JP4664587B2 - Image density detection method and image forming apparatus - Google Patents

Description

The present invention relates to an image density detection method, and more particularly to an image density detection method for a patch pattern and an image forming apparatus that performs image density detection using the image density detection method .

In an image forming apparatus such as a copying machine, a facsimile, a printer, or a printing machine, a visible image carried on a photosensitive member that is a latent image carrying member is transferred to a transfer member.
In addition to a recording sheet that directly faces and contacts the photosensitive member, a belt-like transfer member may be used as the transfer member. One of the latter cases is multicolor image formation including full color.
As one configuration for forming a multicolor image, an electrostatic latent image corresponding to a color separation color is formed for each photoconductor using a plurality of photoconductors, and moves while facing each photoconductor. There is a configuration in which a belt is used as an intermediate transfer member or a conveying member that carries a recording sheet on the surface (for example, Patent Document 1).
When the belt is used as an intermediate transfer member, a primary transfer step for sequentially transferring images of respective colors formed on the respective photosensitive members and a secondary transfer for collectively transferring the images sequentially transferred and superimposed onto the recording sheet. In the case where a belt is used as a conveying member, a process of superimposing and transferring an image on each photosensitive member in a process of moving the recording sheet carried on the surface so as to face each photosensitive member. Is used.

In this type of image forming apparatus used for multicolor image formation including full color, it is required to achieve stabilization of image quality including color reproducibility, etc. As disclosed in Patent Document 1, there is the following content.
A density detection pattern is formed on the photoreceptor or an intermediate transfer belt on which an image from the photoreceptor is transferred, this density detection pattern is optically read, and various parameters used for image formation conditions are fed back based on the read result Control.

  The feedback control in this case will be described in detail. When the amount of toner constituting the patch pattern formed in the intermediate transfer belt shape is measured by the image density detection sensor, and the measurement result does not satisfy the predetermined condition, Various parameters such as writing output characteristics, charging characteristics of the photoconductor, charging characteristics that affect the adhesion of toner in the developer, and development bias characteristics that control the amount of toner adhesion are fed back to match the specified conditions. Control.

  The patch pattern formed on the intermediate transfer belt is formed larger than the detection range by the image density detection sensor, and the patch pattern is formed in the portion where the output from the density detection sensor is saturated (the entire detection range of the image density detection sensor). And the toner adhesion amount is calculated based on the detection result. The calculated toner adhesion amount is used for discrimination with respect to a predetermined density.

JP-A-10-161388 (paragraph "0005" column, "0016" column)

In a configuration that optically detects a patch pattern, it is necessary to detect a high toner adhesion region, and thus a diffused light sensor that can take a wide detection range may be used.
However, when such a configuration is used, it is necessary to make the size of the patch pattern larger than the detection range of the image density detection sensor, so the patch pattern formation time becomes longer. For this reason, normal image forming processing cannot be executed while the patch pattern is being created, and the user may feel that the apparatus is not operating, that is, the downtime is large, which may deteriorate convenience. .

On the other hand, when detecting the image density of a patch pattern, a plurality of detection points are detected, and an average value of the obtained detection results is calculated. Is also included.
In general, the edge effect is remarkable at the edge portion of the image, and for this reason, the density tends to be different from that in other portions. Therefore, since it is desired to detect the toner adhesion amount in the image area of the patch pattern, that is, in the range not affected by the edge effect, the patch pattern is larger than the detection range of the image density detection sensor as shown in FIG. It is necessary to measure a plurality of locations in the central portion of the patch pattern which is further enlarged. For this reason, when detecting the image density, the number of detection points increases in addition to the creation of a plurality of patch patterns, resulting in a further increase in the downtime described above, and impressing the user on the deterioration of work efficiency. Become.

  In addition, when the size of the patch pattern is increased, the burden on the cleaning device mounted on the intermediate transfer belt also increases, which may cause cleaning failure.

An object of the present invention is to solve the above-described conventional image forming apparatus, in particular, image density detection, and image density detection having a configuration capable of reducing downtime that prevents normal image formation and preventing cleaning failure. It is an object of the present invention to provide a method and an image forming apparatus that performs image density detection by this method .

  According to the first aspect of the present invention, the image density sensor for detecting the density of the patch pattern formed on the image carrier is connected to the input side, and a control unit including a memory capable of storing the input detection output is used. In the image density detection method, a detection output ratio between a patch pattern smaller than the detection range of the image density sensor and a patch pattern larger than the detection range is stored in a memory in advance, and is smaller than the detection range of the image density sensor. The patch pattern output larger than the detection range of the image density sensor is calculated from the detection output ratio stored in the memory when the image density of the patch pattern is detected.

That is, the density of “a patch pattern smaller than the detection range of the image density detection sensor” is measured in advance at a plurality of relative positions while changing the relative position with respect to the image density sensor, and “from the detection range of the image density detection sensor”. The density of the “large patch pattern” is measured at a plurality of detection points, and the average value of the detection results is calculated.
The output ratio between the “measurement output for the small patch pattern” obtained at each relative position and the “average value of detection results for the large patch pattern” is obtained and stored in the memory.
At the time of image density detection, a patch pattern smaller than the detection range of the image density detection sensor is formed, and the “small patch pattern density” is measured at multiple points while changing the relative position with respect to the image density sensor. The density of the patch pattern larger than the detection range of the image density sensor is calculated for a plurality of points based on the density of the image and the “output ratio stored in the memory”, and the average value of the calculated results is calculated. Thus, the image density is detected .

The invention described in claim 2 is characterized by the following points.
That is, in the first aspect of the invention, the patch pattern smaller than the detection range of the image density sensor is “a rectangular patch that is short in the image density sensor scanning direction and has an edge effect on the edge of the image density sensor scanning direction. "Pattern" is used.
Then, in order to remove the “effect of density different from the others” at the edge of the patch pattern, the “distance from the center position of the sensor to the edge of the patch pattern” is determined from the sensor output at the first position with respect to the patch pattern. The sensor output at a second position equal to the position of 1 is subtracted.

The invention described in claim 3 is characterized in that, in addition to the invention described in claim 1 or 2 , an intermediate transfer member capable of supporting images of a plurality of colors is used as an image carrier on which the patch pattern is formed. Yes.

The invention according to claim 4 is characterized in that, in addition to the invention according to any one of claims 1 to 3 , the image density detection sensor is a light diffusion detection sensor.

The invention described in claim 5 is characterized in that, in addition to the invention described in any one of claims 1 to 4, the sampling interval by the image density sensor is set to 1 mm or less.

According to a sixth aspect of the invention, in addition to any one of the first to fifth aspects of the invention, the patch pattern size along the scanning direction of the image density sensor is set to 10 mm or less. It is said.
According to a seventh aspect of the present invention, there is provided an image forming apparatus for forming a visible image on a photosensitive member which is a latent image carrier and transferring the visible image carried on the photosensitive member to a transfer member to form an image. The present invention relates to an image forming apparatus that detects image density and feedback-controls various parameters used for image forming conditions based on the result, and detects the density of a patch pattern formed as a visible image And a control unit having the image density sensor connected to the input side and having a memory capable of storing the input detection output.
The image density detection is performed by the image density detection method according to any one of claims 1 to 6 .

According to the first aspect of the present invention , the detection output ratio between the patch pattern smaller than the detection range of the image density sensor and the patch pattern larger than the detection range is stored in the memory in advance, and the detection of the image density sensor is performed. When detecting the image density of a patch pattern smaller than the range, the output of the patch pattern larger than the detection range of the image density sensor is calculated from the detection output ratio stored in the memory. This makes it possible to determine the density of a patch pattern larger than the sensor detection range based on a small patch pattern, unlike the conventional case. The time can be reduced, and the size of the patch pattern is small, so that the cleaning load can be reduced.

According to the second aspect of the present invention, density measurement is performed at two points equidistant from the edge of the patch pattern, and the difference between the measurement results is obtained so that the edge of the patch pattern differs from the density of other parts. Even in the case of being set, it is possible to avoid the influence of the edge effect at the end. Accordingly, it is possible to prevent an increase in downtime and an increase in cleaning load due to an increase in the patch pattern without causing an increase in the patch pattern based on the edge effect.

According to the third aspect of the present invention, since the target for forming the patch pattern is an intermediate transfer body capable of supporting a plurality of color images, the image density using a small patch pattern even when the density for each color is the target. Can be detected. As a result, even when the number of image types that affect downtime increases, it is possible to reduce downtime and cleaning load.

According to the fourth aspect of the present invention, even when a light diffusion detection sensor is used as an image density sensor that is advantageous when forming an image of a plurality of colors, the image density is reduced using a small patch pattern without increasing the size of the patch pattern. Detection is possible, thereby preventing an increase in downtime and cleaning load.

According to the fifth and sixth aspects of the invention, by setting the sampling interval and the patch pattern size of the image density sensor, it is possible to prevent the images of the respective colors from overlapping when forming images of a plurality of colors. Thus, it is possible to accurately detect the image density for each color. According to the seventh aspect of the present invention, it is possible to realize an image forming apparatus that takes advantage of the image density detection method .

  The best mode for carrying out the present invention will be described below with reference to the illustrated embodiments.

  FIG. 1 shows an image forming apparatus to which an image density detection method according to an embodiment of the present invention is applied. An image forming apparatus 100 shown in FIG. 1 shows a color printer capable of forming images of a plurality of colors. The present invention is not limited to a printer as an image forming apparatus, but includes a copying machine, a facsimile machine, a printing machine, and an apparatus that combines these functions.

In FIG. 1, an image forming apparatus 100 includes photosensitive drums 20Y, 20M, and 20C as image carriers that can form images as images corresponding to colors separated into yellow, magenta, cyan, and black, respectively. , 20Bk is used in parallel.
In the image forming apparatus 100 having the configuration shown in FIG. 1, the visible images formed on the photosensitive drums 20Y, 20M, 20C, and 20Bk are in the direction of arrow A1 while facing the photosensitive drums 20Y, 20M, 20C, and 20Bk. A transfer sheet on which an image is superimposed and transferred by performing a primary transfer process on an intermediate transfer body (hereinafter referred to as an intermediate transfer belt) 11 using an endless belt that can be moved to a transfer sheet. By performing a secondary transfer process on S, a batch transfer is performed.

Around each photosensitive drum, an apparatus for image formation processing is arranged according to the rotation of the photosensitive drum. Now, the photosensitive drum 20Y for forming a yellow image in FIG. A charging device 30Y, a developing device 40Y, a primary transfer roller 12Y, and a cleaning device 50Y that perform image forming processing along the rotation direction of the drum 20Y are arranged.
For writing performed after charging, an optical scanning device 8 described later is used. The photosensitive drum 12Y is also provided with a neutralization device (not shown) that performs neutralization after the residual toner is removed by the cleaning device 50Y.

In the configuration shown in FIG. 2 , the photosensitive drum 20Y, the charging device 30Y opposite to the photosensitive drum 20Y, the developing device 40Y including the developing sleeve 40Y1, and the cleaning device 50Y are housed together in a process cartridge. By being provided so as to be detachable from the apparatus 100, the consumable parts can be exchanged collectively. In FIG. 2 , a symbol L indicates a writing laser beam emitted from the writing device 8.

  In the superimposing transfer to the intermediate transfer belt 11, visible images formed on the photosensitive drums 20 </ b> Y, 20 </ b> M, 20 </ b> C, and 20 </ b> Bk are in the same position on the intermediate transfer belt 11 in the process of moving the intermediate transfer belt 11 in the A1 direction. A1 is applied by voltage application by primary transfer rollers 12Y, 12M, 12C, and 12Bk disposed opposite to the respective photoconductive drums 20Y, 20M, 20C, and 20Bk with the intermediate transfer belt 11 interposed therebetween. The timing is shifted from the upstream side to the downstream side.

  The photosensitive drums 20Y, 20M, 20C, and 20Bk are arranged in this order from the upstream side in the A1 direction. Each of the photosensitive drums 20Y, 20M, 20C, and 20Bk is provided in a process cartridge that forms an image station for forming yellow, magenta, cyan, and black images.

The image forming apparatus 100 is disposed so as to face four image stations that perform image forming processing for each color, and above each of the photosensitive drums 20Y, 20M, 20C, and 20Bk, as well as the intermediate transfer belt 11 and the primary transfer belt. A transfer belt unit 10 having rollers 12Y, 12M, 12C, and 12Bk, and a secondary transfer roller serving as a transfer roller as a transfer member that is disposed opposite to the intermediate transfer belt 11 and is driven by the intermediate transfer belt 11 The roller 5, the intermediate transfer belt cleaning device 13 that is disposed opposite to the intermediate transfer belt 11 and cleans the intermediate transfer belt 11, and the optical writing device disposed below these four image stations. The optical scanning device 8 is provided.
The optical scanning device 8 in this embodiment is equipped with a semiconductor laser as a light source, a coupling lens, an fθ lens, a toroidal lens, a mirror, a rotary polygon mirror, and the like, and each of the photosensitive drums 20Y, 20M, 20C, and 20Bk. On the other hand, writing light L corresponding to each color is emitted (in FIG. 2, the process cartridge for yellow image formation is assigned a target, but the same applies to process cartridges used for other image stations). Thus, an electrostatic latent image is formed on the photosensitive drums 20Y, 20M, 20C, and 20Bk.

  The image forming apparatus 100 includes a sheet feeding device 61 having a sheet feeding cassette on which transfer sheets S transported between the photosensitive drums 20Y, 20M, 20C, and 20Bk and the intermediate transfer belt 11 are stacked, and a sheet. The recording sheet S conveyed from the feeding device 61 is placed between the photosensitive drums 20Y, 20M, 20C, and 20Bk and the intermediate transfer belt 11 at a predetermined timing in accordance with the toner image formation timing by the image station. A registration roller pair 4 that is fed out toward the transfer portion and a sensor (not shown) that detects that the leading edge of the transfer sheet S has reached the registration roller pair 4 are provided.

  The image forming apparatus 100 includes a fixing device 6 as a heat roller fixing type fixing unit for fixing the toner image onto the transfer sheet S on which the toner image is transferred, and the fixed transfer sheet S of the image forming apparatus 100. A paper discharge roller 7 that discharges to the outside of the main body, a paper discharge tray 17 that is disposed on the top of the main body of the image forming apparatus 100 and loads the transfer paper S discharged to the outside of the main body of the image forming apparatus 100 by the discharge roller 7, Located below the paper tray 17 are toner bottles 9Y, 9M, 9C, and 9Bk that are filled with toners of yellow, cyan, magenta, and black.

In addition to the intermediate transfer belt 11 and primary transfer rollers 12Y, 12M, 12C, and 12Bk, the transfer belt unit 10 includes a secondary transfer backup roller 72, a cleaning backup roller 73, and a tension roller around which the intermediate transfer belt 11 is wound. 74. The secondary transfer backup roller 72 is used to form a secondary transfer nip by sandwiching the intermediate transfer belt 11 together with the secondary transfer roller 5.
The cleaning backup roller 73 and the tension roller 74 also have a function as tension urging means for the intermediate transfer belt 11, and for this reason, these rollers are provided with urging means using a spring or the like. Such a transfer belt unit 10, the primary transfer rollers 12Y, 12M, 12C, and 12Bk, the secondary transfer roller 5, and the cleaning device 13 constitute a transfer device 71.

  The sheet feeding device 61 is disposed at the lower part of the main body of the image forming apparatus 100, and includes a feeding roller 3 as a feeding roller that contacts the upper surface of the uppermost transfer sheet S. The uppermost transfer sheet S is fed toward the registration roller pair 4 by being rotationally driven 3 in the counterclockwise direction.

  The fixing device 6 includes a fixing roller 62 having a heat source therein, and a pressure roller 63 pressed against the fixing roller 62. The fixing sheet 62 carrying the toner image is transferred to the fixing roller 62 and the pressure roller 63. By passing through a fixing portion that is a pressure contact portion, the carried toner image is fixed on the surface of the transfer paper S by the action of heat and pressure.

  Although not shown in detail, the cleaning device 13 provided in the transfer device 71 includes a cleaning brush and a cleaning blade disposed so as to abut against the intermediate transfer belt 11, and the intermediate transfer belt. The intermediate transfer belt 11 is cleaned by scraping and removing foreign matter such as residual toner on the belt 11 with a cleaning brush and a cleaning blade. The cleaning device 13 also has a discharge means (not shown) for carrying out and discarding the residual toner removed from the intermediate transfer belt 11.

The image forming apparatus 100 having the above configuration is controlled by a control unit 110 shown in FIG.
FIG. 3 is a block diagram for explaining the configuration of the control unit 110 applied to the image forming apparatus 100. In FIG. 3, the control unit 110 executes a sequence program related to image formation and performs arithmetic processing and a CPU 110A. Developing units 40Y, 40M, and 40C used as toner image forming units are connected to an input / output unit via an interface (not shown). , 40Bk, optical scanning device 8, paper feeding device 61, registration roller 4, transfer device 10, and reflection type photosensor 111 are connected.
The reflection type photosensor 111 is arranged at a position facing the secondary transfer backup roller 72 in the transfer device 10 and has a configuration capable of outputting a signal corresponding to the light reflectance from the intermediate transfer belt 11 and detects diffused light. Or a regular reflection light detector that can obtain a sufficient output value as a difference between the amount of reflected light on the surface of the intermediate transfer belt 11 and the amount of reflected light from a reference pattern image to be described later. In the embodiment, a diffusion type that has an advantage of detecting a high density portion of color toner is used.

The controller 110 performs image forming performance in each developing device at a predetermined timing, such as when a main power supply (not shown) is turned on, when waiting after a predetermined time has elapsed, or when waiting after outputting a predetermined number of prints or more. It is configured to test image forming performance such as image density.
Specifically, when the predetermined timing arrives, first, the photosensitive drum 20 Y, 20 M, 20 C , 20 Bk is uniformly charged while rotating the. With respect to this charging, unlike a uniform belt dragon (for example, −700 V) during normal printing, the potential is gradually increased. Then, visible image processing, that is, development is performed by the developing devices 40Y, 40M, 40C, and 40Bk while forming an electrostatic latent image for the reference pattern image by scanning with the laser light L from the optical scanning device 8.
The bias developed pattern images of the respective colors by the developing is formed on the photosensitive drum 20 Y, 20 M, 20 C , on 20 Bk. At the time of development, the controller 110 gradually increases the value of the developing bias applied to the developing sleeve (the member indicated by reference numeral 40Y1 in FIG. 2 for the yellow image) in each developing device. To control.

The bias development pattern images of these colors are transferred on the intermediate transfer belt 12 so as not to overlap. By this transfer, a pattern block constituted by the reference pattern image of each color is formed on the intermediate transfer belt 11.
When the reference image of each reference pattern image in the pattern block passes through a position facing the reflection type photosensor 111 as the intermediate transfer belt 11 moves endlessly, the amount of reflected light is detected and an electric signal is sent to the control unit. 110 is output. The control unit 110 calculates the light reflectance of each reference image based on the data sequentially output from the reflective photosensor 111, and stores it in the RAM 110B as density pattern data. The pattern block that has passed the position facing the reflective photosensor 111 is cleaned by the cleaning device 13.

Reference patterns described above are formed in the procedure shown in FIG.
In FIG. 4 , the reference pattern images P (PY, PM, PC, PBk) formed on the photosensitive drums 20Y, 20M, 20C, and 20Bk are three reference lines arranged at intervals of 15 mm for each photosensitive drum. It is composed of statues.
In the image forming apparatus 100 according to the present exemplary embodiment, each reference image 101 is 15 mm long × 15 mm wide and is formed through a 15 mm gap. As a result, the lengths of the reference pattern images PY, PM, PC, and PBk on the intermediate transfer belt 11 are L2 = 75 mm, respectively. The reference pattern images PY, PM, PC, and PBk are transferred so as to be arranged on the intermediate transfer belt 11 without overlapping, unlike the toner images of the respective colors formed during the printing process. By such a transfer procedure, one pattern block PB composed of the reference pattern images PY, PM, PC, and PBk for each color is formed on the intermediate transfer belt 11.

Since the pattern block PB is required to be transferred so that the colors do not overlap each other, the photosensitive drums 20Y, 20M, 20C, and 20Bk juxtaposed in the extending direction of the transfer belt 11 are required. The arrangement configuration is as shown in FIG.
FIG. 5 is a schematic diagram showing the installation pitch of the photosensitive drums 20Y, 20M, 20C, and 20Bk.
As shown in FIG. 5, the photosensitive drums 20Y, 20M, 20C, and 20Bk are each set to L1 = 90 mm. Accordingly, since the length L2 of each of the reference pattern images PY, PM, PC, and PBk is 75 mm, the formation pitch of the reference pattern images is shorter than the installation pitch of the photosensitive drums. As a result, the reference pattern images PY, PM, PC, and PBk can be transferred such that the respective end portions do not overlap each other.

As shown in FIG. 6 , the reference pattern images PY, PM, PC, and PBk are provided at two positions almost at the relative positions of the intermediate transfer belt 11. That is, the pattern blocks PB composed of the four reference pattern images PY, PM, PC, and PBk are formed at substantially relative positions as indicated by the symbols PB1 and PB2.

The pattern blocks PB1 and PB2 are formed by the following procedure.
In FIG. 6, when the reference pattern images PBk1, PC1, PM1, and PY1 in the first pattern block PB1 are transferred along with the movement of the intermediate transfer belt 11 (in FIG. 6, the transfer is performed according to the moving direction of the intermediate transfer belt 11). Intermediate transfer belt from the end of transfer until the most upstream reference pattern image PY1 passes through the transfer nip of the most downstream photosensitive drum 20Bk. The reference pattern image moves with the movement of 11.
Therefore, the control unit 110 waits for a predetermined timing and each reference pattern image PBk2, PC2, PM2, PY2 of the second reference pattern block PB2 (the arrangement order is the most downstream side in the moving direction of the intermediate transfer belt 11). (In order of passing through the photosensitive drums 20Bk) is formed on each photosensitive drum. The predetermined timing in this case is that the reference pattern image PY1 on the rear side in the movement direction of the intermediate transfer belt 11 in the first pattern block PB1 passes through the transfer nip of the photosensitive drum 20Bk located on the most downstream side in the movement direction. The reference pattern image PBk2, PC2, PM2, PY2 of the second pattern block PB2 starts to be transferred to the intermediate transfer belt 11 when it is further moved by a predetermined amount. The reference pattern image of each of the pattern blocks PB1 and PB2 is detected by the reflection type photosensor 111 facing the secondary transfer backup roller 72, and is removed by the cleaning device 13 after the detection.

The reflection type photosensor 111 includes reference pattern images PBk1, PC1, PM1, and PY1 from the front end to the rear end of the first pattern block PB1 (the arrangement order is the photosensitive drum on the most downstream side in the moving direction of the intermediate transfer belt 11). The amount of light reflected from each of the reference images 101 constituting (the order of passing 20 Bk) is detected by the following procedure.
That is, three reference images 101 formed as the reference pattern images PBk1, PC1, PM1, PY1 of the reference pattern images PBk1, PC1, PM1, PY1 are converted into the order of the reference pattern images for each color (Bk, C, M , Y). At this time, the reflective photosensor 111 detects the amount of reflected light from each reference image by a method described later and outputs the detected amount to the control unit 110.

  The controller 110 sequentially calculates the image density of each reference image 101 based on the voltage signal output from the reflective photosensor 111 and stores it in the RAM 110B.

Next, an image density detection procedure for the reference image will be described.
FIG. 7 shows the output state of the reflection type photosensor (shown as an image density sensor in FIG. 7) 111 according to the formation state of the reference image 101 and the amount of light reflected from the reference image. In this case, the case where the amount of reflected light from the intermediate transfer belt 11 itself is negligible and can be ignored is targeted.

In FIG. 7 , while reflecting a short patch pattern in the scanning direction (1) to (5) in the scanning direction of the reflective photosensor 111 (for convenience, the following description uses the name of the image density sensor shown in the figure) The output of the image density sensor 111 corresponding to the amount of reflected light is plotted for each relative position between the image density sensor 111 and the patch pattern. This result is the output distribution of the image density sensor 111 (in this embodiment, the detection range of the image density sensor is set to −3.5 mm to 3.5 mm).

Next, the output ratio of the small patch pattern and the large patch pattern at each measurement position is obtained using the measured output distribution.
A method for obtaining an output of a small patch pattern (here, a pattern of 3 mm) will be described with reference to FIG. 8 showing a case where the pattern is at a relative position of −1 mm to 2 mm.
The small pattern in FIG. 8 is considered to be a pattern smaller than the patch pattern shown in FIG. 7 combined between the relative positions −1 mm and 2 mm. Therefore, the output of the image density sensor 111 is the sum of all the values of −1 mm to 2 mm in the output distribution of the image density sensor 111 obtained in FIG.

On the other hand, the amount of light reflected from the patch pattern with respect to the image density sensor 111 has a density different from that of the other parts at the edge due to the influence of the edge effect. For this reason, there is a possibility that a result that does not correspond to the image density based on the amount of reflected light in the actual patch pattern may be caused. Therefore, in this embodiment, the influence at both ends of the patch pattern image portion is removed. As a procedure for this, as shown in FIG. 9, measurement is performed at a point on the near side (front side in the scanning direction) of the end portion 1 with respect to the case shown in FIG. In both cases, the difference in sensor output shown in FIG. 9 is obtained from the sensor output shown in FIG. 8 by utilizing the fact that the sensor output from the end 1 is equal, so that the influence of the edge effect is avoided. This relationship is expressed by the following equation (1).
Sensor output shown in FIG. 8−sensor output shown in FIG. 9 = sensor at the center of the pattern
Output + sensor output at end 2 (1)
As a result, the sensor output component at the end 1 disappears. In order to avoid the influence of the edge effect related to the end 2, in the sensor output shown in FIG. 8, the same distance from the end 2 as far as the end 2 (backward in the scanning direction) in the sensor output shown in FIG. This is possible by measuring at points and subtracting the output from the sensor output shown in FIG.

In this embodiment, the detection output ratio between the small patch pattern and the large patch pattern is stored in the memory 110B in advance, and the detection output ratio stored in the memory 110B is collated by detecting the small patch pattern. The detection output with a large patch pattern can be calculated without forming a large patch pattern. For this reason, it is necessary to obtain a large patch pattern output in order to obtain a detection output ratio with a small patch pattern. In this embodiment, an output for a larger patch pattern is obtained in the following procedure.
FIG. 10 shows a large patch pattern that covers the entire detection area of the image density sensor 111. The large patch pattern is obtained by combining the small patch pattern shown in FIG. 7 over the entire detection area. Conceivable.

For this reason, the sensor output is the sum of all of -3.5 mm (detection region end) to 3.5 mm (detection region end) in the output distribution of the image density sensor 111 shown in FIG.
With such a relationship, the detection result excluding the edge effect of the small patch pattern and the output of the large patch pattern can be calculated. As shown in Table 1, this value is obtained in the memory (RAM) 110B by obtaining the output ratio at each relative position. The output ratio stored in the memory 110B is measured before the factory shipment of the image forming apparatus, and the output ratio is registered and stored in the memory 110B at the time of shipment.

Next, a procedure for evaluating the image forming performance using the output ratio stored in the memory 110B, that is, measuring the image density of the patch pattern for controlling the image forming conditions will be described.
When evaluating the image forming performance, a patch pattern is formed, and the formed patch pattern is positioned at the position shown in Table 2 at the front and center of the end 1 (shown as Edge 1 in Table 2). Measure the sensor output at the rear part and end part 2 (denoted as edge 2 in Table 2).

  The patch pattern formed in this case is the same pattern (3 mm) as the patch pattern obtained when the output ratio shown in Table 1 is obtained, and the sampling interval is set to 0.2 mm. In each table, the distance between the center portion and the end portion 1 indicated as edge 1 and the distance between the center portion and the end portion 2 indicated as edge 2 are made equal.

When measurement is performed at each relative position of the patch pattern with respect to the image density sensor 111, Expression 2 for removing an edge effect component from outputs measured at the end portion 1, the center portion, and the end portion 2 is used.
Output after edge processing = center portion− (front portion of end portion 1 + rear portion of end portion 2) (2)
In Expression 2, the right side uses the output of each part.

The output after the edge processing according to Expression 2 is calculated for all of Tables 1 to 6, and the output regarding the large patch pattern is calculated using Table 1 using the output after the edge processing after the calculation. Now, calculating Table1 as an example,
Large pattern sensor output = output after edge processing × (100/66) (3)
It is calculated by. Thereafter, calculation is performed for Tables 2 to 6 in the same manner.

  In this embodiment, the output of a large patch pattern is equal to the output when a patch pattern wider than the detection area of the image density sensor obtained by the conventional method is detected by the control as described above. Even if the pattern is not formed, it is possible to calculate the toner adhesion amount of the patch pattern by a conventional method without setting any special pattern formation condition by forming a small patch pattern.

Although the above procedure is based on the assumption that the amount of reflected light from the intermediate transfer belt 11 itself can be ignored, there are naturally cases where the amount of reflected light cannot be ignored. Therefore, in this embodiment, in such a case, image density detection is performed according to the following procedure.
When the amount of reflected light from the intermediate transfer belt 11 cannot be ignored, the output from the image density sensor 111 corresponding to the amount of reflected light from the belt background is shifted as shown in FIG. Results are obtained.
Based on this result, an output distribution similar to that shown in FIG. 7 can be obtained by performing a process of subtracting the output of the belt background from the obtained sensor output value at each measurement point.

  Even when the edge effect is removed, the same processing as when the amount of reflected light from the intermediate transfer belt 11 can be ignored is used. However, since it is necessary to consider the influence of the background portion for all outputs, for example, Equation 1 changes to Equation 4 below.

Sensor output in FIG. 8−sensor output in FIG. 9 = sensor output at the center of the pattern + sensor output at the end 2 + sensor output at the background portion (4)
The sensor output of the background portion in FIG. 8 is the sum of outputs from the relative positions 2 mm to 3.5 mm and −1 mm to −3.5 mm, and the sensor output of the background portion in FIG. 9 is the relative position of 1 mm to −3.5 mm. This is the sum of output.

The output ratio of the output from the small background portion and the output from the large background portion covering all the detection area of the image density sensor 111 can be obtained from the output distribution of the image density sensor in the same manner as the patch pattern.
The end 2 is measured at a point on the back side (scanning direction rear side) from FIG. 8 and at the same distance from the end 2 in the same procedure as the end 1, and the output is subtracted from the sensor output of FIG. in can remove the influence of the end portion 2 Dee Tsu di effect. In this case, the sensor output from the background portion is obtained in the same manner, the output ratio at each relative position shown in Table 3 is obtained, and the result is stored in the memory 110B. This storage is performed at the factory of the image forming apparatus 100. Done before shipment. In Table 3, the output of the background portion after the edge processing is negative because the output of the background portion from the front portion of the end portion 1 and the rear portion of the end portion 2 rather than the background output from the center portion of the pattern. Is large.

Next, a procedure for evaluating the image forming performance using the output ratio stored in the memory 110B, that is, measuring the image density of the patch pattern for controlling the image forming conditions will be described.
When evaluating the image forming performance, a patch pattern is formed, and the formed patch pattern is positioned at the position shown in Table 2 at the front and center of the end 1 (shown as Edge 1 in Table 2). Measure the sensor output at the rear part and end part 2 (denoted as edge 2 in Table 2).

  The patch pattern formed in this case is the same pattern (3 mm) as the patch pattern obtained when the output ratio shown in Table 1 is obtained, and the sampling interval is set to 0.2 mm. In each table, the distance between the center portion and the end portion 1 indicated as edge 1 and the distance between the center portion and the end portion 2 indicated as edge 2 are made equal.

Next, the processing of excluding the influence of the edge of the output measured at the front part, the central part of the end part 1 and the rear part of the end part 2 of each of Tables 1 to 6 in Table 3 is executed by the following equation (5).
Output after edge processing = center portion− (front portion of end portion 1 + rear portion of end portion 2) (5)
This calculation is performed for Tables 1 to 6. Thereafter, an output for a large patch pattern is calculated according to Table 1 using the output after edge processing of the calculated Tables 1 to 6. Using Table 1 as an example,
Output after edge processing = sensor output of large pattern x (66/100)-center of background
Sensor output x 166/100) (6)
And
Sensor output of large pattern = {output after edge processing + sensor output of background area ×
(166/100)} × (100/66) (7)
As required. Hereinafter, similarly, Tables 2 to 6 are calculated using the output ratio of Table 3.

  In this embodiment, the output of a large patch pattern is equal to the output when a patch pattern wider than the detection area of the image density sensor obtained by the conventional method is detected by the control as described above. Even if the pattern is not formed, it is possible to calculate the toner adhesion amount of the patch pattern by a conventional method without setting any special pattern formation condition by forming a small patch pattern.

1 is a schematic diagram illustrating a configuration of an image forming apparatus to which an image density detection method according to an embodiment of the present invention is applied. FIG. 2 is a schematic diagram illustrating a configuration within a process cartridge used in the image forming apparatus illustrated in FIG. 1. It is a block diagram for demonstrating the structure of the control part used for the image density detection method by this invention Example. It is a schematic diagram for demonstrating the patch pattern used for the image density detection method by an Example of this invention. FIG. 5 is a schematic diagram for explaining an arrangement configuration of photosensitive members for satisfying a patch pattern forming condition shown in FIG. 4. It is a schematic diagram showing a state of a patch pattern formed on the intermediate transfer member. It is a diagram showing a sensor output distribution at a relative position between a patch pattern and an image density sensor. It is a diagram showing a sensor output distribution at a relative position with respect to an image density sensor when a small patch pattern is formed. FIG. 9 is a diagram showing an output distribution of a patch pattern used when performing edge processing on the sensor output shown in FIG. 8. It is a diagram showing a sensor output distribution at a relative position with respect to the image density sensor when a large patch pattern is formed. It is a diagram which shows output distribution at the time of considering the background output which comes in sensor output distribution. It is a schematic diagram for demonstrating the procedure of the conventional image density detection method.

Explanation of symbols

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 11 Intermediate transfer belt 40 Photoconductor 101 Reference image of reference pattern 110 Control unit 110B Memory 111 Reflective photosensor

Claims (7)

An image density sensor for detecting the density of the patch pattern formed on the image carrier is connected to the input side, and a control unit having a memory capable of storing the input detection output is used to obtain a plurality of detection points for the patch pattern. In an image density detection method for detecting an image density by calculating an average value of detection results obtained by detection ,
In advance,
While measuring the density of the patch pattern smaller than the detection range of the image density detection sensor at a plurality of the relative positions while changing the relative position with respect to the image density sensor,
The density of the patch pattern that is larger than the detection range of the image density detection sensor is measured at a plurality of detection points, and the average value of the detection results is calculated.
The measurement output for the small patch pattern obtained at each relative position and the output ratio of the average value of the detection result for the large patch pattern is obtained and stored in a memory,
At the time of image density detection, a patch pattern smaller than the detection range of the image density detection sensor is formed, and the density of the small patch pattern is measured at a plurality of points while changing the relative position with respect to the image density sensor,
Based on the measured density of the plurality of points and the output ratio stored in the memory, the density of the patch pattern larger than the detection range of the image density sensor is calculated for the plurality of points, and the calculated plurality of points An image density detection method comprising detecting an image density by calculating an average value of results . The image density detection method according to claim 1.
As a patch pattern smaller than the detection range of the image density sensor, a rectangular patch pattern that is short in the image density sensor scanning direction and has an edge effect on the edge of the image density sensor scanning direction is used.
To remove the influence of density different from the others at the edge of the patch pattern,
From the sensor output at the first position relative to the patch pattern,
The distance from the center position of the sensor to the edge of the patch pattern is equal to the first position, etc.
An image density detection method comprising subtracting a sensor output at a new second position . The image density detection method according to claim 1 or 2,
Intermediate transfer member capable of supporting a plurality of color images as an image carrier on which the patch pattern is formed
An image density detection method characterized in that is used . The image density detection method according to any one of claims 1 to 3,
  An image density detection method, wherein the image density detection sensor is a light diffusion detection sensor. In the image density detection method according to any one of claims 1 to 4,
The sampling interval by the image density sensor is set to 1 mm or less.
Image density detection method . In the image density detection method according to any one of claims 1 to 5,
The patch pattern size along the scanning direction of the image density sensor is set to 10 mm or less.
An image density detection method characterized by being defined . An image forming apparatus for forming a visible image on a photosensitive member, which is a latent image carrier, and forming the image by transferring the visible image carried on the photosensitive member to a transfer member. In an image forming apparatus that performs feedback control of various parameters used for image forming conditions based on the result,
An image density sensor for detecting the density of a patch pattern formed as a visible image;
The image density sensor is connected to the input side, and includes a control unit having a memory capable of storing the input detection output,
An image forming apparatus that performs image density detection by the image density detection method according to claim 1 .

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