JP7242226B2 - image forming device - Google Patents

Description

The present invention relates to an image forming apparatus capable of forming a color image by superimposing a plurality of different color images.

An electrophotographic image forming apparatus forms an image on a sheet by performing respective steps of charging, exposure, development, transfer, and fixing. Charging is a process of uniformly charging the surface of the photoreceptor with a charger. Exposure is the process of emitting a light beam from a laser scanner onto a charged photoreceptor to form a latent image on the photoreceptor. Development is a process of visualizing a latent image with a developer such as toner to form a toner image on a photoreceptor. Transfer is a process of transferring a toner image onto a sheet directly from the photoreceptor or from the photoreceptor via an intermediate transfer member. Fixing is a process of fixing the image (toner image) to the sheet by heating and pressing the sheet to which the toner image has been transferred. The product is completed by fixing the image on the sheet.

A laser scanner includes a light source, a rotating polygon mirror that deflects a light beam output from the light source, and an optical system such as lenses and mirrors that guides the light beam deflected by the rotating polygon mirror to a photosensitive member. A light source, a rotating polygon mirror, and an optical system are housed in one housing. When the temperature inside the image forming apparatus changes, the housing of the laser scanner thermally expands. In addition, due to the anisotropy of the heat distribution inside the housing of the laser scanner and the glass filler contained in the material of the housing, complicated thermal expansion deformation occurs inside the housing, causing the position of the optical system such as lenses and mirrors to fluctuate. I have something to do. This affects the irradiation position of the light beam that scans the photoreceptor, causing the image forming position to shift. A phenomenon in which the color tone of a product changes due to a shift in the image forming position of each color is called color misregistration. If color misregistration occurs, the quality of the product is significantly degraded.

The image forming apparatus performs color misregistration correction to correct color misregistration. Color misregistration correction is performed based on a detection image for detecting color misregistration formed on the intermediate transfer member at a predetermined timing. The image forming apparatus calculates the amount of color misregistration based on the result of detection of the detection image by the color misregistration detection sensor. The image forming apparatus corrects the color shift by correcting the image forming position based on the calculated amount of color shift. It should be noted that, in the image forming apparatus, performing color misregistration correction causes downtime and lowers productivity.

On the other hand, Japanese Patent Application Laid-Open No. 2002-200001 proposes an image forming apparatus that performs color shift correction after image formation when the temperature change in the apparatus is small, and performs color shift correction before image formation when the temperature change in the apparatus is large. do. When the image forming process is performed intermittently, this image forming apparatus is likely to perform color misregistration correction after image formation. Therefore, the user is less likely to experience downtime during image formation than in the case where color shift correction is performed before image formation.

JP 2015-132643 A

Here, color shift correction is a phenomenon that changes the color tone of a color image. Therefore, for example, when an image is formed in a single black color, there is little need to perform color shift correction. However, the image forming apparatus described in Japanese Patent Application Laid-Open No. 2002-200000 corrects color misregistration in preparation for the next image formation even when forming a black monochrome image. In other words, since there is a possibility that a color image will be formed in the subsequent image forming process, the image forming apparatus described in Japanese Patent Application Laid-Open No. 2002-200001 corrects the color misregistration.

In the image forming apparatus described in Japanese Patent Laid-Open No. 2004-100000, color misregistration correction is performed even though monochrome image formation is frequently performed, so the life of component parts such as the developing device, photoreceptor, and intermediate transfer member does not need to last. can be shortened to

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to appropriately set conditions for executing color misregistration correction.

The image forming apparatus of the present invention comprises: a plurality of image forming means for forming images of different colors; an image carrier for carrying the images of respective colors formed by the plurality of image forming means; a transfer section for transferring from an image carrier to a sheet; a detection means for detecting a pattern for detecting color misregistration formed on the image carrier; a control means for forming a plurality of patterns including a pattern of a second color different from the second color, and causing the detection means to detect the plurality of patterns formed on the image carrier; and detection of the plurality of patterns by the detection means. correction means for correcting color misregistration of the images formed by the plurality of image forming means based on the result; The correction mode is determined to be the first mode when the ratio of the number of images formed in color to the total number of output sheets is lower than a predetermined threshold, and the correction mode is determined when the ratio is higher than the predetermined threshold. is the second mode , and the control means, when the determined correction mode is the first mode , is instructed to form a multi-color image and the temperature change amount of the machine interior temperature is greater than the predetermined first temperature difference If it is larger, it determines that the first execution condition is satisfied, causes the correction means to perform the color misregistration correction, and then causes the plurality of image forming means to perform image formation, and the determined correction mode is the second mode. In this case, it is determined that a second execution condition different from the first execution condition is satisfied if the temperature change amount of the machine interior temperature is greater than a predetermined second temperature difference, and image formation is performed by the plurality of image forming means. It is characterized in that the correcting means is caused to perform the color misregistration correction after the correction.

According to the present invention, it is possible to appropriately set the conditions for executing color misregistration correction.

1 is a configuration diagram of an image forming apparatus; FIG. Explanatory drawing of a controller. FIG. 10 is an explanatory diagram of color misregistration correction in the sub-scanning direction; 4A and 4B are explanatory diagrams of color misregistration correction in the main scanning direction; FIG. 4 is an exemplary diagram of a detection image for detecting color misregistration; 5 is a flowchart showing execution timing determination processing for color misregistration correction; 4 is a flowchart showing image forming processing including color misregistration correction. Explanatory drawing of an exposure device. FIG. 4 is an exemplary diagram of a selection screen; 4 is a flow chart showing processing at the time of the first image formation of the day. 5 is another flowchart showing image forming processing including color misregistration correction.

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the dimensions, materials, relative positions, and the like of the components of the image forming apparatus of this embodiment are not intended to limit the scope of the present invention unless otherwise specified. In addition, the parts with the same reference numerals in each figure have the same configuration or function, and overlapping descriptions thereof are omitted as appropriate.

(overall structure)
FIG. 1 is a configuration diagram of an image forming apparatus according to this embodiment. The image forming apparatus 1 is a full-color image forming apparatus realized by, for example, a copier, a printer, and a multifunction machine having facsimile functions. The image forming apparatus 1 includes a plurality of image forming sections 2a to 2d, an intermediate transfer unit 100, a fixing device 15, and a feeding mechanism for a sheet S on which an image is formed.

The image forming units 2a to 2d are provided in a number corresponding to the colors of images to be formed. In this embodiment, four image forming units 2a to 2d are provided to form yellow, magenta, cyan, and black images. The image forming section 2a forms a yellow image. The image forming section 2b forms a magenta image. The image forming section 2c forms a cyan image. The image forming section 2d forms a black image. An exposure unit 6, which is a laser scanner, is provided below the image forming units 2a to 2d. Each image forming section 2a to 2d has the same configuration. Here, the configuration of the image forming section 2a will be described.

The image forming section 2a is provided with a photosensitive drum 3a, a charging roller 5a, a developing device 7a, and a cleaner blade 4a. The photosensitive drum 3a is a drum-shaped photosensitive member. The photosensitive drum 3a rotates clockwise in the figure. The charging roller 5a uniformly charges the image-forming surface of the photosensitive drum 3a. An electrostatic latent image is formed on the surface of the photosensitive drum 3a, the surface of which is uniformly charged, as the exposure unit 6 scans the photosensitive drum 3a with a laser beam. The exposure device 6 irradiates the photosensitive drum 3a with a laser beam according to the yellow image signal. The exposure device 6 irradiates the photosensitive drums 3b to 3d of other colors with laser light according to the image signal corresponding to each color.

The developing device 7a develops the electrostatic latent image on the photosensitive drum 3a with yellow toner to form a yellow toner image on the photosensitive drum 3a. Similarly, the developing device 7b forms a magenta toner image on the photosensitive drum 3b with magenta toner. The developing device 7c forms a cyan toner image on the photosensitive drum 3c with cyan toner. The developing device 7d forms a black toner image on the photosensitive drum 3d with black toner.

The intermediate transfer unit 100 includes an intermediate transfer belt 103 that is an endless transfer body. The intermediate transfer belt 103 is stretched by a plurality of support rollers including the inner secondary transfer roller 102, and is rotatable counterclockwise in the figure. The photosensitive drums 3a to 3d of the image forming units 2a to 2d are arranged in the order of the photosensitive drum 3a, the photosensitive drum 3b, the photosensitive drum 3c, and the photosensitive drum 3d from upstream in the rotation direction of the intermediate transfer belt 103. FIG. Primary transfer rollers 101a to 101d are provided at positions facing the photosensitive drums 3a to 3d with the intermediate transfer belt 103 interposed therebetween. The toner images formed on the photosensitive drums 3a to 3d are transferred to the intermediate transfer belt 103 by applying a predetermined pressure and electrostatic load bias from the primary transfer rollers 101a to 101d. At this time, as the intermediate transfer belt 103 rotates, the toner images of the respective colors are sequentially transferred from the photosensitive drums 3a to 3d so as to overlap each other. Thus, the intermediate transfer belt 103 functions as an image carrier that carries toner images (images) formed by the image forming units 2a to 2d.

A secondary transfer outer roller 8 is provided at a position opposed to the secondary transfer inner roller 102 with the intermediate transfer belt 103 interposed therebetween. The secondary transfer outer roller 8 is rotatably supported by bearings at both ends. The secondary transfer outer roller 8 is elastically biased by an elastic member toward the intermediate transfer belt 103 via bearings. The inner secondary transfer roller 102 and the outer secondary transfer roller 8 constitute a secondary transfer portion Ts. The intermediate transfer belt 103 rotates to convey the transferred toner image to the secondary transfer portion Ts. A color misregistration detection sensor 200 is provided near the intermediate transfer belt 103 between the image forming section 2d and the secondary transfer section Ts.

The image forming apparatus 1 includes sheet feed cassettes 9a and 9b in which sheets S can be accommodated, and a manual feed tray 10 in which sheets S can be placed. A sheet S is fed to the image forming apparatus 1 from one of the sheet feed cassettes 9 a and 9 b and the manual feed tray 10 . The feeding mechanism for the sheet S is provided with feeding rollers 11 a , 11 b , 11 c , registration rollers 12 , and other conveying rollers. The paper feed roller 11a feeds the sheet S from the paper feed cassette 9a to the conveying path 14 . The paper feed roller 11b feeds the sheet S from the paper feed cassette 9b to the transport path 14. As shown in FIG. The paper feed roller 11 c feeds the sheet S from the manual feed tray 10 to the transport path 14 . The registration rollers 12 correct the skew of the fed sheet S. As shown in FIG. The registration roller 12 conveys the sheet S to the secondary transfer portion Ts via the pre-transfer guide 13 in accordance with the timing at which the intermediate transfer belt 103 conveys the toner image to the secondary transfer portion Ts.

The secondary transfer portion Ts transfers the four-color toner image on the intermediate transfer belt 103 to a predetermined pressure and electrostatic force at the secondary transfer nip portion formed by the secondary transfer outer roller 8 and the intermediate transfer belt 103 . The image is transferred to the sheet S by a load bias. The sheet S onto which the toner image has been transferred is conveyed from the secondary transfer portion Ts to the fixing device 15 . The fixing device 15 heats and presses the sheet S to fix the image on the sheet S. FIG. The sheet S on which the image is fixed is discharged onto one of discharge trays 160 and 161 .

The image forming apparatus 1 includes an in-machine temperature sensor 130 for detecting the inside of the apparatus (in-machine temperature). The image forming apparatus 1 includes an external temperature sensor 70 for detecting the temperature outside the apparatus (external temperature). The external temperature sensor 70 is arranged near a fan (not shown) for taking in air from the outside.

Such an image forming apparatus 1 has a color misregistration correction function for correcting color misregistration between a plurality of images of different colors. The color misregistration detection sensor 200 detects detection images of yellow, magenta, cyan, and black for color misregistration detection formed on the intermediate transfer belt 103 . The detection image is a toner mark made up of a toner image of each color. The color misregistration detection sensor 200 is located at a position where detection images of all four colors can be detected and the shape of the detection image is not destroyed by the roller pressure of the secondary transfer outer roller 8 of the secondary transfer portion Ts. Positioned to detect images.

(controller)
FIG. 2 is an explanatory diagram of a controller for controlling the operation of the image forming apparatus 1. As shown in FIG. The controller 600 includes a CPU (Central Processing Unit) 601 , a RAM (Random Access Memory) 603 , a memory 604 , an input IF 605 and an output IF 606 . The CPU 601 controls the overall operation of the image forming apparatus 1 by executing computer programs stored in the memory 604 using the RAM 603 as a work area.

The CPU 601 of this embodiment operates in at least two modes, a first mode and a second mode, as correction modes for executing color misregistration correction. The CPU 601 alternatively selects and executes one of the two types of correction modes. The first mode is a correction mode in which color misregistration correction is executed before image forming processing when a first execution condition is satisfied. The second mode is a correction mode in which color misregistration correction is executed after the image forming process when the second execution condition is satisfied.

The input IF 605 is an input interface to which the color shift detection sensor 200, the internal temperature sensor 130, and the external temperature sensor 70 are connected. The input IF 605 acquires detection results from the color misregistration detection sensor 200 , the internal temperature sensor 130 , and the external temperature sensor 70 and transmits them to the CPU 601 . An input device (not shown) is connected to the input IF 605 . The input device is, for example, a touch panel or various key buttons provided in the image forming apparatus 1 . The input IF 605 transmits instructions and the like from the input device to the CPU 601 .

The output IF 606 is an output interface, and transmits various signals to external devices according to instructions from the CPU 601 . The external device is, for example, a display provided in the image forming apparatus 1 . For example, the output IF 606 outputs a signal for displaying an image on the display according to an instruction from the CPU 601 .

The RAM 603 is provided with storage areas 607 and 609 to 611 in addition to being used as a work area as described above. A storage area 607 stores a color misregistration correction flag indicating the necessity of color misregistration correction. The necessity of color misregistration correction is determined, for example, based on the amount of temperature change in the internal temperature of the apparatus from the time of the previous color misregistration correction. A storage area 609 stores the detection result (pattern reading data) of the detection image formed on the intermediate transfer belt 103 by the color misregistration detection sensor 200 . A storage area 610 stores color shift amount data representing the amount of color shift detected from the pattern reading data. The amount of color misregistration is, for example, an amount representing the amount of misalignment from the reference of the formation position of the image of magenta, cyan, and black, with the formation position of the image of yellow as a reference. A region 611 stores color misregistration correction data calculated from the color misregistration amount data. When correcting the color shift, the write timing of the light beam by the exposure device 6 is corrected based on the amount of color shift.

The memory 604 is composed of a non-volatile memory, a HDD (Hard Disk Drive), etc., and has storage areas 623 to 629 in addition to the above computer programs. A memory area 623 stores the color misregistration correction execution timing that determines the timing for correcting the color misregistration. A storage area 624 stores execution conditions for color misregistration correction, such as temperature differences T1 and T2, which serve as criteria (threshold values) for color misregistration correction flags. A storage area 625 stores, as the previous temperature Tz, the result of detection by the internal temperature sensor 130 (machine internal temperature) at the time of the most recent color shift correction. A storage area 626 stores the accumulated number of sheets S output by image formation as the total number of output sheets P. FIG. A storage area 627 stores, as a color ratio C, the ratio of the number of sheets on which color images have been formed to the total number P of output sheets. A storage area 628 stores a color ratio determination condition Y, which is a threshold for determining whether the color ratio C is high or low. A storage area 629 stores an output number determination condition X, which is a threshold for determining the amount of the total output number P. FIG.

As the color ratio C stored in the storage area 627, in addition to the ratio to the total number of output sheets P, the following values can be used. For example, it is the ratio of instructions for color image formation, the ratio of the rotation times of the photosensitive drums 3a, 3b, and 3c corresponding to yellow, magenta, and cyan, and the ratio of color image formation as the printing tendency of the user.

The CPU 601 basically performs color misregistration correction in the same manner as in the conventional art. That is, the CPU 601 forms detection images for detecting color misregistration of each color on the intermediate transfer belt 103 by the image forming units 2a to 2d. The CPU 601 acquires the detection result (pattern reading data) of the detection image on the intermediate transfer belt 103 by the color shift detection sensor 200 . The CPU 601 acquires a correction value (color misregistration correction data) from the amount of color misregistration (color misregistration amount data) calculated from the detection result. The CPU 601 performs feedback control by, for example, correcting the write timing of the light beam by the exposure device 6 in accordance with the correction value during subsequent image formation. However, in the present embodiment, the execution timing (correction mode) of color misregistration correction is determined according to the color ratio C, unlike the conventional art.

(Description of color shift correction)
3, 4, and 5 are explanatory diagrams of color misregistration correction according to the present embodiment. In the following description, the direction in which the exposure device 6 scans the photosensitive drums 3a to 3d with a light beam is the main scanning direction, and the direction perpendicular to the main scanning direction is the sub-scanning direction. Note that the main scanning direction is a direction perpendicular to the direction in which the intermediate transfer belt 103 rotates (conveyance direction). The sub-scanning direction is the direction (conveyance direction) in which the intermediate transfer belt 103 rotates.

FIG. 3 is an explanatory diagram of color misregistration correction in the sub-scanning direction. The detection image for color misregistration detection in the sub-scanning direction includes a yellow correction pattern 501Y, a magenta correction pattern 501M, a cyan correction pattern 501C, and a black correction pattern 501K. The correction patterns 501Y, 501M, 501C, and 501K for each color are linear images extending in the main scanning direction. A yellow correction pattern 501Y, a magenta correction pattern 501M, a cyan correction pattern 501C, and a black correction pattern 501K are formed on the intermediate transfer belt 103 parallel to the main scanning direction and at predetermined intervals in the sub-scanning transverse direction. . The reference color for color shift correction is the yellow correction pattern 501Y. The four-color correction patterns 501Y, 501M, 501C, and 501K form one set of detection images for color misregistration detection in the sub-scanning direction.

The amount of color misregistration in the sub-scanning direction is measured as follows. Here, the amount of color misregistration in the sub-scanning direction for magenta will be described. The CPU 601 detects the centroid position of each of the correction patterns 501Y, 501M, 501C, and 501K from the detection result of the color shift detection sensor 200. FIG. YR1, MR1, CR1, and KR1 are the center positions of the respective correction patterns 501Y, 501M, 501C, and 501K when no color shift occurs.

When the exposure position in the sub-scanning direction changes due to thermal expansion of the exposing device 6 or the like, the magenta correction pattern 501M is shifted in the sub-scanning direction and formed at the position of the correction pattern 501M'. The center-of-gravity position of the magenta correction pattern 501M' is a position MR1' shifted from the position MR1. The amount of color shift in the sub-scanning direction of the magenta correction pattern 501M' with respect to the yellow correction pattern 501Y is expressed by the following formula.
Sub-scanning color shift amount=(MR1′−YR1)−(MR1−YR1)=MR1′−MR1

The CPU 601 uses the calculated amount of color shift in the sub-scanning direction as a correction value, and adjusts the image writing timing of the exposing device 6 to correct the color shift in the sub-scanning direction. Color misregistration correction in the sub-scanning direction is also performed in the same manner with reference to yellow, which is another color. Although yellow is used as the reference color here, other colors may be used as the reference color.

FIG. 4 is an explanatory diagram of color misregistration correction in the main scanning direction. The detection image for color misregistration detection in the main scanning direction includes yellow correction patterns 521Y and 522Y, magenta correction patterns 521M and 522M, cyan correction patterns 521C and 522C, and black correction patterns 521K and 522K. The correction patterns 521Y, 521M, 521C, and 521K of each color are linear images inclined at a predetermined angle θ with respect to the main scanning direction. The correction patterns 522Y, 522M, 522C, and 522K of each color are linear images inclined by a predetermined angle -θ with respect to the main scanning direction. The correction patterns 521Y, 521M, 521C, 521K and the correction patterns 522Y, 522M, 522C, 522K are formed with the same inclination in the opposite direction to the main scanning direction. A yellow correction pattern 521Y, a magenta correction pattern 521M, a cyan correction pattern 521C, and a black correction pattern 521K are formed in parallel on the intermediate transfer belt 103 at predetermined intervals in the sub-scanning direction. A yellow correction pattern 522Y, a magenta correction pattern 522M, a cyan correction pattern 522C, and a black correction pattern 522K are formed in parallel on the intermediate transfer belt 103 at predetermined intervals in the sub-scanning direction. The reference colors for color shift correction are yellow correction patterns 521Y and 522Y. The four-color correction patterns 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, and 522K form one set of detection images for color shift detection in the main scanning direction.

The amount of color misregistration in the main scanning direction is measured as follows. Here, the amount of color misregistration for magenta in the main scanning direction will be described. The amount of color shift in the main scanning direction is also measured based on the position of the center of gravity in the sub-scanning direction. The CPU 601 detects the centroid position of each correction pattern 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, 522K from the detection result of the color shift detection sensor 200. FIG. YR3, YR4, MR3, MR4, CR3, CR4, KR3, and KR4 are the center positions of the correction patterns 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, and 522K when no color shift occurs.

When the exposure position in the main scanning direction changes due to thermal expansion of the exposing device 6 or the like, the magenta correction patterns 521M and 522M are shifted in the main scanning direction and formed at the positions of the correction patterns 521M' and 522M'. The centroid positions of the magenta correction patterns 521M' and 522M' are at positions MR3' and MR4' shifted from the positions MR3 and MR4. The reading position of the color misregistration detection sensor 200 is indicated by a dotted line in the drawing. The amount of color misregistration in the sub-scanning direction of the magenta correction patterns 521M' and 522M' with respect to the yellow correction patterns 521Y and 522Y is geometrically the same, and is expressed by the following formula.
Sub-scanning color shift amount={(MR3'-YR3)-(MR4'-YR4)}/2

The CPU 601 converts the calculated amount of color shift in the sub-scanning direction into an amount of color shift in the main scanning direction using the angle θ at which the correction pattern is tilted with respect to the main scanning direction.
Main scanning color shift amount={(MR3'-YR3)-(MR4'-YR4)}/2 tan θ

The CPU 601 uses the calculated amount of color shift in the main scanning direction as a correction value, and adjusts the image writing timing of the exposing device 6 to correct the color shift in the main scanning direction. Color misregistration correction in the main scanning direction is also performed in the same manner with reference to yellow, which is another color. Although yellow is used as the reference color here, other colors may be used as the reference color.

FIG. 5 is an exemplary diagram of a detection image for color misregistration detection formed on the intermediate transfer belt 103 during actual color misregistration correction. In this embodiment, the detection image in FIG. 3 and the detection image in FIG. 4 are combined. In FIG. 5, six sets of detection images for detecting color misregistration in the sub-scanning direction and two sets of detection images for detecting color misregistration in the main scanning direction are combined. formed at both ends of the Note that the number of sets of each detection image and the order in which they are formed are not limited to this. Further, the shape of each correction pattern is not limited to those illustrated in FIGS. 3 and 4, and may be a vertical line, a cross line, a triangle, or the like.

(Execution timing of color misregistration correction)
FIG. 6 is a flow chart showing the execution timing determination process for correcting the color misregistration. The execution timing of color misregistration correction is determined using the total output number P, the output number determination condition X, the color ratio C, and the color ratio determination condition Y as conditions. The number-of-outputs determination condition X is set to 2000 sheets here. This generally corresponds to the number of sheets that the image forming apparatus 1 feeds in one month. The color ratio determination condition Y is set to 30% here as an example. The execution timing determination value determines the correction mode to be either the first mode or the second mode.

When the image forming apparatus 1 is activated, the CPU 601 waits for reception of a print signal instructing image formation (S101). A print signal is input from, for example, an input device or an external computer. Upon receiving the print signal, the CPU 601 executes image forming processing (S102). When the image forming process ends (S103), the CPU 601 confirms the total output number P at that time stored in the storage area 626 (S104). The CPU 601 compares the total output number P with the output number determination condition X (S105). When the total output number P is equal to or less than the output number determination condition X (S105: N), the CPU 601 determines that color shift correction is not necessary. In this case, the CPU 601 waits for reception of the next print signal.

When the total output number P is larger than the output number determination condition X (S105: Y), the CPU 601 determines that the number of sheets S on which the image forming process has been performed satisfies the conditions for color shift correction. In other words, the CPU 601 determines to perform color shift correction when the number of times (number of sheets) of image formation is greater than a predetermined number of sheets. The CPU 601 confirms the current color ratio C stored in the storage area 627 (S106). The CPU 601 compares the color ratio C with the color ratio determination condition Y (S107). The CPU 601 determines the correction mode according to the color ratio C. FIG.

When the color ratio C is less than the color ratio determination condition Y (S107: Y), the CPU 601 determines that the ratio of color image formation is lower than the determination condition as the printing tendency of the user. In this case, the CPU 601 determines the first mode in which the execution timing (correction mode) of color shift correction is set before image formation (S108). The CPU 601 stores in the storage area 623 that the execution timing of color misregistration correction has been determined to be the first mode.

If the color ratio C is equal to or greater than the color ratio determination condition Y (S107: N), the CPU 601 determines that the ratio of color image formation is higher than the determination condition as the printing tendency of the user. In this case, the CPU 601 determines the execution timing (correction mode) of color shift correction to be the second mode that is set after image formation (S109). The CPU 601 stores in the storage area 623 that the execution timing of the color misregistration correction is set to the second mode.

(Color shift correction processing)
FIG. 7 is a flow chart showing image forming processing including color misregistration correction. This process is performed under the conditions of temperature difference T1 (first temperature difference), temperature difference T2 (second temperature difference), color misregistration correction execution timing (correction mode), and color confirmation result of the print signal. The temperature differences T1 and T2 are set to 4° C. and 3° C., respectively, for example. However, the temperature differences T1 and T2 are not limited to the illustrated values regardless of the magnitude relationship.

When the image forming apparatus 1 is activated, the CPU 601 waits for reception of a print signal instructing image formation (S201). When the print signal is received, the CPU 601 confirms the color shift correction execution timing stored in the storage area 623 (S202). The CPU 601 determines whether or not the color misregistration correction execution timing is the first mode (S203).

If the color misregistration correction execution timing is the first mode (S203: Y), the CPU 601 confirms the color used for image formation instructed by the received print signal (S204). Here, the CPU 601 determines whether the print signal instructs color printing (image formation using a plurality of colors) or black single-color printing. If the print signal instructs black monochrome printing (S205: N), there is no need to perform color misregistration correction. Therefore, the CPU 601 performs image forming processing according to the print signal (S209).

When the print signal indicates color printing (S205: Y), the CPU 601 checks the previous temperature Tz stored in the storage area 625, which is the internal temperature detected by the internal temperature sensor 130 during the previous color shift correction. The CPU 601 checks the current temperature inside the machine from the detection result of the inside temperature sensor 130 . The CPU 601 calculates the temperature change amount ΔT, which is the difference between the previous temperature Tz and the current temperature inside the machine (S206). The CPU 601 compares the temperature change amount ΔT with the temperature difference T1 (S207).

When the temperature change amount ΔT is less than the temperature difference T1 (S207: N), the CPU 601 determines that there is no need to perform color misregistration correction, and performs image forming processing according to the print signal (S209). If the temperature change amount ΔT is equal to or greater than the temperature difference T1 (S207: Y), the CPU 601 performs color shift correction before performing image forming processing (S208). After correcting the color misregistration, the CPU 601 performs image forming processing according to the print signal (S209).

If the color misregistration correction execution timing is the second mode (S203: N), the CPU 601 calculates the temperature change amount ΔT, which is the difference between the previous temperature Tz and the current temperature inside the machine, by the same processing as that of S206. (S210). The CPU 601 compares the temperature change amount ΔT with the temperature difference T2 (S211).

When the temperature change amount ΔT is less than the temperature difference T2 (S211: N), the CPU 601 determines that there is no need to perform color misregistration correction, and performs image forming processing according to the print signal (S213). When the temperature change amount ΔT is equal to or greater than the temperature difference T2 (S211: Y), the CPU 601 performs image forming processing according to the print signal (S211). The CPU 601 performs color misregistration correction after the image forming process (S214).

Thus, the image forming process is completed. In the first mode, the CPU 601 executes color shift correction before image forming processing using the color used for image formation indicated by the print signal and the temperature change amount of the internal temperature as the first execution condition. In the case of the second mode, the CPU 601 uses the amount of temperature change in the internal temperature as the second execution condition and executes the color misregistration correction after the image forming process.

According to the processes of FIGS. 6 and 7, the color ratio determination condition Y is a threshold value for determining whether to perform color misregistration correction before or after image formation according to the printing tendency of the user. The number-of-sheets determination condition X is a threshold value for determining the print tendency of the user. The temperature differences T1 and T2 serve as thresholds for determining execution of the color misregistration correction itself.

When the total number of output sheets P exceeds a predetermined value (sheet number determination condition X=2000 sheets), the CPU 601 compares the color ratio C as the printing tendency of the user with a predetermined value (color ratio determination condition Y=30%). do. Depending on the result of this comparison, a correction mode (first mode or second mode) is determined which indicates whether the color misregistration correction is performed before or after image formation.

When the color ratio C is smaller than the color ratio determination condition Y, the CPU 601 determines that the user frequently forms images in black alone. In this case, the CPU 601 determines the first mode as the correction mode for color misregistration correction. In the first mode, image forming processing is performed after correcting color misregistration.
Image formation using black alone does not cause color misregistration. Therefore, in the first mode, the CPU 601 does not perform color misregistration correction when the print signal instructs black monochrome printing. When the print signal instructs color printing in the first mode, the CPU 601 determines the difference between the temperature change amount ΔT of the machine internal temperature from the machine internal temperature Tz at the time of the previous color misregistration correction and a predetermined value (temperature difference T1=4° C.). It is determined whether or not to perform color misregistration correction based on the comparison result. If the temperature change amount ΔT is greater than the temperature difference T1, the CPU 601 performs color misregistration correction before image forming processing.

Through such processing in the first mode, color misregistration correction is performed only when the first execution condition is satisfied and necessary. Therefore, an increase in the number of color shift corrections can be suppressed. Suppressing an increase in the number of color misregistration corrections prevents an increase in the rotation time of components such as the developing devices 7a to 7d, the photosensitive drums 3a to 3d, and the intermediate transfer belt 103, thereby reducing the life of the components. Also, for a user with a small color ratio, color misregistration correction is performed only during color printing. Therefore, the number of times of color misregistration correction can be reduced, and downtime felt by the user can be reduced. In the present embodiment, an example in which color misregistration correction is not performed in the case of black monochromatic printing has been shown, but color misregistration correction may not be performed in the case of yellow, magenta, and cyan monochromatic printing as well.

When the color ratio C is greater than the color ratio determination condition Y, the CPU 601 determines that the user frequently forms images in multiple colors. In this case, the CPU 601 determines the second mode as the correction mode for color misregistration correction. In the second mode, color misregistration correction is performed after the image forming process. In the second mode, whether the print signal instructs color printing or black single-color printing is not included in the conditions for performing color misregistration correction. The CPU 601 determines whether or not to perform color misregistration correction based on the result of comparison between the amount of temperature change ΔT in the machine interior temperature from the machine interior temperature Tz at the time of the previous color misregistration correction and a predetermined value (temperature difference T2=3° C.). . If the temperature change amount ΔT is greater than the temperature difference T2, the CPU 601 performs color misregistration correction after the image forming process.

Through such processing in the second mode, color misregistration correction is performed only when the second execution condition is satisfied and necessary. Since the color ratio is relatively high in the second mode, the number of times color misregistration correction is executed during black monochrome printing tends to decrease, and the effect on shortening the service life of components is small. In addition, since the timing at which the color misregistration correction is performed is after the image forming process, the downtime felt by the user can be greatly reduced.

(when exposure unit temperature is added to execution conditions)
The image forming apparatus 1 may predict the amount of color misregistration according to the temperature of the exposing device 6 . In this case, temperature sensors are arranged inside and around the exposure device 6 . FIG. 8 is an explanatory diagram of the exposing device 6. As shown in FIG. The exposure device 6 includes the rotary polygon mirror unit 41 and the exposure device internal temperature sensor 65 inside the housing 66 , and the exposure device external temperature sensor 56 and the circuit board 60 outside the housing 66 .

The rotating polygon mirror unit 41 scans the photosensitive drums 3a to 3d with light beams. The operation of the rotating polygon mirror unit 41 causes the temperature inside the housing 66 to rise. The exposure device internal temperature sensor 65 detects the internal temperature of the housing 66 (exposure device internal temperature). The circuit board 60 controls the operation of the exposing device 6 according to instructions from the CPU 601 . The temperature around the housing 66 rises due to the operation of the circuit board 60 . The exposure device external temperature sensor 56 detects the temperature (exposure device external temperature) around the housing 66 (around the circuit board 60). The detection results of the exposure device internal temperature sensor 65 and the exposure device external temperature sensor 56 are transmitted to the CPU 601 . Note that the temperature outside the exposure device is also the temperature inside the image forming apparatus 1 .

The operator of the image forming apparatus 1 can select which of waiting time reduction and image quality should be prioritized at the time of the first image formation of the day. FIG. 9 is an exemplary view of a selection screen for such selection. This selection screen is displayed on a touch panel display (not shown) provided in the image forming apparatus 1 . The CPU 601 displays the selection screen on the touch panel display via the output IF 606 .

The operator selects either button 401 or 402 from the selection screen. The operator selects the button 401 when priority is given to shortening the waiting time. When giving priority to image quality (color deviation), the operator selects button 402 . Selection of the buttons 401 and 402 is performed, for example, by pressing a touch panel or operating an input device such as a key button. The selected content is input to the CPU 601 via the input IF 605 .

FIG. 10 is a flow chart showing processing during the first image formation of the day. In this case, the memory 604 stores the time when the previous image formation was performed. The operator selects which of waiting time reduction and image quality should be prioritized from the selection screen of FIG. The selection is stored in memory 604 . The memory 604 also stores the external temperature, the external temperature of the exposing device, and the internal temperature of the exposing device at the time of the previous correction of color misregistration. In this process, the external temperature, the external temperature of the exposing device, and the internal temperature of the exposing device are the execution conditions for color misregistration correction.

When the CPU 601 receives a print signal (S301), it calculates the elapsed time t1 from the previous image forming process (S302). The CPU 601 calculates the elapsed time t1 from the time of the previous image forming process stored in the memory and the current time. The CPU 601 determines whether or not the elapsed time t1 is equal to or longer than a predetermined time (eight hours or longer in this case) (S303). The predetermined time is set, for example, to a time corresponding to the time from the last image forming process on the previous day to the first image forming process on the current day.

If the elapsed time t1 is equal to or longer than the predetermined time (eight hours or longer) (S303: Y), the CPU 601 determines whether or not the selection on the selection screen shown in FIG. 9 gives priority to waiting time reduction (S304). . If priority is given to shortening the waiting time (S304: Y), the CPU 601 acquires the detection result of the temperature inside the exposure device from the temperature sensor 65 and detects the temperature outside the exposure device from the temperature sensor 56 outside the exposure device. Get the detection result of . The CPU 601 calculates the amount of temperature change between the acquired external and internal temperatures of the exposure device and the external and internal temperatures of the exposure device at the time of the previous color misregistration correction. The CPU 601 predicts the current amount of color misregistration based on the calculated amount of temperature change, and performs color misregistration correction based on the prediction result (S306). The CPU 601 performs image forming processing after image adjustment (S310). The amount of color misregistration may be predicted using a predetermined correction formula, or using a table representing the relationship between the calculated amount of temperature change and the amount of color misregistration.

If the elapsed time t1 is less than the predetermined time (less than 8 hours) (S303: N), or if the selection on the selection screen is prioritizing image quality (S304: N), the CPU 601 controls the external temperature T2 and the exposing device external temperature T2. A temperature T3 and an exposure device internal temperature T4 are obtained (S305). The CPU 601 acquires the outside temperature T2 from the outside temperature sensor 70, acquires the detection result of the exposure unit outside temperature T3 from the exposure unit outside temperature sensor 56, and detects the exposure unit inside temperature T4 from the exposure unit inside temperature sensor 65. Get results.

The CPU 601 stores the acquired external temperature T2, exposure device external temperature T3, and exposure device internal temperature T4, as well as the external temperature, the exposure device external temperature, and the exposure device internal temperature at the time of the previous color misregistration correction. Change amounts ΔT2, ΔT3, and ΔT4 are calculated (S307). The CPU 601 determines whether or not the temperature change amount ΔT2 of the outside temperature, the temperature change amount ΔT3 of the temperature outside the exposure device, and the temperature change amount ΔT4 of the temperature inside the exposure device are equal to or greater than predetermined temperature differences set respectively. (S308). Here, the CPU 601 compares the temperature change amount ΔT2 of the outside temperature with a predetermined temperature difference (4° C.), compares the temperature change amount ΔT3 of the exposure device outside temperature with a predetermined temperature difference (3° C.), and performs exposure. A temperature change amount .DELTA.T4 of the temperature inside the device is compared with a predetermined temperature difference (3.degree. C.). As a result of the comparison, if any one temperature change amount is equal to or greater than the predetermined temperature difference (S308: Y), the CPU 601 executes color shift correction (S309), and then performs image forming processing (S310). The CPU 601 predicts the current amount of color misregistration based on the calculated amount of temperature change and corrects the color misregistration. The amount of color misregistration may be predicted using a predetermined correction formula, or using a table showing the relationship between the calculated amounts of temperature change ΔT2, ΔT3, ΔT4 and the amount of color misregistration. As a result of the comparison, if the amount of temperature change is less than the predetermined temperature difference (S308: N), the CPU 601 performs image forming processing without executing color shift correction (S310).

As described above, the image forming apparatus 1 can select which of waiting time reduction and image quality should be prioritized at the time of the first image forming process of the day. The image forming apparatus 1 performs color misregistration correction according to the selection result. At the time of correcting the color shift, the amount of temperature change between the internal and external temperatures of the exposing device 6 can be used as the execution condition for correcting the color shift. Through such processing, the image forming apparatus 1 can both reduce downtime and prevent deterioration in the life of components.

(Another example of color shift correction processing)
FIG. 11 is another flow chart showing image forming processing including color misregistration correction. This process is performed under the conditions of temperature difference Ta (first temperature difference), temperature difference Tb (second temperature difference), color misregistration correction execution timing (correction mode), and color confirmation result of the print signal. The temperature differences Ta and Tb are set to, for example, 5° C. and 3° C., respectively. However, the temperature differences Ta and Tb are not limited to the illustrated values regardless of the magnitude relationship.

When the image forming apparatus 1 is activated, the CPU 601 waits for reception of a print signal instructing image formation (S201). When the print signal is received, the CPU 601 confirms the color shift correction execution timing stored in the storage area 623 (S202). The CPU 601 determines whether or not the color misregistration correction execution timing is the first mode (S203).

If the color misregistration correction execution timing is the first mode (S203: Y), the CPU 601 determines whether the received print signal instructs color printing (image formation using multiple colors) or black single-color printing. (S401). If the print signal instructs black monochrome printing (S401: N), there is no need to perform color misregistration correction. Therefore, the CPU 601 performs image forming processing according to the print signal (S404).

When the print signal indicates color printing (S401: Y), the CPU 601 compares the temperature change amount ΔT, which is the difference between the previous temperature and the current temperature inside the machine, with the temperature difference Ta (S402). When the temperature change amount ΔT is less than the temperature difference Ta (S402: N), the CPU 601 determines that color misregistration correction is unnecessary, and performs image forming processing according to the print signal (S404). If the temperature change amount ΔT is equal to or greater than the temperature difference Ta (S402: Y), the CPU 601 performs color misregistration correction before performing image forming processing (S403). After correcting the color misregistration, the CPU 601 performs image forming processing according to the print signal (S404).

If the color misregistration correction execution timing is the second mode (S203: N), the CPU 601 determines whether the print signal is color printing (image formation using multiple colors) or black single-color printing, as in the processing of S401. It is determined whether to instruct (S405). When the print signal instructs color printing (S405: Y), the CPU 601 compares the temperature change amount ΔT with the temperature difference Ta (S406), as in the process of S402. When the temperature change amount ΔT is less than the temperature difference Ta (S406: N), the CPU 601 determines that there is no need to perform color misregistration correction, and performs image forming processing according to the print signal (S404). When the temperature change amount ΔT is equal to or greater than the temperature difference Ta (S406: Y), the CPU 601 corrects the color misregistration before performing the image forming process (S403). After correcting the color misregistration, the CPU 601 performs image forming processing according to the print signal (S404).

When the print signal instructs black monochrome printing (S405: N), the CPU 601 performs image forming processing according to the print signal (S407). After the image forming process, the CPU 601 compares the temperature change amount ΔT with the temperature difference Tb (S408). If the temperature change amount ΔT is equal to or greater than the temperature difference Tb (S408: Y), the CPU 601 performs color misregistration correction and ends the process (S409). On the other hand, if the temperature change amount ΔT is less than the temperature difference Tb (S408: N), the CPU 601 determines that there is no need to correct the color misregistration, and terminates the process.

Thus, the image forming process is completed. In the case of the first mode, the CPU 601 controls whether or not to execute color misregistration correction before image forming processing, using the color used for image formation indicated by the print signal and the amount of change in temperature inside the machine as the first execution condition. do. In the case of the second mode, the CPU 601 controls whether or not to execute the color misregistration correction after the image forming process, using the temperature change amount of the internal temperature as the second execution condition.

Claims (11)

a plurality of image forming means each forming an image of a different color;
an image carrier that carries the images of each color formed by the plurality of image forming means;
a transfer unit that transfers the image from the image carrier to a sheet;
a detecting means for detecting a pattern for detecting color misregistration formed on the image carrier;
causing the plurality of image forming means to form a plurality of patterns including a pattern of a first color and a pattern of a second color different from the first color; and causing the detecting means to form the plurality of patterns formed on the image carrier. a control means for detecting
correcting means for correcting color misregistration of images formed by the plurality of image forming means based on detection results of the plurality of patterns by the detecting means;
a temperature sensor that detects the temperature inside the machine ,
The control means determines the correction mode to be the first mode when the ratio of the number of sheets on which image formation is performed in color to the total number of output sheets on which image formation is performed is lower than a predetermined threshold value, and the ratio is set to the first mode . determining the correction mode as a second mode if the correction mode is higher than a predetermined threshold ;
When the determined correction mode is the first mode, the control means satisfies the first execution condition if an instruction is given to form a multi-color image and the temperature change amount of the machine interior temperature is greater than a predetermined first temperature difference. If the correction mode is determined to be the second mode, the temperature of the machine interior temperature If the amount of change is greater than a predetermined second temperature difference different from the first temperature difference, it is determined that a second execution condition different from the first execution condition is satisfied, and image formation is performed by the plurality of image forming means. characterized by causing the correction means to perform the color misregistration correction after the
Image forming device. The control means determines that the first execution condition is not satisfied when the correction mode is the first mode and the single-color image formation is instructed, and causes the correction means to perform the color misregistration correction. characterized by not
The image forming apparatus according to claim 1 . When the correction mode is the first mode, the control means instructs the correction means to correct the color misregistration if a multi-color image formation is instructed and the temperature change amount of the machine internal temperature is greater than a predetermined first temperature difference. characterized by causing the plurality of image forming means to perform image formation after performing correction,
3. The image forming apparatus according to claim 1 . When the correction mode is the second mode and a single-color image formation is instructed, the control means causes the image forming means corresponding to the single-color image to form an image. characterized in that if the temperature difference is larger than a predetermined third temperature difference, the correcting means is caused to correct the color misregistration.
4. The image forming apparatus according to claim 3 . The control means determines the correction mode when the total number of output sheets is greater than a predetermined number of output sheets,
The image forming apparatus according to any one of claims 1 to 4. The control means causes the correction means to perform the color misregistration correction if a temperature change amount of the internal temperature from the time of the previous correction is equal to or greater than a predetermined temperature difference,
The image forming apparatus according to claim 1. The control means predicts the amount of color shift corresponding to the amount of temperature change when the elapsed time from the previous image forming process is equal to or longer than a predetermined time, and corrects the color shift based on the amount of color shift. Characterized by performing deviation correction,
7. The image forming apparatus according to claim 6 . exposure means for irradiating light beams for forming images on the plurality of image forming means;
a second temperature sensor that detects the temperature outside the machine;
a third temperature sensor that detects the internal temperature of the exposure means;
When the elapsed time is less than a predetermined time, the control means provides a first temperature change amount of the internal temperature from the time of the previous correction, a second temperature change amount of the external temperature from the time of the previous correction, and calculating a third temperature change amount of the internal temperature from the time of the previous correction, wherein the first temperature change amount is greater than or equal to the first temperature difference, the second temperature change amount is greater than or equal to the second temperature difference, and the third If the amount of temperature change is equal to or greater than a third temperature difference, the correction means is caused to perform the color shift correction,
The image forming apparatus according to claim 7 . When none of the first temperature change amount is greater than or equal to the first temperature difference, the second temperature change amount is greater than or equal to the second temperature difference, and the third temperature change amount is greater than or equal to the third temperature difference, (2) causing the plurality of image forming means to perform image formation without causing the correcting means to perform the color misregistration correction;
9. The image forming apparatus according to claim 8 . The control means predicts the amount of color shift according to the amount of change in the first temperature, the amount of change in the second temperature, and the amount of change in the third temperature, and instructs the correction means to correct the color deviation based on the amount of change in color. Characterized by performing deviation correction,
The image forming apparatus according to claim 8 or 9 . a selection means for selecting which of image formation waiting time reduction and image quality should be prioritized,
When the waiting time reduction priority is selected, the control means performs processing when the elapsed time is equal to or greater than the predetermined time, and when the image quality priority is selected, the elapsed time is the predetermined time. Characterized by performing processing when it is less than
The image forming apparatus according to any one of claims 8 to 10 .

Images