JP2007065641A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately measure the density of toner deposited on a belt-like moving medium even in the case that foreign matter adheres to a density sensor-counter roller. <P>SOLUTION: An output of an optical sensor produced in an area where a toner image is not formed on the belt-like moving medium is stored, and an output of the optical sensor produced when a toner patch image for detection which has been formed by an image forming part is detected by the optical sensor is corrected on the basis of an optical sensor output acquired in the same position of the sensor-counter roller, whereby the density of the toner patch image is calculated. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for measuring the toner amount or toner density of a toner patch formed on a belt-like moving medium suspended by a plurality of rollers in a color image forming apparatus.

  As conventional image forming apparatuses, various methods such as an electrophotographic method, a thermal transfer method, and an ink jet method are used. Among these, those using the electrophotographic method are superior to other methods in terms of high speed, high image quality, and quietness, and have been popularized in recent years. This electrophotography is also divided into various methods. For example, in addition to the well-known multiple transfer method and intermediate transfer member method, a multiple development method in which a color image is superimposed on the surface of the photoconductor and then transferred at once to form an image, and a plurality of different color image formations There is an in-line method in which means (process stations) are arranged in series and a developed image is transferred onto a transfer material conveyed by a transfer belt. Of these methods, the in-line method is excellent because it is possible to increase the speed and the number of times of image transfer is small, which is advantageous for image quality.

  FIG. 3 shows an inline configuration. In FIG. 3, an electrostatic attraction / conveying belt (hereinafter referred to as ETB) 1 is suspended by each of a driving roller 6, an attraction opposing roller 7, tension rollers 8 and 9, and rotates in a direction indicated by an arrow. Process stations 201 (yellow), 202 (magenta), 203 (cyan), and 204 (black) of different colors are arranged in a row on the peripheral surface of the ETB 1, and the photoconductors in the process stations pass through the ETB 1. It is in contact with the transfer roller 3. Further, the suction roller 5 is disposed upstream of the process station and is in contact with the suction counter roller 7. Here, the transfer material p is biased by the power source 7 when passing through the nip formed by the suction roller 5 and the suction counter roller 7, electrostatically attracted to the ETB 1, and conveyed in the direction indicated by the arrow. Is done.

  As ETB1, a resin film of PVdF, ETFE, polyimide, PET, polycarbonate, etc. having a thickness of 50 to 200 μm and a volume resistivity of 109 to 1016 Ωcm is used. Alternatively, a surface layer of a rubber base layer such as EPDM having a thickness of about 0.5 to 2 mm and having a fluorine resin such as PTFE dispersed in urethane rubber is used. In order to improve the glossiness, an acrylic layer or the like may be coated on the resin film.

  Here, the image forming process will be described. First, an image forming process in the process station will be described. The description will be made using a yellow process station, but the same applies to other color stations.

  FIG. 4 shows the configuration of the process station. The photosensitive member 211 is uniformly charged by the charger 212, and a latent image is formed by the scanning light 214 by the exposure optical system 213. The latent image is developed by the toner in the toner storage unit 216 being attached by the developing roller 215, and a toner image is formed on the photoreceptor 211. Transfer residual toner that has not been transferred in a transfer process described later is scraped off by a cleaning blade 217 and stored in a waste toner container 218.

  Next, the transfer process will be described. In a generally used reversal development method, when the photosensitive member is, for example, a negative OPC photosensitive member, negative toner is used when developing the exposed portion. Therefore, a positive transfer bias is applied to the transfer roller 3 from the bias power source 4. Here, a low resistance roller is generally used as the transfer roller.

  In the actual printing process, considering the moving speed of the ETB 1 and the distance between the transfer positions of each process station, image formation at the process station is performed at the timing when the positions of the toner images of the respective colors formed on the transfer material coincide.・ Transfer process ・ Transfer the transfer material p. Then, a toner image is completed on the transfer material while the transfer material p passes through the process stations 201 to 204 once. After the toner image is completed on the transfer material, the transfer material p is passed through a conventionally known fixing device 12 to fix the toner image on the transfer material p.

  Also, the image density varies depending on the temperature and humidity conditions in which the image forming apparatus is used and the degree of use of the process station. In order to correct this variation, the image density is controlled. Here, this image density control will be described. The configuration is shown in a block diagram 13 of FIG.

  The image forming apparatus 30 includes a controller unit 31 and an engine unit 32, and forms a toner patch image of each color by a host computer 20 or a controller 31 on a photosensitive member, an intermediate transfer member (hereinafter referred to as ITB), or an ETB. Perform toner patch density control. The control means has a CPU 34 and a memory 35, detects the toner patches of the respective colors by the density sensor 13, stores them in the memory 35, and calculates by the CPU 34 the density of the toner patches. There is a means for adjusting the maximum density of each color by feeding back the result to process forming conditions such as charging or developing high-pressure 37 conditions or laser 36 power, and canceling the γ characteristic of each color and adjusting the halftone gradation characteristics. It is used. In general, the density detection sensor 13 irradiates a toner patch with a light source and detects the reflected light intensity with a light receiving element. The reflected light intensity signal is A / D converted, then processed by the CPU, and fed back to the process formation conditions.

  The purpose of image density control is to keep the maximum density of each color constant (hereinafter referred to as Dmax control) and to keep the halftone gradation characteristics linear with respect to the image signal (hereinafter referred to as Dhalf control). . In addition, Dmax control has a large meaning of keeping the color balance of each color constant, and preventing scattering of overlaid characters and fixing failure due to excessive toner loading.

  In Dmax control, a plurality of toner patches formed by changing image forming conditions are detected by an optical sensor, and a condition for obtaining a desired maximum density is calculated from the result, and the image forming conditions are changed. . Here, it is often preferable that the toner patch is formed in a halftone. The reason is that when a so-called solid image is detected, the width of the change in the sensor output with respect to the change in the toner amount becomes small, and sufficient detection accuracy cannot be obtained. In a system in which the maximum density of each color is affected by the film thickness of the OPC photoreceptor and the image forming environment rather than the image forming conditions, it is not necessary to perform Dmax control by toner patch detection. In this case, it is possible to set the image forming condition from the result of the environment detection and the CRG tag information, which is advantageous in terms of usability and toner consumption.

  On the other hand, Dhalf control cancels the γ characteristic in order to prevent the output density from deviating from the input image signal due to the nonlinear input / output characteristic (γ characteristic) peculiar to electrophotography. Perform image processing to keep the input / output characteristics linear. A plurality of toner patches having different input image signals are detected by an optical sensor to obtain a relationship between the input image signal and density. From this relationship, the image signal input to the image forming apparatus is converted by the controller of the image forming apparatus so that a desired density is obtained with respect to the input image signal from the host computer. This Dhalf control is generally performed after the image forming conditions are determined by Dmax control.

The toner patch formed on the ETB is electrostatically collected by the process device by a cleaning process. At the time of the cleaning process, a bias having a polarity opposite to the charging polarity of the toner is applied to the photosensitive member, the toner is attracted to the photosensitive member at the transfer portion, and scraped off by the cleaning blade 14 in the same manner as the transfer residual toner. The cleaning of the ETB may be physically recovered by contacting a cleaning blade on the ETB without depending on the electrostatic recovery method.
JP2003-186350

  By the way, when the circulating moving body is in a belt shape and is suspended by a plurality of rollers, and the sensor is installed to face one of the plurality of rollers, the adhering matter or the like on the rollers There was a problem affecting the sensor output. Even if the gloss variation due to the location on the belt-like circulation moving body is small, it can occur particularly in the detection of a toner patch having a low toner concentration. This problem is the same even when the sensor output of the toner patch is standardized by the sensor output of the circulating moving body base in the system in which the gloss variation due to the location of the belt-shaped circulating moving body is large. In addition, this problem can be avoided by making the circumference of the belt-like circulation moving body an integral multiple of the circumference of the opposing roller in the method of canceling the variation in the amount of reflected light of the background as described above. Thus, the selection of the circumference of the belt-like moving medium and the circumference of the roller itself is limited to the configuration such as the height of the main body, and in fact, it is often impossible to select the above-described integer multiple relationship. In addition, when the reflected light amount from the belt substrate swings in a sin curve with the outer diameter fluctuation of the opposing roller, it is possible to correctly estimate the reflected light amount fluctuation by devising the averaging process of the reflected light amount. For example, if the detection range of the belt or toner patch is set to one rotation of the opposing roller, the amount of reflected light is detected at equal intervals, and the detected result is averaged, the detection deviation by the opposing roller can be canceled. Then, if the reflected light amount fluctuation from the belt surface is removed, the correct reflected light amount can be estimated. On the other hand, when the reflected light amount fluctuates due to an adhering matter or the like on the opposing roller, the reflected light amount waveform has a periodicity, but the waveform is asymmetrical, and it is impossible to cancel the shake by the averaging process.

  The present invention has been made in view of the above problems. Even when a problem such as foreign matter adhering to the density sensor facing roller occurs, the toner density on a belt-like moving medium such as an intermediate transfer belt or a transfer conveyance belt is obtained. The purpose is to perform measurement accurately.

  The present invention provides a belt-shaped moving medium suspended by a plurality of rollers, an image forming unit that forms a toner image on the belt-shaped moving medium, and one of the plurality of rollers, and is provided with light emission. An optical sensor that irradiates light to the belt-like moving medium from an element, receives light reflected from the belt-like moving medium by a light receiving element, and outputs a signal corresponding to the amount of received light; and on the belt-like moving medium Storage means for storing the output of the optical sensor in an area where the toner image does not exist, and an output of the optical sensor when the optical sensor detects a detection toner patch image formed by the image forming unit, The density of the toner patch image is calculated by correcting based on the optical sensor output acquired at the same position of the sensor facing roller among the stored values stored in the storage means. It characterized by having a calculating means.

  According to another aspect of the present invention, there is provided a belt-shaped moving medium suspended by a plurality of rollers, an image forming unit that forms a toner image on the belt-shaped moving medium, and one of the plurality of rollers. An optical sensor that emits light from the light emitting element to the belt-like moving medium, receives light reflected from the belt-like moving medium by a light receiving element, and outputs a signal corresponding to the amount of received light; and Calibration means for calibrating the output based on an output value in a state where no toner image exists at the same position of the belt-like moving medium, and the calibration result in an area where the toner image on the belt-like moving medium does not exist The storage means for storing, and the calibration result when the optical sensor detects the detection toner patch image formed by the image forming unit, among the stored values stored in the storage means By correcting on the basis of the serial sensor opposing roller has been calibrated result acquired at the same position of, characterized by comprising a calculating means for calculating the density of the toner patch image.

  According to the present invention, it is possible to improve the measurement accuracy of the toner patch density.

(First embodiment)
A first embodiment of the present invention will be described. FIG. 3 is a schematic diagram of the image forming apparatus according to the first embodiment. Hereinafter, description will be made based on FIG. 3, but those having the same configuration and operation as those of the conventional example are denoted by the same reference numerals and description thereof is omitted.

  In this embodiment, a resin belt obtained by applying a 1 μm thick acrylic coating to a PVdF resin film having a peripheral length of 700 mm and a thickness of 100 μm is used as the ETB1. The optical sensor shown in FIG. 5 is used. Here, this optical sensor will be described.

  As shown in FIG. 5, the optical sensor 13 includes a light emitting element 301 such as an LED and a light receiving element 302 such as a photodiode. Irradiation light from the light emitting element 301 is incident on the ETB 1 at an angle of 30 ° and reflected at the detection position 303. The light receiving element 302 is provided at a position for detecting reflected light reflected at the same angle as the irradiated light of the reflected light, and detects so-called specular reflected light. The optical sensor used in this embodiment has a higher voltage as the reflected light intensity increases as a characteristic.

  The characteristics of the reflected light detected when the optical sensor 13 detects the toner patch will be described in detail. As shown in FIG. 5, the light irradiated on the base ETB is reflected according to the refractive index specific to the ETB material and the refractive index determined by the surface state, and is detected by the light receiving element. When a toner patch is formed here, the base of the portion where the toner is present is hidden, and the amount of reflected light is reduced (FIG. 6). Therefore, as shown in FIG. 7, the amount of reflected light decreases as the toner amount of the toner patch increases, and the density of the toner patch is obtained based on this decrease amount.

  Further, such a density sensor that detects the specular reflection light can measure the amount of black toner on the black ETB from its characteristics. Since carbon black is generally dispersed for resistance adjustment, the color of ETB is often black or dark gray, and a type that detects specular reflection light as a density sensor is desirable. In order to detect a high density chromatic color with high accuracy, a light receiving element (not shown) for detecting the amount of diffusely reflected light may be provided in the density sensor.

  In this embodiment, a density sensor is provided to face a drive roller having a circumferential length of 74 mm. The reason why the density sensor is disposed facing the roller is that the ETB behavior is stabilized even during rotation when there is a backup on the back side of the ETB. In this embodiment, the density sensor is installed facing the drive roller. However, any roller may be used as long as it is a roller that suspends the ETB, such as a tension roller or a suction counter roller. However, since the position accuracy in the rotation direction of the density sensor is required as the circumferential length of the counter roller is smaller, in this embodiment, the counter roller is installed facing the drive roller having the longest circumferential length.

  When the density sensor is placed facing the ETB suspension roller, the behavior of the ETB is stable as described above, but the ETB circumference is not an integral multiple of the density sensor facing roller circumference as in this embodiment. The sensor output is easily affected by the state of the roller. That is, the method according to the conventional example is caused by the adhesion of foreign matters that are difficult to predict the size and position, such as dust adhering to the sensor facing roller in the manufacturing process or scraping powder of the ETB member itself that may be generated during use of the printer. However, the toner patch density may not be detected accurately.

  Specifically, unlike the sensor output (roughly draws a sine wave) due to the outer diameter fluctuation of the roller, the sensor output fluctuates with the period of the roller facing the sensor, but the waveform has no symmetry (no sine wave is drawn). For this reason, in the sensor output averaging process on the premise of the symmetrical waveform, the output fluctuation due to the deposit on the sensor facing roller cannot be removed. In addition, fluctuations in the amount of reflected light caused by the opposing roller are different for each machine and have a complicated shape, so that a large number of sampling points are required to grasp the waveform.

  A Dhalf control operation in the present embodiment that can cancel the influence of the foreign matter adhering to the sensor facing roller will be described.

  In this method, instead of obtaining and subtracting the reflected light amount fluctuation from the belt surface that causes the detection deviation or the reflected light quantity fluctuation caused by the sensor facing roller, the detection deviation caused by the foreign matter adhering to the opposing roller is eliminated. The toner density measurement operation is performed using the belt surface that does not contain any toner. Then, the deviation of the toner density measurement result due to the opposing roller appearing in the calculation result is subtracted from the detection of the toner density of each color to finalize the measurement of the toner density.

  That is, the detection result of the belt surface on which the toner is not placed should have a toner density of 0. However, when a specific toner density is detected, the result is detected as a detection deviation caused by the sensor facing roller. The result is fed back to the toner density detection result.

  In this embodiment, as described in the conventional example, toner cleaning on the ETB is recovered by the electrostatic recovery method, and there is no cleaning member that physically scrapes the toner on the ETB. The toner image formed on the ETB is held. The same applies to the case where the ETB cleaning member can be separated from the ETB.

  In the present embodiment, the toner patch group includes a toner-free portion for one circumference of the drive roller.

  The distance between the heads of the respective color patches is the same as the circumference of the drive roller. That is, in the present embodiment, as shown in FIG. 1, the distance Ld between the heads of the patches yellow, magenta, magenta and cyan, and cyan and black is 74 mm. According to this configuration, by actually performing the toner density measurement operation using the toner-free portion for one rotation of the driving roller, which patch has a detection deviation caused by foreign matter on the driving roller in each phase of the driving roller. It can be determined whether or not it affects the degree. Using this value, the density measurement value of each color toner patch in each phase can be corrected. Since correction is possible by detecting only a specific range of the toner-free portion, the memory area of the firmware can be reduced, which is advantageous in terms of cost.

  A specific correction method will be described below. The configuration is the same as that of the conventional example, and description thereof is omitted here. FIG. 14 shows a flowchart in the present embodiment.

  In this embodiment, as a precondition for gradation correction, high voltage conditions for charging and development and laser power are adjusted. After gradation correction start (STEP 1), the above-described concentration factor setting (STEP 2) is performed. To do. Thereafter, the tone correction toner patch formed on the ETB is detected by the controller.

As shown in FIG. 1, the patch configuration is 9 mm long by 8 gradations and 72 mm in the process direction for each color, and 6 points near the center of 1 gradation patch 9 mm are detected at regular intervals and averaged. In this configuration, the density of one patch is measured by processing. The configuration of the patch in this example is
-To secure the number of tones for grasping the γ characteristics of the device-To ensure the detection accuracy of one tone patch-To determine the patch length of each color to be equal to or less than the length of the sensor facing roller.

  One averaged sensor output value per gradation is stored in the memory area. Since the reflected output from the background of the ETB used in the present embodiment varies relatively, the toner patch sensor output is standardized by the background sensor output, as is generally done. As a result, a method of canceling the reflected light variation from the background and measuring the density of the toner patch is employed. In this embodiment, first, the sensor output of the ETB background at the position where the toner patch is formed on the first round of the belt is detected and stored, and the sensor output of the toner patch formed on the belt is detected on the second round of the belt. Then, it is standardized by the sensor output of the ETB base.

  In this embodiment, a reference patch is formed on the ETB and the time required for one rotation of the ETB is measured and stored in order to match the detection positions of the ground and the patch. The reference for grasping the ETB rotation time may be a reference mark or a reference tape provided on the ETB at the time of ETB molding.

  As described above, when the sensor output Ps of the toner patch is normalized by the background sensor output Pb, the sensor output Ps / Pb of the patch with respect to the background is ideally Ps / Pb = 1.00 in the toner-free portion. . That is, the closer the value of Ps / Pb is to 1.00, the lower the density of the toner patch is, and the closer the value is to 0, the higher the density is. The actual density is calculated by converting the value of Ps / Pb according to the characteristics of each color.

  Here, when foreign matter is present on the driving roller, the ETB swells in a convex shape, so that a part of the reflected light is not detected by the light receiving element (FIG. 2). For this reason, even if there is no toner on the belt, if the sensor output after standardization deviates greatly from 1.00 and becomes less than 1.00, the toner patch has a predetermined density according to the value. Will be detected. In addition, the amount of reflected light from the belt is shifted regardless of the absence of toner, so that the toner patch density detection result also shifts. In this way, in the past, even in a portion where the toner is not actually placed, a detection shift caused by a foreign matter on the driving roller occurs, and it is detected as if the toner is placed, or conversely, it is detected thinner than the actual patch. I was doing.

  Detection deviation due to foreign matter adhering to the drive roller is highly dependent on the size and shape of the foreign matter, and occurs almost at the same rate each time the drive roller rotates. By doing so, the measured density value of the patch can be corrected. As an example, if all the toner patches of each color are set to density 0 and the ratio of the first and second rounds of the ETB is taken, it can be seen that almost stable detection deviation occurs in the drive roller cycle as shown in FIG. On the other hand, in this embodiment, a toner-free portion for one rotation of the driving roller is provided upstream in the process direction of each color toner patch group, and toner patch data is converted based on the data, thereby obtaining a result close to an ideal value. It was.

A specific conversion method will be described by taking the measurement of yellow toner density as an example. The sensor output after normalization of the nth toner patch obtained by the conventional measuring method is Y (n), and the sensor output after normalization of the position corresponding to the nth patch (= the same phase on the driving roller) in the toner-free portion. Is W (n). The normalized sensor output Y (n) ′ of the nth toner patch after correction is
Y (n) ′ = Y (n) / W (n)
It is represented by

  In the present embodiment, the measurement procedure for W (n) is the same as that of a normal toner patch. In this embodiment, a toner-free portion corresponding to 8 gradations is detected and stored in a memory (STEP 3). ).

  When detection of the toner-free portion is completed (STEP 4), detection of each color patch is started.

  Next, Y (n) is measured, and the toner patch correction calculation is performed and stored in the memory (STEP 5).

In addition, other colors are similarly detected repeatedly, and the sensor output after the standard is
Bk (n) ′ = Bk (n) / W (n), C (n) ′ = C (n) / W (n), M (n) ′ = M (n) / W (n)
(STEP 6).

  After storing the normalized sensor output after correction for all four colors in the memory (STEP 7), the numerical values are converted according to the characteristics of each color, the density is calculated (STEP 8), and γ correction is performed (STEP 9). The gradation correction control ends (STEP 10). As described above, it is possible to calculate density with higher accuracy by converting the sensor output after normalization according to the characteristics of each color.

  The conversion method is not limited to the above, and it is possible to select a method for compensating for the detection deviation. The toner concentration calculation method on the ETB based on the sensor output is not limited to a specific method, and conversion may be performed using a normal conversion table or a conversion formula as described in the present embodiment. . FIG. 9 shows the result of measuring the toner patch density by the method of this embodiment. The ideal value is the result of inversely converting the result of measuring the density with Macbeth after transferring the toner onto the paper to the sensor measurement value. By the above method, the variation in the reflected light amount of the conventional belt substrate can be canceled, and the deviation of the reflected light amount due to the influence of foreign matter on the sensor facing roller can also be canceled. In particular, in the case of low density patches, detection deviation caused by foreign matter on the density sensor facing roller, which occurred 10% or more at the maximum, can be accommodated within 4% at maximum by this method, greatly increasing the detection accuracy of the toner patch. Improved. In addition, a stable image can be obtained by performing γ correction using the patch density detection result obtained by the above method.

  In this configuration, a toner-free portion corresponding to one circumference of the sensor-facing roller is provided in the toner patch group that fits within one ETB circumference. This is because the detection deviation caused by the driving roller is used for more accurate correction. This is a desirable configuration. In a system where the circumference of the ETB is very stable, since the circumference relationship between the drive roller and the ETB is stable, even if the toner patch group and the toner-free portion do not fit within the ETB1 circumference, the detection caused by the drive roller The deviation can be predicted. On the other hand, it is desirable to correct the measured value of the toner patch with the configuration of the present embodiment in a system in which the environmental variation of the ETB perimeter is large or the dimensional variation in manufacturing is large. The length of the toner-free portion may be equal to or longer than the length of the patch per color (72 mm in this embodiment). In this embodiment, the circumferential length of the driving roller, which is a sensor facing roller, and the total patch per color The length is set to a close value, and the length of the toner-free portion is provided for the circumference of the drive roller. The linear expansion coefficient of the PVdF resin used in the ETB of this example is about 14 × 10 −5 / ° C., and the circumference change of 1 to 3 mm occurs depending on the use environment. Therefore, the ETB circumference correction method in this example In this case, a shift occurs in the patch detection position for the circumference change. Therefore, as described above, the toner patch group is provided with a toner-free portion corresponding to one circumference of the driving roller, and the distance between the heads of the respective color patches is made equal to the circumference of the driving roller. It is possible to perform toner patch density correction. Further, in this configuration, it is not necessary to hold down the profile for one round of the sensor facing roller even in the toner-free portion, and only the sensor output of the toner-free portion at the required roller phase needs to be stored. Can be suppressed.

In ETB using a polyimide resin or the like that does not vary in the sensor output of the ground, the toner patch density may be calculated using the sensor output of the toner patch as it is. In this case, the sensor output of the nth toner patch obtained by the conventional measurement method is y (n), and the sensor output after normalization of the position corresponding to the nth patch (= the same phase on the driving roller) in the toner-free portion. Is w (n). Then, the sensor output y (n) ′ of the nth toner patch after correction is
y (n) ′ = y (n) / w (n). Since it is not necessary to standardize the reflected output of the ground, the control time can be shortened, which is advantageous from the viewpoint of usability.

  When the sensor output from the toner patch is normalized by the sensor output from the ETB surface as in this embodiment, the order of obtaining the sensor output may be from the toner patch or the ETB surface. However, when there is no ETB cleaning member in contact with the ETB, it is better to obtain the sensor output from the ETB surface first, and the Dhalf operating time is shortened and the usability is excellent.

  Further, the toner-free portion near the toner patch may be located upstream or downstream in the process direction of the toner patch group or between any of the colors.

  In the present embodiment, only the ETB has been described. However, as described in the conventional example, the present invention can be similarly applied to an ITB suspended on a suspension roller and provided with a density sensor facing one of the rollers.

  As described above, a blank portion longer than the circumferential length of the density sensor facing roller is provided in the toner patch group, and the detection deviation caused by the foreign matter on the sensor facing roller is estimated from the sensor output of the blank portion. As a result, the density detection accuracy can be improved by correcting the density detection result of the actual toner patch.

(Second Embodiment)
The second embodiment of the present invention has substantially the same configuration as that of the first embodiment except that a toner-free portion corresponding to two or more circumferences of the density sensor facing roller is provided in the vicinity of the toner patch group. It is possible to more accurately estimate the detection shift caused by the foreign matter on the density sensor facing roller in the blank portion of two or more circumferences.

  In the method of the first embodiment, even if a detection deviation due to the detection variation itself of the density sensor occurs, it is difficult to determine whether the detection deviation is caused by a foreign substance on the density sensor facing roller. On the other hand, as shown in FIG. 10, when a blank portion longer than the circumference of the roller is provided and the detection results are averaged, stable detection deviations caused by foreign matters remain as they are, and unstable elements such as detection variations are small. (Fig. 11). The longer the blank portion is with respect to the circumference of the density sensor facing roller, the more stable the result. Further, the toner-free portion may be provided separately before and after the toner patch group as in the first embodiment.

  According to the method of this embodiment, it is possible to more accurately estimate the detection deviation caused by the foreign matter on the density sensor facing roller, and the maximum detection deviation can be suppressed to 3% or less.

(Third embodiment)
In the third embodiment of the present invention, a toner-free portion corresponding to two or more circumferences of the density sensor facing roller is provided upstream in the process direction of the toner patch group. The configuration is almost the same as in the second embodiment except that the density detection deviation of the toner-free portion is stored and compared for each circumference of the density sensor facing roller, and the toner patch density is corrected based on the comparison result. It is. In the case where the toner-free portion is a blank portion corresponding to two rounds of the density sensor facing roller, if the results of the first and second rounds of the density sensor facing roller show the same tendency, averaging is performed as in the second embodiment. After processing, it may be used as toner patch density correction data. On the other hand, if the results show a tendency that differs greatly, the toner patch density measurement correction is performed by the output immediately before the toner patch.

  For example, when the sensor output of the toner-free portion shows a profile as shown in FIG. 12, there is a foreign object on the density sensor facing roller in the blank portion of the first round, but the density in the blank portion of the second round. The result that there is a foreign object on the sensor facing roller cannot be obtained. For this reason, it is determined that the foreign matter adhesion state on the sensor facing roller has changed, and the density correction of the toner patch is performed using the output of the toner-free portion immediately before the toner patch. With this method, it is possible to accurately measure the density of the toner patch even when there is a foreign matter that does not remain at a specific position, such as a foreign matter having low viscosity. In this embodiment, after standardizing the sensor output from the toner patch, the data for the first and second rounds of the toner patch density-free toner portion are compared for each nth patch. When the difference is 2.5% or more, it is considered that the foreign matter has moved, and the method of using only the data of one round immediately before the toner patch as the correction data without performing the averaging process of the toner-free portion. The method is not limited to the above. For example, when the data of the toner-free portion shows a tendency to greatly differ between the first and second rotations of the sensor facing roller, a method of performing Dhalf control itself again is adopted. You may do it. Thereby, the density measurement accuracy of the toner patch can be increased.

  According to the method of the present embodiment, since the movement of the foreign matter can be detected, it is possible to reduce the occurrence of correction failure such as excessive correction or insufficient correction that occurs more rarely while maintaining the correction accuracy as described in the above embodiment. It becomes possible. In this embodiment, a blank portion is provided at the head of the toner patch group. However, when a blank portion is provided downstream in the process direction of the toner patch group, the toner patch density correction is performed using the value of the blank portion immediately after the toner patch. You may do it.

  The present invention has been described above with reference to some preferred embodiments. However, the present invention is not limited to these embodiments, and various modifications and applications are possible within the scope of the claims. it is obvious.

An example of a toner patch according to the first embodiment of the present invention Schematic diagram of belt-shaped moving medium surface detection when there is foreign matter on the density sensor facing roller Schematic of an image forming apparatus in the present invention Schematic diagram of process station Schematic diagram of concentration sensor Schematic diagram of concentration measurement by specular reflection detection Relationship between amount of toner on belt-like moving medium and amount of specular reflection Detection result of belt-like moving medium surface by conventional method An example of a toner patch density measurement result according to the first embodiment An example of a toner patch group used in the second and third embodiments Example of sensor output after normalization in the second embodiment An example of sensor output fluctuation accompanying movement of foreign matter on the sensor facing roller of the third embodiment Block diagram in the present invention Flow chart in the present invention

Explanation of symbols

1 ETB (electrostatic adsorption conveyor belt)
13 Optical sensor

Claims (12)

A belt-like moving medium suspended by a plurality of rollers;
An image forming unit for forming a toner image on the belt-like moving medium;
It is provided facing one of the plurality of rollers, irradiates light from the light emitting element to the belt-like moving medium, receives light reflected from the belt-like moving medium by the light receiving element, and the amount of light received An optical sensor that outputs a signal according to
Storage means for storing the output of the optical sensor in a region where the toner image on the belt-like moving medium does not exist;
The output of the optical sensor when the optical sensor detects the detection toner patch image formed by the image forming unit is acquired at the same position of the sensor facing roller among the stored values stored in the storage unit. An image forming apparatus comprising: a calculating unit that calculates the density of the toner patch image by performing correction based on the output of the optical sensor. The length of the area where the toner image does not exist in the moving direction of the belt-like moving medium is at least equal to or greater than the circumferential length of the facing roller.
The image forming apparatus according to claim 1, wherein the storage unit stores the output of the optical sensor for one period in an area where the toner image does not exist. The image forming unit forms a toner patch group formed under a plurality of conditions for a plurality of colors,
The image forming apparatus according to claim 1, wherein the calculation unit acquires the density of each toner patch image included in the toner patch group for the plurality of colors.   The image forming apparatus according to claim 3, wherein a total length of the toner patch group for the plurality of colors and a region where the toner image does not exist is equal to or less than a circumference of the belt state moving medium.   4. The image forming apparatus according to claim 3, wherein a distance between the heads of the toner patch groups of the respective colors is the same as a circumferential length of the sensor facing roller.   Obtaining the optical sensor output in a state where no toner image of the belt-like moving medium is present, obtaining the optical sensor output in a state in which a toner image of a detection toner patch image is not present on the belt-like moving medium; The image forming apparatus according to claim 1, wherein the toner adhering to the belt-like moving medium is recovered by an electrostatic recovery method. A belt-like moving medium suspended by a plurality of rollers;
An image forming unit for forming a toner image on the belt-like moving medium;
It is provided facing one of the plurality of rollers, irradiates light from the light emitting element to the belt-like moving medium, receives light reflected from the belt-like moving medium by the light receiving element, and the amount of light received An optical sensor that outputs a signal according to
Calibration means for calibrating the output of the optical sensor based on an output value in a state where no toner image exists at the same position of the belt-like moving medium;
Storage means for storing the calibration result in an area where the toner image on the belt-like moving medium does not exist;
The calibration result when the optical sensor detects the detection toner patch image formed by the image forming unit is acquired at the same position of the sensor facing roller among the stored values stored in the storage unit. An image forming apparatus comprising: a calculating unit that calculates the density of the toner patch image by correcting based on a calibration result. The length of the area where the toner image does not exist in the moving direction of the belt-like moving medium is at least equal to or greater than the circumferential length of the facing roller.
The image forming apparatus according to claim 7, wherein the storage unit stores the output of the optical sensor for one period in an area where the toner image does not exist. The image forming unit forms a toner patch group formed under a plurality of conditions for a plurality of colors,
The image forming apparatus according to claim 7, wherein the calculating unit acquires the density of each of the toner patch images included in the toner patch group for the plurality of colors.   The image forming apparatus according to claim 9, wherein a total length of the toner patch group for the plurality of colors and a region where the toner image does not exist is equal to or less than a circumferential length of the belt state moving medium.   The image forming apparatus according to claim 9, wherein a distance between the heads of the toner patch groups of the respective colors is the same as a circumferential length of the sensor facing roller.   Obtaining the optical sensor output in a state where no toner image of the belt-like moving medium is present, and obtaining the optical sensor output in a state where a toner image of a detection toner patch image is not present on the belt-like moving medium; The image forming apparatus according to claim 7, wherein the toner attached to the belt-like moving medium is collected by an electrostatic collection method.

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