JP2010262243A - Image-forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image-forming apparatus capable of performing gradation correction control while suppressing toner consumption and capable of shortening a time required for the correction control without reducing gradation correction accuracy. <P>SOLUTION: The electrophotographic color image-forming apparatus is configured to optically detect density of each of a plurality of gradation toner patches formed on an intermediate transfer belt by a sensor, and correct the gradation properties based on the detected values. One high-light gradation patch (4) and one shadow gradation patch (8) are formed, and the density detection values of the two gradation patches (4) and (8) are compared with the density detection values of the two gradation patches (4) and (8) obtained in the last gradation correction control process, and in accordance with each difference between the density detection values obtained in the last process and the current process, the number and the gradation-level of gradation patches (1) to (12) to be formed are selected, and the gradation correction control is performed. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an image forming apparatus, and more particularly to an image forming apparatus that finally transfers and fixes a toner image on a recording material by an electrophotographic method or the like.

  2. Description of the Related Art Conventionally, an apparatus for forming a color image by an electrophotographic process has juxtaposed process units for forming toner images of Y (yellow), M (magenta), C (cyan), and K (black) in the recording sheet conveyance direction. The tandem method is generally adopted. Each process unit irradiates a photoconductive drum with light modulated based on image data to form an electrostatic latent image, develops the latent image with the respective color toners, and forms a primary image on the intermediate transfer belt. Transcribe and synthesize. Thereafter, the synthesized toner image is secondarily transferred from the intermediate transfer belt onto the recording sheet, and is heat-fixed.

  In this type of image forming apparatus, gradation correction control is generally adopted. That is, the density of the toner image formed on the intermediate transfer belt varies depending on conditions such as environment and durability even if the development conditions are the same. For this reason, the image forming apparatus has a gradation correction function that optically detects the density of a plurality of gradation patches formed by toner formed on the intermediate transfer belt and corrects gradation characteristics according to the detected value. ing. The toner used for gradation correction control is discarded after density detection.

  In order to reduce the size of the image forming apparatus, there is a problem of reducing the capacity of the waste toner box, and it is necessary to reduce the amount of toner consumption. From this point of view, attempts have been made to reduce toner consumption in tone correction control.

  By the way, tone correction control is performed periodically, but if the tone characteristics do not change significantly from the time of this tone correction, a tone conversion table that does not change much from the correction in the previous tone correction control is obtained. It will be set. In such a case, there is no point in performing gradation correction control again, and as a result, wasteful gradation patches are formed to increase the amount of toner consumption and increase the amount of waste toner, which is necessary for gradation correction. Time is wasted.

  For this reason, in the image forming apparatus described in Patent Document 1, a gradation patch is formed with toner for each of several copies / prints, and the gradation characteristic measured by the density sensor is within the range of the target gradation characteristic. The tone correction control is automatically executed only when it is not within the range, so that unnecessary correction control is not performed. However, in this tone correction control, one tone patch is formed as a test, and when the tone patch density is more than a predetermined value, a plurality of toner patches are subsequently formed in a predetermined number. For this reason, when there is a gradation area where the change in gradation characteristics from the previous gradation correction is small, there is a problem that an excessive toner patch is formed more than necessary in the gradation area. ing.

  Further, in the image forming apparatuses described in Patent Documents 2 and 3, the shaded gradation patch is formed at least twice, and the image data of the patch formed after the second time is the result of the first gradation correction. A patch is formed as the image data based on it, and the accuracy of gradation correction is improved. However, this gradation correction control has a problem that it always takes two or more patches and takes time.

Japanese Patent Laid-Open No. 9-230644 JP-A-10-333377 JP 2003-241446 A

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to provide an image forming apparatus capable of controlling tone correction by reducing toner consumption and reducing time without reducing tone correction accuracy.

In order to achieve the above object, an image forming apparatus according to an aspect of the present invention includes:
In an image forming apparatus having a gradation correction function for optically detecting the density of a plurality of gradation patches by toner formed on an image carrier and correcting gradation characteristics according to the detected value,
The gradation patch of the highlight part and the gradation patch of the shadow part are formed one by one, and the density detection values of the two gradation patches are detected as the density detection of the two gradation patches in the previous gradation correction control. Compare the value and select the number of gradation patches to be formed, the gradation according to the difference between the current time and the previous time, and execute the gradation correction control.
It is characterized by.

  In the image forming apparatus, for example, when the difference between the current time and the previous time is smaller than a predetermined value, the gradation correction control is performed only by the density detection values of the two gradation patches. If the difference between the shadow patch in the shadow area is smaller than the predetermined value and the difference in the highlight patch in the highlight area is larger than the predetermined value, multiple gradation patches covering all gradations A gradation patch is formed by removing the vicinity of the gradation of the gradation patch in the shadow portion, and gradation correction control is performed based on the detected density value. In addition, if the difference between the gradation patches in the highlight area is smaller than the predetermined value and the difference in the gradation patches in the shadow area is larger than the predetermined value, the multiple gradations covering all gradations are displayed. A tone patch is formed by removing the vicinity of the tone of the tone patch in the highlight portion from the tone patch, and tone correction control is performed based on the detected density value. If the difference between the current time and the previous time is greater than a predetermined value, a plurality of gradation patches covering all gradations are formed, and gradation correction control is performed based on the detected density values.

  The gradation area that does not form a gradation patch in the current density detection is an area where there is little change from the previous gradation correction control. Therefore, even if the result of the previous gradation correction control is updated as it is, the gradation correction accuracy is improved. The toner consumption is not reduced and the time required for correction is shortened.

  According to the present invention, in gradation correction control, the accuracy of gradation correction is not lowered, toner consumption can be suppressed and time can be shortened.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. 6 is a graph showing output characteristics of a toner density sensor with respect to toner density of a gradation patch. 6 is a graph showing a density detection value with respect to an output of a toner density sensor. It is explanatory drawing which shows typically the case where a gradation characteristic is reproduced linearly, and an actual reproduction image. It is a graph which shows the relationship between the input gradation of original image data, and the reproduced image density. It is explanatory drawing of the gradation patch formed at the time of gradation correction. 6 is a graph showing the relationship between gradation and toner density. 6 is a graph (gradation conversion table) showing input gradations of original image data and corrected gradations. It is explanatory drawing which shows two gradation patches used as a reference | standard. It is a graph which shows the density | concentration detection value in the 1st example of gradation correction control. It is explanatory drawing which shows the gradation patch formed in the 2nd example of gradation correction control. It is a graph which shows the density | concentration detection value in the 2nd example last time. It is explanatory drawing which shows the gradation patch formed in the 3rd example of gradation correction control. It is a graph which shows the density | concentration detection value in the last 3rd example. It is explanatory drawing which shows the gradation patch formed in the 4th example of gradation correction control. It is a graph which shows the density | concentration detection value in the last 4th example. It is a graph which shows the method of determining two gradation patches used as a standard. It is a flowchart figure which shows the control procedure of gradation correction | amendment. FIG. 19 is a flowchart (continuation of FIG. 18) showing a control procedure of gradation correction.

  Embodiments of an image forming apparatus according to the present invention will be described below with reference to the accompanying drawings.

(Schematic configuration of image forming apparatus, see FIG. 1)
An image forming apparatus according to an embodiment of the present invention is a tandem type electrophotographic printer as shown in FIG. 1, and is a process unit for forming a toner image of each color of Y, M, C, K roughly 10 (10Y, 10M, 10C, 10K), an intermediate transfer unit 20, a paper feed unit 30 containing a recording sheet, a fixing unit 35, and an image reading unit 40.

  Each process unit 10 is provided with a photosensitive drum 11, a charging charger 12, a developing device 13, an exposure device 14, etc., and is drawn on each photosensitive drum 11 by light emitted from the exposure device 14. The electrostatic latent image is developed by the developing device 13 to form a toner image of each color. The image data is transferred from the image reading unit 40 or from the computer to the control unit 50.

  The intermediate transfer unit 20 includes an intermediate transfer belt 21 that is rotationally driven endlessly in the arrow Z direction. The formed toner image is primarily transferred onto the intermediate transfer belt 21 and synthesized. Note that such an electrophotographic image forming process is well known, and a detailed description thereof will be omitted.

  A sheet feeding unit 30 for feeding recording sheets one by one is disposed at the lower part of the apparatus main body, and the recording sheet is conveyed from the sheet feeding roller 31 to the nip portion between the intermediate transfer belt 21 and the secondary transfer roller 25. Here, the toner image (synthesized color image) is secondarily transferred. Thereafter, the recording sheet is conveyed to the fixing unit 35 where the toner is heated and fixed, and is discharged to a tray portion 36 disposed on the upper surface of the apparatus main body.

(Toner density detection sensor, see FIGS. 1 to 3)
A sensor SE1 for detecting the density of the gradation patch of toner formed on the intermediate transfer belt 21 for performing gradation correction control is disposed opposite to the surface of the intermediate transfer belt 21 on the downstream side of the process unit 10K. Has been. The sensor SE1 is an optical reflection type sensor composed of a light emitting element and a light receiving element.

  The reflected light from the gradation patch formed on the intermediate transfer belt 21 is received by the light receiving element and converted into an electrical output value. The toner patch includes a belt surface and a toner surface, and the sensor SE1 detects a toner concealment rate (a ratio of the toner to the entire patch area). As the reflected light decreases, the sensor output value decreases, and as shown in FIG. 2, the reflected light from the belt surface decreases as the toner concealment rate increases (the toner density increases), so the sensor output value decreases. . The density detection value with respect to the sensor output value is as shown in FIG. The sensor output values shown on the vertical axis in FIG. 2 and the horizontal axis in FIG. 3 are shown as 256 levels. In the present invention, the toner density detecting means is not limited to such a sensor SE1.

(Tone correction, see FIGS. 4 to 8)
By the way, the image forming apparatus is required to reproduce the density (shading) corresponding to the input original image data. If the density of the original image data to be output as an image is OD (Original Density) and the reproduced density on the paper is ID (Image Density), the ID is maintained in a linear relationship with respect to OD as gradation characteristics. Is required. FIG. 4A shows the case where the gradation characteristics are reproduced linearly. However, in practice, since there is a non-linear relationship in the image forming process, the density reproduced with respect to the input gradation of the original image data changes greatly for each gradation.

  Normally, as shown in FIG. 4B, an image is skipped in a low density highlight portion, and is reproduced thinly with respect to the gradation of the original image data, and an image is crushed in a high density shadow portion. It is reproduced darkly with respect to the gradation of the original image data. Further, if the sensitivity characteristics and development characteristics of the photosensitive drum 11 change due to environmental conditions such as humidity, the degree of durability, and individual differences between apparatuses, the gradation characteristics also change. FIG. 5 shows the relationship between the input gradation of the original image data and the reproduced image density. When the gradation characteristic is linear, it is as indicated by a straight line, but in reality, an image is formed with the gradation characteristic indicated by a curve.

  Therefore, it is necessary to correct the gradation characteristics so that the output image density does not change corresponding to the input gradation of the original image data. That is, in order to stably reproduce the output gradation in a linear manner, the gradation correction is executed at an appropriate timing, and the input level of the original image data is obtained so that a predetermined density is always obtained in all gradations. The key needs to be converted.

  As shown in FIG. 6, the gradation correction control is normally performed with gradation patches (1) to (12) that comprehensively represent all gradations from a low density (highlight part) to a high density (shadow part). Are formed on the intermediate transfer belt 21, and the density (concealment rate) of each of the gradation patches (1) to (12) is detected by the sensor SE1, and converted from the sensor output value to the density. Then, gradation correction is calculated based on the detected density value, and the input gradation of the original image data is converted so that an image is output with the corrected appropriate gradation characteristics. That is, the input gradation of the original image data is converted as indicated by the arrow so that the gradation detected by the sensor SE1 matches the input gradation of the original image data, and is used as the image data of the actual printing operation.

  Specifically, in FIG. 7, the horizontal axis represents the input gradation of the image data, and the vertical axis represents the density corresponding to the output value of the sensor SE1. Black circles represent sensor output values of the respective gradation patches (1) to (12). The sensor output value and the corresponding density are created in advance as a conversion table as shown in FIGS. 2 and 3, and converted from the sensor output value shown in FIG. 7 to the density. The converted density is referred to as a density detection value.

  The gradation characteristics that are actually output must be linear so that the gradation difference becomes a constant density difference in all gradations. The input gradation of the original image data is converted (corrected) so that the gradation characteristics are linear. A table used for this conversion (correction) is referred to as a gradation conversion table (see FIG. 8). In this way, gradation correction control determines a gradation conversion table that can correct the output gradation characteristics to a density corresponding to the input gradation of the original image data, and corrects all gradations.

(Gradation correction control, see FIGS. 9 to 19)
Hereinafter, the gradation correction control in this embodiment will be described. The step numbers referred to in the following description are the numbers given to the flowcharts of FIGS.

  The gradation correction control is executed at a predetermined timing (YES in step S1). The gradation correction control may be automatically performed at a preset timing or may be forcibly performed by a user or a service person. Normally, this is executed when the power is turned on, before or after a print job, or whenever a predetermined number of print operations are performed. Also executed immediately after replacement of consumables.

  In the gradation correction control, first, as shown in FIG. 9, the gradation patch (4) of the highlight part and the gradation patch (8) of the shadow part are formed on the intermediate transfer belt 21 one by one (step). S2). Then, the density of the two gradation patches (4) and (8) is detected by the sensor SE1 (step S3), and the density detection value is obtained. The density detection value of the gradation patch (4) is Dh, and the density detection value of the gradation patch (8) is Ds. The values Dh and Ds are compared with the density detection values Dh_r and Ds_r of the same patch in the previous gradation correction control (step S4). The differences ΔD are ΔDh = Dh−Dh_r and ΔDs = Ds−Ds_r, respectively. In accordance with the difference ΔD, the number of gradation patches to be formed and the gradation are selected, and gradation correction is performed (the gradation conversion table is changed). The difference ΔD is determined from the allowable range of image density, and for example, ΔD = 0.1. Based on the difference ΔD, gradation correction is executed by dividing the case into the first example, the second example, the third example, and the fourth example shown in Table 1 below.

  The first example is a case where the difference ΔDh in the gradation patch (4) and the difference ΔDs in the gradation patch (8) are both small (YES in steps S5 and S6). In this first example, even if the tone correction is performed this time, it is almost the same as the tone conversion table by the previous tone correction, so the two density detection values of the tone patches (4) and (8). Based on the above, simple gradation correction is performed (see FIG. 10, steps S8, S9, S10). That is, the gradation characteristics corrected by the previous gradation correction control are only slightly modified with the two detected values of this time. As a result, the toner consumption is reduced and the correction control time is shortened. Further, the accuracy of gradation correction does not decrease more than necessary.

  The second example is a case where the difference ΔDh in the gradation patch (4) is large and the difference ΔDs in the gradation patch (8) is small (YES in step S5, NO in step S7). In this second example, since the gradation in the vicinity of the gradation patch (8) has not changed in density since the previous gradation correction control, gradation patches (6) to (9) are formed as the next procedure. In this case, the gradation patches (1) to (3), (5), (11), and (12) are formed on the intermediate transfer belt 21 (see FIG. 11, step S11), and their density is measured by the sensor SE1. To obtain a density detection value. Together with the density detection values of the gradation patches (4) and (8) formed first, gradation characteristics are determined with 8 gradations (see FIG. 12, step S12). For the gradations corresponding to the gradation patches (6) to (10), the gradation characteristics corrected by the gradation correction control are updated as they are, and both are synthesized to create a new gradation conversion table (step S9). ). When a tone conversion table is created by synthesis, if a discontinuous part appears, a correction is made so that the part becomes smooth. Also in this second example, the toner consumption is reduced and the correction control time is shortened. Further, the accuracy of gradation correction does not decrease more than necessary.

  The third example is a case where the difference ΔDh in the gradation patch (4) is small and the difference ΔDs in the gradation patch (8) is large (NO in step S5, YES in step S6). In this third example, since the gradation in the vicinity of the gradation patch (4) has no change in density since the previous gradation correction control, gradation patches (2) to (6) are formed as the next procedure. Without any adjustment, gradation patches (1), (7), (9) to (12) are formed on the intermediate transfer belt 21 (see FIG. 13, step S13), and their density is detected by the sensor SE1, Obtain the density detection value. Together with the density detection values of the gradation patches (4) and (8) formed first, gradation characteristics are determined with 8 gradations (see FIG. 14, step S12). For the gradations corresponding to the gradation patches (6) to (10), the gradation characteristics corrected by the gradation correction control are updated as they are, and both are synthesized to create a new gradation conversion table (step S9). ). When a tone conversion table is created by synthesis, if a discontinuous part appears, a correction is made so that the part becomes smooth. Also in the third example, the toner consumption is reduced and the correction control time is shortened. Further, the accuracy of gradation correction does not decrease more than necessary.

  The fourth example is a case where the differences ΔDh and ΔDs in the gradation patches (4) and (8) are both large (NO in steps S5 and S7). In this fourth example, since the gradations near the gradation patches (4) and (8) have changed greatly since the previous gradation correction control, the gradation patches (1) to (1) to ( 3), (5) to (7), and (9) to (12) are formed on the intermediate transfer belt 21 (see FIG. 15, step S14), their densities are detected by the sensor SE1, and the density detection values are obtained. Ask. Together with the density detection values of the gradation patches (4) and (8) formed first, gradation characteristics are determined with 12 gradations (see FIG. 16, step S12), and a new gradation conversion table is created (step S9).

  As the gradation of the patch to be formed in advance, a gradation having a large variation in the density detection value is selected as shown in FIG. 17 according to the gradation characteristic detection history information. This improves the accuracy when correcting the gradation characteristics. However, since the gradations of the highlight part and the shadow part to be selected are meaningless when they are close to each other, it is necessary to select them with a certain gradation difference.

(Other examples)
Note that the image forming apparatus according to the present invention is not limited to the above-described embodiment, and can be variously modified within the scope of the gist thereof.

  In particular, in the above embodiment, the gradations (1) to (12) shown in FIG. 6 are used as gradations covering all gradations, but other gradations may be used, and the number is 12 pieces. It is not limited to. In addition to the tandem electrophotographic copying machine, the image forming apparatus to which the present invention is applied may be a printer, a facsimile, a complex machine of these, or a monochrome image forming apparatus. Further, the image carrier for forming the gradation patch may be a photosensitive drum, a photosensitive belt, or an intermediate transfer drum in addition to the intermediate transfer belt.

  As described above, the present invention is useful for an image forming apparatus, and in particular, can perform gradation correction control by reducing toner consumption and shortening time without reducing gradation correction accuracy. Is excellent.

DESCRIPTION OF SYMBOLS 10 ... Process unit 11 ... Photosensitive drum 12 ... Charger charger 13 ... Developing device 14 ... Exposure apparatus 20 ... Intermediate transfer unit 21 ... Intermediate transfer belt SE1 ... Toner density detection sensor

Claims (6)

In an image forming apparatus having a gradation correction function for optically detecting the density of a plurality of gradation patches by toner formed on an image carrier and correcting gradation characteristics according to the detected value,
The gradation patch of the highlight part and the gradation patch of the shadow part are formed one by one, and the density detection values of the two gradation patches are detected based on the density detection values of the two gradation patches. Compare the value and select the number of gradation patches to be formed, the gradation according to the difference between the current time and the previous time, and execute the gradation correction control.
An image forming apparatus. The gradation patch of the highlight part and the gradation patch of the shadow part are formed one by one, and the density detection values of the two gradation patches are detected based on the density detection values of the two gradation patches. If the difference between the current and previous times is smaller than a predetermined value as a result of comparison with the value, gradation correction control is performed only by the density detection value of the two gradation patches.
The image forming apparatus according to claim 1. The gradation patch of the highlight part and the gradation patch of the shadow part are formed one by one, and the density detection values of the two gradation patches are detected based on the density detection values of the two gradation patches. As a result of comparison with the values, if the difference between the gradation patch in the shadow area is smaller than the predetermined value and the difference in the gradation patch in the highlight area is larger than the predetermined value, all gradations are covered. Forming gradation patches excluding the vicinity of the gradation of the gradation patch of the shadow part from the plurality of gradation patches, and performing gradation correction control by their density detection values;
The image forming apparatus according to claim 1. The gradation patch of the highlight part and the gradation patch of the shadow part are formed one by one, and the density detection values of the two gradation patches are detected based on the density detection values of the two gradation patches. As a result of comparison with the values, if the difference between the gradation patch in the highlight area is smaller than the predetermined value and the difference in the gradation patch in the shadow area is larger than the predetermined value, all gradations are covered. Forming gradation patches excluding the vicinity of the gradation patch of the highlight part from the plurality of gradation patches, and performing gradation correction control according to their density detection values;
The image forming apparatus according to claim 1. The gradation patch of the highlight part and the gradation patch of the shadow part are formed one by one, and the density detection values of the two gradation patches are detected based on the density detection values of the two gradation patches. If the difference between the current value and the previous value is greater than a predetermined value as a result of comparison with the value, a plurality of gradation patches covering all gradations are formed, and gradation correction control is performed based on the detected density values. thing,
The image forming apparatus according to claim 1.   2. The gradation of the gradation patch of the highlight part and the gradation patch of the shadow part is selected from gradations having a large variation in density detection value according to a history of gradation characteristic detection. The image forming apparatus according to claim 5.

Images