JP6107102B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus that forms an image by an electrophotographic method such as a copying machine, a printer, a facsimile machine, or the like.

  Conventionally, a copying machine using an electrophotographic method has a problem that the image density changes with changes in usage environment such as temperature and humidity, and changes with time. Therefore, in order to always obtain a stable image density, a gradation pattern for density detection is created on an image carrier such as a photoconductor, and the patch density is detected by an optical detection means (also referred to as an optical sensor) and detected. A method of optimizing each image forming condition by obtaining the toner adhesion amount of the gradation pattern from the value and obtaining a relational expression of the toner adhesion amount with respect to the development potential (slope: development γ, x intercept: development start voltage Vk). Is widely used. In these methods, the image forming conditions are changed so that the target adhesion amount is obtained from the relational expression between the obtained development potential and the toner adhesion amount (specifically, LD power, charging bias, and development bias are changed). Therefore, a stable image density is always obtained. This adjustment operation is called process control.

  The process control described above is executed when the power is turned on or after a predetermined number of sheets have passed. However, there are cases where the developing ability changes and the image density changes between the previous process control and the next execution. In such a case, since it is impossible to control the image density, it may be possible to increase the execution frequency of the process control. However, since it is necessary to create a toner patch to implement this, the toner consumption amount Will increase. Further, since it takes time to perform the process control, there is a problem that the downtime of the apparatus becomes longer if the execution frequency of the process control is increased.

  In order to solve the above-mentioned problems, a method is known in which a toner patch is formed between papers during image formation and the image density is controlled to be constant. For example, “Patent Document 1” and “Patent Document 2” have means for detecting the toner density in the developing device, and the toner density control target value in the developing device according to the density of the toner pattern created in the non-image portion. A method of maintaining the image density by changing the above is disclosed. Recently, however, there is a desire to reduce the excessive consumption of toner by creating a toner pattern between papers, and correction by creating a reference toner pattern between papers tends to widen or not perform the toner pattern interval. It is coming.

  Further, when the toner pattern is formed on the intermediate transfer belt, if the secondary transfer roller is not separated for each image formation, the toner of the patch between the papers adhered to the secondary transfer roller is cleaned. It is necessary to provide a cleaning device. Further, when the secondary transfer roller is separated for each image formation or every several image formations, it is not necessary to provide a cleaning device, but a mechanical configuration capable of withstanding the frequently occurring secondary transfer contact / separation is required. Become. For these reasons, it is necessary to suppress the toner pattern creation between sheets as much as possible from the viewpoint of cost reduction.

  Therefore, for example, in “Patent Document 3”, the image density control reference value is obtained by grasping the transition of the image area ratio of the output image (the amount of toner replacement in the developer within a certain period) by the moving average of the image area ratio. And a method for stably maintaining a high-quality image is disclosed. According to this technique, the toner density control reference value can be optimally corrected according to the toner replacement amount within a certain period, and therefore any image output pattern can be dealt with. In addition, since it is not necessary to create a toner pattern during image formation, it is possible to reduce the amount of toner consumption, and since there is no need to provide a cleaning device for the secondary transfer roller, it is also very cost-effective. It is an effective method.

  However, in the above-described technique, the toner density control reference value is changed by predicting the change in the image density according to the toner replacement amount. Therefore, feedback control is performed by detecting the actual image density (toner adhesion amount). Therefore, there is a problem in that the correction amount set in advance may be shifted depending on the usage environment such as temperature and humidity, or changes with time, and the correction may not be performed properly.

  The present invention solves the above-described problems, makes it possible to control image density constant without executing image formation condition adjustment control using a reference patch, and without increasing toner consumption and apparatus downtime. An object is to provide an image forming apparatus.

According to the first aspect of the present invention, the developer carried on the developer carrying member is conveyed to the developing area, and the electrostatic latent image formed on the latent image carrying member is developed with the developer to form a toner image. a developing device for a material to be transferred to the toner image is photographed rolling, the and a detection means to provided to detect the toner image, with the number of pixels of the output image can be obtained from the writing device In the image forming apparatus capable of changing the image forming condition of the developing device based on the detection result of the detecting means in order to obtain an appropriate toner adhesion amount, the output image is analyzed and a predetermined writing condition is analyzed. A specific area that matches the image is extracted, and the toner image on the transfer medium in the specific area is detected by the detection means, and the image forming conditions are changed, and image formation using four image forming colors is possible. And the detection means is the same as that of the transfer object. There are two in the scanning direction, and the first detection means is on the transfer object between the first image formation color and the second image formation color or the second image formation color and the third image formation. The second detection means is arranged to detect the image on the transferred object downstream in the running direction from the fourth image forming color, and is arranged in two colors. When the specific area is formed by the color superimposition, the toner adhering amount before the color superposition is detected by the first detection means is detected, and then the color superposition is performed by the second detection means. And detecting the adhesion amount of the two superimposed colors by subtracting the detection result by the first detection means from the detection result by the second detection means. And

  According to the present invention, a specific area is extracted from the information of the output image, and the specific area is detected by the optical sensor, whereby the toner adhesion amount can be calculated, and the image forming conditions can be adjusted from the result. As a result, it is not necessary to create a toner pattern for adjustment, the toner consumption can be reduced, and the apparatus downtime is not increased to detect an image during image formation, and stable image density control is performed. Can do.

1 is a schematic front view of an image forming apparatus to which an embodiment of the present invention can be applied. 1 is a schematic plan view of a main part of a developing device to which an embodiment of the present invention can be applied. It is a flowchart explaining the process control operation | movement performed by one Embodiment of this invention. It is the schematic which shows an example of the gradation pattern used for one Embodiment of this invention. FIG. 6 is a diagram illustrating a relationship between a development potential and a toner adhesion amount used in an embodiment of the present invention. It is the schematic explaining the conventional image information acquisition method. It is the schematic explaining the image information acquisition method in one Embodiment of this invention. It is the schematic explaining the image information acquisition method in one Embodiment of this invention. It is the schematic explaining the image information acquisition method in one Embodiment of this invention. It is a flowchart explaining the image density control method in one Embodiment of this invention. It is a figure explaining the development bias correction control in one embodiment of the present invention. FIG. 5 is a diagram illustrating toner density control reference value correction control according to an embodiment of the present invention. It is the schematic explaining the image information acquisition method of the image in which color superposition in one Embodiment of this invention was performed. It is a schematic front view of the image forming apparatus used for the modification of one Embodiment of this invention. It is a schematic front view of the image forming apparatus used for the other modification of one Embodiment of this invention.

  FIG. 1 shows a main part of a full-color printer as an image forming apparatus used in an embodiment of the present invention. In the figure, four photosensitive drums 1Y (yellow), 1M (magenta), 1C (cyan), and 1K (black), which are latent image carriers, are equally spaced at the center of the main body of the full-color printer 10. It is installed side by side. Hereinafter, the photosensitive drum 1Y for the yellow image will be described, but the same applies to the photosensitive drums 1M, 1C, and 1K of other colors except that the toner colors are different.

  The photosensitive drum 1Y is rotationally driven in the clockwise direction in the drawing by a drive motor (not shown). Image forming means such as a charging roller 2, a developing device 4 having a developing roller 3 as a developer carrying member, and a cleaning device 7 are arranged around the photosensitive drum 1Y in accordance with an electrophotographic process. The surface of the photosensitive drum 1Y is uniformly charged by the charging device 2 and then exposed to light from a writing device (not shown), and an electrostatic latent image corresponding to image information is formed on the surface. The developer in the developing device 4 is conveyed by the developing roller 3 to a developing nip region facing the photosensitive drum 1Y, and toner is attached to the electrostatic latent image on the photosensitive drum 1Y to visualize it.

  The toner image on the photosensitive drum 1Y is transferred to an intermediate transfer belt 8 serving as a transfer target disposed on the upper side of each photosensitive drum 1, and the toner images of the respective colors are transferred onto the intermediate transfer belt 8 as the movement proceeds. Overlapping is performed by sequentially transferring. The color-superposed toner images move to the position of the secondary transfer device 12 and are transferred onto the transfer paper at this position to form an image on the transfer paper. The cleaning device 7 removes unnecessary toner remaining on the photosensitive drum 1 and stores unnecessary toner in a waste toner bottle (not shown). By repeating the above procedure, image formation is continuously performed.

  FIG. 2 is a plan view of the developing device 4. The developing device 4 includes the developing roller 3 as described above, and the developing roller 3 is disposed so as to face the photosensitive drum 1. The developing device 4 is provided with a biaxial conveying screw including a first screw 13 and a second screw 19, and the developer is circulated and conveyed in the developing device 4 by the rotation of the screws 13 and 19. In the portion where the first screw 13 is provided, the developer is pumped up to the surface of the developing roller 3, and the developer that has passed through the developing region is returned. A toner density sensor 5 is disposed below the developer chamber on the second screw 19 side. As the toner concentration sensor 5, for example, a sensor that measures the toner permeability in the developing device 4 is used. Here, in the toner density control, the output value (Vt) of the toner density sensor 5 is compared with the control reference value (Vtref) of the toner density, and the toner replenishing amount is calculated from an arithmetic expression according to the difference, and the toner replenishing device is operated. To drive. As a result, the toner is supplied into the developing device 4 through the toner supply port 20.

  In the image forming apparatus 10 shown in the present embodiment, a process control operation for optimizing the image density of each color is performed when the power is turned on or after a predetermined number of sheets are passed, in addition to the image forming mode described above. In this process control operation, in order to perform density detection, an image of a plurality of gradation patterns for each color is formed on the intermediate transfer belt 8 by sequentially switching between a charging bias and a developing bias at an appropriate timing. These gradation patterns are detected by an optical sensor 6 as a detecting means disposed in the vicinity of the driving roller 15 of the intermediate transfer belt 8 as shown in FIG. 1, and the output voltage is converted into a toner adhesion amount. Γ representing the developing ability and the development start voltage Vk are calculated. Based on the calculated values, control is performed to change the development bias and toner density control target values.

  Next, the process control operation performed in this embodiment will be described based on the flowchart shown in FIG. First, the apparatus is started up (ST01). In this case, the bias of various motors and various devices is turned on when the power is turned on or when a predetermined number of sheets are passed, and preparation for executing process control is performed. Next, the LED current of the optical sensor 6 is adjusted as necessary (ST02). This irradiates the background portion of the intermediate transfer belt 8 with LED light, detects the regular reflection light, and adjusts the LED current so that the detected regular reflection light output is 4V. This adjustment operation is called Vsg adjustment, and the Vsg adjustment is performed for all sensors. However, since it takes time to adjust Vsg, the LED current value at the previous adjustment is used to irradiate the background portion of the intermediate transfer belt 8 with LED light for a predetermined time, and the specular reflection light detected by detecting the specular reflection light. Find the average output. This is called Vsgave detection. If the obtained average value is within a predetermined range, it is determined that there is no need to adjust the LED current, and Vsg adjustment is not executed. Next, the output (Vt) of the toner density sensor 5 is acquired (ST03). This is measured in order to know the current toner density, and is necessary for toner density correction (Vtref) described later.

  Next, a gradation pattern is created (ST04). This is necessary to detect the development γ. In the present embodiment, specifically, the width in the main scanning direction is 10 mm and the sub-scanning direction corresponds to the position where the optical sensor 6 is provided as shown in FIG. A gradation pattern is created with a width in the scanning direction of 14.4 mm and a pattern interval of 5.6 mm. Here, it is desirable that the number of gradation patterns for each color to be created be a number that fits in the pitch between the photosensitive drums. This is because, when the total length of the gradation pattern of each color to be created becomes longer than the pitch between the photosensitive drums, it overlaps with other colors. It is necessary to start writing the gradation pattern of the next color after waiting. In such an operation, it takes a long time to create gradation patterns for all colors, and the time required for the adjustment operation becomes long.

  Next, the gradation pattern is detected by the optical sensor 6 (ST05). The optical sensor 6 detects the toner adhesion amount of each color pattern in the gradation pattern created and transferred to the intermediate transfer belt 8 as described above. In this embodiment, the black pattern detects only regular reflection light, and the cyan, magenta, and yellow patterns detect both regular reflection light and diffuse reflection light. Further, a plurality of optical sensors 6 for density detection are arranged as shown in FIG. 4, and a gradation pattern of all colors is detected by a center sensor provided at the center of the image.

  Next, the detection value of the optical sensor 6 is converted into the toner adhesion amount (ST06). This calculates the toner adhesion amount from the output value of the optical sensor 6. In the present embodiment, an optical sensor 6 including a light receiving element that receives specularly reflected light and a light receiving element that receives diffusely reflected light is used, and a toner patch having a high adhesion amount can be detected. In the optical sensor 6, the output of the light emitting element changes or the output of the light receiving element changes due to temperature change or deterioration with time, and the output of the light receiving element also changes due to deterioration of the image carrier over time. For this reason, if the toner adhesion amount is uniquely determined from the output value of the light receiving element without any correction (calibration) of the output value of the light receiving element, there is a problem that it is not possible to accurately detect the toner adhesion amount. . Therefore, correction control of the optical sensor 6 is performed, and the toner patch adhesion amount is obtained from the output value of the light receiving element (diffuse reflection light receiving element) that receives the diffuse reflected light. In this embodiment, the toner patch adhesion amount is calculated using the method described in Japanese Patent Application Laid-Open No. 2006-139180.

  Next, development γ and development start voltage Vk are obtained (ST07). This determines the development γ and the development start voltage Vk from the relationship between the development potential at the time of toner patch image formation and the toner adhesion amount obtained in step ST06. Specifically, as shown in FIG. 5, the horizontal axis represents the development potential, the vertical axis represents the toner adhesion amount, and a linear equation is obtained by the least square method. The slope of this linear equation is called development γ, and the x-intercept is called development start voltage Vk.

Next, the developing bias necessary for obtaining the target toner adhesion amount is obtained (ST08). This obtains the development potential (horizontal axis) from the target adhesion amount (vertical axis) based on the above-described linear linear equation. The target adhesion amount is determined in advance to a value necessary for obtaining the top concentration (determined by the degree of coloring of the toner pigment and the toner particle diameter, but is generally about 0.4 to 0.6 mg / cm ² . is there). Then, the obtained development potential is converted into a development bias. This is calculated as developing bias Vb [−V] = developing potential [−V] + exposed portion potential V1 [−V]. The development bias value obtained individually is set as the development bias Vb of the image portion. The charging bias Vc is determined in advance so that the carrier does not fly to the photoconductor (Vb = 400 to 750 [−V], Vc = Vb + 100 to 200 [−V] is generally used). In this way, the obtained Vb and Vc are set as the bias at the time of image formation. Finally, the toner density control reference value (Vtref) is corrected (ST09).

Here, an output image information acquisition method according to the present invention will be described. First, as a comparison, acquisition of output image information in a conventional image forming apparatus will be described. In the conventional machine, the number of pixels of the output image is acquired from the writing device and used for toner replenishment control or the like, and in the conventional method, the number of pixels for each sheet of recording paper is acquired from the writing device. For example, a case where an image having a pixel density of 600 dpi × 600 dpi and an image area of 100 [cm ² ] is formed will be described. This 600 dpi × 600 dpi can be converted as follows.
Pixel density [dot / cm ² ] = 600 [dot] × 600 [dot] / (2.54 [cm] × 2.54 [cm]) ≈55800 [dot / cm ² ]
That is, in the case of 600 dpi × 600 dpi, 55800 dots can be formed per unit area. Therefore, when an image having an image area of 100 [cm ² ] is formed as described above, the number of pixels that can be acquired from the writing device is
Number of pixels [dot] = image area [cm ² ] × pixel density [dot / cm ² ] (1)
= 100 [cm ² ] × 55800 [dot / cm ² ] = 5580000 [dot].

For example, as shown in FIG. 6A, when a front solid image is output on A4 recording paper, the paper size of A4 recording paper is 21.0 cm × 29.7 cm = 623.7 cm ^2. From 1), the number of pixels is 623.7 × 55800 = 3482460 [dot]. Further, as shown in FIGS. 6B and 6C, when a solid image having a half area is output on A4 recording paper, the number of pixels that can be obtained is 3482460/2 = 17401230 [dot], respectively. , (B) and (c) have the same value. Thus, when the area of the image to be formed is the same, the number of pixels to be acquired is the same value even if the image forming position on the recording paper is different.

  As described above, when the number of pixels is acquired for each recording sheet as in the past, it can be determined how many images are formed per recording sheet, but what kind of image is recorded. It was not possible to specify where the paper was formed. On the other hand, the present embodiment employs a method of acquiring image information by dividing it instead of for each recording sheet. Specifically, as shown in FIG. 7, the recording paper is divided into the main scanning direction and the sub-scanning direction to acquire an image. In the example shown in FIG. 7, the recording paper is divided into five in the main scanning direction and 10 in the sub-scanning direction. The number of pixels of the output image is obtained by dividing.

  In the present embodiment, as shown in FIG. 8, an output image will be described in which a solid image is provided only on a part of an A4 size recording sheet and no image is displayed on all other parts. As in the prior art shown in FIG. 8A, when image information is acquired for each recording sheet, the number of pixels can be acquired as 3482460 / 50≈696049 [dot]. On the other hand, when the image information is acquired by dividing as shown in FIG. 8B, the number of pixels of the solid image portion is 696049 [dot], and the number of pixels of the other non-image portion is 0 [dot]. Become. The number of pixels that can be acquired in this way is the same, but it is possible to specify in which area the image is formed if the image information is acquired by dividing it.

Next, a method for determining whether or not the area is a solid image from the image information acquired by dividing will be described. In this embodiment, the image information is divided and acquired. However, since the number of image divisions at that time is determined in advance, each divided area area can be obtained by the following equation.
Divided area area [cm ² ] = paper area [cm ² ] ÷ number of divisions (2)
For example, when image information is acquired by dividing A4 recording paper into 50, one divided area is 21.0 [cm] × 29.7 [cm] ÷ 50 = 12.474 [cm ² ]. If the area of the divided area can be calculated in this way, the number of pixels in the reference area that can be acquired for each area can be calculated from the following equation.
Reference area pixel number [dot] = divided area area [cm ² ] × pixel density [dot / cm ² ] (3)
For example, when the pixel density is 600 dpi × 600 dpi and divided into 50, the number of reference area pixels is 12.474 × 55800≈6996049.

Here, the number of pixels acquired for each divided area is the maximum value when writing is performed in all the divided areas, that is, a solid image. That is, if the number of pixels acquired for each divided area matches the reference area pixel number, it can be determined that the divided area is a solid image. However, when determining a solid image, it is not necessary to determine that the image is a solid image only when the acquired number of pixels matches the number of reference area pixels. This is because if 95% of the divided areas (661246 [dot] in this embodiment) are solid images, the areas can be regarded as almost solid images.

If it is determined that the image is a solid image only when the acquired number of pixels matches the number of pixels in the reference area, it is determined that the image is not a solid image because most of the area is a solid image but does not match. This can reduce the chance of detecting a solid image. For this reason, a certain threshold value is set in advance, and if the number of acquired pixels is equal to or greater than the threshold value, a solid image may be determined. As will be described later, when a solid image is detected by a sensor, the detection results are averaged and calculated as a sensor output value of the solid image. Therefore, if 95% is solid, the sensor output is almost equivalent to 100% solid. A value is obtained. Therefore, the determination of a solid image is determined as a solid image when the number of acquired pixels is equal to or greater than a predetermined pixel number determination threshold as shown in the following equation. In addition, it is desirable that the pixel number determination threshold is set after confirming in advance an experiment that does not affect the determination of a solid image.
Number of pixels ≧ pixel number determination threshold value (4)
Alternatively, the determination may be made by calculating the printing rate from the number of pixels acquired using the following equation.
Print rate [%] = number of pixels / number of reference area pixels × 100 (5)
For example, when the acquired pixel number is 696049 [dot] and the reference area pixel number is 696049 [dot], the printing rate is calculated as 100%. Since the printing rate of 100% indicates that writing is performed in all the divided areas, it can be specified as a solid image. Therefore, the print rate is determined using the following equation, and if the print rate is equal to or greater than the threshold, it can be determined that the area is a solid image.
Printing rate ≧ printing rate judgment threshold value (6)
In order to specify a solid image, the printing rate determination threshold value in Equation (6) may be set to 100%. However, as described above, the sensor output value is averaged when an image is detected. Similarly, when performing the determination, the printing rate determination threshold value may be set to a value such as 95%.

  In this way, the solid image can be specified even if the printing rate is calculated instead of using the acquired number of pixels as it is. Furthermore, if the printing rate is calculated, the number of digits to be handled can be reduced as compared to using the value of the number of pixels as it is. As a result, the storage area in the memory can be reduced. Further, when the resolution is increased, for example, in the case of 1200 dpi × 1200 dpi, the number of pixels per unit area is four times that of 600 dpi × 600 dpi, and the number of digits of the number of pixels further increases. Thus, it is preferable to perform determination by calculating the printing rate rather than handling the acquired number of pixels as it is.

  As described above, if the image information of the output image is obtained by being divided, it is possible to specify whether or not the image for each divided area is a solid image using the information. Therefore, if it can be specified that a solid image is created at the same main scanning position as the optical sensor 6, it is possible to detect at the timing when the solid image reaches the sensor position and calculate the toner adhesion amount. Then, if the image forming conditions are adjusted using the detection result so that the amount of adhesion is constant, a toner pattern is created between the sheets and the like, and the image density is controlled to be constant without wastefully consuming the toner. It becomes possible.

  Next, a method for detecting the specified solid image with a sensor will be described. First, the image information acquired for each divided area is sequentially stored in the RAM, and at this time, the position information and the printing rate of the divided area are simultaneously stored in the RAM. And the detection timing of the optical sensor 6 is set using this preserve | saved information. For example, a case where an image as shown in FIG. 9A is output will be described. In this output image, since the area 4C is a solid image, 4C = 100 [%] is stored in the RAM. Non-image area 1A, area 1B,... = 0 = 0%. Since half of the area 10A is an image portion, 10A = 50 [%] is saved.

  In order to specify the solid image area of the recording paper, it is only necessary to extract the printing rate information that is equal to or higher than the printing rate determination threshold from the stored information and acquire the corresponding divided area information. If the area of the solid image can be identified, the distance from the leading edge of the recording paper to the solid image position can be identified. In the present embodiment, since it is divided into 10 in the sub-scanning direction, the sub-scanning length to the solid image in the area 4C is (recording paper sub-scanning length) / 10 × 3. In the case of A4 recording paper, the sub-scanning length from the leading edge of the recording paper to the solid image can be calculated as 29.7 [cm] /10×3=8.91 [cm]. Writing is actually performed, and a delay is performed so that detection is performed at the timing when the formed image reaches the sensor position.

  For image output, since a writing start signal is output for each sheet, the detection timing can be set using this signal as a trigger. Specifically, a solid image can be detected if detection is started with a delay of the time calculated by the following equation after the writing start signal is turned on.

{(Sub-scanning length from the leading edge of the recording paper to the solid image) + Distance from exposure to sensor (color)} / Linear velocity (7)
As described above, the sub-scanning length from the leading edge of the recording paper to the solid image can be obtained from the area information corresponding to the solid image stored in the RAM. The distance (color) from the exposure to the sensor is determined by the layout distance from the exposure position to the sensor detection position. Since this distance differs for each color, the distance of each color is calculated by the following equation.

Distance from exposure to sensor (color) = distance from exposure (K) to sensor + inter-image pitch × n (where n = 0, 1, 2, 3 K: 0, C: 1, M: 2, Y: 3) Formula (8)
If the detection is started at the timing shown in Expression (7) and detection is performed for the time obtained by dividing the sub-scanning length of the divided area that is known to be a solid image by the linear velocity, only the solid portion of the output image is detected. be able to. The above is a method for identifying a solid image area from an output image and detecting the area.

  As described above, if a solid image at the same main scanning position as the optical sensor 6 can be identified in the output image, it can be detected using the optical sensor 6. That is, when there is no solid image at the sensor detection position, detection cannot be performed. Therefore, as shown in FIG. 9B, the image information of only the same main scanning position as the optical sensor 6 may be stored in the RAM. According to this configuration, since the information of the area where detection cannot be performed is not saved, the storage area of the RAM can be reduced. As shown in the present embodiment, when the optical sensors 6 are provided at the three locations of the front, center, and rear, it is only necessary to store image information only at the respective main scanning positions.

  Next, an image on which color superposition has been performed as shown in FIG. 13 will be described. FIG. 13 is a solid red image, which shows an image in which yellow and magenta are overlaid. As described above, the position of the solid image can be specified by dividing and obtaining the output image. However, when color superposition is performed, the optical sensor 6 detects the position of the solid image as compared with a single color. It will be detected as twice the amount of adhesion. This is because the color cannot be determined because the optical sensor 6 uses infrared light, and when two colors are superimposed, the amount of adhesion is simply twice that of a single color. This is because it will be detected. For example, even when the yellow adhesion amount is large and the magenta adhesion amount is small, even when the yellow adhesion amount is small and the magenta adhesion amount is large, the same adhesion amount is detected. For this reason, when adjusting the image forming condition from the detection result, it is impossible to determine which color (or both colors) should be adjusted.

  There are three types of solid images created by overlapping two colors: red (yellow + magenta), blue (magenta + cyan), and green (cyan + yellow). When creating a solid image, Color superposition is generally not performed. Also, there is almost no formation of a solid image by superimposing three colors of yellow, magenta, and cyan. This is because if the amount of adhesion is too large, problems such as winding may occur in fixing, and the total amount of adhesion is configured to be regulated.

  As described above, in the present invention, as shown in FIG. 14, the same as the optical sensor 6 so as to detect on the intermediate transfer belt 8 between yellow as the first image forming color and magenta as the second image forming color. The optical sensor 9 is arranged as the first detection means. Then, an optical sensor 11 similar to the optical sensor 6 is disposed as a second detection unit at the same position as the optical sensor 6 on the downstream side in the belt running direction of black as the fourth image forming color. At this time, the sensors 9 and 11 are arranged so as to have the same main scanning position.

  By arranging the two optical sensors 9 and 11 in this way, it is possible to obtain the adhesion amount of each color for a red image in which yellow and magenta as shown in FIG. 13 are superimposed. Specifically, the solid image portion of the red image is specified by dividing and acquiring pixel information, and this specification is performed from the information of the divided areas of each color and the printing rate. From the yellow and magenta information, when both of the printing ratios of the same divided area are 100%, it is possible to determine that the two colors are superimposed and that the image is a red solid image.

  In such a case, the optical sensor 9 is used to detect the adhesion amount of the yellow solid color image before color superposition, and the red solid image after magenta color superimposition is optically detected. It is detected by the sensor 11. The adhesion amount detected by the optical sensor 11 is the adhesion amount for two colors of yellow and magenta. Since the amount of yellow monochrome adhesion is detected by the optical sensor 9, the amount of magenta monochrome adhesion can be measured by subtracting the amount of adhesion detected by the optical sensor 9 from the detection result of the optical sensor 11. By the above method, the adhesion amount of each color can be detected from a solid image in which two colors are superimposed.

  In the case of a green solid image, an image is created by overlaying yellow and cyan colors. Therefore, similarly to the above-described method, the adhesion amount of a single yellow color is obtained by the optical sensor 9, and the adhesion amount of two colors obtained by superimposing yellow and cyan is measured by the optical sensor 11. Then, by subtracting the adhesion amount obtained by the optical sensor 9 from the adhesion amount obtained by the optical sensor 11, the adhesion amount of cyan single color can be obtained.

  On the other hand, in the case of a blue solid image, an image is formed by superimposing magenta and cyan colors. In this case, the optical sensor 9 cannot detect magenta and cyan because they are arranged at a position before being transferred onto the intermediate transfer belt 8. For this reason, the detection is performed by the optical sensor 11, but in this case, the adhesion amounts of two colors superimposed are detected, so that the adhesion amounts of magenta and cyan cannot be obtained.

  Therefore, in the present embodiment, the previously measured magenta and cyan adhesion amount information is stored in the memory. This value is stored as a result of detecting a solid image of magenta and cyan single colors or a result obtained by detecting a solid image of red and green as described above. The magenta and cyan adhesion amounts are always updated and stored after detection. Then, from the result of detecting the blue image using this information, for example, the magenta adhesion amount is subtracted to calculate the cyan adhesion amount. At this time, the calculation may be performed using any of the stored magenta and cyan adhesion amounts, but the update may be performed using the newer one of the stored adhesion amounts. This is because the amount of adhesion changes depending on the state of the developing device, and the state of the developing device when the amount of adhesion stored in the memory is obtained may be different from the current state. For this reason, it is considered that the adhesion amount closer to the current state can be obtained by using the newly updated adhesion amount.

  However, if the amount of magenta and cyan that have been saved has not been updated for a while, it is considered that there is a difference between the current state and the state at the time of storage, so the detection of the blue solid image detected this time The adhesion amount is not calculated from the result. For this determination, it is preferable to use, for example, how many sheets have been detected and stored in the past. In an image forming apparatus with a small amount of developer, since the change in developer is large, the number of sheets should be set small. By the method described above, the adhesion amount of each color can be calculated from a blue solid image.

  In the above embodiment, the optical sensor 9 is disposed between the first image forming color and the second image forming color. However, the optical sensor 9 is disposed between the second image forming color and the third image forming color. You may arrange in. In this case, when the red solid image is detected, only the adhesion amount after two colors are superimposed can be detected, but the adhesion amount of each color can be obtained using the same method as the blue solid image described above.

  As a modification of the above embodiment, a configuration in which one more optical sensor is added as shown in FIG. In FIG. 15, the optical sensor 14 as the third detecting means is arranged in the same manner as the optical sensor 9, and the optical sensor 16 as the fourth detecting means is set between the second image forming color and the third image forming color. It is arranged to detect the intermediate transfer belt 8 between them. Further, the optical sensor 17 as the fifth detection means is arranged in the same manner as the optical sensor 11. The optical sensors 14, 16, and 17 are disposed at the same main scanning position, and the amount of adhesion of each color can be obtained using a solid image in which two colors are superposed. Specifically, in the case of a red solid image, the adhesion amount of yellow and magenta can be calculated from the detection results of the optical sensors 14 and 16. In the case of a green solid image, the yellow and cyan adhesion amounts can be calculated from the detection results of the optical sensors 14 and 17. In the case of a blue solid image, the magenta and cyan adhesion amounts can be calculated from the detection results of the optical sensors 16 and 17.

  Next, a method of performing image density control using an image during image formation, which is a feature of the present invention, will be described based on a flowchart shown in FIG. First, the LED of the optical sensor 6 is turned on (ST10). This prepares for starting up the apparatus for starting the image forming operation, and at the same time, the shutter of the optical sensor 6 is opened and the LED is turned on so that detection can be performed. The detection is always performed during the image forming operation. Next, image forming conditions are acquired (ST11). The acquisition conditions are linear velocity, writing resolution, and paper size.

  Next, image information of the formed image is acquired (ST12). This is obtained for each divided area of the number of pixels of the output image, and in this embodiment, it is divided into 5 in the main scanning direction and 10 in the sub-scanning direction. The image area information is acquired by dividing into 50. However, the number of image divisions is not limited to this. Next, the printing rate is calculated (ST13). This is calculated from the acquired number of pixels, and is calculated using the above-described equations (2), (3), and (5). At this time, calculation is performed using the writing resolution and paper size of the image forming conditions acquired in step ST11. Therefore, an appropriate printing rate can be calculated even when the paper size and writing resolution are changed. The storage in the RAM is performed by setting the divided area and the printing rate as a set, such as area 1A = 0%, area 1B = 50%, area 1C = 100%, and so on. Further, only the information in the same main scanning direction as that of the optical sensor 6 may be stored as described above.

  Next, it is determined whether or not the solid image is at the detection position of the optical sensor 6 (ST14). Here, the solid portion at the same main scanning position as the sensor detection position is specified. In this case, after extracting data with a printing rate equal to or higher than the printing rate determination threshold from the result stored in the RAM, it is determined whether the position information of the extracted data is the same main scanning position as the optical sensor 6. Further, the print ratios of the respective colors are compared to determine whether the print ratio of only one color in the same area is equal to or higher than the print ratio determination threshold and the print ratios of the other colors are 0%. Further, it is determined whether the printing rate of only two colors in the same area is equal to or higher than the printing rate determination threshold and the printing rates of the other colors are 0%. Whether the print rate of other colors is 0% or not is determined when the half of the divided area is a solid image of a single color and the other half is a solid image of two colors. This is because it is possible. As a result of the determination, if there is a solid image at the sensor position and the solid image is single color or two colors, the process proceeds to step ST15. On the other hand, if there is no single-color or two-color solid image, the process proceeds to step ST21.

  Next, a solid image is detected (ST15). In this case, when it is determined that the solid portion is at the same main scanning position as the sensor detection position, the solid image portion is extracted from the sensor output value that is always detected. Since the method for extracting the solid image can identify the position of the solid image on the recording paper in order to obtain the image information by dividing as described above, the solid image from the leading edge of the recording paper to the solid image can be specified. The sub-scanning length can be grasped. From the divided area position information corresponding to the solid image read from the RAM, the sub-scan length from the leading edge of the recording paper to the solid image position is obtained, and the delay time is obtained from the write start signal as a trigger from equation (7). After the delay time elapses, sensor output values in the detection time for the divided area are extracted, and the values are averaged to obtain the sensor output value of the solid image portion.

  Next, the toner adhesion amount is calculated (ST16). This converts the sensor output value obtained in step ST15 into a toner adhesion amount. Here, the method of calculating the toner adhesion amount uses step ST06 in the flowchart shown in FIG. Then, it is determined whether the solid image portion is a single color or two colors, and the divided area and the printing rate of each color are confirmed. If the printing rate of one color is equal to or higher than the printing rate determination threshold in the same divided area and the printing rate of the other colors is 0%, it is determined that the image is a single color solid image, and the process proceeds to step ST17. In the case of black, since the solid image does not perform color superposition, the process proceeds to step ST17. If only two colors in the same area are equal to or greater than the printing rate determination threshold and the printing rates of other colors are 0%, it is determined that the image is a solid image of two colors, and the toner adhesion amount of each color is calculated.

  In FIG. 14, the optical sensor 9 as the first detection means is arranged so as to detect the intermediate transfer belt 8 between yellow as the first image forming color and magenta as the second image forming color. . Then, an optical sensor 11 similar to the optical sensor 6 is disposed as a second detection unit at the same position as the optical sensor 6 on the downstream side in the belt traveling direction from the fourth image forming color. Hereinafter, this case will be described.

  If the yellow and magenta print rates are equal to or higher than the print rate determination threshold, it can be determined that the image is a red solid image. In this case, the optical sensor 9 detects the yellow monochrome adhesion amount, the optical sensor 11 detects the yellow and magenta adhesion amount, and subtracts the optical sensor 9 adhesion amount from the optical sensor 11 adhesion amount. Thus, the amount of magenta monochrome is measured. Thus, the adhesion amount of yellow and magenta can be calculated.

  Similarly, when the yellow and cyan printing rates are equal to or higher than the printing rate determination threshold, it can be determined that the image is a green solid image. In this case, the optical sensor 9 detects the adhesion amount of yellow single color, the optical sensor 11 detects the adhesion amount of yellow and cyan, and subtracts the adhesion amount of the optical sensor 9 from the adhesion amount of the optical sensor 11. Thus, the adhesion amount of cyan single color is measured. Thus, the adhesion amount of yellow and cyan can be calculated.

  When the magenta and cyan printing rates are equal to or higher than the printing rate determination threshold, it can be determined that the image is a blue solid image. In this case, since the detection cannot be performed by the optical sensor 9, the toner adhesion amount is obtained by subtracting the magenta or cyan adhesion amount detected last time from the result detected by the optical sensor 11. At this time, the color of the latest detection result is subtracted. If the previous detection result is less than a predetermined number, the amount of toner adhesion for each color is not calculated from the detection result of the current blue solid image, so that deviation due to changes in the developing device can be prevented. Can do. The calculated toner adhesion amount of each color is stored in a memory.

  Next, the correction amount of the image forming condition is calculated (ST17). This determines whether or not the toner adhesion amount obtained in step ST16 is in an appropriate range, and determines the image forming condition correction amount according to the result. First, the toner adhesion amount is calculated from the detection result, and when the calculated toner adhesion amount is higher than the target value, the image forming condition is changed so that the toner adhesion amount becomes lower, and the calculated toner adhesion amount becomes the target value. If it is lower than the image forming condition, the image forming conditions are changed so that the toner adhesion amount becomes higher. The image forming conditions to be changed are (1) to (3) shown below, and the toner adhesion amount can be controlled to be constant by implementing this change.

(1) When the development bias is changed As shown in FIG. 11, when the calculated toner adhesion amount is higher than the target value, correction is performed so that the development bias becomes a small value. On the other hand, when the calculated toner adhesion amount is lower than the target value, correction is performed so that the developing bias becomes a large value. In this embodiment, two threshold values are provided for the upper limit and the lower limit for the target value of the toner adhesion amount, and the correction amount is changed according to the difference value from the target value of the toner adhesion amount. By providing two threshold values, when the difference value from the target value is large, the correction amount is increased so as to approach the target value quickly. On the other hand, when the difference value is small, the correction amount is reduced so as not to overcorrect.

  Specifically, in FIG. 11A, when the toner adhesion amount calculated by detecting a solid image exceeds the upper limit threshold 2, the developing bias is changed in a decreasing direction. Further, when the toner adhesion amount falls below the lower limit threshold 2, the developing bias is changed. The amount of change of the bias is set as shown in FIG. As described above, the value for correcting the development bias at once is obtained by obtaining in advance a value that does not change the image density in appearance before and after the change. As described above, the toner adhesion amount can be controlled to be constant by adjusting the developing bias based on the toner adhesion amount calculated from the solid image detection result.

(2) When the toner density control reference value (Vtref) is changed As shown in FIG. 12A, when the calculated toner adhesion amount is higher than the target value, Vtref is corrected to a larger value (toner Lower concentration target). Thereby temporarily decreasing the toner supply amount is increased by the early goal electrostatic 圧Ma the output voltage Vt. Thus, by reducing the toner concentration in the developing device, the charge amount can be increased, and as a result, the toner adhesion amount (image density) can be decreased.

On the other hand, when the calculated toner adhesion amount is lower than the target value, Vtref is corrected to a smaller value (the target value of the toner density is increased). Accordingly temporarily increasing the amount of toner supply, it is lowered by quickly target electric 圧Ma the output voltage Vt. As a result, the toner concentration in the developing device increases, the charge amount decreases, and the toner adhesion amount can be increased.

  In this way, it is possible to approach the target adhesion amount by changing the toner density in the developing device according to the toner adhesion amount calculated from the detected solid image. Also, as in this embodiment, threshold values are provided for the upper limit and the lower limit for the target value of toner adhesion amount, and the correction value is changed according to the difference value from the target value of toner adhesion amount. If it is larger, the target adhesion amount can be corrected more quickly. In the present embodiment, the amount for changing the toner density control reference value is the value shown in FIG. Thus, by adjusting the toner density control reference value from the toner adhesion amount calculated from the solid image detection result, the toner adhesion amount can be controlled to be constant.

(3) When changing the laser diode light amount of the writing device When the calculated toner adhesion amount is higher than the target value, the laser diode light amount of the writing device (not shown) that forms an electrostatic latent image on the photosensitive member is small. Correction is performed to obtain a value. On the other hand, when the calculated toner adhesion amount is lower than the target value, correction is performed so that the laser diode light quantity becomes a large value. Thus, by adjusting the laser diode light quantity based on the toner adhesion amount calculated from the detection result of the solid image, the toner adhesion amount can be controlled to be constant.

  The image forming condition can be changed by changing any one of (1) to (3) described above, but may be changed in combination. For example, when the calculated toner adhesion amount is very small compared to the target adhesion amount, the developing bias is increased and Vtref is set small to increase the toner density. This makes it possible to approach the target adhesion amount more quickly. As described above, the toner adhesion amount is calculated based on the detection result of the solid image, and the correction amount of the image forming condition is determined according to the calculation result.

Next, the image forming condition correction amount is stored (ST18). This stores the correction amount of the image forming condition calculated in step ST17 in a memory.
Next, it is determined whether or not the image forming conditions can be changed (ST19). In this embodiment, the timing for changing the image forming condition is changed at every laser diode writing interval corresponding to the switching of the recording paper. This is because if the image forming condition is changed in the middle of one recording sheet, the image density will change in the same recording sheet. To prevent this, the image forming condition is changed at the timing when the recording sheet is switched. We are carrying out. Then, it is determined whether or not it is the timing when the recording paper writing operation ends and the recording paper is switched. If it is the timing when the image forming condition can be changed, the process proceeds to step ST20. If the image forming condition cannot be changed (during the writing operation), the process proceeds to step ST21.

  However, when forming an image on long paper, it is difficult to change the image forming condition if the image forming condition is changed at the above timing. It is good also as a structure which changes. Specifically, for example, the image forming conditions may be changed at the timing for each A4 size. In this case, as described above, the image density may change in the recording paper. Therefore, it is desirable to change the setting, for example, by making the correction amount of the image forming condition smaller than usual. In addition, as a result of acquiring the image information, the image forming condition may be switched when there is no image after the area from which the solid image is extracted. In the present embodiment, the imaging condition is changed at intervals of the writing operation. However, the imaging condition may be changed immediately after the solid image is detected and the correction amount of the imaging condition is obtained.

  Next, the image forming conditions are changed (ST20). As a result of the determination in step ST17, when it is determined that the writing operation is not performed by the laser diode, the imaging condition is changed based on the correction amount stored in step ST18. . After the image forming condition is changed, the stored correction amount is cleared to zero. If the stored correction amount is 0, the image forming condition is maintained at the previous value as no change.

  Next, it is determined whether or not the image forming operation is finished (ST21). When the image forming operation is continuously performed, the process returns to step ST11 and steps ST11 to ST19 are repeated again. If step ST19 is No and the process proceeds to step ST21, step ST21 is always No and the process returns to step ST11. When the image forming operation is completed, the process proceeds to step ST22.

Next, the LED of the optical sensor 6 is turned off (ST22). If it is determined in step ST21 that the image forming operation has been completed, the LED of the optical sensor 6 is turned off and the shutter is closed to end the process.
The above is the method for detecting the output image, adjusting the image forming condition, and controlling the image density in the present embodiment.

  According to the above-described configuration, the toner adhesion amount can be calculated by extracting a specific area from the information of the output image and detecting the specific area with the optical sensor, and the image forming conditions can be adjusted based on the result. As a result, it is not necessary to create a toner pattern for adjustment, the toner consumption can be reduced, and the apparatus downtime is not increased to detect an image during image formation, and stable image density control is performed. Can do. Further, since the toner adhesion amount of each color can also be calculated for an image on which color superposition has been performed, the image forming conditions can be adjusted and stable image density control can be performed.

  Furthermore, according to the present invention, by dividing and acquiring the image information of the output image, it is possible to extract at which position of the recording paper the specific area is present, and compared with the case where the image information is acquired for each sheet. Information can be acquired quickly. As a result, feedback to the image forming conditions can be performed quickly, and the image density can be adjusted at a more appropriate timing. In addition, when the image information of the output image is acquired in a divided manner and the information is stored, the image information of only the same main scanning position as that of the optical sensor is stored in the RAM, so that the information on the area that cannot be detected is stored. Therefore, the RAM storage area can be reduced.

  According to the present invention, the toner adhesion amount calculated by detecting a specific area of the output image is low when it is higher than the target value, and is higher when it is lower than the target value. By changing the image forming conditions as described above, stable image density control can be performed. Further, when there is a difference between the toner adhesion amount and the target value, it is possible to approach the target value by changing the developing bias, thereby enabling stable image density control. In addition, when there is a difference between the toner adhesion amount and the target value, the toner density control reference value is changed to change the toner concentration to control the charge amount in the developing device, thereby approaching the target value. Thereby, stable image density control can be performed. In addition, when there is a difference between the toner adhesion amount and the target value, it is possible to approach the target value by changing the laser diode light quantity of the writing device, thereby enabling stable image density control.

  Furthermore, according to the present invention, the toner adhesion amount can be calculated by extracting a specific area from the information of the output image and detecting this by an optical sensor arranged on the intermediate transfer belt. Adjustments can be made. In the present invention, since the toner adhesion amount can be detected in a single color state before the colors are superimposed, the toner adhesion amount can be calculated regardless of other colors, and the image forming conditions can be controlled. As a result, stable image density control can be performed.

  In the flowchart shown in FIG. 10, the LED of the optical sensor 6 is turned on at the start of image formation to always detect during the image forming operation. However, instead of this configuration, the LED may be turned on only when the divided area including the line image reaches the detection position, and the LED may be turned off when the detection of the divided area including the line image is completed. If the optical sensor 6 is turned on only when detecting in this way, the power consumption can be reduced as compared with the case where the detection is always performed. Further, since the detection is performed by opening the shutter only when the detection is performed, it is possible to prevent the occurrence of the problem that the sensor detection surface becomes dirty due to the influence of toner scattering, toner dropping or the like.

  Here, a case where there are a plurality of detectable solid images in one sheet of recording paper will be described. As a specific example, the description will be given using “(1) When changing development bias” in step ST17 of the flowchart shown in FIG. For example, it is assumed that the toner adhesion amount is calculated to be very small as a result of first detection among a plurality of solid images, and the correction amount of the developing bias Vb is +4 [−V]. This correction amount is stored in step ST18. If the image forming condition can be changed in step ST19, the image forming condition is changed, and the stored correction amount is cleared to zero. However, if there is no timing at which the imaging conditions can be changed in step ST19, the process returns to step ST11 to detect the next solid image. As a result, when it is calculated that the toner adhesion amount is small, the correction amount of the developing bias Vb is +2 [−V]. In such a case, in the present embodiment, a new detection result is stored, and updating is performed so that the latest result is always the correction amount. This is because the toner density in the developing device constantly changes depending on toner replenishment and toner consumption. Therefore, if the image forming condition is corrected using the latest detection result, an appropriate image density can be maintained. This is because it can.

  In the above embodiment, the intermediate transfer belt of the intermediate transfer system is shown as the transfer target. However, the transfer sheet of the direct transfer method (paper, envelope, postcard, OHP sheet, resin film, etc. can be transferred as the transfer target. Anything may be used. In the above embodiment, copying is shown as the image forming apparatus. However, the image forming apparatus to which the present invention is applicable is not limited to this, and the present invention is also applicable to image forming apparatuses such as printers, plotters, facsimiles, and multifunction peripherals. Applicable.

1 Latent image carrier (photosensitive drum)
3 Developer carrier (developing roller)
4 Developing device 6 Detection means (optical sensor)
8 Transfer object (intermediate transfer belt)
9 First detection means (optical sensor)
10 Image forming device (color printer)
11 Second detection means (optical sensor)
14 Third detection means (optical sensor)
16 Fourth detection means (optical sensor)
17 Fifth detection means (optical sensor)

JP-A-57-136667 JP-A-2-34877 JP 2007-148260 A

Claims (9)

A developing device for transporting the developer carried on the developer carrying member to a developing region and developing the electrostatic latent image formed on the latent image carrying member with the developer to form a toner image; and the toner image In order to obtain an appropriate amount of toner adhesion, the number of pixels of the output image can be obtained from the writing device, and a transfer means to which the toner is transferred and a detecting means provided to detect the toner image In the image forming apparatus capable of changing the image forming condition of the developing device based on the detection result of the detecting means,
The output image by analyzing and extracting a specific area that matches the predetermined write conditions, by changing the image forming condition of said toner image on said transfer object in the specific area is detected by said detecting means, 4 It is possible to form an image using a color image forming color, and to have two detection means in the same main scanning direction of the transfer object, and the first detection means includes the first image forming color and the second image forming color. The second detection means is arranged to detect on the transferred body between the image forming colors or on the transferred body between the second image forming color and the third image forming color. 4 is arranged to detect the above-mentioned transferred body on the downstream side in the running direction from the image forming color of 4,
When the specific region is formed by color superposition of two colors, the first detection unit detects the toner adhesion amount before color superposition, and then the second detection unit performs color superposition. And detecting the adhesion amount of each of the two superimposed colors by subtracting the detection result by the first detection unit from the detection result by the second detection unit. An image forming apparatus. The image forming apparatus according to claim 1.
The image forming apparatus according to claim 1, wherein the image in the specific area is a solid image . The image forming apparatus according to claim 1 or 2,
The image forming apparatus is characterized in that the specific area is extracted using pixel information obtained by dividing all output images . The image forming apparatus according to any one of claims 1 to 3 ,
When the toner adhesion amount obtained by detecting the toner image on the transfer medium in the specific area by the second detection means is compared with a target value, the toner adhesion amount is higher than the target value. An image forming apparatus, wherein the image forming condition is changed so as to be low, and the image forming condition is changed so that the toner adhesion amount is high when the image forming condition is lower than the target value . The image forming apparatus according to any one of claims 1 to 4,
The image forming apparatus is characterized in that the image forming condition is changed by changing a developing bias . The image forming apparatus according to any one of claims 1 to 4 ,
The image forming apparatus is characterized in that the image forming condition is changed by changing a toner density control reference value . The image forming apparatus according to any one of claims 1 to 4 ,
An image forming apparatus having a writing device for forming the electrostatic latent image on the latent image carrier, wherein the image forming condition is changed by changing a light amount of the writing device. . A developing device for transporting the developer carried on the developer carrying member to a developing region and developing the electrostatic latent image formed on the latent image carrying member with the developer to form a toner image; and the toner image And a third to fifth detecting means provided in the same main scanning direction of the transferred body for detecting the toner image, and writing the number of pixels of the output image Image formation using four image forming colors that can be acquired from the device and that changes the image forming conditions of the developing device based on the detection results of the detection means in order to obtain an appropriate toner adhesion amount is possible. In an image forming apparatus,
Analyzing the output image to extract a specific area that matches a predetermined writing condition, detecting the toner image on the transfer medium in the specific area by the detection means, and changing the image forming condition, The fourth detecting means detects the second image forming color with the second image forming color so that the third detecting means detects on the transferred body between the first image forming color and the second image forming color. The fifth detecting means detects on the transferred body downstream in the traveling direction from the fourth image forming color so as to detect on the transferred object between the third image forming color and the third image forming color. Each placed in
When the specific region is formed by color superposition of two colors, the third adhesion detection unit detects the toner adhesion amount before color superposition is performed, and then the fifth detection unit performs color superposition. Is detected, and the color detection is performed by subtracting the detection result by the third detection unit from the detection result by the fifth detection unit or by the fourth detection unit. The previous toner adhesion amount is detected, and then the toner adhesion amount after color superposition is performed by the fifth detection means, and the fourth detection means detects the detection result by the fifth detection means. An image forming apparatus, wherein the amount of adhesion of two superimposed colors is detected by subtracting the detection result . The image forming apparatus according to any one of claims 1 to 8 ,
The image forming apparatus according to claim 1, wherein the transfer target is an intermediate transfer belt on which the toner image is intermediately transferred .

Images