JP2008309931A - Method for adjusting image forming position, and color image forming apparatus equipped with same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for adjusting an image forming position by which an image forming position is automatically adjusted at high speed only by printing a pattern for alignment once and measuring the average density thereof, and to provide a color image forming apparatus using the method. <P>SOLUTION: Firstly, K printing (pattern printing with black toner) 51 is continuously transferred to a belt by fifteen with printing of a dot line corresponding to a progression "000100110101111" of an M sequence of 15-bit length as basic form. M printing (pattern printing with magenta toner) 52 is superposed and printed on the fifteen basic forms by changing the number of dots of deviation from -7 to +7, so as to form fifteen different patterns of K+M printing 54 in total. When the pattern of the K printing 51 and the pattern of the M printing 52 agree with each other, the average density of the K+M printing 54 is 0.533, and in all the cases other than when they agree with each other, the average density is 0.800, so that positional deviation is known by detecting the position of the pattern whose average density is 0.533. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming position adjusting method for automatically adjusting a toner image forming position by a plurality of image forming units at high speed, and an electrophotographic color image forming apparatus including the image forming position adjusting method.

  In recent years, color printer apparatuses (color image forming apparatuses) have been widely used in conjunction with the increase in the number of personal computers sold. In particular, tandem color image forming apparatuses have excellent printing speed and are attracting attention today. Yes.

  In such a color image forming apparatus, toner images of four colors including yellow (Y), magenta (M), cyan (C) or black (K) are sequentially transferred onto a transfer medium (paper). The images are superimposed and transferred, the fixing process is performed, and an image is formed on the paper.

  In addition, since an image is formed on a sheet that moves in the sub-scanning direction, accuracy is required for alignment of each color. In the color image forming apparatus, the hue is also important, and even if the toner density of one color is deviated from the reference, the hue of the composite color becomes different.

  This means that the four-color toner image is directly transferred to the belt even in the case of positioning each color on the paper-conveying belt in which the paper is conveyed by the belt and the four-color toner image is directly transferred to the paper ( There is no change in the alignment of each color on the intermediate transfer belt in which the four-color superimposed toner images are transferred onto the paper (secondary transfer) in a batch (intermediate transfer, primary transfer).

  For this reason, conventionally, in the color image forming apparatus described above, an expensive CCD (Charge Coupled Device), a laser sensor, or the like is used to align the image forming position for image alignment and color alignment. There is a method in which a correction amount is automatically calculated by detecting an image that has been detected, and a hue or the like is adjusted. Further, the test printed image pattern has been visually observed and adjusted.

  However, the method of detecting the test printed image and automatically calculating the correction amount increases the cost of the apparatus. In addition, the visual method causes individual differences in judgment and accuracy, and the correction method becomes complicated. Furthermore, it is difficult to actually employ the apparatus with only the technical idea of automation.

Therefore, a resist patch method sharing an inexpensive density sensor has been proposed. This method repeats printing while decreasing the interval between parallel line patches of approximately equal intervals from the wide adjustment range to the narrower one, and measures the average density of each patch using a density sensor. This is a method of matching resists. (For example, refer to Patent Document 1.)
JP 2002-040746 A

  However, the method of measuring the average density of parallel line print patches with substantially equal intervals using a density sensor is effective even if the density sensor is inexpensive, but the line intervals of the print patches are gradually reduced. When the adjustment printing range is wide, there is a problem that not only adjustment time is required but also toner is wasted.

  In view of the above-described conventional situation, an object of the present invention is to provide an image forming position adjustment method capable of automatically adjusting the image forming position at a high speed by simply printing a predetermined alignment pattern once and measuring the average density thereof, and the image forming position adjusting method. The present invention provides a color image forming apparatus using the above.

  First, a color image forming apparatus according to a first aspect of the present invention is a transfer belt that circulates around at least two rollers, a driving roller and a driven roller, and an outer periphery of the transfer belt that is detachably attached to the apparatus body. A plurality of image forming units arranged along the surface and forming images with different color toners, and different color toner images formed on the transfer belt by the plurality of image forming units in sequence on the sheet. An electrophotographic color image forming apparatus that performs batch transfer, a misregistration measurement pattern generating means for generating a misregistration measurement pattern composed of a periodic dot line pattern of pseudo random numbers, and generated by the misregistration measurement pattern generating means A positional deviation measurement pattern transfer means for converting the positional deviation measurement pattern into a toner image and transferring the toner image onto the transfer belt; A toner density measuring means for measuring the density of the positional deviation measurement pattern transferred to the transfer belt by the positional deviation measuring pattern transfer means, and a positional deviation for determining the deviation amount of the image forming position based on the measurement result by the toner density measuring means. And a quantity determination means.

  Then, for example, the misregistration measurement pattern transfer means sets one cycle of the misregistration measurement pattern as one pattern, and at least the same number of reference color patterns as the number of dots forming the one cycle on the transfer belt. The toner density measuring means transfers the position deviation measurement pattern of the color to be aligned with the reference color, and superimposes it on the position shifted by one dot for each pattern of the reference color. The toner density is measured for each pattern for one cycle in which the reference color and the color to be aligned with respect to the reference color are transferred, and the measurement result of the toner density for one pattern is measured. The density deviation value is outputted as the average density value, and the positional deviation amount determination means determines the transfer position of one pattern in which the density average value outputted from the toner density measurement means is maximum or minimum. Determining the position displacement amount depending on whether a 1 pattern transferred to the number from the first one pattern transcription initiation, thus constituted.

  The pseudo-random number is preferably an M-sequence pseudo-random number, for example.

  Next, an image forming position adjusting method according to a second aspect of the invention comprises a belt that circulates around at least two rollers, a driving roller and a driven roller, and a belt that is detachably attached to the apparatus main body, A plurality of toner image forming units disposed along the surface, and the toner images are sequentially stacked on the belt or directly on the paper conveyed by the belt by the plurality of toner image forming units. An image forming position adjusting method in an electrophotographic image forming apparatus for generating a misalignment measurement pattern comprising a pseudo random number periodic dot line pattern, and a misregistration measurement pattern generation Misregistration measurement pattern transfer process in which the misregistration measurement pattern generated in the process is converted into a toner image and transferred onto the belt. A toner density measuring step for measuring the density of the misregistration measurement pattern transferred to the belt in the misregistration measurement pattern transfer step, and determining a deviation amount of the image forming position based on a measurement result of the toner density measuring step. A positional deviation amount determination step, wherein the positional deviation measurement pattern transfer step uses one period of the positional deviation measurement pattern as one pattern, and the reference color pattern of the one pattern forms at least the number of dots forming the one period. The same number is transferred to the belt, and the misregistration measurement pattern of the color to be aligned with respect to the reference color is transferred by superimposing on the position shifted by one dot for each pattern of the reference color, In the toner density measurement step, the reference color and the color to be aligned with respect to the reference color are transferred in a pattern for each pattern for one cycle. -The density is measured, and the measurement result of the toner density of one pattern is output as the density average value of the one pattern. In the positional deviation amount determination step, the density average value output from the toner density measurement step is maximum or minimum. The position shift amount is determined based on the transfer position of one pattern indicating the number of patterns transferred from the first pattern at the start of transfer.

  The pseudo-random number is preferably an M-sequence pseudo-random number, for example.

  According to the present invention, an image forming position adjusting method capable of performing high-speed automatic adjustment of an image forming position by simply printing a predetermined alignment pattern once and measuring its average density, and a color image forming apparatus provided with the same Can be provided.

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

(Embodiment 1)
FIG. 1 is a central cross-sectional view illustrating an internal configuration of a color image forming apparatus (hereinafter simply referred to as a printer) provided with an image forming position adjusting method according to the first embodiment.

  A printer 1 shown in FIG. 1 is an electrophotographic secondary transfer tandem color image forming apparatus, and includes an image forming unit 2, an intermediate transfer belt unit 3, a paper feeding unit 4, and a duplex printing conveyance unit 5. It consists of

  The image forming unit 2 has a configuration in which four image forming units 6 (6M, 6C, 6Y, and 6K) are arranged in a multistage manner from right to left in FIG.

  Of the four image forming units 6, three image forming units 6M, 6C and 6Y on the upstream side (the right side in the figure) are magenta (M), cyan (C) and yellow (subtractive three primary colors, respectively). A mono-color image is formed with the color toner of Y), and the image forming unit 6K forms a monochrome image with black (K) toner mainly used for dark portions of characters and images.

  Each of the image forming units 6 has the same configuration except for the color of the toner stored in the toner container (toner cartridge). Accordingly, the configuration of the black (K) image forming unit 6K will be described below as an example.

  The image forming unit 6 includes a photosensitive drum 7 at the bottom. The peripheral surface of the photosensitive drum 7 is made of, for example, an organic photoconductive material. A cleaner 8, a charging roller 9, an optical writing head 11, and a developing roller 13 of the developing device 12 are arranged around the periphery of the photosensitive drum 7.

  The developing device 12 puts one of magenta (M), cyan (C), yellow (Y), and black (K) toners in the upper toner container as indicated by M, C, Y, and K in the drawing. An intermediate portion is provided with a toner replenishing mechanism for the lower portion.

  In addition, the developing roller 13 is provided in the lower portion of the developing device 12 at the side opening, and includes a toner stirring member, a toner supply roller for supplying toner to the developing roller 13, and a toner layer on the developing roller 13 as a fixed layer. It has a doctor blade that regulates the thickness.

  The intermediate transfer belt unit 3 has an endless transfer belt 14 extending in a flat loop shape from substantially the end of the front and rear sides in the center of the main body device, and the transfer belt 14 is stretched over the intermediate transfer belt unit 3. A driving roller 15 and a driven roller 16 are provided to circulate and move the transfer belt 14 counterclockwise in the figure.

  The transfer belt 14 transfers the toner image directly onto the belt surface (primary transfer) and conveys the toner image to the transfer position to the paper for further transfer (secondary transfer). The whole is called an intermediate transfer belt unit.

  The intermediate transfer belt unit 3 includes a belt position control mechanism 17 in the loop of the flat loop-shaped transfer belt 14. The belt position control mechanism 17 includes a primary transfer roller 18 made of a conductive foam sponge that presses against the lower peripheral surface of the photosensitive drum 7 via the transfer belt 14.

  The belt position control mechanism 17 has three primary transfer rollers 18 corresponding to the three image forming units 6M, 6C, and 6Y of magenta (M), cyan (C), and yellow (Y) as vertical support shafts. Rotate to the center with the same period.

  Then, the belt position control mechanism 17 rotates and moves one primary transfer roller 18 corresponding to the black (K) image forming unit 6K at a rotational movement cycle different from the cycle of the three primary transfer rollers 18. The belt 14 is moved away from the photosensitive drum 7.

  That is, the belt position control mechanism 17 moves the position of the transfer belt 14 of the intermediate transfer belt unit 3 to full color mode (all four primary transfer rollers 18 are in contact with the transfer belt 14), monochrome mode (to the image forming unit 6K). Only the corresponding primary transfer roller 18 is in contact with the transfer belt 14) and all non-transfer modes (all four primary transfer rollers 18 are separated from the transfer belt 14).

  In the intermediate transfer belt unit 3, a belt cleaner unit is disposed further upstream of the uppermost image forming unit 6M on the upstream side in the belt movement direction, and is flat and thin so as to be substantially along the entire lower surface. The waste toner collection container 19 is detachably disposed.

  The intermediate transfer belt unit 3 is provided with a density sensor 20 in the vicinity of the end surface on the most downstream side in the belt moving direction.

  The paper feed unit 4 includes two paper feed cassettes 21 arranged in two upper and lower stages, and in the vicinity of the paper feed opening (right side in the figure) of the two paper feed cassettes 21, respectively, A feeding roller 23, a separating roller 24, and a standby conveying roller pair 25 are disposed.

  In the paper conveyance direction (vertical upward direction in the figure) of the standby conveyance roller pair 25, a secondary transfer roller 26 that is in pressure contact with the driven roller 16 via the transfer belt 14 is disposed, and the secondary transfer portion to the paper is arranged. Forming.

  A belt-type heat fixing device 27 is disposed downstream (upward in the drawing) of the secondary transfer portion, and the sheet after fixing is fixed to the belt-type heat fixing device 27 further downstream of the belt-type heat fixing device 27. A pair of carry-out rollers 28 for carrying out the paper and a pair of paper discharge rollers 31 for discharging the carried paper to a paper discharge tray 29 formed on the upper surface of the apparatus are disposed.

  The duplex printing conveyance unit 5 includes a start return path 32a that branches from the intermediate conveyance path between the carry-out roller pair 28 and the discharge roller pair 31 to the right lateral direction in the drawing, and then an intermediate return path 32b that bends downward. A terminal return path 32c that bends in the left lateral direction opposite to the above and eventually reverses the return sheet, and four return roller pairs 33a, 33b, 33c, and 33d disposed in the middle of these return paths. ing.

  The exit of the end return path 32 c communicates with a conveyance path to the standby conveyance roller pair 25 corresponding to the sheet feeding cassette 21 below the sheet feeding unit 4.

  In this example, a cleaning unit 35 and a take-in roller 36 are disposed on the upper surface of the intermediate transfer belt unit 3.

  The cleaning unit 35 comes into contact with the upper surface of the transfer belt 14 to scrape and remove the waste toner, and the take-in roller 36 takes over the waste toner removed by the cleaning unit 35, and a temporary storage unit of the belt cleaner unit (not shown). The accumulated waste toner is conveyed to the upper part in the dropping cylinder by a conveying screw and sent to the waste toner collecting container 19 through the dropping cylinder.

  Further, in order to bring the cleaning unit 35 into pressure contact with the transfer belt 14 with an appropriate pressure, a pressure roller 37 is provided on the intermediate transfer belt unit 3 side to press the transfer belt 14 toward the cleaning unit 35 from below. ing.

  As shown in FIG. 1, the printer 1 does not directly transfer a toner image onto a conventional sheet, but uses an intermediate transfer belt 14 on a sheet that is vertically conveyed to a secondary transfer unit by a standby conveyance roller pair 25. Thus, a toner image is transferred through the system.

  Therefore, it is possible to cope with a maintenance process for recovering from a problem such as a paper jam occurring in the paper transport path by simply opening the right side of FIG.

  In addition, since troubles such as paper jam do not occur in the arrangement section of the kits, the operation for attaching and detaching consumables such as kits concentrated on the left side of FIG. It is configured as follows.

  Thereby, the dimension between kits is reduced as much as possible, and size reduction of the whole apparatus main body is achieved. Further, the optical writing head itself is also miniaturized and is configured closer to the photosensitive drum.

  FIG. 2 is a circuit block diagram including the control device of the printer 1 described above. As shown in FIG. 2, the circuit block is centered on a central processing unit (CPU) 40, and an interface controller (I / F_CONT) 41 and a printer controller (PR_CONT) 42 are connected to the CPU 40 via a data bus. ing. A printer printing unit 43 is connected to the PR_CONT 42.

  Connected to the CPU 40 are a ROM (read only memory) 44, an EEPROM (electrically erasable programmable ROM) 45, an operation panel 46 of the main body operation unit, and a sensor unit 47 to which outputs from sensors arranged in the respective units are input. Has been.

  A system program is stored in the ROM 44, and the CPU 40 performs processing by controlling each unit in accordance with the system program.

  That is, in each unit, first, the I / F_CONT 41 converts print data supplied from a host device such as a personal computer into bitmap data and develops it in the frame memory 48. In the frame memory 48, storage areas are set for each of black (K), magenta (M), cyan (C), and yellow (Y), and data of each color is developed in the corresponding area.

  The data developed in the frame memory 48 is output to the PR_CONT 42 and is output from the PR_CONT 42 to the printer printing unit 43.

  The printer printing unit 43 is an engine unit, and under the control of the PR_CONT 42, the rotational drive system including the photosensitive drum 7, the primary transfer roller 18 and the like shown in FIG. 1, the charging roller 9, the optical writing head 11, etc. An image forming unit having a driven portion, a belt driving unit 15 that moves the intermediate transfer unit 3 up and down and rotationally drives the transfer belt 14, and a rotationally driven unit such as a paper take-out roller 22 to a paper discharge roller pair 31. A drive output to a process load such as a conveyance mechanism, a heat generating drive, and a belt-type fixing device 27 driven to rotate is controlled.

  The black (K), magenta (M), cyan (C), and yellow (Y) data output from the PR_CONT 42 are respectively sent from the printer printing unit 43 to the corresponding optical writing heads 11 shown in FIG. To be supplied.

  Next, the basic operation of the printer 1 having the above configuration will be described. In the following description of the basic operation, the operation in the color printing state will be described.

  First, printing (printing) is started when the power is turned on and the number of sheets to be used, the print mode, and other designations are input as keys or as signals from the connected host device.

  That is, the driving roller 15 rotates counterclockwise in FIG. 1 to start the circulating movement of the transfer belt 14. The image forming units 6 are sequentially driven, and the photosensitive drum 7 rotates in the clockwise direction in the figure.

  The charging roller 9 applies a uniform high negative charge to the circumferential surface of the photosensitive drum 7 and initializes it, and the optical writing head 11 performs exposure according to the image signal on the circumferential surface of the photosensitive drum 7 to perform initialization. An electrostatic latent image including a high negative potential portion and a low negative potential portion by the exposure is formed.

  The developing roller 13 transfers the toner in the developing device 12 to the low potential portion of the electrostatic latent image and forms a toner image (reverse development) on the circumferential surface of the photosensitive drum 7.

  A magenta toner image formed on the peripheral surface of the photosensitive drum 7 of the image forming unit 6M at the most upstream in the sheet conveying direction is rotated and conveyed to the surface facing the transfer belt.

  The primary transfer roller 18 applies a transfer current output from a transfer bias power source (not shown) to the transfer belt 14. As a result, the magenta toner image on the photosensitive drum 7 is primarily transferred to the transfer belt 14.

  A cyan toner image formed on the peripheral surface of the photosensitive drum 7 of the image forming unit 6C is superposed on the toner image primarily transferred to the transfer belt 14, and then the primary transfer roller 18 directly below the image forming unit 6C. Transcribed.

  Further, the yellow toner image formed on the peripheral surface of the photoconductive drum 7 of the image forming unit 6Y is transferred onto the primary transfer roller 18 directly below the image forming unit 6Y, and finally, the photoconductor of the image forming unit 6K. The black toner image formed on the peripheral surface of the drum 7 is overlaid and transferred by the primary transfer roller 18 directly below the image forming unit 6K.

  As described above, the toner images of four colors of magenta (M), cyan (C), yellow (Y), and black (K) are sequentially superimposed and primarily transferred to complete a full-color image on the transfer belt 14.

  The transfer belt 14 on which the four-color toner images are primarily transferred is continuously circulated to convey the four-color toner images to the secondary transfer position where the driven roller 16 and the secondary transfer roller 26 face each other. To do.

  On the other hand, the paper take-out roller 22 rotates to take out the paper stored in the paper feed cassette 21 slightly earlier than the printing timing on the paper. The rolling roller 24 rotates in the reverse direction in order to inhibit the lower sheet from being fed so as to feed out only the uppermost sheet of the sheet taken out from the sheet cassette 21.

  The feeding roller 23 rotates in the forward direction and feeds the uppermost sheet to the standby conveyance roller pair 25.

  The standby conveyance roller pair 25 temporarily stops rotation to stop the paper advance, corrects the conveyance posture such as the skew of the paper, waits for the conveyance timing, and the print start position of the paper is set by the transfer belt 14. In accordance with the timing coincident with the leading end of the four-color toner image conveyed to the secondary transfer position, the conveyance of the sheet is resumed and the sheet is fed to the secondary transfer position.

  At the secondary transfer position, the secondary transfer roller 26 applies a bias voltage supplied from a bias power source (not shown) to the sheet. As a result, the four color toner images on the transfer belt 14 are secondarily transferred to the paper.

  The sheet onto which the four color toner images have been transferred is carried into the belt type fixing device 27 as it is. The belt-type fixing device 27 presses and holds the sheet with an appropriate pressure contact force by the heat roller and the pressure roller, and discharges upward while fixing the four color toner images on the sheet surface by applying heat and pressure to the sheet.

  The sheet discharged from the belt-type fixing device 27 is nipped by the carry-out roller pair 28 and taken over, and the discharge roller pair 31 places the image forming surface of the four color toner images on the discharge tray 29. Discharged.

  In the above description, color printing is described. However, for monochrome printing, the transfer belt 14 contacts only the photosensitive drum 7 of the image forming unit 6K and moves to a position away from the other photosensitive drums 7, and image formation. Except for the point that only the unit 6K is operated, the other operations are almost the same as those in the color printing described above.

  In the intermediate transfer type tandem type printer 1 operating in this way, when switching from monochrome printing to color printing, or when starting color printing from the rest position, the transfer belt 14 moves up and down, Distortion occurs on the surface of the transfer belt 14.

  Regarding the deviation of the transfer position consistency (hereinafter simply referred to as “registration”) for each color on the transfer belt 14, the belt body meandering control mechanism (not shown) is used in a large point. The meandering control mechanism corrects meandering of the belt body, and is generally provided as an accessory to belts.

  However, the registration deviation after the start of continuous printing cannot be easily corrected by only the meandering control mechanism of the belt body.

  However, the present inventor has found that the image forming position can be automatically adjusted at high speed by measuring the density of a misregistration measurement pattern composed of a periodic dot line pattern based on pseudorandom numbers, particularly M-sequence pseudorandom numbers. did.

  According to the free encyclopedia “Wikipedia”, the pseudo-random number looks like a random number sequence (random number), but is actually included in a sequence that can be obtained by deterministic calculation. It is a number.

  A pseudo-random number is a number included in a number sequence that can be obtained by deterministic calculation. However, a number sequence represented by one number is nothing but a cycle in the number sequence.

  In other words, a random number sequence is generated within one period, but since the number sequence has a period, such a number sequence is called a pseudo-random number.

  A device (or algorithm) that generates pseudo-random numbers is called a pseudo-random number generator (or pseudo-random number generation method), and the pseudo-random numbers are used for simulation experiments, encryption, and the like.

  The present inventor uses a number sequence obtained by a pseudo-random number sequence of M sequence (algorithm called M-sequence-random-number) among the number sequences that can be obtained by the above deterministic calculation as one pattern. The dot lines according to the sequence to be formed were used as a series of misregistration measurement patterns formed according to a predetermined rule.

  Then, it was discovered that the amount of misalignment at the image forming position can be measured simply by printing this series of misregistration measurement patterns once and measuring the average density.

  That is, if the shift amount of the image forming position can be automatically measured, the image forming position can be automatically adjusted based on the measurement result. This will be described in detail below.

  There are various researches on random number generation methods by computers. Among them, M series is a 1-bit number sequence that can be easily handled by a computer, and any number sequence with a long period can be easily generated with a dedicated arithmetic expression. There are features.

  A dedicated arithmetic expression for generating a pseudo-random number composed of an M-sequence 1-bit number sequence is the following linear recurrence expression.

Xn = Xn-p + Xn-q (p> q) (1)
In this expression, the value of each term is 0 or 1, and the “+” sign is an exclusive OR (XOR). That is, the nth term is obtained by performing an XOR operation on the np-th and n-qth terms. Here, the values of p and q are selected so that the expression “X ^ p + X ^ q + 1 (p> q)” is an irreducible polynomial.

  For example, in the above formula, when p = 5 and q = 2, as shown below, X8 is generated by XORing X3 (= X8-5) and X6 (= X8-2). Is done.

n: 012345678
Xn: 100001111
↓ ↓ ↑
→→→ + → ↑

  In order to actually generate M-sequence pseudorandom numbers in this way, it is necessary to give p (1 bit each) values, that is, xn-1, xn-2,..., Xn-p as initial values. . Here, simply, an M-sequence with a short period is generated and its characteristics are seen.

  Accordingly, in Equation 1, it is assumed that M series are generated from n = 0 to 9 with p = 3 and q = 1. Assuming that X0, X1, and X2 are “1, 0, 0”, Xn = Xn-3 + Xn-1

n: 0123456789
Xn: 10011010100
Thus, initial value patterns appear from n = 7 to n = 9. That is, n = 6 (seventh from the beginning) makes a sequence of several sequences. The period of this M series is “7”.

  After the above, the same pattern appears from n = 10 to n = 13 and from n3 to n = 6, and the same pattern from n = 14 to n = 0 to 6 is repeated. That is, the same pattern consisting of an 8-bit number sequence is repeated with a period “7”.

  Also, in Equation 1, when p = 4 and q = 1 and an M sequence is generated from n = 0 to 18, initial values X0, X1, X2, X4 are set to “1, 0, 0, 0”. , Xn = Xn-3 + Xn-1 produces a sequence of "10000111101011001000" consisting of 19 bits from X0 to X18.

  In this case, an initial value pattern appears from n = 14 (15th from the beginning). That is, the number sequence goes through 15th from the beginning. The period of this M series is “15”.

  Generally, the period T of the M sequence can be expressed by “T = 2 ^ p−1”. That is, the period T is a value determined by the value of p.

  FIG. 3 is a diagram illustrating an example of a misalignment measurement pattern using M-sequence pseudorandom numbers in the present embodiment. This figure shows a printing pattern according to an M-sequence pseudo-random number consisting of 15 bit strings.

  The 15-bit M-sequence sequence shown in the figure is “000100110101111”. This figure shows a basic form with a 0-bit shift amount at the upper left. In this basic form, both the K printing (pattern printing with black toner, the same applies hereinafter) 51 and the M printing (pattern printing with magenta toner, the same applies hereinafter) 52, both “0” indicates no printing according to the above sequence 53 (000100110101111). “1” is printed as being printed.

  In the figure, the K print 51 and the M print 52 are shown side by side. However, in actual printing, printing is performed like a K + M print 54. In the K + M print 54 in the basic form of the print pattern using the above-mentioned number sequence, as shown by the number sequence 55 surrounded by a vertically long solid oval at the upper left of FIG. “1” has a total of 8 lines.

  Taking the K + M print 54 in this basic form as one pattern, the average density value of 15 lines per pattern was 0.533.

  Further, the left center of FIG. 3 shows an M print 52 having a shift amount of 1 bit with respect to the basic K print 51 and a K + M print 54 as a result of the overlap printing. The non-printing “0” of the K + M printing 54 with 1-bit deviation is a total of 3 lines, and the printing “1” is a total of 12 lines. The average density value of 15 lines per pattern was 0.800.

  Further, the lower left of FIG. 3 shows an M print 52 having a deviation amount of 2 bits with respect to the basic K print 51 and a K + M print 54 as a result of the overlap printing. This 2-bit K + M printing 54 with a deviation amount of “0” without printing has a total of 3 lines and “1” with printing has a total of 12 lines. Therefore, the average density value of 15 lines per pattern was 0.800.

  In the upper right of FIG. 3, a basic K print 51, an M print 52 with a shift amount of 3 bits, and a K + M print 54 as a result of the overlap printing are shown.

  The right center of FIG. 3 shows a basic K print 51, an M print 52 with a shift amount of 4 bits, and a K + M print 54 as a result of these overlapping prints.

  3 shows a basic K print 51, an M print 52 with a shift amount of 5 bits, and a K + M print 54 as a result of the overlap printing.

  The K + M print 54 as a result of the overlap printing from the upper right misalignment amount 3 bits to the lower right misalignment amount 5 bits in FIG. 3 is the case of the misalignment amount 1 bit and the misalignment amount 2 bits shown on the left. Similarly, “0” without printing has a total of 3 lines, “1” with printing has a total of 12 lines, and the average density value of 15 lines in one pattern was 0.800.

  FIG. 4 shows a basic K print 51 from the upper left to the lower right, an M print 52 with a shift amount of 6 bits to a shift amount of 11 bits continuing from FIG. 3, and a K + M print 54 of the overlap print result. Show.

  In any case, in the K + M printing 54, “0” without printing has a total of 3 lines, “1” with printing has a total of 12 lines, and the average density value of 15 lines in one pattern is 0.800.

  In FIG. 4, when the shift amount of the bit string of the M print 52 is viewed in detail, the shift amount of 8 bits is the same as the shift amount minus 7 bits, the shift amount of 9 bits is the same as the shift amount of minus 6 bits, and the shift amount is 10 bits. Is the same as the amount of deviation minus 5 bits, and the amount of deviation of 11 bits is the same as the amount of deviation minus 4 bits.

  FIG. 5 shows a basic K print 51 from the top to the bottom, an M print 52 with a shift amount of 12 bits to a shift amount of 14 bits continuing from FIG. 4, and a K + M print 54 of the overlap print result. ing.

  In any case, in the K + M printing 54, “0” without printing has a total of 3 lines, “1” with printing has a total of 12 lines, and the average density value of 15 lines in one pattern is 0.800.

  In FIG. 5, in the misalignment amount of the M print 52, the misalignment amount 12 bits is the same as the misalignment amount minus 3 bits, the misalignment amount 13 bits is the same as the misalignment amount minus 2 bits, and the misalignment amount 14 bits is the misalignment amount minus 1 bit. Is the same.

  FIG. 6 (a) shows a displacement amount m bits (m = −7, −6,..., 0, 1, 2,...) Of the M print 52 with respect to the basic K print 51 shown in FIGS. .. 7) and a table showing the relationship between the toner density of the K + M print 54 at that time and FIG. 6B is a diagram showing the relationship as a graph.

  As shown in FIGS. 6A and 6B, when there is a deviation in the M print 52 with respect to the basic K print 51, the toner density of the K + M print 54 regardless of how many bits the deviation is. Is 0.800, and it can be seen that the toner density of the K + M print 54 becomes 0.533 only when there is no deviation, that is, when the deviation amount is 0 bits.

  Accordingly, when the K + M print 54 shown in FIGS. 3 to 5 is printed on the transfer belt 14 in the form of 15 patterns arranged in the order shown in FIG. The deviation of the image forming position occurring in the apparatus (mechanism) of the M print 52 with respect to the print 51 is found.

  In other words, as described above, the K printing and M printing image forming position alignment on the intermediate transfer belt will be described as an example. First, the basic pattern shown as the K printing 51 in FIGS. Fifteen images are continuously printed on the intermediate transfer belt 14.

  Next, the pattern of the M printing 52 is printed on the intermediate transfer belt 14 with the K printing 51 superimposed on the K printing 51 and with a phase shifted gradually with respect to the K printing 51 as shown in FIGS.

  However, when printing on the intermediate transfer belt 14 in this way, the order shown in FIGS. 3 to 5 is different from, for example, the first pattern with respect to the K print 51 as shown in FIG. Prints the amount of misalignment as "-7 dots".

  Hereinafter, similarly, the number of misaligned dots is overprinted as -6, -5, -4, -3, -2, -1, ± 0, +1, +2, +3, +4, +5, +6, +7, A total of 15 different K + M prints 54 are formed.

  The density of these 15 patterns of the K + M print 54 is sequentially measured by the density sensor 20. In this density measurement, as shown in FIG. 3 to FIG. 5, the average density of 15 lines is measured with 0 indicating no toner and 1 indicating presence of toner.

  When the basic pattern of the K print 51 and the misalignment pattern of the M print 52 do not match, the average toner density output from the density sensor 20 is 0.800 for all those that do not match as described above.

  When the deviation amount of the deviation pattern of the M print 52 is ± 0 dots, the average toner density output from the density sensor 20 is 0.533 as described above. That is, when the deviation amount is ± 0 dots, the average toner density is 0.533, and in all other cases, the average toner density is 0.800.

  This property comes from the property of a pseudo-random number sequence such as an M sequence. Then, as shown in FIGS. 6A and 6B, the toner density changes drastically only when the basic pattern for K printing and the deviation pattern for M printing completely coincide.

  If no mechanical error is included in the apparatus, the average toner density is minimized at a predetermined place, that is, a print pattern in which the seventh deviation amount is ± 0 dots from the first print pattern.

  However, if a mechanical error is included on the apparatus, the position where the average toner density is minimized is shifted. For example, in the case of a K + M print pattern in which the deviation amount of the deviation pattern of M printing is printed as −3 dots, when the basic pattern of K printing and M printing coincide with each other and the average toner density is minimized, +3 dots, The writing timing for M printing is shifted.

  Therefore, in that case, a value corresponding to +3 dots may be given as a correction value to the optical writing head 11 of the image forming unit 6M with respect to the M printing writing timing. Note that plus / minus is applied in an appropriate direction because of the definition of the correction value.

  Further, in this example, whether or not the positions match can be confirmed one dot at a time in one pattern length of K + M printing. Therefore, all 14 patterns by one pattern of K + M printing capable of 14 dot correction can be performed. Since a correction value having a long length (this is an alignment pattern) and a matching position can be detected at a time, the image forming position can be automatically adjusted at a very high speed.

  Up to this point, the detection of misalignment of M printing has been described with reference to K printing, but the same applies to Y printing and C printing of other colors performed with K printing as a reference.

  FIG. 7 (a) is a diagram showing one pattern length of K + M printing printed based on another number sequence of 15 bits of M series, and FIG. 7 (b) is a diagram of a certain position of K + M printing. It is a figure which shows the relationship between the visual field (reading range) of the density sensor which is measuring the pattern, and one pattern.

  As shown in FIG. 7B, one pattern length a of K + M printing is configured in a range that substantially matches the length in the vertical direction of the visual field 20-1 of the density sensor. The printing width b of one pattern of K + M printing is configured in a range that substantially matches the horizontal width of the visual field 20-1 of the density sensor. The density sensor 20 detects an average toner density in the entire visual field within one pattern area.

  Note that the direction indicated by the double-headed arrow c in the figure indicates the alignment direction of image formation, and as described above, which of the upper and lower sides is to be positive or negative is defined in the correction value definition. Set accordingly.

  FIG. 8A is a diagram showing a state in which two identical K + M print patterns having one pattern length a shown in FIG. 7A are continuously printed, and FIG. It is a figure which shows the relationship between the visual field (reading range) of the density sensor which is measuring the continuous pattern, and two continuous patterns.

  As shown in FIG. 8B, the two continuous pattern lengths (a + a) of K + M printing are configured in a range that substantially matches the vertical length of the visual field 20-1 of the density sensor. The printing width (b × 2) of the two continuous patterns of K + M printing is configured in a range that substantially matches the horizontal width of the visual field 20-1 of the density sensor.

  Also in this case, the density sensor 20 detects the average toner density in the entire visual field within the area of the two continuous patterns.

  As in the case of one pattern, the adjustment range is correction of 14 dots from −7 to −1 and +1 to +7 excluding the coincidence position of ± 0 dots from 15 dots corresponding to one cycle of one pattern. It can be carried out. Since the average density of two continuous patterns is measured, the accuracy is higher than in the case of one pattern.

  In this figure as well, the direction indicated by the double-pointed arrow c indicates the image forming alignment direction, and as described above, which of the upper and lower sides is set to the plus direction or the minus direction is defined as a correction value. Set accordingly.

(Embodiment 2)
9 to 11 are diagrams illustrating examples of other misregistration measurement patterns using the same pseudorandom numbers as those in the first embodiment of the M series in the second embodiment.

  In the upper left of FIG. 9, the basic pattern of the K print 51 printed according to the M-sequence number 53 “000100110101111” of the 15-bit length shown in the upper left of FIG. 3 is shown on the left.

  Further, in the upper left of FIG. 9, M printing 57 is printed at the center in accordance with a numerical sequence 56 “111011001010000” obtained by replacing “1” and “0” of the numerical sequence 53 “000100110101111”. Is shown.

  9 shows a K + M print 58, which is a print state as a result of printing with the center M print 57 superimposed on the left K print 51.

  In the K + M printing 58 in the basic form of this printing pattern, as indicated by a numerical sequence 59 surrounded by a vertically long solid ellipse, there is no “0” without printing and only “1” with printing of 15 lines. The output value of the density measurement result by the density sensor 20 for one pattern of the basic form of the deviation amount ± 0 dots is “1.000”.

  The misalignment pattern of 1 to 5 dots of misalignment of the M print 57 shown from the left center to the lower right of FIG. 9 and the misalignment of 6 to 11 dots of the M print 57 shown from the upper left to the lower right of FIG. In the misalignment pattern and the misalignment pattern of the misalignment amount 12 dots to 14 dots of the M print 57 shown from the top to the bottom of FIG. 11, the K + M print 58 has 4 lines for no print and 1 for print. Is 14 lines.

  The output value of the density measurement result by the density sensor 20 for each of these shift patterns is “0.733”.

  FIG. 12 (a) shows a displacement amount m bits (m = −7, −6,..., 0, 1, 2,...) Of the M print 57 with respect to the basic K print 51 shown in FIGS. .. 7) and the relationship between the toner density of the K + M print 58 at that time in a list, and FIG. 12B is a diagram showing the relationship in a graph.

  As shown in FIGS. 12A and 12B, when there is a deviation in the M print 57 with respect to the basic K print 51, the toner density of the K + M print 58 regardless of how many bits the deviation is. Is 0.733, and it can be seen that the toner density of the K + M print 58 becomes 1.000 only when there is no deviation, that is, when the deviation amount is ± 0 bits.

  Therefore, also in this case, the K + M printing 58 shown in FIGS. 9 to 11 is printed on the transfer belt 14 with 15 patterns arranged in the order shown in FIG. 12A, and the toner density is measured by the density sensor. When the measurement is performed, the deviation of the image forming position occurring in the apparatus (mechanism) of the M printing 57 with respect to the K printing 51 is found.

  That is, first, 15 basic patterns shown as K printing 51 in FIGS. 9 to 11 are printed on the intermediate transfer belt 14 with K printing as a reference.

  Next, the pattern of the M print 57 is printed on the intermediate transfer belt 14 so as to overlap the K print 51 and gradually shift the phase with respect to the K print 51 as shown in FIGS.

  However, also in this case, when printing on the intermediate transfer belt 14, the order is different from the order shown in FIGS. 9 to 11, for example, one pattern for the K print 51 as shown in FIG. The eyes are printed with a displacement amount of “−7 dots”.

  Hereinafter, similarly, the number of misaligned dots is overprinted as -6, -5, -4, -3, -2, -1, ± 0, +1, +2, +3, +4, +5, +6, +7, Different patterns of a total of 15 K + M prints 58 are formed.

  The density of these 15 K + M print 58 patterns is sequentially measured by the density sensor 20 as shown in FIG. In this density measurement, as shown in FIGS. 9 to 11, the average density of 15 lines is measured with 0 for no toner and 1 for toner.

  When the basic pattern of the K print 51 and the misalignment pattern of the M print 57 do not match, the average toner density output from the density sensor 20 is 0.733 for all those that do not match as described above.

  When the deviation amount of the deviation pattern of the M print 57 is ± 0 dots, the average toner density output from the density sensor 20 is 1.000 as described above. That is, when the deviation amount is ± 0 dot, the average toner density is 1.000, and in all other cases, the average toner density is 0.733.

  This property also comes from the property of a pseudo-random number sequence such as an M series. Then, as shown in FIGS. 12A and 12B, the toner density changes drastically only when the basic pattern for K printing and the deviation pattern for M printing completely coincide.

  If no mechanical error is included in the apparatus, the average toner density is maximized at a predetermined place, that is, a print pattern in which the seventh shift amount is ± 0 dots from the first print pattern.

  However, if a mechanical error is included on the apparatus, the position where the average toner density is minimized is shifted. For example, in the case of a K + M print pattern in which the deviation amount of the deviation pattern of M printing is printed as -3 dots, when the basic pattern of K printing and M printing coincide with each other and the average toner density is maximized, +3 dots, The writing timing for M printing is shifted.

  Therefore, in that case, a value corresponding to +3 dots may be given as a correction value to the optical writing head 11 of the image forming unit 6M with respect to the M printing writing timing. Note that plus / minus is applied in an appropriate direction because of the definition of the correction value.

  Also in this example, whether or not the positions match can be confirmed one dot at a time in one pattern length of K + M printing. Therefore, all patterns for 14 times by one pattern of K + M printing capable of 14 dot correction are possible. Since the correction value with the matching position can be detected at a time using the length (or the total pattern length of 14 continuous patterns of 14) as the alignment pattern, the image forming position can be automatically adjusted at a very high speed.

  In this case as well, not only the detection of misalignment of M printing with reference to K printing but also the Y printing and C printing of other colors performed with K printing as a reference are the same as described above.

(Embodiment 3)
FIGS. 13 to 15 are diagrams showing examples of still another misregistration measurement pattern using the same pseudorandom numbers as those in the first embodiment of the M series in the third embodiment.

  In this example, a 1/4 dot position shift is detected. FIG. 13 (a) is a diagram showing the basic pattern of the K mark print 51 shown in the upper left of FIG. 3 again. On the left side of FIG. 13 (b), the basic pattern is shown in an enlarged manner as typically shown by four arrows, and each bit is divided into four (0000 or 1111). One pattern is indicated by a.

  As shown in FIGS. 13 to 15, 17 patterns (however, some of the 17 patterns are omitted in order to avoid complication) are continuously formed on the transfer belt. 14 is printed.

  Subsequently, as shown on the right side of FIG. 13B, the M print 61 is printed in an overlapping manner. Note that pattern numbers 1, 2, and 3 are shown consecutively to the right of the M print 61. In addition, the first pattern (pattern number 1) of the M print 61 is printed by shifting upward by 2 dots (in this example, −2 dots) with respect to the pattern of the K print 51.

  That is, in pattern number 1, M printing is performed with a shift amount of −2 dots, that is, “−8/4 dots”. The average toner density detected by the density sensor 20 with respect to the pattern of the K + M print 62 shown in FIG.

  In the subsequent M print 61 of pattern number 2, a pattern shifted downward by 1/4 dot (0 for 1/4 dot is added to the pattern boundary 63) is printed.

  That is, in pattern number 2, M printing is performed with a shift amount of “−7/4 dots”. The average toner density detected by the density sensor 20 for the K + M print 62 pattern shown in FIG.

  Further, in the M print 61 of pattern number 2, a pattern shifted by 1/4 dot downward (0 for 1/4 dot is added to the pattern boundary 64) is printed.

  That is, in pattern number 3, M printing is performed with a shift amount of “−6/4 dots”. Also in this case, the average toner density detected by the density sensor 20 for the pattern of the K + M print 62 shown in FIG.

  Similarly, as shown in FIGS. 14 (a) and 14 (b) and FIGS. 15 (a) and 15 (b), the superposition printing of the M print 61 and the basic K print 51, which are sequentially shifted downward by 1/4 dot. A pattern of K + M printing 62, which is a pattern, is continuously formed.

  4 (a) and 4 (b), the upper half of pattern number 4 and pattern number 5 is not shown. In FIGS. 5 (a) and 5 (b), the illustration after pattern number 15 is omitted. It is omitted.

  In this way, the amount of deviation from “−8/4 dots” to “−1/4 dots” is centered around the pattern of deviation number ± 0 dots of pattern number 9 shown in FIG. 8 deviation patterns are continuously printed, and eight deviation patterns with deviation amounts of “+1/4 dots” to “+8/4 dots” are continuously printed behind.

  That is, a total of 17 patterns are continuously printed, and an alignment pattern with an adjustment range of 1/4 dot to 2 dots is formed.

  In this example, as shown in FIGS. 14A and 14B, the density sensor 20 detects the K + M print 62 pattern of the pattern numbers 6, 7 and 8 preceding the pattern number 9 of the deviation amount ± 0 dot. The average toner densities are 0.733, 0.677, and 0.6, respectively.

  Further, as shown in FIG. 15 (a), the average toner density detected by the density sensor 20 with respect to the pattern of the K + M print 62 of the pattern numbers 10, 11, and 12 following the pattern number 9 of the deviation amount ± 0 dot is respectively , 0.6, 0.677, and 0.733.

  FIG. 16 (a) shows a displacement amount m bits (M = −8 / 4, −7/4, −6/4,...) Of the M print 61 with respect to the basic K print 51 shown in FIGS. .., 0, +1/4, +2/4,... +8/4) and the toner density of the K + M print 62 at that time are shown in a list, and FIG. It is a figure which shows a relationship in a graph.

  As shown in FIGS. 16A and 16B, when the M print 61 has a deviation from the basic K print 51, the toner density of the K + M print 62 varies in the range of 0.8 to 0.6. When the amount of deviation is ± 0 bits, it can be seen that the toner density of the K + M print 62 takes the minimum value of 0.533.

  Accordingly, when the K + M print 62 shown in FIGS. 13B and 13C to FIGS. 15A and 15B is formed on the transfer belt 14 and its toner density is measured by the density sensor, the M for the K print 51 is measured. The deviation of the image forming position occurring in the apparatus (mechanism) of the print 61 is found in units of 1/4 dots.

  The correction value given to the optical writing head 11 of the image forming unit 6M when the amount of deviation is found is the same as in the first or second embodiment. In this example, the correction value is not 1 dot unit but 1 / The only difference is that it is in units of 4 dots.

  In each of the first to third embodiments described above, the transfer belt position shift correction of the electrophotographic color image forming apparatus shown in FIG. 1 has been described. However, the present invention is not limited thereto, and the image of the present invention is not limited thereto. The forming position correction method can be applied to an image forming apparatus having two image forming units, for example, even in a monochrome image forming apparatus.

2 is a central cross-sectional view illustrating an internal configuration of a color image forming apparatus (printer) including the image forming position adjusting method according to Embodiment 1. FIG. FIG. 2 is a circuit block diagram including a printer control device according to the first embodiment. 6 is a diagram illustrating an example of a misalignment measurement pattern using M-sequence pseudorandom numbers in Embodiment 1. FIG. FIG. 4 is a diagram showing basic K printing from the upper left to the lower right, and M printing from a shift amount of 6 bits to a shift amount of 11 bits continuing from FIG. 3 and K + M printing of the overlapped printing result. FIG. 5 is a diagram showing basic K printing from the top to the bottom, M printing from 12 bits to 14 bits shifted from FIG. 4, and K + M printing of the overlapped printing result. (a) is a diagram showing a list of the relationship between the deviation amount of M printing with respect to the basic K printing shown in FIGS. 3 to 5 and the toner density of K + M printing at that time, and (b) is a graph showing the relationship. FIG. (a) is a diagram showing the basic pattern length of K + M printing printed based on another M-sequence 15-bit number sequence, and (b) is a density measuring one pattern of K + M printing at a certain position in that case. It is a figure which shows the relationship between the visual field of a sensor, and the magnitude | size of 1 pattern. (a) is a diagram showing a state in which two identical K + M print patterns having a pattern length a are continuously printed, and (b) is a field of view (reading range) of a density sensor that measures the two continuous patterns. It is a figure which shows the relationship with two continuous patterns. FIG. 10 is a diagram (part 1) illustrating an example of another misregistration measurement pattern using the same pseudorandom numbers as in the first embodiment of the M series in the second embodiment. FIG. 12 is a diagram (part 2) illustrating an example of another misregistration measurement pattern using the same pseudo-random numbers as in the first embodiment of the M series in the second embodiment. FIG. 11 is a third diagram illustrating an example of another misregistration measurement pattern using the same pseudo-random numbers as in the first embodiment of the M series according to the second embodiment. (a) is a diagram showing a list of the relationship between the misregistration amount of M printing with respect to the basic K printing in Embodiment 2 and the toner density of K + M printing at that time, and (b) is a diagram showing the relationship as a graph. is there. It is FIG. (1) which shows an example of the further another position shift measurement pattern using the same pseudorandom numbers as Embodiment 1 of the M series in Embodiment 3. FIG. FIG. 12 is a diagram (part 2) illustrating an example of still another misregistration measurement pattern using the same pseudo-random numbers as in the first embodiment of the M series in the third embodiment. FIG. 11 is a diagram (part 3) illustrating an example of still another misregistration measurement pattern using the same pseudo-random numbers as in the first embodiment of the M series in the third embodiment. (a) is a diagram showing a list of the relationship between the misregistration amount of M printing with respect to the basic K printing in Embodiment 3 and the toner density of K + M printing at that time, and (b) is a diagram showing the relationship as a graph. is there.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Printer 2 Image formation part 3 Intermediate transfer belt unit 4 Paper feed part 5 Duplex printing conveyance unit 6 (6M, 6C, 6Y, 6K) Image formation unit 7 (7m, 7c, 7y, 7k) Photosensitive drum 8 Cleaner 9 Charging roller 11 Optical writing head 12 Developer 13 Developing roller 14 Transfer belt 15 Drive roller 16 Driven roller 17 Belt position control mechanism 18 Primary transfer roller 19 Waste toner collection container 20 Concentration sensor 20-1 Field of view (reading range)
DESCRIPTION OF SYMBOLS 21 Paper feeding cassette 22 Paper taking-out roller 23 Feeding roller 24 Rolling roller 25 Standby conveyance roller pair 26 Secondary transfer roller 27 Belt type heat fixing device 28 Unloading roller pair 29 Paper discharge tray 31 Paper discharge roller pair 32a Start return path 32b Intermediate Return path 32c End return path 33a, 33b, 33c, 33d Return roller pair 35 Cleaning unit 36 Capture roller 37 Press roller 40 CPU (central processing unit)
41 Interface controller (I / F_CONT)
42 Printer Controller (PR_CONT)
43 Printer printing section 44 ROM (read only memory)
45 EEPROM (electrically erasable programable ROM)
46 Operation panel 47 Sensor section 48 Frame memory 51 K printing (pattern printing with black toner)
52 M printing (pattern printing with magenta toner)
53 Number sequence 54 K + M printing (overprinting of black toner and magenta toner)
55 Number sequence for K + M printing 56 Number sequence for swapping 1 and 0 57 M printing 58 K + M printing 59 Number sequence for K + M printing 61 M printing 62 K + M printing

Claims (5)

A transfer belt that circulates between at least two rollers, a driving roller and a driven roller, and a transfer belt that is detachably attached to the main body of the apparatus and that is disposed along the outer peripheral surface of the transfer belt. An electrophotographic color image forming apparatus that collectively transfers different color toner images formed on the transfer belt by the plurality of image forming units onto a sheet. And
An alignment pattern generating means for generating an alignment pattern consisting of a pseudo-random periodic dot line pattern;
An alignment pattern transfer means for converting the alignment pattern generated by the alignment pattern generating means into a toner image and transferring the toner image onto the transfer belt;
Toner density measuring means for measuring the density of the alignment pattern transferred to the transfer belt by the alignment pattern transfer means;
A positional deviation amount determining means for determining a deviation amount of the image forming position based on a measurement result by the toner density measuring means;
A color image forming apparatus comprising: The alignment pattern transfer means transfers one reference color pattern of the one pattern to the transfer belt as many as the number of dots forming the one period, with one period of the alignment pattern as one pattern, The pattern for alignment of the color to be aligned with respect to the reference color is transferred to the position shifted by one dot for each pattern of the reference color,
The toner density measuring means measures the toner density of each pattern for one cycle in which the reference color and the color to be aligned with the reference color are transferred in an overlapping manner. The measurement result is output as the density average value of the one pattern,
The misregistration amount determination means is a pattern in which the transfer position of one pattern in which the average density value output from the toner density measurement means is maximum or minimum is transferred from the first pattern at the start of transfer. Determining the amount of misalignment depending on whether
The color image forming apparatus according to claim 1.   The color image recording apparatus according to claim 1, wherein the pseudo-random number is an M-sequence pseudo-random number. A belt that is circulated and moved over at least two rollers, a driving roller and a driven roller, and a plurality of toner image forming units that are detachably attached to the apparatus main body and are disposed along the outer peripheral surface of the belt; And an image forming position adjusting method in an electrophotographic image forming apparatus that sequentially forms toner images directly on the belt or on paper conveyed by the belt by the plurality of toner image forming units. There,
An alignment pattern generating step for generating an alignment pattern consisting of a pseudo-random periodic dot line pattern;
An alignment pattern transfer step of converting the alignment pattern generated in the alignment pattern generation step into a toner image and transferring the toner image onto the belt;
A toner concentration measurement step for measuring the concentration of the alignment pattern transferred to the belt by the alignment pattern transfer step;
A positional deviation amount determining step of determining a deviation amount of the image forming position based on the measurement result of the toner density measuring step;
Have
In the alignment pattern transfer step, one cycle of the alignment pattern is defined as one pattern, and the reference color pattern of the one pattern is transferred to the belt at least as many as the number of dots forming the one cycle. Transferring the alignment pattern of the color to be aligned with respect to the reference color, overlaid at a position shifted by one dot for each pattern of the color,
The toner density measurement step measures the toner density for each pattern for one cycle in which the reference color and the color to be aligned with respect to the reference color are transferred, and determines the toner density of one pattern. The measurement result is output as the density average value of the one pattern,
In the misregistration amount determination step, the transfer position of one pattern in which the average density value output from the toner concentration measurement step indicates the maximum or minimum is one pattern from which the first transfer start pattern is transferred. Determining the amount of misalignment depending on whether
And an image forming position adjusting method.   5. The image forming position adjusting method according to claim 4, wherein the pseudo random number is an M-sequence pseudo random number.