JP2005018094A - Method for detection image deviation and image density and color image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To ensure efficient image deviation detection and efficient image density detection without involving increases in the size and cost of the apparatus. <P>SOLUTION: Misregistration detection/correction is carried out when a belt 30 makes turns an odd number of times from the start of conveyance. When the belt 30 makes rotations an even number of times, density detection/correction is carried out using the same detecting part 28. Since the misregistration detection/correction and density detection/correction are carried out using the same detecting part 28, increases in the size and cost of the apparatus can be avoided. In addition, structure is such that misregistration detection/correction are carried out when the belt 30 makes a first rotation. This prevents an image density detection process when the belt 30 makes turns even number of times from being carried out having misregistration. Since a black registration control pattern and a black process control pattern are formed on a part of the area of the previously formed color pattern, black registration and black density can accurately be detected. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for detecting image misregistration and image density, and a color image forming apparatus. More specifically, the present invention relates to a color toner image and a black toner image which are transferred onto an intermediate transfer member by transferring the color toner image and the black toner image on the intermediate transfer member. The present invention relates to a method for detecting image position deviation and image density, which detects image position deviation and image density in a color image forming apparatus having a function of forming an image, and the color image forming apparatus.

  Conventionally, a plurality of image forming units are provided, and toner images of different colors (generally yellow (Y), magenta (M), cyan (C), black (K) toner images) are provided in each image forming unit). Is formed on a photoconductor, and a toner image formed on each photoconductor is transferred onto the same transfer material (for example, recording paper) to form a color image, a so-called tandem color image. Various forming apparatuses have been proposed.

  In such a color image forming apparatus, toner images of different colors formed by a plurality of image forming units are superimposed on the same transfer material. It is important to stabilize the concentration.

  Therefore, in the color image forming apparatus as described above, the density of the toner image formed on the photoconductor is detected by each image forming unit, and the density control is performed so that the detected density is within an appropriate range. It was.

  On the other hand, in recent years, for the purpose of enlarging the size of the transfer material to be supported and improving the stability of transferability, the toner images of each color of YMCK are transferred from the photoreceptor to the intermediate transfer body to form the desired color image, A tandem type color image forming apparatus using an intermediate transfer body that collectively transfers the color image from an intermediate transfer body to a transfer material has been proposed.

  However, in this tandem type color image forming apparatus using the intermediate transfer member, the toner image density is detected on the intermediate transfer member in order to remove the influence of the transfer property from the photosensitive member to the intermediate transfer member. It is necessary to detect the density of the formed toner image.

  By the way, the density of an image to be detected is often obtained from the ratio between the amount of light reflected from the image and the amount of light reflected from the background by irradiating the surface on which the image is formed with a predetermined amount of light. In this case, it is known that if the difference between the light reflectance of the image and the light reflectance of the ground is small, it is difficult to detect the density of the image with high accuracy.

  Considering the light reflectance of the toner of each color of YMCK described above, the light reflectance of YMC color toner is high, and particularly in the wavelength in the infrared region (900 nm to 1200 nm), FIG. 3 (B), FIG. 4 (B), As shown in FIG. 5B, it can be seen that the light reflectance is 90% or more. On the other hand, the light reflectance of the black toner is 10% or less in any wavelength region as shown in FIGS. On the other hand, the light reflectance of a dielectric that is generally used as an intermediate transfer member and whose volume resistance is adjusted by carbon is about 10 to 20%. For this reason, it may be difficult to accurately detect the density of the black toner image formed on the intermediate transfer member.

  As a method for solving the above problems, a method may be considered in which a color toner image serving as a base is formed on an intermediate transfer member, a black toner image is formed on the intermediate transfer member, and then the density of the black toner image is detected. It is done.

  In relation to this, Patent Document 1 discloses a technique for controlling the density so that the density of the color toner image serving as the background becomes the target value before detecting the density of the black toner image as described above. . In this technology, before detecting the density of the black toner image, the density of the color toner image that is the background is always detected, and only when the density value is within the target range, the density of the black toner image is detected. If the density value of the color toner image is outside the target range, process control such as development bias and exposure amount is performed, and the density detection of the black toner image is performed when the color toner image density value falls within the target range. .

  However, in the above technique, since a single photoconductor is used, the density of the color toner image serving as the background is detected on the intermediate transfer body, and the density of the black toner image is detected after controlling the density as necessary. By the time, the intermediate transfer member needs to be driven at least one rotation or more, and may be two or more rotations. As a result, the processing efficiency at the start of the image forming process is abruptly reduced, and there is a possibility that the time from when the user issues a print output to when the print is output is prolonged.

  On the other hand, in a conventional tandem type color image forming apparatus, for example, as described in Patent Document 2, a black toner image forming unit is generally arranged upstream of a color toner image forming unit. Met.

  However, when the black toner image forming unit is arranged on the most upstream side as described above, the density of the color toner image serving as the background is detected and the density is controlled, as in the case of using the single photoconductor described above. Further, it is necessary to drive the intermediate transfer member at least once or more before the density detection of the black toner image is performed. The processing efficiency at the start of the image forming process is drastically reduced, and the user instructs print output. Inconveniences such as prolonging the time from print to print output may occur.

  By the way, conventionally, in a tandem type color image forming apparatus, there is a possibility that a transfer position shift between colors, that is, a color shift, occurs due to a light scan position shift in each light scan apparatus, and the image quality deteriorates. It was. Therefore, a color misregistration is detected by forming a predetermined color misregistration detection pattern (registon pattern) on the intermediate transfer body immediately after power-on or before image forming processing and detecting the position of the resist pattern. There has been proposed a technique for performing correction to eliminate the problem.

  That is, a color image forming apparatus is required to accurately perform both density detection and color misregistration detection of each color toner image.

However, in order to accurately perform the above two detections with a single color image forming apparatus, it is necessary to have a density detection mechanism and a color misregistration detection mechanism, leading to an increase in size and cost of the apparatus. There was concern.
JP-A-7-168401 JP-A-6-289670

  The present invention has been made to solve the above-described problems, and is capable of efficiently performing detection of image displacement and detection of image density while avoiding an increase in size and cost of the apparatus. It is an object of the present invention to provide a method for detecting misregistration and image density and a color image forming apparatus.

  In order to achieve the above object, an image positional deviation and image density detection method according to a first invention corresponding to the first aspect of the invention is an intermediate method in which the image is conveyed in a predetermined conveyance direction along a predetermined circulation path. In a color image forming apparatus for forming a black toner image and a color toner image on a transfer body, each color registration pattern for image position detection is formed on the intermediate transfer body, and a positional deviation of each color registration pattern is detected by a sensor. Image position shift detection processing and image density detection processing in which a color toner image is formed on the intermediate transfer member, a black toner image is formed on the color toner image, and the density of each color toner image is detected by a sensor. An image position deviation and image density detection method, wherein the image position deviation detection process is executed on an odd number of turns from the start of conveyance of the intermediate transfer member, and the intermediate transfer is performed. The even-th revolution from the conveyance start of the body, using the same sensors and the image position deviation detecting operation, and executes the image density detection processing, characterized in that.

  According to a second aspect of the present invention corresponding to the second aspect of the present invention, there is provided a method for detecting an image positional deviation and an image density, wherein a black toner image is formed on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path. And a color image forming apparatus for forming a color toner image, a series of image forming processes for forming a regicon pattern of a predetermined color on the intermediate transfer member and forming a toner image of the color on the intermediate transfer member. The process is performed for each color in a predetermined color order with black as the last, and the positional shift of the resister pattern of each color and the density of the toner image of each color are detected by the same sensor.

  According to a third aspect of the invention corresponding to the third aspect of the invention, there is provided a method for detecting an image misregistration and an image density, wherein a black toner image is formed on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path. And a color image forming apparatus for forming a color toner image, a regicon pattern of a predetermined color near one end in the width direction of the intermediate transfer member, and a toner image of the color near the other end, respectively. The image forming process to be formed simultaneously is executed for each color in a predetermined color order with black as the last, and the positional deviation of each color resist pattern and the density of the toner image of each color are the same sensor for each color at the same time for all colors. It detects by.

  According to a fourth aspect of the invention corresponding to the fourth aspect of the invention, there is provided a method for detecting an image misregistration and an image density, wherein a black toner image is formed on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path. And a color image forming apparatus for forming a color toner image, wherein a regicon pattern of a predetermined color is formed near both ends in the width direction of the intermediate transfer member, and a toner image of the color is formed simultaneously near the center. The formation process is executed for each color in a predetermined color order with black as the last, and the misregistration of the color resist pattern of each color and the density of the toner image of each color are detected by the same sensor simultaneously for each color and for all colors. It is characterized by that.

  According to a fifth aspect of the invention corresponding to the fifth aspect of the invention, there is provided a method for detecting an image position shift and an image density, wherein a black toner image is formed on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path. And a color image forming apparatus that forms three color toner images of cyan, magenta, and yellow. The three colors are formed from one end portion in the width direction of the intermediate transfer member to the other end portion. Among them, a first color register pattern, a second color register pattern, a first color register pattern, and a second color register pattern are simultaneously formed, and one end in the width direction of the intermediate transfer member. A third color registration pattern, a black registration pattern, a third registration pattern, and a black registration pattern are formed simultaneously from the vicinity of one portion to the other end, and the width of the intermediate transfer member Over from the vicinity of one end of the direction to the vicinity the other end to form a toner image of each color at the same time, to detect the concentration of the positional deviation and the respective color toner images of each color registration control pattern, characterized in that.

  In order to achieve the above object, a color image forming apparatus according to a sixth aspect of the invention corresponding to the seventh aspect of the invention includes an intermediate transfer member that is transported in a predetermined transport direction along a predetermined circulation path, and a photosensitive member. A color toner image and a resister pattern are formed on the photoreceptor, and the color toner image and the resister pattern are formed on the intermediate transfer member by transferring the formed color toner image and the resister pattern to the intermediate transfer member. A color image forming unit that is disposed downstream of the color image forming unit in the transport direction and includes a photoconductor, and a black toner image and a resister pattern are formed on the photoconductor, and the formed black toner image and the resister pattern are formed A black image forming unit that forms a black toner image and a resist pattern on the intermediate transfer member by transferring the toner image to the intermediate transfer member; Detecting means for detecting a density of a toner image of each color formed on the intermediate transfer member and detecting a positional deviation of a registration control pattern of each color formed on the intermediate transfer member; and On the odd-numbered circumference from the start of conveyance of the transfer body, the color image forming means and the black image forming means form a color resist pattern of each color on the intermediate transfer body, and the detection means detects a positional shift of the color resist pattern of each color. In the even number of turns, a color toner image is formed on the intermediate transfer member by the color image forming unit, a black toner image is formed on the intermediate transfer member by the black image forming unit, and the toner of each color is formed by the same detection unit. And fourth control means for controlling to detect the density of the image.

  A color image forming apparatus according to a seventh aspect of the invention corresponding to the eighth aspect of the invention includes an intermediate transfer member that is conveyed in a predetermined conveyance direction along a predetermined circulation path, and a photosensitive member, and the photosensitive member. A color image forming means for forming a color toner image and a resister pattern on the body, and forming the color toner image and the resister pattern on the intermediate transfer member by transferring the formed color toner image and the resister pattern to the intermediate transfer member; And a photosensitive member disposed on the downstream side in the transport direction with respect to the color image forming means, forming a black toner image and a resister pattern on the photosensitive member, and forming the formed black toner image and the resister pattern on the intermediate transfer member. A black image forming unit that forms a black toner image and a resiston pattern on the intermediate transfer member by transferring, and is disposed in the vicinity of the circulation path; Detecting means for detecting the density of the toner image of each color formed on the intermediate transfer member, and detecting a positional shift of the registration control pattern of each color formed on the intermediate transfer member; the color image forming means; and the black image A series of image forming processes in which a regicon pattern of a predetermined color is formed on the intermediate transfer member and a toner image of the color is formed on the intermediate transfer member by an image forming unit is performed in a predetermined color order with black as the last. And a fifth control unit that performs the control for each color and controls the same detection unit to detect the positional deviation of the registration control pattern of each color and the density of the toner image of each color.

  A color image forming apparatus according to an eighth aspect of the invention corresponding to the ninth aspect of the invention includes an intermediate transfer body that is transported in a predetermined transport direction along a predetermined circulation path, and a photoconductor. A color image forming means for forming a color toner image and a resister pattern on the body, and forming the color toner image and the resister pattern on the intermediate transfer member by transferring the formed color toner image and the resister pattern to the intermediate transfer member; And a photosensitive member disposed on the downstream side in the transport direction with respect to the color image forming means, forming a black toner image and a resister pattern on the photosensitive member, and forming the formed black toner image and the resister pattern on the intermediate transfer member. A black image forming means for forming a black toner image and a resiston pattern on the intermediate transfer member by transferring, and along the width direction of the intermediate transfer member; Each of the toner images of each color formed on the intermediate transfer body is detected near the end of the circumference path near the edge, and the misregistration of the color resist pattern of each color formed on the intermediate transfer body is detected. By the detecting means, the color image forming means, and the black image forming means, a regicon pattern of a predetermined color is provided near one end in the width direction of the intermediate transfer member, and a toner image of the color is provided near the other end. The image forming process for forming each color is executed for each color in a predetermined color order with black as the last, and the misregistration pattern of each color and the density of the toner image are the same for each color simultaneously and for all colors. And sixth control means for controlling to detect by the detection means.

  A color image forming apparatus according to a ninth aspect of the invention corresponding to the tenth aspect includes an intermediate transfer member that is conveyed in a predetermined conveyance direction along a predetermined circulation path, and a photoconductor, A color image forming means for forming a color toner image and a resister pattern on the body, and forming the color toner image and the resister pattern on the intermediate transfer member by transferring the formed color toner image and the resister pattern to the intermediate transfer member; And a photosensitive member disposed on the downstream side in the transport direction with respect to the color image forming means, forming a black toner image and a resister pattern on the photosensitive member, and forming the formed black toner image and the resister pattern on the intermediate transfer member. A black image forming means for forming a black toner image and a resiston pattern on the intermediate transfer member by transferring, and a width direction of the intermediate transfer member; The positions of the regicon patterns of the respective colors formed on the intermediate transfer body by detecting the density of the toner images of the respective colors formed on the intermediate transfer body, which are respectively arranged in the vicinity of the circular path near the both ends and the center. By the detecting means for detecting deviation, the color image forming means, and the black image forming means, a regicon pattern of a predetermined color is provided near both ends in the width direction of the intermediate transfer member, and a toner image of the color is provided near the center. The image forming process for forming each color is executed for each color in a predetermined color order with black as the last, and the misregistration of the color resist pattern of each color and the density of the toner image of each color are simultaneously adjusted for each color and for all colors. And seventh control means for controlling so as to be detected by the same detection means.

  Next, in the image displacement and image density detection method according to the first aspect of the present invention, a black toner image and a color toner image are formed on the intermediate transfer member that is conveyed in a predetermined conveyance direction along a predetermined circulation path. In a color image forming apparatus, an image misregistration detection process for forming a resist pattern for each color for image position detection on an intermediate transfer member and detecting a misregistration of the resist pattern for each color by a sensor, and a color toner image as an intermediate transfer member An image density detection process is performed in which a black toner image is formed on the color toner image formed thereon and the density of each color toner image is detected by a sensor.

  Here, in the first invention, the image misregistration detection process is executed on the odd-numbered rounds from the start of the conveyance of the intermediate transfer member, and the same as the image misregistration detection process on the even-numbered cycles from the start of the conveyance of the intermediate transfer member. Image density detection processing is executed using the sensor.

  As described above, the image misregistration detection process and the image density detection process are executed using the same sensor, so that an increase in size and cost of the apparatus can be avoided.

  In addition, since the image misalignment detection process is executed in the first cycle (the first round of the intermediate transfer member), for example, the image misalignment detected in the image misalignment detection process in the first cycle is corrected. Thereafter, the image density detection process can be executed in the next cycle (the second turn of the intermediate transfer member) in a state where the image position deviation is corrected. Thereby, it can be avoided that the image density detection process is executed in a state where there is an image position shift.

  By the way, the misregistration of the color resist pattern of each color can be detected as follows. For example, when a predetermined amount of light is irradiated to the formation part of each color resiston pattern in the intermediate transfer body, the amount of reflected light suddenly increases and the predetermined threshold value is considered as the boundary part of the resister pattern, The displacement of the resist pattern is detected based on the amount of displacement of the detection position from the design position of the boundary (details will be described later with reference to FIG. 23).

  The black regicon pattern is desirably formed so as to overlap the color toner image previously formed on the intermediate transfer member. In this way, when the black regicon pattern is formed in the color toner image, the difference in diffuse reflectance between the base and the black regicon pattern becomes larger than when the black regicon pattern is formed using the intermediate transfer member as the base. Therefore, it is possible to detect the boundary portion of the black resister pattern with higher accuracy, and to detect the positional deviation with higher accuracy. This also applies to the following second to fifth inventions.

  In the first aspect of the invention, a plurality of registration control patterns of each color are formed along the width direction of the intermediate transfer member, the positions of the plurality of registration control patterns are detected, and the positional deviation of the registration control pattern can be obtained from the detection results. Thus, it is possible to obtain an accurate positional deviation amount with little error and variation.

  As the misregistration of the registration control pattern, the inclination of the entire registration control pattern (hereinafter referred to as skew), the magnification error in the width direction of the intermediate transfer member, the misalignment in the width direction of the intermediate transfer member, and the misalignment in the transport direction of the intermediate transfer member. There are four. Of these, three of the magnification error in the width direction of the intermediate transfer member, the positional shift in the width direction of the intermediate transfer member, and the positional shift in the transport direction of the intermediate transfer member are obtained based on the position detection result of the single registration control pattern. Can do.

  However, it is necessary to obtain the skew based on the position detection results of a plurality of registration control patterns arranged along the width direction of the intermediate transfer member. Therefore, it is possible to detect the skew by forming a plurality of regicon patterns for each color along the width direction of the intermediate transfer member and detecting the position.

  Next, according to a second aspect of the present invention, in a color image forming apparatus for forming a black toner image and a color toner image on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path, a regicon pattern of a predetermined color Is formed on the intermediate transfer member, and a series of image forming processes for forming a toner image of the color on the intermediate transfer member is executed for each color in a predetermined color order with black as the last.

  For example, first, a yellow regicon pattern and a yellow toner image are formed on the intermediate transfer member, then a magenta regicon pattern and a magenta toner image are formed on the intermediate transfer member, and then a cyan regicon pattern and cyan cyan image. A toner image is formed on the intermediate transfer member. Finally, a black regicon pattern and a black toner image are formed on the intermediate transfer member. Thus, for example, as shown in FIG. 26, on the intermediate transfer member 30, the resister pattern 402, the yellow toner image 404, the resister pattern 406, the magenta toner image 408, the resister pattern 410, the cyan toner image 412, the resister A pattern 414 and a black toner image 416 are sequentially formed.

  Then, the same sensor detects the positional shift of the regicon pattern of each color and the density of the toner image of each color. For example, as shown in FIG. 26, a single sensor 28 arranged in the vicinity of the conveyance path of the intermediate transfer member 30 can detect the positional deviation of each color registration pattern and the density of each color toner image.

  As described above, according to the second invention, similarly to the first invention, it is possible to avoid an increase in size and cost of the apparatus. In addition, since the positional deviation of the resist pattern is detected before the toner image density in each color, the image density can be detected in a state where the image positional deviation is corrected.

  Next, according to a third aspect of the present invention, in the color image forming apparatus for forming the black toner image and the color toner image on the intermediate transfer member conveyed in the predetermined conveyance direction along the predetermined circulation path, the width direction of the intermediate transfer member Image forming processing for simultaneously forming a resist pattern of a predetermined color near one end of the toner and a toner image of the color near the other end is performed for each color in a predetermined color order with black as the last. To do.

  For example, first, a yellow regicon pattern and a yellow toner image are simultaneously formed on the intermediate transfer member, then a magenta regicon pattern and a magenta toner image are simultaneously formed on the intermediate transfer member, and further a cyan regicon pattern, A cyan toner image is simultaneously formed on the intermediate transfer member. Finally, a black regicon pattern and a black toner image are simultaneously formed on the intermediate transfer member.

  Thus, for example, as shown in FIG. 28, the regicon patterns 422, 426, 430, 434, the yellow toner image 424, the magenta toner image 428, the cyan toner image 432, and the black toner image 436 are intermediately transferred. Formed on the body 30.

  Then, the misregistration of each color resist pattern and the density of the toner image of each color are detected by the same sensor simultaneously for each color and for all colors. For example, in the case of FIG. 28, the positional deviation of the registration control pattern is detected by the same sensor 28A, and the density of the toner image of each color is detected by the same sensor 28B.

  The positional deviation of the registration control pattern and the density of the toner image may be detected by separate sensors 28A and 28B as shown in FIG. 28, or a single line whose detection target is the entire width direction of the intermediate transfer member. You may detect with a sensor.

  In this way, it is possible to improve the efficiency of the detection process by simultaneously detecting the misregistration of the color resist pattern of each color and the density of the toner image of each color for each color. Increase in size and cost can be avoided.

  Next, according to a fourth aspect of the present invention, in the color image forming apparatus for forming the black toner image and the color toner image on the intermediate transfer member conveyed in the predetermined conveyance direction along the predetermined circulation path, the width direction of the intermediate transfer member An image forming process for simultaneously forming a regicon pattern of a predetermined color in the vicinity of both ends and a toner image of the color in the vicinity of the center is executed for each color in a predetermined color order with black as the last.

  For example, first, a yellow regicon pattern is formed near both ends of the intermediate transfer member, and a yellow toner image is formed simultaneously near the center portion of the intermediate transfer member, and then a magenta regicon pattern is formed near both ends of the intermediate transfer member. A magenta toner image is simultaneously formed near the center of the intermediate transfer member.

  In addition, a cyan regicon pattern is formed near both ends of the intermediate transfer member, a cyan toner image is formed near the center of the intermediate transfer member, and finally a black regicon pattern is formed near both ends of the intermediate transfer member. A black toner image is simultaneously formed near the center of the intermediate transfer member.

  Thus, for example, as shown in FIG. 31, regicon patterns 442, 448, 450, 456, 458, 464, 466, 472 are formed near both ends of the intermediate transfer member 30, and near the center of the intermediate transfer member. Yellow toner images 444 and 446, magenta toner images 452 and 454, cyan toner images 460 and 462, and black toner images 468 and 470 are formed on the intermediate transfer body 30.

  Then, the misregistration of each color resist pattern and the density of the toner image of each color are detected by the same sensor simultaneously for each color and for all colors. For example, in the case of FIG. 31, the misregistration pattern misregistration is detected by the common sensors 28A and 28D, and the density of the toner image of each color is detected by the common sensors 28B and 28C.

  The registration pattern displacement and the toner image density may be detected by a total of four sensors 28A, 28B, 28C, and 28D as shown in FIG. 31, or the entire width of the intermediate transfer member is detected. It may be detected by one line sensor. Alternatively, detection may be performed by a line sensor whose detection target is one side from the central portion in the width direction of the intermediate transfer member and a line sensor whose detection target is the other side.

  In this way, it is possible to improve the efficiency of the detection process by simultaneously detecting the misregistration of the color resist pattern of each color and the density of the toner image of each color for each color. Increase in size and cost can be avoided.

  In addition, since the misregistration pattern of each color and the density of the toner image of each color are detected at two locations for each color, the misregistration detection result and image density with little variation and error are obtained by averaging the detection results. A detection result can be obtained. In addition, the skew can be detected based on the detection result of the misregistration pattern detected at two locations.

  Next, in the fifth aspect of the invention, a color image formation for forming a black toner image and three color toner images of cyan, magenta, and yellow on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path In the apparatus, first, from the vicinity of one end in the width direction of the intermediate transfer member to the vicinity of the other end, the first color register pattern, the second color register pattern, The color control pattern of the second color and the color control pattern of the second color are formed at the same time, and then, from the vicinity of one end in the width direction of the intermediate transfer member to the vicinity of the other end, A pattern, a black register pattern, a third color register pattern, and a black register pattern are simultaneously formed. Then, toner images of the respective colors are formed simultaneously from the vicinity of one end in the width direction of the intermediate transfer member to the vicinity of the other end.

  For example, when the first color is yellow, the second color is magenta, and the third color is cyan, the image is formed on the intermediate transfer member 30 as shown in FIG. A row R1 in which the registration control patterns 502, 504, 506, and 508 are arranged in the width direction, a row R2 in which the registration control patterns 510, 512, 514, and 516 are arranged in the width direction, and toner images 518, 520, 522, and 524 are arranged in the width direction. A total of three rows R3 are formed.

  Then, the positional deviation of each color resist pattern and the density of each color toner image are detected by a sensor.

  In this case, the misregistration detection and the image density detection may be performed on the three rows of regicon patterns and toner images along the conveyance direction of the intermediate transfer member, and at least as in the fourth to seventh inventions. The time required for detection can be shortened as compared with the case where detection is performed on four or more rows of resister patterns and toner images.

  By the way, the color image forming apparatus according to the sixth invention can be cited as a color image forming apparatus that performs the detection process based on the image displacement and image density detecting method according to the first invention.

  The color image forming apparatus according to the sixth aspect of the present invention includes a photoconductor, forms a color toner image and a resiston pattern on the photoconductor, and transfers the formed color toner image and the resiston pattern to an intermediate transfer member. A color image forming unit for forming a color toner image and a resister pattern on the intermediate transfer member, and a photoconductor disposed on the downstream side in the transport direction with respect to the color image forming unit. There is provided black image forming means for forming a black toner image and a resister pattern on the intermediate transfer member by forming a pattern and transferring the formed black toner image and the resister pattern to the intermediate transfer member.

  The fourth control unit forms a color resist pattern of each color on the intermediate transfer member by the color image forming unit and the black image forming unit on the odd-numbered circumference from the start of conveyance of the intermediate transfer member, and the detection unit sets the resist pattern of each color. Control to detect misalignment.

  The fourth control unit forms a color toner image on the intermediate transfer member by the color image forming unit and the black toner on the intermediate transfer member by the black image forming unit at an even number of turns from the start of conveyance of the intermediate transfer member. An image is formed, and control is performed so as to detect the density of each color toner image by the same detection means as that at the time of detecting the displacement.

  As described above, the image misregistration detection process and the image density detection process are executed using the same sensor, so that an increase in size and cost of the apparatus can be avoided. In addition, since the positional deviation of the resist pattern is detected before the toner image density in each color, the image density can be detected in a state where the image positional deviation is corrected.

  Next, the color image forming apparatus according to the seventh invention can be cited as a color image forming apparatus that performs the detection processing based on the image positional deviation and image density detection method according to the second invention.

  In the color image forming apparatus according to the seventh aspect of the invention, the fifth control means forms a regicon pattern of a predetermined color on the intermediate transfer member by the color image forming means and the black image forming means, and the toner image of the color. A series of image forming processes for forming the image on the intermediate transfer member is executed for each color in a predetermined color order with black as the last. Then, the same sensor detects the positional shift of the regicon pattern of each color and the density of the toner image of each color.

  Thus, according to the seventh aspect, as in the sixth aspect, it is possible to avoid an increase in size and cost of the apparatus. In addition, since the positional deviation of the resist pattern is detected before the toner image density in each color, the image density can be detected in a state where the image positional deviation is corrected.

  Next, the color image forming apparatus according to the eighth invention can be cited as a color image forming apparatus that performs the detection processing based on the image positional deviation and image density detecting method according to the third invention.

  In the color image forming apparatus according to the eighth aspect of the present invention, the sixth control means uses the color image forming means and the black image forming means to generate a resist pattern of a predetermined color near one end in the width direction of the intermediate transfer member. The image forming process for simultaneously forming toner images of the color near the other end is executed for each color in a predetermined color order with black as the last.

  For example, first, a yellow regicon pattern and a yellow toner image are simultaneously formed on the intermediate transfer member, then a magenta regicon pattern and a magenta toner image are simultaneously formed on the intermediate transfer member, and further a cyan regicon pattern, A cyan toner image is simultaneously formed on the intermediate transfer member. Finally, a black regicon pattern and a black toner image are simultaneously formed on the intermediate transfer member. Then, the misregistration of each color resist pattern and the density of the toner image of each color are detected by the same sensor simultaneously for each color and for all colors.

  In this way, it is possible to improve the efficiency of the detection process by simultaneously detecting the misregistration of the color resist pattern of each color and the density of the toner image of each color for each color. Increase in size and cost can be avoided.

  Next, the color image forming apparatus according to the ninth aspect can be cited as a color image forming apparatus that performs the detection process based on the image positional deviation and image density detection method according to the fourth aspect.

  In the color image forming apparatus according to the ninth aspect of the present invention, the seventh control means uses the color image forming means and the black image forming means to generate a regicon pattern of a predetermined color near both ends in the width direction of the intermediate transfer member. An image forming process for simultaneously forming toner images of the color near the center is executed for each color in a predetermined color order with black as the last.

  For example, a yellow regicon pattern is first formed near both ends of the intermediate transfer member, and two yellow toner images are formed simultaneously near the central portion of the intermediate transfer member, and then magenta is formed near both ends of the intermediate transfer member. Two magenta toner images are simultaneously formed in the vicinity of the central portion of the intermediate transfer member with the regicon pattern. In addition, a cyan regicon pattern is formed near both ends of the intermediate transfer member, two cyan toner images are formed simultaneously near the center of the intermediate transfer member, and finally a black regicon pattern is formed near both ends of the intermediate transfer member. Two black toner images are formed simultaneously near the center of the intermediate transfer member.

  Then, the misregistration of each color resist pattern and the density of the toner image of each color are detected by the same sensor simultaneously for each color and for all colors.

  In this way, it is possible to improve the efficiency of the detection process by simultaneously detecting the misregistration of the color resist pattern of each color and the density of the toner image of each color for each color. Increase in size and cost can be avoided. In addition, since the misregistration pattern of each color and the density of the toner image of each color are detected at two locations for each color, the misregistration detection result and image density with little variation and error are obtained by averaging the detection results. A detection result can be obtained. In addition, the skew can be detected based on the detection result of the misregistration pattern detected at two locations.

  As described above, according to the first, second, sixth, and seventh inventions, the image misregistration detection process and the image density detection process are executed using the same sensor, so that the size of the apparatus is increased. And an increase in cost can be avoided. In addition, since the positional deviation of the resist pattern is detected before the toner image density in each color, the image density can be detected in a state where the image positional deviation is corrected.

  Further, according to the third, fourth, eighth, and ninth inventions, the detection processing efficiency is improved by simultaneously detecting the misregistration of each color resist pattern and the density of each color toner image for each color. It is possible to avoid the increase in size and cost of the apparatus by detecting all colors with the same sensor.

  According to the fifth aspect of the present invention, it is only necessary to detect misregistration and image density for the three rows of regicon patterns and toner images along the conveyance direction of the intermediate transfer member. The time required for detection can be shortened as compared with the case where detection is performed on at least four rows of regicon patterns and toner images as in the seventh aspect of the invention.

  DESCRIPTION OF EMBODIMENTS Hereinafter, various embodiments according to the present invention will be described in detail with reference to the drawings. Before describing various embodiments, a basic form of the present invention will be described.

[First basic form]
First, the first basic form of the present invention will be described.

(Configuration of color image forming apparatus)
In the following, the configuration of the color image forming apparatus according to the basic embodiment will be described first. As shown in FIG. 1, the color image forming apparatus 10 exposes and scans an image of a document 16 placed at a predetermined position on a platen glass 14 and converts it into image signal data read by a CCD sensor 13. 12 and an image forming unit 18 that forms a color image on a sheet 50 according to a procedure to be described later based on image signal data obtained by reading an image by the image reading device 12.

  Among these, the image forming unit 18 includes an image storage unit 82 that stores image signal data obtained by reading an image with the CCD sensor 13, and a process in the color image forming apparatus 10 that includes a CPU, ROM, RAM, and the like. A control unit 80 for controlling the whole is provided.

  The image forming unit 18 includes an endless belt-shaped intermediate transfer belt 30, a yellow image forming unit 20 that forms a yellow toner image on the intermediate transfer belt 30, and a magenta toner image on the intermediate transfer belt 30. A magenta image forming unit 22 that forms a cyan toner image on the intermediate transfer belt 30, and a black image forming unit 26 that forms a black toner image on the intermediate transfer belt 30. Is provided.

  Among these, the yellow image forming unit 20 is provided with a photoconductor 20C which is substantially cylindrical and rotates around the central axis in the direction of arrow A and whose outer peripheral surface is in contact with the intermediate transfer belt 30. In the vicinity of the outer peripheral surface of 20C, a charging device 20D that charges the outer peripheral surface to a predetermined potential, and modulates laser light based on image signal data, and irradiates the outer peripheral surface of the charged photoreceptor 20C with the modulated laser light. The latent image forming unit 20A that forms a latent image corresponding to the yellow component of the image, the developing device 20B that develops the latent image formed by the latent image forming unit 20A, and the development by the developing device 20B A transfer device 20F that transfers the yellow toner image to the intermediate transfer belt 30 and a cleaning device 20E that removes the toner from the outer peripheral surface of the photoreceptor 20C are provided in order along the arrow A direction. . In addition, a toner supply unit 20G that supplies yellow toner to the developing device 20B is provided in the vicinity of the developing device 20B. The laser beam from the latent image forming unit 20A is reflected by the mirror 20H and then irradiated to the outer peripheral surface of the photoreceptor 20C.

  As is clear from FIG. 1, the configurations of the other image forming units, that is, the magenta image forming unit 22, the cyan image forming unit 24, and the black image forming unit 26 are the same as those of the yellow image forming unit 20 described above. It is.

  The intermediate transfer belt 30 is a dielectric whose volume resistance is adjusted by carbon to electrostatically transfer the developed toner image. The intermediate transfer belt 30 is driven by a drive roll 32, 34, 36, 38 in a predetermined direction (an arrow between the drive rolls 32, 38). B direction). Here, the peripheral length of the intermediate transfer belt 30 is 1920 mm as an example, and the conveyance speed (process speed) of the intermediate transfer belt 30 is 160 mm / second. For this reason, the intermediate transfer belt 30 rotates in 12 seconds.

  Above the intermediate transfer belt 30, the four image forming units are arranged in the order of the arrow B in the order of the yellow image forming unit 20, the magenta image forming unit 22, the cyan image forming unit 24, and the black image forming unit 26. A density detector 28 is provided downstream of the black image forming unit 26 in the direction of arrow B.

  On the other hand, on the upstream side in the arrow B direction with respect to the yellow image forming unit 20, an adsorption roll 40 that maintains the surface potential of the intermediate transfer belt 30 at a predetermined potential in order to improve the toner adsorption property of the intermediate transfer belt 30. A cleaning device 42 that removes toner from the transfer belt 30 and a reference position detection sensor 44 that detects a reference position in the intermediate transfer belt 30 are sequentially provided.

  On the upper surface of the color image forming apparatus 10, an operation unit 84 is provided that includes a display 84A for displaying messages and the like, and a keyboard 84B for an operator to input various commands and the like.

  A paper storage unit 54 that stores paper 50 is provided below the image forming unit 18, and the uppermost paper 50 in the paper storage unit 54 is sent out to a predetermined paper transport path by a feed roll 52. The fed paper 50 is conveyed on the paper conveyance path by conveyance rollers 55, 56, and 58 and reaches the vicinity of the intermediate transfer belt 30. A transfer roll 60 is provided on the sheet conveyance path so as to be opposed to the conveyance roll 36 with the intermediate transfer belt 30 interposed therebetween. When the sheet 50 is conveyed through the nipping portion between the conveyance roll 36 and the transfer roll 60, an intermediate position is provided. A color image formed on the transfer belt 30 (a color image forming process will be described later) is transferred to the paper 50.

  The transferred paper 50 is transported to the fixing device 46 by the transport roll 62, subjected to fixing processing by the fixing device 46, and then discharged to the paper tray 64.

  Incidentally, as shown in FIG. 9A, the detection position by the density detection unit 28 and the transfer position 26G of the black toner image by the black image forming unit 26 are set at an interval of 100 mm. The black toner image transfer position 26G by the black image forming unit 26, the cyan toner image transfer position 24G by the cyan image forming unit 24, the magenta toner image transfer position 22G by the magenta image forming unit 22, and the yellow image forming unit. The yellow toner image transfer positions 20G by 20 are set at an interval of 196 mm. Further, the transfer position 20G of the yellow toner image and the detection position by the reference position detection sensor 44 are set at an interval of 320 mm along the circumferential conveyance path of the intermediate transfer belt 30.

  In addition, the ROM in the control unit 80 is used to adjust the density detection value of each color of YMCK so that it is within the reference range, and to the developing device according to the amount of deviation of the density detection value of each color of YMCK from the reference range. Information on the adjustment amount of the toner supply amount is stored in advance.

(Configuration related to concentration detection)
By the way, as shown in FIG. 2, an LED 70 is provided in the vicinity of the density detection unit 28, and the density detection unit 28 detects the amount of reflected light emitted from the LED 70 onto the detection target surface. The density of the detection target is detected from the amount of reflected light. In addition, as LED70, the infrared type LED which inject | emits the laser beam of the wavelength (900 nm-1200 nm) of an infrared region is used, The reason is demonstrated below.

  3A shows the yellow spectral sensitivity characteristic in the visible region, and FIG. 3B shows the yellow spectral sensitivity property in the infrared region. As is clear from these figures, the yellow spectral sensitivity characteristic is shown in FIG. It can be seen that 95% or more is reflected at wavelengths in the infrared region (900 nm to 1200 nm). Similarly, as shown in FIGS. 4A and 4B showing the spectral sensitivity characteristics of magenta and FIGS. 5A and 5B showing the spectral sensitivity characteristics of cyan, the magenta and cyan colors are clear. It can be seen that both reflect at 95% or more at wavelengths in the infrared region (900 nm to 1200 nm).

  On the other hand, since the spectral sensitivity characteristic of the intermediate transfer belt 30 serving as the background of the density detection target image is about 10 to 20%, light is emitted between the underlying intermediate transfer belt 30 and each color toner image at wavelengths in the infrared region. The difference in reflectance (that is, the difference ΔRY, ΔRM, ΔRC in the amount of reflected light when a predetermined amount of light shown in FIG. 7 is irradiated) becomes large, and the density of each color toner image can be detected with high accuracy. In order to realize such accurate concentration detection, an infrared type LED that emits laser light having a wavelength in the infrared region (900 nm to 1200 nm) was used as the LED 70.

  6A and 6B showing the black spectral sensitivity characteristics, black has a spectral sensitivity characteristic of 10% or less in the region of 350 nm to 1200 nm, and the intermediate transfer belt 30 and the black toner. Since the difference in light reflectance from the image is small, it is difficult to accurately detect the density of the black toner image using the intermediate transfer belt 30 as a base.

  Therefore, in this basic form, as shown in FIG. 7, a black toner image 86 is formed on a part of the color toner image 88 formed on the intermediate transfer belt 30, and the black toner image 88 is used as a background. A concentration of 86 is detected. As a result, the difference in light reflectance between the underlying color toner image 88 (yellow toner image as an example in FIG. 7) and the black toner image 86 (that is, the amount of reflected light when irradiated with the predetermined amount of light shown in FIG. 7). The difference ΔRK) becomes large, and the density of the black toner image 86 can be detected with high accuracy.

  In this basic mode, the YMC color toner image and the black toner image are respectively formed in regions on both sides along the width direction of the intermediate transfer belt 30. For this reason, a pair of density detectors 28 and LEDs 70 shown in FIG. 2 are also provided.

(Overview of color image formation processing)
Next, an outline of the color image forming process executed in the color image forming apparatus 10 will be described with reference to the flowchart of FIG. Note that the color image forming process described below is executed by the control unit 80.

  First, in step 100 of FIG. 8, the image reading device 12 reads an image of the document 16 placed at a predetermined position on the platen glass 14 by the CCD sensor 13, and in the next step 102, the reading of step 100 is performed. The image signal data obtained in the above is converted into YMCK color image signals.

  Then, in the next step 104, in each of the black image forming unit 26, the cyan image forming unit 24, the magenta image forming unit 22, and the yellow image forming unit 20, each color toner image based on the image signal of each color is as follows. Are formed on the photoreceptor of each forming portion. For example, in the yellow image forming unit 20, the surface of the photoreceptor 20C rotating in the direction of arrow A is charged to a predetermined potential by the charging device 20D, and the laser is modulated on the charged surface by the yellow image signal by the latent image forming unit 20A. By irradiating light, a latent image corresponding to the yellow component of the image is formed. The latent image is developed by the developing device 20B to be visualized as a yellow toner image. In the image forming units other than the yellow image forming unit 20, similarly, a toner image of each color or a black toner image is formed on the photoreceptor of each image forming unit.

  In the next step 106, the intermediate transfer belt 30 is conveyed, and the toner images of the respective colors are transferred onto the intermediate transfer belt 30 so as to form a target color image.

  Specifically, a yellow toner image is first transferred to the intermediate transfer belt 30 rotating in the direction of arrow A in FIG. 1 by the transfer device 20F of the yellow image forming unit 20 on the most upstream side in the direction of arrow B in FIG. Is done. Since the intermediate transfer belt 30 is conveyed in the direction of arrow B between the drive rollers 32 and 38 where the toner image is transferred by the image forming units to the intermediate transfer belt 30, the intermediate transfer belt 30 used below is used. The conveying direction of FIG. 1 means the direction of arrow B in FIG.

  Then, the magenta toner image is transferred onto the yellow toner image forming portion of the intermediate transfer belt 30 by the transfer device of the magenta image forming portion 22. Thereafter, similarly, a cyan toner image is transferred by the transfer device of the cyan image forming unit 24, and a black toner image is transferred by the transfer device of the black image forming unit 26 in order. Thus, the four color toner images of YMCK are transferred onto the intermediate transfer belt 30 so as to form a target color image on the intermediate transfer belt 30.

  In the next step 108, the color image formed on the intermediate transfer belt 30 as described above is transferred by the transfer roll 60 to the paper 50 that has been transported along a predetermined paper transport path. As a result, a target color image is formed on the paper 50.

  In the next step 110, as post-processing, the paper 50 on which the color image has been formed is discharged to the paper tray 64, the toner on the intermediate transfer belt 30 is removed by the cleaning device 42, and the cleaning device for each image forming unit. The toner on each photoconductor is removed by the above, and the process is terminated.

  Through the color image forming process as described above, the image of the document 16 is formed on the paper 50, and the paper 50 on which the image is formed can be obtained.

  Note that the image signal data to be converted into the YMCK color image signals in step 102 is not limited to the image signal data obtained by reading the document with the image reading device 12 in step 100, and the image signal data in advance. It may be image signal data that has been read by the reading device 12 and stored in the image storage unit 82, or image signal data that is input from an external image reading device via a communication line (not shown).

(Operation of the first basic form)
Next, as the operation of the first basic form, the density adjustment processing for the black image according to the present invention among the density adjustment processing for each color of YMCK will be described with reference to the flowchart of FIG. This density adjustment processing is executed under the control of the control unit 80 when the color image forming apparatus 10 is turned on and at a predetermined time interval. Of course, even when the installation environment of the color image forming apparatus 10 changes suddenly, it is desirable that the operator manually execute the density adjustment process. For example, the temperature changes by 3 degrees or more after the previous density adjustment process is executed. It is desirable to execute the density adjustment process when the humidity has changed or when the humidity has changed by 20% or more.

  In step 120 of FIG. 10, the conveyance rolls 32, 34, 36, and 38 are driven to start conveyance of the intermediate transfer belt 30 in the arrow B direction. In the next step 122, the black image forming unit 26, the cyan image forming unit 24, the magenta image forming unit 22, and the yellow image forming unit 20 are based on image signal data of a pattern image to be described later stored in advance in the image storage unit 82. Each YMCK pattern image is formed on each photoconductor. Here, for each YMC color, a 15 mm × 15 mm square pattern image with an image signal density of 50% (hereinafter referred to as Cin = 50%) and a 20 mm × 20 mm square pattern image with Cin = 100% are formed. For black, a square pattern image of 15 mm × 15 mm with Cin = 50% is formed.

  Note that the image signal data of the pattern image may not be stored in the image storage unit 82 in advance, and image signal data of the pattern image supplied from a pattern generator (not shown) may be used.

  In the next step 124, the yellow image forming unit 20, the magenta image forming unit 22, and the cyan image forming unit 24 (hereinafter, these three are collectively referred to as a color image forming unit) 15 mm × Cin = 50% of each color of YMC. By transferring a 15 mm square pattern image from each photoconductor to the intermediate transfer belt 30, a YMC square pattern image is formed on the intermediate transfer belt 30. Hereinafter, a square pattern image of Cin = 50% of the color (any of YMC) formed on the intermediate transfer belt 30 is referred to as a 50% color density patch.

  Note that the formation timing of the 50% density patch on the intermediate transfer belt 30 in steps 122 and 124 is determined by the reference position sensor 44 using the reference mark of the intermediate transfer belt 30 (for example, # 850 polyester silver color manufactured by Sumitomo 3M Limited). ) Is detected by the yellow image forming unit 20 after 2.0 seconds (= distance 320 mm between the reference position sensor 44 and the yellow toner image transfer position 20G ÷ process speed 160 (mm / second)). Control is performed so that the yellow 50% density patch is transferred to the intermediate transfer belt 30.

  Thereafter, as shown in FIG. 9B, the magenta 50% density patch is spaced from the yellow 50% density patch by a distance of 5 mm by the magenta image forming unit 22, and the magenta color by the cyan image forming unit 24. A cyan 50% density patch is formed on the intermediate transfer belt 30 with a space of 5 mm from the 50% density patch.

  In the next step 126, when the 50% density patch of each color of YMC shown in FIG. 9B reaches the detection position of the density detection unit 28, each density is detected by the density detection unit 28. As described above, a pair of 50% density patches of each color of YMC is formed, and the density is detected by the density detection unit 28 for each of them. The two density detection values here are added and averaged in order to reduce the detection error, and this added average value is used as a density detection value in the subsequent determination processing and the like.

  In the next step 130, it is determined whether or not all the detected density values of the 50% density patches of each color of YMC are within a predetermined reference range. As the reference range here, for example, when the density is detected by an output voltage correlated with the amount of light reflected from the target density patch, a range of 1 V to ± 0.2% corresponding to 50% density may be adopted. it can.

  Here, if any one of the detected density values of each color of YMC is not within the reference range, the process proceeds to step 132, and it is determined whether or not all detected density values of each color of YMC are out of the reference range. If all the detected density values of each color of YMC are outside the reference range, the process proceeds to step 134, and the adjustment amount of the toner supply amount corresponding to the deviation amount of the detected density value of each color from the reference range is set in the ROM in the control unit 80. The toner supply amount by the toner supply unit is adjusted by the adjustment amount in each color image forming unit. Then, the process returns to step 122, and a pattern image is formed again by each adjusted color image forming unit.

  On the other hand, if at least one of the density detection values of each color of YMC is within the reference range in step 132, the process proceeds to step 136, and the color image formation in which the density detection value of the formed color density patch is out of the reference range. As with step 134, the toner supply amount is adjusted by the toner supply unit.

  After the adjustment in step 136 is completed, and if all the density detection values of each color of YMC are within the reference range in step 130, the process proceeds to step 138, and the color density where the density detection value is within the reference range. By transferring a 20 mm × 20 mm square pattern image of Cin = 100% of the color to the intermediate transfer belt 30 by the color image forming unit of the same color as the patch, the square pattern of the color is transferred onto the intermediate transfer belt 30. Form an image. Hereinafter, a square pattern image of Cin = 100% of the color (any of YMC) formed on the intermediate transfer belt 30 is referred to as a 100% color density patch.

  Specifically, as shown in FIG. 9 (B), a 100% density patch of magenta color is spaced from a yellow 100% density patch with an interval of 5 mm, and an interval of 5 mm is spaced from the 100% density patch of magenta color. A 100% density patch of cyan color is formed on the intermediate transfer belt 30.

  In the next step 140, as shown in FIG. 9B, a black Cin = 50% 15 mm × 15 mm square pattern image is superimposed and transferred onto the 100% density patch of each color by the black image forming unit 26. Thus, a black square pattern image is formed on the intermediate transfer belt 30 (however, FIG. 9B shows an example in which the density detection values of each color of YMC are all within the reference range). Hereinafter, the black square pattern image formed on the intermediate transfer belt 30 is referred to as a black density patch.

  In the next step 142, when the black density patch reaches the detection position of the density detection unit 28, the density is detected by the density detection unit 28. A pair of black density patches is also formed in the same manner as the density patches for each color of YMC, and the density is detected by the density detection unit 28 for each. The two density detection values here are added and averaged in order to reduce detection errors, and this added average value is used as a density detection value in subsequent determination processing and the like.

  In the next step 144, it is determined whether or not the density detection value of the black density patch is within a predetermined reference range. As the reference range here, for example, when the density is detected by an output voltage correlated with the amount of light reflected from the target density patch, a range of 1 V to ± 0.2% corresponding to 50% density may be adopted. it can.

  In this basic mode, as an example, as the density detection value of the black density patch to be determined in step 144, the density detection value of the black density patch based on the yellow 100% density patch, the 100% density of magenta color It is assumed that the density detection value of the black density patch with the patch as the background and the density detection value of the black density patch with the cyan 100% density patch as the background are used with priority. That is, from the spectral sensitivity characteristics of FIGS. 3B, 4B, and 5B, yellow, magenta, and black are used as the background of the black toner image in terms of the high reflectance and its stability. Since the colors are suitable in the order of cyan, the priority order as described above is adopted.

  If the black density detection value is not within the reference range, the process proceeds to step 146, where the toner supply amount adjustment amount corresponding to the deviation amount of the density detection value from the reference range is read from the ROM in the control unit 80, and the black color is detected. In the image forming unit 26, the toner supply amount by the toner supply unit is adjusted by the adjustment amount.

  After such adjustment is completed and if the black density detection value is within the reference range in step 144, the process proceeds to step 148 to inform the display 84A of the operation unit 84 that the black image density adjustment processing has been completed. As a post-processing, the toner on the intermediate transfer belt 30 is removed by the cleaning device 42 and the toner on each photoconductor is removed by the cleaning device of each image forming unit, and the conveyance of the intermediate transfer belt 30 is stopped. Then, the process ends.

  After determining that the density detection values of all the color density patches are out of the reference range in step 132 and completing the adjustment of each color image forming unit in step 134, the process returns to steps 122 and 124, and FIG. As shown in FIG. 9, color density patches (described as C complement, M complement, and Y complement in FIG. 9C) are formed again by each adjusted color image forming unit, and color density patches are executed in steps 126 to 132. The density detection and determination are performed again.

  According to the first basic form described above, since the black image forming unit 26 is disposed downstream of the color image forming unit in the conveyance direction of the intermediate transfer belt 30, the color density patch on the intermediate transfer belt 30 is formed. The portion (color density patch forming portion) reaches the black image forming portion 26 before the intermediate transfer belt 30 makes a half turn.

  For this reason, since the color density patch forming unit reaches the black image forming unit 26 earlier than the conventional case where the black image forming unit 26 is arranged on the upstream side of the color image forming unit in the transport direction. It is possible to quickly form a black density patch on the color density patch and quickly perform density detection of the black density patch, density adjustment of a black image, and the like. This makes it possible to efficiently execute the black image density adjustment processing.

[Second basic form]
Next, the second basic form will be described. The configuration of the color image forming apparatus 10 in the second basic form is different from the first basic form in that a density detection unit 28 is provided for each image forming unit, as shown in FIG.

  That is, the density detection unit 28K corresponding to the black image forming unit 26, the density detection unit 28C corresponding to the cyan image forming unit 24, and the density detection unit 28M corresponding to the magenta image forming unit 22 form the yellow image. Corresponding to the unit 20, the density detection unit 28 </ b> Y is installed on the downstream side in the conveyance direction (arrow B direction) of the intermediate transfer belt 30. Further, the detection position by each density detection unit and the transfer position by the corresponding image forming unit are set at an interval of 100 mm (for example, 100 mm between the detection position by the density detection unit 28Y and the transfer position 20G of the yellow toner image). Set to). Since the configuration other than the above is the same as that of the first basic mode, the description thereof is omitted.

(Operation of the second basic form)
Next, as an operation of the second basic mode, a black image density adjustment process will be described with reference to the flowchart of FIG. The execution timing of the density adjustment process in the second basic form is the same as the execution timing of the density adjustment process in the first basic form. In the flowchart of FIG. 12, the same step numbers are assigned to the same processing steps as those of the flowchart of FIG. 10 described above, and detailed description of the processing steps is omitted.

  In step 120 of FIG. 12, the conveyance rollers 32, 34, 36, and 38 are driven to start conveyance of the intermediate transfer belt 30 in the direction of arrow B. In the next step 122, the image is stored in advance in the image storage unit 82. Based on image signal data of a pattern image to be described later, the following YMCK pattern images are formed on each photoconductor in each image forming unit. Here, a 20 mm × 20 mm square pattern image of Cin = 100% is formed for each color of YMC, and a 15 mm × 15 mm square pattern image of Cin = 50% is formed for black.

  In the next step 123, each color image forming unit transfers a 20 mm × 20 mm square pattern image of Cin = 100% of each color of YMC from each photoconductor to the intermediate transfer belt 30, so that the YMC is transferred onto the intermediate transfer belt 30. A square pattern image (100% color density patch) of each color is formed, and in the next step 126, the density of the 100% density patch of each color of YMC is detected by the density detection unit 28 corresponding to each color image forming unit. That is, the density of the yellow color density patch is detected by the density detector 28Y, the density of the magenta color density patch is detected by the density detector 28M, and the density of the cyan color density patch is detected by the density detector 28C. In the second basic mode, since the density detection unit 28 is installed on the downstream side in the transport direction of the intermediate transfer belt 30 with respect to each image forming unit, after the 100% color density patch of each color is formed in step 123, immediately. Density detection can be performed by the density detection unit 28 corresponding to each color image forming unit.

  In the next step 130, it is determined whether or not all the detected density values of the 100% density patch for each color of YMC are within a predetermined reference range. As the reference range here, for example, when the density is detected by an output voltage correlated with the amount of light reflected from the target density patch, a range of 2 V to ± 0.2% corresponding to 100% density may be adopted. it can.

  Here, if any one of the detected density values of each color of YMC is not within the reference range, the process proceeds to step 132, and it is determined whether or not all detected density values of each color of YMC are out of the reference range. If all the detected density values of each color of YMC are outside the reference range, the process proceeds to step 134, and the adjustment amount of the toner supply amount corresponding to the deviation amount of the detected density value of each color from the reference range is set in the ROM in the control unit 80. The toner supply amount by the toner supply unit is adjusted by the adjustment amount in each color image forming unit. Then, the process returns to step 122, and a pattern image is formed again by each adjusted color image forming unit.

  On the other hand, if at least one of the density detection values of each color of YMC is within the reference range in step 132, the process proceeds to step 136, and the color image formation in which the density detection value of the formed color density patch is out of the reference range. As with step 134, the toner supply amount is adjusted by the toner supply unit.

  After the adjustment in step 136 is completed, and if the density detection values of each color of YMC are all within the reference range in step 130, the process proceeds to step 139, and as shown in the lower part of FIG. On the intermediate transfer belt 30, a black image forming unit 26 transfers a black Cin = 50% 15 mm × 15 mm square pattern image onto the color density patch whose density detection value was within the reference range. A black density patch is formed.

  In this way, in the second basic form, as shown in FIG. 11B, a black density patch is formed on the color density patch that is the target of density detection in step 126, and the black density patch is formed in the next step 142. When the detection position of the concentration detector 28K is reached, the concentration is detected by the concentration detector 28K. However, FIG. 11B shows an example in which the density detection values of each color of YMC are all within the reference range.

  Thereafter, as in the first basic mode, it is determined whether or not the density detection value of the black density patch is within a predetermined reference range (step 144). If the density detection value of black is within the reference range, If not, the adjustment amount of the toner supply amount corresponding to the deviation amount of the density detection value from the reference range is read from the ROM in the control unit 80, and the toner supply amount by the toner supply unit in the black image forming unit 26 is set to the adjustment amount. Only the adjustment is made (step 146).

  Then, after the completion of such adjustment and if the black density detection value is within the reference range in step 144, the fact that the black image density adjustment processing has been completed is displayed on the display 84A of the operation unit 84. As post-processing, the toner on the intermediate transfer belt 30 is removed by the cleaning device 42 and the toner on each photoconductor is removed by the cleaning device of each image forming unit, and the conveyance of the intermediate transfer belt 30 is stopped ( Step 148), the process ends.

  Note that, after the density detection values of all color density patches are determined to be out of the reference range in step 132 and the adjustment of each color image forming unit is completed in step 134, the process returns to steps 122 and 123, and FIG. As shown in FIG. 11, each adjusted color image forming unit forms a color density patch (described as “Y” in FIG. 11C) again, and the density detection and determination of the color density patch are performed in steps 126 to 132. Try again.

  In the second basic form described above, since the density detector 28 is disposed downstream of the intermediate transfer belt 30 in the conveyance direction with respect to each image forming unit, after forming the 100% color density patch of each color as a base, the speed is quickly determined. In addition, it is possible to detect the density of the color density patch, and to form a black density patch on the color density patch that is the target of density detection, and to quickly detect the density of the black density patch. Therefore, it is possible to efficiently execute the black image density adjustment processing.

[Third basic form]
Next, the third basic form will be described. Note that the configuration of the color image forming apparatus 10 in the third basic form is the same as that in the first basic form, and thus the description thereof is omitted.

(Operation of the third basic form)
Next, as an operation of the third basic mode, a black image density adjustment process will be described with reference to the flowchart of FIG. The execution timing of the density adjustment process in the third basic form is the same as the execution timing of the density adjustment process in the first basic form. In the flowchart of FIG. 15, the same step numbers are assigned to the same processing steps as those in the flowchart of FIG. 10 in the first basic form described above, and detailed description of the processing steps is omitted.

  In step 120 of FIG. 15, the conveyance rollers 32, 34, 36, and 38 are driven to start conveyance of the intermediate transfer belt 30 in the direction of arrow B, and in the next step 122, the image is stored in advance in the image storage unit 82. Based on image signal data of a pattern image to be described later, the following YMCK pattern images are formed on each photoconductor in each image forming unit. Here, a 15 mm × 15 mm square pattern image with Cin = 50% and a 20 mm × 20 mm square pattern image with Cin = 100% are formed for each color of YMC, and 15 mm × Cin = 50% with black. A 15 mm square pattern image is formed.

  In the next step 125, each color image forming unit generates a 15 mm × 15 mm square pattern image of Cin = 50% and a 20 mm × 20 mm square pattern image of Cin = 100% from each photoconductor to the intermediate transfer belt 30. By transferring, 50% color density patches and 100% color density patches of each color of YMC are formed on the intermediate transfer belt 30.

  Note that the formation timing of the 50% density patch on the intermediate transfer belt 30 in steps 122 and 125 is determined by the reference position sensor 44 using the reference mark of the intermediate transfer belt 30 (for example, # 850 polyester silver color manufactured by Sumitomo 3M Limited). The yellow image forming unit 20 controls to transfer the yellow 50% density patch to the intermediate transfer belt 30 2.0 seconds after the detection of the (seal etc. in FIG. 14). (It is described that the first yellow 50% density patch Y1 is formed on the intermediate transfer belt 30 after 2.0 seconds from TR0).

  Thereafter, as shown in FIG. 13B, following the yellow 50% density patch, the magenta 50% density patch, the cyan 50% density patch, the yellow 100% density patch, and the magenta color 100%. A density patch and a cyan 100% density patch are formed on the intermediate transfer belt 30 with an interval of 5 mm along the conveyance direction of the intermediate transfer belt 30.

  In the next step 127, on the 100% color density patch of each color shown in FIG. 13B formed in step 125 above, the black image forming unit 26 uses a black Cin = 50% 15 mm × 15 mm square pattern image. As a result, the black density patch is formed on the intermediate transfer belt 30. As described above, in the third basic form, the color density patch and the black density patch are formed on the intermediate transfer belt 30 before the density detection of the color density patch and the black density patch is performed.

  In the next step 128, when the 50% color density patch of each color of YMC shown in FIG. 13B reaches the detection position of the density detection unit 28, each density is detected by the density detection unit 28. In step 130, it is determined whether or not all the detected density values of the 50% density patches of each color of YMC are within a predetermined reference range.

  Here, if any one of the detected density values of each color of YMC is not within the reference range, the process proceeds to step 132, and it is determined whether or not all detected density values of each color of YMC are out of the reference range. If all the detected density values of each color of YMC are outside the reference range, the process proceeds to step 134, and the adjustment amount of the toner supply amount corresponding to the deviation amount of the detected density value of each color from the reference range is set in the ROM in the control unit 80. The toner supply amount by the toner supply unit is adjusted by the adjustment amount in each color image forming unit. Then, the process returns to step 122, and a pattern image is formed again by each adjusted color image forming unit.

  On the other hand, if at least one of the density detection values of each color of YMC is within the reference range in step 132, the process proceeds to step 136, and the color image formation in which the density detection value of the formed color density patch is out of the reference range. As with step 134, the toner supply amount is adjusted by the toner supply unit.

  After the adjustment in step 136 is completed, and in step 130, if all the density detection values of each color of YMC are within the reference range, the process proceeds to step 141, and the color density where the density detection value is within the reference range. The density detection unit 28 detects the density of the black density patch on the 100% color density patch of the same color as the patch when the black density patch reaches the detection position of the density detection unit 28.

  Thereafter, as in the first basic mode, it is determined whether or not the density detection value of the black density patch is within a predetermined reference range (step 144). If the density detection value of black is within the reference range, If not, the adjustment amount of the toner supply amount corresponding to the deviation amount of the density detection value from the reference range is read from the ROM in the control unit 80, and the toner supply amount by the toner supply unit in the black image forming unit 26 is set to the adjustment amount. Only the adjustment is made (step 146).

  Then, after the completion of such adjustment and if the black density detection value is within the reference range in step 144, the fact that the black image density adjustment processing has been completed is displayed on the display 84A of the operation unit 84. As post-processing, the toner on the intermediate transfer belt 30 is removed by the cleaning device 42 and the toner on each photoconductor is removed by the cleaning device of each image forming unit, and the conveyance of the intermediate transfer belt 30 is stopped ( Step 148), the process ends.

  If it is determined in step 132 that the density detection values of all the color density patches are out of the reference range, each color image forming unit is adjusted in step 134, and then the process returns to steps 122 and 125, and FIG. As shown in (C), a color density patch (correction patch in FIG. 13C) is formed again by each adjusted color image forming unit, and the density detection of the color density patch is performed again.

  Here, as shown in FIG. 14, for example, for the corrected yellow color density patch (Y complement), the density detection is performed on the previous yellow color density patch (Y1), and then 4. After 5 seconds, density detection is performed. The 4.5 seconds is obtained by (the distance between the yellow image forming unit 20 and the density detecting unit 28 / process speed) + the response time, where the response time is 200 milliseconds. That is, (688/160) + 0.2 = 4.5.

  In the third basic mode described above, unlike the first and second basic modes, the color density patch and the black density patch are first formed on the intermediate transfer belt 30, and then the density of the color density patch and the black density patch is changed. Although the detection is executed, even in such a procedure, the black image forming unit 26 is arranged downstream of the color image forming unit in the transport direction of the intermediate transfer belt 30, and thus two color density patches. After forming (Cin = 50%, 100%), the black density patch can be immediately formed on the 100% color density patch on the upstream side in the transport direction, thereby forming the color density patch and the black density patch. The time required is shorter than before.

  Also, since the black density patch is formed on the 100% color density patch on the upstream side in the transport direction of the two color density patches, the density of the 50% color density patch on the downstream side in the transport direction is detected in step 128 and then immediately. In step 141, the density of the black density patch on the 100% color density patch upstream in the transport direction can be detected.

  As described above, according to the third basic form, it is possible to efficiently execute the black image density adjustment processing.

[Fourth basic form]
Next, the fourth basic form will be described.

  Note that, in the color image forming apparatus 10 in the fourth basic form, as shown in FIG. 16A, four image forming units are magenta image forming units along the conveyance direction (arrow B direction) of the intermediate transfer belt 30. 22, the cyan image forming unit 24, the yellow image forming unit 20, and the black image forming unit 26 are arranged in this order, and the density detecting unit 28 on the downstream side of the black image forming unit 26 is as shown in FIG. The three density detectors 28Y, 28M, and 28C are arranged along the width direction of the intermediate transfer belt 30. Other configurations are the same as those of the first basic form, and thus the description thereof is omitted.

(Operation of the fourth basic form)
Next, black image density adjustment processing will be described as an operation of the fourth basic mode. The procedure of black image density adjustment processing in the fourth basic form is the same as that in the third basic form, and the flowchart of FIG. 15 can be applied.

  However, in the fourth basic form, in step 125 of FIG. 15, 50% color density patches (15 mm × 15 mm) of each color of YMC are formed along the width direction of the intermediate transfer belt 30 as shown in FIG. Further, 100% color density patches (20 mm × 20 mm) of each color of YMC are formed along the width direction of the intermediate transfer belt 30 with an interval of 5 mm along the transport direction.

  In the next step 127, a black 50% density patch (15 mm × 15 mm) is superimposed on the 100% color density patch of each color shown in FIG. 16B formed in step 125 by the black image forming unit 26. Form.

  In the next step 128, the density detection unit 28Y in FIG. 16B sets the density of the yellow 50% color density patch, the density detection unit 28M sets the density of the magenta 50% color density patch, and the density detection unit 28C. The density of the cyan 50% color density patch is detected in parallel.

  Thereafter, when the density detection of the black density patch is performed in step 141, the color closest to the black image forming unit 26 among the background color density patches whose density detection value is determined to be within the reference range in step 130. The density of the black density patch on the color density patch formed by the image forming unit is detected by the corresponding density detection unit 28 (any one of the density detection units 28Y, 28M, and 28C).

  By the way, assuming a case where the density of the color density patch is not appropriate and the process returns to step 122 and a color density patch as a background is recreated, as shown in FIGS. The yellow color density patch re-formed by the yellow image forming unit 20 closest to 26 is detected in 2.05 seconds after the previous density detection / determination. The 2.05 seconds is obtained by (the distance between the yellow image forming unit 20 and the density detecting unit 28 / process speed) + the response time, where the response time is 200 milliseconds. That is, (296/160) + 0.2 = 2.05.

  On the other hand, the density of the cyan color density patch re-formed by the cyan image forming unit 24 is detected in 3.275 seconds, and that of the magenta color density patch re-formed by the magenta image forming unit 22 is 4.5 seconds. The concentration is detected. Note that 3.275 = (distance between cyan image forming unit 24 and density detecting unit 28 / process speed) + response time = ((492/160) +0.2). 4.5 = (distance between magenta image forming unit 22 and density detecting unit 28 / process speed) + response time = ((688/160) +0.2).

  Therefore, by setting the density of the black density patch on the color density patch formed by the color image forming unit closest to the black image forming unit 26 as described above as the detection target, the density of the color density patch is not appropriate and color When the density patch is re-formed, the color density patch can be re-formed and the density can be detected earliest.

  In the fourth basic mode, the density of the 50% color density patch of YMC can be detected in parallel by the three density detection units, so that the density detection processing efficiency is good and the color density patch is re-read as described above. Formation can be performed quickly, and black density adjustment processing can be performed efficiently.

  3B shows the spectral characteristics of the yellow toner image, FIG. 4B shows the spectral characteristics of the magenta toner image, and FIG. 5B shows the spectral characteristics of the cyan toner image. FIG. 6B shows the spectral characteristics of the black toner image. The reflectance of the yellow toner image is higher than that of the magenta or cyan toner image. It can be seen that the difference from the reflectance of the image is the largest. Therefore, when the density of the black density patch is detected using the yellow color density patch as the background, the difference in reflectance between the background and the black density patch is the largest, and the density can be detected with the highest accuracy.

  In the fourth basic mode, since the yellow image forming unit 20 is disposed closest to the black image forming unit 26, when the color density patch as the background is re-created, the density detection of the black density patch is most accurately performed. Possible yellow background black density patches can be formed on the intermediate transfer belt 30 in a shorter time. That is, it is possible to efficiently execute the density detection of the black density patch with high accuracy.

[Fifth basic form]
Next, the fifth basic form will be described.

  In the color image forming apparatus 10 in the fifth basic form, as shown in FIG. 18A, four image forming units along the conveyance direction (arrow B direction) of the intermediate transfer belt 30 are yellow image forming units. 20, a magenta image forming unit 22, a cyan image forming unit 24, and a black image forming unit 26 are arranged in this order. The density detecting unit 28 on the downstream side of the black image forming unit 26 is as shown in FIG. Similar to the fourth basic mode, the image forming apparatus includes three density detectors 28Y, 28M, and 28C arranged along the width direction of the intermediate transfer belt 30. Other configurations are the same as those of the first basic form, and thus the description thereof is omitted.

(Operation of the fifth basic form)
Next, as an operation of the fifth basic mode, the black image density adjustment processing will be described with reference to the flowchart of FIG. The execution timing of the density adjustment process in the fifth basic form is the same as the execution timing of the density adjustment process in the first basic form.

  In step 170 of FIG. 19, the conveyance rollers 32, 34, 36, and 38 are driven to start conveyance of the intermediate transfer belt 30 in the direction of arrow B, and in the next step 172, the image is stored in advance in the image storage unit 82. Based on image signal data of a pattern image to be described later, the following YMCK pattern images are formed on each photoconductor in each image forming unit. Here, for each color of YMC, two square pattern images having a different size of Cin = 100%, two square pattern images having a different size of Cin = 95%, and a size of Cin = 90% shown in FIG. Two different square pattern images, two square pattern images with different sizes of Cin = 85%, two square pattern images with different sizes of Cin = 80%, and two square pattern images with different sizes of Cin = 75% Form. The sizes are 15 mm × 15 mm and 20 mm × 20 mm. On the other hand, three square pattern images of 15 mm × 15 mm with Cin = 50% arranged side by side are formed in order.

  In the next step 174, as shown in FIG. 18B, each of the color image forming units forms the above-mentioned two sets of square pattern images for six sets (Cin = 100% to 75%) of the intermediate transfer belt 30. Then, the light is transferred from each light body to the intermediate transfer belt 30 so as to be formed in parallel with the YMC along the transport direction. Thus, two sets of color density patches are formed on the intermediate transfer belt 30 for six sets (Cin = 100% to 75%) in parallel with the YMC along the conveyance direction. However, in each of the above groups, the color density patch on the upstream side in the conveyance direction is formed to be 15 mm × 15 mm, and the color density patch on the downstream side is formed to be 20 mm × 20 mm.

  In the next step 176, as shown in FIG. 18B, the black image forming unit 26 applies black Cin = 50% 15 mm × on the 20 mm × 20 mm color density patch upstream in the transport direction in each set. A black density patch is formed on the intermediate transfer belt 30 by transferring the 15 mm square pattern image in an overlapping manner.

  In the next step 178, the density of the 100% density patch of each color of YMC is detected by the density detection unit 28 corresponding to each color image forming unit. That is, the density of the yellow color density patch is detected by the density detector 28Y, the density of the magenta color density patch is detected by the density detector 28M, and the density of the cyan color density patch is detected by the density detector 28C.

  Then, in the next step 180, it is determined whether or not all the density detection values of the color density patches for each color of YMC are within a predetermined reference range. As the reference range here, for example, when the density is detected by an output voltage correlated with the amount of light reflected from the target density patch, a range of 2 V to ± 0.2% corresponding to 100% density may be adopted. it can.

  Here, if any one of the density detection values of each color of YMC is not within the reference range, it is confirmed in step 181 that the above determination has not been completed for all color density patches, and the process proceeds to step 182. The adjustment processing of the color image forming unit in which the color density patch whose density detection value is outside the reference range is formed is activated. That is, the adjustment amount of the toner supply amount corresponding to the deviation amount of the density detection value of the color density patch from the reference range is read from the ROM in the control unit 80, and the toner supply amount by the toner supply unit in the target color image forming unit. Is adjusted by the adjustment amount.

  In step 182, the density of the color density patch of the next density is detected by the density detection unit 28 corresponding to each color image forming unit. Here, the density of the color density patch of the next Cin = 95% of 100% is the detection target, and the process returns to step 180, and the density detection values of the color density patches of each color of YMC are all within the predetermined reference range. It is determined whether or not. If the determination in step 180 is negative again, the process proceeds to step 182 again, and the density detection of the color density patch of the next density (Cin = 90%) is performed together with the adjustment process of the color image forming unit.

  If the density detection values of the color density patches of the respective colors of the YMC of the next density (Cin = 90%) are all within the reference range, the process proceeds to step 184, and the upstream side in the transport direction with the same set as the color density patch at that time. The densities of the three black density patches formed on the color density patch are detected by the density detection units 28Y, 28M, and 28C.

  As described above, in the fifth basic form, the density detection / determination is performed in a predetermined order for a plurality of sets of color density patches formed on the intermediate transfer belt 30, and the black density is determined when the density of the color density patch is determined to be normal. Performs patch density detection. Therefore, the density of the three black density patches (black density patches K1, K2, and K3 shown in FIG. 18C) on the upstream side in the transport direction of the set of density (Cin = 90%) determined to be normal as described above. Is detected.

  Thereafter, as in the first basic mode, it is determined whether or not the density detection value of the black density patch is within a predetermined reference range (step 186). If the density detection value of black is within the reference range, If not, the adjustment amount of the toner supply amount corresponding to the deviation amount of the density detection value from the reference range is read from the ROM in the control unit 80, and the toner supply amount by the toner supply unit in the black image forming unit 26 is set to the adjustment amount. Only the adjustment is made (step 188).

  Then, after completing such adjustment and if the black density detection value is within the reference range in step 186, the fact that the black image density adjustment processing has been completed is displayed on the display 84A of the operation unit 84 ( Step 190) As post-processing, the toner on the intermediate transfer belt 30 is removed by the cleaning device 42 and the toner on each photoconductor is removed by the cleaning device of each image forming unit, and the conveyance of the intermediate transfer belt 30 is stopped. (Step 192), and the process ends.

  If all the density detection values of each color are not determined to be within the reference range in step 180 for all sets of color density patches, an affirmative determination is made in step 181 to perform density detection and density adjustment of the black density patch. Instead, the post-process of step 192 is executed, and the process is terminated.

  In the fifth basic form described above, a plurality of sets (six sets as an example) of color density patches having different densities are formed on the intermediate transfer belt 30 as color density patches serving as the background of the black density patch. In one set of color density patches, the density detection value of the color density patch is likely to be within the reference range. For this reason, it is possible to avoid a situation in which the color density patch as the background of the black density patch is formed again with a high probability, and it is possible to quickly detect and adjust the density of the black density patch. That is, the black image density adjustment process can be executed efficiently.

  In the first to fifth basic forms, the density adjustment of the color image and the black image is performed by adjusting the toner supply amount to the developing device in each image forming unit. You may carry out by adjusting a voltage, the charging bias voltage applied with a charging device, the transfer bias voltage in a transfer device, etc.

  Further, the color image forming apparatus 10 according to the first to fifth basic forms is characterized in that the black image forming unit 26 is arranged downstream of the color image forming unit along the conveyance direction of the intermediate transfer belt 30. It is said. Among these, the fourth basic form is characterized in that, among the three color image forming units, the yellow image forming unit 20 is arranged on the most downstream side and is closest to the black image forming unit 26. Therefore, in the fourth basic form, there is no particular limitation on the arrangement of the magenta image forming unit 22 and the cyan image forming part 24 along the transport direction, and in the first to third and fifth basic forms, yellow image formation is performed. There are no particular restrictions on the arrangement of the three color image forming units of the unit 20, the magenta image forming unit 22, and the cyan image forming unit 24 along the transport direction.

  In addition to the black image density detection procedure of the first to fifth basic forms, a color density patch and a black density patch are formed on the intermediate transfer belt 30 to detect not only the density of the color density patch but also the black density patch. If density detection is also performed, and then the density detection value of the color density patch is within the reference range, the density detection value of the black density patch is adopted, and the density detection value of the color density patch is outside the reference range Alternatively, the procedure of not using the density detection value of the black density patch can be adopted.

[First Embodiment]
Next, a first embodiment corresponding to the first and seventh aspects of the present invention will be described.

  The color image forming apparatus 10 in the first embodiment has the same configuration as that of the first basic form. However, the color image forming apparatus 10 according to the first embodiment has a function of forming a misregistration detection pattern (hereinafter, referred to as a resist pattern) 600 shown in FIGS. 21 and 22A.

  As will be described in detail later, the color image forming apparatus 10 according to the first embodiment forms a resister pattern 600 on the intermediate transfer belt 30 at odd-numbered rotations of the intermediate transfer belt 30 as shown in FIG. The position of the registration control pattern 600 is detected, and registration deviation correction processing is executed when the amount of deviation of the detected position from the normal position (hereinafter referred to as registration deviation) exceeds a prescribed allowable value. In addition, the color image forming apparatus 10 forms a density detection pattern 700 (hereinafter referred to as a process control pattern) 700 on the intermediate transfer belt 30 at an even number of rotations of the intermediate transfer belt 30, and detects the density of the process control pattern 700. Then, based on the detected density, the density correction processing as in the first to fifth basic forms described above is executed as necessary.

(Registered pattern and its position detection method)
Here, the resist pattern 600 formed on the intermediate transfer belt 30 in this embodiment will be described. As shown in FIG. 22A, the registration pattern 600 includes a rectangular pattern 600A that is long in the width direction of the intermediate transfer belt 30 (left and right in FIG. 22A) and the conveyance direction of the intermediate transfer belt 30 (FIG. 22). It is roughly divided into a rectangular pattern 600B that is long in the direction of arrow H in FIG.

  The pattern 600A and the pattern 600B are both a yellow pattern (hereinafter referred to as a Y regicon pattern), a magenta pattern (hereinafter referred to as an M regicon pattern), and a cyan pattern along the conveyance direction H of the intermediate transfer belt 30. (Hereinafter referred to as a C-resin pattern) and a black pattern (hereinafter referred to as a K-resin pattern). The black pattern is formed so as to be superimposed on the yellow toner image.

  Each of the register control patterns 601A, 601B, 601C, and 601D is sized to be included in a 15 mm × 15 mm process control pattern, and is formed by the same image forming units 20, 22, 24, and 26 as the process control pattern. Is done.

  The resist pattern 600 formed on the intermediate transfer belt 30 is irradiated with laser light from the infrared type LED 70, and the amount of reflected light is detected by the density detector 28. The detection signal is shown in FIG. On the right side of FIG. 23, the correspondence between the detection location of the concentration detector 28 and the detection signal is shown in time series.

  For example, when the position of the Y resister pattern 602 is detected by the density detector 28, the positions G1 and G2 where the magnitude of the detection signal Q1 exceeds a predetermined threshold value J are detected as the left and right boundary positions of the Y resister pattern 602. To do. Also for the Y register pattern 604, the points G3 and G4 where the magnitude of the detection signal Q1 exceeds a predetermined threshold value J are detected as the left and right boundary positions of the Y register pattern 604.

  Further, regarding the upper and lower boundary positions of the Y register pattern 602, the upper boundary position is determined when the magnitude of the detection signal Q1 at the predetermined position C near the central portion has changed from a state not exceeding the threshold value J to an exceeding state. The lower boundary position is detected when the magnitude of the detection signal Q1 at the predetermined position C has changed from a state where the threshold value J has been exceeded to a state where the threshold value J has not been exceeded.

  The position detection of the M register pattern 606, 608 and the C register pattern 610, 612 is the same as that of the Y register pattern 602, 604.

  The K regicon patterns 614 and 616 are formed so as to overlap the yellow toner image. For this reason, for example, when detecting the position of the K regicon pattern 614, the point G5 where the magnitude of the detection signal Q2 changes from a state where the predetermined threshold value J exceeds the predetermined threshold J (a surrounding yellow toner image region) to a state where it does not exceed , G6 are detected as the left and right boundary positions of the K regicon pattern 614.

  As for the upper and lower boundary positions of the K regicon pattern 614, the magnitude of the detection signal Q2 at the predetermined position C near the center is changed from the state where the threshold value J has been exceeded (the surrounding yellow toner image region) to the state where it is not exceeded. The upper boundary position is detected when it changes, and the lower boundary position is detected when the magnitude of the detection signal Q2 at the predetermined position C changes from a state where it does not exceed the threshold value J to an excess state.

  By the way, the registration misalignment (registration pattern misalignment) detected in this embodiment includes (1) skew (inclination of the entire resister pattern), (2) magnification error in the main scanning direction, and (3) main scanning direction misalignment. There are four types of misalignment and (4) misalignment in the sub-scanning direction.

  Among these, (2) the magnification error in the main scanning direction is obtained from the length of the pattern 600A obtained from the left and right boundary positions of the pattern 600A of each color in FIG. (3) The positional deviation in the main scanning direction is obtained from the left and right boundary positions of the color pattern 600A and the specified left and right boundary positions.

  (4) The positional deviation in the sub-scanning direction is obtained from the left and right boundary positions of the color pattern 600B in FIG. 22A and the specified left and right boundary positions.

  (1) The skew is obtained from the difference between the upper boundary positions or the difference between the lower boundary positions of each color pattern 600A on both sides of the intermediate transfer belt 30 in the width direction. Alternatively, it may be obtained from the difference between the left boundary positions or the difference between the right boundary positions of the plurality of patterns 600 </ b> B separated in the conveyance direction of the intermediate transfer belt 30.

(Register misalignment correction)
Here, an outline of various misregistration correction processing executed in the present embodiment will be described.

(1) Skew correction The skew is corrected by adjusting the angle of the mirror 20H of each image forming unit 20.

(2) Correction of magnification error in the main scanning direction (magnification correction)
FIG. 34 shows an apparatus configuration relating to driving of an LD 668 as a light source. The source clock signal output from the frequency setting circuit 652 and the horizontal synchronization signal (SOS signal) output from the horizontal synchronization signal generation circuit 654 are input to the phase synchronization circuit 656.

  Here, the horizontal synchronization signal generation circuit 654 includes, for example, a one-shot multivibrator, and outputs a horizontal synchronization signal composed of pulses having a predetermined time width triggered by detection of horizontal synchronization. The phase synchronization circuit 656 adjusts the phase of the source clock signal to the phase of the horizontal synchronization signal and outputs a synchronization source clock signal delayed for a predetermined time from the trailing edge of the horizontal synchronization signal.

  The first timing control circuit 658 receives the horizontal synchronization signal and the synchronization source clock signal, and the first timing control circuit 658 is a predetermined first register in the control unit 650 constituted by a microcomputer or the like. A video clock having a phase setting based on the value set to 650A is output.

  The video clock is supplied to the second timing control circuit 660 and the image buffer memory 662. The second timing control circuit 660 uses a value set in a predetermined second register 650B in the control unit 650 as an enabling signal for allowing the image buffer memory 662 to read out the image signal from the input of the horizontal synchronizing signal. The output is delayed by the timing based on. By this permission signal, the writing line writing position on the photosensitive drum 20C is controlled.

  The image buffer memory 662 sequentially reads the stored image signals for one line one pixel at a time in synchronization with the video clock from the time when the permission signal is input, and supplies the image data to the screen generator 664 as image data.

  The screen generator 664 modulates the image data in synchronization with the video clock, and supplies an image signal obtained thereby to the laser driving circuit 666. As a result, the laser driving circuit 666 controls on / off of the LD 668 based on the image signal, and an electrostatic latent image is formed on the photosensitive drum 20C by the laser light from the LD 668.

  In the configuration as described above, the magnification correction in the main scanning direction of the image is performed based on the Y color printed first among the four colors of YMCK. That is, when the laser beam scans the photosensitive drum from the image writing position to the position where the image ends is called a print line, the print line of another color is based on the length L of the Y print line. The frequency of the video clock used for recording each color is adjusted so that the length of the video is matched with the length L.

  For example, the control unit 650 adjusts the frequency of the video clock by adjusting the frequency of the source clock signal output from the frequency setting circuit 652.

(3) Correction of misalignment in the main scanning direction (main scanning direction correction)
The main scanning direction correction is performed by changing the count value of the video clock (set value of the first register 650A) from the horizontal sync signal detection position to the print line writing position and resetting the video clock phase.

  Specifically, by changing the value set in the second register 650B in the control unit 650, the timing at which the permission signal is output by the second timing control circuit 660 is changed, and printing on the photosensitive drum 20C is performed. Correct the line start position.

  Further, by changing the value set in the first register 650A in the control unit 650, the phase of the video clock is reset and the writing position of the print line is corrected.

(4) Correction of displacement in the sub-scanning direction (sub-scanning direction correction)
In this embodiment, as a correction of the positional deviation in the sub-scanning direction, correction in units of one dot is performed by changing the number of clocks of the line sync signal, and correction for one dot or less is performed in the rotary polygon mirror drive motor control circuit for each color. This is done by changing the phase of the supplied reference clock. The line sync signal is an image writing timing signal for one line in the main scanning direction, and is output based on the SOS signal.

  The above four correction processes are executed in the order of magnification correction, main scanning direction correction, and sub-scanning direction correction as shown in FIG. 24A when skew correction is not performed. In the case of performing the skew correction, as shown in FIG. 24B, the skew correction is performed at the head, and thereafter, magnification correction, main scanning direction correction, and sub-scanning direction correction are executed in this order.

(Operation of the first embodiment)
Next, as an operation of the first embodiment, registration error correction and density correction processing will be described with reference to the flowchart of FIG. This process is executed under the control of the control unit 80 when the color image forming apparatus 10 is powered on and at a predetermined time interval. Of course, even when the installation environment of the color image forming apparatus 10 suddenly changes, it is desirable that the operator manually execute the density adjustment process. For example, the temperature changes by 3 degrees or more after the previous density adjustment process is executed. It is desirable to execute the density adjustment process when the humidity has changed or when the humidity has changed by 20% or more.

  In step 202 in FIG. 25, the conveyance rolls 32, 34, 36, and 38 are driven to start conveyance of the intermediate transfer belt 30 in the direction of arrow B in FIG. In the next step 204, it is determined whether or not it is an odd number of rotations from the start of conveyance of the intermediate transfer belt 30. Since the first cycle (first rotation) is an odd-numbered rotation, an affirmative determination is made in step 204 and the process proceeds to step 206 where the yellow image forming unit 20 applies a yellow regicon pattern along the width direction of the intermediate transfer belt 30. Form. As a result, a pair of yellow pattern portions in the regicon pattern shown in FIG. 22A is formed on the intermediate transfer belt 30. However, only one of the pair is shown in FIG. Note that the yellow pattern portion also includes a region serving as a base for the black regicon pattern.

  Thereafter, in steps 208 to 212, a magenta regicon pattern is formed by the magenta image forming unit 22, a cyan regicon pattern is formed by the cyan image forming unit 24, and a black regicon pattern is formed by the black image forming unit 26, respectively. 30 is formed. As a result, the regicon pattern shown in FIG. 22A is formed on the intermediate transfer belt 30.

  In the next step 214, the position of each of the resist pattern is detected by the density detector 28 in the manner described above. At this time, the skew is also detected by obtaining the positional deviation between the pair of resister patterns for each color.

  In the next step 216, it is determined whether or not the misregistration pattern misregistration (registration misalignment) exceeds a predetermined allowable value. Here, if the registration error does not exceed the allowable value, it can be determined that the correction of the registration error is not particularly necessary, and the process returns to step 204. On the other hand, if the registration error exceeds the allowable value, the process proceeds to step 218, and various registration error corrections (skew correction, magnification correction, main scanning direction correction, sub-scanning direction correction) as described above are executed.

  When the registration error detection and correction for the first rotation of the intermediate transfer belt 30 is completed as described above, the second rotation of the intermediate transfer belt 30 is entered. Since this is an even-numbered rotation, a negative determination is made in step 204 and the process proceeds to step 220 to execute the density adjustment processing described in the first to fifth basic forms. In this density adjustment processing, the density detection unit 28 used in the registration error detection is used.

  As the density adjustment processing here, any of the processing in FIGS. 10, 12, 15, and 19 may be adopted. However, it is not necessary to start conveyance of the intermediate transfer belt 30 at the beginning of each density adjustment process.

  As described above, in the registration deviation correction and density correction processing according to the first embodiment, registration deviation detection / correction is performed on the odd-numbered rounds from the start of conveyance of the intermediate transfer belt 30, and the same density detection unit on the even-numbered rounds. 28 is used to execute density detection / correction.

  As described above, the registration deviation detection / correction and the density detection / correction are executed by using the same density detection unit 28, so that an increase in the size of the color image forming apparatus 10 and an increase in apparatus cost can be avoided.

  Also, since registration error detection / correction is executed in the first cycle (the first cycle of the intermediate transfer member), after correcting the registration error in the first cycle, the next cycle (with the registration error corrected) The image density detection process can be executed in the second round of the intermediate transfer member. Accordingly, there is an advantage that it is possible to avoid the image density detection process being executed in a state where there is a registration error.

[Second Embodiment]
Next, a second embodiment corresponding to the second and eighth aspects of the present invention will be described.

  As shown in FIG. 26, the color image forming apparatus 10 of the second embodiment forms a regicon pattern and a procon pattern alternately on the intermediate transfer belt 30 with the regicon pattern at the head, and the same density detection unit. 28 detects the positional shift of the resist pattern of each color and the density of the toner image of each color.

  Here, the registration error correction and density correction processing in the second embodiment will be described with reference to the flowchart of FIG. In step 232 in FIG. 27, the transport rollers 32, 34, 36, and 38 are driven to start transport of the intermediate transfer belt 30 in the direction of arrow B in FIG. In the next step 234, a pair of yellow regicon patterns is formed along the width direction of the intermediate transfer belt 30 by the yellow image forming unit 20. Accordingly, a pair of yellow pattern portions in the regicon pattern shown in FIG. 26 is formed on the intermediate transfer belt 30. However, only one of the pair is shown in FIG. Note that the yellow pattern portion also includes a region serving as a base for the black regicon pattern. In the next step 236, the yellow image forming unit 20 forms a pair of yellow process control patterns 404 along the width direction of the intermediate transfer belt 30.

  Thereafter, in steps 238 to 248, a magenta pattern portion, a magenta procon pattern 408, a cyan pattern portion, a cyan procon pattern 412, a black pattern portion, and a black procon pattern 416 in the registration control pattern are each paired as an intermediate transfer belt. 30 is formed. As a result, the regicon pattern and the procon pattern shown in FIG. 26 are formed on the intermediate transfer belt 30.

  In the next step 250, the same density detection unit 28 sequentially executes position detection and density detection of each of the above-mentioned regicon patterns. At this time, the skew is also detected by obtaining the positional deviation between the pair of resister patterns for each color.

  In the next step 252, it is determined whether or not the misregistration pattern misregistration (registration misalignment) exceeds a predetermined allowable value. Here, if the registration error exceeds the allowable value, the process proceeds to step 254, and various registration error corrections (skew correction, magnification correction, main scanning direction correction, sub-scanning direction correction) as described above are executed. Then, after the registration deviation correction is completed, the process returns to step 234, and the registration control pattern and the process control pattern for each color are re-formed.

  On the other hand, if the registration error does not exceed the allowable value in step 252, the process proceeds to step 256 to determine whether or not density correction is required. If it is determined that density correction is required, density correction is performed in step 258 as in the first basic form described above. After the density correction is completed, a process control pattern of each color of yellow, magenta, cyan, and black is formed in step 260, and density detection is performed again in the next step 262. Then, the process returns to step 256 to determine again whether or not density correction is required. Here, if the density correction is unnecessary, the registration error correction and the density correction process are ended.

  Even when the resist pattern and the process control pattern are alternately formed on the intermediate transfer belt 30 as in the second embodiment described above, the same density detection unit 28 causes the misregistration of each color resist pattern and the toner image of each color. By detecting the concentration, the increase in size and cost of the apparatus can be avoided as in the first embodiment. In addition, since the positional deviation of the resist pattern is detected before the toner image density in each color, the image density can be detected in a state where the image positional deviation is corrected.

[Third Embodiment]
Next, a third embodiment corresponding to the third and ninth aspects of the present invention will be described. The third embodiment is effective in a case where it can be considered that there is no significant difference in the density of images formed using both ends of the intermediate transfer belt 30 in the width direction.

  As shown in FIG. 28, the color image forming apparatus 10 according to the third embodiment has a resister pattern near one end in the width direction of the intermediate transfer belt 30 and a process control pattern of each color near the other end. Each of them is formed in parallel, and the registration deviation is detected by the common density detection unit 28A for the resist pattern, and the density is detected by the common density detection unit 28B for the process control pattern.

  Here, the registration error correction and density correction processing in the third embodiment will be described with reference to the flowcharts of FIGS. 29 and 30. In step 272 of FIG. 29, the conveyance rolls 32, 34, 36, and 38 are driven to start conveyance of the intermediate transfer belt 30 in the direction of arrow B in FIG. In the next step 274, the yellow image forming unit 20 causes the yellow pattern portion of the registration control pattern to be near one end in the width direction of the intermediate transfer belt 30, and the yellow process control pattern 424 to be near the other end. Form in parallel.

  Thereafter, in step 276, the magenta pattern portion and the magenta proc pattern 428 of the regicon pattern, the cyan pattern portion and the cyan proc pattern 432 in step 278, and the black pattern portion and the black proc pattern 436 in step 280, respectively. Each is formed on the intermediate transfer belt 30. As a result, the resist pattern and the process pattern shown in FIG. 28 are formed on the intermediate transfer belt 30.

  In the next step 282, the registration deviation is detected by the common density detection unit 28A for the registration pattern, and the density is detected by the common density detection unit 28B for the process control pattern.

  In the next step 284, it is determined whether or not the misregistration pattern misregistration (registration misalignment) exceeds a predetermined allowable value. Here, if the registration error exceeds the allowable value, the process proceeds to step 286, and magnification correction, main scanning direction correction, and sub-scanning direction correction among the above-described registration error correction are executed. Then, after the registration deviation correction is completed, the process returns to step 274, and the registration control pattern and the process control pattern for each color are re-formed.

  On the other hand, if the registration error does not exceed the allowable value in step 284, the process proceeds to step 288, and the density pattern is detected. If the density pattern cannot be detected normally due to a large skew (see FIG. 35 for details such as two colors other than black overlapping or black cannot be detected because they do not overlap), go to step 298. Then, the subroutine of the skew correction process shown in FIG. 30 is executed.

  On the other hand, if the density pattern has been detected normally in step 288, the process proceeds to step 290 to determine whether or not density correction is required. If it is determined that density correction is required, density correction is performed in step 292 as in the first basic mode described above. After the density correction is completed, a yellow, magenta, cyan, and black color process control pattern is formed in step 294, and density detection is performed again in the next step 296. Then, the process returns to step 290 to determine again whether density correction is required. If density correction is unnecessary, the process proceeds to step 298 to execute a subroutine of skew correction processing in FIG.

  In step 302 in FIG. 30, the yellow image forming unit 20 forms yellow pattern portions of the regicon pattern in the vicinity of both ends in the width direction of the intermediate transfer belt 30. Thereafter, in steps 304 to 308, a magenta pattern portion, a cyan pattern portion, and a black pattern portion are formed on the intermediate transfer belt 30 one by one. In the next step 310, the skew is detected by obtaining the positional deviation between the resister patterns for each color.

In the next step 312, it is determined whether or not the detected skew exceeds a predetermined allowable value. Here, if the skew exceeds the allowable value, the process proceeds to step 314, and the angle of the mirror of the image forming unit for which the skew is generated as described above (for example, the mirror 20H in the case of the yellow image forming unit 20). The skew correction is performed by adjusting. After the skew correction is completed, the process returns to step 302.
In this way, the processing is continued until the skew falls within the allowable value. When the skew falls within the allowable value, the process returns from the subroutine of FIG. 30, and proceeds to Step 299 of FIG. , Main scanning direction correction and sub-scanning direction correction). The correction process is illustrated in FIG. 24B as a case with skew. This completes the registration error correction and density correction processing of FIG.

  As in the third embodiment described above, when the registration pattern and the process control pattern are formed on the intermediate transfer belt 30 in parallel, and the registration shift detection and the density detection are executed in parallel, the registration control pattern and the process control pattern Are sequentially formed, and the registration deviation correction and density correction processing can be completed faster than when registration deviation detection and density detection are sequentially executed. That is, it is possible to improve the efficiency of the registration error correction and density correction processing.

  Further, since the registration deviation is detected by the common density detection unit 28A for the registration control pattern and the density is detected by the common density detection unit 28B for the process control pattern, two density detection units are sufficient, and the large size of the apparatus And cost increase can be avoided.

  The positional deviation of the registration control pattern and the density of the toner image may be detected by separate sensors 28A and 28B as shown in FIG. 28, or a single line whose detection target is the entire width direction of the intermediate transfer member. You may detect with a sensor.

[Fourth Embodiment]
Next, a fourth embodiment corresponding to the inventions of claims 4, 5, and 10 described in the claims will be described. In the fourth embodiment, it can be considered that there is no significant difference between the density of the image formed using both ends of the intermediate transfer belt 30 in the width direction and the density of the image formed using the center. Effective for cases.

  As shown in FIG. 31, the color image forming apparatus 10 according to the fourth embodiment has a resister pattern near both ends in the width direction (left and right direction in FIG. 31) of the intermediate transfer belt 30 and a pair of each color near the center. The process control patterns are simultaneously formed in parallel, the registration deviation is detected by the common density detection units 28A and 28D for the resist pattern, and the density is detected by the common density detection units 28B and 28C for the process control pattern. To go.

  Here, the registration error correction and density correction processing in the fourth embodiment will be described with reference to the flowchart of FIG. In step 322 in FIG. 32, the conveyance rolls 32, 34, 36, and 38 are driven to start conveyance of the intermediate transfer belt 30 in the direction of arrow B in FIG. In the next step 324, the yellow image forming unit 20 causes the yellow pattern portion of the regicon pattern near the both ends in the width direction of the intermediate transfer belt 30 and the yellow procon patterns 444 and 446 near the center simultaneously. Form with.

  Thereafter, in steps 326 to 330, a resist pattern and a process pattern are formed on the intermediate transfer belt 30 for each of magenta, cyan, and black.

  In the next step 332, the registration deviation is detected by the common density detectors 28A and 28D for the resist pattern, and the density is detected by the common density detectors 28B and 28C for the process control pattern.

  In the next step 334, it is determined whether or not the displacement of the registration control pattern (registration displacement) exceeds a predetermined allowable value. Here, if the registration error exceeds the allowable value, the process proceeds to step 336, and various registration error corrections (skew correction, magnification correction, main scanning direction correction, sub-scanning direction correction) as described above are executed. Then, after the registration error correction is completed, the process returns to step 324, and the registration control pattern and the process control pattern for each color are re-formed.

  On the other hand, if the registration error does not exceed the allowable value in step 334, the process proceeds to step 338 to determine whether or not density correction is required. If it is determined that density correction is required, density correction is performed in step 340 in the same manner as in the first basic mode described above. After completing the density correction, in step 342, a yellow, magenta, cyan, and black color process pattern is formed, and in the next step 344, density detection is performed again. Then, the process returns to step 338 to determine again whether or not density correction is required. Here, if the density correction is unnecessary, the registration error correction and the density correction process are ended.

  As in the fourth embodiment described above, when the registration pattern and the process control pattern are simultaneously formed on the intermediate transfer belt 30 and the registration shift detection and the density detection are performed simultaneously, the registration control pattern and the process control pattern The registration error correction and the density correction process can be completed faster than when the registration error detection and the density detection are sequentially executed. That is, it is possible to improve the efficiency of the registration error correction and density correction processing.

  In addition, since the misregistration pattern of each color and the density of the toner image of each color are detected at two locations for each color, the misregistration detection result and image density with little variation and error are obtained by averaging the detection results. A detection result can be obtained. In addition, the skew can be detected based on the detection result of the misregistration pattern detected at two locations.

  In addition, since the registration deviation is detected by the common density detectors 28A and 28D for the resist pattern, and the density is detected by the common density detectors 28B and 28C for the pro-con pattern, a maximum of four density detectors is sufficient. It is.

  The registration pattern displacement and toner image density may be detected by a total of four sensors 28A, 28B, 28C, and 28D as shown in FIG. 31, or the entire width direction of the intermediate transfer belt 30 is detected. You may detect by one line sensor made into object. Alternatively, detection may be performed by a total of two line sensors: a line sensor whose detection target is one side from the central portion in the width direction of the intermediate transfer belt 30 and a line sensor whose detection target is the other side.

  Incidentally, as an example of the resist pattern and the process control pattern formed on the intermediate transfer belt 30, an example shown in FIG. In the example of FIG. 33, in the first row R1, the yellow resister pattern (= the resister pattern including a yellow pattern part long in the conveying direction of the belt 30) 502 and 506 and the magenta resister pattern (= the belt 30) (Registered pattern including magenta pattern portions long in the transport direction) 504 and 508.

  The second row R2 includes cyan registration control patterns (= registration pattern including a cyan pattern portion that is long in the conveyance direction of the belt 30) 510 and 514 and black registration control patterns (= black black that is long in the conveyance direction of the belt 30). (Register pattern including pattern portion) 512 and 516 are formed.

  In the third row R3, a yellow toner image 518, a magenta toner image 520, a cyan toner image 522, and a black toner image 524 are formed.

  In such a regicon pattern and a procon pattern, with respect to three of the regicon patterns 502 and 510 and the procon pattern 518 arranged along the conveyance direction of the belt 30, the density detector 28A causes the misregistration of the regicon pattern and the procon pattern. The concentration is detected. Similarly, with respect to three of the registration control patterns 504 and 512 and the process control pattern 520 arranged along the conveyance direction of the belt 30, the density detection unit 28B detects the displacement of the registration control pattern and the density of the process control pattern.

  Similarly, the resister pattern 506, 514 and the procon pattern 522 are detected by the density detector 28C, and the resister pattern 508, 516 and the procon pattern 524 are detected by the density detector 28D. The concentration of the procon pattern is detected.

  With respect to the resister pattern and the process control pattern arranged as shown in FIG. 33 as described above, the detection of misalignment and the detection of the density are performed on the resister pattern and the process control pattern in three rows along the conveyance direction of the belt 30. It ’s fine. For this reason, it is possible to reduce the time required for the detection process as compared with the case where the positional deviation and the density are detected for at least four columns or more of the regicon patterns and procon patterns as in the first to fourth embodiments described above. it can.

  In the above description, the intermediate transfer belt is used as the intermediate transfer member. However, other image carriers such as a photosensitive drum may be used.

  In the above, the square density patch is formed on the intermediate transfer belt as the process control pattern. However, the density patch may have another shape such as a circle, an ellipse, or a rectangle, and the size thereof is also particularly limited. It is not a thing.

  Similarly, the shape and size of the regi-con pattern can be set to an arbitrary shape and size, and is not particularly limited.

1 is a schematic configuration diagram of a color image forming apparatus. It is a block diagram of a density | concentration detection part. (A) is a graph showing the spectral characteristics in the visible region of the yellow toner image, and (B) is a graph showing the spectral characteristics in the infrared region of the yellow toner image. (A) is a graph showing spectral characteristics in the visible region of a magenta toner image, and (B) is a graph showing spectral characteristics in the infrared region of a magenta toner image. (A) is a graph showing the spectral characteristics in the visible region of the cyan toner image, and (B) is a graph showing the spectral characteristics in the infrared region of the cyan toner image. (A) is a graph showing spectral characteristics in the visible region of a black toner image, and (B) is a graph showing spectral characteristics in the infrared region of a black toner image. It is a figure for demonstrating the density detection of a color density patch and a black density patch. It is a flowchart which shows the basic process sequence of a color image formation process. (A) is a schematic configuration diagram of an image forming unit in the first basic form, and (B) shows a density patch formed on an intermediate transfer belt when the density of a color density patch as a base is appropriate. FIG. 6C is a diagram illustrating density patches formed on the intermediate transfer belt when the density of the color density patch serving as the background is not appropriate. It is a flowchart which shows the process routine of the density adjustment process of the black image in a 1st basic form. (A) is a schematic configuration diagram of an image forming unit in the second basic form, and (B) shows a density patch formed on an intermediate transfer belt when the density of a color density patch as a base is appropriate. FIG. 6C is a diagram illustrating density patches formed on the intermediate transfer belt when the density of the color density patch serving as the background is not appropriate. It is a flowchart which shows the process routine of the density adjustment process of the black image in a 2nd basic form. (A) is a schematic configuration diagram of an image forming unit in the third basic form, and (B) shows a density patch formed on an intermediate transfer belt when the density of a color density patch serving as a base is appropriate. FIG. 6C is a diagram illustrating density patches formed on the intermediate transfer belt when the density of the color density patch serving as the background is not appropriate. It is a time chart which shows the timing when various density patches in the 3rd basic form are formed. It is a flowchart which shows the processing routine of the density adjustment process of the black image in a 3rd, 4th basic form. (A) is a schematic configuration diagram of an image forming unit in the fourth basic form, and (B) shows a density patch formed on an intermediate transfer belt when the density of a color density patch as a base is appropriate. FIG. 6C is a diagram illustrating density patches formed on the intermediate transfer belt when the density of the color density patch serving as the background is not appropriate. It is a time chart which shows the timing when various density patches in the 4th basic form are formed. (A) is a schematic configuration diagram of an image forming unit in the fifth basic form, and (B) shows a density patch formed on an intermediate transfer belt when the density of a color density patch serving as a base is appropriate. FIG. 6C is a diagram illustrating density patches formed on the intermediate transfer belt when the density of the color density patch serving as the background is not appropriate. It is a flowchart which shows the process routine of the density adjustment process of the black image in a 5th basic form. It is a figure which shows the various examples which overlap and form a black density patch on the background color density patch, (A) is an example formed so that a black density patch may be included in a color density patch, (B) FIG. 4 is a diagram illustrating examples in which a part of a black density patch is formed so as to protrude from a color density patch. It is a perspective view which shows the regicon pattern and the process control pattern which are formed in 1st Embodiment. (A) is a figure which shows the regicon pattern formed in odd number rotation, (B) is the figure which shows the proc pattern formed in even number rotation, respectively. It is a figure for demonstrating the position detection method using a resiston pattern. (A) is a figure which shows the outline | summary of the position shift correction at the time of assuming that there is no skew, (B) is a figure which shows the outline | summary of position shift correction including skew correction. 5 is a flowchart showing a control routine for registration deviation correction and density correction processing in the first embodiment. It is a top view which shows the registration control pattern and the process control pattern which are formed in 2nd Embodiment. 10 is a flowchart illustrating a control routine for registration deviation correction and density correction processing according to the second embodiment. It is a top view which shows the regicon pattern and the process control pattern which are formed in 3rd Embodiment. 14 is a flowchart illustrating a control routine for registration deviation correction and density correction processing according to the third embodiment. It is a flowchart which shows the subroutine of a skew correction process. It is a top view which shows the registration control pattern and the process control pattern which are formed in 4th Embodiment. 16 is a flowchart illustrating a control routine for registration deviation correction and density correction processing according to the fourth embodiment. It is a top view which shows the register control pattern and the process control pattern in the modification of 4th Embodiment. It is a block diagram which shows the structure of the apparatus which concerns on magnification correction and position shift correction in the main scanning direction. It is a figure which shows the case where the density pattern was not able to be normally detected because skew remained after performing magnification correction, main scanning direction correction, and sub-scanning direction correction.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Color image forming apparatus 18 Image forming part 20 Yellow image forming part 22 Magenta image forming part 24 Cyan image forming part 26 Black image forming part 28 Density detection part 30 Intermediate transfer belt 80 Control part 600 Resistor pattern 700 Procon pattern

Claims (10)

In a color image forming apparatus for forming a black toner image and a color toner image on an intermediate transfer body conveyed in a predetermined conveyance direction along a predetermined circulation path, each color transfer resist pattern for image position detection is formed on the intermediate transfer body. An image misregistration detection process in which a misregistration pattern of each color resist pattern formed by the sensor is detected by a sensor, and a color toner image is formed on the intermediate transfer member and is superimposed on the color toner image to form a black toner image. An image positional deviation and image density detection method for executing an image density detection process for detecting a toner image density by a sensor,
The odd-numbered rotation from the start of conveyance of the intermediate transfer member, the image positional deviation detection processing is executed,
The image density detection process is executed using the same sensor as the image misregistration detection process on an even number of turns from the start of conveyance of the intermediate transfer member.
Image misalignment and image density detection method. In a color image forming apparatus for forming a black toner image and a color toner image on an intermediate transfer body conveyed in a predetermined conveyance direction along a predetermined circulation path, a regicon pattern of a predetermined color is formed on the intermediate transfer body. A series of image forming processes for forming a toner image of the color on the intermediate transfer member is executed for each color in a predetermined color order with black as the last,
The same sensor detects the misregistration of each color registration pattern and the density of each color toner image.
Image misalignment and image density detection method. In a color image forming apparatus for forming a black toner image and a color toner image on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path, near one end in the width direction of the intermediate transfer member. An image forming process for simultaneously forming a regicon pattern of a predetermined color and a toner image of the color in the vicinity of the other end of each color is executed for each color in a predetermined color order with black as the last,
The misregistration of each color registration pattern and the density of the toner image of each color are detected by the same sensor simultaneously for each color and for all colors.
Image misalignment and image density detection method. In a color image forming apparatus for forming a black toner image and a color toner image on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circular path, a predetermined value is provided near both ends in the width direction of the intermediate transfer member. An image forming process for forming a color regicon pattern near the center of the color regicon pattern and simultaneously forming each color toner image is executed for each color in a predetermined color order with black as the last,
The misregistration of each color registration pattern and the density of the toner image of each color are detected by the same sensor simultaneously for each color and for all colors.
Image misalignment and image density detection method. In a color image forming apparatus for forming a black toner image and three color toner images of cyan, magenta, and yellow on an intermediate transfer member conveyed in a predetermined conveyance direction along a predetermined circulation path, the intermediate transfer member Of the three colors, the first color register pattern, the second color register pattern, the first color register pattern, the second color pattern, and the second color pattern from one end in the width direction to the other end. Color regicon patterns are formed simultaneously,
From the vicinity of one end in the width direction of the intermediate transfer member to the vicinity of the other end, a third color register pattern, a black register pattern, a third color register pattern, and a black register pattern are respectively provided. Forming at the same time,
A toner image of each color is formed simultaneously from near one end in the width direction of the intermediate transfer member to near the other end,
Image misregistration and image density detection method for detecting misregistration of each color registration pattern and density of toner image of each color.   6. The image misregistration according to claim 1, wherein the black regicon pattern is formed so as to overlap with a color toner image previously formed on the intermediate transfer member. Image density detection method. An intermediate transfer member transported in a predetermined transport direction along a predetermined circulation path;
A color toner image and a resiston pattern are formed on the photoreceptor, and the formed color toner image and the resiston pattern are transferred to the intermediate transfer member, whereby the color toner image and the resiston pattern are formed on the intermediate transfer member. Color image forming means for forming;
Disposed on the downstream side in the transport direction with respect to the color image forming means, and provided with a photoconductor, forming a black toner image and a resiston pattern on the photoconductor, and transferring the formed black toner image and the resiston pattern to the intermediate transfer member A black image forming means for forming a black toner image and a resiston pattern on the intermediate transfer member,
A detecting unit that is disposed in the vicinity of the circulation path and that detects a density of a toner image of each color formed on the intermediate transfer member, and detects a displacement of a registration control pattern of each color formed on the intermediate transfer member; ,
On the odd-numbered laps from the start of conveyance of the intermediate transfer body, the color image forming means and the black image forming means form a color resist pattern for each color on the intermediate transfer body, and the detection means detects the misregistration of each color resist pattern. The color image forming unit forms a color toner image on the intermediate transfer member and the black image forming unit forms a black toner image on the intermediate transfer member on the even number of turns. Fourth control means for controlling to detect the density of the toner image;
A color image forming apparatus. An intermediate transfer member transported in a predetermined transport direction along a predetermined circulation path;
A color toner image and a resiston pattern are formed on the photoreceptor, and the formed color toner image and the resiston pattern are transferred to the intermediate transfer member, whereby the color toner image and the resiston pattern are formed on the intermediate transfer member. Color image forming means for forming;
Disposed on the downstream side in the transport direction with respect to the color image forming means, and provided with a photoconductor, forming a black toner image and a resiston pattern on the photoconductor, and transferring the formed black toner image and the resiston pattern to the intermediate transfer member A black image forming means for forming a black toner image and a resiston pattern on the intermediate transfer member,
A detecting unit disposed in the vicinity of the circulation path for detecting a density of a toner image of each color formed on the intermediate transfer member and detecting a displacement of a registration pattern of each color formed on the intermediate transfer member; ,
A series of image forming processes for forming a regicon pattern of a predetermined color on the intermediate transfer member and forming a toner image of the color on the intermediate transfer member by the color image forming unit and the black image forming unit, A fifth control unit that executes the process for each color in a predetermined color order, and detects the displacement of the registration pattern of each color and the density of the toner image of each color by the same detection unit;
A color image forming apparatus. An intermediate transfer member transported in a predetermined transport direction along a predetermined circulation path;
A color toner image and a resiston pattern are formed on the photoreceptor, and the formed color toner image and the resiston pattern are transferred to the intermediate transfer member, whereby the color toner image and the resiston pattern are formed on the intermediate transfer member. Color image forming means for forming;
Disposed on the downstream side in the transport direction with respect to the color image forming means, and provided with a photoconductor, forming a black toner image and a resiston pattern on the photoconductor, and transferring the formed black toner image and the resiston pattern to the intermediate transfer member A black image forming means for forming a black toner image and a resiston pattern on the intermediate transfer member,
Each of the toner images of each color formed on the intermediate transfer member is detected on the intermediate transfer member, and is disposed on the intermediate transfer member in the width direction of the intermediate transfer member. Detecting means for detecting misregistration of the resiston pattern of each color;
By the color image forming unit and the black image forming unit, a regicon pattern of a predetermined color is formed near one end in the width direction of the intermediate transfer member, and a toner image of the color is simultaneously formed near the other end. The image forming process to be formed is executed for each color in a predetermined color order with black as the last, and the misregistration of the resist pattern of each color and the density of the toner image are detected for each color simultaneously and by the same detection means for all colors. Sixth control means for controlling to perform,
A color image forming apparatus. An intermediate transfer member transported in a predetermined transport direction along a predetermined circulation path;
A color toner image and a resiston pattern are formed on the photoreceptor, and the formed color toner image and the resiston pattern are transferred to the intermediate transfer member, whereby the color toner image and the resiston pattern are formed on the intermediate transfer member. Color image forming means for forming;
Disposed on the downstream side in the transport direction with respect to the color image forming means, and provided with a photoconductor, forming a black toner image and a resiston pattern on the photoconductor, and transferring the formed black toner image and the resiston pattern to the intermediate transfer member A black image forming means for forming a black toner image and a resiston pattern on the intermediate transfer member,
A density of each color toner image formed on the intermediate transfer member is detected in the vicinity of the circumferential path near both ends and near the central portion along the width direction of the intermediate transfer member, and is detected on the intermediate transfer member. Detecting means for detecting misregistration of the regicon pattern of each color formed on,
Image formation in which the color image forming unit and the black image forming unit simultaneously form a resiston pattern of a predetermined color near both ends in the width direction of the intermediate transfer member and a toner image of the color near the center. The process is executed for each color in a predetermined color order with black as the last, and the misregistration of each color resist pattern and the density of the toner image of each color are detected simultaneously for each color by the same detection means for all colors. Seventh control means for controlling;
A color image forming apparatus.

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