JP2016061976A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an image forming apparatus for deciding a process condition at another process speed from a calibration result at a predetermined process speed, without degrading image quality.SOLUTION: The image forming apparatus using a plurality of process speeds includes an image carrier, image forming means for forming an image on the image carrier, measuring means for measuring the density of an image for measurement formed on the image carrier, and decision means for deciding a second process condition at a second process speed on the basis of the first density of the image for measurement formed at the first process speed by the image forming means, the second density of the image for measurement formed at the second process speed different from the first process speed by the image forming means, and a first process condition at the first process speed.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a calibration technique for an image forming apparatus.

  The image forming apparatus is provided with a fixing device that heats and pressurizes the unfixed image in order to fix the unfixed image formed on the recording material on the recording material. On the other hand, an image forming apparatus is required to be able to use recording materials having various basis weights. For example, when an unfixed image is fixed on a thick paper having a larger basis weight than that of plain paper, the amount of heat applied to the thick paper needs to be increased more than the amount of heat applied to the plain paper. In order to fix an unfixed image on a thick paper, there is a method in which the amount of heat per unit time that the fixing device applies to the thick paper is increased more than the amount of heat per unit time that the fixing device applies to plain paper. Further, for example, there is a method of increasing the time for which the recording material passes through the fixing device by decreasing the conveyance speed of the recording material. Here, in order to increase the time for the recording material to pass through the fixing device, it is necessary to reduce the process speed. The process speed (image forming speed) means, for example, the rotational speed of the photoconductor.

  Incidentally, it is known that development efficiency and the like change as the process speed changes. Therefore, the gradation characteristics of the image formed on the recording material change according to the process speed. However, if calibration for correcting gradation characteristics is executed for each process speed, the time required for calibration increases. Therefore, Patent Document 1 generates a correction condition for correcting the gradation characteristics by performing calibration at a predetermined process speed, and changes to another process speed based on the correction condition corresponding to the predetermined process speed. A configuration for generating a corresponding correction condition is disclosed. Specifically, a correction condition A is generated by calibration at a predetermined process speed, and a measurement image is formed on the image carrier with a predetermined input value using the correction condition A. The image density is stored as a reference density. Then, the process speed is changed to another process speed, based on the difference between the density of the measurement image formed on the image carrier using the correction condition A with the predetermined input value and the reference density, The correction condition B corresponding to the process speed is generated. In the configuration described in Patent Document 1, when an image is formed at another process speed, the scale is based on the correction condition A corresponding to a predetermined process speed and the correction condition B corresponding to another process speed. Tonal characteristics are corrected.

JP 2011-10882 A

  However, if a correction condition B at another process speed is generated based on the correction condition A at a predetermined process speed and the gradation characteristics of the image are corrected by these correction conditions A and B, an image defect may occur. There is. Here, the image defect means that jaggy as shown in FIG. 11 occurs and the image quality is deteriorated. On the other hand, when the correction condition is generated based on the measurement results of the plurality of measurement images formed for each process speed, the number of measurement images increases, and the time required for calibration increases.

  An object of the present invention is to suppress the occurrence of image defects at an arbitrary process speed different from a predetermined process speed.

  According to one aspect of the present invention, an image forming apparatus using a plurality of process speeds includes an image carrier, image forming means for forming an image on the image carrier, and a measurement image formed on the image carrier. Measuring means for measuring the density of the toner, a first density of the measurement image formed at the first process speed by the image forming means, and a second process speed different from the first process speed by the image forming means. Determining means for determining the second process condition at the second process speed based on the second density of the formed measurement image and the first process condition at the first process speed; It is characterized by.

  According to the present invention, image defects can be suppressed from occurring at an arbitrary process speed different from a predetermined process speed.

1 is a configuration diagram of an image forming apparatus. FIG. 3 is a control configuration diagram of the image forming apparatus. The flowchart of the 1st calibration. The flowchart of the 2nd calibration. The figure which shows the relationship between humidity and a charging bias. The figure which shows the relationship between humidity and contrast potential. The figure which shows the relationship between charging bias, laser power, and contrast potential. The figure which shows a test chart. The flowchart of the 1st calibration. The flowchart of the 2nd calibration. The figure which shows the image which jaggy produced.

  Hereinafter, exemplary embodiments of the present invention will be described with reference to the drawings. In addition, the following embodiment is an illustration and does not limit this invention to the content of embodiment. In the following drawings, components that are not necessary for the description of the embodiments are omitted from the drawings.

<First embodiment>
An example in which the present embodiment is applied to an electrophotographic color (multicolor) copying machine having a plurality of photoconductors will be described. However, the image forming apparatus of the present invention can also be applied to a monochromatic image forming apparatus. In addition, the image forming apparatus of the present invention may be a multifunction peripheral or an apparatus that combines a host computer, an image reading apparatus, and a printer. Further, the image forming method is not limited to the electrophotographic method, and the present invention can be similarly applied as long as it is an image forming method that requires gradation correction over time.

  A color copying machine 100 shown in FIG. 1 is an example of an image forming apparatus that can be used by switching a plurality of process speeds. The color copying machine 100 is roughly divided into an image reading unit (hereinafter, reader unit A) and an image forming unit (printer unit B). The document 101 is placed on the document table glass 102 of the reader unit A, and is irradiated with light from the light source 103. Reflected light from the original is imaged on the CCD sensor 105 via the optical system 104. By scanning the reading optical system unit constituted by these in the direction of the arrow K1, the image of the original 101 is converted into an electric signal data string (image signal) for each line. The image signal obtained by the CCD sensor 105 is appropriately subjected to image processing by the reader image processing unit 108 and then transmitted to the printer control unit 109 of the printer unit B.

  The printer control unit 109 generates and outputs a laser output signal by performing pulse width modulation (PWM) on the image signal. The exposure unit 110 outputs a laser beam according to the laser output signal. Further, the exposure unit 110 scans the laser beam and irradiates the photoconductors 121, 131, 141, and 151 that are image carriers of the image forming units 120, 130, 140, and 150. The image forming units 120, 130, 140, and 150 correspond to yellow (Y), magenta (M), cyan (C), and black (Bk). Since the configurations of the image forming units 120 to 150 are substantially the same, the image forming unit 120 for Y will be described below.

  The charger 122 charges the surface of the photoreceptor 121 to a predetermined potential based on the charging bias. The exposure unit 110 exposes the charged surface of the photoconductor 121 based on the image data. As a result, an electrostatic latent image is formed on the photoreceptor 121. The developing device 123 develops the electrostatic latent image on the photoreceptor 121 using a developer based on the developing bias. As a result, an image is formed on the photoreceptor 121. At the time of calibration, the exposure unit 110 and the developing unit 123 form a measurement image on the photosensitive member 121 at a set process speed. The transfer belt 111 is a recording material carrier that carries and conveys a recording material. The transfer blade 124 transfers the image on the photoconductor 121 to the recording material on the transfer belt 111. A cylindrical transfer roller may be employed instead of the transfer blade 124. After the transfer, the surface of the photoconductor 121 is cleaned by a cleaner 127, neutralized by an auxiliary charger 128, and residual charges are erased by a pre-exposure lamp 129. The toner images of the respective colors are sequentially transferred to the recording material. As a result, a full-color image is formed on the recording material. Thereafter, the recording material is conveyed to the fixing device 114. The fixing device 114 heats and pressurizes the recording material to fix the toner image on the recording material. The photo sensor 160 is provided in each of the image forming units 120, 130, 140, and 150, and measures the density of the measurement image formed on the photoconductor 121. Note that the image forming apparatus includes a sensor (not shown) that acquires environmental conditions such as temperature and humidity.

  FIG. 2 is a block diagram illustrating a control mechanism of the image forming apparatus. The reader image processing unit 108 performs A / D conversion on the image signal from the CCD sensor 105, performs gamma correction, color processing, MTF correction, and the like to generate and output image data. The CPU 28 of the printer control unit 109 performs color processing and gamma correction on the input image data, generates a laser output signal, and outputs the laser output signal to the exposure unit 110. Note that the CPU 28 also performs gradation characteristic calibration processing indicating the correspondence between the input value of the image data and the density of the image. A look-up table (LUT) created by calibration and stored in the memory 29 is a correction condition for correcting the gradation characteristic (γ characteristic) of the printer unit B. The correction condition may be a multidimensional function. The exposure unit 110 includes a laser driver and a semiconductor laser. The laser driver causes the semiconductor laser to emit light in accordance with the PWM modulated signal. The operation unit 30 is a user interface that allows the user to input to the image forming apparatus and display the status of the image forming apparatus.

  Next, calibration in the present embodiment will be described using the flowcharts of FIGS. In the present embodiment, it is assumed that the first calibration shown in FIG. 3 has a longer execution interval than the second calibration shown in FIG. For example, the first calibration in FIG. 3 is performed by a service person during installation of the image forming apparatus, or by the user according to an instruction displayed by the image forming apparatus by satisfying a predetermined condition. On the other hand, the second calibration in FIG. 4 is executed, for example, when the image forming apparatus is turned on, after a predetermined period, or every predetermined number of prints.

  First, the first calibration in FIG. 3 will be described. In step S10, the printer control unit 109 performs initial setting of process conditions (image forming conditions) from the tables previously stored in the memory 29 of the printer control unit 109 shown in FIGS. First, the printer control unit 109 determines the charging bias from the table showing the relationship between the humidity and the charging bias shown in FIG. 5 and the humidity acquired by the image forming apparatus at the time of the processing of S10. For example, it is assumed that the humidity at the time of processing of S10 is 45%. According to the table of FIG. 5, the charging bias is −660 V at a humidity of 35% and −651 V at a humidity of 50%. In this case, the printer control unit 109 determines the charging bias at 45% humidity as −654 V by linear interpolation of the values shown in the table of FIG. Further, the developing bias is determined based on the determined charging bias. Specifically, the developing bias is determined so as to have a predetermined potential difference from the determined charging bias. In this example, this potential difference is 175V. Therefore, in this example, the developing bias is −479V.

  Subsequently, the initial value of the contrast potential for each color is determined from the table of FIG. 6 showing the relationship between humidity and contrast potential for each color. Note that the humidity not shown in the table of FIG. 6 is obtained by linearly interpolating the values before and after the charge bias as in the case of the charging bias. Since the humidity in this example is 45%, the initial value of development contrast is set to 160 V for yellow, magenta, and cyan from the table of FIG. On the other hand, black is set to 223V. Note that the contrast potential is the difference between the potential on the surface of the photosensitive member (bright portion potential) charged by the charger 122 and the developing bias.

  Finally, the initial value of the laser power (exposure intensity) is determined from the table shown in FIG. In the table of FIG. 7, each value for the charging bias and the laser power is a contrast potential. In this example, since the charging bias is −654 V, the contrast potential for each laser power at −654 V is obtained by linearly interpolating the value related to −650 V and the value related to −700 V in FIG. Specifically, at a charging bias of −654 V, the contrast potential for the laser power value “112” is 135.2 V, and the contrast potential for the laser power 128 is 182.6 V. In this example, since the contrast potential of yellow, magenta, and cyan is 160V, the laser power for the contrast potential of 160V is obtained by linearly interpolating the above two values. Specifically, in this example, the laser power for yellow, magenta, and cyan is about 120.4, and the initial value is 120 rounded off after the decimal point. The same applies to black.

  Returning to FIG. 3, in step S11, the printer control unit 109 forms the solid density correction test chart 1 shown in FIG. 8 on the recording material at the first process speed. The first process speed is a process speed used for the recording material forming the test chart 1. Each square in FIG. 8 indicates an image (solid image) formed by the value of the image data indicating the maximum density, and the characters Y, M, C, and K shown on the left side of FIG. It indicates that the colors of the image are yellow, cyan, magenta, and black, respectively. Each row of the test chart 1 in FIG. 8 includes eight images, and the laser power for forming these eight images is shifted by a predetermined amount with respect to the initial value determined in S10. For example, eight images are formed with laser powers of −20%, −15%, −10%, −5%, + 5%, + 10%, + 15%, and + 20% with respect to the initial value. That is, when the initial value of the laser power is 120, the laser power is changed to 96, 102, 108, 114, 126, 132, 138, 144. The test chart 1 in FIG. 8 includes four sets of eight images formed by switching the laser power. The printer control unit 109 shifts the development contrast when forming each set by a predetermined amount with respect to the initial value determined in S10. For example, each set of images is formed with a development contrast of −10%, −5%, + 5%, and + 10% with respect to the initial value. That is, when the initial value of the development contrast is 160V, the development contrast is 144V, 152V, 168V, 176V. When changing the development contrast, only one of the charging bias and the developing bias determined in S10 may be changed, or both may be changed.

  Returning to FIG. 3, when a user inputs an instruction to place the recording material on which the test chart 1 is formed on the reader unit A and starts reading from the operation unit 30, the printer control unit 109 determines in step S12. Read test chart 1. Since each image of the test chart 1 in FIG. 7 is formed by changing the development contrast and the laser power, the density is different. The printer control unit 109 determines the density of each measurement image from the reading result of the reader unit A for each color, and determines the charging bias and laser power at which the target density of the solid image is obtained for each color in S13. That is, a process condition in which the maximum density is a target value is determined.

  Subsequently, in S14, the printer control unit 109 forms the test chart 2 on the recording material according to the image forming conditions determined in S13. The test chart 2 is formed by applying a dither process for each color using input values of a plurality of image data, for example, 20 different values. Then, 20 images having different densities are formed. When the user or the like places the recording material on which the test chart 2 is formed on the reader unit A and inputs an instruction to start reading from the operation unit 30, the printer control unit 109 reads the test chart 2 in S15. . The printer control unit 109 obtains the gradation characteristic (γ characteristic) of the printer unit B from the input value of the image data used in S14 and the density of each measurement image read in S15. Then, the printer control unit 109 generates a lookup table A (LUT-A) for converting the input values so that the image formed with the input values has the respective target densities.

  In S17, the printer control unit 109 uses the LUT-A to form the pattern image 1 as the measurement image on each photoconductor at the first process speed. In S18, the photosensor 121 applies the photoconductor 121 to the corresponding photoconductor 121. The density of the formed pattern image 1 is detected. The pattern image 1 is formed by input values of a plurality of image data, for example, ten different values. For example, assuming that the input value of image data is 8 bits, 10 types of values of 10h, 20h, 40h, 60h, 80h, 90h, A0h, C0h, E0h, and FFh can be used. In this example, since the image data is 8 bits, the input value FFh is an input value for forming a solid image, that is, an image having the maximum density. For each color, the printer control unit 109 stores the density of each image formed on the photoconductor by a plurality of input values as a target density. The target density for input values other than the input values used for forming the pattern image 1 is obtained by interpolation.

  Next, the second calibration shown in FIG. 4 will be described. In step S20, the printer control unit 109 sets the process conditions, that is, the laser power and the development contrast to values determined for the first process speed by the calibration in FIG. In step S21, the printer control unit 109 forms the pattern image 1 on each photoconductor at the first process speed. In step S22, the photosensor 160 measures each density of the pattern image 1. Note that the density of the solid image in the pattern image 1 measured in S22 is D1. In step S23, the printer control unit 109 forms the pattern image 1 on each photoconductor at a second process speed different from the first process speed. In step S24, the printer controller 109 measures each density of the pattern image 1 using the photosensor 160. Note that the density of the solid image in the pattern image 1 measured in S24 is D2. In step S25, the printer control unit 109 determines process conditions at the second process speed from the solid image density D1 measured in step S22 and the solid image density D2 measured in step S24. In this example, the laser power at the second process speed is determined by multiplying the laser power at the first process speed used in S20 by the ratio D1 / D2 of the density D1 and the density D2. However, the contrast potential at the second process speed may be determined by correcting the contrast potential at the first process speed based on the ratio of the density D1 and the density D2. Thereafter, in S26, the printer control unit 109 generates a lookup table LUT-B at the second process speed from the density of each image in the pattern image 1 measured in S24 and the target density obtained in S19. To do. Thereafter, when image formation is performed at the first process speed, the process conditions determined in S13 of FIG. 3 and the LUT-A generated in S16 are used. On the other hand, when image formation is performed at the second process speed, the process conditions determined in S25 of FIG. 4 and the LUT-B generated in S26 are used. Here, in S26, after the second process condition is determined, LUT-B is generated without forming a measurement image again based on the determined second process condition. This suppresses downtime for generating gradation characteristics (γ characteristics) suitable for the second process condition.

  As described above, in the present embodiment, the process condition for the second process speed is determined based on the density ratio of the solid image at the two process speeds. In the prior art, the same process condition is used for different process speeds, and gradation correction is performed by LUT. Therefore, jaggy as shown in FIG. 11 may occur when the density is excessively corrected by the LUT. In the present embodiment, the process condition for the second process speed is used based on the process condition for the first process speed and the density ratio of the solid image at the first process speed and the second process speed. Therefore, the density is not corrected excessively by the LUT-B, and the occurrence of jaggy can be suppressed and the image quality can be maintained.

  In the second calibration of the present embodiment, the recording material is not consumed and no user operation is required. Then, it is only necessary to form the pattern image 1 for determining the process condition for the second process speed only once. That is, for the calibration of the second process speed, the recording material for image formation at the second process speed is not consumed, and the image formation at the second process speed is performed only once on each photoconductor. Quality can be maintained.

  Note that the image forming apparatus of the present embodiment directly transfers the toner image formed on each photoconductor to a recording material. However, the present invention can also be applied to an image forming apparatus that transfers a toner image formed on each photosensitive member to an intermediate transfer member and then transfers it to a recording material. In this case, the photosensor can measure the density of the toner image transferred to the intermediate transfer member, instead of measuring the toner image formed on each photoconductor. Furthermore, in the process of FIG. 3, the test chart is read by the reader unit A. However, the test chart may be read by a sensor provided on the downstream side of the fixing unit 116. In S10 of FIG. 3, the process conditions are initially set based on the humidity. However, other environment information, for example, a configuration in which the process conditions are initialized by using temperature instead of or in addition to humidity may be used.

  Further, in the above embodiment, the first calibration and the second calibration are different processes. However, the second calibration may be performed after the first calibration. In the present embodiment, the pattern images formed in S18 of FIG. 3, S21 of FIG. 4, and S24 of FIG. 4 are the same. That is, the toner image is formed by a plurality of the same input values. However, different input values can be used. Moreover, in S22, the structure which forms only a solid image may be sufficient.

<Second embodiment>
Next, the second embodiment will be described focusing on the differences from the first embodiment. In this embodiment, the user selects an arbitrary recording material, the process speed of the selected recording material is the first process speed, and the remaining one or more process speeds are the second process speed. The process conditions for each of the one or more second process speeds are determined based on the process conditions at the first process speed. In the following description, n + 1 (n is an integer of 1 or more) is the number of process speeds used in the image forming apparatus.

  FIG. 9 is a flowchart of the first calibration in the present embodiment. Note that the same step number is assigned to the same process as the first calibration in the first embodiment shown in FIG. 3, and the description thereof is omitted. In this embodiment, the user designates a recording material in S30, and the printer control unit 109 sets the process speed for the recording material designated by the user in S31 to the first process speed. Then, the printer control unit 109 performs numbering from the 2-1 process speed to the 2-n process speed for the remaining second process speeds. In the present embodiment, the recording material that the user wants to emphasize the gradation characteristics can be selected from among the plurality of recording materials. This is also useful when the recording materials that can be prepared at hand are limited. The subsequent processing is the same as that of the first embodiment, and the process condition and the LUT-A of the first process speed are generated by the processing of FIG.

  FIG. 10 is a flowchart of the second calibration in the present embodiment. Note that the same processing as in the second calibration in the first embodiment shown in FIG. 4 is assigned the same step number, and description thereof is omitted. In this embodiment, when the concentration at the first process speed is measured in S22, the variable i indicating the individual speed of the second process speed is initialized to 1 in S40. The processing from S41 to S44 is the same as the processing from S23 to S26 in FIG. After the process of S44, the printer control unit 109 increases i by 1 in S45, and determines whether i is equal to n + 1 in S46. If i is not equal to n + 1, the processing for all the second process speeds is not completed, and the printer control unit 109 repeats the processing from S41. On the other hand, if i is equal to n + 1 in S46, the processing for all the second process speeds has been completed, and the printer control unit 109 ends the second calibration.

  As described above, the image forming conditions and the LUT-B corresponding to each second process speed can be created. Also in the present embodiment, the recording material is used only for calibration at the first process speed, and the recording material is not consumed for each second process speed. Therefore, the burden on the user, processing time, and cost of the recording material can be reduced. Furthermore, in this embodiment, since the user can designate a recording material that is easy to prepare at hand, user convenience is improved.

  Note that if the difference between the plurality of process speeds increases, the control error may increase. Therefore, for example, in S30 and S31 of FIG. 9, instead of selection by the user, the image forming apparatus selects a speed having the smallest difference from other process speeds as the first process speed. Can do. Further, the recording material corresponding to the first process speed selected in this way may be presented to the user by the image forming apparatus, and the user may select an arbitrary recording material.

  The first calibration uses a test chart actually formed on the recording material. Therefore, by setting the fastest process speed as the first process speed, highly accurate density correction can be performed, and the time required for calibration can be shortened. Therefore, in S30 and S31 of FIG. 9, instead of selection by the user, the image forming apparatus can select the fastest process speed as the first process speed. Further, the recording material corresponding to the first process speed selected in this way may be presented to the user by the image forming apparatus, and the user may select an arbitrary recording material.

[Other Embodiments]
The present invention can also be realized by executing the following processing. That is, software (program) that realizes the functions of the above-described embodiments is supplied to a system or apparatus via a network or various storage media, and a computer (or CPU, MPU, or the like) of the system or apparatus reads the program. It is a process to be executed.

  121: Photoconductor, 120, 130, 140, 150: Image forming unit, 160: Photo sensor, 109: Printer control unit

Claims (12)

An image forming apparatus using a plurality of process speeds,
An image carrier;
An image forming means for forming an image on the image carrier;
Measuring means for measuring the density of the measurement image formed on the image carrier;
A first density of the measurement image formed at the first process speed by the image forming unit and a second density of the measurement image formed at the second process speed different from the first process speed by the image forming unit. Determining means for determining a second process condition at the second process speed based on the concentration and the first process condition at the first process speed;
An image forming apparatus comprising:   The image forming apparatus according to claim 1, wherein the determination unit determines the second process condition by correcting the first process condition based on a ratio between the first density and the second density. .   The image forming apparatus according to claim 1, wherein the determining unit determines a second process condition for each of the plurality of second process speeds.   The image forming apparatus according to claim 1, wherein the image bearing member is a photosensitive member or an intermediate transfer member to which an image formed on the photosensitive member is transferred.   5. The image forming apparatus according to claim 1, wherein the measurement image includes at least a solid image, and the first density and the second density are densities of the solid image. 6. . Transfer means for transferring an image formed on the image carrier directly or via an intermediate transfer member to a recording material;
Fixing means for fixing the image transferred to the recording material to the recording material;
Further comprising
The determining means uses a plurality of process conditions, and at the first process speed, is formed on the image carrier, transferred to a recording material, and fixed on the recording material. The image forming apparatus according to claim 1, wherein the first process condition is determined.   The image forming apparatus according to claim 6, wherein the determining unit determines the plurality of process conditions based on environment information of the image forming apparatus.   The image forming apparatus according to claim 7, wherein the environmental information is humidity.   The image forming apparatus according to claim 1, wherein the first process speed is a fastest speed among the plurality of process speeds.   9. The image forming apparatus according to claim 1, wherein the first process speed is a speed at which a maximum value of a difference from another process speed is minimized.   The image forming apparatus according to claim 1, wherein the first process speed is a process speed used for a recording material designated by a user.   The first process condition and the second process condition are a charging bias for charging the photosensitive member, an exposure intensity for forming an electrostatic latent image on the photosensitive member, and developing the electrostatic latent image formed on the photosensitive member. The image forming apparatus according to claim 1, further comprising at least one developing bias for performing the above operation.