阅读说明：本技术 图像形成装置 (Image forming apparatus with a toner supply device ) 是由 滨野晃 石川林 辻村宗士 今井雄一郎 后久齐文 于 2019-09-05 设计创作，主要内容包括：本公开涉及图像形成装置。一种图像形成装置,通过多个图像形成部分在中间转印带上形成不同颜色的多个图像。该图像形成装置检测在中间转印带上形成的图像的颜色配准失调量,并使用基于颜色配准失调量的校正值来执行图像形成。如果从前一次图像形成起的经过时间小于预定时间,则图像形成装置使用那时的温度和前一校正值来预测校正值,并执行颜色配准失调校正。如果从前一次图像形成起的经过时间是预定时间或更长,则图像形成装置使用当经过时间变为预定时间或更长时的校正值和温度来预测校正值,并执行颜色配准失调校正。(The present disclosure relates to an image forming apparatus. An image forming apparatus forms a plurality of images of different colors on an intermediate transfer belt by a plurality of image forming sections. The image forming apparatus detects a color misregistration amount of an image formed on an intermediate transfer belt, and performs image formation using a correction value based on the color misregistration amount. If the elapsed time from the previous image formation is less than a predetermined time, the image forming apparatus predicts a correction value using the temperature at that time and the previous correction value, and performs color misregistration correction. If the elapsed time from the previous image formation is a predetermined time or longer, the image forming apparatus predicts a correction value using the correction value and the temperature when the elapsed time becomes the predetermined time or longer, and performs color misregistration correction.)

1. An image forming apparatus, characterized by comprising:

a plurality of image forming units configured to form a plurality of images of different colors;

an intermediate transfer member to which an image is transferred;

a transfer portion in which an image is transferred from the intermediate transfer member to a sheet;

a sensor configured to measure a color pattern on the intermediate transfer member, the color pattern being used to detect a color misregistration;

a detector configured to detect a temperature;

a control device configured to:

controlling the plurality of image forming units to form color patterns of different colors;

controlling a sensor to measure a color pattern;

detecting color misregistration based on the measurement results of the sensors;

controlling relative positions of images to be formed by the plurality of image forming units based on the detected color misregistration and a detection result of the detector; and

a memory configured to store a reference color misregistration,

wherein the control device controls the relative position based on the reference color misregistration stored in the memory and the detection result of the detector without forming the color pattern in a case (i) an elapsed time from a previous output image formation of the image forming apparatus on the sheet is longer than a predetermined time and (ii) a predetermined condition relating to a temperature of the image forming apparatus is satisfied.

2. The image forming apparatus as claimed in claim 1,

wherein the control device controls the sensor to measure the color pattern in a case (iii) the elapsed time is longer than the predetermined time and (iv) a predetermined condition relating to a temperature of the image forming apparatus is not satisfied.

3. The image forming apparatus as claimed in claim 1, further comprising another detector provided at a position different from the detector and configured to detect another temperature,

wherein the control device is further configured to determine whether a predetermined condition is satisfied based on a detection result of the other detector.

4. The image forming apparatus as claimed in claim 1, further comprising another detector provided at a position different from the detector and configured to detect another temperature,

wherein the predetermined condition is satisfied in a case where a difference between the temperature detected by the other detector and the reference temperature is less than a threshold temperature.

5. The image forming apparatus as claimed in claim 1,

wherein the plurality of image forming units include a scanner unit configured to expose a photosensitive body provided in each of the plurality of image forming units to light,

wherein the scanner unit comprises a light source and a mirror for deflecting light from the light source, and

wherein the detector is arranged in the scanner unit.

6. The image forming apparatus as claimed in claim 1,

wherein the control device controls the sensor to measure the color pattern, and generates the reference color misregistration based on the measurement result of the sensor in a case (v) the elapsed time is longer than a predetermined time and (vi) the reference color misregistration is not stored in the memory.

7. The image forming apparatus as claimed in claim 1,

wherein the control device is further configured to control whether to form the color pattern based on a detection result of the detector.

8. The image forming apparatus as claimed in claim 1, further comprising another detector provided at a position different from the detector and configured to detect another temperature,

wherein the control device is further configured to control whether to form a color pattern based on a detection result of the other detector.

Technical Field

The present disclosure relates to an image forming apparatus, such as a laser printer, a digital copying machine, or the like, which performs image formation by scanning a laser beam.

Background

In order to increase the speed, an image forming apparatus that forms a color image by an electrophotographic system includes a plurality of image forming portions. Each image forming portion forms an image of a corresponding color on the photoreceptor through each step of, for example, charging, exposure, and development. The image formed on the photoconductor of each image forming portion is sequentially superimposed and transferred onto a transfer member and a sheet, and a full-color image is formed. In such an image forming apparatus, a laser scanner is used to expose the photoreceptor. The laser scanner exposes the photoreceptor by deflecting the laser beam by the deflector. The deflector generates heat. In the laser scanner, due to heat generated by the deflector, an optical component (such as a lens, a mirror, or the like) is deformed, or the position or posture of the optical component is changed. These changes of the optical system cause a deviation in the irradiation position of the laser beam. When images of the respective colors are superimposed, a deviation in the irradiation position causes a deviation between the images. Due to the deviation between images, color misregistration occurs in color images.

The image forming apparatus performs color misregistration correction on the color misregistration. The color misregistration correction is performed by forming a detection image for detecting color misregistration on a transfer member onto which an image is transferred from a photosensitive body, detecting a color misregistration correction value by reading the detection image by a sensor, and by adjusting an image writing start timing or the like in accordance with the color misregistration correction value. The image writing start timing is a timing at which exposure of the photoreceptor by the laser scanner is started. The color misregistration correction is hereinafter referred to as "automatic registration".

The automatic registration is performed at appropriate time intervals, or is performed for every predetermined number of sheets on which image formation is performed. In particular, since the influence of the hysteresis of the temperature rise and fall between the time of the first image formation of one day and the time of the image formation of the previous night is large, the necessity of performing the automatic registration increases. Frequent auto-registration results in increased downtime. In practice, the state in the image forming apparatus when the power is turned on is often similar to the state when the power was turned on last time. Therefore, U.S. patent No.8107833B2 proposes an image forming apparatus in which, if the difference from the temperature of the image forming apparatus at the time of the previous power-on is less than a predetermined temperature, the color misregistration correction value of the image forming apparatus at the time of the previous power-on is used, and if the difference is the predetermined temperature or higher, a new color misregistration value is detected.

The timing of turning on the power of the image forming apparatus varies depending on the date. Therefore, the temperature outside the image forming apparatus and the temperature inside the image forming apparatus also change. The change in temperature directly affects the amount of color misregistration, so that a correction residual due to the color misregistration correction becomes large. If the correction residual is unacceptably large, the frequency with which automatic registration is performed increases. The conventional image forming apparatus determines whether to perform automatic registration when the power is turned on. In actual operation, the image forming apparatus also performs automatic registration after the image forming apparatus has been inoperative for a long time. Therefore, an image forming apparatus that reduces the frequency of performing automatic registration to reduce downtime is desired.

Disclosure of Invention

An image forming apparatus according to the present disclosure includes: a plurality of image forming units configured to form a plurality of images of different colors; an intermediate transfer member to which the image is transferred; a transfer portion in which the image is transferred from the intermediate transfer member to a sheet; a sensor configured to measure a color pattern on the intermediate transfer member, the color pattern being used to detect a color misregistration; a detector configured to detect a temperature; a control device configured to control the plurality of image forming units to form color patterns of different colors; controlling a sensor to measure a color pattern; detecting color misregistration based on the measurement results of the sensors; controlling relative positions of images to be formed by the plurality of image forming units based on the detected color misregistration and a detection result of the detector; and a memory configured to store a reference color misregistration, wherein the control device controls the relative position based on the reference color misregistration stored in the memory and a detection result of the detector without forming a color pattern in a case (i) an elapsed time from a previous output image formation of the image forming apparatus on the sheet is longer than a predetermined time and (ii) a predetermined condition relating to a temperature of the image forming apparatus is satisfied.

Other features of the present invention will become apparent from the following description of exemplary embodiments (with reference to the attached drawings).

Drawings

Fig. 1 is a diagram illustrating the configuration of an image forming apparatus.

Fig. 2 is an explanatory diagram of the laser scanner.

Fig. 3 is an explanatory diagram of the laser scanner.

Fig. 4 is an explanatory diagram of color misregistration correction in the sub-scanning direction.

Fig. 5 is an explanatory diagram of color misregistration correction in the main scanning direction.

Fig. 6 is an illustration of a detection image for detecting color misregistration.

Fig. 7 is an explanatory diagram of the controller.

Fig. 8 is a graph showing the change in temperature inside the laser scanner and the temperature outside the apparatus with time.

Fig. 9 is a graph showing a relationship between the temperature inside the laser scanner and the amount of color misregistration.

Fig. 10 is a flowchart showing the processing from the start of the job to the calculation of the correction value.

Fig. 11 is a graph showing a relationship between the correction residual and the temperature.

Fig. 12 is a flowchart showing the processing from the start of the job to the calculation of the correction value.

Fig. 13 is a flowchart showing the processing from the start of the job to the calculation of the correction value.

Fig. 14 is a diagram explaining the color misregistration prediction appropriateness determination of the placement job.

Fig. 15 is a diagram explaining the color misregistration prediction appropriateness determination of the placement job.

Fig. 16 is a flowchart showing the processing from the start of the job to the calculation of the correction value.

Detailed Description

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

Arrangement of image forming apparatus

Fig. 1 is a diagram illustrating the configuration of an electrophotographic image forming apparatus. The image forming apparatus 100 includes four image forming portions 101Y, 101M, 101C, and 101K, a laser scanner 200, an intermediate transfer belt 106, a fixing device 108, and a sheet feeding mechanism. The image forming portion 101Y is an image forming portion for forming a toner image of yellow (Y). The image forming portion 101M is an image forming portion for forming a toner image of magenta (M). The image forming portion 101C is an image forming portion for forming a toner image of cyan (C). The image forming portion 101K is an image forming portion for forming a toner image of black (K). The sheet feeding mechanism feeds the sheets from the storage portion 109 for storing the sheets to the discharge portion 110. An image is formed on the sheet during conveyance. The laser scanners 200 are disposed between the image forming portions 101Y, 101M, 101C, and 101K and the storage portion 109 in the vertical direction.

The image forming portions 101Y, 101M, 101C, and 101K are provided with photosensitive drums 102Y, 102M, 102C, and 102K as photosensitive bodies, respectively. The photosensitive drums 102Y, 102M, 102C, and 102K are arranged in parallel in the horizontal direction along the intermediate transfer belt 106. The photosensitive drums 102Y, 102M, 102C, and 102K rotate in the clockwise direction in fig. 1. Transfer rollers 105Y, 105M, 105C, and 105K are provided at positions opposite to the photosensitive drums 102Y, 102M, 102C, and 102K with the intermediate transfer belt 106 interposed therebetween. The transfer portions Ty, Tm, Tc, and Tk are formed between the photosensitive drums 102Y, 102M, 102C, and 102K and the transfer rollers 105Y, 105M, 105C, and 105K.

Chargers 103Y, 103M, 103C, and 103K, developing devices 104Y, 104M, 104C, and 104K, and drum cleaners 111Y, 111M, 111C, and 111K are disposed around the photosensitive drums 102Y, 102M, 102C, and 102K in the rotational direction. The chargers 103Y, 103M, 103C, and 103K uniformly charge the surfaces of the corresponding photosensitive drums 102Y, 102M, 102C, and 102K. When the charged photosensitive drums 102Y, 102M, 102C, and 102K are exposed by the laser scanner 200, electrostatic latent images are formed on the surfaces. The laser scanner 200 emits light beams (laser beams) LY, LM, LC, and LK. The laser scanner 200 scans the photosensitive drums 102Y, 102M, 102C, and 102K with laser beams LY, LM, LC, and LK to form electrostatic latent images.

The developing devices 104Y, 104M, 104C, and 104K develop the electrostatic latent images formed on the photosensitive drums 102Y, 102M, 102C, and 102K with a developer (such as toner of a corresponding color). Accordingly, toner images of the corresponding colors are formed on the photosensitive drums 102Y, 102M, 102C, and 102K. The toner images formed on the respective photosensitive drums 102Y, 102M, 102C, and 102K are transferred to the intermediate transfer belt 106 by transfer rollers 105Y, 105M, 105C, and 105K in transfer portions Ty, Tm, Tc, and Tk. The intermediate transfer belt 106 is an image carrier that rotates counterclockwise in fig. 1. The toner images of the respective colors are transferred in order from the upstream side in the rotation direction. When toner images corresponding to respective color components formed in the image forming portions 101Y, 101M, 101C, and 101K are sequentially superimposed and transferred onto the intermediate transfer belt 106, a full-color toner image is formed on the intermediate transfer belt 106. The intermediate transfer belt 106 carries a full-color toner image in this manner. The drum cleaners 111Y, 111M, 111C, and 111K remove toner remaining on the photosensitive drums 102Y, 102M, 102C, and 102K after transfer. By the rotation, the intermediate transfer belt 106 conveys the toner image to the transfer portion T2. The transfer portion T2 corresponds to a position at which the toner image is transferred from the intermediate transfer belt 106 to the sheet, and is provided on a conveying path that conveys the sheet.

The sheet is fed from the storage portion 109 to the conveying path. The conveying path is provided with a sheet feeding roller 120, a registration roller 121, a transfer roller 107 constituting a transfer portion T2, and a fixing device 108 in this order from the upstream side in the sheet conveying direction. The sheet feed roller 120 feeds sheets one by one from the storage portion 109 to the conveying path. The sheet feed roller 120 conveys the sheet to the registration roller 121. The registration roller 121 performs skew correction on the sheet, and conveys the sheet to the transfer member T2 in accordance with the timing at which the intermediate transfer belt 106 conveys the toner image to the transfer portion T2.

When the toner image and the sheet on the intermediate transfer belt 106 enter the transfer portion T2, the transfer roller 107 is applied with a transfer voltage. Thereby, the toner image on the intermediate transfer belt 106 is transferred onto the sheet. The sheet to which the toner image is transferred is conveyed to a fixing device 108. The fixing device 108 fixes the toner image on the sheet by conveying the sheet while heating. This completes the image formation on the sheet. Thereafter, the sheet is discharged to the discharge portion 110. It should be noted that transfer member cleaner 112 is disposed in the vicinity of intermediate transfer belt 106. The transfer member cleaner 112 has a blade that contacts the intermediate transfer belt 106. The transfer member cleaner 112 cleans the intermediate transfer belt 106 by scraping toner remaining on the intermediate transfer belt 106 after transfer with a blade.

The image forming portions 101Y, 101M, 101C, and 101K, the intermediate transfer belt 106, and the transfer roller 107 as described above function as image forming portions, which are disposed between the storage portion 109 and the discharge portion 110 in the vertical direction.

The image forming apparatus 100 according to the present embodiment has a color misregistration correction function for correcting color misregistration (deviation of image forming positions) between images of different colors. For this reason, the image forming apparatus 100 includes a color misregistration detection sensor 400 for detecting a detection image (color pattern) for detecting a color misregistration formed on the intermediate transfer belt 106 described later. A detection image including a full-color pattern (toner image) of yellow, magenta, cyan, and black is formed. The color misregistration detection sensor 400 is arranged to detect the detection images at positions where the detection images of all four colors can be detected and the shapes of the detection images are not deformed by the rolling of the transfer roller 107 of the transfer portion T2.

The image forming apparatus 100 according to the present embodiment performs color misregistration correction using the amount of temperature change as a trigger. For this reason, the image forming apparatus 100 includes a temperature sensor 601 for detecting an ambient temperature (temperature outside the apparatus) of a place where the image forming apparatus 100 is installed and a temperature sensor 602 for detecting a temperature inside the laser scanner 200. The image forming apparatus 100 determines whether the color misregistration correction can be performed depending on the magnitude of the respective temperature change amounts of the temperature outside the apparatus and the temperature inside the laser scanner. It should be noted that the temperature sensor may be provided at a position where the outside temperature of the apparatus and the inside temperature of the apparatus can be detected. For example, temperature sensors for detecting the internal temperature of the apparatus may be provided on the substrate of the laser scanner 200, in the image forming portions 101Y, 101M, 101C, and 101K, in the fixing device 108, and the like. In this case, the image forming apparatus 100 determines whether or not the color misregistration correction can be performed according to the amount of temperature change detected by these temperature sensors. Each temperature sensor is a temperature detecting portion.

Laser scanner

Fig. 2 and 3are explanatory diagrams of the laser scanner 200. Fig. 2 is a sectional view of the laser scanner 200, and fig. 3 is a transparent perspective view of the laser scanner 200. Light source units 93a and 93b including semiconductor lasers (not shown) are disposed on the side surface of the housing 85 of the laser scanner 200 to expose the photosensitive drums 102Y, 102M, 102C, and 102K. The light source unit 93a includes a semiconductor laser for irradiating the photosensitive drums 102Y and 102M with laser beams LY and LM. The light source unit 93b includes a semiconductor laser for irradiating the photosensitive drums 102C and 102K with laser beams LC and LK. An opening is provided in a side wall of the housing 85. The semiconductor lasers of the light source units 93a and 93b are disposed at positions such that emitted laser beams enter the housing 85 via the openings.

The housing 85 is provided with a rotary polygon mirror (polygon mirror) 42, a drive motor 41 for rotating to drive the polygon mirror 42, and a deflection unit including therein a circuit board (not shown) for controlling the drive motor 41. Further, the housing 85 is provided with an optical system including optical lenses 60a to 60d and mirrors 62a to 62 h. Laser beams emitted from semiconductor lasers are guided to the photosensitive drums 102Y, 102M, 102C, and 102K via the housing 85.

The laser beam LK irradiated on the photosensitive drum 102K enters the housing 85 from the semiconductor laser in the light source unit 93b, is deflected by the polygon mirror 42, passes through the optical lenses 60a and 60b, and is reflected by the reflecting mirror 62 a. The laser beam LK reflected by the mirror 62a passes through a transparent window (not shown) provided on the casing 85 and irradiates the photosensitive drum 102K. The laser beam LK scans the photosensitive drum 102K by a change in the deflection angle of the laser beam LK caused by the rotation of the polygon mirror 42.

The laser beam LC irradiated on the photosensitive drum 102C enters the housing 85 from the semiconductor laser in the light source unit 93b, is deflected by the polygon mirror 42, passes through the optical lenses 60a and 60b, and is reflected by the reflection mirrors 62b, 62C, and 62 d. The laser beam LC reflected by the mirror 62d passes through a transparent window (not shown) provided on the casing 85 and irradiates the photosensitive drum 102C. The laser beam LC scans the photosensitive drum 102C by a change in the deflection angle of the laser beam LC caused by the rotation of the polygon mirror 42.

The laser beam LM irradiated on the photosensitive drum 102M enters the housing 85 from the semiconductor laser in the light source unit 93a, is deflected by the polygon mirror 42, passes through the optical lenses 60c and 60d, and is reflected by the reflection mirrors 62e, 62f, and 62 g. The laser beam LM reflected by the mirror 62g passes through a transparent window (not shown) provided on the housing 85 and irradiates the photosensitive drum 102M. The laser beam LM scans the photosensitive drum 102M by a change in the deflection angle of the laser beam LM caused by the rotation of the polygon mirror 42.

The laser beam LY irradiated on the photosensitive drum 102Y enters the housing 85 from the semiconductor laser in the light source unit 93a, is deflected by the polygon mirror 42, passes through the optical lenses 60c and 60d, and is reflected by the reflecting mirror 62 h. The laser beam LY reflected by the reflecting mirror 62h passes through a transparent window (not shown) provided on the housing 85 and irradiates the photosensitive drum 102Y. The laser beam LY scans the photosensitive drum 102Y by a change in the deflection angle of the laser beam LY caused by the rotation of the polygon mirror 42.

Laser beams LY, LM, LC, and LK emitted from the light source units 93a and 93b are guided to the photosensitive drums 102Y, 102M, 102C, and 102K through the polygon mirror 42 and the optical system in the housing 85 and form images. The exposure position where the laser beams LY, LM, LC, LK are imaged on the photosensitive drums 102Y, 102M, 102C, and 102K is moved in accordance with the rotation of the polygon mirror 42. Thereby, the photosensitive drums 102Y, 102M, 102C, and 102K are scanned by the laser beams LY, LM, LC, and LK, respectively.

Description of color misregistration correction

Fig. 4, 5, and 6 are explanatory diagrams of color misregistration correction of the present embodiment. It should be noted that, in the following description, the direction in which the laser scanner 200 scans the photosensitive drums 102Y, 102M, 102C, and 102K with the laser beams LY, LM, LC, and LK is the main scanning direction, and the direction orthogonal to the main scanning direction is the sub-scanning direction. The main scanning direction is a direction orthogonal to the direction in which the intermediate transfer belt 106 rotates (conveying direction). The sub-scanning direction is a direction in which the intermediate transfer belt 106 rotates (conveying direction).

Fig. 4 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 the respective colors are line-type 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 in parallel in the main scanning direction and at predetermined intervals in the sub-scanning direction on the intermediate transfer belt 106. The reference color for color misregistration correction is a yellow correction pattern 501Y. The four-color correction patterns 501Y, 501M, 501C, and 501K become a set of detection images for detecting color misregistration in the sub-scanning direction.

The color registration misregistration amount in the sub-scanning direction is measured as follows. Here, the color misregistration amount of magenta in the sub-scanning direction will be described. The barycentric positions of the respective correction patterns 501Y, 501M, 501C, and 501K are detected based on the detection results of the color misregistration detection sensors 400. The barycentric positions of the respective correction patterns 501Y, 501M, 501C, and 501K when no color misregistration is caused are set to YR1, MR1, CR1, and KR 1.

If the exposure position in the sub-scanning direction changes due to thermal expansion or the like of the laser scanner 200, the magenta correction pattern 501M is displaced in the sub-scanning direction and is formed at the position of the correction pattern 501M'. The center of gravity position of the magenta correction pattern 501M 'is shifted from the position MR1 to the position MR 1'. The color misregistration amount of the magenta correction pattern 501M' in the sub-scanning direction with respect to the yellow correction pattern 501Y is represented by the following expression.

Color misregistration amount in the sub-scanning direction (MR1'-YR1) - (MR1-YR1) ═ MR1' -MR1

Using the calculated color misregistration amount in the sub-scanning direction as a correction value, color misregistration correction in the sub-scanning direction is performed by adjusting the image writing start timing of the laser scanner 200. Color misregistration correction in the yellow-based sub-scanning direction of the other colors is similarly performed. Here, yellow is used as the reference color for the sake of description, but the reference color may be a different color.

Fig. 5 is an explanatory diagram of color misregistration correction in the main scanning direction. The detection image for detecting color misregistration 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 are line-type images inclined by a predetermined angle θ with respect to the main scanning direction. The correction patterns 522Y, 522M, 522C, and 522K are line-type images inclined by a predetermined angle- θ with respect to the main scanning direction. The correction patterns 521Y, 521M, 521C, and 521K and the correction patterns 522Y, 522M, 522C, and 522K are formed to be inclined at the same angle in opposite directions 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 in parallel and at predetermined intervals in the sub-scanning direction, respectively, on the intermediate transfer belt 106. The yellow correction pattern 522Y, the magenta correction pattern 522M, the cyan correction pattern 522C, and the black correction pattern 522K are formed in parallel and at predetermined intervals in the sub-scanning direction, respectively, on the intermediate transfer belt 106. The reference colors for color misregistration correction are yellow correction patterns 521Y and 522Y. The four-color correction patterns 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, and 522K become a set of detection images for detecting color misregistration in the main scanning direction.

The amount of color registration misregistration in the main scanning direction is measured as follows. Here, the color misregistration amount of magenta in the main scanning direction is described. The amount of color registration misregistration in the main scanning direction is measured based on the position of the center of gravity in the sub-scanning direction. The barycentric positions of the respective correction patterns 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, and 522K are detected from the detection result of the color misregistration detection sensor 400. The barycentric positions of the respective correction patterns 521Y, 522Y, 521M, 522M, 521C, 522C, 521K, and 522K when no color misregistration is caused are set to YR3, YR4, MR3, MR4, CR3, CR4, KR3, and KR 4.

If the exposure position in the main scanning direction changes due to thermal expansion or the like of the laser scanner 200, 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 barycentric positions of the magenta correction patterns 521M 'and 522M' are shifted from the positions MR3 and MR4 to the positions MR3 'and MR 4'. The reading position of the color misregistration detection sensor 400 is indicated by a broken line in fig. 5. The color misregistration amount of the magenta correction patterns 521M 'and 522M' in the sub-scanning direction with respect to the yellow correction patterns 521Y and 522Y is represented by the following equation because they are geometrically equal.

Color registration misregistration amount in the sub-scanning direction { (MR3'-YR3) - (MR4' -YR4) }/2

The calculated color registration misregistration amount in the sub-scanning direction is converted into a color registration misregistration amount in the main scanning direction by the following expression using the angle θ at which the correction pattern is inclined with respect to the main scanning direction.

Color registration misregistration amount in the main scanning direction { (MR3'-YR3) - (MR4' -YR4) }/2tan θ

The color misregistration correction in the main scanning direction is performed by adjusting the image writing start timing of the laser scanner 200 using the calculated color misregistration amount in the main scanning direction as a correction value. Color misregistration correction of other colors in the main scanning direction based on yellow is similarly performed. Here, yellow is used as the reference color for the sake of description, but the reference color may be a different color.

Fig. 6 is an illustration of a detection image for detecting color misregistration formed on the intermediate transfer belt 106 when color misregistration correction is actually performed. The detection image for detecting color misregistration of the present embodiment includes the detection image shown in fig. 4 and the detection image shown in fig. 5. In fig. 6, 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. The combined images are formed at both ends of the intermediate transfer belt 106 in the main scanning direction. It should be noted that the number of sets of the respective detection images and the order of forming the images are not limited thereto. In addition, the shape of each correction pattern is not limited to the shapes shown in fig. 4 and 5. The shape may be a vertical line, a cross line, a triangle, etc.

Controller

Fig. 7 is an explanatory diagram of a controller for controlling the operation of the image forming apparatus 100. The controller 700 includes a Central Processing Unit (CPU)703, a Random Access Memory (RAM)704, a memory 705, an input IF 701, and an output IF 702. The CPU703 controls the overall operation of the image forming apparatus 100 by executing a computer program stored in the memory 705 using the RAM 704 as a work area.

The input IF 701 is an input interface to which the color misregistration detection sensor 400, the temperature sensor 601, and the temperature sensor 602 are connected. The input IF 701 obtains detection results detected by the color misregistration detection sensor 400, the temperature sensor 601, and the temperature sensor 602, and sends the obtained results to the CPU 703. In addition, an input device (not shown) is connected to the input IF 701. The input devices are, for example, a touch panel and various key buttons provided in the image forming apparatus 100. The input IF 701 transmits an instruction or the like from the input device to the CPU 703.

The output IF 702 is an output interface, and sends various control signals to the image forming portions 101Y, 101M, 101C, and 101K, the laser driver 707, the transfer portion T2, and the fixing device 108 in response to instructions of the CPU 703. The laser driver 707 controls to drive the laser scanner 200 in response to the received control signal.

As described above, the RAM 704 is used as a work area. In addition to this, the RAM 704 is provided with storage areas 7041 to 7045. The storage area 7041 stores a color misregistration correction flag indicating the necessity of color misregistration correction. The CPU703 determines the necessity of color misregistration correction from, for example, detection results (device external temperature, laser scanner internal temperature) detected by the temperature sensor 601 and the temperature sensor 602. The storage area 7042 stores the detection result (pattern read data) of the detection image formed on the intermediate transfer belt 106 detected by the color misregistration detection sensor 400. The storage area 7043 stores the current temperature, which is the current detection results of the temperature sensor 601 and the temperature sensor 602 (the temperature Tout outside the apparatus, the temperature Tscn inside the laser scanner). The storage area 7044 stores the current time t. The storage area 7045 stores the color misregistration correction value X based on the amount of color misregistration detected from the pattern read data. When the color misregistration correction is performed, the image writing start timing of the laser scanner 200 is corrected based on the color misregistration correction value X.

The memory 705 is composed of a nonvolatile memory, a Hard Disk Drive (HDD), and the like. In addition to the above computer programs, storage areas 7051 to 7060 are formed in the memory 705. The storage area 7051 stores the correction value aregX calculated at the time of the previous automatic registration. The storage area 7053 stores the detection result of the temperature sensor 601 (the temperature aregTout outside the apparatus) and the detection result of the temperature sensor 602 (the temperature aregtsn inside the laser scanner) at the previous automatic registration. The storage area 7052 stores the correction value m1aregX calculated during automatic registration at the time of the previous placement job. The storage area 7054 stores the detection result (temperature m1aregTout outside the apparatus) of the temperature sensor 601 in the case where automatic registration is performed before forming an image based on the previous placing job. In addition, the storage area 7054 stores the detection result of the temperature sensor 602 (the temperature m1aregtsc n inside the laser scanner) in the case where the automatic registration is performed before the image is formed based on the previous placing job. The "placement job" will be described later.

The storage area 7055 stores the time prevt at which the previous job is completed. The storage area 7056 stores image data of a detection image formed on the intermediate transfer belt 106 during automatic registration. The storage areas 7057 and 7058 store two thermal shift predictors. The storage area 7059 stores a time threshold tth. The storage region 7060 stores a temperature threshold value Tth1 and a temperature threshold value Tth 2.

The CPU703 includes an automatic registration operation portion 7031, a thermal shift prediction operation portion 7032, and a placement job determination portion 7033. The CPU703 forms a detection image for detecting color misregistration on the intermediate transfer belt 106 through the image forming portions 101Y to 101K. The CPU703 obtains the detection result (pattern read data) of the detection image formed on the intermediate transfer belt 106 detected by the color misregistration detection sensor 400. The CPU703 obtains a color misregistration correction value X from the color misregistration amount (color misregistration amount data) calculated from the detection result.

The CPU703 calculates a color misregistration correction value X by an automatic registration operation section 7031, a thermal shift prediction operation section 7032, and a placement job determination section 7033. At this time, the CPU703 predicts the color registration misregistration amount based on the detection result of the temperature sensor 601 (the temperature outside the apparatus) and the detection result of the temperature sensor 602 (the temperature inside the laser scanner). In the image formation thereafter, the CPU703 reduces color misregistration by correcting the image writing start timing of the laser scanner 200 in accordance with the correction value X.

The automatic registration operation section 7031 calculates the amount of color misregistration (pattern read data) based on the detection result of the detection image formed on the intermediate transfer belt 106 detected by the color misregistration detection sensor 400. Details of the processing of the thermal shift prediction operation portion 7032 and the placement job determination portion 7033 will be described later.

Fig. 8 is a graph showing changes over time in the temperature inside the laser scanner and the temperature outside the device. This graph shows the change with time of each temperature from the day before the image forming apparatus 100 was left inoperative to the next morning. When about 6 hours has elapsed after the start of the setting of the image forming apparatus 100, the temperature inside the laser scanner becomes almost the same as the temperature outside the apparatus. At the time point when the temperature starts to rise, the image forming apparatus 100 executes the job immediately after the power is turned on. The image forming apparatus 100 performs other jobs during the transition period of temperature increase. Therefore, the internal state of the deformation model of the laser scanner 200 at the time point when the corresponding job is executed is different.

Differences in internal states also occur in the relationship between actual temperature and color misregistration.

Fig. 9 is a graph showing a relationship between the temperature inside the laser scanner and the amount of color misregistration. This graph shows the relationship after the power of the image forming apparatus 100 is turned on after the image forming apparatus 100 is left at a constant temperature for about 15 hours after the image forming apparatus 100 is used. In fig. 9, squares represent the relationship between the temperature inside the laser scanner and the amount of color registration misregistration immediately after the power is turned on. The circles represent the relationship between the temperature inside the laser scanner and the amount of color misregistration when the job is executed. The relational expression between the temperature inside the laser scanner and the color misregistration amount immediately after the power is turned on is different from the relational expression when the job is executed.

For example, when the temperature inside the laser scanner is shifted to the temperature inside the laser scanner when the power is turned on after the image forming apparatus 100 is left for a long time without operation after performing automatic registration at the asterisk point, if color misregistration prediction is performed by a prediction formula shown by a dotted line, a color misregistration prediction residual of about 30 μm is generated. As the temperature difference increases, the color misregistration prediction residual increases. Therefore, color misregistration is generally reduced by performing automatic registration in a preliminary operation after power-on. It should be noted that the image forming apparatus performs image formation on a sheet after the completion of the preliminary operation. It should be noted that the "pre-operation" is an initial operation required to perform image formation.

As described above, if the predictive expression of the color misregistration used in the job at another point in time is similarly used in the job after the image forming apparatus 100 is placed for a long time without operation, a prediction error corresponding to the difference in the internal state is generated. If, in order to avoid this, automatic registration is performed in a pre-operation of the job immediately after the image forming apparatus 100 is placed for a long time, the downtime increases. The image forming apparatus 100 according to the present embodiment performs color misregistration correction (automatic registration) while suppressing the occurrence of downtime. The embodiments will be described below.

First embodiment

Fig. 10 is a flowchart showing the processing from the start of the job to the calculation of the correction value. In the following description, a "placement job" is a job that is executed after the elapsed time Δ t from the completion of the previous job has passed the predetermined time threshold tth or more. The "normal work" is a work other than the placing work. "Tout" indicates the detection result (temperature outside the apparatus) of the current temperature sensor 601. "Tscn" indicates the detection result (temperature inside the laser scanner) of the current temperature sensor 602. "X" denotes a color misregistration correction value. The suffix attached to the left side of each symbol represents a value stored in the memory 705. "areg" represents a value stored at the previous auto-registration. "m 1 areg" represents a value stored at the time of automatic registration during the previous placing job. For example, m1aregTout represents a detection result (temperature outside the apparatus) of the temperature sensor 601 when automatic registration is performed before an image is formed based on a previous placing job. The temperature m1aregTout outside the device is stored in the memory 705.

When receiving the print job (step S101), the CPU703 obtains the current time t, the temperature Tout outside the apparatus as the detection result of the temperature sensor 601, and the temperature Tscn inside the laser scanner as the detection result of the temperature sensor 602 (step S102). The CPU703 obtains an elapsed time Δ t from the completion of the previous job from the current time t and the time prevt of the completion of the previous job (step S103). The CPU703 determines whether the elapsed time Δ t is the time threshold tth or more (step S104). This means that the CPU703 determines whether the elapsed time since the previous image formation is a predetermined time or longer.

In this case, the CPU703 calculates a correction value X in a normal job, from the current temperature Tscn inside the laser scanner, the temperature aregTscn inside the laser scanner at the time of the previous automatic registration, and the correction value argX at the time of the previous automatic registration using the following formula (1) in which the CPU703 calculates the correction value X α 2X is a predetermined coefficient, the formula (1) is a predictive formula of thermal shift, and the correction value X calculated here is a predicted value.

Formula (1) is α 2 × (Tscn-aregtsch) + aregx

If it is determined that the elapsed time Δ t is the time threshold tth or more (step S104: yes), that is, if the elapsed time from the previous image formation is a predetermined time or more, the CPU703 processes the received job as a set job. In this case, the CPU703 determines whether the correction value m1aregX in the memory 705, the temperature m1aregTout outside the apparatus, and the temperature m1aregtsc n inside the laser scanner are cleared (step S106). In the process of step S106, if the correction value is an initial value and the temperature is an initial temperature, the CPU703 determines that the correction value m1aregX, the temperature m1aregTout outside the device, and the temperature m1aregtsc n inside the laser scanner are cleared. If it is determined that the correction value m1aregX, the temperature m1aregTout outside the device, and the temperature m1aregTscn inside the laser scanner are not cleared (step S106: NO), the CPU703 determines whether the absolute value of the temperature difference between the current temperature Tout outside the device and the temperature m1aregTout outside the device when automatic registration is performed in the previous placing job is smaller than a temperature threshold value Tth (step S107). The CPU703 determines whether or not a temperature difference between the temperature out of the apparatus Tout detected before the image forming operation after the image forming apparatus 100 is placed in a non-operation for a predetermined time or more this time and the temperature out of the apparatus m1aregTout detected before the image forming operation after the previous image forming apparatus 100 is placed in a non-operation for a predetermined time or more is less than a predetermined temperature. This means that the CPU703 determines whether the temperature detected at this time of the preliminary operation has changed by a predetermined temperature or more from the temperature detected at the previous time of the preliminary operation.

On the other hand, if it is determined that the correction value m1aregX, the temperature m1aregTout outside the device, and the temperature m1aregTscn inside the laser scanner are cleared (step S106: YES), the CPU703 performs automatic registration in a pre-operation (step S108). Also, if the absolute value of the temperature difference between the device-external temperature Tout and the device-external temperature m1aregTout is the temperature threshold value Tth or more (step S107: no), the CPU703 performs automatic registration in a preliminary operation (step S108). This means that the CPU703 performs automatic registration in the preliminary operation even in a case where the temperature difference between the device-outside temperature Tout and the device-outside temperature m1aregTout is a predetermined temperature or more. This is because the current color misregistration is likely to be different from the color misregistration in the previous preliminary operation. The CPU703 updates the value stored in the memory 705 when the automatic registration is performed to the value calculated by the following equation (2).

X0 is an initial value of the correction value, which is a predetermined value.

The CPU703 updates the value stored in the memory 705 by performing the automatic registration during the placement job to the value calculated by the following expression (3) (step S109). After updating the value, the CPU703 calculates a correction value X by a normal job (step S105).

Here, when it is necessary to obtain a new color misregistration correction value, the respective values of the correction value m1aregX, the temperature m1aregTout outside the apparatus, and the temperature m1aregtsc n inside the laser scanner are cleared. When image formation-related components (such as the laser scanner 200, the photosensitive drums 102Y to 102K, and the intermediate transfer belt 106) are replaced, a new color misregistration value needs to be obtained when the image forming apparatus 100 is mounted, and when automatic registration is performed by an instruction from an input device.

Also, if it is determined that the absolute value of the temperature difference between the device-external temperature Tout and the device-external temperature m1aregTout is smaller than the temperature threshold value Tth (step S107: YES), the CPU703 updates the value stored in the memory 705 when the automatic registration is performed, to the value calculated by the following equation (4) (step S110).

The CPU703 calculates a correction value X using the following expression (5) (step S111.) in the setting job, the CPU703 calculates a correction value X from the current temperature Tscn inside the laser scanner, the temperature m1 aregttscn inside the laser scanner at the time of automatic registration during the previous setting job, and the correction value m1aregX at the time of automatic registration during the previous setting job α 1 is a predetermined coefficient, expression (5) is a predictive expression of thermal shift, and the correction value X to be calculated here is a predicted value.

Formula (5) α 1 × (Tscn-m1 aregtsch) + m1aregx

As described above, the color misregistration correction value X is calculated by the normal job or the setting job. The CPU703 reflects the calculated correction value X to correct the corresponding control timing, and executes image forming processing according to the print job (step S112, step S113). After the image formation, the CPU703 calculates the time prevt at which the previous job is completed using the following expression (6), and updates the value in the memory 705 (step S114).

Formula (6)

In the above process, the coefficient α 2 used in equation (1) and the coefficient α 1 used in equation (5) are coefficients of a predictive formula of thermal shift, which is found through experiments, and the image forming apparatus 100 according to the present embodiment is configured such that the temperature sensor 601 detects the temperature Tout outside the apparatus, but the temperature sensor 601 may detect the temperature outside the laser scanner 200 (the temperature outside the laser scanner). in this case, the temperature item outside the apparatus used in the predictive formula may be replaced by the temperature outside the laser scanner.furthermore, the CPU703 may determine whether to perform automatic registration based on the result of comparison of the current temperature outside the laser scanner with the reference temperature of the laser scanner outside temperature stored in the memory 705.

As described above, the color misregistration correction value X is calculated by applying a prediction expression dedicated to predicting the amount of color misregistration to a job (such as a setting job immediately after the image forming apparatus 100 is set for a long time) whose relational expression between the amount of color misregistration and the temperature is different from that when other jobs are executed. By calculating the correction value X in this manner, the frequency of performing automatic registration in the preliminary operation can be reduced without deteriorating color misregistration.

Fig. 11 shows the relationship between the correction residual and the temperature when the automatic registration is performed. Here, a case where three types of color misregistration correction are performed, specifically, the correction of the formula (1) is performed on a normal job, the correction of the formula (1) is performed on a setting job, and the correction of the formula (5) is performed on a setting job will be described. Fig. 11 shows that, regardless of the type of the prediction expression, performing correction by the placement job significantly improves the correction accuracy as compared with the case where correction is performed by a normal job.

Moreover, even by the same placing work, the correction using the expression (5) reduces the inclination of the relational expression between the correction residual and the temperature to about half as compared with the correction using the expression (1). Therefore, the temperature range in which automatic registration is not required in the preliminary operation is doubled with respect to the color misregistration tolerance. For example, if the color misregistration allowable range is 20 μm, the temperature threshold value Tth is approximately equal to 3 ℃ (the temperature threshold value Tth ≈ 3 ℃) by the correction using equation (1), and the temperature threshold value Tth is approximately equal to 6 ℃ (the temperature threshold value Tth ≈ 6 ℃) by the correction using equation (5).

As described above, the image forming apparatus 100 of the present embodiment can reduce the downtime due to the automatic registration in the preliminary operation while maintaining the performance of the color misregistration correction after the image forming apparatus 100 is placed for a long time by switching the two correction modes of performing the placing job and the normal job. In addition, by predicting the amount of color misregistration in the placement job and the normal job separately using the prediction formulae, color misregistration correction can be accurately performed.

Second embodiment

Fig. 12 is a flowchart showing the processing from the start of a job to the calculation of a correction value according to the second embodiment. The processing from step S101 to step S113 is the same as that of the first embodiment shown in fig. 10. In the second embodiment, after the image forming process at step S113, the CPU703 determines whether the absolute value of the temperature difference between the current device-external temperature Tout and the device-external temperature m1aregTout is less than the temperature threshold value Tth2 (step S115). The temperature threshold value Tth2 is set to a value smaller than the temperature threshold value Tth.

If it is determined that the absolute value of the temperature difference between the current temperature outside the device Tout and the temperature outside the device m1aregTout is smaller than the temperature threshold value Tth2 (step S115: yes), the CPU703 executes the process of step S114. If it is determined that the absolute value of the temperature difference between the current temperature outside the device Tout and the temperature outside the device m1aregTout is the temperature threshold value Tth2 or more (step S115: no), the CPU703 performs automatic registration in post-processing after execution of the print job (step S116). "post-processing" is a preliminary operation required to complete image formation. The CPU703 updates the value stored in the memory 705 when the automatic registration is performed to the value calculated by equation (2). Thereafter, the CPU703 updates the value stored in the memory 705 to the value calculated by equation (3) (step S117), and executes the processing of step S114.

If the color misregistration correction value is calculated using the result of the automatic registration performed in the post-process, the influence of the temperature rise due to the image formation can be considered. However, in general, the number of sheets on which image formation is performed at one time is small, and the increase in the internal temperature of the apparatus caused by the setting job is negligible, which has little effect on the calculation of the correction value. Similarly to the first embodiment, the detected temperature for prediction and determination of the job is not limited to the temperature outside the apparatus, but may also be used in combination with the temperature of the substrate of the laser scanner 200 or the like. For example, in the process of step S115, instead of using the temperature Tout outside the apparatus and the temperature m1aregTout outside the apparatus, the current temperature Tscn inside the laser scanner and the temperature m1aregtsc n inside the laser scanner when automatic registration is performed during the previous placing job may be used.

In the second embodiment as described above, the values in the memory 705 can be updated at the time of placing a job while suppressing an increase in the downtime, so that the number of times automatic registration is performed in the pre-operation by the processing of step S108 can be reduced. Thus, a further reduction in downtime may be achieved.

Third embodiment

Even in the case of the setting job, there is a case where the internal state of the image forming apparatus 100 is not similar to the internal state of the image forming apparatus 100 at the time of the previous setting job. For example, in an environment where the temperature outside the apparatus greatly differs depending on the date (such as when the season changes), or an environment where the temperature outside the apparatus is unstable due to air conditioning control or the like, the temperature outside the apparatus is unstable at the time of daily setting work. Since the temperature outside the device is unstable, the temperature inside the device is unstable. This is why the internal state of the image forming apparatus 100 is not similar to the internal state at the time of the previous setting job. If color misregistration correction is performed based on the values stored in the memory 705 at the time of daily placement of a job, it is possible to perform erroneous correction. Thus, the image forming apparatus 100 installed in an environment where the temperature outside the apparatus greatly varies at the time of the daily setting job is configured not to perform the color misregistration correction based on the values stored in the memory 705 at the time of the setting job.

Fig. 13 is a flowchart showing the processing from the start of a job to the calculation of a correction value according to the third embodiment. The processing in steps S101 to S104 is the same as that of the first embodiment shown in fig. 10. In the following description, suffixes attached to the left side of each symbol denote values stored in the memory 705. "m 1 areg" represents a value stored at the time of automatic registration during the previous placing job. The number included in "m 1 areg" indicates that it is a value earlier than that at the time of automatic registration of the number. For example, m1aregTout represents the detection result (temperature outside the apparatus) of the temperature sensor 601 stored once before (i.e., at the time of automatic registration during the previous placing job). "ave" represents the average of the values stored at the time of automatic registration during the past several placing jobs. It should be noted that in this embodiment, the average value of the values of the past three times is described as an example, but is not limited to the past three times as long as it is a plurality of times.

If it is determined in step S104 that the elapsed time Δ t is less than the time threshold tth (step S104: no), the CPU703 executes processing as a normal job, and executes processing of step S105. If it is determined in the process of step S104 that the elapsed time Δ t is the time threshold tth or more (step S104: yes), the CPU703 executes the process of placing the job. The CPU703 determines whether or not the results of automatic registration at the time of the past several times (three times in the present embodiment) of placing jobs stored in the memory 705 are cleared (step S201).

If it is determined that the result is not cleared (step S201: YES), the CPU703 calculates an average value of the values of the automatic registration results at the time of the last three placing jobs (step S202). The CPU703 calculates an average value aveTout of the temperatures m1aregTout, m2aregTout, and m3aregTout outside the device. The CPU703 calculates an average aveTscn of the temperatures m1 aregttscn, m2 aregttscn, and m3 aregttscn inside the laser scanner. The CPU703 calculates an average value aveX of the correction values m1aregX, m2aregX, and m3 aregX.

The CPU703 determines whether the temperature changes m1aregtsc n, m2aregtsc n, and m3aregtsc n of the past three times inside the laser scanner are within a predetermined range (step S203). Here, the CPU703 determines whether or not a temperature difference between each of the past three temperatures m1aregtsc n, m2aregtsc n, and m3aregtsc n inside the laser scanner and the average value aveTout is less than a temperature threshold value Tth 1. This means that the CPU703 determines whether or not the temperature difference between the plurality of temperatures inside the laser scanner and their average value is less than a predetermined temperature. If it is determined that the temperature difference is smaller than the temperature threshold value Tth1, the CPU703 determines that the changes in the temperatures m1aregTscn, m2aregTscn, and m3aregTscn inside the laser scanner are within the predetermined range (smaller than the predetermined temperature) (step S203: YES). In this case, the CPU703 determines whether the absolute value of the temperature difference between the average value aveTout of the temperature inside the laser scanner and the current temperature Tscn inside the laser scanner is smaller than the temperature threshold value Tth2 (step S204).

If it is determined that the result of the automatic registration in the memory 705 is cleared (step S201: yes), the CPU703 executes the process of step S108. Even in the case where the temperature variation inside the laser scanner is not within the predetermined range (no in step S203), that is, in the case where the temperature difference is the predetermined temperature or higher, the CPU703 executes the processing of step S108. Moreover, if the absolute value of the temperature difference between the average value aveTout and the temperature Tscn inside the laser scanner is the temperature threshold value Tth2 or more (step S204: NO), the CPU703 also executes the process of step S108. After the process of step S108, the CPU703 updates the value stored in the memory 705 when the automatic registration is performed in the set job to the value calculated by the following expression (6) (step S207). When updating the values in the memory 705, the CPU703 discards the results of the automatic registration three times before. Thereafter, the CPU703 executes the processing of step S105.

Here, when it is necessary to obtain a new color misregistration correction value, the respective values of the correction values of the past three times, the temperature outside the apparatus, and the temperature inside the laser scanner are cleared. When image formation-related components (such as the laser scanner 200, the photosensitive drums 102Y to 102K, the intermediate transfer belt 106, and the like) are replaced, a new color misregistration correction value needs to be obtained when the image forming apparatus 100 is mounted and when automatic registration is performed by an instruction from an input device.

If it is determined that the absolute value of the temperature difference between the average value aveTout and the temperature Tscn inside the laser scanner is smaller than the temperature threshold value Tth2 (step S204: no), the CPU703 updates the value stored in the memory 705 when automatic registration is performed to the value calculated by the following equation (7) (step S205).

The CPU703 calculates a correction value X using equation (8) from the current temperature Tscn inside the laser scanner, the average aveTscn of the temperature inside the laser scanner, and the average aveX of the correction values (step S206). Equation (8) is a predictive equation of the thermal shift. The correction value X calculated here is a predicted value. Thereafter, the CPU703 executes the same processing as steps S112 to S114 of the first embodiment shown in fig. 10, and ends the processing.

Formula (8) is as follows, α 1(Tscn-aveTscn) + avex

Fig. 14 and 15 are diagrams each explaining the determination of the suitability of color misregistration prediction of the placement job. The color misregistration prediction appropriateness determination of the placement job is performed by determining whether or not the changes in the temperatures m1 aregttscn, m2 aregttscn, and m3 aregttscn inside the laser scanner of the process of step S203 are within a predetermined range.

Fig. 14 and 15 show the relationship between the laser scanner internal temperature and the amount of color misregistration variation (prediction) in the setting job or the result of automatic registration performed in the setting job. In performing the color misregistration correction, the laser scanner 200 adjusts the image writing start timing according to the color misregistration variation prediction amount. In fig. 14 and 15, circles represent the relationship between the temperatures m1 aregtsccn, m2 aregtsccn, and m3 aregtsccn inside the laser scanner and the amount of color registration shift change when automatic registration is performed in the last three setting jobs. The asterisks indicate the relationship between the average aveTscn and the average aveX. aveTscn represents the average of the temperatures m1aregTscn, m2aregTscn and m3aregTscn inside the laser scanner. aveX represents an average value of the amount of color misregistration change. The solid-line box indicates a region in which the difference between the temperature inside the past laser scanner and the average value aveTscn thereof is within the temperature threshold value Tth 1. The black diamonds indicate the relationship between the temperature Tscn inside the laser scanner and the actual color misregistration variation amount in this setting operation. The white diamonds represent the relationship between the temperature Tscn inside the laser scanner and the color misregistration variation prediction amount X this time. This is predicted based on the average aveTscn of the temperatures inside the laser scanners and the average aveX of the color misregistration variation amounts using the prediction formula in this setting job and the temperatures Tscn inside the laser scanners.

In fig. 14, the temperatures m1aregtsc n, m2aregtsc n, and m3aregtsc n inside the laser scanner as a result of the automatic registration at the time of the last three placing jobs fall in the regions in the solid line frame. In this case, the internal state in the past three setting jobs was considered to be stable and similar. Therefore, the CPU703 determines that the color registration misregistration amount can be predicted. In fig. 15, the temperatures m1aregtsc n, m2aregtsc n, and m3aregtsc n inside the laser scanner as a result of the automatic registration at the time of the last three placing jobs do not fall in the regions in the solid line frame. In this case, it is considered that the internal state is different in the past three setting jobs. Therefore, the CPU703 determines that the color registration misregistration amount prediction error may become large, so that the CPU703 performs automatic registration in a pre-operation.

It should be noted that the temperature used for prediction and determination of the job is not limited to the temperature inside the laser scanner, but may also be used in combination with the temperature outside the apparatus, the temperature of the substrate of the laser scanner 200, and the like. For example, in the process of step S204, instead of using the temperature Tscn inside the laser scanner and the average aveTscn, the current temperature Tout outside the device and the average aveTout of the temperature outside the device may be used. The temperature Tout outside the device and the temperature near the outside of the device (such as the temperature on the substrate of the laser scanner 200) have good responsiveness to changes in the temperature outside the device, and therefore, by determining the job using the temperatures, it is possible to determine that the internal states are dissimilar with high accuracy.

Fourth embodiment

Fig. 16 is a flowchart showing the processing from the start of a job to the calculation of a correction value according to the fourth embodiment. The processing of steps S101 to S105, S108, S201 to S207 is the same as that of the third embodiment shown in fig. 13. In the fourth embodiment, after the image forming process of step S113, the CPU703 determines whether the absolute value of the temperature difference between the temperature Tscn inside the laser scanner and the average aveTscn of the temperatures inside the laser scanner is smaller than the temperature threshold value Tth3 (step S208). The temperature threshold value Tth3 is set to a value smaller than the temperature threshold value Tth2 and is stored in the storage area 7060 of the memory 705.

If it is determined that the absolute value of the temperature difference between the temperatures inside the laser scanner is smaller than the temperature threshold value Tth3 (step S208: yes), the CPU703 executes the process of step S114. If it is determined that the absolute value of the temperature difference between the temperatures inside the laser scanner is the temperature threshold value Tth3 or higher (step S208: no), the CPU703 performs automatic registration in the post-operation of the print job by the same processing as that of step S116 of the first embodiment (step S209). After that, the CPU703 updates the value stored in the memory 705 to the value calculated by equation (6), and executes the processing of step S114.

If the color misregistration correction value is calculated using the result of the automatic registration performed in the post-operation, the influence of the temperature rise due to the image formation can be considered. However, since the number of sheets on which image formation is performed at one time is generally small, an increase in the internal temperature of the apparatus caused by the setting job is negligible, which has little effect on the calculation of the correction value. Similarly to the third embodiment, the detected temperature for prediction and determination of the job is not limited to the temperature inside the laser scanner, but may also be used in combination with the temperature outside the apparatus, the temperature of the substrate of the laser scanner 200, and the like. For example, in the process of step S115, instead of using the temperature Tscn inside the laser scanner and the average aveTscn, the current temperature Tout outside the device and the average aveTout of the temperature outside the device may be used.

In the fourth embodiment as described above, since the values stored in the memory 705 at the time of placing a job can be updated while suppressing an increase in the downtime, the number of times automatic registration is performed in the preliminary operation can be reduced by the processing of step S108. This achieves a further reduction in downtime.

As described in the first to fourth embodiments, the image forming apparatus 100 of the present disclosure can reduce the downtime by reducing the frequency of performing the automatic registration.

While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments. The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

This application claims the benefit of japanese patent application No.2018-169153, filed on 10.9.2018, which is incorporated herein by reference in its entirety.