JP2007052111A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the color smear and nonuniform pitch uneven of a color image caused by speed variations of a conventional transfer belt by correcting nonuniform rotation of the transfer belt taking account of a drive system for drive of the transfer belt and thickness variations of the transfer belt. <P>SOLUTION: The image forming apparatus that forms an image by transferring a toner image to the surface of an image carrier belt or the surface of paper held on the image carrier belt includes: a belt drive means in which two or more rollers for transmitting drive force to the image carrier belt are attached to the transfer belt; a speed detecting means disposed on the image carrier belt and used to detect the rotating speed of a roller other than the drive rollers; and a reference position detecting means for detecting the reference position of the image carrier belt. After the reference position is detected by the reference position detecting means, a rotation correction is made to a drive means for the drive rollers by the speed detecting means from a change in the speed of the image carrier belt made at least one rotation. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an image forming apparatus having a rotating body such as a photoreceptor or a transfer belt.

  In order to generate a color image, a latent image is formed by scanning a laser beam on a photosensitive drum rotating at a constant speed at regular intervals, and developed with toner to form a toner image. This toner image is transferred to a transfer belt. A color toner image is formed on the transfer belt by superimposing magenta (M), cyan (C), yellow (Y), and black (K) toner images at the same position on the transfer belt. The toner image becomes a permanent image by transferring the toner image from the transfer belt onto a sheet and fixing the toner image on the sheet with a fixing device. In this color image forming apparatus, a DC brushless motor is conventionally used to rotate the photosensitive drum and the transfer belt at a constant rate. Further, the transfer belt is driven to rotate by a drive transmission system of a reduction gear. If the transfer belt does not rotate at a constant speed, the four color images cannot be superimposed at the same position on the transfer belt, causing color misregistration and image density unevenness at the rotational uneven frequency of the drive system. Because it ends up.

  Since the DC brushless motor detects the speed and phase of the motor shaft and performs feedback control so as to obtain a constant speed and phase, the rotation unevenness on the motor shaft is small. However, the rotation of the transfer belt after the drive transmission system causes uneven rotation according to the thickness unless the thickness of the transfer belt is constant. Therefore, conventionally, Patent Document 1 proposes a method of reducing color misregistration by previously storing thickness data for one rotation of the transfer belt and correcting the timing of image formation.

Furthermore, various methods for forming and reading a predetermined pattern on the transfer belt in the adjustment mode and correcting the speed fluctuation component on the belt surface due to the thickness variation for one rotation have been proposed (see, for example, Patent Documents).
JP 2000-356875 A JP 2001-228777 A

  However, in the case of the conventional configuration, the inertial body attached to the transfer belt drive shaft becomes a large object, which is an obstacle to downsizing and cost reduction of the device. Further, as a method for detecting the thickness of the belt, an expensive sensor must be used in order to detect a minute variation in the thickness of the belt by the thickness sensor, and commercialization is difficult. Furthermore, as a method for detecting the belt thickness variation, there is a method in which a toner image having a predetermined pattern is formed on the transfer belt and the transfer belt thickness variation is detected based on the pattern variation. However, the belt thickness is different from the image forming sequence. It was necessary to carry out in the detection sequence, resulting in a decrease in device productivity.

  The present invention has been made based on such a background. In a color image forming apparatus such as an electrophotographic apparatus, the transfer system for driving the transfer belt and the rotation unevenness of the transfer belt including variations in the thickness of the transfer belt are corrected. Thus, it is intended to reduce color misregistration and pitch unevenness of a color image due to speed variation of a conventional transfer belt.

  The present invention can solve the above problems by providing the following configuration.

(1) An image forming apparatus that forms an image by transferring a toner image onto an image bearing belt or a sheet held on the image bearing belt.
Belt driving means in which two or more rollers for transmitting driving force to the image bearing belt are attached to the transfer belt;
A speed detecting means for detecting a rotational speed of a roller different from the driving roller, disposed on the image bearing belt;
Having a reference position detecting means for detecting a reference position of the image bearing belt;
An image forming apparatus characterized in that after the reference position is detected by the reference position detecting means, the speed detecting means corrects the rotation of the driving means of the driving roller based on a speed fluctuation corresponding to at least one rotation of the image bearing belt.

  According to the present invention, in an image forming apparatus such as electrophotography using an intermediate transfer belt such as electrophotography, it is possible to correct a transfer belt speed error due to a difference in the thickness of the transfer belt. The transfer belt can be rotated at a constant speed regardless of the thickness, thereby reducing color misregistration and density unevenness in the color image. Furthermore, productivity can be maximized without interrupting image formation by a special correction sequence during image formation.

  Hereinafter, the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a configuration diagram of a full-color printer which is an example of an image forming apparatus according to the present invention.

  100 is a copying apparatus main body, 142 is a circulation type automatic document feeder (hereinafter referred to as RDF) for automatically feeding documents, and when a plurality of documents are stacked upward, the document is at the bottom. Are read in order.

  The operation of the image forming apparatus of this embodiment will be described below.

  In FIG. 1, reference numeral 101 denotes an original table glass as an original placement table, and reference numeral 102 denotes an original illumination lamp, which constitutes a scanner together with a scanning mirror 103. The scanner is reciprocally scanned in a predetermined direction by a motor (not shown), and the reflected light of the original is transmitted through the lens 107 through the scanning mirrors 103 to 105 to form an image on the CCD sensor 108.

  Reference numeral 117 denotes a laser that irradiates the photosensitive drum 1 with laser light that is converted into an electrical signal by the image sensor unit 106 and modulated based on an image signal that has been subjected to predetermined image processing by the image control unit 139.

  A photosensitive drum (hereinafter simply referred to as “photosensitive member”) 1 as an image carrier is provided so as to be rotated in the direction of arrow A by a motor (not shown). Around the photosensitive member 1, a primary charger 7, an exposure device 117, a color developing unit 13, a black developing unit 14, a transfer charger 10, and a cleaner device 12 are arranged.

  The color developing unit 13 includes three developing devices 13Y, 13M, and 13C for color development. The developing devices 13Y, 13M, and 13C develop the latent images on the photoreceptor 1 with Y, M, and C toners, respectively. When developing the toner of each color, the developing unit 13 is rotated in the direction of arrow R by a motor (not shown), and the developing device for that color is aligned so as to contact the photoreceptor 1.

  In developing black toner used for full-color and black single-color images, the black developing device 14 develops the latent image with black toner.

  The toner images of the respective colors developed on the photosensitive member 1 are sequentially transferred to the belt 2 as an intermediate transfer member by the transfer device 10, and the four color toner images are superimposed. The belt 2 is stretched around rollers 17, 18, 19, 170 and 180. Among these, the roller 17 is coupled to a driving source (not shown) and functions as a driving roller that drives the belt 2, the roller 18 functions as a tension roller that adjusts the tension of the belt 2, and the roller 19 serves as a secondary transfer device. It functions as a backup roller for the transfer roller 21.

  A belt cleaner 22 is provided at a position facing the roller 17 with the belt 2 interposed therebetween, and residual toner on the belt 2 is scraped off by a blade.

  The recording paper drawn from the recording paper cassette 122 to the conveyance path by the pickup roller 123 is fed to a nip portion, that is, a contact portion between the secondary transfer device 21 and the belt 2 by a pair of rollers 138 and 126. The toner image formed on the belt 2 is transferred onto the recording paper at the nip portion, thermally fixed by the fixing device 150, and discharged outside the device.

  The fixing device 150 is composed of upper and lower two rollers and an external heating roller. The upper heater 132 is inserted into the upper roller, and the lower heater 133 is inserted into the lower roller. An external heater 141 is inserted into the heating roller 140. Further, the output of the upper thermistor 134 that is pressed against the surface of the upper roller, the lower thermistor 135 that is pressed against the surface of the lower roller, and the heater (not shown) on the surface of the outer roller by the output of the external thermistor 142 The controller controls on / off of the upper heater 132, the lower heater 133, and the external heater 141 to keep the temperature of the roller surface constant. The image is fixed by pressure and heat in the fixing device 150 and is discharged out of the main body by the discharge roller 131.

  In the color printer configured as described above, an image is formed as follows. First, a voltage is applied to the charging device 7 so that the surface of the photoreceptor 1 is uniformly negatively charged with a predetermined charged portion potential. Subsequently, exposure is performed by an exposure device 117 formed of a laser scanner so that the charged image portion on the photosensitive member 1 has a predetermined exposure portion potential, and a latent image is formed. The exposure device 117 is turned on / off based on the image signal to form a latent image corresponding to the image.

  A developing bias set in advance for each color is applied to the developing roller of the developing device 13Y and the like, and the latent image is developed with toner when passing through the position of the developing roller and visualized as a toner image. The toner image is transferred to the belt 2 by the transfer device 10, further transferred to the recording paper by the secondary transfer device 21, and then fed to the fixing device 5. In full-color printing, toners of four colors are superimposed on the belt and then transferred onto the recording paper. The toner remaining on the photosensitive member 1 is made easy to clean with a preliminary cleaning device, and is removed and collected by the cleaner device 12. Finally, the photosensitive member 1 is uniformly removed by a static eliminator (not shown). The charge is removed to near 0 volts to prepare for the next image forming cycle.

  The image forming timing of the color printer is controlled with reference to a predetermined position on the belt 2. The belt 2 is stretched around rollers including a driving roller 17, a tension roller 18, and a backup roller 19, and a predetermined tension is applied by the tension roller 18.

  Reflective sensors 160 and 161 for detecting the reference position are arranged between the drive roller 17 and the roller 19. The reflective sensors 160 and 161 detect markings such as a reflective tape provided at the end of the outer peripheral surface of the belt 2 and output an image top signal (hereinafter referred to as an ITOP signal).

  The peripheral length of the photoreceptor 1 and the peripheral length of the belt 2 have an integer ratio represented by 1: n (n is an integer). With this setting, the photosensitive member 1 rotates an integer during one revolution of the belt 2 and returns to the same state as before one revolution of the belt, so that the four colors are superimposed on the intermediate transfer belt 2. In this case (the belt rotates four times), it is possible to avoid color misregistration due to uneven rotation of the photoreceptor 1.

  Next, a configuration for performing rotation control of the color developing unit 13 (rotating developer) with low vibration will be described with reference to the drawings.

  FIG. 2 is a schematic diagram of an image forming apparatus using a drum / intermediate transfer member. Reference numeral 210 denotes a photosensitive drum. The intermediate transfer member 202 is rotationally driven by a stepping motor 212 that drives a belt driving roller 206. A sensor 213 generates a reference signal, detects a mark attached to the intermediate transfer body 202, and sends a detection signal to the control unit 211 of the image forming apparatus.

  In a laser scanning unit (not shown), a latent image corresponding to the image signal is formed on the photosensitive drum 210. The developing device is contained in a rotating developing device 207, and the rotating developing device is driven to rotate in accordance with the developing color, so that the developing device of a predetermined developing color is brought into contact with the photosensitive drum. Then, the latent image is developed with development color toner, whereby a visualized toner image is formed on the photosensitive drum. A toner image formed on the photosensitive drum, for example, a magenta toner image, is formed, and the toner image is transferred to the intermediate transfer member 202 by the primary transfer roller unit 204 at a position on the intermediate transfer member according to the reference signal of the intermediate transfer member. Is done. In this series of image formation control, a toner image can be formed at a predetermined position of the intermediate transfer member by controlling based on a reference signal that is generated by the sensor 212 and represents the position on the intermediate transfer member.

  Further, by rotating the rotary developing device 207 to change the development color, cyan, yellow, and black toner images are developed on the photosensitive drum, and the toner image is developed on the photosensitive drum 201 in accordance with the reference signal. Transfer the image to an intermediate transfer member. In order to form a toner image on the intermediate transfer member based on the reference signal, four color toner images of magenta, cyan, yellow, and black are formed at the same position on the intermediate transfer member 202 to form a color image. Is done.

  A tension roller 203 detects a belt drive speed error by an encoder 214 attached to the roller. The speed error signal is sent to the control circuit 211, and the transfer belt speed error for one rotation of the transfer belt is taken in from the reference signal generation. By correcting the drive speed of the drive motor 212 from this speed error data, the speed unevenness of the transfer belt 202 is corrected, and correction is performed so that the four color toner images are exactly at the same position.

  In order to transfer the toner image visualized on the intermediate transfer body 202 onto the paper, the secondary transfer roller unit 205 moves the paper to the registration roller unit so that the leading edge of the toner image is aligned with the phase of the leading edge of the image on the paper. The sheet is conveyed from 208 and the toner image is transferred onto the sheet. This phase matching control is also possible by generating registration roller driving start timing by the control circuit 211 based on the reference signal and conveying the paper.

  Further, in order to make the toner image on the paper a permanent image, it is necessary to apply heat and pressure to the toner image to fix the toner on the paper. Therefore, the toner image transferred onto the sheet by the secondary transfer roller unit 205 is conveyed to the fixing device 210 by the sheet conveying unit 209 before fixing. Then, a permanent image is obtained through the fixing device 210. The fixing device 210 is configured to make toner a permanent image and mainly apply a predetermined amount of heat.

  FIG. 3 shows a conceptual diagram of the transfer belt speed difference due to the belt thickness difference. In the figure, reference numeral 901 denotes a transfer belt, and the transfer belt speed reference is represented by the thickness center 903 of the transfer belt in the figure. With the thickness h906 of the transfer belt outer side 902 and the transfer belt inner side 904, the radius of the drive roller and the tension roller is r, the angular velocity ω907 of the drive roller, and the transfer belt speed Va can be expressed by the following equation (1).

  Va = (r + h / 2) × ω (1)

  Therefore, assuming that the angular velocity of the driving roller is constant, the transfer belt speed Va also changes when the belt thickness h changes. On the other hand, since the tension roller 909 is rotationally driven by the rotation of the transfer belt, the rotational angular speed also varies in accordance with the speed variation of Va 905. Therefore, it is possible to grasp the variation in the thickness of the transfer belt by reading the change in the angular velocity of the tension roller 909. Furthermore, there is an advantage that the fluctuation of the radius of the driving roller and the rotation fluctuation of the driving roller mainly caused by the driving gear can be read at the same time.

  FIG. 4 shows a schematic diagram of the control of the present invention. In the figure, 501 is the outside of the thickness of the transfer belt, 502 is the central portion of the thickness of the transfer belt, and 503 is the inside of the thickness of the transfer belt. Reference numeral 505 denotes an encoder attached to the tension roller, which outputs a speed signal corresponding to the speed inside the transfer belt. A stepping motor 504 drives the driving roller. Reference numeral 518 denotes a sensor for detecting a reference mark inside the transfer belt. Reference numeral 517 denotes a reference mark of the transfer belt. Since this transfer belt has the same inner diameter and outer diameter for one rotation of the belt with respect to the center of the belt thickness, the speed for one rotation after the detection of the reference mark is the speed error for the outer shape, the center and the inner diameter. No. The speed of the TOP signal 519 after the rising edge is detected is constant, such as speed 520.

  When there is an error in the thickness of the transfer belt, a speed error occurs. Reference numeral 506 denotes an outside of the transfer belt thickness, 507 denotes a central portion of the transfer belt thickness, and 508 denotes an inside of the transfer belt thickness. Reference numeral 510 denotes an encoder attached to the tension roller, which outputs a speed signal corresponding to the speed inside the transfer belt. A stepping motor 509 drives the driving roller. Reference numeral 512 denotes a sensor for detecting a reference mark inside the transfer belt.

  Reference numeral 511 denotes a transfer belt reference mark. If the speed at the center of the belt is a reference speed, the belt surface speed increases when the belt thickness is large, and the belt surface speed decreases when the belt thickness is small. Therefore, the speed on the belt surface can be kept constant by controlling the speed of the driving roller to be slow when the belt thickness is large, and to increase the speed of the driving roller when the belt thickness is small. It becomes possible.

  A motor 509 that drives the driving roller of the transfer belt is rotated at a constant speed as indicated by Va514. Vb515 shows the speed error data of the tension roller after the TOP signal 513 is detected at this time. Immediately after the TOP signal is detected, the belt on the drive roller side is thick, so that the speed of the tension roller attached at a position 180 degrees out of phase with the drive roller is high. The speed error for one rotation is as shown in FIG.

  Reference numeral 516 denotes a rotational speed correction profile applied to the drive motor for the speed error detected by the encoder 510. Reference numeral 522 denotes a rotation error for one rotation caused by the thickness error of the transfer belt. Here, the drive motor is driven with a speed profile 521 having an opposite phase so as to cancel the rotation error of one rotation of the transfer belt from the generation of the reference position signal of the transfer belt. Therefore, the speed error due to the thickness of the belt can be corrected by correcting the speed of the motor that drives the driving roller to the motor driving speed as indicated by 521 from the detection of the TOP signal 513.

  FIG. 5 is a control flow of the belt-driven drive motor of the control circuit 211 of the present invention.

  First, the belt drive motor is driven at a speed corresponding to a predetermined belt rotation speed (step 1001). After that, after the belt rotation speed reaches a constant rotation, it is determined whether a rising edge of the TOP signal is detected. (Step 1002). If the edge of the TOP signal is not detected, the motor continues to rotate. When the edge of the TOP signal is detected, the speed error of the tension roller is sampled for one rotation of the transfer belt (step 1003). When the sampling for one rotation is completed, the speed correction value of the driving roller is calculated and transferred. The speed correction value for one rotation of the belt is stored in the memory (step 1004). Next, it is determined whether there is correction data for one rotation of the transfer belt. If there is no correction data, the stepping motor is rotated at a predetermined speed. If there is correction data, the rotation control of the drive motor for one rotation of the transfer belt after TOP detection is driven according to the speed correction value stored in the memory (step 1006).

  FIG. 6 shows a schematic diagram of the control of the present invention. In the figure, reference numeral 701 denotes a transfer belt, and reference numeral 702 denotes an encoder attached to a tension roller in the transfer belt, which outputs a speed signal corresponding to the rotation speed of the tension roller. A stepping motor 703 is attached to a driving roller in the transfer belt, and is driven to rotate at the rotation speed of the transfer belt used for image formation. A sensor 704 detects a reference mark attached to the transfer belt and generates a reference signal. Reference numeral 705 denotes a reference mark attached inside the transfer belt. This reference signal is generated every time the transfer belt 701 rotates once. A calculation unit 706 applies a low-pass filter to the signal of the encoder 702 and stores speed error data for one cycle of the transfer belt. Fast Fourier transform is performed on the data for one round of the transfer belt. Of the fast Fourier transformed data, only the frequency with a large speed fluctuation is reduced, and the frequency band is determined so as not to control other frequencies. Further, based on the speed error data for one rotation, a motor drive profile for one cycle of the transfer belt is generated so as to cancel the speed error of the transfer belt. Reference numeral 707 denotes a motor drive pulse generator, which generates a phase signal of the stepping motor in accordance with the motor drive profile from the calculator. A motor driver unit 708 rotationally drives the stepping motor 703 in accordance with the phase signal of the stepping motor generated by the motor drive pulse generation unit 707.

  FIG. 7 is an FFT graph of the fluctuation amount for one rotation of the transfer belt.

  The vertical axis indicates the position fluctuation amount Δd (μm) 1101 of each frequency component. The horizontal axis indicates the frequency f (Hz) 1102. In this example, the time for one rotation of the transfer belt is 1 sec, the frequency is 1 Hz, and the rotation time of the driving roller is 1/6 sec, 6 Hz. In this example, it can be seen that the frequency component of one rotation period of the transfer belt has a position fluctuation component of 30 μm or more. Further, the frequency component of the rotation period of the driving roller is a position fluctuation component of 30 μm or less. Therefore, the positional deviation of the transfer belt can be reduced to 30 μm or less by eliminating the positional fluctuation amount in one rotation period of the transfer belt. This 30 μm is generally said to be an amount of deviation of 30 μm or more that can be seen by human eyes with respect to color shifts and pitch deviations of electrophotographic images. Therefore, by suppressing the fluctuation amount to 30 μm or less, the image quality can be greatly improved.

  FIG. 8 is an FFT graph after rotation correction for the frequency component of one transfer belt rotation.

  The vertical axis indicates the position fluctuation amount Δd (μm) 1201 of each frequency component. The horizontal axis indicates the frequency f (Hz) 1202. Reference numeral 1205 denotes the characteristics of a low-pass filter for mainly extracting the frequency component of one rotation period of the transfer belt. In this example, by correcting the rotation of the transfer belt drive motor using the frequency component of one rotation period of the transfer belt by the low-pass filter, the fluctuation amount that was 30 μm or more before correction is corrected to 10 μm. I understand.

  FIG. 9 is processed by the control circuit 211 in the control flow of the second embodiment of the present invention. When driving of the transfer belt is started, an initial constant is set in the low-pass filter (step 801). Then, the speed fluctuation signal passing through the initial filter constant is sampled for one belt revolution. An error from the reference speed is calculated for one round of the belt with respect to the sampled data and stored in the memory (step 802). A fast Fourier transform is performed on the speed error data for one revolution of the belt to derive a relationship between the speed fluctuation amount and the frequency (step 803). The frequency that is dominant in color shift is selected from the frequency of the speed fluctuation amount that has been subjected to the fast Fourier transform. For example, when superimposing an image on a transfer belt, if it is desired to make it 30 μm or less, a frequency dominant to the speed fluctuation amount for making it 30 μm or less is selected, and a speed fluctuation signal below this frequency is reliably passed. Such a filter constant is calculated (step 804). The calculated filter constant is set in the low-pass filter (step 805). Further, the speed error data for one revolution of the belt is sampled with a new filter constant (step 806). Thereafter, the motor drive correction profile is calculated so as to cancel the speed error for one belt revolution.

  This is based on the speed error data read by the encoder connected to the tension roller, and the speed error for one rotation of the transfer belt of the drive roller is calculated in consideration of the mounting phase of the drive roller and tension roller in the transfer belt. . Then, a drive pulse rate profile for one rotation of the transfer belt of the drive motor that cancels out the speed error in the drive roller section is created (step 807). Then, the motor is driven with the profile created from the reference signal (step 808). As a result of driving the transfer belt with the correction profile, it is confirmed whether the speed fluctuation value eliminates color misregistration. If the speed fluctuation value has no color misregistration, the correction is terminated and the speed fluctuation value without color misregistration is reached. If not, the correction sequence is performed again (step 809).

  In the above-described embodiment, the intermediate transfer belt has been described. However, a conveyance belt for conveying paper or a photosensitive belt may be used.

1 is a configuration diagram of a full-color printer which is an example of an image forming apparatus according to the present invention. Schematic diagram of an image forming apparatus using a drum / intermediate transfer member Conceptual diagram of transfer belt speed difference due to belt thickness difference Schematic diagram of the control of the present invention Control flow of belt-driven drive motor of control circuit of the present invention Schematic diagram of the control of the present invention FFT graph of fluctuation amount for one rotation of transfer belt FFT graph after rotation correction for the frequency component of one rotation of the transfer belt Control flow of the present invention

Explanation of symbols

510 Encoder 509 Stepping motor 517 Transfer belt reference mark 518 Sensor

Claims (3)

An image forming apparatus that forms an image by transferring a toner image onto an image bearing belt or a sheet held on the image bearing belt.
Belt driving means in which two or more rollers for transmitting driving force to the image bearing belt are attached to the transfer belt;
A speed detecting means for detecting a rotational speed of a roller different from the driving roller, disposed on the image bearing belt;
Having a reference position detecting means for detecting a reference position of the image bearing belt;
An image forming apparatus characterized in that after the reference position is detected by the reference position detecting means, the speed detecting means corrects the rotation of the driving means of the driving roller based on a speed fluctuation corresponding to at least one rotation of the image bearing belt.   2. The image forming apparatus according to claim 1, wherein a stepping motor is used as a detecting means for detecting the rotation speed of the roller. An image forming apparatus that forms an image by transferring a toner image onto an image bearing belt or a sheet held on the image bearing belt.
A driving roller for transmitting a driving force to the image bearing belt; and a driving means for rotationally driving the driving roller;
A speed detection unit that is disposed on the image bearing belt and detects a rotation speed of a roller disposed at a predetermined phase with respect to the drive roller to generate a first speed signal;
Filter means for generating a second speed signal having a component equal to or lower than a predetermined frequency with respect to the speed signal output from the speed detection means,
Fourier transform means for performing a Fourier transform process on the output signal from the filter means;
A selection means for selecting a frequency band that needs to be corrected from a frequency and an amplitude value from among the frequency components of the rotational speed obtained from the Fourier transform means;
In order to generate the speed signal of the frequency band selected by the selection means, the filter constant of the filter means is changed, and the driving means is rotated according to the second speed signal generated by the changed filter means. An image forming apparatus that performs correction.

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