JP2009128440A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To register an accurate image and a sheet in the conveyance direction in a registration correction technique in which a toner mark is imaged on an image conveyance belt for leading edge registration alignment in an image forming apparatus and takes a timing with the sheet. An image forming apparatus capable of stably obtaining accuracy is provided.
Toner marks for removing noise factors such as scratches and dirt generated on a belt are generated.
[Selection] Figure 1

Description

  The present invention relates to an image forming apparatus that forms an image on a sheet material, and more particularly to an image forming apparatus that improves image position accuracy with respect to the sheet material and forms images on both sides of the sheet material. More specifically, the present invention relates to an image forming apparatus having a registration correction function.

  Conventionally, there has been proposed an image forming apparatus that adjusts a transfer timing with a transfer material by generating an image of a registration mark for registration detection on a transfer belt and optically detecting the mark. FIG. 8 shows an image forming apparatus 100 provided with registration mark detecting means 137. As shown in FIG. 8, the image forming apparatus provided with the resist detecting means includes an image forming unit 110 including an exposure unit 109 for forming an image image, a photosensitive drum 112 and a developing device 111, and a primary transfer unit 117 from the image forming unit 110. A transfer belt 131 for transferring the image, a secondary transfer unit 135 for transferring the image from the transfer belt 131 to the sheet, and a registration roller 123 for conveying the transfer material P to the secondary transfer unit 135. In addition, a paper detection sensor S120 that detects the presence or absence of paper is provided at a position upstream of the secondary transfer position in the transfer material conveyance path. The paper detection sensor detects the timing of the leading or trailing edge of the paper transported.

  In this type of image forming apparatus 100, the position of the paper and the image may not match due to an optical path length error or optical path change in exposure, or a transfer belt transport distance error or fluctuation.

  For this reason, a registration mark (registration correction pattern) formed by transferring from the image forming unit 110 onto the transfer belt 131 is read by a photosensor mounted on the registration mark detection unit 137 to detect a positional deviation amount and start image formation. Image position deviation with respect to the paper has been corrected by correcting the position and adjusting the paper conveyance timing.

  FIG. 9 shows a change in the light reception output of the photosensor 200 that detects the belt 31 on which the toner mark 203 is formed. FIG. 4 shows a light receiving circuit that converts the light reception output of the photosensor 200 into a pulse signal.

  When the reflected light of the light irradiated to the belt 31 from the LED 201 of the photosensor 200 is received by the phototransistor 202, a photocurrent flows through the phototransistor 202, and this output current is converted into a voltage by the resistor 407 of the light receiving circuit. Thereafter, the output voltage is amplified by the resistors 402, 403, and 404 and the operational amplifier 401. When light from the LED 201 detects a portion of the belt 31 where the toner mark 203 is not formed, the amount of reflected light at that portion is large, so that a large amount of photocurrent flows through the phototransistor 202 that has received this, and the output voltage after amplification Becomes a high voltage level (belt detection level). Next, when the toner mark 203 is detected, the amount of reflected light is small, so that a smaller photocurrent flows in the phototransistor 202 than in the belt portion, and the output voltage after amplification becomes a low voltage level (toner mark detection level).

  Therefore, when the photosensor 200 detects the belt in the order of belt portion → toner mark portion → belt portion, the output voltage 301 protrudes downward from the belt detection level to the toner mark detection level as shown in FIG. 10a. This curve is obtained. A threshold level is set between the transfer belt detection level and the toner mark detection level by the variable resistor 406 of the light receiving circuit, and the detected voltage value (output voltage) is compared with the threshold level by the comparator 405. As shown, a pulse pattern detection output 302 can be created.

  The center timing tg of this pulse pattern signal is recognized as the center of gravity of the toner mark, the timing of the toner mark on the transfer belt is detected, the timing with the transfer material detection means is adjusted, and the conveyance speed of the registration roller pair is adjusted or image The formation timing is adjusted, and registration correction in the image conveyance direction with respect to the sheet is performed.

As examples of the above, Patent Document 1 and Patent Document 2 below can be cited.
JP 2002-174992 JP JP2003-241472

  However, if scratches, dents, stains, etc. occur on the transfer belt, they may be erroneously detected as marks, which significantly deteriorates the resist accuracy. Specifically, as shown in FIG. 11, when there is a scratch or the like on the transfer belt that overlaps with the toner mark, the digital sensor output indicates the position of tg ′ including an error of Δtg from the original toner mark gravity center position tg. It was erroneously detected as the center of gravity of the mark. As a result, the leading edge position of the transfer material and the leading edge position of the image are transferred with an error corresponding to Δtg, and the accuracy of image alignment with the transfer material is significantly deteriorated.

According to the first aspect of the present invention, the sheet conveying means for conveying the sheet along the sheet conveying path, the image forming means for forming a toner image on the image carrier belt, and the image carrier belt formed on the image carrier belt. From a toner image detection means for detecting the presence or absence of a toner image, a transfer means for transferring an image formed on the image carrier belt to a sheet conveyed by the conveyance means, and a transfer position of the toner image by the transfer means Also, a sheet detection unit that is provided in the upstream sheet conveyance path and detects the passage of the sheet, and the sheet conveyance unit conveys the sheet based on the detection results of the toner image detection unit and the sheet detection unit. In the image forming apparatus provided with the control means for controlling the speed,
In order to control a sheet conveyance speed, the control unit forms at least two or more continuous image timing detection marks in the image conveyance direction that is not transferred to the sheet on the image carrier belt, The image formation is characterized in that the toner image detection means detects the leading edge and the trailing edge of the image timing detection mark and compares the theoretical timing width of the image position detection mark with the image timing. Get the device.

  This makes it possible to accurately measure the image timing even if two or more toner marks overlap a scratch on the transfer belt, and prevent deterioration of the registration accuracy of the transfer material. It becomes possible.

  According to a second aspect of the present invention, the formation position of the image position detection mark is arranged outside the image area to be transferred after being aligned with the paper in the orthogonal direction of conveyance. An image forming apparatus according to claim 1 is obtained.

  If a toner mark is generated in the transfer image area in the direction perpendicular to the transfer belt conveyance, the toner mark is formed between the images, and the productivity may be significantly reduced. However, by generating a toner mark outside the image area to be transferred, the interval between images can be set to a minimum, and productivity can be improved.

  Further, according to claim 3 of the present invention, the sheet conveying means is provided with a first conveying speed and a second conveying speed, and the control means adds the first conveying speed to the second conveying speed. The image forming apparatus according to claim 1, wherein the deceleration timing is controlled.

  As a result, the transfer material can be efficiently conveyed with respect to the image timing, and alignment in the conveyance direction can be performed only by adjusting the timing of decelerating and decelerating, and good resist accuracy can be achieved without causing downtime due to alignment. It can be secured.

  According to a fourth aspect of the present invention, the paper transporting means is a registration roller that is stopped when the leading edge of the paper enters, and the control means is provided for each of the toner image detecting means and the paper detecting means. The image forming apparatus according to claim 1, wherein a timing at which the registration roller is driven is controlled based on a detection result from a state in which the sheet hits the registration roller.

  As a result, even with a configuration of a registration timing roller (so-called registration roller) of a type that performs skew feeding by stopping driving and driving operation, it is possible to control the alignment between the sheet and the toner image.

  According to the first aspect of the present invention, it is possible to accurately measure the image timing even when a transfer belt scratch or the like overlaps with any of two or more toner marks, and the accuracy of registration of the transfer material is deteriorated. Invitation can be prevented. Further, according to the second invention, when the toner mark is generated in the transfer image area in the direction perpendicular to the transfer belt conveyance, the toner mark is formed between the images, and the productivity may be significantly reduced. However, productivity can be improved by generating toner marks outside the image area to be transferred. Further, according to the third invention, it is possible to efficiently transfer the transfer material with respect to the image timing and adjust the timing, and to ensure good resist accuracy without causing downtime due to alignment. Is possible.

  The image forming apparatus according to the present invention will be described below in more detail with reference to the drawings.

  FIG. 1 is a sectional view of an image forming apparatus embodying the present invention. The image forming apparatus of this embodiment is an electrophotographic color image forming apparatus, and a plurality of image forming units considered to be particularly effective in the present invention are arranged in parallel and an intermediate transfer system is adopted.

  The color image forming apparatus includes an image reading unit 1R and an image output unit 1P. The image reading unit 1R optically reads a document image, converts it into an electrical signal, and sends it to the image output unit 1P. Its configuration is well known and has no particular relationship with the present invention, so detailed description thereof is omitted. .

  The image output unit 1P is roughly divided into an image forming unit 10 in which four stations a, b, c, and d are arranged in parallel (the basic configuration of each station a to d is the same), a paper feeding unit 20, an intermediate transfer unit. 30, a fixing unit 40, a cleaning unit 50, and a control unit 800.

  Each unit will be described in detail. Each station a, b, c, and d of the image forming unit 10 has photosensitive drums 11a, 11b, 11c, and 11c as image carriers, and the photosensitive drums 11a to 11d are pivotally supported at the centers thereof in the arrow direction. Driven by rotation. Opposing to the outer peripheral surfaces of the photosensitive drums 11a, 11b, 11c, 11d, in the rotation direction, primary chargers 12a, 12b, 12c, 12d, optical systems 13a, 13b, 13c, 13d, folding mirrors 16a, 16b, 16c, 16d and developing devices 14a, 14b, 14c, and 14d are disposed.

  A toner image is formed on the photosensitive drum 11 (11a to 11d) by an image forming process. First, the surface of the photosensitive drum 11 is given a uniform charge amount by the primary charger 12 (12a to 12d), and then modulated according to the recording image signal generated by the optical system 13 (13a to 13d), for example. A light beam such as a laser beam is exposed on the photosensitive drum 11 through the folding mirror 16 (16a to 16d), and an electrostatic latent image is formed on the surface of the photosensitive drum 11. The electrostatic latent image on the photosensitive drum 11 is developed by the developing device 14 (14a to 14d) and visualized as a toner image. The developing devices 14a, 14b, 14c, and 14d contain developers of four colors (toner) of black, magenta, cyan, and yellow, and latent images on the photosensitive drums 11 are black, magenta, and cyan by development. A yellow toner image is formed.

  Under the photosensitive drums 11a, 11b, 11c, and 11d, primary transfer areas Ta, Tb, Tc, and Td are formed in which the intermediate transfer belt 31 comes into contact with the toner image on the photosensitive drum and is transferred to the intermediate transfer belt 31. Yes. Primary transfer chargers 35a, 35b, 35c, and 35d are disposed on the back side (inner side) of the intermediate transfer belt 31 in the primary transfer region. Cleaning devices 15a, 15b, 15c, and 15d are installed downstream of the photosensitive drums 11a, 11b, 11c, and 11d in the primary transfer areas Ta, Tb, Tc, and Td in the rotation direction, and are not transferred to the intermediate transfer belt 31. The surface of the photosensitive drum 11 is cleaned by scraping off the untransferred toner remaining on each photosensitive drum 11.

  A sheet feeding deck 10 on which sheets P are stacked and stored is detachably attached to the lower part of the copying machine. The paper feed deck 20 includes a transport belt 23, a suction fan 22, and a paper surface detection sensor S20. The paper picked up from the paper feed deck 20 is conveyed to the registration unit 40 via the vertical path conveyance unit 30. The registration unit 40 includes a sheet correction plate that corrects registration in the conveyance orthogonal direction, a skew feeding roller 42, and a registration roller 43. In addition, a sheet detection sensor S40 is disposed in the vicinity of the registration roller 43, and performs sensing for registration adjustment for a sheet and an image in the transport direction, and the sheet P is matched with the image formation timing of the image forming unit 10. To the secondary transfer region Te.

  The intermediate transfer unit 30 includes a secondary roller that sandwiches the intermediate transfer belt 31 with a plurality of rollers, that is, a driving roller 32 d that transmits driving to the belt 31, a driven roller 32 s driven by the rotation of the belt 31, and the belt 31. A secondary transfer counter roller 33 facing the transfer region Te is wound around, and a primary transfer plane A is formed between the drive roller 32d and the driven roller 32s.

  The drive roller 32d is formed by coating the surface of a metal roller with rubber (urethane rubber or chloroprene rubber) having a thickness of several millimeters to prevent a slip portion with the transfer belt 31, and the drive roller 32d is a pulse motor (see FIG. (Not shown).

  A secondary transfer roller 34 is disposed opposite to the secondary transfer counter roller 33 with the intermediate transfer belt 31 interposed therebetween, and the secondary transfer roller 34 is pressed and brought into contact with the intermediate transfer belt 31 with an appropriate pressure. The secondary transfer region Te is formed by the contact nip portion. Further, downstream of the secondary transfer region Te of the intermediate transfer belt 31 is provided cleaning means 36 for cleaning the surface (image forming surface) of the intermediate transfer belt 31. The cleaning means 36 rubs the surface of the belt 31. And a waste toner box (not shown) that stores toner removed from the surface of the belt 31 by the brush roller.

  The fixing unit 50 includes a fixing roller 51 provided with a heat source such as a halogen heater therein, a pressure roller 52 that is pressed against the fixing roller 51 (the pressure roller 52 may also include a heat source), and a roller pair 51. , 52 guide 53 for guiding the sheet P to the abutting nip portion, fixing heat insulating covers 56, 57 for confining heat in the unit 50, and the sheet P discharged from the pair of rollers 51, 52 by the discharge roller 54 Lead outside 50.

  Thereafter, the paper is discharged and stacked on the paper discharge tray 61 by the paper discharge unit 60. Further, in the case of double-sided image formation, the reverse unit 70 performs switchback inversion, and the double-sided pass unit 80 is again conveyed to the vertical path conveying unit to repeat a series of operations.

  As shown in FIG. 2, the control unit 800 includes a CPU 801 and a motor driver unit 802 for controlling the operation of the mechanism in each unit. The control unit 800 will be described later.

  Next, an image forming operation of the image forming apparatus will be described. When an image forming operation start signal is issued from the CPU 801 of the control unit 800, the sheet P is fed by feeding the sheet P sucked up by the suction fan 22 downstream by the transport belt 23. Here, the lifter plate 21 is moved up and down continuously based on the information of the paper surface detection sensor S20 to control the paper surface position where there is no non-feed or multiple feed. Further, the sheet is spun from the transport direction and the transport orthogonal direction (the direction penetrating deeply in front of the sheet surface) to prevent the sheets from being further fed by being sent. Thereafter, the single sheet P is conveyed to the registration unit 40 via the vertical path conveyance unit 25.

  An outline of the operation of the resist unit 40 is shown in FIGS. The sheet P fed from the vertical path transport unit 25 is movable in the thrust direction according to the lateral width of the sheet P, and a skew feeding roller 42 that applies a transport force that presses the sheet P against the sheet correction plate 41. Thus, positioning in the conveyance orthogonal direction is performed. First, as shown in FIG. 2A, the sheet P conveyed obliquely with respect to the conveyance direction by the skew feeding roller 42 is conveyed to the registration roller 43 while being abutted against the sheet correction plate 41. The registration roller 43 can perform conveyance driving and reciprocating operation in the conveyance orthogonal direction. The sheet P adjusted by abutting the conveyance orthogonal direction is slid again to the conveyance center position 44 to correct registration in the conveyance orthogonal direction. (See Fig. 2-2). Further, the registration roller 43 performs the nip releasing operation upward after feeding the sheet P to the secondary transfer region Te (see FIG. 2-3). Then, the reciprocating operation and the nip pressurizing operation are performed again at the thrust standby position shown in FIG. This series of operations is performed for each sheet.

  Also, the registration roller 43 adjusts the amount of movement of the sheet to the secondary transfer region Te by the number of roller rotations from the state in which the sheet detection sensor S40 has detected the leading edge of the sheet P in order to align the leading edge of the sheet and the leading edge of the image. I manage. As will be described later, the sheet conveyance timing adjustment in the conveyance direction by the registration rollers 43 is performed based on the information of the toner mark detection sensor 37 and the deceleration timing control is performed.

  Regarding the registration roller 43 as a drive system, a registration roller driving motor M1 connected via a coupling (not shown) for rotationally driving the registration roller 43, and a rack (not shown) for performing a reciprocating operation of the registration roller 43, There is a registration roller reciprocating drive motor M2 that transmits drive from the pinion. Further, a skew feeding roller driving motor (not shown) for rotationally driving the skew feeding roller 42 and a skew feeding roller attaching / detaching motor which is performed via a cam (not shown) for performing the attaching / detaching operation of the pair of skew feeding rollers. Become.

  In the image forming unit 10, when an image forming operation start signal is issued, a toner image is formed on the photosensitive drum 11d of the station d that is the most upstream in the rotation direction of the intermediate transfer belt 31 by the image forming process described above. The toner image is primarily transferred to the intermediate transfer belt 31 in the primary transfer region Td by the action of the primary transfer charger 35 to which a high voltage is applied. The primarily transferred toner image is conveyed to the primary transfer region Tc of the next station c as the transfer belt 31 moves. At the station c, image formation is performed with a delay of the time during which the toner image is conveyed between the stations d and c, and the next toner image is transferred with the position (resist) aligned on the previous toner image. . Thereafter, the same process is repeated in the stations b and a, so that the four color toner images are transferred onto the intermediate transfer belt 31 in a superimposed manner.

  Thereafter, when the sheet P enters the secondary transfer region Te and contacts the intermediate transfer belt 31, a high voltage is applied to the secondary transfer roller 34 in accordance with the passage timing of the sheet P. Then, the four color toner images formed on the intermediate transfer belt 31 by the above-described process are secondarily transferred collectively onto the surface of the recording material P. The sheet P on which the toner image is secondarily transferred is accurately guided to the roller nip portion of the fixing unit 50 by the pre-fixing conveyance 58, and the toner image is applied to the surface of the sheet P by heat and pressure from the fixing roller 51 and the pressure roller 52. The image is fixed and formed into a four-color full-color permanent image. Thereafter, the sheet P is conveyed outside the apparatus by the inner and outer discharge rollers 54 and the discharge unit 60 and is stacked on the discharge tray 61.

  The image forming apparatus includes a registration correction device including a photo sensor 200 as a toner pattern detection unit and a control unit 800 in FIG. The photo sensor 200 is disposed close to the belt at both ends in the width direction perpendicular to the moving direction of the intermediate transfer belt 31 at a position downstream of the final color image forming station a. Each color resist pattern (registration correction pattern) formed along the belt moving direction at both ends in the width direction is detected and read, and resist correction control is performed by the correction means of the control unit 800.

  As shown in FIG. 10, the photo sensor 200 is composed of a light emitting element LED 201 and a light receiving element phototransistor 202 as in the prior art, and the output of detecting the pattern on the intermediate transfer belt 31 is the control shown in FIG. The pattern is detected by receiving signal processing in a light receiving circuit 807 similar to the light receiving circuit of FIG. 4 installed in the unit 800. Similarly, the resist pattern is used as an example in the form of a first line segment and a second line segment arranged symmetrically at a predetermined angle across an imaginary line perpendicular to the moving direction of the intermediate transfer belt 31. .

  The control unit 800 receives the output from the CPU 801 that controls the image output unit, the ROM 806 and the RAM 803 that store control programs and data, the motor driver unit 802 that drives various motors, and the photosensor 200, and outputs the pattern output. The circuit 807 includes a pattern width detection unit 804 that receives a pattern output from the light receiving circuit and detects a pattern width and position, and a pattern width & position storage unit 805. The pattern width & position storage unit 805 includes a plurality of registers.

  When the registration correction operation starts in response to an instruction from the CPU 801 of the control unit 800 and the photosensor 200 receives and detects the reflected light from the resist pattern, the output current is converted and amplified, and the obtained output voltage is changed to the pattern. Input to the width detector 804. The pattern width detection unit 804 has a predetermined width T set by the CPU 801, and the width detection unit 804 cuts an output having a width equal to or smaller than the predetermined width T as a noise component, and other widths equal to or larger than the predetermined width T. For only the output having the pattern width, the pattern width and the pattern position are output as pattern data used for resist correction and stored in the pattern width & position storage unit (registers A to K) 805.

  A state where a registration mark is detected and read by the photo sensor 200 and a registration mark output is output from the light receiving circuit 807 is shown. A magenta registration mark is formed on the intermediate transfer belt 31 by an image forming station c serving as a reference for each color.

  Next, a registration process in the conveyance direction leading to image formation will be described.

  FIG. 5 shows a conveyance relationship diagram for sheet conveyance and image conveyance. First, a sheet feeding time is set as a reference time and a reference transfer distance, and a timing at which the sheet is fed to the vertical path transfer unit 25 and accelerated is set as ta. At this time, the time when the toner mark is laser-written in the c image forming unit of the reference station is defined as the image formation reference time (t0 for sheet conveyance reference) and the reference conveyance distance (l0 for sheet conveyance distance). At this time, in the present embodiment, as shown in FIG. 5a, the image is formed by matching the distance between the centers of the two toner marks in the transport direction with the leading edge of the image to be transferred. Thereafter, the image is transported at a constant speed along the photosensitive drum and the intermediate transfer belt 30 to the secondary transfer region Te. The time when the toner mark reaches the registration detection unit 37 is detected as tg, and the predicted timing td of the secondary transfer is calculated. On the other hand, in the sheet conveyance, the sheet is conveyed through the vertical path conveyance unit 25 and the registration unit 40, passes through the sheet detection sensor S40, and the sheet detection sensor passage time ts is detected. At the secondary transfer timing te, it is necessary to set the conveyance speed of the sheet and the image to substantially the same speed. Therefore, td is calculated based on tg and ts at which timing during the registration roller conveyance should be decelerated. After that, the leading edge of the sheet and the image are conveyed at the same equal speed, and the leading edge is aligned at the secondary transfer position to perform the secondary transfer. For example, FIG. 5 b shows the fluctuation of the conveyance time when the belt circumference of the intermediate transfer belt fluctuates or the optical path length of the laser imaging system fluctuates with the environmental change. As shown in FIG. 5b, it can be detected in the toner mark detection time that the inclination of the theoretical straight line of the image conveyance has changed. Thus, the leading edge alignment between the image and the sheet can be corrected by advancing the sheet deceleration timing td by Δtd.

  In this way, control is performed so as to minimize timing deviation due to sheet conveyance variation and timing deviation due to image conveyance variation.

  In this series of sheet and image leading edge alignment processes, it is very important to accurately detect image and sheet timing.

  However, scratches, dirt, dents, dents and the like are generated on the intermediate transfer belt, and unless the position of the leading edge of the image can be determined accurately, the image accuracy is significantly deteriorated. In order to detect these scratches and the like in advance, it is conceivable that the intermediate transfer belt is pre-rotated separately from the image forming process, or is pre-rotated in a down sequence. However, particularly in a tandem type color copying machine, the intermediate transfer belt is long, so that it takes time to detect, and the warm-up time and productivity may be reduced.

  In the following, a method for accurately detecting the front end position of the image (the position of the front end of the image by the toner mark) will be described even if a scratch or the like is generated on the belt.

FIG. 6 shows a detection pattern from the light receiving circuit when the toner mark is detected. In the figure, tg is the distance between the centers of the toner marks, and at the same time the front end position of the image. Here, Tm ₁ is a theoretical time width for detecting the width of the toner mark, and Tm ₂ is an interval between the trailing edge of the first toner mark and the leading edge of the second toner mark. Therefore, Tm ₃ in the figure is Tm ₁ + Tm ₂ , and Tm ₄ is 2 × Tm ₁ + Tm ₂ . Here, since tg is the time tf1 + Tm _2/2, when calculating the tg is tg it becomes possible to easily calculate if one accurately detect the Tm ₂ to Tm _4.

Next, a detection pattern such as a scratch on the intermediate transfer belt will be described. In this embodiment, the time width of the digital signal OFF is measured and compared with the theoretical toner mark conveyance width, and it is determined whether or not the OFF signal is a toner mark, and the signal is turned ON / OFF. Store the timing in a register. The toner mark count is approximately the same as the time width Tm _1-1 ', Tm _1-2 ',... Tm _1-8 'of the OFF signal compared to the theoretical toner transport width Tm _1. or it determines, the Tm _1-1 ', Tm _1-2', is set to count how OFF signals having the same width as the number is 'Tm _1-1 in' ··· Tm _1-8. Therefore, it can be determined whether or not the belt mark or the like overlaps with the toner mark and affects the detection of reading at the front and rear ends of the toner mark. If the toner mark count is two, it is possible to detect the toner mark normally. As shown in FIG. 7A (pattern A), even if a scratch on the belt has occurred, it does not overlap with the toner mark. The image leading edge position tg is calculated while ignoring only such signals. Therefore, the toner mark detection widths Tm _1-1 ′, Tm _1-2 ′, Tm _1-3 ′, and Tm _1-4 ′ are compared with the theoretically calculated toner transport time width Tm1 under the following conditions. calculate.

If Tm _1-1 '≒ Tm _1-2 ' ≒ Tm ₁ (Condition 1-1), tg = tf2 + (tf3-tf2) / 2 (Formula 1-1)
If Tm _1-1 ´ ≒ Tm _1-3 ´ ≒ Tm ₁ (Condition 1-2), tg = tf2 + (tf5-tf2) / 2 (Formula 1-2)
If Tm _1-1 ´ ≒ Tm _1-4 ´ ≒ Tm ₁ (Condition 1-3), then tg = tf2 + (tf7-tf2) / 2 (Formula 1-3)
If Tm _1-2 '≒ Tm _1-3 ' ≒ Tm ₁ (Condition 1-4), tg = tf4 + (tf5-tf4) / 2 (Formula 1-4)
If Tm _1-2 '≒ Tm _1-4 ' ≒ Tm ₁ (Condition 1-5), tg = tf4 + (tf7-tf4) / 2 (Formula 1-5)
If Tm _1-3 ´ ≒ Tm _1-4 ´ ≒ Tm ₁ (Condition 1-6), tg = tf6 + (tf7-tf6) / 2 (Formula 1-6)
Therefore, since the condition of the toner mark and the scratch on the belt as shown in FIG. 7A is (Condition 1-2), tg can be calculated by (Equation 1-2).

  However, when the toner mark count is 1, and when it is 0, scratches on the belt overlap the toner mark and the toner mark count may be erroneously detected. It is necessary to calculate the toner mark detection timing.

  Here, in this embodiment, when three or more belt scratches or the like are generated in the vicinity of the toner mark, the intermediate transfer belt is judged to be an abnormal belt because there are too many scratches on the intermediate transfer belt, and a display prompting belt replacement is displayed on the display unit. In addition, the image forming operation is stopped to prevent image failure and machine failure due to belt abnormality.

First, a method for calculating the image leading edge position tg when the toner mark count is one will be described. If the toner mark count is 1, two patterns can be generated. As shown in FIG. 7-2, the first pattern (pattern B) is a state where one scratch on the belt overlaps the toner mark, and the second pattern (pattern C) is as shown in FIG. 12-1. This is a state in which one belt scratch or the like overlaps the toner mark, and another belt scratch or the like does not overlap the toner mark. The case where the toner mark count is two can be determined as the pattern B, and the case where the toner mark count is one and the OFF count is three can be determined as the pattern C. In the case of the pattern B, Tg ₂ ′ and Tm ₄ ′ are measured and compared with the theoretical values Tm ₂ and Tm _2, and when either one matches the theoretical value, tg is calculated as in the following equation.

If Tm ₂ ′ ≈Tm ₂ (Condition 2-1), tg = tf2 + Tm ₂ ′ / 2 (Formula 2-1)
If Tm ₄ ′ ≈Tm ₄ (Condition 2-2), tg = tf1 + Tm ₄ ′ / 2 (Formula 2-2)
Accordingly, since the condition of the toner mark and the scratch on the belt as shown in FIG. 7-2 is (Condition 2-1), tg can be calculated by (Equation 2-1).

In the case of pattern C, Tm _2-1 ′, Tm _4-1 ′, Tm _2-2 ′, Tm _4-2 ′, Tm _2-3 ′, and Tm _4-3 ′ are measured. By comparing as in the above conditions, at least one matches the theoretical value, and tg can be calculated.

If Tm _2-1 '≒ Tm ₂ (Condition 3-1), tg = tf2 + Tm _2-1 ' / 2 (Formula 3-1)
If Tm _4-1 '≒ Tm ₄ (Condition 3-2), then tg = tf1 + Tm ₁ + (Tm _4-1 ' -Tm ₁ ) / 2 (Formula 3-2)
If Tm _2-2 '≒ Tm ₂ (Condition 3-3), tg = tf2 + Tm _2-2 ´ / 2 (Formula 3-3)
If Tm _4-2 ′ ≈Tm ₄ (Condition 3-4), tg = tf3 + Tm ₁ + (Tm _4-1 ′ −Tm ₁ ) / 2 (Formula 3-4)
If Tm _2-3 ′ ≒ Tm ₂ (Condition 3-5), tg = tf2 + Tm _2-3 ′ / 2 (Formula 3-5)
If Tm _4-3 ′ ≈Tm ₄ (Condition 3-6), tg = tf1 + Tm ₁ + (Tm _4-3 ′ −Tm ₁ ) / 2 (Formula 3-6)
Therefore, since the condition of toner marks and scratches on the belt as shown in FIG. 12-1 is (Condition 3-5), tg can be calculated by (Expression 3-5).

Next, a method for calculating the image leading edge position tg when the toner mark count is 0 will be described. When the toner mark count is 0, as shown in FIG. 12-2, the two belt scratches and the like overlap each of the two toner marks (pattern D). In this case, Tm ₂ ′, Tm _3-1 ′, Tm _3-2 ′, and Tm ₅ ′ are measured and compared with the respective theoretical values under the following conditions. At least one of them agrees with the theoretical value and tg It can be calculated.

If Tm _2-1 '≒ Tm ₂ (Condition 4-1), tg = tf2 + Tm ₂ ' / 2 (Formula 4-1)
If Tm _3-1 ′ ≈Tm ₃ (Condition 4-2), tg = tf1 + Tm ₁ + (Tm _3-1 ′ −Tm ₁ ) / 2 (Formula 4-2)
If Tm _3-2 ′ ≈Tm ₃ (Condition 4-3), tg = tf2 + (Tm _3-2 ′ −Tm ₁ ) / 2 (Formula 4-3)
If Tm ₄ ′ ≒ Tm ₄ (Condition 4-4), tg = tf1 + Tm ₁ + Tm ₄ ′ / 2 (Formula 4-4)
Therefore, in the toner mark and belt scratch pattern as shown in FIG. 12-2, (condition 4-3) is satisfied, and therefore tg can be calculated by (Equation 4-3). If the pattern for calculating is determined, it is possible to accurately detect the image timing even if the toner mark overlaps with a scratch on the belt.

  By performing the above-described scratch detection operation, it is possible to detect the presence or absence of scratches or dirt on the intermediate transfer belt. Therefore, stable image alignment can be performed semipermanently.

  In the above embodiment, the timing of the leading edge of one image is determined by two toner marks continuous in the transport direction. However, three, four, or more toner marks are generated and the toner marks are generated. It may be configured to determine the position of the leading edge of the image from the detection. In this case, as the number of toner marks is increased, it is possible to further reduce the risk of erroneous detection due to the overlap of a plurality of belt scratches as compared with the configuration of the present embodiment.

  In the embodiments, the registration correction in the image forming apparatus using the intermediate transfer belt has been described. However, as will be understood, the present invention provides image formation using a recording material conveyance belt which is a belt-like recording material carrier. The present invention can also be applied to the apparatus, and the same effect can be obtained by detecting the resist pattern formed on the transport belt and correcting the resist.

  Furthermore, in the embodiment, the registration roller drive control is of a type that adjusts the acceleration / deceleration timing of the registration roller driving operation during image formation. However, the registration roller driving stop and the driving operation are repeated for each sheet, and the position of the registration roller is controlled. A similar effect can be obtained even in an image forming apparatus that performs alignment control.

1 is a cross-sectional view of an image forming apparatus according to an embodiment of the present invention. 1 is a schematic diagram of a resist portion of an image forming apparatus according to an embodiment of the present invention. 1 is a block diagram showing a control unit of an image forming apparatus according to an embodiment of the present invention. 1 is a light receiving circuit diagram of a photosensor of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a diagram illustrating sheet conveyance and an image conveyance diagram of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a correspondence diagram of photosensor output with respect to a toner mark of the image forming apparatus according to the embodiment of the present invention. FIG. 6 is a correspondence diagram of photosensor output with respect to a toner mark, a belt scratch, and the like of the image forming apparatus according to the embodiment of the present invention. Sectional drawing of the conventional image forming apparatus. FIG. 4 is an explanatory diagram showing detection of a toner mark on a belt by a photo sensor. Explanatory drawing which shows the change of the light reception output of a photosensor. Explanatory drawing of a mode that the light reception output change of a photosensor is erroneously detected by the crack on a belt. FIG. 6 is a correspondence diagram of photosensor output with respect to a toner mark, a belt scratch, and the like of the image forming apparatus according to the embodiment of the present invention.

Explanation of symbols

1R image reading unit 1P image output unit 10 image forming unit 11a to 11d photosensitive drum 12a to 12d primary charger 13a to 13d optical system 14a to 14d developing device 15a to 15d cleaning device 16a to 16d folding mirror 20 feeding deck 22 suction fan DESCRIPTION OF SYMBOLS 23 Conveyance belt 25 Vertical path conveyance part 30 Intermediate transfer unit 31 Transfer belt 32d Drive roller 32s Tension roller 33 Secondary transfer counter roller 34 Secondary transfer roller 35a-35d Charger for primary transfer 36 Cleaning means 37 Toner image detection means 40 Resist Section 41 Sheet correction plate 42 Inclination roller 43 Registration roller 50 Fixing unit 60 Paper discharge unit 61 Paper discharge tray 70 Reversing unit 80 Double-sided path unit 200 Photo sensor 201 LED
202 Phototransistor 203 Toner mark 800 Control unit 801 CPU
803 RAM
804 Pattern width observation part 805 Pattern width & position storage part 806 ROM
S20 Paper surface detection sensor S40 Sheet detection sensor

Claims (4)

A sheet conveying unit that conveys the sheet along the sheet conveying path, an image forming unit that forms a toner image on the image carrier belt, and a toner image that detects the presence or absence of the toner image formed on the image carrier belt A detection unit; a transfer unit configured to transfer an image formed on the image carrier belt to a sheet conveyed by the conveyance unit; and a paper conveyance path upstream of a transfer position of the toner image by the transfer unit. And a paper detection unit that detects passage of the paper and a control unit that controls a paper conveyance speed by the paper conveyance unit based on detection results of the toner image detection unit and the paper detection unit. In the forming device,
In order to control a sheet conveyance speed, the control unit forms at least two or more continuous image timing detection marks in the image conveyance direction that is not transferred to the sheet on the image carrier belt, The image formation is characterized in that the toner image detection means detects the leading edge and the trailing edge of the image timing detection mark and compares the theoretical timing width of the image position detection mark with the image timing. apparatus.   2. The image forming apparatus according to claim 1, wherein the formation position of the image position detection mark is arranged outside the image area to be transferred after being aligned with the paper in the conveyance orthogonal direction. Image forming apparatus.   The image forming apparatus according to claim 1, wherein the paper transport unit has a first transport speed and a second transport speed, and the control unit adds the first transport speed to the second transport speed. An image forming apparatus that controls deceleration timing.   The image forming apparatus according to claim 1, wherein the sheet conveying unit is a registration roller that is stopped when the leading end of the sheet enters, and the control unit includes each of the toner image detecting unit and the sheet detecting unit. An image forming apparatus that controls a timing at which the registration roller is driven based on a detection result from a state in which a sheet hits the registration roller.

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