JP2009020172A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming apparatus capable of preventing the deterioration of image position precision. <P>SOLUTION: The image forming apparatus primarily successively transfers toner images on a plurality of photosensitive drums 1 on an endless intermediate transfer belt 5, and collectively transfers on a paper sheet with a secondary transfer part 24. The image forming apparatus premises that collection should be made on a toner image position transferred on the paper sheet from a detected result of a pattern detection sensor 7 for detecting the toner images on the intermediate transfer belt 5 and a paper detection sensor 8 for detecting the conveyed paper sheet. The image forming apparatus makes natural number times of circumferential length of a belt drive roller 2 of a part between the pattern detection sensor 7 and the secondary transfer part 24, and makes natural number times of circumferential length of a resist roller 13 of a part between the paper detection sensor 8 and the secondary transfer part 24. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus such as a printer, a copying machine, and a facsimile machine that performs image formation by electrophotographic technology, and is particularly characterized by a technique for detecting a registration correction pattern formed on an intermediate transfer belt (image carrier belt). The present invention relates to an image forming apparatus.

  2. Description of the Related Art Conventionally, image transfer apparatuses such as printers, copiers, and facsimiles use an intermediate transfer belt that conveys a developed toner image and transfers it onto a sheet. Such an image forming apparatus forms a registration correction pattern on an intermediate transfer belt to perform registration correction for multiple colors and image position correction on a sheet, and detects the correction pattern to detect a registration error amount. Is calculated and corrected.

As an image position correction technique, Patent Document 1 proposes the following technique in order to accurately align a sheet and an image position. That is, a technique has been proposed in which a pattern for specifying an image position is formed on the intermediate transfer belt, and the image position on the sheet is corrected by adjusting the sheet conveyance speed in accordance with the detection timing of the pattern and the sheet. ing.
Japanese Patent Laid-Open No. 11-194561

  In the case of the image position correction technique described in Patent Document 1, the pattern detection sensor and the paper detection sensor are usually arranged upstream of the image transfer position on the paper to detect the correction pattern (registration correction pattern) and the paper passing timing. To do. Accordingly, it is necessary to reduce the speed fluctuation in the conveyance of the intermediate transfer belt and the sheet as much as possible after the correction pattern and the sheet are detected by the sensor until they reach the transfer position.

  However, in the image transfer structure using the intermediate transfer belt as described above, the intermediate transfer belt speed fluctuates because the roller fluctuates due to the eccentric component of the intermediate transfer belt roller that conveys the intermediate transfer belt or the drive gear. Thus, it is difficult to stably convey the image to the transfer position.

  Further, even in a paper transport structure using a transport roller, the transport speed fluctuates due to the eccentric components of the transport roller and the drive gear, and similarly, the paper cannot be stably transported to the transfer position.

  Therefore, conventionally, an encoder for detecting the rotational speed is provided on the roller shaft, and the drive motor is controlled so as to cancel the rotational fluctuation due to the eccentricity from the drive motor to the roller via the gear.

  However, even in this case, the speed fluctuation due to the eccentric component of the roller shaft and the surface property of the roller cannot be eliminated, and the conveyance variation of about 60 μm at maximum occurs due to these factors. In recent image forming apparatuses, an improvement in the accuracy of the image position on the paper is required, and a specification of 400 μm or less is required.

  Accordingly, the ratio of the conveyance speed fluctuation of the intermediate transfer belt to the image position accuracy is about 15%, and when combined with the fluctuation of the paper conveyance speed, it is close to 30%. Therefore, when these speed fluctuations are combined with the detection accuracy of other sensors and the correction accuracy by driving the conveyance roller, it becomes difficult to satisfy the required image position accuracy.

  An object of the present invention is to provide an image forming apparatus capable of preventing a decrease in image position accuracy.

  In order to achieve the above object, an image forming apparatus according to claim 1, wherein toner images on a plurality of image carriers are sequentially primary-transferred onto an endless intermediate transfer belt, and are transferred onto a sheet at a secondary transfer portion. A toner image that is transferred onto the sheet based on the detection result of the first detection unit for detecting the toner image on the intermediate transfer belt and the second detection unit for detecting the conveyed sheet as well as the batch transfer In the image forming apparatus for correcting the position, the distance between the first detection unit and the secondary transfer unit is set to be a natural number times the circumference of a belt driving roller that drives the intermediate transfer belt.

  The image forming apparatus according to claim 3, wherein the toner images on the plurality of image carriers are sequentially primary-transferred onto an endless intermediate transfer belt, transferred onto a sheet at a secondary transfer portion, and the intermediate transfer In an image forming apparatus for correcting a position of a toner image transferred onto a sheet from detection results of a first detection unit for detecting a toner image on a belt and a second detection unit for detecting a conveyed sheet. The distance between the first detection unit and the secondary transfer unit is a natural number times the circumference of a belt driving roller that drives the intermediate transfer belt, and between the second detection unit and the secondary transfer unit. Is a natural number times the circumference of the transport roller for transporting the paper.

  According to the image forming apparatus of the present invention, it is possible to prevent a decrease in image position accuracy.

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

  FIG. 1 is a schematic configuration diagram of an image forming unit of an image forming apparatus according to an embodiment of the present invention.

  The image forming apparatus of the present invention is a type in which toner images on a plurality of photosensitive drums (on an image carrier) are sequentially primary-transferred to an endless intermediate transfer belt, and are collectively transferred onto a sheet by a secondary transfer unit. belongs to. The position of the toner image transferred onto the paper is corrected based on the detection results of the pattern detection sensor for detecting the toner image on the intermediate transfer belt and the paper detection sensor for detecting the conveyed paper.

  Hereinafter, the configuration will be described together with the operation.

  In FIG. 1, laser writing means 15 (15a, 15b, 15c, 15d) are arranged in the order of yellow (Ye), cyan (Cy), magenta (Ma), and black (Bk). The latent image formed on the photosensitive drum 1 (1a, 1b, 1c, 1d) as the image carrier by the laser writing means 15 is developed by the developing device 16 (16a, 16b, 16c, 16d).

  The toner image formed on the photosensitive drum 1 is transferred onto the intermediate transfer belt 5 moved by the belt driving roller 2 in the order of Ye, Cy, Ma, and Bk by the primary transfer units 20, 21, 22, and 23. As a result, a color toner image 6 is formed. The color toner image 6 is transferred onto a sheet by a secondary transfer unit 24 where the belt support roller 3 and the transfer roller 4 are joined.

  The endless intermediate transfer belt 5 is given a constant tension by a belt driven roller 30, is stretched by a belt driving roller 2 and a belt support roller 3, is driven by the belt driving roller 2, and conveys a color toner image 6. To do. The home position of the intermediate transfer belt 5 is detected by a belt home position sensor 14.

  The sheet is conveyed from the sheet storage unit to the registration roller (conveyance roller) 13 along the conveyance path 11 by the conveyance roller 10. Then, the conveyance speed of the registration roller 13 is adjusted according to the detection timing of the paper by the paper detection sensor (second detection means) 8, and the color toner image 6 is transferred to a predetermined position on the paper by the secondary transfer unit 24. Transcribed. The sheet on which the color toner image 6 has been transferred is sent to a fixing unit (not shown) by the conveyor belt 12, the toner image is fixed on the sheet, and is discharged outside the apparatus.

  A registration correction pattern (image position correction pattern; hereinafter may be simply referred to as a correction pattern) 9 is for indirectly detecting the position of the color toner image 6, and is a pattern detection sensor (first detection). Means) 7 is detected.

  As the pattern detection sensor 7, a reflection type optical sensor that receives light reflected on the intermediate transfer belt 5 is used. In addition to the toner image such as the correction pattern 9 on the intermediate transfer belt 5, the intermediate transfer belt 5. Surface scratches and dust can also be detected.

  Here, the image forming apparatus of the present embodiment includes a belt driven roller 30 that stretches the intermediate transfer belt 5, and the belt driving roller 2 and the belt driven roller 30 are disposed with the photosensitive drum 1 interposed therebetween. In addition, the belt driving roller 2, the belt driven roller 30, and the secondary transfer unit 24 are positioned in order from the upstream along the moving direction of the intermediate transfer belt 5. Further, the distance between the plurality of photosensitive drums 1 (the distance between the image carriers) is made constant, and the distance is made a natural number times the circumferential length of the belt driving roller 2. The pattern detection sensor 7 is disposed between the belt driven roller 30 and the secondary transfer unit 24.

  FIG. 2 is a basic timing chart showing image position correction control for accurately transferring the color toner image in FIG. 1 onto a sheet.

  Image position correction is performed by adjusting the paper conveyance speed by the registration roller 13 in accordance with the detection timing of the registration correction pattern 9 by the pattern detection sensor 7 and the detection timing of the paper by the paper detection sensor 8.

  This will be specifically described below.

  After the registration correction pattern 9 conveyed on the intermediate transfer belt 5 at the speed Vd is detected by the pattern detection sensor 7, the sheet conveyed by the registration roller 13 at the speed Vu (Vu> Vd) is detected by the paper detection sensor 8. The time Tpp until detection is measured.

  After the Tpp measurement, a time Trd that is the deceleration timing of the registration roller 13 is calculated. Here, Trd = Tpp−T, where T is a constant determined by the distance between the pattern detection sensor 7 and the paper detection sensor 8 and the transfer position, the distance between the registration correction pattern 9 and the color toner image 6, and Vd and Vu. .

  The color toner image 6 can be transferred to a certain position on the sheet by controlling the conveyance speed of the registration roller 13 from Vu to Vd after the time Trd after the sheet detection sensor 8 detects the sheet.

  Here, the speed control by the registration roller 13 is finished before the paper reaches the secondary transfer unit 24, and then the color toner image 6 whose image position on the paper is adjusted is transferred by the secondary transfer unit 24, It is transported to the fixing device and discharged.

  FIG. 3 is a schematic block diagram of a portion related to image position correction processing in the image forming apparatus of FIG.

  As described above, the pattern detection sensor 7 is a reflective optical sensor for detecting a toner pattern formed on the intermediate transfer belt 5. In the pattern detection sensor 7, the amount of reflected light received from the surface of the intermediate transfer belt 5 or the toner pattern formed thereon is voltage-converted and output.

  The output is input to the comparator 101 and the A / D converter 102. The comparator 101 determines whether or not the output voltage signal from the pattern detection sensor 7 exceeds a predetermined threshold value, and outputs a binarized digital signal. The A / D converter 102 converts the analog output voltage from the pattern detection sensor 7 into a digital signal.

  The ASIC 103 is a digital integrated circuit, and includes a pattern generation unit 104, a pattern reading control unit 105, a registration deviation calculation unit 106, and a registration timing adjustment unit 107.

  The pattern generation unit 104 generates image data of a toner pattern generated by pattern detection control. The pattern reading control unit 105 reads the output signal of the binarized pattern detection sensor 7 and temporarily stores the data.

  The registration deviation calculation unit 106 calculates a timing deviation between the paper and the image based on the read pattern data. The registration timing adjustment unit 107 controls the sheet conveyance timing based on the calculated timing deviation.

  The motor 108 is a drive source for driving the belt drive roller 2 and the registration roller 13 according to the present embodiment, and is controlled by a drive signal given by the motor driver 110 based on a control signal from a CPU 109 described later. The

  The CPU 109 is the center of the control system, and controls various commands including the execution timing of image position correction control. The control of the CPU 109 is performed based on program data stored in the ROM 111. The SRAM 112 stores device-specific data such as the LED drive current value of the pattern detection sensor 7 and the density of the registration correction pattern 9.

  In the image processing control unit 113, various image processing controls are executed in accordance with instructions from the CPU 109, and halftone density adjustment and the like are performed. In addition, the apparatus is provided with an environmental sensor 114 for detecting temperature and humidity. The sensor output is converted into a digital signal by the A / D converter 102 and input to the CPU 109.

  FIG. 4 is a table showing driving specifications of the belt driving roller and the registration roller in FIG.

  First, the drive specifications of the belt drive roller 2 will be described.

  The belt drive roller 2 has a roller diameter of 80 mm, and is driven by a belt drive motor (not shown) at a rotation period of 0.838 seconds in order to drive the intermediate transfer belt 5 at 300 mm / s. Here, if the sum of the tolerances of the diameter and shaft of the belt driving roller 2 is 0.04 mm at the maximum, the position of the intermediate transfer belt 5 is changed by a maximum of 0.08 mm due to the speed fluctuation of the belt driving roller 2, which is on the sheet. Appears as image position shift.

  FIG. 5 shows (a) the roller diameter, (b) the belt position per unit time, and (c) the fluctuation of the integrated belt position with respect to the time t of the belt driving roller 2 for explaining the position fluctuation of 0.08 mm at the maximum. It is a figure which shows quantity X. Here, the change in the roller diameter of the curve (a) is approximated by a SIN curve having a maximum of 0.04 mm, and the roller diameter changes.

  As shown in FIG. 5, the belt position variation per unit time of the curve (b) is 3 μm at the maximum due to the roller diameter variation, and the integrated belt position variation of the curve (c) is 0.08 mm at the maximum.

  Since the image position accuracy target of the present embodiment is 0.4 mm, the integrated belt position fluctuation accounts for 20%, which is one factor of deterioration of the position accuracy.

  As a countermeasure against this, the distance between the pattern detection sensor 7 and the secondary transfer portion is set to a natural number multiple of 251 mm, which is the circumference of the belt driving roller 2. As a result, the phase of the speed fluctuation period of the intermediate transfer belt 5 detected by the pattern detection sensor 7 and the speed fluctuation period when the image passes through the secondary transfer unit 24 coincide with each other. The image position shift due to the speed fluctuation of the belt 5 becomes almost zero.

  Here, it is ideal that the distance between the pattern detection sensor 7 and the secondary transfer portion is exactly matched to the circumference of the belt driving roller 2, but it is difficult to theoretically match due to the tolerance of the arrangement position. Therefore, when the integrated belt position fluctuation is 4 μm or less, which is 1% of the image position accuracy of the present embodiment, the tolerance between the pattern detection sensor 7 and the secondary transfer unit 24 is 15 mm or less as shown in FIG. It is technically possible to arrange with this tolerance.

  In this way, even when the belt length varies or varies due to variations in the intermediate transfer belt 5 or environmental variations, the belt is applied to the intermediate transfer belt 5 by the belt driven roller 30 and is in contact with the photosensitive drum 1. Differences or variations in individual belt lengths are absorbed. Therefore, there is no variation between the pattern detection sensor 7 and the secondary transfer unit 24, and stable image position accuracy can be obtained.

  Next, the drive specifications of the registration roller 13 will be described.

  The registration roller 13 has a roller diameter of 20 mm, and is driven by a registration conveyance motor (not shown) at a rotation period of 0.209 seconds in order to convey the paper at 600 mm / s and 300 mm / s.

  Here, if the total of the tolerances of the diameter and the shaft of the registration roller 13 is 0.02 mm at the maximum, the position of the sheet is changed by a maximum of 0.04 mm due to the speed fluctuation of the registration roller 13. Appears as the upper image position shift.

  FIG. 6 shows (a) roller diameter, (b) paper position per unit time, and (c) accumulated paper position fluctuation amount with respect to time t of the registration roller 13 in order to explain the paper position fluctuation of 0.04 mm at the maximum. FIG. Here, the change in the roller diameter of the curve (a) is approximated by a SIN curve having a maximum of 0.02 mm, and the roller diameter changes.

  As shown in FIG. 6, due to fluctuations in the roller diameter, the paper position fluctuation per unit time of the curve (b) is 6 μm at the maximum, and the paper position fluctuation integrated by the curve (c) is 0.04 mm at the maximum. .

  Since the image position accuracy target of the present embodiment is 0.4 mm, the integrated belt position fluctuation accounts for 10%, which is one factor in the deterioration of the position accuracy like the belt driving roller 2.

  As a countermeasure, the sheet detection sensor 8 and the secondary transfer portion are arranged at a natural number multiple of 63 mm, which is the circumference of the registration roller 13. Thus, the phase of the speed fluctuation period of the registration roller 13 when the paper detection sensor 8 detects and the speed fluctuation period when the paper passes through the secondary transfer unit 24 coincide with each other. The image position shift due to the speed fluctuation is almost zero.

  Here, it is ideal that the distance between the sheet detection sensor 8 and the secondary transfer portion is accurately matched to the circumferential length of the registration roller 13, but theoretically due to the tolerance of the arrangement position as in the case of the belt driving roller 2. It is difficult to match. Therefore, when the accumulated sheet position variation is 4 μm or less, which is 1% of the image position accuracy of the present embodiment, the tolerance between the sheet detection sensor 8 and the secondary transfer unit 24 is 5 mm or less as shown in FIG. It is technically possible to arrange with this tolerance.

  As described above, in the image forming apparatus according to the present embodiment, the interval from the pattern detection sensor 7 to the secondary transfer unit 24 is set to a natural number times the circumference of the belt drive troller 2, so that the pattern detection sensors 7 and 2. The phase of the speed fluctuation period of the intermediate transfer belt 5 is matched at the next transfer unit 24. As a result, the image position shift due to the speed fluctuation of the intermediate transfer belt 5 is eliminated.

  Further, the interval from the paper detection sensor 8 to the secondary transfer unit 24 is a natural number multiple of the peripheral length of the registrar 2, and the phase of the paper speed fluctuation cycle is matched between the paper detection sensor 8 and the secondary transfer unit 24. The image position shift due to the registrar 2 is eliminated.

  As described above, it is possible to prevent a decrease in image position accuracy due to speed fluctuation due to the eccentricity of the belt driving roller 2 and the registration roller 13.

1 is a schematic configuration diagram of an image forming unit of an image forming apparatus according to an embodiment of the present invention. 2 is a basic timing chart showing image position correction control for accurately transferring the color toner image in FIG. 1 onto a sheet. FIG. 2 is a schematic block diagram of a portion related to image position correction processing in the image forming apparatus of FIG. 1. 2 is a chart showing driving specifications of a belt driving roller and a registration roller in FIG. 1. FIG. 2 is a diagram illustrating (a) a roller diameter, (b) a belt position, and (c) a variation amount X of an accumulated belt position with respect to time t of the belt driving roller in FIG. 1. FIG. 2 is a diagram illustrating a variation amount X of (a) roller diameter, (b) sheet position, and (c) accumulated sheet position with respect to time t of registration rollers in FIG. 1.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Photosensitive drum 2 Belt drive roller 3 Belt support roller 4 Transfer roller 5 Intermediate transfer belt 6 Color toner image 7 Pattern detection sensor 8 Paper detection sensor 9 Registration correction pattern 10 Conveyance roller 11 Conveyance path 12 Conveyance belt 13 Registration roller 14 Belt Home position sensor 15 Laser writing means 24 Secondary transfer unit 103 ASIC

Claims (4)

To sequentially transfer toner images on a plurality of image carriers to an endless intermediate transfer belt in sequence, transfer them onto a sheet at a secondary transfer portion, and detect the toner images on the intermediate transfer belt In the image forming apparatus for correcting the position of the toner image transferred onto the paper from the detection result of the first detection means and the second detection means for detecting the conveyed paper,
An image forming apparatus characterized in that a distance between the first detection unit and the secondary transfer unit is a natural number times a circumference of a belt driving roller for driving the intermediate transfer belt.   2. The image forming apparatus according to claim 1, wherein a distance between the second detection unit and the secondary transfer unit is set to a natural number multiple of a circumferential length of a conveyance roller for conveying a sheet. To sequentially transfer toner images on a plurality of image carriers to an endless intermediate transfer belt in sequence, transfer them onto a sheet at a secondary transfer portion, and detect the toner images on the intermediate transfer belt In the image forming apparatus for correcting the position of the toner image transferred onto the paper from the detection result of the first detection means and the second detection means for detecting the conveyed paper,
The distance between the first detection unit and the secondary transfer unit is a natural number times the circumference of a belt driving roller that drives the intermediate transfer belt, and the interval between the second detection unit and the secondary transfer unit is An image forming apparatus characterized in that it is a natural number multiple of the circumferential length of a transport roller for transporting paper. A belt driven roller that stretches the intermediate transfer belt; and the belt driving roller and the belt driven roller are disposed with the image carrier interposed therebetween, and the intermediate transfer belt is sequentially moved from the upstream along the moving direction of the intermediate transfer belt. A belt driving roller, the belt driven roller, and the secondary transfer portion are located;
A plurality of the distances between the image carriers, and the distance between the image carriers is a natural number times the circumference of the belt driving roller;
The image forming apparatus according to claim 1, wherein the first detection unit is disposed between the belt driven roller and the secondary transfer unit.

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