JP2008203733A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus achieving both reduction in downtime and waste toner while stably measuring density without lowering accuracy of sampling patch patterns for correcting image density or for correcting image gradation. <P>SOLUTION: The image forming apparatus forms the image of the patch pattern for correcting the image density or the image gradation and measures reflected light quantity by a reflected light quantity sensor 108 for feedback. When continuously arranging a plurality of color patch patterns or a plurality of gradation patch patterns, the length of the top patch pattern 303y in the forward direction F of an intermediate transfer body 104 is longer than the length of other patch patterns 303m to 303k, and then the patch patterns 503 and 508 having a large difference in a gradation level from the previous patch pattern out of the plurality of gradation patch patterns arranged continuously are formed longer than other patch patterns 504 to 507 and 509 to 512. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to a method for correcting an output image in an image forming apparatus such as a printer, a copier, or a multifunction peripheral that forms a visible image on a surface of a sheet or the like.

  Currently, in an image forming apparatus such as a copying machine using an electrophotographic process, it is required to perform stable image formation without being affected by a change with time due to use of the apparatus or a change in an environment where the apparatus is placed. . For this purpose, various automatic adjustment controls are performed in order to stably output an image.

  In the electrophotographic process, a surface of an image carrier such as a photosensitive drum is uniformly charged by applying a uniform charge amount, and an electrostatic latent image is formed by scanning with an exposure unit such as a laser. Then, a visible toner image is formed by rotating (or approaching) a developing device using toner or the like on the developing device, and an image is formed by transferring the image onto a sheet. However, in using the electrophotographic process, the charging member, the developer, and the transfer member are affected by various factors such as temperature and humidity. For this reason, it is difficult to keep the formed toner image in a uniform state, and therefore it is necessary to take appropriate image stabilization control as needed.

  Among image stabilization controls, control for keeping the image density constant is important. As one of the means, the following control is performed. That is, by forming a specific pattern image as a toner image on an image carrier such as a photosensitive drum or an intermediate transfer member, and measuring the amount of reflected light obtained by irradiating the pattern image with light emitted from an LED or the like. Concentration information is acquired. Then, control is performed to feed back this to a control amount of toner when forming a visible toner image. Patent Document 1 and Patent Document 2 are examples thereof.

  A sensor used to measure the amount of reflected light of these pattern images (hereinafter referred to as a patch pattern) uses an element such as a phototransistor in the light receiving portion. However, instead of following the change in the amount of incident reflected light without delay and outputting an electrical signal, the output signal changes with a delay that depends on the semiconductor material used as the material and the configuration of the signal amplification circuit. To do. Further, the delay amount of the output signal change with respect to the change of the incident light amount depends on the change amount of the incident light amount.

  The amount of reflected light is greatly different between the patch pattern portion formed on the intermediate transfer member and the base portion of the intermediate transfer member on which nothing is formed. For this reason, since it takes some time for the output signal voltage of the sensor that obtains the reflected light amount to change, the size of the patch pattern in the traveling direction is set according to the followability of the output signal change in order to perform stable density measurement. There was a need to expand.

In addition, in image formation by the electrophotographic process, there is often a shift in the linearity of output density with respect to input data of intermediate gradation. For this reason, various means for correcting halftones are taken, such as Patent Document 3 and Patent Document 4. For example, a gradation pattern (patch pattern) consisting of a plurality of gradations is read by an optical sensor to obtain a correlation between intermediate gradation input data and output density in advance, and the input data is corrected during normal image formation. It has been proposed to form an image after that.
Japanese Patent Laid-Open No. 06-011936 Japanese Patent Laid-Open No. 10-186831 JP 07-264212 A JP 09-037080 A

  However, in order to suppress the variation among the reflected light quantity sensors among the plurality of reflected light quantity sensors, if the gradation pattern of each color is continuously read with a single reflected light quantity sensor, the density difference between adjacently arranged patterns is different. It is possible that a large portion will occur. This is because each gradation pattern is a pattern that transitions from a high density gradation to a low density gradation (or vice versa). That is, for example, when transitioning from yellow to magenta, the transition is from a low density gradation of yellow to a high density gradation of magenta, and in this case, a large density difference occurs. Even in such cases, the difference in the amount of reflected light is greatly different, so in order to perform stable density measurement, the size of the patch pattern in the direction of travel must be increased for each gradation level in accordance with the followability of the output signal change. was there.

  However, while the patch pattern is created only to measure the output density under the current imaging conditions, the normal pattern is used to form an image using the same process unit as the image output on normal paper. It is impossible to form a patch pattern simultaneously with image output. Therefore, normal image output must be temporarily interrupted in order to create a patch pattern.

  Further, since the patch pattern is not transferred onto the paper, it is necessary to collect it as waste toner using a cleaning blade after measuring the amount of reflected light of the patch pattern.

  For this reason, if the size of the patch pattern in the advancing direction is increased in order to perform stable density measurement as described above, the time during which the user cannot form an image (that is, the down time) is increased correspondingly, and the waste toner is removed. There was a problem of increasing.

  The present invention has been made paying attention to the above points, and reduces downtime while performing stable density measurement without degrading the sampling accuracy of patch patterns for image density correction and image gradation correction. An object of the present invention is to provide an image forming apparatus capable of reducing waste toner.

  The image forming apparatus of the present invention has the following features in order to solve the above problems.

  That is, in an image forming apparatus for forming an image on an image carrier, the pattern forming unit for forming a pattern image on the image carrier and the pattern forming unit are used to control the density of the image. Measuring means for irradiating the pattern image with light and measuring the amount of reflected light; and image density correcting means for correcting the density of the image based on the amount of reflected light measured by the measuring means; When correcting the density of the image by the correcting unit, the pattern forming unit sequentially forms a plurality of pattern images in parallel with the traveling direction of the image carrier, and among the plurality of pattern images, The pattern image located at the head is formed longer in the traveling direction of the image carrier than the other pattern images.

  According to the present invention, it is possible to achieve both reduction of downtime and reduction of waste toner without reducing the sampling accuracy of the correction patch pattern.

  An embodiment of the present invention is shown below. Of course, the individual embodiments described below will be helpful in understanding various concepts, such as the superordinate concept, intermediate concept and subordinate concept of the present invention. Further, the technical scope of the present invention is determined by the scope of the claims, and is not limited by the following individual embodiments.

[First Embodiment]
(1) Configuration of image forming apparatus: FIG.
FIG. 1 is a schematic cross-sectional view of an image forming apparatus according to an embodiment. The image forming apparatus includes a document reading unit 1R and a printer unit 1P for performing a document copying operation.

  The printer unit 1P mainly has the following components. The toner bottles 101y, 101m, 101c, and 101k (hereinafter referred to as 101y to 101k) are filled with developer (toner) of yellow, magenta, cyan, and black (hereinafter referred to as YMCK), respectively. In the process units 102y to 102k (corresponding to the pattern forming means), a charging roller (primary charger), a developing device, and a photosensitive drum cleaner are arranged in the rotation direction facing the outer peripheral surface of the photosensitive drum.

  The charging roller applies a uniform charge amount to the surface of the photosensitive drum to charge the photosensitive drum. Laser scanner units 103y to 103k, which are optical scanning units, perform laser exposure on the uniformly charged photosensitive drums in the process units 102y to 102k according to input image information to form electrostatic latent images. The formed electrostatic latent image is developed into a toner image (corresponding to an image) by a developing device in the process units 102y to 102k.

  The intermediate transfer member (corresponding to an image carrier) 104 is constituted by an endless belt. The toner image formed on the photosensitive drum is primary-transferred by sequentially superimposing each color on the intermediate transfer member 104, and the image formed on the intermediate transfer member 104 is secondary-transferred onto various types of paper. The The intermediate transfer member 104 is rotationally driven at a speed of 150 mm / s during the image forming operation.

  The primary transfer rollers 105y to 105k are for realizing stable transfer when performing primary transfer from the photosensitive drum to the intermediate transfer member 104.

  The toner image primarily transferred to the intermediate transfer member 104 is secondarily transferred onto the sheet by the secondary transfer roller 106. Residual toner that could not be transferred by the secondary transfer roller 106 and adjustment toner image (patch pattern) that is not intended to be transferred onto the paper are collected by the intermediate transfer body cleaner 107. A reflected light amount sensor (corresponding to a measuring unit) 108 detects the toner density on the intermediate transfer member 104 based on the reflected light amount.

  The sheet is conveyed from the sheet cassette 109 by the sheet feeding roller 110, and after skew correction is corrected by the registration roller 112, the sheet is sent to the secondary transfer roller 106. After the toner image is transferred from the intermediate transfer member 104 by the secondary transfer roller 106, the toner image is heat-fixed by the fixing roller 113 and the pressure roller 114. Further, the sheet is sent to the inner discharge tray 116 or the discharge tray 117 by the discharge flapper 115. Reference numeral 111 denotes a manual feed tray.

(2) Configuration of reflected light amount sensor: FIG.
FIG. 2 is a schematic cross-sectional view showing the configuration of the reflected light amount sensor 108.

  The reflected light amount sensor 108 includes a light emitting unit 202 configured by an LED or the like, and a light receiving unit 203 configured by a phototransistor or the like. The light emitting unit 202 and the light receiving unit 203 are attached at such an angle that the light emitted from the light emitting unit 202 is reflected by the intermediate transfer member 104 and the reflected light is incident on the light receiving unit 203. The reflected light received by the light receiving unit 203 is converted into an electrical signal corresponding to the amount of reflected light. The voltage of the output electrical signal is low when the amount of reflected light is small, and the voltage is high when the amount of reflected light is large. Generally, the greater the amount of toner placed on the intermediate transfer member 104, the smaller the amount of reflected light. For this reason, the higher the output signal voltage of the reflected light amount sensor 108, the lower the density of the imaged toner, and the lower the output signal voltage, the higher the density of the imaged toner (higher). The voltage and the toner density are in a proportional relationship. Reference numeral 205 denotes a case where the toner image 205 is placed on the intermediate transfer member 104. In the figure, an arrow F indicates the traveling direction of the intermediate transfer member 104.

  As described in the background art section, the output signal of the reflected light amount sensor 108 responds with a delay to the incident reflected light, and the time until the voltage level of the output signal matches the incident light amount (that is, stable). Time) changes according to the amount of change in the amount of incident light.

(3) Patch pattern for correcting image density: FIG.
Next, a patch pattern for image density correction (corresponding to a pattern image) will be described with reference to FIG. FIG. 3 is a view of the intermediate transfer member 104 as viewed from above. Since the intermediate transfer member 104 is an endless belt, it is assumed that the left and right sides (the front-rear direction of the arrow F) are loops with respect to the drawing. The reflected light amount sensor 108 is arranged with respect to the intermediate transfer member 104 in the positional relationship as shown in the figure.

  The image density correction patch patterns 303y to 303k are formed by the process units 102y to 102k on the intermediate transfer member 104 (on the image carrier) with a plurality of colors (YMCK colors) using predetermined laser modulation patterns. It is a thing. The sizes of the patch patterns 303y to 303k are 20 mm in common with the length in the direction perpendicular to the traveling direction F, that is, in the main scanning direction. Further, the length in the traveling direction F, that is, the sub-scanning direction, is 20 mm for the patch pattern 303y positioned at the head, but 15 mm for the subsequent patch patterns 303m to 303k, and the head patch pattern 303y is longer by 5 mm.

  Providing a plurality of reflected light amount sensors 108 leads to an increase in cost, so that the patch pattern density of each color is read continuously using one reflected light amount sensor 108. For this reason, each color of YMCK is sequentially arranged in parallel with the traveling direction F of the intermediate transfer body 104, and the single reflected light amount sensor 108 can continuously read the reflected light amount.

  The formed toner images of the patch patterns 303y to 303k proceed to the reflected light amount sensor 108 according to the rotation of the intermediate transfer body 104, and the reflected light amount is measured. The reflected light amount sensor 108 outputs a signal proportional to the density of each patch pattern in accordance with the reflected light amount. According to this output signal level, the charging bias voltage and the developing bias voltage in the process units 102y to 102k are controlled to correct the image forming density so as to be maintained at a constant level. Note that a control unit 704 (corresponding to an image density correction unit), which will be described later, performs control of charging bias voltage and development bias voltage and correction for maintaining the image forming density at a constant level.

  The patch pattern 303y is 20 mm, which is 5 mm (difference) longer than the subsequent 303 m to 303 k. This is an example of the case where the intermediate transfer member 104 is rotated at a speed of 150 mm / s. In general, an electrophotographic printer engine (image forming unit) has a thick paper mode when the paper to be used is thick paper. In this thick paper mode, the image forming unit operates at a lower speed than usual. In the printer engine of this embodiment, in the thick paper mode, the rotation speed of the intermediate transfer member 104 is rotated at a speed of 90 mm / s. At this time, the patch pattern 303y is 3 mm (difference amount) longer than the subsequent 303m to 303k. 18 mm.

(4) Control block diagram: FIG.
FIG. 7 is a control block diagram for controlling the image forming apparatus according to the embodiment.

  The CPU 701, ROM 702, RAM 703, control unit 704, scanner control ASIC 705, and controller unit 706 are mounted on the control unit 700. The ROM 702 stores a control program such as firmware.

  The CPU 701 is a control microcomputer that controls the driving load of the printer unit 1P. The CPU 701 executes programs stored in the ROM 702 and the RAM 703 and controls the process units 102 y to 102 k via the control unit 704. The CPU 701 drives and controls the laser scanner units 103y to 103k by designating parameters such as a driving speed to the scanner control ASIC 705.

  The CPU 701 controls the process units 102y to 102k based on the output signal from the reflected light amount sensor 108.

  The controller unit 706 accepts a copy command by pressing the copy start button on the operation panel by an operator (user) (print job is input and start command), issues a print command to the printer unit 1P, and transmits image data. . At the same time, the document image data is read by communication with the document reading unit 1R.

(5) Output signal of reflected light amount sensor: FIG.
The graph of FIG. 4 shows a waveform of an output signal obtained by reading the reflected light amount of the patch patterns 303y to 303k by the reflected light amount sensor 108. The horizontal axis is the time axis (t [ms]), and the vertical axis indicates the voltage (V [v]) of the output signal.

  A waveform 401 is an output signal voltage of the reflected light amount sensor 108. A section 402 indicates a base portion from the base portion of the intermediate transfer member 104 to the patch pattern 303y. An interval 403 and an interval 404 are output signal portions provided by the patch pattern 303y (amount of reflected light from the patch pattern 303y), and an interval 405 is a signal output portion provided by the patch pattern 303m. The section 406 is an output signal portion provided by the patch pattern 303c, the section 407 is an output signal portion provided by the patch pattern 303k, and the section 408 is a base portion of the intermediate transfer member 104 following the patch pattern 303k.

  Since the length of each level of the output signal is proportional to the size of the patch pattern, the lengths in the traveling direction of the patch patterns 303m to 303k are the same, so the sections 405 to 407 are substantially the same time. Further, since the length of the patch pattern 303y is longer than the patch patterns 303m to 303k of other colors (only the patch pattern 303y is 5 mm longer), the length obtained by adding the section 403 and the section 404 is the length of each of the sections 405 to 407. Longer than.

  Since the section 402 is a base portion of the intermediate transfer member 104 and the amount of reflected light is large, the output signal voltage is high. After the section 403 where the patch patterns 303y to 303k are placed on the intermediate transfer member 104, the output signal voltage rapidly decreases. . A section 403 is a stabilization waiting period when the background portion of the intermediate transfer member 104 changes to the reflected light amount of the patch pattern 303y, and the sampling value of the signal in this portion is not used for image density correction. The output signal values in the sections 404 to 407 are actually used for the image density correction as a result of sampling the output signal. The times of the section 404 and the sections 405 to 407 are equal.

  A portion where the top patch pattern 303y shown in FIG. 3 is longer than the other patch patterns corresponds to the section 403 (that is, 5 mm which is extra long). In the section 403, the reflected light amount sensor 108 does not follow the sudden change in the reflected light amount and absorbs the gradual change in the output signal voltage, thereby reading the density correctly in a stable state of the leading patch pattern 303y. It is possible. Since only the first patch pattern 303y lengthens the patch pattern, it is possible to reduce the amount of waste toner as compared with lengthening all the patch patterns 303y to 303k, and it takes an image. Time can be shortened.

  Such a patch pattern for image density correction is often formed continuously a plurality of times while changing the operation parameters of the process units 102y to 102k. The operation parameters of the process units 102y to 102k are the output values of the charging bias and the developing bias, and it takes a stabilization time of about 100 ms to change them. Therefore, the interval between patch patterns for image density correction is several tens. It will open about mm. When patch patterns are not closely imaged and a patch pattern for image density correction is formed multiple times, only the first patch pattern 303y can be made a long pattern as in the present invention. This is an effective means from the viewpoint of reducing the amount of waste toner and shortening the correction time. Further, this is an effective means not only from the viewpoint of reducing the amount of waste toner and the correction time, but also from the viewpoint of the life of consumable members such as a photosensitive drum.

  In the above-described thick paper mode, the speed of the intermediate transfer member 104 is 90 mm / s, which is a normal 3/5. When the speed of the intermediate transfer member 104 is decreased, the reading time of each patch pattern becomes longer if the patch pattern length is the same. However, in the phototransistor used in the light receiving unit 203 of the reflected light amount sensor 108 (308), the change time of the output signal with respect to the change of the incident light amount does not change, so the output signal value follows the incident light amount and becomes stable. The time until is the same. For this reason, in order to stabilize the output signal value, the time required to form an extra image for the leading patch pattern 303y may be the same as that for the other patch patterns 303m to 303k. The length will be different.

  In the case of this printer engine, the leading patch pattern 303y is 5 mm longer than the subsequent patch patterns 303m to 303k in the normal mode in which the intermediate transfer member 104 rotates at 150 mm / s. In the thick paper mode in which the rotation speed of the intermediate transfer member 104 is rotated at a speed of 90 mm / s, the leading patch pattern 303y is 3 mm longer than the subsequent patch patterns 303m to 303k. This numerical value is calculated by the ratio of the rotational speed of the intermediate transfer member 104 in the normal mode and the thick paper mode.

  In other words, by changing the length of the leading patch pattern 303y in accordance with the speed of the intermediate transfer body 104 from which the reflected light amount sensor 108 reads the patch patterns 303y to 303k, the following is possible. That is, it is possible to achieve both a more stable reading of the density of the patch patterns 303y to 303k according to the image forming speed and a reduction in the amount of waste toner.

[Second Embodiment]
The same components as those in the first embodiment will be described with the same reference numerals.

  Even if an electrophotographic printer engine performs image formation at the same gradation level, the density actually formed on the intermediate transfer member 104 is not necessarily proportional. For this reason, a predetermined gradation pattern (patch pattern) is formed and read by the reflected light amount sensor 108 to measure the density difference between the ideal gradation level and the actual gradation level, and the input image data In general, control is performed such as correcting the output gradation level for. These controls are performed by the control unit 704 described in FIG. 7 (corresponding to image gradation correction means).

  FIG. 5 shows an example in which a patch pattern for gradation correction (corresponding to a pattern image) is formed, and the intermediate transfer member 104 is viewed from above. An arrow F in FIG. 5 indicates the traveling direction of the intermediate transfer member 104.

  The gradation correction patch patterns 503 to 512 each have a gradation level of 8 bits, and a laser PWM modulation pattern according to five gradation levels from 00h to FFh in hexadecimal notation. A patch pattern is being created. The higher the gradation level, the higher the density of the visible toner image. Each patch pattern is formed by changing only the PWM modulation pattern of the laser scanner units 103y to 103k according to the gradation level without changing the charging bias voltage and the developing bias voltage, which are the operation parameters of the process units 102y to 102k. It is.

  The patch patterns 503 to 507 are formed with Y toner, and are arranged in descending order of gradation level. The patch pattern 503 is a patch pattern with a gradation level FFh, the patch pattern 504 is a patch pattern with a gradation level D0h, and the patch pattern 505 is a patch pattern with a gradation level A0h. The patch pattern 506 is a patch pattern with a gradation level of 60h, and the patch pattern 507 is a patch pattern with a gradation level of 20h.

  The five patterns of gradation levels are treated as one set, and one set of patch patterns is created for each color YMCK.

  The patch patterns 508 to 512 are formed with M toner, and are arranged in descending order of gradation level. The patch pattern 508 is a patch pattern having a gradation level FFh, the patch pattern 509 is a patch pattern having a gradation level D0h, and the patch pattern 510 is a patch pattern having a gradation level A0h. The patch pattern 511 is a patch pattern with a gradation level of 60h, and the patch pattern 512 is a patch pattern with a gradation level of 20h.

  Although not shown in FIG. 5, similarly, the same patch pattern is imaged for each set of C and K toners.

  The lengths of the patch patterns 503 to 512 in the main scanning direction are common and 20 mm, respectively. Further, the patch pattern 503 and the patch pattern 508 of the gradation level FFh at the head of the gradation of each color are 20 mm in length in the sub-scanning direction, and the patch patterns 504 to 507 and the patch pattern 509 to other gradation levels. The length of 512 in the sub-scanning direction is 15 mm. For C and K toners not shown in the drawings, the patch pattern of gradation level FFh has a length in the sub-scanning direction of 20 mm. The lengths in the sub-scanning direction of patch patterns of other gradation levels are 15 mm.

  Immediately before the patch pattern 503 imaged at the gradation level FFh is the base portion of the intermediate transfer body 104. Similarly, immediately before the patch pattern 508, the lowest gradation level is 20h in the previous color Y pattern. This is a patch pattern 507 having a low density. The main scanning direction is a direction perpendicular to the traveling direction F of the intermediate transfer member 104, and the sub-scanning direction is a direction parallel to the traveling direction F.

  The graph of FIG. 6 shows an output signal waveform obtained by reading the reflected light amount of the patch patterns 503 to 512 by the reflected light amount sensor 108. The horizontal axis is the time axis (t [ms]), and the vertical axis indicates the voltage (V [v]) of the output signal. Reference numeral 601 denotes the waveform of the output signal voltage of the reflected light amount sensor 108.

  A section 602 is a base portion from the base portion of the intermediate transfer member 104 to the patch pattern 503.

  An interval 603 and an interval 604 are portions of an output signal provided by the patch pattern 503, an interval 605 is an output signal portion provided by the patch pattern 504, and an interval 606 is an output signal portion provided by the patch pattern 505. A section 607 is a portion of the output signal provided by the patch pattern 506, and a section 608 is a portion of the output signal provided by the patch pattern 507.

  Subsequently, a section 609 and a section 610 are output signal parts provided by the patch pattern 508, a section 611 is a signal output part provided by the patch pattern 509, and a section 612 is an output signal part provided by the patch pattern 510. A section 613 is a part of an output signal provided by the patch pattern 511, and a section 614 is a part of an output signal provided by the patch pattern 512. The section 615 is a portion of an output signal that is brought about by a patch pattern having a high density that is formed at the gradation level FFh of the next color C following the patch pattern 512.

  Since the length of each level of the output signal is proportional to the size of the patch pattern, since the patch patterns 504 to 507 and the patch patterns 509 to 512 have the same length in the sub-scanning direction, the sections 605 to 608 and the sections 611 to 611 614 is the same time. Further, since the lengths of the patch patterns 503 and 508 of the gradation level FFh are equal, the length obtained by adding the sections 603 and 604 is equal to the length obtained by adding the sections 609 and 610.

  Since the lengths of the patch patterns 503 and 508 are longer than the patch patterns 504 to 507 and patch patterns 509 to 512 of other colors, the sections 603 and 604 are added to the sections 603 to 608 and sections 611 to 614. Longer than each of.

  When attention is paid to the section 603, the section 602 before the section 603 is a base portion of the intermediate transfer member 104 and has a high output signal voltage. Further, since the section 603 and the subsequent toner images are formed at the gradation level FFh, the output signal voltage changes from the section 602 to the section 603 toward a very low value. Indicates a stable value. Therefore, a stable output signal can be read in the section 604 even in the pattern area of the same gradation level FFh than in the section 603.

  Similarly, when attention is paid to the section 609, the section 608 before the section 609 is a portion of the patch pattern 507 formed at the level of 20h having the lowest gradation level among the patch patterns formed by the Y toner. For this reason, the output signal voltage is higher in the section 608 than in the background portion of the intermediate transfer member 104. In the section 609 and thereafter, the output signal voltage changes toward a very low value because it is a toner image formed at the gradation level FFh by the M toner of the next color. Indicates a stable value. Therefore, it is possible to read a more stable output signal in the section 610 than in the section 609 even in the patch pattern region having the same gradation level FFh.

  The section 604 has the same length of time as the subsequent sections 605 to 608, and the output signal voltage can be sampled at the same reading interval. Similarly, the section 610 has the same length of time as the subsequent sections 611 to 614, and the output signal voltage can be sampled at the same reading interval.

  The output signal voltages in the sections 604 to 608 and sections 610 to 614 are sampled, and the γ table is created by calculating the sampling result of each section and each gradation level when the patch pattern is formed. In this way, an image formation having gradation characteristics close to linear is realized by correcting the gradation level for input data at the time of normal user image creation.

  As described above, in the patch pattern for gradation correction arranged so that a plurality of gradation levels are continuous, the length in the sub-scanning direction is made longer than the other patch patterns by the gradation pattern located at the head. As a result, it is possible to realize stable reading of the reflected light amount without lengthening the entire tone correction patch pattern.

  Also, when the gradation pattern is arranged such that a plurality of gradation levels are continuous and the gradation level difference is large in the middle of the arrangement, only the patch pattern arranged immediately after the gradation level change is in the sub-scanning direction. The length of is longer than other patch patterns. For example, when attention is paid to the patch pattern 507 having the gradation level 20h and the patch pattern 508 having the gradation level FFh in FIG. 5, the difference between the gradation levels of the two continuous patch patterns 507 and 508 is large. Thus, when the gradation level difference is large, the length of the subsequent patch pattern 508 in the sub-scanning direction is made longer than the other patch patterns. Note that the determination of the magnitude of the gradation level difference is performed, for example, by setting a threshold value in advance and comparing it with the threshold value (determining whether or not the threshold level is exceeded). Accordingly, it is possible to realize stable reading of the reflected light amount without lengthening the entire tone correction patch pattern.

  If the patch pattern for gradation correction can be kept short, the amount of waste toner generated during the gradation correction operation can be reduced, and the downtime due to the gradation correction operation can be reduced. It can be said that it is effective in reducing

1 is a schematic cross-sectional view showing an internal configuration of an image forming apparatus according to the present invention. 1 is a schematic cross-sectional view illustrating a configuration of a reflected light amount sensor included in an image forming apparatus according to the present invention. FIG. 3 is a diagram illustrating the size and positional relationship of an image density correction patch pattern formed in the first embodiment. 5 is a graph illustrating an output waveform when an image density correction patch pattern formed in the first embodiment is measured by a reflected light amount sensor. FIG. 10 is a diagram exemplifying a size and a positional relationship of an image gradation correction patch pattern formed in the second embodiment. It is the graph which illustrated the output waveform when the patch pattern for image gradation correction formed in the 2nd embodiment is measured with the reflected light amount sensor. FIG. 3 is a control block diagram for controlling the image forming apparatus according to the present invention.

Explanation of symbols

101y, 101m, 101c, 101k Toner bottles Y, M, C, K
102y, 102m, 102c, 102k Process units Y, M, C, K (corresponding to pattern forming means)
103y, 103m, 103c, 103k Laser scanner units Y, M, C, K
104 Intermediate transfer member (equivalent to an image carrier)
105y, 105m, 105c, 105k Primary transfer rollers Y, M, C, K
106 Secondary transfer roller 107 Intermediate transfer body cleaner 108 Reflected light quantity sensor (corresponding to measuring means)
109 Paper cassette 110 Paper feed roller 112 Registration roller 113 Fixing roller 114 Pressure roller 115 Paper discharge flapper 116 Inner paper discharge tray 117 Paper discharge tray 202 Light emitting part 203 of reflected light quantity sensor Light receiving parts 303y, 303m, 303c of reflected light quantity sensor 303k Patch pattern Y, M, C, K for image density correction
401 Output signal voltage waveforms 402 and 408 of the reflected light amount sensor Output signal sections 403 and 404 corresponding to the background portion of the intermediate transfer member Output signal sections 405 to 407 corresponding to the patch pattern 303y Output corresponding to the patch patterns 303m to 303k Signal section 503 to 507 Tone correction patch pattern (Y toner)
508 to 512 Tone correction patch pattern (M toner)
601 Output signal voltage waveform of reflected light amount sensor 602 Output signal sections 603 to 608 corresponding to the background portion of the intermediate transfer member Output signal sections 609 to 614 corresponding to patch patterns 503 to 507 Output corresponding to patch patterns 508 to 512 Signal section 704 Control unit (corresponding to image density correction means and image gradation correction means)

Claims (6)

In an image forming apparatus for forming an image on an image carrier,
Pattern control means for forming a pattern image on the image carrier in order to control the density of the image;
Measuring means for irradiating the pattern image formed by the pattern forming means with light and measuring the amount of reflected light;
Image density correction means for correcting the density of the image based on the amount of reflected light measured by the measurement means;
When correcting the density of the image by the image density correction means,
The pattern forming means sequentially forms a plurality of pattern images parallel to the traveling direction of the image carrier,
An image forming apparatus characterized in that a pattern image positioned at the head of the plurality of pattern images with respect to the traveling direction is formed longer in the traveling direction of the image carrier than other pattern images.   Of the plurality of pattern images formed by the pattern forming means, the amount of difference in the length in the traveling direction of the image carrier between the pattern image located at the head and the other pattern image is the image carrier. The image forming apparatus according to claim 1, wherein the image forming apparatus is made different according to the rotation speed of the image forming apparatus. In an image forming apparatus for forming an image on an image carrier,
Pattern forming means for forming a pattern image on the image carrier in order to control the gradation of the image;
Measuring means for irradiating the pattern image formed by the pattern forming means with light and measuring the amount of reflected light;
Image gradation correction means for correcting the gradation of the image based on the amount of reflected light measured by the measurement means;
When correcting the gradation of the image by the image gradation correcting means,
The pattern forming means sequentially forms a plurality of pattern images parallel to the traveling direction of the image carrier,
An image forming apparatus characterized in that a pattern image positioned at the head of the plurality of pattern images with respect to the traveling direction is formed longer in the traveling direction of the image carrier than other pattern images.   Of the plurality of pattern images formed by the pattern forming means, the amount of difference in the length in the traveling direction of the image carrier between the pattern image located at the head and the other pattern image is the image carrier. The image forming apparatus according to claim 3, wherein the image forming apparatus is made different according to the rotation speed of the image forming apparatus. In an image forming apparatus for forming an image on an image carrier,
Pattern forming means for forming a pattern image on the image carrier in order to control the gradation of the image;
Measuring means for irradiating the pattern image formed by the pattern forming means with light and measuring the amount of reflected light;
Image gradation correction means for correcting the gradation of the image based on the amount of reflected light measured by the measurement means;
When correcting the gradation of the image by the image gradation correcting means,
The pattern forming means sequentially forms a plurality of pattern images parallel to the traveling direction of the image carrier,
When the gradation level difference between two consecutive pattern images among the plurality of pattern images is greater than or equal to a preset threshold value, the pattern that is arranged later in the traveling direction among the two consecutive pattern images The image forming apparatus is characterized in that the image is formed longer in the traveling direction of the image carrier than the other pattern images.   Of the two consecutive pattern images, the amount of difference in the length of the image carrier in the traveling direction between the pattern image disposed in front of the traveling direction and the pattern image disposed later is the 6. The image forming apparatus according to claim 5, wherein the image forming apparatus is made different according to the rotation speed of the image carrier.

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