance load), and the like also occur.
[0014]
In addition, since the reference image is usually formed in an inter-image portion between images, the width of the inter-image portion needs to be equal to or greater than the length of the reference image in the process direction. Since the inter-image portion is not used for print output, the longer the inter-image portion is, the lower the productivity of the image output device is. For example, when the width of the inter-image portion is set to 50 mm in the A4 horizontal feed (210 mm), the productivity is reduced by 23%.
[0015]
On the other hand, there is also known an image forming apparatus in which a reference image is formed as a fixed image on a sheet and detected by a sensor (for example, see Patent Document 4). In this device, more accurate control can be realized by detecting the image quality of the final image.
[0016]
In this case, since the toner for the reference image is discharged out of the apparatus as an image on paper, the load on the cleaner, the waste toner bottle, and the like can be eliminated. However, in order to form a reference image on a sheet, a sheet for the reference image is required separately, and there is a problem that not only the toner but also the cost of the sheet are required. In addition, when a reference image is formed on a sheet, normal print output cannot be performed, so that a new problem that productivity is lowered occurs.
[0017]
As a device for reducing such adverse effects, a density measuring device and an image forming device capable of accurately measuring a micronized reference image have been proposed (for example, see Patent Document 5).
[0018]
However, when the reference image is micronized, depending on various environmental conditions such as the ambient temperature and humidity of the apparatus, when the reference image is transferred to the image carrier, particularly in a high density portion (a portion having a high halftone dot coverage). In other words, the central portion of the reference image is not transferred to the image carrier side and comes off. This causes a problem that the density measurement value of the reference image becomes abnormally low and the density of the reference image cannot be measured correctly.
[0019]
As an apparatus for solving such a problem, an image signal corresponding to a reference image is input to measure the density, and if there is defective density data that deviates from a monotonically increasing tendency in a function of the measured density with respect to the input signal, it is used. There is known a density correction device that performs density correction by performing interpolation calculation on the removed data by using peripheral measurement values (see, for example, Patent Document 6).
[0020]
[Patent Document 1]
JP-A-6-102732
[Patent Document 2]
JP-A-6-230641
[Patent Document 3]
JP-A-9-329923
[Patent Document 4]
JP-A-62-291265
[Patent Document 5]
JP-A-2002-244371
[Patent Document 6]
JP-A-5-137002
[0021]
[Problems to be solved by the invention]
However, as described above, since the holographic character is more likely to occur in a higher-density reference image, it is difficult to measure the density of a high-density portion simply by removing an abnormal value as in a conventional density correction device, and it is difficult to control the density. Problem. That is, since an abnormal value is often found in the measurement of a portion having a density equal to or higher than a predetermined density, interpolation calculation cannot be performed, and it becomes impossible to obtain a measurement value on the high density side with high accuracy.
[0022]
SUMMARY An advantage of some aspects of the invention is to provide an image forming apparatus that accurately measures a physical quantity related to the image quality of a reference image and controls the formation conditions of an output image with high accuracy. And
[0023]
[Means for Solving the Problems]
In order to achieve the above object, an image forming apparatus according to the present invention includes an image forming unit that forms a reference image and an output image on an image carrier, and a physical quantity related to image quality of the reference image formed on the image carrier. A measuring means for measuring, a determining means for determining whether or not the reference image needs to be re-formed based on the measurement value of the measuring means; and a case where the determining means determines that the re-forming is necessary. A first control unit that controls the image forming unit so as to re-form a reference image different from the formed reference image, and controls a formation condition of the output image based on a measurement value of the measurement unit. And second control means.
[0024]
In the present invention, the reference image is formed on the image carrier by the image forming means. A physical quantity relating to the image quality of the reference image formed on the image carrier is measured by the measuring means, and based on the measured value, it is judged by the judging means whether or not the reference image needs to be re-formed. The first control means controls the image forming means to re-form a reference image different from the previously formed reference image when the judgment means judges that re-formation is necessary. The second control means controls the output image forming condition based on the measurement value of the measurement means.
[0025]
Note that the physical quantity related to image quality includes at least one of density, color, and gradation. For example, if the reference image is a single color and has a single halftone dot coverage, the density is used and a plurality of reference images are used. In this case, if the reference image has a plurality of colors, the color can be obtained, and if the value of the halftone dot coverage is two or more, gradation can be obtained.
[0026]
If the measured value of the physical quantity related to the image quality of the reference image becomes an abnormal value, the physical quantity related to the image quality of the reference image can be accurately determined by re-forming a reference image different from the reference image so that the measured value does not become an abnormal value. Can be measured high. Further, since the toner is not re-formed if there is no problem in the measured value, the amount of consumed toner can be suppressed. This makes it possible to accurately measure the physical quantity related to the image quality of the reference image while suppressing the amount of toner consumed, and to appropriately control the conditions for forming the output image, thereby maintaining the image quality of the output image in a good state. it can.
[0027]
When the reference image is re-formed, the reference image may be re-formed with a predetermined formation content, or the formation content is determined based on the measurement value of the reference image, and the reference image is determined based on the formation content. May be reformed.
[0028]
When the reference image is re-formed, for example, the density (halftone dot coverage) of the reference image may be changed, or the number of reference images to be formed may be changed.
[0029]
Further, as for the reference image to be re-formed, if there are a plurality of types of reference images formed last time, all of the types of reference images may be re-formed. May be re-formed only with respect to the reference image having a high density (having a high halftone dot coverage) which causes the occurrence of.
[0030]
Furthermore, the reference image may be a test pattern image for the output image or the output image itself.
[0031]
The second control unit controls the output image forming condition based on the measurement value of the measurement unit. When the reference image is re-formed, the measured value of the physical quantity related to the image quality of the re-formed reference image is used. , The formation conditions can be controlled.
[0032]
The determining means may compare the measured value measured by the measuring means with a predetermined reference value, and determine whether or not the reference image needs to be re-formed based on the comparison result.
[0033]
As a result, with respect to the physical quantity relating to the image quality, a value that is likely to cause a state (for example, a holographic character or the like) that needs to be re-formed is previously confirmed by an experiment or the like, and the measurement result of the reference image is set using the value as a threshold. Can be determined, and as a result, a physical quantity related to the image quality of the reference image can be accurately measured.
[0034]
Further, in the present invention, the determination means determines whether or not it is necessary to re-create the reference image based on a correlation between measured values of physical quantities related to the image quality of the plurality of types of reference images formed by the image forming means. Judgment can also be made.
[0035]
This makes it possible to determine whether or not to re-create the physical quantity relating to the image quality of the plurality of types of reference images based on the correlation between the measured values, and particularly to improve the gradation characteristics and the like when the output image is color. It can be adjusted, and the image quality of the output image can be improved.
[0036]
Further, in the present invention, the re-formed reference image may include at least one or more types of reference images having a size larger than the previously formed reference image.
[0037]
That is, depending on various environmental conditions such as the state of the apparatus, the ambient temperature of the apparatus, and the humidity, for example, in general, a holographic character is likely to occur as the size of the reference image decreases. Therefore, if the measured value of the physical quantity related to the image quality of the reference image is a value that causes the problem of the holographic character as a result of micronizing the reference image, if the size of the reference image is increased and re-formed, the holographic character Can be prevented, and a physical quantity related to the image quality of the reference image can be measured with high accuracy.
[0038]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings.
[0039]
FIG. 1 is a schematic configuration diagram of an image forming apparatus using an electrophotographic method to which the present invention is applied.
[0040]
The illustrated image forming apparatus 10 forms an electrostatic latent image by irradiating a laser beam after charging the photoreceptor surface with a contact charger, and uses a xerography engine that develops the electrostatic latent image with toner to yellow ( This is a tandem type color electrophotographic image forming apparatus (a so-called laser printer) provided for each color of Y), magenta (M), cyan (C), and black (K). In FIG. 1, an image reading unit and an image processing unit (corresponding to an image processing circuit in FIG. 5 described later) of the image forming apparatus 10 and the like are not shown, and only an IOT (image output terminal: image output unit) is provided. It is shown.
[0041]
The image forming apparatus (IOT) 10 includes a contact charger 14Y that charges the surfaces of four photoconductors 12Y, 12M, 12C, and 12K rotating in directions indicated by arrows, four photoconductors 12Y, 12M, 12C, and 12K. The surfaces of the charged photoconductors 12Y, 12M, 12C, and 12K are exposed by exposure light modulated based on image information for each color, and are exposed on the photoconductors 12Y, 12M, 12C, and 12K. The ROSs (laser output units) 16Y, 16M, 16C, and 16K that form the electrostatic latent images and the electrostatic latent images on the photoconductors 12Y, 12M, 12C, and 12K are developed with the respective color developers, and the photoconductors 12Y, 12M, and 12C are developed. , 12K, and developing devices 18Y, 18M, 18C, and 18K, and the respective color toner images on photoconductors 12Y, 12M, 12C, and 12K are transferred to intermediate transfer belt 22. Primary transfer units 20Y, 20M, 20C, and 20K for transfer, a secondary transfer unit 24 for transferring the toner image on the intermediate transfer belt 22 to the paper P, a fixing unit 28 for fixing the toner image transferred to the paper P, and paper A paper tray 29 for storing P, a cleaner (not shown) for cleaning the surfaces of the photoconductors 12Y, 12M, 12C and 12K, a static eliminator (not shown) for removing residual charges on the surfaces of the photoconductors 12Y, 12M, 12C and 12K, and an intermediate transfer body The image forming apparatus includes a density sensor 30 for detecting the density of the control reference image transferred to the surface of the belt 22, and a belt cleaner 26 for cleaning the surface of the intermediate transfer belt 22.
[0042]
Here, the output image forming process of the image forming apparatus 10 will be briefly described with reference to FIG.
[0043]
First, an input image signal read from a document by an image reading unit (not shown) or an input image signal formed by an external computer (not shown) or the like is input to an image processing circuit (described later), and an appropriate Image processing is performed. The input image signal thus obtained is decomposed for each color and output to ROSs 16Y, 16M, 16C and 16K to modulate the laser beam R.
[0044]
The laser beam R modulated by the input image signal is raster-irradiated onto the surfaces of the photoconductors 12Y, 12M, 12C, and 12K uniformly charged by the contact chargers 14Y, 14M, 14C, and 14K. When the surface of the four photoconductors 12Y, 12M, 12C, and 12K is irradiated with the laser beam R in a raster manner, electrostatic latent images corresponding to the input image signals for each color are formed on the photoconductors 12Y, 12M, 12C, and 12K. You. Next, the electrostatic latent images on the four photoconductors 12Y, 12M, 12C, and 12K are developed with toner by the respective color developing units 18Y, 18M, 18C, and 18K, and toner images are formed on the photoconductors 12Y, 12M, 12C, and 12K. It is formed.
[0045]
The toner images formed on the photoconductors 12Y, 12M, 12C, and 12K are transferred to the intermediate transfer belt 22 by the primary transfer units 20Y, 20M, 20C, and 20K. On the photoconductors 12Y, 12M, 12C, and 12K, on which the transfer of the toner image to the intermediate transfer belt 22 has been completed, the adhering matter such as residual toner adhering to the surface is cleaned by a cleaner (not shown), and the residual charges are removed by a static eliminator (not shown). Removed.
[0046]
On the other hand, after the toner image on the intermediate transfer belt 22 is transferred onto the sheet P sent from the sheet tray by the secondary transfer device 24, the toner image transferred onto the sheet P is And a desired image is obtained. After the transfer of the toner image onto the sheet P is completed, the intermediate transfer belt 22 is cleaned by a belt cleaner 26 to remove extraneous matter such as residual toner adhered to the surface. One image forming process is completed by the above operation.
[0047]
In the image forming apparatus (IOT) 10 of the present embodiment, a reference image as a test pattern is formed for each of CMYK colors on the intermediate transfer belt 22, and based on a density measurement value of the reference image by the density sensor 30. An output image forming condition is controlled, and an output image is formed under the forming condition.
[0048]
FIG. 2 is a schematic configuration diagram of the density sensor 30. In the figure, the horizontal direction is the main scanning direction. The density sensor 30 includes a red LED irradiator 32 that illuminates the reference image Pa surface on the intermediate transfer belt 22 at an angle of 45 °, a lens 34, and light reflected from the reference image Pa via the lens 34. Is provided at an angle of 90 ° with respect to the reference image Pa surface. Further, as shown, the density sensor 30 is configured as a conjugate optical system in which the distance from the reference image Pa to the lens 34 and the distance from the lens 34 to the photodiode 38 are equal to 8 mm.
[0049]
The lens 34 has a diameter of 3 mm and a focal length of 4 mm, and the magnification of the optical system is 1.
[0050]
On the front surface of the photodiode 38, a mask 36 for regulating the detection area of the reference image Pa is provided. In the present embodiment, the size of the detection window provided on the mask 36 is 300 μm in the process direction × 300 μm in the main scanning direction. Portions of the mask 36 other than the detection window are black to prevent stray light.
[0051]
The density sensor 30 includes a current-voltage converter (not shown) that converts a current output from the photodiode 38 into a voltage, and converts an analog signal of the converted voltage into an 8-bit (0 to 255) digital signal. An A / D converter (not shown) is provided, and the converted digital signal is output as a density measurement value to an output image quality control unit described later.
[0052]
Further, the density sensor 30 is provided with a shutter 40, and is configured to receive light from the reference image Pa when the shutter 40 is opened.
[0053]
FIG. 3 is a view of the shutter 40 as viewed from the red LED irradiation unit 32 and the photodiode 38 side, and shows the configuration of the shutter 40. As illustrated, the shutter 40 is provided with a measurement window 42 and a reference plate 44 for obtaining a reference value of the output voltage of the density sensor 30. Further, the shutter 40 includes a mechanism for moving the shutter 40 in the left-right direction in the figure by a driving device (not shown). In FIG. 2, the shutter 40 is normally located at a position where the reference plate 44 is arranged on the optical axis of the light receiving system (when the shutter 40 is closed), and the measurement window 42 receives light only when the reference image Pa is measured. Move so as to be arranged on the system optical axis (shutter 40 is open).
[0054]
FIG. 4 shows an example of the waveform of the output voltage of the concentration sensor 30. In the figure, the horizontal axis represents time, and the vertical axis represents output voltage. Vref is an output voltage corresponding to the reference plate 44 of the shutter 40, Vb is an output voltage corresponding to the surface of the intermediate transfer belt, and Vp1 and Vp2 are output voltages corresponding to the reference image Pa.
[0055]
FIG. 5 illustrates the configuration of an output image quality control unit that controls the output image quality of the IOT 10 based on the output voltage (measured density value) obtained by the density sensor 30 and the flow of input / output signals between the output image quality control unit and the IOT 10. It is the block diagram shown.
[0056]
As illustrated, the output image quality control unit 60 includes an operation amount memory 64, a control rule memory 66, a target value memory 68, a conversion table 62, a CPU 70, and an input / output port 72, each of which is connected to a bus. It is connected.
[0057]
The operation amount memory 64 stores the operation amounts of the ROS 16 and the contact charger 14 constituting the IOT 10. The operation amount for forming the reference image is stored in advance, and the operation amount for forming the output image quality is calculated and stored in an output image quality control process described later.
[0058]
The operation amount is an adjustment amount of a parameter that changes the output value of the controlled object. For example, the operation amount is a set value of the charging voltage of the contact charger 14, a laser power set value of the exposure light by the ROS 16, It refers to the set value of the developing bias voltage, the set value of the transfer current of the primary transfer device 20 and the transfer current of the secondary transfer device 24, and the like.
[0059]
In the present embodiment, a description will be given using a laser power set value (hereinafter abbreviated as an LP set value) of the ROS 16 as an operation amount for output image quality control. Note that the LP set value is standardized to a value from 0 to 255.
[0060]
The control rule memory 66 stores a control rule. Here, the control rule is a correspondence relationship between the density measurement value of the reference image and the operation amount set value.
[0061]
The target value memory 68 stores a density target value of the reference image.
[0062]
The conversion table 62 is a table used for converting an input image signal so that an output image has good gradation.
[0063]
The I / O port 72 is a port for transmitting and receiving I / O signals to and from the IOT 10.
[0064]
The CPU 70 controls processing of re-forming the reference image and forming conditions of the output image based on the density measurement value of the reference image by the density sensor 30 by a program stored in a non-volatile memory such as a ROM (not shown) (that is, the output image quality). Control processing).
[0065]
The output image quality control unit 60 may be a control computer connected to the IOT 10 or may be provided in the IOT 10 itself, and is not particularly limited.
[0066]
The configuration of the IOT 10 shown in FIG. 5 is the same as that of FIG. 1, but illustrations other than the ROS 16, the photoconductor 12, the intermediate point copying belt 22, and the density sensor 30 are omitted. Further, in the present embodiment, the density of the reference image is measured for each color of each of CMYK, and control is performed based on the measurement result. However, for simplicity of description, any one of CMYK will be described below. An example of controlling one color will be described. The illustrated ROS 16 indicates any one of ROS 16Y, 16M, 16C, and 16K, and the illustrated photoconductor 12 is one of the photoconductors 12Y, 12M, 12C, and 12K and the color of the ROS 16 illustrated. Are shown.
[0067]
The IOT 10 further includes an image processing circuit 50, a ROS drive circuit 52, and a reference image signal generator 54, which are not shown in FIG.
[0068]
The image processing circuit 50 converts the input image signal using the conversion table 62. The ROS drive circuit 52 controls driving of the ROS 16. The reference image signal generator 54 instructs formation of a reference image, and outputs a reference image signal to the ROS drive circuit 52 of the IOT in synchronization with the reference image formation timing.
[0069]
Next, an output image quality control process by the CPU 70 of the present embodiment will be described with reference to the flowchart of FIG.
[0070]
In step 100, the shutter 40 of the density sensor 30 is moved by the driving device, the output voltage value is obtained from the reflected light from the reference plate 44 (in FIG. 4, the voltage value at the level indicated by Vref), and calibration is performed. .
[0071]
Specifically, when a calibration instruction signal is input from the output image quality control unit 60 to a drive circuit (not shown) via the input / output port 72, the drive circuit moves the reference plate 44 of the shutter 40 onto the optical axis of the light receiving system. The shutter 40 is moved to the position. The red LED irradiator 32 illuminates the reference plate 44 at an angle of 45 °, and reflects the reflected light from the reference plate 44 on the light receiving surface of the photodiode 38 via the lens 34 at an angle of 90 ° with respect to the surface of the reference plate 44. Image. The photodiode 38 that has received the light outputs a current according to the received light. The output current is subjected to current-voltage conversion and further A / D conversion, then output to the output image quality control unit 60 and taken in by the CPU 70. The CPU 70 confirms that the density sensor 30 operates properly.
[0072]
Next, in step 102, the operation amount for forming the reference image is read from the operation amount memory 64, and the first reference image formation instruction signal including this operation amount is output to the reference image signal generator 54 of the IOT 10. You. When the first reference image formation instruction signal is input, the reference image signal generator 54 outputs the reference image signal to the ROS drive circuit 52 to instruct the formation of the first reference image. The ROS driving circuit 52 receives the reference image forming instruction and drives the ROS 16 to form a first reference image.
[0073]
FIG. 7 is a plan view of a first reference image formed on the intermediate transfer belt 22 according to the present embodiment. In the present embodiment, the first reference images Pa1 and Pa2 having a size of 500 μm × 500 μm and halftone coverage Cin = 50% and 100% are arranged along the measurement line L1 where the reflected light amount is measured by the density sensor 30. Formed on the intermediate transfer belt 22.
[0074]
Next, in step 104, a density measurement instruction is output to the density sensor 30. The density sensor 30 measures the density of the first reference image similarly to the calibration using the reference plate 44. Specifically, the shutter 40 is opened just before the reference images Pa1 and Pa2 formed on the intermediate transfer belt 22 pass the density sensor 30, and the light receiving by the photodiode 38 and the current-voltage conversion are performed as shown in FIG. The voltage Vb corresponding to the surface of the intermediate transfer member belt 22 is output to the output image quality control unit 60 so that the output image quality is controlled. After that, when the reference images Pa1 and Pa2 pass, the pulse-like waveforms (Vp1 and Vp2) are obtained, and after passing the reference image, the voltage returns to the voltage Vb corresponding to the surface of the intermediate transfer belt 22 again. Thereafter, the shutter closes, and the output voltage becomes the Vref level.
[0075]
In step 106, it is determined whether or not the density measurement result of the first reference image has been input from the density sensor 30. If it is determined that the input has been input, in step 108, the relative reflectance Dn of the input output waveform with respect to the output voltage Vref of the reference plate 44 is calculated by the following equation.
[0076]
Dn = (Vpn−Vb) / Vref x Normalization coefficient
Note that Dn is the relative reflectance of the reference image Pan, and the normalization coefficient is a coefficient set in advance.
[0077]
Thereby, the relative reflectances D1, D2 of the first reference images Pa1, Pa2 are calculated. The relative reflectance calculated in this manner is used as a measured density value.
[0078]
The reason for using the relative reflectance with respect to the reference surface as the density measurement value is to measure the density of the reference image with high accuracy even if the sensor becomes dirty, changes over time, or changes in sensitivity due to temperature changes.
[0079]
Next, in step 110, the density is determined.
[0080]
In the present embodiment, the ratio between the relative reflectances D1 and D2 of the first reference image calculated in step 108 is obtained, and the value of this ratio is compared with a preset threshold to make a determination. . The threshold value is a threshold value for determining whether or not a hollow character is generated, and is obtained in advance by an experiment or the like. Each numerical value is the following relational expression
D2 / D1> 1.2 (threshold)
, And if the relational expression holds, it is determined to be normal, and the process proceeds to step 120. When the relational expression does not hold (that is, when D2 / D1 is 1.2 or less), it is determined that there is an abnormality (the occurrence of a hollow character), and the process proceeds to step 112.
[0081]
In step 112, a second reference image formation instruction signal is output to the reference image signal generator 54 of the IOT 10. When the second reference image formation instruction signal is input, the reference image signal generator 54 outputs a reference image signal different from the first reference image to the ROS drive circuit 52, and performs the formation of the second reference image. Instruct. The ROS drive circuit 52 receives the reference image formation instruction and drives the ROS 16 to form a second reference image different from the first reference image.
[0082]
As shown in FIG. 8, in the present embodiment, the formation content of the second reference image is set in advance, and the dot coverage is Cin = 50% and 100% equal to the first reference image. The second reference images Pa3 and Pa4 are formed with a size of 2 mm × 2 mm larger than the first reference image. Such a second reference image is formed on the intermediate transfer belt 22 similarly to the first reference image.
[0083]
Note that the size of the second reference images Pa3 and Pa4 is set to a size that does not generate a hollow character, and is obtained in advance by experiments or the like.
[0084]
Next, in step 114, a density measurement instruction is output to the density sensor 30. The density sensor 30 measures the densities of the second reference images Pa3 and Pa4 as in the case of the first reference image.
[0085]
In step 116, it is determined whether or not the density measurement result of the second reference image has been input from the density sensor 30. If it is determined that the input has been made, the relative reflectances D3 and D4 are calculated in step 118 as in the case of the first reference image.
[0086]
In the present embodiment, the process of determining the density of the re-formed second reference images Pa3 and Pa4 is omitted. It should be noted that three or more types of reference image sizes may be prepared, and the re-forming and determination processing may be repeated until the determination result becomes normal.
[0087]
Next, in step 120, an error between the target value stored in the target value memory 68 and the calculated relative reflectance is calculated. When the relative reflectance used here is determined to be normal in step 110, the relative reflectance D2 of Pa2 of the first reference image calculated in step 108 is used, and it is determined that the relative reflectance is abnormal in step 110. In this case, the relative reflectance D4 of the second reference image Pa4 calculated in step 118 is used.
[0088]
In step 122, a correction amount of the LP set value (operation amount) is calculated using the calculated error. The correction amount ΔLP of the LP set value is obtained as follows.
[0089]
ΔLP = ΔD / M
Here, ΔD is an error between the reference image Pa2 or the reference image Pa4 calculated in step 120 and the target value, and M is a control rule stored in the control rule memory 66, where LP setting value and reference image Is a coefficient indicating a correspondence relationship with the reflected light amount measurement value. This coefficient is obtained in advance by an experiment or the like. By subtracting the thus determined ΔLP from the LP set value stored in the operation amount memory 64 in advance when forming the first reference image, the corrected LP set value is obtained. The obtained LP setting value is stored in the operation amount memory 64 as an operation amount setting value at the time of output image formation.
[0090]
In step 124, if it is determined in step 110 that it is normal, the conversion table 62 is corrected based on the relative reflectances D1 and D2 of Pa1 and Pa2 of the first reference image, and it is determined in step 110 that it is abnormal. In this case, the conversion table 62 is corrected based on the relative reflectances D3 and D4 of the second reference images Pa3 and Pa4. Note that the conversion table 62 is corrected using a general tone correction method, and thus detailed description is omitted.
[0091]
In step 126, the LP set value for forming the output image stored in the manipulated variable memory 64 is supplied to the ROS drive circuit 52 of the IOT 10, whereby the ROS drive circuit 52 sets the laser power according to the LP set value. Can be supplied to the ROS 16. On the other hand, the correction value of the conversion table 62 is also supplied to the image processing circuit 50 of the IOT 10, where the input image signal is converted according to the correction value and supplied to the ROS drive circuit 52. The ROS drive circuit 52 drives the ROS 16 so as to form an output image using the input image signal input from the image processing circuit 50. Thus, the ROS 16 can irradiate the converted input image signal with the above laser power, and can form an output image with good image quality.
[0092]
With the above operation, one output image quality control process ends. Thereafter, this process is periodically repeated during the above-described image forming process, so that the output image quality is kept constant. Note that this output image quality control processing is performed for each of CMYK colors.
[0093]
Although the above-described output image quality control processing has been described as being performed by the CPU 70 of the output image quality control unit 60, the output image quality control processing by the CPU 70 can be subdivided and represented as functional blocks as shown in FIG. .
[0094]
9, a density calculator 70a, a density determiner 70b, a timing generator 70c, an error calculator 70d, an operation amount correction calculator 70e, an operation amount output unit 70f, and a conversion table corrector that constitute the output image quality controller 60. Each of 70 g is a functional block obtained by subdividing the processing of the CPU 70 in FIG.
[0095]
The density calculator 70a calculates the relative reflectance based on the measurement result input from the density sensor 30 (corresponding to steps 108 and 118 in FIG. 6).
[0096]
The density determination unit 70b determines the density of the relative reflectance (measured density value) of the first reference image input from the density calculation unit 70a, and if the determination result is abnormal, sends the second An instruction is issued to output an instruction signal for forming the second reference image. If the relative reflectance of the first reference image input from the density calculator 70a is normal, the relative reflectance is directly transferred to the error calculator 70d and the conversion table corrector 70g (step 110 in FIG. 6). Corresponding to). If the relative reflectance input from the density calculator 70a is the second reference image, the determination processing is not performed, and the input relative reflectance is directly transferred to the error calculator 70d and the conversion table corrector 70g. .
[0097]
The timing generator 70c outputs the first reference image formation instruction to the reference image signal generator 54 and, when receiving an instruction from the density determiner 70b, outputs a reference image for forming a second reference image. Output a formation instruction. Further, after outputting the second reference image formation instruction, a density measurement instruction is output to the density sensor 30 (corresponding to steps 102, 104, 112, and 114 in FIG. 6).
[0098]
The error calculating section 70d calculates an error between the density target value stored in the target value memory 68 and the measured density value calculated by the density calculating section 70a (corresponding to step 120 in FIG. 6).
[0099]
The error calculated by the error calculating unit 70d is input to the manipulated variable correction calculating unit 70e, and the control rule stored in the control rule memory 66 is used so that the error becomes zero with respect to the density target value. The correction amount of the operation amount is calculated. Further, an operation amount setting value for output image formation is calculated from the obtained correction amount and the operation amount setting value for reference image formation stored in the operation memory 64, and the calculation result is stored in the operation amount memory 64. It is stored (corresponding to step 122 in FIG. 6).
[0100]
The operation amount output unit 70f reads the operation amount (here, the LP set value) calculated by the operation amount correction operation unit 70e from the operation amount memory 64, and outputs the operation amount to the ROS drive circuit 52 of the IOT 10 (step 126 in FIG. 6). Correspondence).
[0101]
The conversion table correction unit 70g corrects the conversion table 62 used for converting the input image signal in the image processing circuit 50 based on the density measurement value, and outputs the correction table to the image processing circuit 50 (step 124 and FIG. 6). 126).
[0102]
Other configurations of the illustrated IOT 10 and the output image quality control unit 60 are the same as those described above, and thus description thereof will be omitted.
[0103]
Although the output image quality control processing has been described for each function of the CPU 70 with reference to FIG. 9, each function may be configured by an independent circuit, and the output image quality control processing may be executed by each circuit.
[0104]
As described above, it is determined whether or not the reference image is to be re-formed based on the measured value of the physical quantity (density in the present embodiment) relating to the image quality of the formed reference image. , The output image forming conditions are controlled using the measured density values, and if re-formation is necessary, the re-formed image is re-formed in a size larger than the previous reference image (a size that does not generate a hollow character or the like) and re-formed. Since the formation conditions of the output image are controlled by using the density measurement value of the reference image, even when the reference image is micronized, it is possible to prevent occurrence of a horochara or the like, and correct the density of the reference image correctly. Can be measured. Further, since the toner is not re-formed if there is no problem in the measured value, the amount of consumed toner can be suppressed. Furthermore, since a highly accurate measurement result of the density of the reference image can be obtained, the formation conditions of the output image can be favorably controlled.
[0105]
Further, in the above-described embodiment, an example has been described in which, when it is determined that the measurement result of the first reference image is abnormal, all of the first reference image is reformed. Of these, only the high-density reference image may be re-formed.
[0106]
For example, when the density of the first reference image is determined to be abnormal in the above-described embodiment, as shown in FIG. 10, only the high-density reference image of the first reference image is re-formed. I do. As the second reference image, a second reference image Pa5 having a dot coverage of Cin = 100% equal to the first reference image Pa2 and an image size of 2 mm × 2 mm larger than the first reference image is used as the density. The image is re-formed on the intermediate transfer body belt along the measurement line L1 where the amount of reflected light is measured by the sensor 30. The size of the reference image Pa5 is set to a size that does not cause a hollow character, and is obtained in advance by an experiment or the like.
[0107]
When a plurality of reference images are used as described above, if only a high-density reference image that is a main cause of the occurrence of a hollow character is re-formed, the amount of toner consumption can be reduced and the image quality control process can be performed more efficiently. .
[0108]
In the above-described embodiment, the formation content of the reference image is changed by focusing on the omission in the transfer (holographic character). However, the present invention is not limited to the hollow character, and the reference image is changed depending on the environmental condition and the adjustment state of the device. Even if the image quality of the image is affected, it is also possible to judge whether or not the re-formation is necessary, whereby the image quality of the reference image can be measured with high accuracy, and the image quality of the output image is controlled to a more preferable state. It becomes possible.
[0109]
Further, in the above-described embodiment, an example has been described in which the LP setting value and the conversion table of the input image signal are used as image forming conditions for adjusting output image quality. However, the present invention is not limited to this, and any forming condition may be used as long as the output image quality can be adjusted. For example, a charging voltage set value of the contact charger 14, a developing bias set value, a toner supply amount, or the like may be used. Control may be performed using a plurality of these operation amounts.
[0110]
Furthermore, in the above-described embodiment, an example in which a control rule stored in the control rule memory 66 in advance is used as an output image quality control method has been described, but any output image control method may be used.
[0111]
Further, in the above-described embodiment, the density measurement position of the reference image is on the intermediate transfer belt 22. However, the density measurement position may be on the photoreceptor 12, on the paper transport belt, or on the paper P. That is, the reference image may be formed anywhere as long as its density can be measured. Further, the configuration of the density sensor 30 may be changed according to the measurement location.
[0112]
Further, in the above-described embodiment, an example has been described in which a plurality of reference images are formed for each of the CMYK colors on the intermediate transfer body belt 22, but a single color or two or more colors may be used. In particular, when a reference image is formed on the paper P, the reference image can be only one type of full-color reference image.
[0113]
Further, in the above-described embodiment, an example has been described in which the halftone dot coverage of the reference image is set to two types of Cin 50% and 100%, but the scope of the present invention is not limited to this embodiment. , The dot coverage (Cin value) can be arbitrarily set according to the image forming apparatus 10. Also, the number of reference images is not limited to two types, and one type or three or more types may be used. Further, the size of the reference image is not limited to 500 μm and 2 mm, but may be changed according to the transfer characteristics of the image forming apparatus.
[0114]
Furthermore, in the above-described embodiment, an example has been described in which the second reference images Pa3 and Pa4 are formed in a predetermined size. However, the second reference images Pa3 and Pa4 are formed according to the value of D2 / D1. The size may be determined. For example, when D2 / D1 ≦ 1.6, it is determined that the image needs to be re-formed (abnormal), and the sizes of the second reference images Pa3 and Pa4 are
Reference image size = 5-2.5xD2 / D1 (mm)
It may be determined by an equation such as
[0115]
Further, in the above-described embodiment, an example has been described in which the determination by the CPU 70 (the density determination unit 70b) is performed using a determination formula, but any method may be used as long as it can determine normal / abnormal. For example, a method may be used in which the value of the density measurement value (relative reflectance) D2 of the second reference image Pa2 itself is compared with a certain threshold to determine the value. In this case, the effect of the present invention can be sufficiently obtained even if only one type of reference image is formed.
[0116]
Furthermore, in the above-described embodiment, an example has been described in which the CPU 70 (the density determiner 70b) performs the determination process only once. For example, three or more types of reference image sizes are prepared, and the determination result is normally determined. The formation of the reference image may be repeated until the size of the reference image is changed.
[0117]
Further, in the above-described embodiment, an example has been described in which two or one second reference image is formed. However, the number of second reference images may be increased from the number of first reference images. For example, for example, three reference images having a size larger than that of the first reference image and halftone coverage values of Cin 20%, 50%, and 100% may be formed. In a state where a holochara or the like occurs, the density measurement value of the reference image becomes high. By adding the highlight reference image in this way, the accuracy of gradation correction can be improved.
[0118]
Further, the number of second reference images may be changed according to the value of D2 / D1. For example, when D2 / D1 ≦ 1.6, it is determined that it is necessary to re-form (abnormal), and the value of D2 / D1 is 1.2 <D2 / D1 ≦ 1.6. In this case, the number of the second reference images to be re-formed is set to the above three (= Cin 20%, 50%, 100%), and when D2 / D1 ≦ 1.2, four ( = Cin 10%, 30%, 50%, 100%).
[0119]
Alternatively, the value of the halftone dot coverage of the second reference image may be changed according to the value of D2 / D1. For example, when D2 / D1 ≦ 1.6, it is determined that the image needs to be re-formed (abnormal), and the number of the second reference images is set to three. The values of Cin are set to 50% and 100%, which are the same as the values of the halftone coverage of the image.
Cin = 50 × D2 / D1-40% (however, the minimum value is 10%)
May be determined by
[0120]
The output image quality control unit 60 may be provided in the image forming apparatus 10 or may be a host computer connected to the image forming apparatus 10, and is not particularly limited.
[0121]
Furthermore, in the above-described embodiment, an example has been described in which the necessity of re-forming the reference image is determined by measuring the density. For example, if the reference image is a single color and has a single halftone dot coverage, In the case where a plurality of reference images are used, if the reference image has a plurality of colors, the colors can be obtained. If the values of the halftone dot coverage are two or more, gradation can be obtained.
[0122]
Further, the reference image may be a test pattern image for the output image or the output image itself.
[0123]
Furthermore, in the above-described embodiment, only an example in which the image forming apparatus 10 is a laser printer has been described. However, the scope of the present invention is not limited to the above-described embodiment, and an analog type copier For example, the present invention can be applied to various image forming apparatuses.
[0124]
【The invention's effect】
As described above, according to the present invention, since it is determined whether to re-create the reference image based on the measurement result of the physical quantity related to the image quality of the reference image, even when the reference image is micronized, It is possible to prevent the occurrence of hollow characters and the like. Further, even when a holographic character or the like occurs, a reference image having a size larger than the previously formed reference image (a reference image having a size that does not generate a holographic character or the like) can be re-formed and measured. It is possible to obtain a highly accurate measurement result.
[0125]
In addition, since the output image forming conditions are controlled using the highly accurate measurement results, it is possible to maintain the image quality of the output image with higher accuracy.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an image forming apparatus (IOT) according to an embodiment of the present invention.
FIG. 2 is a schematic configuration diagram of a density sensor.
FIG. 3 is a configuration diagram of a shutter.
FIG. 4 is an output voltage waveform of a density sensor.
FIG. 5 is a block diagram illustrating a configuration of an output image quality control unit that controls an output image quality of an IOT based on an output voltage obtained by a density sensor, and a flow of input / output signals between the output image quality control unit and the IOT. .
FIG. 6 is a flowchart of an output image control process.
FIG. 7 is a plan view of a first reference image.
FIG. 8 is a plan view of a second reference image.
FIG. 9 is a diagram in which output image quality control processing executed by a CPU is subdivided and represented as functional blocks.
FIG. 10 is a plan view of a second reference image when only a high-density reference image of the first reference image is re-formed.
[Explanation of symbols]
10 Image forming apparatus
12Y, 12M, 12C, 12K photoreceptor
14Y, 14M, 14C, 14K contact charger
16Y, 16M, 16C, 16K laser output unit (image forming means)
18Y, 18M, 18C, 18K developing unit
20Y, 20M, 20C, 20K Primary transfer unit
22 Intermediate transfer belt (image carrier)
24 Secondary transfer unit
30 Concentration sensor (measuring means)
32 Red LED irradiator
34 lenses
38 Photodiode
40 shutter
42 Measurement window
44 Reference plate
50 Image processing circuit
52 ROS drive circuit
54 Reference Image Signal Generator
60 Output image quality control unit
62 Conversion table
64 operation amount memory
66 Control rule memory
68 Target value memory
70 CPU (determination means, first control means, second control means)
70a density calculation unit
70b density determination unit
70c Timing generator
70d error calculator
70e operation amount correction calculation unit
70f manipulated variable output section
70g conversion table correction unit
Pa1, Pa2 First reference image
Pa3, Pa4, Pa5 Second reference image

Claims (3)

Image forming means for forming a reference image and an output image on an image carrier,
Measuring means for measuring a physical quantity related to the image quality of the reference image formed on the image carrier,
Based on the measurement value of the measurement unit, a determination unit that determines whether the reference image needs to be re-formed,
When it is determined that the re-formation is necessary by the determination unit, a first control unit that controls the image forming unit to re-form a reference image different from the formed reference image,
Based on the measurement value of the measurement unit, a second control unit that controls the formation conditions of the output image,
An image forming apparatus including: 2. The method according to claim 1, wherein the determining unit determines whether or not it is necessary to re-create the reference image based on a correlation between measured values of physical quantities related to image quality of the plurality of types of reference images formed by the image forming unit. Image forming apparatus. The image forming apparatus according to claim 1, wherein the re-formed reference image includes at least one or more types of reference images having a size larger than a previously formed reference image.

Images