JP2007193172A - Image forming apparatus and control method for the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus for detecting relative displacement in the main scanning direction of image formation between an image formation position and the density measurement position of a density sensor, on an image carrier. <P>SOLUTION: The image forming apparatus includes: the image carrier 12; an image forming section 13 that forms images on the image carrier 12; and a density sensor 16 that measures the density value of a formed image by detecting the density in the predetermined density measurement position. The image forming apparatus causes the image forming section 13 to form a predetermined density adjustment image. Based upon the density value of the density adjustment image, the density of the formed image is adjusted. The image forming apparatus causes the image forming section 13 to form a displacement detection image so that the density value measured by the density sensor 16 changes with time by relative displacement in the main scanning direction of image formation between the image formation position and density measurement position on the image carrier 12. Based upon the change with time in the density value of the displacement detection value measured by the density sensor 16, the image forming apparatus detects the relative displacement. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image on a medium by transferring an image formed on an image carrier onto the medium, such as a printer or a copying machine, and a control method thereof.

  In an image forming apparatus such as a printer or a copying machine, first, an image forming unit forms a toner image by attaching a developer such as toner on an image carrier such as a drum or an intermediate transfer member, and the toner image is transferred to a medium. As a result, an image is formed on the medium. In such an image forming apparatus, the density of an image formed on the image carrier varies depending on the environment in which it is used. As a result, the color tone of the image formed on the medium may differ from the original color tone of the image data to be output.

  In order to cope with such a problem, the image forming apparatus performs the following density adjustment control. That is, a predetermined density adjustment image is formed on the image carrier, and the density value of the formed density adjustment image is measured using a density sensor. Then, based on the density value obtained by the measurement, the density of image formation is adjusted by adjusting control parameters for the image forming unit such as the toner supply amount.

In the density adjustment control, a density adjustment image is formed at a predetermined position on the image carrier in accordance with the position where the density sensor is to detect the density. However, the position of the density-adjusted image formed on the image carrier and the range in which the density sensor measures the density due to errors in the mounting positions of the respective parts such as the density sensor and the laser beam irradiation unit constituting the image forming unit. There may be a relative deviation from the density measurement position. Therefore, for the mark provided in advance on the image carrier or formed by the image forming unit, the distance from the reference position obtained in advance to the mark and the reference position obtained based on the measurement timing of the density sensor. There is a technique for detecting this relative deviation by comparing the distance to the mark (see Patent Document 1).
Japanese Patent Laid-Open No. 10-288880

  However, according to the technique of the conventional example, a shift in the sub-scanning direction (rotation direction of the image carrier) of image formation can be detected, but a relative shift in the main scanning direction (width direction of the image carrier) cannot be detected. .

  In order to avoid such a problem, there is a method in which density adjustment control is performed using a density adjustment image having a horizontal width equal to or larger than a predetermined size in consideration of the amount of relative shift that may occur. However, according to this method, a relatively large amount of toner or the like is consumed each time density adjustment control is performed, and efficiency is poor.

  The present invention has been made in view of the above circumstances, and one of its purposes is to make a relative relationship between the image forming position on the image carrier and the density measuring position of the density sensor in the main scanning direction of image formation. An object of the present invention is to provide an image forming apparatus capable of detecting misalignment and a control method therefor.

  In order to solve the above problems, an image forming apparatus according to the present invention includes an image carrier, image forming means for forming an image on the image carrier, and detecting the density at a predetermined density measurement position. A density sensor that measures a density value of an image formed on the image carrier by a forming unit, and a predetermined density adjustment image formed on the image forming unit, and based on the density value of the density adjustment image measured by the density sensor The image forming unit adjusts the density of the image formed on the image carrier, and the main scanning direction of image formation between the image forming position and the density measuring position on the image carrier. A positional deviation detection image forming unit for forming an image for the positional deviation detection so that the temporal change of the density value measured by the density sensor differs depending on the relative deviation of the density sensor, and the density sensor. There based on the time variation of the density value of the misalignment detecting image to be measured, characterized in that it comprises a position deviation detection means for detecting the relative displacement.

  As a result, the density sensor measures the density value of the misregistration detection image formed on the image carrier and examines the change over time of the density value obtained by the measurement, so that the relative value in the main scanning direction of image formation can be determined. The presence or absence of misalignment can be detected.

  Here, the image forming apparatus further includes a position adjusting unit that adjusts a position of the density adjustment image formed on the image carrier by the forming density adjusting unit based on the detected relative deviation amount. It may be included.

  The image forming apparatus control method according to the present invention includes: an image carrier; an image forming unit that forms an image on the image carrier; and a density at a predetermined density measurement position. A density sensor for measuring a density value of an image formed on the image carrier, and a predetermined density adjustment image is formed on the image forming unit, and based on the density value of the density adjustment image measured by the density sensor, A method for controlling an image forming apparatus including: a density adjusting unit configured to adjust a density of an image formed on the image carrier by the image forming unit, wherein the image forming position and the density measuring position on the image carrier Forming a misregistration detection image on the image forming means such that a temporal change in density value measured by the density sensor differs depending on a relative deviation in the main scanning direction of image formation between On the basis of the time variation of the density value of the positional deviation detecting image whose serial density sensor measures, characterized in that it comprises the steps of: sensing the relative displacement.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. As shown in FIG. 1, an image forming apparatus 10 according to an embodiment of the present invention includes a paper feed tray 11, an image carrier 12, an image forming unit 13, a transfer unit 14, a fixing unit 15, a density sensor 16, and a control unit. 17 and a storage unit 18 are included.

  The paper fed from the paper feed tray 11 is transported along a paper transport path indicated by a broken line in FIG. As will be described later, the image forming apparatus 10 forms an image on a sheet transported along a sheet transport path, and discharges the image to the outside of the apparatus. Further, the paper transport path may be provided with a reverse path (R) for transporting the paper having an image formed on one side thereof again to the transfer unit 14 during back surface printing.

  The image carrier 12 is, for example, a photosensitive drum or an intermediate transfer belt, and carries an image formed by the image forming unit 12. FIG. 1 illustrates the case where the image carrier 12 is an intermediate transfer belt. In FIG. 1, an arrow shown on the inner side of the intermediate transfer belt indicates the rotation direction of the image carrier 12. The image carrier 12 rotates in the rotation direction based on the control of the control unit 17. This direction corresponds to the sub-scanning direction of image formation on the image carrier 12.

  The image forming unit 13 forms a developer image by attaching a developer such as toner on the image carrier 12. As a specific example, in the example of FIG. 1, the image forming unit 13 includes a photosensitive drum 13a, a laser beam irradiation unit 13b, and a developing device 13c. In this case, the image forming unit 13 forms an image as follows. That is, the laser beam irradiation unit 13b irradiates the laser beam to form an electrostatic latent image on the photosensitive drum 13a. The developing unit 13c attaches a developer such as toner to the photosensitive drum 13a, thereby developing the electrostatic latent image to form a developer image. Thus, the developer image formed on the photosensitive drum 13 a is transferred to the image carrier 12, so that the image forming unit 13 can form a developer image on the image carrier 12.

  The transfer unit 14 includes a transfer roll and the like, and transfers the developer image formed by the image forming unit 13 on the image carrier 12 onto a sheet conveyed along a sheet conveyance path. The fixing unit 15 includes a fixing roller and fixes the image transferred by heat or pressure on the paper. As a result, the image forming apparatus 10 forms an image on the sheet.

  The density sensor 16 detects the density at a predetermined density measurement position, thereby measuring the density value of an image formed on the image carrier 12 by the image forming unit 13. As a specific example, the density sensor 16 includes a light emitting unit and a light receiving unit. Then, the light emitting unit emits light to the density measurement position, and the light receiving unit receives the light reflected by the image carrier 12, whereby the density sensor 16 measures the amount of received light. Since the reflectance of the image carrier 12 changes depending on the density of the formed image formed on the image carrier 12, the density sensor 16 can detect the density at the density measurement position by measuring the amount of received light. The density sensor 16 outputs a measured density value representing the measured density of the formed image to the control unit 17.

  The control unit 17 is a CPU or the like, and operates here according to a program stored in the storage unit 18. The control unit 17 controls the image forming unit 13 to form an image on the image carrier 12. Further, it controls the conveyance of the paper and the rotation operation of the image carrier 12. Further, the control unit 13 acquires information on the density value measured by the density sensor 16, and a formation density adjustment process for adjusting the density of the formed image formed on the image carrier 12 by the image forming unit 13 based on the acquired density value. I do. Further, a misregistration detection process for detecting a relative misalignment between the density measurement position on the image carrier 12 and the image forming position where the image forming unit 13 forms an image is performed. The specific processing contents of the control unit 17 in the present embodiment will be described in detail below.

  The storage unit 18 includes a RAM, an NVRAM (nonvolatile RAM), and the like. The storage unit 18 operates as a work memory for the control unit 17. Further, the storage unit 18 stores information on reference density values used as comparison targets in the positional deviation detection process.

  Here, an example of the formation density adjustment process executed by the control unit 17 will be described.

  First, the control unit 17 controls the image forming unit 13 to form a predetermined density adjustment image Id on the image carrier 12. As an example, the control unit 17 forms a density adjustment image as shown in FIG. 2A on the surface of the image carrier 12. Here, the density measurement reference line La indicated by a broken line in FIG. 2A indicates how the central point of the density measurement position where the density sensor 16 measures density moves on the image carrier 12. It is a line showing. As the image carrier 12 rotates, the density sensor 16 causes the center point of the density measurement position to move in the sub-scanning direction on the density measurement reference line La over time. Measure the concentration. Therefore, the control unit 17 forms the density adjustment image so that the center position of the density adjustment image is positioned on the density measurement reference line La.

  Next, the control unit 17 acquires measured density value data of the density adjusted image obtained by the measurement of the density sensor 16. Here, FIG. 2B is an enlarged explanatory diagram showing the positional relationship between the density adjustment image illustrated in FIG. 2A and the density measurement position. In the example of FIG. 2B, the center position of the density adjustment image coincides with the density measurement reference line La. Therefore, as shown in FIG. 2 (b) as a range surrounded by a one-dot chain line, the concentration sensor 16 has a concentration measurement position P1 at a certain time t and a concentration at a time t + dt when a predetermined time has elapsed from the time t. The measurement position P2 is measured.

  Based on the measured density value obtained in this way, the control unit 17 adjusts the density of the image formed on the image carrier 12 by the image forming unit 13. For example, if the measured density value is lower than a predetermined reference value, various control parameters for the image forming unit 13 such as the toner supply amount are changed so as to increase the density of the formed image. Conversely, if the measured density value is higher than a predetermined reference value, various control parameters are changed so as to reduce the density of the formed image. By performing such a formation density adjustment process, the image forming apparatus 10 can form an image having a color tone that matches the original density of the image data to be output.

  However, there may be a relative shift between the image forming position by the image forming unit 13 on the image carrier 12 and the density measuring position by the density sensor 16. Such a relative shift includes a shift in the mounting position of the density sensor 16 with respect to the image carrier 12, a shift in the mounting position of the laser light irradiation unit 13b with respect to the photosensitive drum 13a, and a mounting position of the photosensitive drum 13a with respect to the image carrier 12. It can be caused by misalignment. Further, the above-described relative shift may occur due to a shift in the irradiation angle of light emitted from the density sensor 16.

  When such a relative deviation occurs, there may occur a case where the density value of the density adjustment image cannot be measured correctly in the formation density adjustment process. Therefore, such a relative shift is detected by performing a positional shift detection process in advance. Below, the example of the position shift detection process which the control part 17 performs is demonstrated based on the flowchart of FIG.

  First, the control unit 17 controls the image forming unit 13 to form a predetermined misregistration detection image on the image carrier 12 (S1). Here, the control unit 17 positions the image reference line Lb representing the center line parallel to the sub-scanning direction of the position shift detection image at a position where it is assumed that the density measurement reference line La on the image carrier 12 coincides. Form an image.

  Here, the positional deviation detection image is a temporal change in density value measured by the density sensor 16 due to a relative deviation in the main scanning direction of image formation between the image forming position and the density measuring position on the image carrier 12. Are different images. As a specific example, the positional deviation detection image is obtained when the distance between the image reference line Lb representing the center line parallel to the sub-scanning direction of the positional deviation detection image and the density measurement reference line La is different. And an image having a shape in which at least one of the length of a portion where the position deviation detection image overlaps and the position in the sub-scanning direction are different. Such an image is, for example, an image having an asymmetric shape with respect to the image reference line Lb. Further, as illustrated in FIG. 4A, the image may have an area defined by a line segment that intersects the density measurement reference line La at an angle that is not perpendicular. Alternatively, the image may be an image in which a plurality of rectangular regions with different relative positions and / or lengths in the main scanning direction with respect to the density measurement reference line La are arranged along the sub-scanning direction.

  As an example, the control unit 17 causes the image forming unit 13 to form a misregistration detection image Ia as shown in FIG. In this case, as shown in FIG. 4B, which is an enlarged explanatory view of the misregistration detection image Ia, the image reference line Lb of the misregistration detection image Ia formed on the image carrier 12 is It is assumed that the density measurement reference line La is shifted by dL1 in the main scanning direction.

  Subsequently, the control unit 17 obtains the measured density value of the image for detecting misregistration measured by the density sensor 16 (S2). The misregistration detection image formed on the image carrier 12 moves along the density measurement reference line La as the image carrier 12 rotates. When the density sensor 16 measures the density of the position shift detection image at the density measurement position, the control unit 17 can acquire a measured density value that changes with time.

  Next, the control unit 17 detects a relative shift in the main scanning direction with respect to the density measurement position of the image forming position based on the time change of the measured density value acquired by the process of S2 (S3). Here, the storage unit 18 holds in advance, as reference density values to be compared, information representing changes over time in measured density values obtained by measuring a position deviation detection image when there is no relative deviation. . The control unit 17 acquires the reference density value and compares it with an actual measured density value that changes with time, thereby detecting the presence or absence of relative deviation.

  As a specific example, in the case of the above-described position shift detection image Ia, the measured density value obtained by measuring the density measurement position P3 shown as the range surrounded by the one-dot chain line in FIG. It is considered that it is not different from the measured density value obtained by measuring the density measurement position P4 when there is no deviation. However, the measured density value obtained by measuring the density measurement position P5 is considered to be different from the measured density value obtained by measuring the density measurement position P6 at the same timing when there is no relative deviation. This is because the areas of the position shift detection images included in the respective density measurement positions are different.

  Thereby, for example, it is assumed that the control unit 17 has obtained the time change of the measured concentration value as represented by the solid line in the graph schematically shown in FIG. In the graph of FIG. 5, the reference density value is represented by a one-dot chain line. Due to the relative deviation, the measured density value is different from the reference density value after time t0. For example, when the maximum difference value between the measured density value and the reference density value is equal to or greater than a predetermined value, the control unit 17 determines that a relative deviation has occurred.

  Furthermore, when a relative shift is detected in the process of S3, the control unit 17 may further adjust the density adjustment image formation position. As a specific example, the control unit 17 executes the following process.

  First, based on the difference value between the measured density value and the reference density value used for detecting the relative shift in the process of S3, a shift amount of the relative shift is acquired (S4). Specifically, the control unit 17 may calculate the shift amount from the maximum value of the difference values acquired in the process of S3, for example, using a predetermined calculation formula. Alternatively, based on a table representing the correspondence between the difference value and the deviation amount held in the storage unit 18, the value associated with the maximum value of the difference value acquired in the process of S3 is set as the actual deviation amount. You may get as

  Further, the control unit 17 adjusts the position of the density adjustment image in the formation density adjustment process based on the deviation value acquired in the process of S4. For example, when the shift amount is calculated as dL1 in the main scanning direction in the process of S4, the control unit 17 determines the position of the density adjustment image that the image forming unit 13 forms on the image carrier 12 in the next and subsequent formation density adjustment processes. Then, the parameter relating to the density adjustment image forming position is changed so as to be shifted by dL1 in the reverse direction of the main scanning direction. Thus, in the next and subsequent formation density adjustment processes, the image formation position and the density measurement position coincide with each other, and the density sensor 16 can correctly measure the density of the density adjustment image.

  Next, an example in which the misregistration detection image is an image made up of a plurality of rectangular regions with different relative positions with respect to the density measurement reference line La will be described. As an example, a description will be given of an example of the case where the misregistration detection process is performed using the misregistration detection image Ib including the three rectangular areas S1, S2, and S3 as shown in FIG. In this case, for example, as shown in FIG. 6B, which is an enlarged explanatory view of the misregistration detection image Ib, the image reference line Lb of the misregistration detection image Ib formed on the image carrier 12 is Assume that the density measurement reference line La is deviated by dL2 in the direction opposite to the main scanning direction.

  Here, the measured density value obtained by measuring the density measurement position P7 shown as the range surrounded by the one-dot chain line in FIG. 6B is obtained by measuring the density measurement position P8 when there is no relative deviation. It is considered to be smaller than the measured concentration value. Similarly, the measured density value obtained by measuring the density measurement position P9 is considered to be smaller than the measured density value obtained by measuring the density measurement position P10 when there is no relative deviation. On the other hand, it is considered that the measured density value obtained by measuring the density measurement position P11 is not different from the measured density value obtained by measuring the density measurement position P12 when there is no relative deviation. This is because the density measurement positions P7 and P9 protrude from the position deviation detection image Ib, whereas the density measurement positions P8, P10, P11, and P12 are included in the position deviation detection image Ib.

  Thereby, for example, the control unit 17 can obtain the time change of the measured concentration value as represented by the solid line in the graph schematically shown in FIG. In the graph of FIG. 7, the reference density value is represented by a one-dot chain line. As shown in the graph of FIG. 7, the measured density value and the reference density value are different in the vicinity of time t1 when the density measurement position P7 is measured and time t2 when the density measurement position P9 is measured. For example, the control unit 17 obtains the maximum value of the difference value between the measured density value and the reference density value for each rectangular area included in the density adjustment image, and compares the maximum value of the difference value to make the relative value. Detect the presence of misalignment. For example, in the example of the positional deviation detection image Ib, if the measured density value is lower than the reference density value by a predetermined value or more in the rectangular areas S1 and S2, a relative deviation occurs in the direction opposite to the main scanning direction. It is determined that If the measured density value is lower than the reference density value by a predetermined value or more in the rectangular areas S2 and S3, it is determined that a relative shift has occurred in the main scanning direction.

  According to the present embodiment described above, the density sensor 16 measures the density value of the misregistration detection image formed on the image carrier 12, and examines the time change of the measured density value obtained by the measurement. Thus, it is possible to detect the presence or absence of relative positional deviation in the main scanning direction of image formation. Furthermore, by adjusting the formation position of the density adjustment image based on the detected displacement amount, the density sensor 16 can correctly measure the density of the density adjustment image when performing the formation density adjustment processing. Further, the formation density adjustment process can be performed using a relatively small density adjustment image in the formation density adjustment process, and consumption of a developer such as toner can be suppressed.

1 is a configuration diagram illustrating a schematic configuration of an image forming apparatus 10 according to an embodiment of the present invention. 3 is an explanatory diagram illustrating an example of a density adjustment image formed on the image carrier 12 by the image forming apparatus 10. FIG. FIG. 6 is a flowchart illustrating an example of misregistration detection processing executed by the image forming apparatus 10. 3 is an explanatory diagram illustrating an example of a misregistration detection image formed on the image carrier 12 by the image forming apparatus 10. FIG. FIG. 6 is an explanatory diagram illustrating an example of a graph of a temporal change in density value obtained by the image forming apparatus 10 measuring the density of an image for detecting misregistration. 6 is an explanatory diagram illustrating another example of a misregistration detection image formed on the image carrier 12 by the image forming apparatus 10. FIG. FIG. 10 is an explanatory diagram illustrating another example of a graph of a change in density value over time obtained by the image forming apparatus 10 measuring the density of an image for detecting displacement.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Image forming apparatus, 11 Paper feed tray, 12 Image carrier, 13 Image forming part, 14 Transfer part, 15 Fixing part, 16 Density sensor, 17 Control part, 18 Storage part.

Claims (3)

An image carrier;
An image forming means for forming an image on the image carrier;
A density sensor for measuring a density value of an image formed on the image carrier by the image forming unit by detecting a density at a predetermined density measurement position;
Forming a predetermined density adjusted image on the image forming unit and adjusting the density of an image formed on the image carrier by the image forming unit based on a density value of the density adjusted image measured by the density sensor; Density adjusting means;
A positional deviation detection image in which a temporal change in density value measured by the density sensor differs depending on a relative deviation in the main scanning direction of image formation between the image forming position on the image carrier and the density measurement position. An image forming means for detecting misalignment that is formed on the image forming means,
A positional deviation detection means for detecting the relative deviation based on a temporal change in density value of the positional deviation detection image measured by the density sensor;
An image forming apparatus comprising: The image forming apparatus according to claim 1.
An image forming apparatus, further comprising: a position adjusting unit that adjusts a position of the density adjusted image that is formed on the image carrier by the forming density adjusting unit based on the detected relative shift amount. . An image carrier;
An image forming means for forming an image on the image carrier;
A density sensor for measuring a density value of an image formed on the image carrier by the image forming unit by detecting a density at a predetermined density measurement position;
Forming a predetermined density adjusted image on the image forming unit and adjusting the density of an image formed on the image carrier by the image forming unit based on a density value of the density adjusted image measured by the density sensor; Density adjusting means;
A method for controlling an image forming apparatus including:
A positional deviation detection image in which a temporal change in density value measured by the density sensor differs depending on a relative deviation in the main scanning direction of image formation between the image forming position on the image carrier and the density measurement position. Forming the image forming means on the image forming means,
Detecting the relative deviation based on a temporal change in the density value of the positional deviation detection image measured by the density sensor;
A control method for an image forming apparatus.

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