JP2009139644A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain an image of high quality while restraining a regulation time dedicated to shift correction to the minimum. <P>SOLUTION: An interval t1 is a temperature interval for executing color shift correction (the first mode), an interval t2 is a temperature interval for executing color shift correction (the second mode), referring to a table, and the t1>t2. The table is corrected by the t2 until a temperature from the last color shift correction reaches the interval t1. That is, a temperature inside the apparatus is monitored by a temperature sensor, a color shift amount is detected therein, and the color shift correction is executed based on the detected color shift amount (S102), when a temperature difference with respect to that in the last correction control exceeds the preset temperature difference t1 or more (S101-Y). A correction value is drawn out referring to the table (S104), based on a temperature detected by the temperature sensor, when the temperature difference with respect to the temperature in the last correction is t2 or more (S103). Then, the shift amount at a current time point is multiplied with the correction value drawn out in the step S104 (S105), to correct a shift. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an image forming apparatus that forms an image by superimposing a plurality of colors, and more particularly to an image forming apparatus such as a printer, a copier, or a fax machine having an engine that writes an image for each color using a light beam writing system. .

  In a so-called tandem type color image forming apparatus that transfers a plurality of image forming devices side by side, conventionally, in main scanning, logic control in units of pixels (dots), that is, the shift amount is changed to dot units, and writing is started according to the shift amount. The position was adjusted by increasing / decreasing the number of dots at the position, and each color was adjusted from the amount of deviation from the image of other colors, so that the accuracy could be adjusted to 1 dot or less. In addition, sub-scanning also performs logic control in units of pixels (lines), that is, shifts the shift amount to line units, finely adjusts the position by increasing or decreasing the number of lines at the position to start writing according to the shift amount, and images of other colors By adjusting each color based on the amount of deviation, the accuracy of one line or less could be achieved.

  However, even if the amount of deviation is adjusted at the time of shipment from the factory and adjusted to a state where there is no deviation, there is expansion and contraction for each part with respect to environmental changes such as temperature and humidity. The position is not aligned and a phenomenon called color shift occurs.

  Conventionally, in response to such environmental changes, a mechanism called color misregistration correction control has been used to form a predetermined pattern mainly on the transport belt (intermediate transfer belt) or transfer paper, and to determine the amount of misregistration for each color on the pattern. By measuring and correcting, the dot formation positions of the respective colors were matched, and a good image without deviation was obtained.

As a known example for performing such correction, for example, the invention described in Patent Document 1 is known. The present invention includes an endless belt and a plurality of support rotators on which the belt is stretched, and two of the support rotators have different diameter change rates per unit temperature change. The temperature change of the roller is calculated from the amount of rotation of the second rotating body (speed detection roller) relative to the amount of rotation of one rotating body, for example, the driving roller, or the amount of change in each rotational speed, and the rotation of the drive source of the endless belt The speed is controlled.
JP 2006-011253 A

  Color matching by such correction control has an effect that accuracy is high and image quality is kept constant, but a dedicated adjustment time is required, and the user cannot use it during that time. In order to avoid this, if the frequency of correction is reduced, color misregistration increases with environmental changes and the image deteriorates.

  The present invention has been made in view of the situation of the prior art, and the problem to be solved by the present invention is to obtain a high-quality image while minimizing the adjustment time dedicated to deviation correction. Is to be able to.

  In order to solve the above problems, the present invention measures in advance a color shift tendency due to an environmental change of the apparatus and forms a table, and a certain degree of environmental change is shifted using the table without forming a misregistration measurement pattern. It is characterized in that correction is performed by predicting the amount.

  Specifically, the first means includes an optical scanning means for optically scanning a light beam emitted from the light source via a plurality of imaging optical systems provided for each color, and a plurality of the light beams arranged for each color. An image forming unit that scans the image forming medium by the optical scanning unit to perform optical writing, forms an image of a different color for each image forming medium, and superimposes the color images to form a multi-color image; In the image forming apparatus having a misregistration amount correction unit that generates a misregistration measurement pattern for each color, measures misregistration between each color, calculates a correction misregistration amount from the measured misregistration amount, and corrects it. The amount of deviation obtained by measuring in advance the amount of deviation from the image color of other stages in response to environmental changes with respect to the reference color stage used as a reference when measuring the deviation between colors in the coupled optical system Deviation amount table storing data and the environment The deviation amount correction means generates a positional deviation measurement pattern for each color and performs the measurement, calculation, and correction in addition to the first mode for performing the measurement, calculation, and correction, and the deviation amount table. The second mode is characterized in that a shift amount corresponding to the detection result of the detection means is acquired from the shift amount table, and the shift amount is corrected based on the acquired shift amount.

  The second means is characterized in that, in the first means, the shift amount correction means increases the correction frequency for a color stage farther from the reference color in the second mode.

  The third means is characterized in that, in the first means, the shift amount correction means performs correction in order from a color stage far from the reference color in the second mode.

  The fourth means is characterized in that, in the first means, the deviation amount correction means moves in the correction direction larger than the correction amount acquired from the table at the time of correction in the second mode.

  A fifth means is the first means, wherein the deviation amount correction means executes deviation correction processing in the first mode in response to a constant environmental change, and with respect to an environmental change smaller than the constant environmental change. Performs the correction process in the second mode.

  In the embodiment described later, the light source is the LD unit 15, the imaging optical system is the writing optical unit 1 including the folding mirror 12, the polygon mirror 13 and the fθ lens 14, and the image forming medium is the photosensitive drums 2Y, 2M, 2C and 2K, the image forming means includes image forming elements such as the photosensitive drums 2Y, 2M, 2C, and 2K and the charging unit, the developing unit, the transfer unit, the cleaning unit, and the charge removing unit disposed on the outer periphery thereof. The shift amount correcting means is in the control unit 20 including the CPU, the detecting means is in the temperature sensor 8, the stage is in each image forming element for each color arranged on each photosensitive drum 2Y, 2M, 2C, 2K and the outer periphery thereof. The table corresponds to the code 21a.

  According to the present invention, a second mode is provided in which a deviation amount corresponding to the detection result of the detection unit is obtained from the deviation amount table with reference to the deviation amount table, and the deviation amount is corrected based on the obtained deviation amount. Therefore, it is possible to obtain a high-quality image while minimizing the adjustment time dedicated to deviation correction.

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

  FIG. 1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. In the figure, an image forming apparatus according to the present embodiment is an indirect transfer type tandem image forming apparatus 100, and includes a writing optical unit 1, an image forming unit 2, an intermediate transfer belt 3, a paper feeding system 4, a conveying system 5, and a fixing. The system basically includes a system 6, a position detection sensor 7, and a temperature detection sensor 8. The image forming unit 2 includes four photosensitive drums 2Y, 2M, 2C, and 2K that form images of each color of YMCK, and a charging unit, a developing unit, and an outer periphery of the photosensitive drums 2Y, 2M, 2C, and 2K. It consists of image forming elements such as a transfer unit, a cleaning unit, and a charge eliminating unit, and an image is written by irradiating laser light from the writing optical unit 1 between the charging unit and the developing unit, and a latent image for each color. Are formed on the photosensitive drums 2Y, 2M, 2C, and 2K.

  The formed latent image is developed with toner by the developing unit, visualized, and then primarily transferred to the transfer belt 6 by the transfer unit. At that time, each time the image passes through the YMCK photosensitive drum, the images of M, C, and K are sequentially superimposed on the Y color image, and when the four color images are superimposed, full color transfer is performed. It becomes a toner image. An image forming stage for each color is constituted by the photosensitive drums 2Y, 2M, 2C, 2K and image forming elements around each drum.

  The toner image on the transfer belt 3 is transferred by the secondary transfer roller 9 onto the paper that has been fed through the paper feed system 4 and the transport system 5 in time with the position of the secondary transfer roller 9. The sheet onto which the toner image has been transferred is sent to the fixing system 6 where it is fixed and discharged.

  FIG. 2 is a diagram showing the sub-scanning deviation amount detection pattern PN, and FIG. 3 is a diagram showing the relationship between the deviation in the sub-scanning direction and the distance. In FIG. 3, reference numeral 2 indicates an ideal position, and reference numerals 1 and 3 indicate positions when they are shifted in the − direction and the positive direction, respectively, and the difference from the position indicated by reference numeral 2 is the shift amount. Such a pattern PN is read by a transmission type optical sensor or a reflection type optical sensor, and the amount of deviation can be detected by relative comparison with a reference color (mainly Bk) from the detection timing.

  FIG. 4 is a diagram showing a main scanning deviation amount detection pattern PN, and FIG. 5 is a diagram showing a relation between deviation and distance on the main scanning side. In FIG. 5, reference numeral 2 indicates an ideal position, and reference numerals 1 and 3 indicate positions when shifted. Since it is difficult to detect the deviation in the main scanning direction directly, the sensor center passage position is determined based on the distance between the diagonal line and the horizontal line. These detection patterns PN are formed on the paper P or the intermediate transfer belt 3 as shown in FIG. 6, read by the position detection sensor (light sensor) 7, the amount of deviation is calculated by calculation processing, and the amount of correction is calculated from the amount of deviation. Calculate and correct. The control mode to be corrected in this way is the first mode.

  Since a technique for detecting and correcting a deviation amount based on such a pattern PN is well known, description of the calculation and correction of the deviation amount is omitted. FIG. 6 is a diagram showing the relationship between the position detection sensor 7 and the pattern PN.

  FIG. 7 is a plan view showing a schematic configuration of the writing optical unit 1, and FIG. 8 is a front view showing the relationship between the writing optical unit 1 and the photosensitive drums 2Y, 2M, 2C, 2K. In the writing optical unit 1 according to the present embodiment, an imaging lens group 14 including an fθ lens is symmetrically arranged around one polygon mirror 13 that is rotationally driven at high speed by a polygon motor 13a, and four lasers corresponding to the respective colors. Laser light is guided to the polygon mirror 13 by the folding mirror 12 by the light source 15, and image data is written on the surfaces of the four photosensitive drums 2Y, 2M, 2C, and 2K through an optical system that is bilaterally symmetrically distributed. It has become. Further, a synchronization detection sensor 11 is provided for setting the laser beam writing start timing at a position upstream of the polygon mirror 13 in the scanning direction and not interfering with the writing positions of the photosensitive drums 2Y, 2M, 2C, and 2K. ing.

  In an image forming apparatus having such a writing system, when the entire optical system extends with temperature, the writing optical unit 1 is fixed to the image forming apparatus main body at both ends in the longitudinal direction. 9, the center portion is bent as shown by a one-dot chain line, and distortion occurs. As shown in FIG. 9, for example, when bent downward, the emitting direction of the laser light emitted from the writing optical unit 1 to the photosensitive drums 2Y, 2M, 2C, and 2K changes according to the bending, so the photosensitive drum 2Y. , 2M, 2C, and 2K irradiation positions themselves are shifted. In the example of FIG. 9, the yellow and magenta photosensitive drums 2Y and 2M are rotated downstream in the drum rotation direction (Ry → Ry ′, Rm → Rm ′), and the cyan and black photosensitive drums 2C and 2K are rotated. The irradiation position is shifted to the upstream side in the direction (Rc → Rc ′, Rk → Rk ′) (one-dot chain line in the figure). Therefore, when this is transferred to the paper P or the intermediate transfer belt 3, yellow and magenta are transported downstream in the transport direction (Gy → Gy ′, Gm → Gm ′) from the ideal position, and cyan and black are transported upstream in the transport direction. This shifts to the side (Gc → Gc ′, Gk → Gk ′) (one-dot chain line in the figure), and color misregistration occurs when four color images are superimposed.

  As shown in FIG. 9, in the case of a deviation caused by the optical system, the greater the distance from the center, the greater the distortion, and the deviation amount increases. Since the time from writing to the photosensitive drums 2Y, 2M, 2C, 2K and the transfer belt 3 changes, color misregistration occurs between a plurality of image forming stages. Although depending on the shape, as shown in FIG.

  That is, in this type of image forming apparatus, the photosensitive member irradiation position shift caused by the thermal expansion of the optical system constituent member due to the temperature change appears as a color shift as shown in FIG. This deviation amount has characteristics as shown in FIG. This characteristic is constant because the material of the optical system constituent member is determined, and since it is constant, the color shift amount with respect to the temperature change amount can be predicted from this characteristic diagram. When such characteristics are tabulated for each member, changes in the apparatus temperature and the color misregistration amount can be converted into numerical values to some extent. Then, it is possible to correct the shift amount using the digitized result. The control mode in which correction is performed using the tabulated correction value without writing a correction pattern in this way is the second mode in the present invention. In FIG. 11 to each characteristic diagram described later, the one-dot chain line indicates the deviation amount on the photosensitive drum 2Y, the solid line indicates the deviation amount on the photosensitive drum 2K, and the broken line indicates the deviation amount on the photosensitive drum 2M. Indicates the amount of deviation due to the photosensitive drum 2C.

  FIG. 12 is a block diagram illustrating a control configuration for correcting the shift amount. In this figure, in this control configuration, the control unit 20 stores a position detection sensor 7 for reading the detection pattern PN, a writing optical unit 1, an image forming unit 2, and the table information. The unit 21 and the temperature sensor 8 for measuring the temperature in the apparatus are connected to each other, and a system centered on the control unit 20 is configured. The control unit includes a CPU, a ROM, and a RAM. The CPU reads a program code stored in the ROM, expands the program code in the RAM, and uses the RAM as a work area to write control and misalignment correction control according to the program code. Execute. The storage unit 21 includes a table 21a used by the CPU.

  FIG. 13 is a flowchart showing a control procedure for color misregistration correction. In this flowchart, t1 is a temperature interval for performing color misregistration correction, t2 is a temperature interval for performing correction with reference to the table 21a, and t1> t2. Table correction is performed at t2 until the temperature from the previous color misregistration correction reaches the interval t1.

  That is, the temperature in the apparatus is monitored by the temperature sensor 8 and when the temperature difference from the previous color misregistration correction control is equal to or greater than the preset temperature difference t1 (step S101-Y), the color misregistration amount is detected and detected. Color misregistration correction is executed based on the amount of misregistration (step S102). When the temperature difference becomes t2 or more with respect to the temperature at the previous correction (step S103), the correction value is derived by referring to the table 21a based on the temperature detected by the temperature sensor 8 (step S104). Next, the correction value derived in step S104 is added to the current shift amount (step S105) to correct the shift.

  By performing processing in this way, correction can be performed without the need to form a pattern in order to perform color misregistration correction. This control procedure is a typical correction control procedure in the second mode.

  The positional shift is caused not only by the temperature change but also by a change in the thickness of the intermediate transfer belt 3 due to humidity, for example. That is, when the belt thickness of the intermediate transfer belt 3 changes mainly due to the influence of humidity, the effective radius with respect to the roller 10 changes, so that the surface linear velocity changes. 14 and 15 are diagrams showing a roller portion of the intermediate transfer belt 3. As can be seen from the figure, the position of the intermediate transfer belt 3 changes at the same distance L on the belt surface due to the change in the thickness of the intermediate transfer belt 3. 14 and 15, when the starting point is P30, the point of the distance L is P31 in the thick intermediate transfer belt 31 shown in FIG. 14, but the same distance L in the thin intermediate transfer belt 32 shown in FIG. The point becomes P32, and there is a difference of distance by | P32−P31 |. For this reason, in the thick intermediate transfer belt 31 in FIG. 14 and the thin intermediate transfer belt 32 in FIG. 15, a difference in writing speed occurs due to the difference in linear velocity at the image forming stage at the end, and the color on the intermediate transfer belt 3. Deviation occurs. In FIG. 16, reference symbols Gk1, Gc1, Gm1, and Gy1 represent images before the environmental change, and Gk1 ', Gc1', Gm1 ', and Gy1' represent the same image after the environmental change. Since the time to reach the same point on the intermediate transfer belt 3 varies depending on the change in belt thickness, the deviation becomes larger in the order of the image forming stages. FIG. 17 shows the amount of deviation in the graph. It can be seen from FIG. 17 that the deviation increases in accordance with the environmental change in the order of the photosensitive drums (image forming stages) 2K, 2C, 2M, and 2Y.

  The characteristics shown in FIG. 11 and FIG. 17 include a method of measuring in advance in a factory or a laboratory and making a table, a method of storing machine color matching control results in accordance with the environment, and making a table. Yes, either can be controlled.

  As can be seen from the characteristics of FIG. 11 and FIG. 17, when the reference is the end, the other end tends to increase, and when the reference is near the middle, both ends tend to increase in the amount of correction. The shift can be made inconspicuous by correcting the shift by increasing. At that time, the image forming stage away from the reference may be prepared in advance by taking detailed steps for environmental changes. FIG. 18 is a flowchart illustrating a simple control procedure when color misregistration correction is performed with reference to a table. In this control procedure, the optical system is corrected using a table based on the monitoring result of the temperature monitor. Specifically, the internal temperature of the apparatus is monitored by the temperature sensor 8, and when the temperature difference from the previous monitoring is larger than t (step S201-Y), a correction value corresponding to the current temperature is derived from the table 21a (step S201). In step S202, the correction value derived from the table 21a is added to the current deviation amount (step S203), and the deviation is corrected. In the flowchart of FIG. 18, the shift amount is corrected based on the detected current temperature. However, humidity can be used as a parameter for environmental change. Also in this case, the color misregistration is corrected according to the procedure shown in the flowchart of FIG. 18 by referring to the table storing the correction value corresponding to the humidity.

  As mentioned before, it can be seen from the characteristics of FIGS. 11 and 17 that the shift amount tends to increase as the image forming stage moves away from the reference position. Therefore, correction is performed from the image forming stage on the side away from the reference position. As a result, the image forming stage that has not yet been corrected can be regarded as having a smaller amount of deviation from the reference position than the image forming stage that has already been corrected, so that the total amount of deviation can be reduced.

  FIG. 19 is a diagram showing an example of the correction frequency for the characteristics shown in FIG. By increasing the correction frequency as the distance from the reference increases and decreasing the correction frequency as much as possible, the deviation amount can be averaged, and the correction frequency itself can be lowered. FIG. 20 is a diagram showing a result of correction according to the frequency of FIG. Here, for example, the regulation value of the deviation amount is set to 20 μm. The frequency shown in FIG. 19 and FIG. 20 is equivalent to the frequency set so as to correct within a range in which the deviation does not become larger than the regulation value when the regulation value of the deviation amount is set.

  That is, when the regulation value for the deviation amount is set, if the deviation is corrected before the deviation becomes larger than the regulation value, the deviation amount is always kept within the regulation value. Therefore, it can be seen that the correction frequency may be set according to the regulation value and the amount of deviation. Conversely, it can be seen from the respective correction steps in the image forming stages of the respective colors shown in FIG. 19 that the correction interval with the environmental temperature as a parameter can be made larger as the deviation amount is smaller.

  When the correction using the correction table (second mode) is executed in accordance with the regulation value of the deviation amount, the deviation amount according to the environmental change without entering the color matching control mode (first mode). Thus, the deviation amount can be prevented from becoming larger than the regulation value of the deviation amount.

  When the environment and the deviation amount are in a proportional relationship or a simple increase phenomenon tendency as in the characteristics shown in FIGS. 11 and 17, the deviation direction when the change further increases with respect to the environment change unit to be corrected. Since it coincides with the correction direction, the correction can be made inconspicuous even if there is a further change by correcting the correction value to be larger than the correction value. FIG. 21 shows an example in which the correction interval is increased and the correction frequency is lowered by adding a larger correction (correcting larger than the regulation value of the deviation amount) to the correction method of FIG. That is, in this embodiment, as can be seen from FIG. 21, the deviation characteristic tends to increase monotonously with respect to the temperature. As a result, it takes a long time to reach the limit shift amount (shift amount that needs to be corrected), and the correction frequency can be lowered. In the figure, the width of the correction step is widened. In actual control, in the case of FIG. 21 with respect to the correction pattern of FIG. 20, the correction pattern of FIG. 21 is changed by putting a larger value in the table showing the relationship between the temperature difference and the correction amount shown in FIG. Can be executed.

  In addition, when correction is performed in a certain unit of environmental change, if it is attempted to perform a large movement control as shown in FIG. 21, if the correction interval is 1 time, the same interval is obtained, and the deviation amount is also 1 time (equal magnification). ) If the correction interval is doubled, the amount of deviation will also be doubled, but since it is shifted with an offset opposite to the correction direction, the actual amount of deviation is the same as one time (the same distance in the minus direction is shifted) To be). Therefore, in the case of large movement as described above, the range shown in FIG. 23, that is, the correction interval is set to a value larger than one correction and smaller than two corrections. FIG. 24 shows an operation when the correction range (regulation value) is moved twice, that is, to the same amount as the regulation value in the positive direction. The interval between corrections widens and the frequency decreases. However, since each color is shifted positively and negatively, the direction of the variation is easily noticeable.

  Further, when correction is performed during continuous sheet passing, if the remaining number is small, the output ends before returning to 0 if it is greatly shifted. With such an operation method, the result is different from the original aim of ending in the opposite direction without converging at the end point. Therefore, when the remaining number is small, it is better to move it small and move it back to near zero at the end.

  FIG. 25 is a flowchart showing an example of a control procedure when the correction shown in FIG. 23 is performed. In this control procedure, it is determined whether the correction is to be moved larger or smaller depending on whether the remaining number is larger or smaller than N. Further, the movement of the correction value is changed to x1.6 and x1.1 with respect to the correction M. Here, when the correction value is M × 1.0, the correction method returns to 0.

  In FIG. 25, the temperature in the apparatus is monitored by the temperature sensor 8, and when the temperature difference becomes larger than t by the previous monitoring (step S301-Y), a correction value M corresponding to the current temperature is derived from the table (step S302). ), The remaining number of sheets when continuously passing is checked (step S303). When the remaining number is N or more, the correction value M acquired at step S302 is multiplied by 1.6 (step S304), and when it is less than N, 1 is set. .Times.1 (step S305), and the correction amount multiplied by 1.6 or 1.1 is added to the current deviation amount (step S306). That is, by applying a value larger than 1.0, correction in the minus direction is applied, and by further increasing this coefficient, the value is moved greatly in the minus direction. In the example, when N is exceeded, it is moved by 1.6 times, that is, 0.6 times the current value in the minus direction, and when it is smaller than N, it is moved 0.1 times in the minus direction.

  In the control described so far, the characteristics of each component are tabulated, and the correction values tabulated are used. Since the component characteristics do not vary greatly, it is possible to correct to some extent by averaging the characteristics of each component and incorporating them into the device, but in the case of replacement parts, a part side table is included in advance, If the values in the table are set in the apparatus at the time of replacement, it is possible to perform corrections that match the characteristics of the parts. The table value set includes a tabular paper with characteristic values as shown in FIG. 22 and is configured such that the user or service person inputs a correction value, or a card type storage. A medium such as a medium can be bundled and loaded into a RAM or the like of the apparatus main body. In addition, preparing multiple tables for parts that deteriorate in advance and enabling them to be used by inputting or loading them, or rewriting the tables according to the time of use, suits the actual characteristics. Can be replaced with a table. As a result, the correction accuracy can be further increased.

  In addition, when the environmental temperature of the apparatus changes suddenly, each unit and part cannot keep up with the rapid temperature change, so that a gap appears between the value in the correction table and the deviation amount due to the actual part. Therefore, a temperature gradient with time as a parameter is calculated, and when a sudden change is detected, a value smaller than the original correction value is corrected. For this small value, the coefficient is different for each part. FIG. 26 is a flowchart showing the control procedure at this time.

In FIG. 26, the temperature in the apparatus is monitored by the temperature sensor 23, and when the temperature difference becomes larger than t by the previous monitoring (step S401-Y), a correction value M corresponding to the current temperature is derived from the table (step S402). Further, the previous temperature ta1 and the current temperature ta2 are acquired, and the previous measurement time ti1 and the current measurement time ti2 are acquired (step S403). Next, the temperature change with respect to time is calculated as a gradient and compared with a preset threshold value R. That is,
| (Ta1-ta2) / (ti1-ti2) | <R (1)
Is determined (step S404). If the expression (1) is determined as a result of this determination, the correction value M is used as it is (step S405). If the expression (1) is negative, the correction value is multiplied by 0.5 (step S406). The correction value is corrected with the correction value as it is or by adding a value obtained by multiplying the correction value by 0.5.

  That is, in this control, the value of the gradient calculation | (ta1-ta2) / (ti1-ti2) | is compared with a predetermined threshold value R, and the process is changed according to the magnitude relationship. Although it depends on the parts, in this example, when the threshold value R is exceeded, the correction is halved by multiplying 0.5. Thus, when a sudden temperature change occurs, the correction value is halved and no rapid correction is performed.

  Also, without calculating the temperature change as a gradient in step S404, for example, when the temperature change for a predetermined time exceeds twice the previous change, the correction value is multiplied by 0.5, and after that, it is corrected as it is. You can also apply a value.

As described above, according to this embodiment,
1) Since corrections can be made in accordance with small environmental fluctuations (temperature fluctuations, humidity fluctuations), it is possible to make the deviation inconspicuous with respect to successive fluctuations and obtain a high-quality image.
2) There is no wasted time during normal use.
3) The precision can always be kept fine even when out of the fine adjustment range.
4) The correction frequency can be lowered without lowering the image quality, thereby reducing the CPU load.
5) Correction can be made without degrading the image quality.
6) A correction difference due to deterioration or replacement of parts can be absorbed, and correction accuracy can be improved. 7) Since corrections can be made according to fine environmental fluctuations, it is possible to make the shift inconspicuous with respect to successive fluctuations outside the color shift correction and to obtain a high-quality image.
8) It becomes possible to absorb the correction difference due to the deterioration or replacement of the parts, and the correction accuracy can be improved.
9) The frequency of time-consuming color misregistration correction control can be reduced, and downtime can be reduced.
There are effects such as.

1 is a diagram illustrating a schematic configuration of an image forming apparatus according to an embodiment of the present invention. It is a figure which shows the pattern for sub-scanning deviation amount detection. It is a figure which shows the relationship between the shift | offset | difference of a subscanning direction, and distance. It is a figure which shows the pattern for main scanning deviation | shift amount detection. It is a figure which shows the relationship between the shift | offset | difference on the main scanning side, and distance. It is a figure which shows the relationship between a position detection sensor and a pattern. It is a top view which shows schematic structure of a writing optical unit. It is a front view showing the relationship between the writing optical unit and the photosensitive drum of each color. It is a figure which shows the state of a laser beam when a writing optical unit bends by temperature rise. It is a figure which shows the state of the image corresponding to the state of FIG. It is a figure which shows the temperature-position shift amount characteristic in the state of FIG.9 and FIG.10. It is a block diagram which shows the control structure for correct | amending deviation | shift amount. It is a flowchart which shows the control procedure of color misregistration correction. It is a figure which shows the roller part of a thick intermediate transfer belt. It is a figure which shows the roller part of a thin intermediate transfer belt. FIG. 6 is a diagram illustrating image misregistration between a thick intermediate transfer belt and a thin intermediate transfer belt. FIG. 17 is a diagram showing the deviation of FIG. 16 in a graph. It is a flowchart which shows the simple control procedure when color misregistration correction is performed with reference to a table. It is a figure which shows the example of the correction frequency with respect to the characteristic of FIG. It is a figure which shows the result corrected according to the frequency of FIG. FIG. 21 is a diagram illustrating an example in which the correction interval is increased and the correction frequency is decreased with respect to the correction method of FIG. 20. It is a figure which shows an example of the table which shows the relationship between a temperature difference and correction amount. It is a figure which shows the example which makes a correction interval a value larger than 1 correction | amendment and smaller than 2 correction | amendments when enlarging a correction | amendment interval. It is a figure which shows operation | movement at the time of moving a correction range to the same amount as the regulation value of the positive direction twice. It is a flowchart which shows an example of the control procedure in the case of performing correction | amendment shown in FIG. It is a flowchart which shows the control procedure when the temperature gradient which uses time as a parameter is calculated and a sudden change is detected.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Writing optical unit 2 Image formation part 2Y, 2M, 2C, 2K Photosensitive drum 7 Position detection sensor 8 Temperature sensor 12 Folding mirror 13 Polygon mirror 14 f (theta) lens 15 LD unit 21a Table

Claims (5)

Optical scanning means for optically scanning a light beam emitted from a light source through a plurality of imaging optical systems provided for each color;
A plurality of image forming media arranged for each color are scanned by the optical scanning means and optical writing is performed, images of different colors are formed for each image forming medium, and each color image is superimposed to obtain a plurality of color images. Image forming means for forming
A misregistration correction means for generating a misregistration measurement pattern for each color, measuring a misregistration between each color, calculating a correction misregistration amount from the measured misregistration amount, and correcting it;
In an image forming apparatus having
Of the plurality of coupled optical systems, it is obtained by measuring in advance the amount of deviation from the image color of another stage corresponding to the environmental change with respect to a reference color stage serving as a reference when measuring the deviation between the colors. Deviation amount table storing deviation amount data;
Detecting means for detecting the environmental change;
With
The deviation correction means is
A first mode for generating a positional deviation measurement pattern for each color and performing the measurement, calculation, and correction;
A second mode for referring to the deviation amount table, obtaining a deviation amount corresponding to the detection result of the detection means from the deviation amount table, and correcting the deviation amount based on the obtained deviation amount;
An image forming apparatus comprising: The image forming apparatus according to claim 1.
In the second mode, the shift amount correction unit increases the correction frequency for a color stage that is farther from the reference color. The image forming apparatus according to claim 1.
In the second mode, the shift amount correction unit performs correction in order from a color stage far from the reference color. The image forming apparatus according to claim 1.
In the second mode, the deviation amount correcting unit moves in the correction direction larger than the correction amount acquired from the table at the time of correction. The image forming apparatus according to claim 1.
The deviation amount correction means executes the deviation correction process in the first mode according to a constant environmental change, and executes the correction process in the second mode for an environmental change smaller than the constant environmental change. An image forming apparatus.

Images