JP2007322675A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To improve reproducibility of image formation by enhancing accuracy in image density detection with a small number of predetermined images for detecting density. <P>SOLUTION: The predetermined image for detecting density of a first color is transferred from a photoreceptor drum to a transfer belt and the transfer belt is rotated by one turn, and the predetermined image for detecting density of a second color is transferred behind the predetermined image for detecting density of the first color and the transfer belt is rotated by one turn. The transfer belt is rotated every time the predetermined image for detecting density is transferred to the transfer belt, and a density sensor measures the density at a plurality of spots on the respective predetermined images for detecting density every time the predetermined image for detecting density passes in front, and an image forming condition is controlled based on a result of measurement. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a technique for controlling the density of each color by forming a predetermined image for detecting the density of each color and detecting the density in an image forming apparatus that forms an image having a plurality of colors on a sheet. The present invention relates to a technique for improving the accuracy of density detection.

  In general, in a color image forming apparatus, toner images of four colors of Y (yellow), M (magenta), C (cyan), and K (black) are formed on a photosensitive drum, and each time a toner image is formed. Then, the toner image of each color is superimposed on the transfer belt to form a color toner image. Then, the color toner image is transferred from the transfer belt to the sheet and then fixed to form a color image. In such an image forming apparatus, if the density balance of each color is disturbed, accurate image formation cannot be performed. For this reason, conventionally, there has been proposed a technique for adjusting the various image forming conditions and the transfer bias by detecting the density of each color toner transferred from the photosensitive drum to the transfer belt.

  For example, in Patent Document 1, a predetermined image for density detection of toner of four colors is transferred to a transfer drum, and the density of each density detection predetermined image is detected by a reflective optical sensor. Based on the density detection result of the predetermined image for density detection, the primary transfer bias of each color when the toner image is primarily transferred from the photosensitive drum to the transfer belt is adjusted.

  In Patent Document 2, thirteen predetermined images for density detection using one color toner are formed on a photosensitive drum, and the density of the predetermined image for density detection is detected by an optical sensor. The development conditions are calculated, and for the second and subsequent colors, five predetermined images for density detection are formed on the photosensitive drum, the density is detected, and the development conditions are adjusted in the vicinity of the conditions for the first color.

JP 2002-72609 A (Abstract) JP-A-11-143164 (abstract)

  By the way, in the color image formation, while the four color toner images are transferred to the transfer belt, a phenomenon occurs in which the toner of the toner image previously transferred is reversely transferred to the photosensitive drum. However, the techniques described in Patent Documents 1 and 2 have a problem that the primary transfer bias corresponding to such reverse transfer cannot be adjusted, and the accuracy of image density detection is low. In particular, the technique described in Patent Document 2 has a problem that a large number of predetermined images for density detection are required to increase the accuracy of image density detection, and the amount of waste toner increases, which is uneconomical.

  Accordingly, an object of the present invention is to provide an image forming apparatus capable of improving the accuracy of image density detection with a small number of predetermined images for density detection and improving the reproducibility of image formation.

  The present invention relates to an image forming apparatus that forms a superimposed image by sequentially transferring toner images of different colors formed on an image carrier by a developing unit onto a transfer surface for each color. In the image forming apparatus, a predetermined image for density detection by toner of each color is transferred to the image forming apparatus, and the detection unit detects the density of the predetermined image for density detection, and controls the image forming conditions based on the detection result. Each time the carrier transfers a predetermined image for density detection onto the transfer surface, the transfer surface is made to make one round to transfer the predetermined image for density detection of the next color so as not to overlap each other.

  In the image forming apparatus having the above-described configuration, every time the image carrier transfers the predetermined image for density detection onto the transfer surface, the transfer surface is rotated substantially once so that the predetermined image for density detection of the next color does not overlap each other. Thus, the influence from the image carrier that each predetermined image for density detection receives is almost the same as in the case of actual image formation. Therefore, the image density detected from the predetermined image for density detection substantially coincides with the image density in actual image formation, and the image density can be detected with high accuracy.

  Since each color toner image in actual image formation has many halftones, the predetermined image for density detection is a halftone toner image. Then, by controlling the image forming conditions and / or the transfer conditions of the toner image based on the density detection result of the predetermined image for density detection by the detection means, a target image can be obtained with certainty. Here, the image forming conditions are charging conditions, developing conditions, exposure conditions, and the like. The transfer condition is a transfer current supplied to a charger for charging the toner.

  In the present invention, it is possible to accurately detect the density of the toner image of each color to optimize the balance of each color and improve the reproducibility of the image. However, if the amount of toner supplied from the developing unit is excessive or insufficient After all, the balance of each color cannot be maintained. In this regard, the present invention can also be used to control the amount of toner (toner concentration) supplied from the developing unit. In this case, the predetermined image for density detection is preferably a solid toner image, and the amount of toner supplied by the developing unit is controlled based on the result of detection of the density of the predetermined image for density detection by the detecting means. Can do. Thereby, the balance of each color can be stabilized. Further, if the predetermined image for solid density detection is transferred to the transfer surface together with the predetermined image for halftone density detection, and the density of each predetermined image for density detection is detected by the detecting means, it is possible to perform one operation. It is possible to detect the density of each color and control the amount of toner supplied by the developing means.

  It is desirable that the detection means repeatedly detects the density of a predetermined image for density detection every time the transfer surface makes a round. For example, when transferring predetermined images for density detection of Y, M, C, and K in this order, Y is detected four times, M is detected three times, C is detected twice, and K is detected once. Detection accuracy can be improved. In the present invention, the number of colors of the predetermined image for density detection is not limited, and may be three colors or two colors. Further, it is not necessary to match the number of detections of the predetermined image for density detection with the number of rotations of the transfer surface. For example, the predetermined number of times is detected by detecting Y three times, M twice, and C and K once. The number of times the color is detected can be made smaller than the number of laps.

  Furthermore, it is desirable that the detecting means detects the density at a plurality of locations in the predetermined image for density detection. If the average value is calculated by detecting the concentration at a plurality of locations, the reliability of the detection result can be increased. In this case, the reliability of the detection result can be further improved by detecting the density at different locations instead of the same location in the predetermined image for density detection. As the detection means, an optical sensor having a light emitting part and a light receiving part is suitable, and the density of an arbitrary part of the predetermined image for density detection can be detected by controlling the detection timing.

  In the above aspect, it is preferable that the length of the predetermined image for density detection in the moving direction of the transfer surface is shortened every time the color of the predetermined image for density detection is changed. Since the number of times of detection decreases each time the color of the predetermined image for density detection is changed, the required length of the color pad can be shortened. In such an embodiment, the amount of waste toner can be further reduced.

  The condition for transferring the predetermined image for detecting the halftone density from the image carrier to the transfer surface is preferably the same as the condition for transferring the toner image of each color to the transfer surface in an actual operation. As a result, a predetermined image for density detection can be reproduced in the same manner as when an image is actually formed, and the manufacture of density detection can be further improved.

  On the other hand, it is desirable that the condition for transferring the predetermined image for density detection of solid coating from the image carrier to the transfer surface is different from the condition for transferring the toner image of each color to the transfer surface in actual operation. . The condition is a transfer current that does not produce an optimal transfer residue for transferring a solid toner image.

  The order of colors forming the predetermined image for density detection can be the same as the order of transferring the toner images of the respective colors onto the transfer surface in actual operation. As a result, the number of times each predetermined image for density detection passes through the image carrier coincides with the number of times each color toner image passes through the image carrier in the actual image formation. Therefore, since processing is performed on a predetermined image for detecting each density in the same manner as in actuality, it is possible to further improve image density detection accuracy.

  Further, the order of colors forming the predetermined image for density detection may be different from the order in which the toner images of the respective colors are transferred to the transfer surface in actual operation. Specifically, the predetermined image for density detection is formed from the last color when the toner image of each color is transferred to the transfer surface in the actual operation, and the other predetermined image for density detection is the actual operation. They can also be formed in the same color order. For example, if toner images are formed in the order of Y, M, C, and K in actual operation, predetermined images for density detection are formed in the order of K, Y, M, and C. In this aspect, when the image density detection is performed after the actual image formation, there is an advantage that the process can be shifted to the image density detection as it is without switching the developing unit of the developing unit. Alternatively, it is possible to experimentally determine the order of colors in which density detection accuracy is stable, and to form a predetermined image for density detection in that order. It is also possible to form a predetermined image for density detection from a color having good transferability.

  A cleaning unit for removing toner on the image carrier, and transferring the predetermined image for density detection of all colors from the image carrier to the transfer surface and detecting the density of the predetermined image for density detection; Desirably, the predetermined image for density detection is reversely transferred to the image carrier, and the toner of the predetermined image for density detection is collected by the cleaning means. In such an embodiment, since it is not necessary to provide a cleaning unit in the transfer unit, the image forming apparatus can be downsized and the manufacturing cost can be reduced. In addition, when the transfer means is constituted by a belt, cleaning with a scraper or a blade cannot easily scrape off the toner because it is dragged on the belt. However, such inconvenience does not occur by processing as described above.

  According to the present invention, it is possible to increase the accuracy of image density detection with a small number of predetermined images for density detection, and to obtain effects such as improving the reproducibility of image formation.

[1] Configuration of Embodiment An embodiment of the present invention will be described below with reference to the drawings.
FIG. 1 is a side sectional view showing an image forming apparatus 1 according to the embodiment. The image forming apparatus 1 shown in this figure is generally configured by a paper feeding unit 10, a developing unit 20, a latent image forming unit 30, a transfer unit 40, and a fixing unit 50. Hereinafter, the structure of each part is demonstrated in order.

1. In FIG. 1, reference numeral 11 denotes a paper feed cassette, and the paper feed cassette 11 is disposed in the lower part of the image forming apparatus 1. On the upper surface of the paper feed cassette 11, a transport roll 12 that is in contact with the upper surface of the paper P accommodated in the paper feed cassette 11 is disposed. Above the transport roll 12, a registration roll 13 is disposed. The registration roll 13 temporarily stops the conveyed paper P and sends it out at the timing of development.

2. Developing unit A developing drum 21 is disposed above the sheet feeding unit 10 so as to be rotatable in the direction of the arrow. The developing drum 21 is supplied with a Y color developing unit 22a for supplying yellow toner, an M color developing unit 22b for supplying magenta toner, a C color developing unit 22c for supplying cyan toner, and a black toner. The K color developing units 22d to be arranged are arranged in the clockwise direction. In the figure, reference numeral 23 denotes a toner cartridge, and the toner filled in the toner cartridge 23 is taken out by the rotation of the toner supply motor 24 and stored in the toner reservoir 25. The toner stored in the toner reservoir 25 is supplied to a photosensitive drum (image carrier) 31 by a developing roll 26. When the development of one color on the photosensitive drum 31 is completed, the developing drum 21 is rotated 90 ° counterclockwise to develop the next color.

3. Latent Image Forming Unit Around the photosensitive drum 31, a charger 32 that charges the photosensitive drum 31 and a cleaner 33 that removes toner remaining on the photosensitive drum 31 are disposed. The cleaner 33 includes a blade 33a that scrapes off the toner on the photosensitive drum 31, and a collection box 33b. An exposure device (ROS) 34 is disposed between the paper feed cassette 11 and the developing drum 21. The exposure device 34 writes an electrostatic latent image on the surface of the photosensitive drum 31 that is uniformly charged by the charger 32. Then, toner is supplied to the photosensitive drum 31 by the developing roll 26, so that a toner image corresponding to the electrostatic latent image is formed.

4). Transfer Section In FIG. 1, reference numeral 41 denotes a transfer belt (transfer means). As shown in FIG. 3, the transfer belt 41 is obtained by coating a release layer 41b in which fluorine is dispersed on the front and back surfaces of an endless annular base material 41a made of an elastic material such as rubber. The transfer belt 41 is wound around a drive roll 42 and a plurality of driven rolls 43, and a part of the transfer belt 41 is disposed so as to contact the surface of the photosensitive drum 31.

  Inside the transfer belt 41, a primary transfer roll 44 is disposed so as to sandwich the transfer belt 41 together with the photosensitive drum 31. The primary transfer roll 44 generates a primary transfer bias when a transfer current is supplied, and transfers the toner image on the photosensitive drum 31 to the transfer belt 41. A charger 45 is disposed on the left side of the transfer belt 41 so as to face the driven roller 43. The charger 45 holds the toner image transferred from the photosensitive drum 31 by the primary transfer roll 44 on the transfer belt 41 by uniformly charging the transfer belt 41.

  A secondary transfer roll 46 is disposed in contact with the rightmost driven roll 43. The secondary transfer roll 46 generates a secondary transfer bias when a transfer current is supplied, and transfers the toner image on the transfer belt 41 to the paper P. A density sensor 47 is disposed below the secondary transfer roll 46. The density sensor 47 is an optical sensor having a light emitting part and a light receiving part. The light received from the light receiving part is reflected by the object (predetermined image for density detection) by the light receiving part, and the amount of received light. Measure the concentration with. A charger 48 facing the transfer belt 41 is disposed on the right side of the transfer belt 41. The charger 48 charges a predetermined image for density detection and toner remaining after the secondary transfer, and reversely transfers the toner to the photosensitive drum 31.

5). Fixing Unit A pair of fixing rolls 51 are arranged on the upper part of the image forming apparatus 1. Heating means such as a heater is disposed inside the fixing roll 51, and the toner image is fixed on the paper P by heating the paper P on which the toner image is transferred. In the figure, reference numeral 52 denotes a paper discharge roll for discharging the paper P.

6). Control Unit FIG. 2 is a control block diagram of the image forming apparatus 1 of the embodiment. The output signal of the density sensor 47 is input to the patch density detection unit 100, and the patch density detection unit 100 calculates the density of a predetermined image for density detection from the output value of the density sensor 47. Various conditions for image formation are set based on the calculated density of the predetermined image for density detection. That is, the patch density detection unit 100 controls the developing unit 20 including the developing roll 26, the chargers 32 and 44, and the exposure device 34 based on the calculated density of the predetermined image for density detection, thereby controlling the image of each color. The toner supply amount (toner concentration) is controlled by controlling the density and the toner supply motor 24, thereby controlling the color balance of the image.

  The patch density detection unit 100 outputs the calculated density of the predetermined image for density detection to the charge amount calculation unit 101, and the charge amount calculation unit 101 is based on the calculated density of the predetermined image for density detection. A charge amount of 32 is calculated. The charge amount calculation unit 101 outputs the calculated charge amount to the charge amount control unit 102, and the charge amount control unit 102 controls the charger 32 so that the input charge amount is obtained.

  The patch density detection unit 100 outputs the calculated density of the predetermined image for density detection to the transfer potential calculation unit 103, and the transfer potential calculation unit 103 performs primary processing based on the calculated density of the predetermined image for density detection. The transfer potential of the transfer roll 44 is calculated. The transfer potential calculation unit 103 outputs the calculated transfer potential to the transfer potential control unit 104, and the transfer potential control unit 104 controls the transfer continuous flow supplied to the primary transfer roll 44 so as to be the input transfer potential. .

  The patch density detection unit 100 outputs the calculated density of the predetermined image for density detection to the exposure amount calculation unit 105, and the exposure amount calculation unit 105 exposes the exposure apparatus based on the calculated density of the predetermined image for density detection. 34 exposure amount is calculated. The exposure amount calculation unit 105 outputs the calculated exposure amount to the ROS control unit 106, and the ROS control unit 106 controls the exposure apparatus 34 so that the input exposure amount is obtained.

  The patch density detection unit 100 outputs the calculated density of the predetermined image for density detection to the development potential calculation unit 107, and the development potential calculation unit 107 develops the developing roller based on the calculated density of the predetermined image for density detection. The development potential (toner potential) at 26 is calculated. The developing power calculating unit 107 outputs the calculated developing potential to the developing potential control unit 108, and the developing potential control unit 108 controls the developing unit 20 including the developing roller 26 so as to become the input developing potential.

[2] Operation of Embodiment Next, the operation of the image forming apparatus 1 having the above configuration will be described. In this embodiment, the density of each color image and the toner density are controlled. The density control is performed after, for example, forming 50 images (step S1 in FIG. 5). If 50 images have been formed, the process proceeds to step S2, and a predetermined image for halftone density detection of the first color and a predetermined image for density detection of the first solid color are transferred to the transfer belt 41. Create on top. FIG. 4A shows a predetermined image for density detection of the first color, and the color is yellow in this embodiment. Note that the predetermined image for density detection of the first color solid is created at a location away from the predetermined image for density detection of the herb tone.

  The transfer belt 41 travels while holding a predetermined image for density detection of the first color. When the predetermined image for density detection reaches the density sensor 47, the density sensor 47 is indicated by a circle in FIG. As described above, the density of, for example, four places in the predetermined image for density detection is detected (step 3). This density detection is performed on a predetermined image for halftone density detection and a predetermined image for solid density detection.

  Next, a predetermined image for density detection of the second color (magenta) halftone and a predetermined image for density detection of the solid color of the second color are created behind the predetermined image for density detection of the first color (step S4). ). The predetermined image for density detection of the second color is formed shorter than the predetermined image for density detection of the first color. When the transfer belt 41 travels and the predetermined image for density detection reaches the density sensor 47, the density sensor 47 detects four positions of the predetermined image for density detection of the first color and 3 of the predetermined image for density detection of the second color. The density at the location is detected (step S5). At this time, the detection position of the predetermined image for density detection of the first color is set to a position shifted from the detection position of the first time.

  Next, a predetermined image for density detection of the third color (cyan) halftone and a predetermined image for density detection of the solid color of the third color are created after the predetermined image for density detection of the second color (step S6). ). The predetermined image for density detection of the third color is formed shorter than the predetermined image for density detection of the second color. When the transfer belt 41 travels and the predetermined image for density detection reaches the density sensor 47, the density sensor 47 detects the four positions of the predetermined image for density detection of the first color and the predetermined image for density detection of the second color. The density of three places and three places of the predetermined image for density detection of the third color are detected (step S7). At that time, the detection position of the predetermined image for density detection of the first color is shifted from the first and second positions, and the detection position of the predetermined image for density detection of the second color is from the detection position of the first time. Misplaced position.

  Next, a predetermined image for density detection of the fourth color (black) halftone and a predetermined image for density detection of the solid color of the fourth color are created after the predetermined image for density detection of the third color (step S8). ). The fourth density detection predetermined image is formed shorter than the third color density detection predetermined image. When the transfer belt 41 travels and the predetermined image for density detection reaches the density sensor 47, the density sensor 47 detects the four positions of the predetermined image for density detection of the first color and the predetermined image for density detection of the second color. The density of three places, the three places of the predetermined image for density detection of the third color, and the three places of the predetermined image for density detection of the fourth color are detected (step S9). At this time, the detection position of the predetermined image for density detection of the first color is shifted from the first, second, and third positions, and the detection position of the predetermined image for density detection of the second color is the first and The detection position of the predetermined image for density detection of the third color is a position shifted from the first detection position.

  Next, all the predetermined images for density detection on the transfer belt 41 are charged by the charger 48 and reversely transferred to the photosensitive drum 31 (step S10). The toner reversely transferred to the photosensitive drum 31 is scraped off by the blade 33a of the cleaner 33 and collected in the collection box 33b.

  6 and 7 are graphs showing the relationship between the transfer current supplied to the primary transfer roll 44, the remaining transfer amount, and the reverse transfer amount. “Transfer residue” means that a part of the toner remains without being transferred from the photosensitive drum 31 to the transfer belt 41. When a predetermined image for solid density detection is transferred, a transfer residue is likely to occur. Therefore, an optimal transfer current is selected from FIG. 6 instead of a transfer current for actual image formation. In reverse transfer, when the toner image of the previous color is transferred to the transfer belt 41 after the toner image is transferred from the photosensitive drum 31 to the transfer belt 41, the toner of the toner image of the previous color is exposed to light. It is transferred to the body drum 31 and returned.

  As shown in FIG. 6, there is a transfer current range in which the transfer residue increases and the transfer residue becomes the smallest even if the transfer current is large or small. Further, as shown in FIG. 7, the reverse transfer increases as the transfer current increases. Hereinafter, a method for controlling the transfer current and the like based on density detection of a predetermined image for density detection will be described.

  Table 1 shows the result of measuring the density of a predetermined image for halftone density detection. In Table 1, “circumferential difference value” is the difference between the maximum value and the minimum value of the average value of density. If this rounding difference value is large, it means that there is much reverse transfer of toner. When the first color in Table 1 is examined, the average density value (106) is significantly higher than the target value 100. The rounding difference value is 3, which is higher in the case of yellow. That is, for the first color, it is necessary to reduce the image density and reduce the reverse transfer. For this reason, the first color is controlled to reduce the exposure amount and the transfer current. Note that the image density can also be lowered by reducing the charge amount, development potential, and toner supply amount.

  In addition, the second and third colors have a considerably large circulation difference value, so that the transfer current is controlled to be lowered. For the fourth color, the average value of the image density is much lower than the target value. In the fourth color, since reverse transfer does not occur, control is performed to increase the image density according to the exposure amount or the like while keeping the transfer current as it is.

  As described above, the influence of reverse transfer is large in the first to third colors. Therefore, the transfer condition for the first color should be the same as that for actual image formation, and the transfer current should be lowered for the second and subsequent colors in order to reduce reverse transfer. If the rotation difference value is within the range of the stable region set for each color, the transfer current used for transferring the predetermined image for density detection can be applied to actual image formation. Alternatively, even when it is out of the range of the stable region, the amount of adjustment of the transfer current is small, so that accurate control can be performed.

  In the image forming apparatus having the above-described configuration, every time the photosensitive drum 31 transfers the predetermined image for density detection to the transfer belt 41, the transfer belt 41 is rotated around to transfer the predetermined image for density detection of the next color to each other. Since the images are transferred so as not to overlap with each other, the influence from the photosensitive belt 31 received by each density detection predetermined image is substantially the same as that in actual image formation. Therefore, the image density obtained from the predetermined image for density detection almost coincides with the actual image density, and the image density can be detected with high accuracy. In addition, since only one predetermined density detection image needs to be formed for each color, the amount of waste toner can be reduced.

  In particular, in the above-described embodiment, the predetermined image for density detection is formed with the same halftone as in the actual image formation, and the exposure amount and the like are determined based on the density detection result of the predetermined image for density detection by the density sensor 47. Since the image forming conditions and the transfer current of the toner image are controlled, the intended image can be obtained reliably. Furthermore, in the present invention, a predetermined image for solid density detection is formed, and the amount of toner supplied by the toner supply motor 24 is controlled based on the density detection result of the predetermined density detection image by the density sensor 47. Thus, the density of the entire image can be stabilized. Further, since the density of a predetermined image for detecting the density of halftone and solid coating is detected, the image density and toner density of each color can be controlled with a single operation.

  In the above embodiment, since the density of a plurality of different locations is detected instead of the same location of the density detection predetermined image, the reliability of the detection result can be improved with one density detection predetermined image. In the above embodiment, since the length of the predetermined image for density detection is shortened every time the color of the predetermined image for density detection is changed, the image is finally reversely transferred to the photosensitive drum 31 and collected by the cleaner 33. It is possible to reduce the amount of waste toner.

  Further, in the above-described embodiment, since the predetermined image for density detection is formed in the same color order as the actual image formation, the number of times each predetermined image for density detection passes through the photosensitive drum 31 is the same as the actual number. . Therefore, the density detection result of the predetermined image for density detection can be more accurately reflected on the actual image formation.

[3] Modifications The present invention is not limited to the above embodiment, and various modifications can be made as follows.
(1) In the above embodiment, the formation of the predetermined image for density detection starts from yellow, but it can also start from black. In this way, it is possible to develop a predetermined image for density detection without rotating the developing drum 21 after the actual image formation is completed.
(2) In the above embodiment, the transfer belt 41 is used, but a drum-type transfer unit may be used.
(3) The transfer current supplied to the secondary transfer roll 46 can be controlled based on the density detection result of the predetermined image for density detection.

1 is a side sectional view showing an image forming apparatus according to an embodiment of the present invention. 2 is a control block diagram of an image forming apparatus according to an embodiment. FIG. It is a figure which shows the transfer belt used by one Embodiment, Comprising: (A) is the perspective view, (B) is sectional drawing. It is a top view which shows the predetermined image for density | concentration detection, Comprising: (A) is a parallel solid figure for the predetermined image for density | concentration detection of each color, in order to compare length, (B) is a density | concentration in the 4th to 4th circumference It is a figure which shows the state which forms the predetermined image for a detection. It is a flowchart which shows operation | movement of one Embodiment. It is a graph which shows the relationship between a transcription | transfer current and a transcription | transfer rest. It is a graph which shows the relationship between a transfer current and reverse transfer.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Image forming apparatus 20 Developing part 21 Developing drum 31 Photosensitive drum (image carrier)
41 Transfer belt (transfer means)
47 Concentration sensor (detection means)
P paper

Claims (14)

An image forming apparatus for forming a superimposed image by sequentially transferring toner images of different colors formed on an image carrier by a developing unit to a transfer surface for each color,
The image carrier transfers a predetermined image for density detection using toner of each color onto the transfer surface, and the detection unit detects the density of the predetermined image for density detection, and based on the detection result, image forming conditions are detected. In an image forming apparatus for controlling
Each time the image carrier transfers the predetermined image for density detection onto the transfer surface, the transfer surface is moved around the transfer surface so as not to overlap each other. An image forming apparatus.   The predetermined image for density detection is a halftone toner image, and the image forming condition and / or the transfer condition of the toner image are determined based on the detection result of the density of the predetermined image for density detection by the detection unit. The image forming apparatus according to claim 1, wherein the image forming apparatus is controlled.   The predetermined image for density detection is a solid toner image, and the amount of toner supplied by the developing unit is controlled based on the result of detection of the density of the predetermined image for density detection by the detection unit. The image forming apparatus according to claim 1 or 2.   The solid-tone density detection predetermined image is transferred to the transfer surface together with the halftone density detection predetermined image, and the density of each density detection predetermined image is detected by the detecting means. The image forming apparatus according to claim 3.   The image forming apparatus according to claim 1, wherein the detection unit repeatedly detects the density of the predetermined image for density detection every time the transfer surface makes a round.   The image forming apparatus according to claim 1, wherein the detection unit detects densities at a plurality of locations of the predetermined image for density detection.   The image forming apparatus according to claim 6, wherein the detection unit detects a density of a different portion of the predetermined image for density detection every time the transfer surface makes a round.   8. The image forming apparatus according to claim 6, wherein the length of the predetermined image for density detection in the moving direction of the transfer surface is shortened each time the color of the predetermined image for density detection is changed.   The condition for transferring the predetermined image for halftone density detection from the image carrier to the transfer surface is the same as the condition for transferring the toner image of each color to the transfer surface in an actual operation. The image forming apparatus according to claim 1.   The condition for transferring the predetermined image for solid density detection from the image carrier to the transfer surface is not the condition for transferring the toner image of each color to the transfer surface in actual operation, but according to the solid image. The image forming apparatus according to claim 3, wherein the image forming apparatus satisfies the following conditions.   The order of colors forming the predetermined image for density detection is the same as the order of transferring the toner images of the respective colors onto the transfer surface in an actual operation. Image forming apparatus.   The order of colors forming the predetermined image for density detection is different from the order of transferring toner images of each color onto the transfer surface in actual operation. Image forming apparatus.   The predetermined image for density detection is formed from the last color when the toner image of each color is transferred to the transfer surface in an actual operation, and the other predetermined images for density detection have the same color as the actual operation. The image forming apparatus according to claim 12, wherein the image forming apparatuses are formed in order.   A cleaning unit is provided for removing toner on the image carrier, and the predetermined images for density detection of all colors are transferred from the image carrier to the transfer surface to detect the density of the predetermined image for density detection. 14. After that, the predetermined image for density detection is reversely transferred to the image carrier, and the toner of the predetermined image for density detection is collected by the cleaning means. The image forming apparatus described.

Images