JP7512457B2 - Image forming device - Google Patents

Description

The present invention relates to an image forming device that can form a color image by superimposing multiple images of different colors.

An image forming device using electrophotography forms an image on a sheet by carrying out the processes of charging, exposing, developing, transferring, and fixing. Charging is a process in which the surface of a photoconductor is uniformly charged by a charger. Exposing is a process in which a laser scanner emits a light beam onto the charged photoconductor to form a latent image on the photoconductor. Developing is a process in which the latent image is visualized with a developer such as toner to form a toner image on the photoconductor. Transfer is a process in which a toner image is transferred to a sheet directly from the photoconductor, or from the photoconductor via an intermediate transfer body. Fixing is a process in which the image (toner image) is fixed to the sheet by heating and pressurizing the sheet to which the toner image has been transferred. The final product is completed by fixing the image to the sheet.

A laser scanner is equipped with a light source, a rotating polygon mirror that deflects the light beam output from the light source, and an optical system such as lenses and mirrors that guide the light beam deflected by the rotating polygon mirror to a photoconductor. The light source, rotating polygon mirror, and optical system are housed in a single housing. When the temperature inside the image forming device changes, the housing of the laser scanner thermally expands. In addition, due to the heat distribution inside the housing of the laser scanner and the anisotropy of the glass filler contained in the material of the housing, complex thermal expansion deformation occurs inside the housing, and the position of the optical system such as lenses and mirrors may fluctuate. This affects the irradiation position of the light beam that scans the photoconductor, and causes the image formation position to shift. The phenomenon in which the color of the finished product changes due to a shift in the image formation position of each color is called color shift. If color shift occurs, the quality of the finished product will be significantly reduced.

The image forming apparatus performs color shift correction to correct color shift. The color shift correction is performed based on a detection image for detecting color shift formed on an intermediate transfer body at a predetermined timing. The image forming apparatus calculates the amount of color shift based on the result of detecting the detection image by a color shift detection sensor. The image forming apparatus corrects color shift by correcting the image formation position based on the calculated amount of color shift. Note that the image forming apparatus incurs downtime by performing color shift correction, resulting in reduced productivity.

In response to this, Patent Document 1 proposes an image forming device that performs color misregistration correction after image formation when the temperature change inside the device is small, and performs color misregistration correction before image formation when the temperature change inside the device is large. This image forming device is highly likely to perform color misregistration correction after image formation when image formation processing is performed intermittently. Therefore, users are less likely to feel downtime during image formation than when color misregistration correction is performed before image formation.

JP 2015-132643 A

Here, since color shift correction is a phenomenon that changes the color tone of a color image, there is little need to perform color shift correction when forming an image in monochrome black, for example. However, the image forming device described in Patent Document 1 performs color shift correction in preparation for the next image formation even when forming a monochrome black image. In other words, since there is a possibility that a color image will be formed in the subsequent image formation process, the image forming device described in Patent Document 1 performs color shift correction.

The image forming device described in Patent Document 1 performs color misregistration correction even though monochrome image formation is often performed, which may unnecessarily shorten the lifespan of components such as the developer, photoconductor, and intermediate transfer body.

The present invention was made in consideration of the above problems, and aims to appropriately set the execution conditions for color shift correction.

The image forming apparatus of the present invention is an image forming apparatus comprising a plurality of image forming means each forming an image of a different color, an image carrier carrying the image formed by the plurality of image forming means, a transfer means for transferring the image from the image carrier to a sheet, a detection means for detecting a pattern for detecting color shift formed on the image carrier, a control means for causing the plurality of image forming means to form the pattern, a correction means for correcting color shift of the image formed by the plurality of image forming means based on a detection result of the pattern by the detection means, and a temperature detection means for detecting a temperature, wherein the control means determines a correction mode as a first mode when a ratio of the number of sheets on which a color image has been formed to a total number of output sheets on which the image forming apparatus has performed image formation is less than a reference value, and determines the correction mode as a second mode when the ratio is equal to or greater than the reference value, and the control means determines the correction mode as a second mode when the correction mode is set to the first mode. When the correction mode is the first mode, if a color image formation is instructed and the difference between the detected temperature of the temperature detection means and the reference temperature is greater than a threshold value , the control means forms the pattern before forming the color image ; when the correction mode is the second mode , if a color image formation is instructed and the difference between the detected temperature of the temperature detection means and the reference temperature is greater than a first threshold value, the control means forms the pattern before forming the color image; when the correction mode is the second mode, if a black monochrome image formation is instructed and the difference between the detected temperature of the temperature detection means and the reference temperature is greater than a second threshold value that is smaller than the first threshold value, the control means forms the pattern after forming the black monochrome image ; and when the correction mode is the first mode, the control means does not form the pattern after image formation based on the difference between the detected temperature of the temperature detection means and the reference temperature .

According to the present invention, the conditions for executing color shift correction can be appropriately set.

FIG. 1 is a diagram illustrating the configuration of an image forming apparatus. FIG. 5 is an explanatory diagram of color misregistration correction in the sub-scanning direction. 5 is an explanatory diagram of color misregistration correction in the main scanning direction. 6A and 6B are diagrams illustrating examples of detection images for detecting color shift. 11 is a flowchart showing a process for determining the execution timing of color misregistration correction. 4 is a flowchart showing an image forming process including color misregistration correction. FIG. FIG. 11 is a flowchart showing a process for forming an image for the first time in a day. 11 is another flowchart showing the image forming process including color registration correction.

The following describes in detail an embodiment of the present invention with reference to the drawings. Note that unless otherwise specified, the dimensions, materials, and relative positions of the components of the image forming apparatus of this embodiment are not intended to limit the scope of the present invention. Furthermore, parts with the same reference numerals in each drawing have the same configuration or function, and duplicate descriptions of these have been omitted as appropriate.

(overall structure)
1 is a diagram showing the configuration of an image forming apparatus according to the present embodiment. The image forming apparatus 1 is a full-color image forming apparatus realized by, for example, a multifunction machine having the functions of a copier, a printer, and a facsimile. 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.

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

The image forming unit 2a is provided with a photosensitive drum 3a, a charging roller 5a, a developing unit 7a, and a cleaner blade 4a. The photosensitive drum 3a is a drum-shaped photosensitive body. The photosensitive drum 3a rotates clockwise in the figure. The charging roller 5a uniformly charges the surface of the photosensitive drum 3a on which the image is formed. The photosensitive drum 3a with a uniformly charged surface is scanned with laser light by the exposure unit 6, so that an electrostatic latent image is formed on the surface. The exposure unit 6 irradiates the photosensitive drum 3a with laser light in accordance with a yellow image signal. The exposure unit 6 irradiates the photosensitive drums 3b to 3d of the other colors with laser light in accordance with the image signals corresponding to each color.

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

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

The secondary transfer outer roller 8 is provided at a position facing the secondary transfer inner roller 102 with the intermediate transfer belt 103 in between. Both ends of the secondary transfer outer roller 8 are rotatably supported by bearings. The secondary transfer outer roller 8 is elastically biased by an elastic member toward the intermediate transfer belt 103 via the bearings. The secondary transfer inner roller 102 and the secondary transfer outer roller 8 constitute the secondary transfer section Ts. The intermediate transfer belt 103 rotates to transport the transferred toner image to the secondary transfer section 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 is equipped with paper feed cassettes 9a, 9b capable of storing sheets S, and a manual feed tray 10 on which sheets S can be placed. Sheets S are fed to the image forming apparatus 1 from either the paper feed cassettes 9a, 9b, or the manual feed tray 10. The feeding mechanism for sheets S is provided with transport rollers such as paper feed rollers 11a, 11b, 11c, and registration roller 12. Paper feed roller 11a feeds sheets S from paper feed cassette 9a to transport path 14. Paper feed roller 11b feeds sheets S from paper feed cassette 9b to transport path 14. Paper feed roller 11c feeds sheets S from the manual feed tray 10 to transport path 14. Registration roller 12 corrects skew of the fed sheets S. The registration rollers 12 transport the sheet S to the secondary transfer unit Ts via the pre-transfer guide 13 in accordance with the timing at which the toner image is transported to the secondary transfer unit Ts by the intermediate transfer belt 103.

The secondary transfer section Ts transfers the four-color toner image on the intermediate transfer belt 103 to the sheet S at the secondary transfer nip formed by the secondary transfer outer roller 8 and the intermediate transfer belt 103 using a predetermined pressure force and electrostatic load bias. The sheet S with the transferred toner image is transported from the secondary transfer section Ts to the fixing device 15. The fixing device 15 fixes the image to the sheet S by applying heat and pressure to the sheet S. The sheet S with the fixed image is discharged to one of the discharge trays 160 and 161.

The image forming device 1 is equipped with an internal temperature sensor 130 for detecting the temperature inside the device (internal temperature). The image forming device 1 is equipped with an external temperature sensor 70 for detecting the temperature outside the device (external temperature). The external temperature sensor 70 is disposed near a fan (not shown) for taking in air from the outside.

Such an image forming apparatus 1 has a color shift correction function for correcting color shift between multiple images of different colors. The color shift detection sensor 200 detects the detection images of each color, yellow, magenta, cyan, and black, formed on the intermediate transfer belt 103 for detecting color shift. The detection images are toner marks made of toner images of each color. The color shift detection sensor 200 is positioned so that it can detect the detection images of all four colors and detects the detection images at a position where the shape of the detection images will not be distorted by the roller pressure of the outer secondary transfer roller 8 of the secondary transfer section Ts.

(controller)
2 is an explanatory diagram of a controller for controlling the operation of the image forming apparatus 1. 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 operation of the entire image forming apparatus 1 by executing a computer program stored in the memory 604 using the RAM 603 as a working area.

The CPU 601 of this embodiment operates in at least two types of correction modes, a first mode and a second mode, for performing 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 that performs color misregistration correction before image formation processing when a first execution condition is satisfied. The second mode is a correction mode that performs color misregistration correction after image formation processing when a second execution condition is satisfied.

The input IF 605 is an input interface to which the color misregistration detection sensor 200, the in-machine temperature sensor 130, and the outside-machine temperature sensor 70 are connected. The input IF 605 acquires the detection results of the color misregistration detection sensor 200, the in-machine temperature sensor 130, and the outside-machine temperature sensor 70 and transmits them to the CPU 601. The input IF 605 is also connected to an input device (not shown). The input device is, for example, a touch panel or various key buttons provided on 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 that transmits various signals to an external device in response to instructions from the CPU 601. The external device is, for example, a display provided in the image forming device 1. For example, the output IF 606 outputs a signal to display an image on the display in response to instructions from the CPU 601.

In addition to being used as a working area as described above, the RAM 603 is provided with memory areas 607, 609 to 611. The memory area 607 stores a color shift correction flag indicating the necessity of color shift correction. The necessity of color shift correction is determined, for example, based on the amount of change in the temperature inside the machine since the previous color shift correction. The memory area 609 stores the detection result (pattern reading data) of the detection image formed on the intermediate transfer belt 103 by the color shift detection sensor 200. The memory area 610 stores color shift amount data representing the amount of color shift detected from the pattern reading data. The color shift amount is, for example, an amount representing the deviation of the formation position of each color image of magenta, cyan, and black from the reference, based on the formation position of the yellow image. The area 611 stores color shift correction data calculated from the color shift amount data. During color shift correction, the writing timing of the light beam by the exposure device 6 is corrected based on the color shift amount.

The memory 604 is composed of a non-volatile memory, a HDD (Hard Disk Drive), etc., and in addition to the above computer programs, memory areas 623 to 629 are formed. The memory area 623 stores the color shift correction execution timing that determines the timing to perform color shift correction. The memory area 624 stores the execution conditions of color shift correction, such as the temperature differences T1 and T2 that are the judgment criteria (threshold value) of the color shift correction flag. The memory area 625 stores the detection result (inside the machine temperature) by the in-machine temperature sensor 130 at the time of the most recently executed color shift correction as the previous temperature Tz. The memory area 626 stores the cumulative number of sheets S output by image formation as the total output number P. The memory area 627 stores the ratio of the number of sheets on which color image formation was performed to the total output number P as the color ratio C. The memory area 628 stores the color ratio judgment condition Y, which is a threshold value for judging whether the color ratio C is high or low. Memory area 629 stores output number determination condition X, which is a threshold value for determining the amount of total output number P.

The color ratio C stored in the memory area 627 can be a ratio to the total number of output sheets P, or any of the following values. For example, the ratio of color image formation instructions, the ratio of rotation times of the photosensitive drums 3a, 3b, and 3c corresponding to yellow, magenta, and cyan, the ratio of color image formation as a user's printing tendency, etc.

The CPU 601 basically performs color misregistration correction in the same manner as in the conventional method. 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 obtains the detection results (pattern reading data) of the detection images on the intermediate transfer belt 103 by the color misregistration detection sensor 200. The CPU 601 obtains a correction value (color misregistration correction data) from the color misregistration amount (color misregistration amount data) calculated from the detection result. During subsequent image formation, the CPU 601 performs feedback control by correcting the writing timing of the light beam by the exposure device 6 according to the correction value. However, in this embodiment, unlike the conventional method, the execution timing of color misregistration correction (correction mode) is determined according to the color ratio C.

(Explanation of color misregistration correction)
3, 4, and 5 are explanatory diagrams of color misregistration correction in this 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. The main scanning direction is the direction perpendicular to the direction in which the intermediate transfer belt 103 rotates (the transport direction). The sub-scanning direction is the direction in which the intermediate transfer belt 103 rotates (the transport direction).

Figure 3 is an explanatory diagram of color misregistration correction in the sub-scanning direction. The detection image for detecting color misregistration 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 of each color are linear images extending in the main scanning direction. The yellow correction pattern 501Y, the magenta correction pattern 501M, the cyan correction pattern 501C, and the black correction pattern 501K are formed on the intermediate transfer belt 103 parallel to the main scanning direction and at a predetermined interval in the sub-scanning lateral direction. The reference color for color misregistration correction is the yellow correction pattern 501Y. The four color correction patterns 501Y, 501M, 501C, and 501K form one set of detection images for detecting color misregistration 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 is explained. The CPU 601 detects the center of gravity positions of each of the correction patterns 501Y, 501M, 501C, and 501K from the detection results of the color misregistration detection sensor 200. The center of gravity positions of each of the correction patterns 501Y, 501M, 501C, and 501K when no color misregistration occurs are defined as YR1, MR1, CR1, and KR1.

When the exposure position in the sub-scanning direction changes due to thermal expansion of the exposure unit 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 of the magenta correction pattern 501M' becomes position MR1' shifted from position MR1. The amount of color shift in the sub-scanning direction of the magenta correction pattern 501M' relative to the yellow correction pattern 501Y is expressed by the following formula.
Sub-scanning color misregistration amount=(MR1'-YR1)-(MR1-YR1)=MR1'-MR1

The CPU 601 corrects color shift in the sub-scanning direction by adjusting the image writing timing by the exposure device 6, using the calculated amount of color shift in the sub-scanning direction as a correction value. Color shift correction in the sub-scanning direction using another color, yellow, as a reference is performed in the same manner. Note that although yellow has been described as the reference color here, the reference color may be another color.

Figure 4 is an explanatory diagram of color misalignment correction in the main scanning direction. The detection image for detecting color misalignment in the main scanning direction includes yellow correction patterns 521Y, 522Y, magenta correction patterns 521M, 522M, cyan correction patterns 521C, 522C, and black correction patterns 521K, 522K. The correction patterns 521Y, 521M, 521C, 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, 522K of each color are linear images inclined at 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 at the same angle inclined in the opposite direction with respect to the main scanning direction. The yellow correction pattern 521Y, the magenta correction pattern 521M, the cyan correction pattern 521C, and the black correction pattern 521K are formed on the intermediate transfer belt 103 in parallel with each other and at a predetermined interval in the sub-scanning direction. The yellow correction pattern 522Y, the magenta correction pattern 522M, the cyan correction pattern 522C, and the black correction pattern 522K are formed on the intermediate transfer belt 103 in parallel with each other and at a predetermined interval in the sub-scanning direction. The reference colors for color misregistration correction are the 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 detecting color misregistration 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 in the main scanning direction for magenta is explained. The amount of color misregistration in the main scanning direction is also measured based on the center of gravity position in the sub-scanning direction. The CPU 601 detects the center of gravity positions of each correction pattern 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, and 522K from the detection results of the color misregistration detection sensor 200. The center of gravity positions of each correction pattern 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, and 522K when no color misregistration occurs are YR3, YR4, MR3, MR4, CR3, CR4, KR3, and KR4.

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

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

The CPU 601 corrects color shift in the main scanning direction by adjusting the image writing timing by the exposure device 6, using the calculated amount of color shift in the main scanning direction as a correction value. Color shift correction in the main scanning direction using another color, yellow, as a reference is performed in the same manner. Note that although yellow has been described as the reference color here, the reference color may be another color.

Figure 5 is an example of a detection image for detecting color misregistration formed on the intermediate transfer belt 103 during actual color misregistration correction. In this embodiment, the detection image of Figure 3 and the detection image of Figure 4 are combined. In Figure 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 and formed at both ends of the intermediate transfer belt 103 in the main scanning direction. Note that the number of sets of each detection image and the order in which they are formed are not limited to this. Furthermore, the shape of each correction pattern is not limited to those exemplified in Figures 3 and 4, and may be vertical lines, cross lines, triangles, etc.

(Color registration correction timing)
6 is a flow chart showing the process of determining the execution timing of color misregistration correction. The execution timing of color misregistration correction is determined using the total number of output sheets P, the output number judgment condition X, the color ratio C, and the color ratio judgment condition Y as conditions. The output number judgment condition X is set to 2000 sheets here, which generally corresponds to the number of sheets that the image forming device 1 passes through in one month. The color ratio judgment condition Y is set to 30% here as an example. Depending on the execution timing determination value, the correction mode is determined to be either the first mode or the second mode.

When the image forming apparatus 1 is started, the CPU 601 waits to receive a print signal that instructs image formation (S101). The print signal is input, for example, from an input device or an external computer. When the CPU 601 receives the print signal, it executes image formation processing (S102). When the image formation processing is completed (S103), the CPU 601 checks the total number of output sheets P at that time stored in the memory area 626 (S104). The CPU 601 compares the total number of output sheets P with the output number judgment condition X (S105). If the total number of output sheets P is equal to or less than the output number judgment condition X (S105: N), the CPU 601 determines that color misregistration correction is not necessary. In this case, the CPU 601 waits to receive the next print signal.

If the total output number P is greater than the output number judgment condition X (S105: Y), the CPU 601 judges that the number of sheets S on which image formation processing has been performed satisfies the condition for performing color shift correction. In other words, the CPU 601 decides to perform color shift correction if the number of times (number of sheets) image formation has been performed is greater than a predetermined number. The CPU 601 checks the color ratio C at that time stored in the memory area 627 (S106). The CPU 601 compares the color ratio C with the color ratio judgment condition Y (S107). The CPU 601 decides the correction mode according to the color ratio C.

If the color ratio C is less than the color ratio judgment condition Y (S107: Y), the CPU 601 judges that the user's printing tendency is that the color image formation ratio is lower than the judgment condition. In this case, the CPU 601 determines that the execution timing (correction mode) of color misregistration correction is the first mode, which is set before image formation (S108). The CPU 601 stores in the memory 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 judgment condition Y (S107:N), the CPU 601 judges that the user's printing tendency is that the ratio of color image formation is higher than the judgment condition. In this case, the CPU 601 determines that the execution timing of color misregistration correction (correction mode) is the second mode, which is set after image formation (S109). The CPU 601 stores in the memory area 623 that the execution timing of color misregistration correction has been determined to be the second mode.

(Color shift correction process)
7 is a flow chart showing an image forming process including color misregistration correction. This process is performed on 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, for example, 4° C. and 3° C., respectively. However, the temperature differences T1 and T2 are not limited to the example values, regardless of their magnitude.

When the image forming device 1 is activated, the CPU 601 waits to receive a print signal that instructs image formation (S201). When the CPU 601 receives the print signal, it checks the color misregistration correction execution timing stored in the memory area 623 (S202). The CPU 601 determines whether the color misregistration correction execution timing is the first mode (S203).

If the timing for executing color misregistration correction is the first mode (S203: Y), the CPU 601 checks the color to be 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 multiple colors) or black monochrome printing. If the print signal instructs black monochrome printing (S205: N), there is no need to perform color misregistration correction. To do this, the CPU 601 performs image formation processing according to the print signal (S209).

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

If the temperature change amount ΔT is less than the temperature difference T1 (S207: N), the CPU 601 determines that color shift correction is not necessary and performs image formation 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 formation processing (S208). After color shift correction, the CPU 601 performs image formation 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 internal temperature, by processing similar to that of S206 (S210). The CPU 601 compares the temperature change amount ΔT with the temperature difference T2 (S211).

If the temperature change amount ΔT is less than the temperature difference T2 (S211: N), the CPU 601 determines that color shift correction is not necessary and performs image formation processing according to the print signal (S213). If the temperature change amount ΔT is equal to or greater than the temperature difference T2 (S211: Y), the CPU 601 performs image formation processing according to the print signal (S211). The CPU 601 performs color shift correction after the image formation processing (S214).

This completes the image formation process. In the first mode, the CPU 601 performs color misregistration correction before the image formation process, with the color used for image formation instructed by the print signal and the temperature change amount inside the machine as the first execution condition. In the second mode, the CPU 601 performs color misregistration correction after the image formation process, with the temperature change amount inside the machine as the second execution condition.

According to the processing in Figures 6 and 7, the color ratio determination condition Y is a threshold value for determining whether color misregistration correction should be performed before or after image formation depending on the user's printing tendency. The number of sheets determination condition X is a threshold value for determining the user's printing tendency. The temperature differences T1 and T2 are threshold values for determining whether to perform color misregistration correction itself.

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

If 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. In this case, the CPU 601 determines the correction mode of the color shift correction to be the first mode. In the first mode, the image formation process is performed after the color shift correction.
Color misregistration does not occur when forming an image in black monochrome. Therefore, when the print signal instructs black monochrome printing in the first mode, the CPU 601 does not perform color misregistration correction. When the print signal instructs color printing in the first mode, the CPU 601 determines whether to perform color misregistration correction based on the result of comparing the temperature change amount ΔT in the inside temperature from the inside temperature Tz at the time of the previous color misregistration correction with a predetermined value (temperature difference T1 = 4°C). If the temperature change amount ΔT is larger than the temperature difference T1, the CPU 601 performs color misregistration correction before image formation processing.

By performing such processing in the first mode, color misregistration correction is performed only when the first execution condition is satisfied and color misregistration correction is necessary. This can prevent an increase in the number of color misregistration corrections. Preventing an increase in the number of color misregistration corrections prevents an increase in the rotation time of components such as the developers 7a-7d, the photosensitive drums 3a-3d, and the intermediate transfer belt 103, and reduces the shortening of the lifespan of the components. In addition, for users with a low color ratio, color misregistration correction is performed only during color printing. This can reduce the number of color misregistration corrections, and the downtime felt by the user can be reduced. In this embodiment, an example is shown in which color misregistration correction is not performed when printing in black alone, but color misregistration correction may also be omitted when printing in yellow, magenta, or cyan alone.

If the color ratio C is greater than the color ratio judgment condition Y, the CPU 601 judges that the user frequently forms images using multiple colors. In this case, the CPU 601 determines the correction mode for color misregistration correction to be the second mode. In the second mode, color misregistration correction is performed after the image formation process. In the second mode, the execution conditions for color misregistration correction do not include whether the print signal indicates color printing or black monochrome printing. The CPU 601 determines whether to perform color misregistration correction based on the result of comparing the temperature change amount ΔT of the inside temperature from the inside temperature Tz at the time of the previous color misregistration correction with 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 formation process.

By performing this type of processing in the second mode, color misregistration correction is performed only when the second execution condition is met and it is necessary. Since the color ratio is relatively high in the second mode, the number of times color misregistration correction is performed during black monochrome printing tends to decrease, and the impact on the shortened lifespan of components is reduced. In addition, since color misregistration correction is performed after the image formation process, the downtime felt by the user can be significantly reduced.

(When the exposure unit temperature is added to the execution conditions)
The image forming apparatus 1 may predict the amount of color misregistration according to the temperature of the exposure unit 6. In this case, temperature sensors are disposed inside and around the exposure unit 6. Fig. 8 is an explanatory diagram of the exposure unit 6. The exposure unit 6 includes a rotating polygon mirror unit 41 and an internal exposure unit temperature sensor 65 inside a housing 66, and an external exposure unit temperature sensor 56 and a circuit board 60 outside the housing 66.

The rotating polygon mirror unit 41 scans the light beams on the photosensitive drums 3a to 3d. When the rotating polygon mirror unit 41 operates, the temperature inside the housing 66 rises. The temperature sensor 65 inside the exposure unit detects the internal temperature of the housing 66 (temperature inside the exposure unit). The circuit board 60 controls the operation of the exposure unit 6 in response to instructions from the CPU 601. When the circuit board 60 operates, the temperature around the housing 66 rises. The temperature sensor 56 outside the exposure unit detects the temperature around the housing 66 (around the circuit board 60) (temperature outside the exposure unit). The detection results of the temperature sensor 65 inside the exposure unit and the temperature sensor 56 outside the exposure unit are sent to the CPU 601. The temperature outside the exposure unit is also the temperature inside the image forming apparatus 1.

The operator of the image forming device 1 can select whether to prioritize reducing waiting time or image quality when forming an image for the first time in a day. FIG. 9 is an example of a selection screen for making such a selection. This selection screen is displayed on a touch panel display (not shown) provided on the image forming device 1. The CPU 601 causes the selection screen to be displayed on the touch panel display via the output IF 606.

The operator selects either button 401 or 402 from the selection screen. If a shorter waiting time is a priority, the operator selects button 401. If an image quality (color shift) is a priority, the operator selects button 402. Selection of buttons 401 or 402 is performed, for example, by pressing a touch panel or by operating an input device such as a key button. The selection is input to the CPU 601 via the input IF 605.

Figure 10 is a flow chart showing the process for the first image formation of the day. In this case, the time when the previous image formation was performed is stored in memory 604. The operator selects whether to prioritize reducing waiting time or image quality from the selection screen in Figure 9. The selection is stored in memory 604. Memory 604 also stores the temperature outside the machine, the temperature outside the exposure unit, and the temperature inside the exposure unit at the time of the previous color shift correction. In this process, the temperature outside the machine, the temperature outside the exposure unit, and the temperature inside the exposure unit are the conditions for executing color shift correction.

When the CPU 601 receives a print signal (S301), it calculates the elapsed time t1 from the previous image formation process (S302). The CPU 601 calculates the elapsed time t1 from the time of the previous image formation process stored in memory and the current time. The CPU 601 determines whether the elapsed time t1 is equal to or greater than a predetermined time (here, equal to or greater than 8 hours) (S303). The predetermined time is set to, for example, a time equivalent to the time from the last image formation process of the previous day to the first image formation process of the current day.

If the elapsed time t1 is equal to or longer than a predetermined time (eight hours or longer) (S303: Y), the CPU 601 judges whether the selection on the selection screen illustrated in FIG. 9 prioritizes shortening the waiting time (S304). If the priority of shortening the waiting time is selected (S304: Y), the CPU 601 acquires the detection result of the temperature inside the exposure unit from the temperature sensor inside the exposure unit 65, and acquires the detection result of the temperature outside the exposure unit from the temperature sensor outside the exposure unit 56. The CPU 601 calculates the temperature change amount between the acquired temperature outside the exposure unit and the temperature inside the exposure unit and the temperature outside the exposure unit and the temperature inside the exposure unit at the time of the previous color shift correction. The CPU 601 predicts the current color shift amount based on the calculated temperature change amount, and performs color shift correction based on the prediction result (S306). The CPU 601 performs image formation processing after image adjustment (S310). The color shift amount may be predicted using a predetermined correction formula, or may be predicted using a table showing the relationship between the calculated temperature change amount and the color shift amount.

If the elapsed time t1 is less than a predetermined time (less than 8 hours) (S303: N), or if the selection on the selection screen is to prioritize image quality (S304: N), the CPU 601 acquires the outside temperature T2, the outside temperature T3, and the inside temperature T4 of the exposure unit (S305). The CPU 601 acquires the outside temperature T2 from the outside temperature sensor 70, acquires the detection result of the outside temperature T3 of the exposure unit from the outside temperature sensor 56, and acquires the detection result of the inside temperature T4 of the exposure unit from the inside temperature sensor 65.

The CPU 601 calculates the temperature change amounts ΔT2, ΔT3, and ΔT4 between the acquired outside-machine temperature T2, outside-exposure unit temperature T3, and inside-exposure unit temperature T4 and the outside-machine temperature, outside-exposure unit temperature, and inside-exposure unit temperature at the time of the previous color shift correction (S307). The CPU 601 determines whether the temperature change amount ΔT2 of the outside-machine temperature, the temperature change amount ΔT3 of the outside-exposure unit temperature, and the temperature change amount ΔT4 of the inside-exposure unit temperature are equal to or greater than the predetermined temperature difference set for each (S308). Here, the CPU 601 compares the temperature change amount ΔT2 of the outside-machine temperature with the predetermined temperature difference (4°C), compares the temperature change amount ΔT3 of the outside-exposure unit temperature with the predetermined temperature difference (3°C), and compares the temperature change amount ΔT4 of the inside-exposure unit temperature with the predetermined temperature difference (3°C). If the comparison result shows that any one of the temperature changes is equal to or greater than the predetermined temperature difference (S308: Y), the CPU 601 performs color shift correction (S309) and then performs image formation processing (S310). The CPU 601 predicts the current color shift amount based on the calculated temperature change amount and performs color shift correction. The color shift amount may be predicted using a predetermined correction formula, or may be predicted using a table showing the relationship between the calculated temperature changes ΔT2, ΔT3, and ΔT4 and the color shift amount. If the comparison result shows that any of the temperature changes is less than the predetermined temperature difference (S308: N), the CPU 601 performs image formation processing without performing color shift correction (S310).

As described above, the image forming device 1 can select whether to prioritize reducing wait time or image quality during the first image formation process of the day. The image forming device 1 performs color shift correction according to the selection result. When correcting color shift, the amount of temperature change inside and outside the exposure device 6 can be set as the execution condition for color shift correction. Through such processing, the image forming device 1 can achieve both a reduction in downtime and prevention of a decrease in the life span of components.

(Another Example of Color Shift Correction Processing)
11 is another flowchart showing an image forming process including color misregistration correction. This process is performed on 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 example values, regardless of the magnitude relationship.

When the image forming device 1 is activated, the CPU 601 waits to receive a print signal that instructs image formation (S201). When the CPU 601 receives the print signal, it checks the color misregistration correction execution timing stored in the memory area 623 (S202). The CPU 601 determines whether the color misregistration correction execution timing is the first mode (S203).

When the timing for executing color misregistration correction is the first mode (S203: Y), the CPU 601 determines whether the received print signal indicates color printing (image formation using multiple colors) or black monochrome printing (S401). When the print signal indicates black monochrome printing (S401: N), there is no need to perform color misregistration correction. To do this, the CPU 601 performs image formation processing according to the print signal (S404).

If 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). If the temperature change amount ΔT is less than the temperature difference Ta (S402: N), the CPU 601 determines that color shift correction is not necessary and performs image formation 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 shift correction before performing image formation processing (S403). After color shift correction, the CPU 601 performs image formation processing according to the print signal (S404).

When the color misregistration correction execution timing is the second mode (S203: N), the CPU 601 determines whether the print signal indicates color printing (image formation using multiple colors) or black monochrome printing (S405), as in the process of S401. When the print signal indicates 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 color misregistration correction is not necessary and performs image formation 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 performs color misregistration correction before performing image formation processing (S403). After color misregistration correction, the CPU 601 performs image formation processing according to the print signal (S404).

If the print signal indicates black monochrome printing (S405: N), the CPU 601 performs image formation processing according to the print signal (S407). After image formation processing, 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 shift correction and ends processing (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 color shift correction is not necessary and ends processing.

This completes the image formation process. In the first mode, the CPU 601 controls whether or not to perform color misregistration correction before the image formation process, using the color used for image formation instructed by the print signal and the temperature change amount inside the machine as the first execution condition. In the second mode, the CPU 601 controls whether or not to perform color misregistration correction after the image formation process, using the temperature change amount inside the machine as the second execution condition.

Claims (6)

a plurality of image forming means each forming an image of a different color;
an image carrier that carries the images formed by the plurality of image forming devices;
a transfer means for transferring the image from the image carrier to a sheet;
a detection unit for detecting a pattern for detecting color shift formed on the image carrier;
A control means for controlling the plurality of image forming means to form the pattern;
a correction unit that corrects color shifts of images formed by the plurality of image forming units based on a result of detection of the pattern by the detection unit;
An image forming apparatus including a temperature detection unit that detects a temperature,
the control means determines a correction mode as a first mode when a ratio of the number of sheets on which color images are formed to a total number of sheets outputted by the image forming apparatus on which images are formed is less than a reference value, and determines a correction mode as a second mode when the ratio is equal to or greater than the reference value;
the control means , when the correction mode is the first mode , if a color image formation is instructed and if a difference between a temperature detected by the temperature detection means and a reference temperature is greater than a threshold value , forms the pattern before forming the color image;
the control means , when the correction mode is the second mode , if a color image formation is instructed and a difference between the temperature detected by the temperature detection means and the reference temperature is greater than a first threshold value, forms the pattern before forming the color image;
the control means, when the correction mode is the second mode, instructs the formation of a black monochrome image and, if a difference between the temperature detected by the temperature detection means and the reference temperature is greater than a second threshold value that is smaller than the first threshold value, forms the pattern after forming a black monochrome image;
the control means, when the correction mode is the first mode, does not form the pattern after the image formation based on the difference between the temperature detected by the temperature detection means and the reference temperature .
Image forming device. The threshold value is equal to the first threshold value .
2. The image forming apparatus according to claim 1. The control means determines the correction mode when the total number of output sheets exceeds a predetermined number of output sheets .
2. The image forming apparatus according to claim 1. the control means, when a black monochrome image formation is instructed , does not form the pattern if the correction mode is the first mode .
2. The image forming apparatus according to claim 1 . The reference temperature is a temperature detected by the temperature detection means when the pattern was previously formed .
2. The image forming apparatus according to claim 1. The temperature detection means is provided inside the image forming apparatus and detects an internal temperature of the image forming apparatus.
The image forming apparatus according to claim 1 .

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