JP2022184013A - Image forming apparatus - Google Patents

Abstract

To solve the problem in which: sweeping in a pattern for misregistration correction occurs in a different way depending on the situation of an image forming apparatus that forms the pattern for misregistration correction; the accuracy of correction may be reduced due to the influence of sweeping depending on the situation of occurrence of sweeping.SOLUTION: A pattern for sweeping correction includes a first color reference pattern, a first color comparison pattern, a second color reference pattern, and a second color comparison pattern. In the direction of movement of an image carrier, a second width of the first color comparison pattern is longer than a first width of the first color reference pattern, and a fourth width of the second color comparison pattern is longer than a third width of the second color reference pattern. Control means performs misregistration correction based on a result of correcting a first detection result of detecting a pattern for misregistration correction with a second detection result of detecting a pattern for sweeping correction.SELECTED DRAWING: Figure 6

Description

The present invention relates to image forming apparatuses such as color laser printers and color copiers that mainly use an electrophotographic process, and more particularly to alignment control of each color developer image formed on an image carrier.

2. Description of the Related Art Conventionally, in a color image forming apparatus having a plurality of photosensitive drums, misalignment occurs between images of respective colors due to mechanical mounting errors of the photosensitive drums, errors in optical path lengths of laser beams of respective colors, changes in optical paths, and the like. Therefore, in order to correct misalignment between images of each color, a misregistration correction pattern is formed on the intermediate transfer belt, and the formed misregistration correction pattern is detected by an optical sensor. A method for correcting the amount of deviation has been proposed.

Japanese Patent Application Laid-Open No. 2002-200000 discloses a method of detecting a positional deviation correction pattern using a sensor for detecting a positional deviation correction pattern using diffusely reflected light. When the positional deviation correction pattern is detected using the diffusely reflected light, the output value of the diffusely reflected light from the black developer formed on the intermediate transfer belt becomes as small as the diffusely reflected light from the intermediate transfer belt. Therefore, as shown in FIG. 11, the misregistration correction pattern is a pattern in which the pattern of the color developer is used as the base and the pattern of the black developer is superimposed on the color developer. In the example of FIG. 11, a black developer pattern 1604 is superimposed on each of the yellow developer pattern 1601, the magenta developer pattern 1602, and the cyan developer pattern 1603. In FIG. It is disclosed that this makes it possible to detect a pattern of black developer with little diffusely reflected light.

Japanese Patent Application Laid-Open No. 2002-200003 discloses a method of suppressing the influence of sweeping when correcting the amount of positional deviation between colors in view of the increase in density at the rear end of an image due to sweeping.

JP 2009-93155 JP 2013-122504

However, depending on the situation of the image forming apparatus that forms the misregistration correction pattern, the way in which the misregistration correction pattern is swept differs. There is a problem that the accuracy of the correction is lowered due to the influence of the sweeping depending on the situation of occurrence of the sweeping.

The invention according to the present application has been made in view of the above circumstances, and is capable of correcting misregistration between images of each color formed on an image carrier in an image forming apparatus using a plurality of color developers. , to suppress the deterioration of accuracy due to the influence of sweeping.

In order to achieve the above object, the present invention provides an image forming means for forming a misregistration correction pattern composed of developer images of a plurality of colors on an image carrier; Detecting means for irradiating a pattern with light and detecting reflected light of the radiated light; and Control means for correcting positional deviation based on the detection result detected by the detecting means, wherein the image forming means comprises: forms a sweeping correction pattern consisting of developer images of a plurality of colors on the image carrier, the sweeping correction pattern comprising a first color reference pattern, a first color comparison pattern, a second color and a comparison pattern of a second color, wherein the second width of the comparison pattern of the first color is larger than the first width of the reference pattern of the first color in the moving direction of the image carrier. is longer than the third width of the reference pattern of the second color, and the fourth width of the comparison pattern of the second color is longer than the third width of the reference pattern of the second color. The positional deviation correction is performed based on the result of correcting the detection result of (1) with the second detection result of detecting the sweep correction pattern.

According to the configuration of the present invention, in an image forming apparatus using a plurality of color developers, positional deviation correction between images of respective colors formed on an image carrier is suppressed from being lowered in accuracy due to the effect of sweeping. can be done.

Schematic diagram of image forming apparatus Schematic diagram of the sensor unit Sensor unit drive circuit diagram FIG. 11 is a diagram showing an example of a misregistration correction pattern when sweeping does not occur; A diagram showing an example of a misregistration correction pattern when sweeping occurs. A diagram showing an example of sweep amount correction pattern A diagram showing an example in which a misregistration correction pattern and a sweep amount correction pattern are formed separately. A diagram showing an example of a reference pattern and a comparison pattern FIG. 11 is a diagram showing an example of forming a pattern that serves both as a positional deviation correction pattern and a sweep amount correction pattern; A diagram showing an example of a reference pattern and a comparison pattern A diagram showing a conventional misregistration correction pattern

Embodiments of the present invention will be described below with reference to the drawings. It should be noted that the following embodiments do not limit the invention according to the claims, and not all combinations of features described in the embodiments are essential to the solution of the invention.

(First embodiment)
[Description of Image Forming Apparatus]
FIG. 1 is a schematic cross-sectional view showing the configuration of a color laser beam printer 201, which is an image forming apparatus according to the present invention. The image forming apparatus used in the present invention has a four-color image forming unit in order to superimpose images of four colors (Y: yellow, M: magenta, C: cyan, Bk: black) to form a full-color image. I have. Hereinafter, developer images formed in yellow, magenta, and cyan are referred to as color developer images, and developer images formed in black are referred to as black developer images.

When the color laser beam printer 201 receives the image data 203 from the host computer 202, the print image generation unit 204 develops the image data into video signal format data to generate a video signal 205 for image formation. The control unit 206 has arithmetic processing means such as a CPU 209, receives the video signal 205 generated by the print image generation unit 204, and controls a plurality of laser diodes 211, which are laser light emitting elements in the scanner unit 210. Drive according to the video signal.

Laser beams 212y, 212m, 212c, and 212k (hereinafter also referred to as laser beams 212) emitted from the laser diode 211 are irradiated onto photosensitive drums 215y, 215m, 215c, and 215k via the following. Specifically, the laser beam 212 passes through the polygon mirror 207, lenses 213y, 213m, 213c and 213k (hereinafter also referred to as lens 213), and folding mirrors 214y, 214m, 214c and 214k (hereinafter also referred to as folding mirror 214). intervene. Then, the photosensitive drums 215y, 215m, 215c, and 215k (hereinafter also referred to as the photosensitive drums 215) are irradiated with the light. Photosensitive drums 215y, 215m, 215c, and 215k, which are a plurality of image carriers, are charged by charging means 216y, 216m, 216c, and 216k (hereinafter also referred to as charging means 216), respectively.

An electrostatic latent image is formed on the surface of the photosensitive drum 215 by irradiating the photosensitive drum 215 with the laser beam 212 and partially lowering the surface potential. A toner image ( A developer image) is formed. As described above, the image forming apparatus 201 includes image forming means for forming toner images of different colors on each of the photosensitive drums 215 . A toner image formed on the photosensitive drum 215 is transferred onto an intermediate transfer belt 219 as a transfer medium by applying a bias voltage to primary transfer members 218y, 218m, 218c, and 218k (hereinafter also referred to as primary transfer members 218). is primarily transcribed to The intermediate transfer belt 219 is an intermediate transfer body composed of a rotating endless belt.

First, a yellow image is primarily transferred to the intermediate transfer belt 219, and a magenta image, a cyan image, and a black image are transferred thereon in multiple layers in this order to form a color image in which toner images of multiple colors are superimposed. . As described above, the image forming apparatus 201 includes the primary transfer member 218 as transfer means for sequentially transferring the toner images formed on each of the photosensitive drums 215 onto the intermediate transfer belt 219 as an intermediate transfer member. Note that the intermediate transfer belt 219 is driven by an intermediate transfer belt drive roller 226 . The recording material P in the cassette 220 is picked up by a paper feed roller 222 and then conveyed to the secondary transfer portion so as to synchronize with the image primarily transferred onto the intermediate transfer belt 219 . Then, the toner image is transferred onto the recording material P by performing secondary transfer with the secondary transfer roller 223 in the secondary transfer portion.

The recording material P on which the toner image has been secondarily transferred is heat-fixed by heat and pressure in a fixing device 224, and then discharged to a paper discharge section above the image forming apparatus. Further, the sensor unit 225 detects a misregistration correction pattern for detecting misregistration amounts between the images of each color transferred onto the intermediate transfer belt 219 . The sensor unit 225 detects reflected light when the misregistration correction pattern of each color formed on the intermediate transfer belt 219 is irradiated with light, and transmits the detection result to the control unit 206 . The control unit 206 calculates the position of the misregistration correction pattern formed on the intermediate transfer belt 219 based on the detection result by the sensor unit 225, and based on the calculated position of the misregistration correction pattern of each color. positional deviation correction between images. Note that the intermediate transfer belt 219 has been described as an example of the transfer medium. However, the transfer medium is not limited to this, and in the present invention, the transfer medium may be a photosensitive drum, a recording material, or a conveying belt that attracts and conveys the recording material, and the correction patterns formed on each are detected. By doing so, it is also possible to perform positional deviation detection.

[Configuration of Color Misregistration Correction Sensor]
FIG. 2 shows a schematic configuration diagram of the sensor unit 225. As shown in FIG. The sensor unit 225 is the optical sensors 301,302. By arranging a plurality of optical sensors 301 and 302 in a direction orthogonal to the conveying direction of the intermediate transfer belt 219 (the arrow direction in the figure), it is possible to detect positional deviation of images in the main scanning direction and the positional deviation in the sub-scanning direction. I do. Optical sensors 301 and 302 detect diffusely reflected light from the intermediate transfer belt 219 and the misregistration correction pattern 305 . Optical sensors 301 and 302 each have a light emitting element 303 and a light receiving element 304 . The light emitting element 303 is arranged so as to emit infrared light at an angle of 15° with respect to the direction perpendicular to the belt surface of the intermediate transfer belt 219 .

The light-receiving element 304 is arranged at a light-receiving angle of 45° with respect to the direction perpendicular to the belt surface of the intermediate transfer belt 219 in order to detect the diffusely reflected light from the intermediate transfer belt 219 and the misregistration correction pattern 305 . be. Infrared light emitted from the light emitting element 303 is applied to the intermediate transfer belt 219 and the misregistration correction patterns 305 of each color on the intermediate transfer belt 219 . The light-receiving element 304 receives the diffusely reflected infrared light from the intermediate transfer belt 219 and the misregistration correction pattern on the intermediate transfer belt 219 . Here, as an example, the angle of the light emitting element 303 is 15 degrees and the angle of the light receiving element 304 is 45 degrees. However, the angle is not limited to this. In other words, there may be some deviation from the above angles depending on the desired positional deviation correction accuracy. Also, although the light emitted from the light emitting element 303 has been described as infrared light, it is not limited to this. In other words, it is also possible to perform detection using light of a color other than infrared light, depending on the desired positional deviation correction accuracy.

Next, FIG. 3 shows a drive circuit diagram of the sensor unit 225. As shown in FIG. Lighting of the light emitting element 303 is controlled by a light emitting element drive signal Vledon from the control unit 206 . A switching element 404 such as a transistor is driven by a light-emitting element drive signal Vledon via a base resistor 403, and a current limiting resistor 405 controls the current flowing through the light-emitting element 303, thereby controlling light emission of the light-emitting element 303. . The light-receiving element 304 receives the diffusely reflected light from the intermediate transfer belt 219 and the misregistration correction pattern, and a current corresponding to the received diffusely reflected light amount flows through the resistor 401, so that the detected value of the diffusely reflected light amount is an analog output signal. is output as

A comparator 402 compares a predetermined threshold voltage determined by the voltage dividing resistors 406 and 407 with an analog output signal voltage indicating the detected value of the amount of diffusely reflected light, thereby converting the analog output signal into a digital output signal Vdout. . The control unit 206 acquires the digital output signal Vout in time series, detects the timing of rising and falling edges of the digital output signal Vout, and sequentially stores the acquisition timing of each edge in a storage device (not shown).

[Position error correction pattern]
Next, the configuration of the misregistration correction pattern, the outline of the misregistration correction pattern formed on the intermediate transfer belt 219 when the misregistration correction control is performed, and the misregistration correction method in this embodiment will be described.

FIG. 4 shows a configuration example of a positional deviation correction pattern, an analog output signal of the positional deviation correction pattern detected by the sensor unit 225, and a digital output signal obtained by binarizing the analog output signal with a predetermined threshold voltage Vth by a comparator. indicates In addition, in FIG. 4, sweeping does not occur.

The misregistration correction patterns are composed of yellow developer patterns 501y and 502y, magenta developer patterns 501m and 502m, cyan developer patterns 501c and 502c, and black developer patterns 501k and 502k. When the sensor unit 225 that uses diffusely reflected light detects the misregistration correction pattern, the diffusely reflected light from the black developer pattern formed on the intermediate transfer belt 219 is approximately the same as the diffusely reflected light from the intermediate transfer belt 219 . low. As a result, since the black developer pattern formed on the intermediate transfer belt 219 cannot be detected, the black developer patterns 501k and 502k are formed so as to overlap the yellow developer patterns 501y and 502y. In order to increase the S/N ratio of the analog output signal of the sensor unit 225, the width of the positional deviation correction pattern is formed to be larger than the spot diameter 505 of the light receiving element of the sensor unit 225. .

The misregistration correction pattern includes a first half misregistration correction pattern 503 arranged on the downstream side in the movement direction of the intermediate transfer belt 219 and a second half misregistration correction pattern 504 arranged on the movement direction upstream side. The positional deviation correction pattern 503 in the first half and the positional deviation correction pattern 504 in the second half have a shape inverted with respect to the moving direction of the intermediate transfer belt 219 , and the two form a positional deviation correction pattern set 506 .

[Calculation of misalignment amount]
Next, a method for calculating the amount of positional deviation based on the position detection result of the positional deviation correction pattern will be described. The positional deviation amount is calculated by detecting the forming positions of the reference color pattern and the correction color pattern with the sensor unit 225 and inputting the detection timing of each pattern to the control unit 206 . In this embodiment, the yellow developer pattern is used as a reference color pattern, and the magenta developer pattern, cyan developer pattern, and black developer pattern are used as correction color patterns, and relative positional deviation amounts of the respective colors are calculated.

The control unit 206 internally operates a timer in order to detect the formation position of the misregistration correction pattern. Then, detection timings corresponding to rising and falling edges of the digital output signal of the positional deviation correction pattern are stored in the memory from the timer reference point. Detection timing is defined as follows.
leading edge position detection timing ty11 of the first yellow developer pattern;
leading edge position detection timing tk11 of the first black developer pattern;
Trailing edge position detection timing tk12 of the first black developer pattern,
the trailing edge position detection timing ty12 of the first yellow developer pattern;
leading edge position detection timing tm11 of the first magenta developer pattern;
Trailing edge position detection timing tm12 of the first magenta developer pattern,
leading edge position detection timing tc11 of the first cyan developer pattern;
the trailing edge position detection timing tc12 of the first cyan developer pattern;
leading edge position detection timing tc21 of the second cyan developer pattern;
Second cyan developer pattern trailing edge position detection timing tc22,
leading edge position detection timing tm21 of the second magenta developer pattern;
Trailing edge position detection timing tm22 of the second magenta developer pattern,
leading edge position detection timing ty21 of the second yellow developer pattern;
leading edge position detection timing tk21 of the second black developer pattern;
Trailing edge position detection timing tk22 of the second black developer pattern,
Trailing edge position detection timing ty22 of the second yellow developer pattern.

Next, in order to calculate the amount of misalignment between colors, the center position of each pattern is calculated by the following equation.
Center position ty1 of the first yellow developer pattern=(ty11+ty12)/2 (1)
Center position tm1 of the first magenta developer pattern=(tm11+tm12)/2 (2)
Center position of first cyan developer pattern tc1=(tc11+tc12)/2 (3)
Center position tk1 of the first black developer pattern=(tk11+tk12)/2 (4)
Center position ty2 of the second yellow developer pattern=(ty21+ty22)/2 (5)
Center position of second magenta developer pattern tm2=(tm21+tm22)/2 (6)
Center position of second cyan developer pattern tc2=(tc21+tc22)/2 (7)
Center position of second black developer pattern tk2=(tk21+tk22)/2 (8)
Based on the center position of each pattern calculated by the above formula, the positional deviation time in the sub-scanning direction of the pattern of each of the other colors with respect to the yellow developer pattern, which is the reference color, is calculated by the following formula.
Sub-scanning position deviation time tpd_my of magenta developer pattern=((tm1-ty1)+(tm2-ty2))/2 (9)
Sub-scanning position deviation time tpd_cy of cyan developer pattern=((tc1-ty1)+(tc2-ty2))/2 (10)
Black developer pattern sub-scanning position shift time tpd_ky=((tk1-ty1)+(tk2-ty2))/2 (11)
The time corresponding to the leading edge position, trailing edge position, and center position of each color pattern indicates the elapsed time from a certain reference time (for example, timer measurement start time). The control unit 206 converts the calculated positional deviation time into a positional deviation amount using the speed PS of the intermediate transfer belt 219, thereby calculating the relative positional deviation amount of each of the other color patterns with respect to the yellow developer pattern which is the reference color. , is calculated by the following formula.
Sub-scanning position deviation amount PDd1_my of magenta developer pattern=PS×tpd_my (12)
Sub-scanning positional deviation amount PDd1_cy of cyan developer pattern=PS×tpd_cy (13)
Sub-scanning position deviation amount PDd1_ky of black developer pattern=PS×tpd_ky (14)
When the calculated positional deviation amounts PDd1_my, PDd1_cy, and PDd1_ky are positive, it indicates that writing of the correction color is slower than that of the reference color. On the other hand, when the calculation result is negative, it indicates that the writing position of the correction color is earlier than the reference color. Positional deviation correction control is performed by feeding back the positional deviation amounts PDd1_my, PDd1_cy, and PDd_ky to the print image generation unit 204 as the amount of writing position correction in the sub-scanning direction. 4 are formed on the intermediate transfer belt 219, and the average value of the misregistration correction amount of each set calculated by calculation is used to obtain the misregistration correction accuracy. increasing.

[Position deviation correction error due to sweeping]
FIG. 5 shows a configuration example of a positional deviation correction pattern, an analog output signal of the positional deviation correction pattern detected by the sensor unit 225, and a digital output signal obtained by binarizing the analog output signal with a predetermined threshold voltage Vth by a comparator. indicates Sweeps 601y, 601m, 601c, and 601k occur at the trailing edge portions of the misregistration correction patterns formed for each color. In such a case, the detection timing of the trailing edge of the analog output signal of the positional deviation correction pattern is delayed as shown by the solid line waveform. Note that the broken-line waveform of the analog output signal is the output waveform in a state in which sweeping is not occurring.

This is because when the misregistration correction pattern is swept together, the edge position of the rear end of the misregistration correction pattern formed on the intermediate transfer belt 219 does not change, but the density of the rear end increases. , due to an increase in the amount of reflected light detected by the sensor unit 225 . As a result, the current flowing through the phototransistor, which is a light-receiving element, increases, and the peak value of the voltage waveform after current-voltage conversion increases, resulting in a delay in the fall timing of the voltage waveform. Since the digital output signal is generated by comparing the analog output signal with the threshold voltage Vth of the comparator, if the fall timing of the analog output signal is delayed, the H/L switching timing of the digital output signal changes from the broken line waveform to the solid line waveform. delay to. Here, as an example, the black developer pattern tends to be less affected by sweeping because the amount of diffusely reflected light is lower than that of other color patterns as described above. Not shown in FIG. 5 is the effect of sweeping the black developer pattern on the analog waveform. However, if it is also desired to correct the effect of black developer sweeping, a black sweeping amount correction pattern may be formed in the following manner.

The detection timing of the center position of each pattern in the state where sweeping occurs is calculated by the following equation.
Center position ty1′ of the first yellow developer pattern=(ty11+ty12′)/2 (15)
Center position of the first magenta developer pattern tm1'=(tm11+tm12')/2 (16)
Center position of first cyan developer pattern tc1'=(tc11+tc12')/2 (17)
Center position ty2' of the second yellow developer pattern=(ty21+ty22')/2 (18)
Center position tm2' of the second magenta developer pattern=(tm21+tm22')/2 (19)
Center position of second cyan developer pattern tc2'=(tc21+tc22')/2 (20)
Therefore, due to the sweeping effect, the detection timing of the center position of the misregistration correction pattern of each color includes the following errors.
Error Δty1 of first yellow developer pattern=(ty1′−ty1) (21)
First magenta developer pattern error Δtm1=(tm1′−tm1) (22)
First cyan developer pattern error Δtc1=(tc1′−tc1) (23)
Second yellow developer pattern error Δty2=(ty2′−ty2) (24)
Second magenta developer pattern error Δtm2=(tm2′−tm2) (25)
Second cyan developer pattern error Δtc2=(tc2′−tc2) (26)
Since the positional deviation correction is calculated based on the detection timing of the center position of each pattern, if the detection timing of the center position includes a detection error due to sweeping, an error will also occur in the positional deviation correction.

[Sweeping amount correction pattern]
In the present embodiment, a sweep amount correction pattern 103 is formed separately from the position shift correction pattern in order to suppress errors in position shift correction due to sweeping. FIG. 6 shows sweep amount correction patterns. The sweep amount correction pattern includes each color reference pattern and a comparison pattern. The reference pattern and the comparison pattern are two types of patterns having different widths in the sub-scanning direction. The sweep amount correction patterns shown in FIG. 6 are a yellow reference pattern 101y, a yellow comparison pattern 102y, a magenta reference pattern 101m, a magenta comparison pattern 102m, a cyan reference pattern 101c, and a cyan comparison pattern 102c. Here, the length of the reference pattern in the sub-scanning direction is 100 dots (approximately 4.2 mm in terms of 600 dpi), and the length of the comparison pattern in the sub-scanning direction is 200 dots (approximately 8.4 mm).

Note that the sweep amount correction pattern 103 may be arranged in the vicinity of the misregistration correction pattern 506 as shown in FIG. By forming in this way, it is possible to acquire a correction parameter for correcting the effect of sweeping occurring in the positional deviation correction pattern when performing positional deviation correction control. However, the timing of forming the sweep amount correction pattern is not limited to this. For example, if it is difficult to form both the misregistration correction pattern and the sweep amount correction pattern on one rotation of the intermediate transfer belt 219, the sweep amount correction pattern is formed at a timing different from the misregistration correction control execution timing. may be formed.

The analog output signal in FIG. 6 is a waveform obtained by detecting the reference pattern and the comparison pattern of each color by the sensor unit 225 . The waveform peak values 104y1, 104m, and 104c at the trailing edge due to the occurrence of sweeping when the comparison pattern of each color is detected are the waveform peak values 105y1 and 105m at the trailing edge due to the occurrence of sweeping when the reference pattern is detected. , 105c. This is because part of the developer that could not be developed onto the photosensitive drum at the development nip portion is collectively developed near the interface between the latent image area and the non-latent image area of the photosensitive drum (the rear end of the image in the sub-scanning direction). This is because The longer the image in the sub-scanning direction, the darker the density at the trailing edge of the image due to the effect of sweeping, and the larger the waveform peak value.

[Method of detecting the amount of sweeping]
FIG. 6 shows an analog output signal and a digital output signal when the sensor unit 225 detects the sweep amount correction pattern. The control unit 206 internally operates a timer in order to detect the formation position of the sweep amount correction pattern. Then, detection timings corresponding to rising and falling edges of the digital output signal of the sweep amount correction pattern are stored in the memory from the timer reference point. Detection timing is defined as follows.
leading edge position detection timing tya1 of the reference yellow developer pattern;
the trailing edge position detection timing tya2 of the reference yellow developer pattern;
Leading edge position detection timing tyb1 of comparative yellow developer pattern,
trailing edge position detection timing tyb2 of comparative yellow developer pattern;
leading edge position detection timing tma1 of the reference magenta developer pattern;
trailing edge position detection timing tma2 of the reference magenta developer pattern;
leading edge position detection timing tmb1 of the comparative magenta developer pattern;
trailing edge position detection timing tmb2 of the comparative magenta developer pattern;
leading edge position detection timing tca1 of the reference cyan developer pattern;
trailing edge position detection timing tca2 of the reference cyan developer pattern;
leading edge position detection timing tcb1 of the comparative cyan developer pattern;
Trailing edge position detection timing tcb2 of the comparative cyan developer pattern.

Next, the pattern width time of the reference pattern of each color and the comparison pattern is calculated by the following equation.
Yellow reference pattern width time Tya=(tya2-tya1) (27)
Yellow comparison pattern width time Tyb=(tyb2-tyb1) (28)
The magenta reference pattern width time Tma=(tma2-tma1) (29)
Magenta comparison pattern width time Tmb=(tmb2-tmb1) (30)
Cyan reference pattern width time Tca=(tca2-tca1) (31)
Cyan comparison pattern width time Tcb=(tcb2-tcb1) (32)
Next, calculation of the amount of sweep will be described with reference to FIG. The amount of sweep generated in the misregistration correction pattern of each color is calculated by comparing the pattern widths of the reference pattern and the comparison pattern. Since the calculation method is common to each color, a method of calculating the sweep amount using the sweep amount correction pattern for yellow will be described here as an example. Incidentally, FIG. 8(a) shows the analog output signal and the digital output signal of the reference pattern. FIG. 8B shows the analog output signal and digital output signal of the comparison pattern.

The detection width of the digital output signal when the reference pattern is detected by the sensor unit 225 includes the following sections. A section TA from when the reference pattern enters part of the spot diameter 505 of the sensor until the reference pattern enters the entire spot diameter 505 . A section TB from when the reference pattern enters the entire spot diameter 505 until the reference pattern completely leaves the spot diameter 505 . Interval TB includes a detection error due to sweeping.

The detection width of the digital output signal when the comparison pattern is detected by the sensor unit 225 includes the following sections. A section TA from when the comparison pattern enters part of the spot diameter 505 of the sensor until the comparison pattern enters the entire spot diameter 505 . A section TC through which the pattern width difference (100 dots) between the comparison pattern and the reference pattern passes. After the section TC, the section TD from the spot diameter 505 to the end of the comparison pattern. The interval TD includes detection errors due to sweeping.

Here, the interval TB includes a detection error due to sweeping that occurs when the pattern width (100 dots) of the reference pattern is formed. On the other hand, the section TD includes detection errors due to sweeping that occurs when the pattern width (200 dots) of the comparison pattern is formed. In other words, by calculating the difference between the detection results of the section TD and the section TB, it is possible to calculate the detection error of the digital output signal due to sweeping that occurs when a pattern of 100 dots, which is the difference in pattern width, is formed.

At this time, the time T_TC required for the section TC through which the difference 100 dots between the pattern width of the comparison pattern and the pattern width of the reference pattern passes can be obtained from the speed of the intermediate transfer belt 219 . The time difference between the section TD and the section TB can be calculated as follows.
Detection error time Terr_y100 due to sweeping per 100 dots of yellow developer pattern=Tyb-Tya-T_TC (33)
Terr_y100 calculated by equation (33) is the detection error time due to sweeping per 100 dots of the yellow developer pattern. From this, the detection error time due to sweeping per dot is calculated by the following equation.
Detection error time Terr_y due to sweeping per dot of yellow developer pattern=(Tyb-Tya-T_TC)/100 (34)
[Correction of misalignment detection result]
Detection error times Terr_y, Terr_m, and Terr_c due to sweeping per dot of each color are obtained by the calculation method described above. Then, the detection timing of the center position of the misregistration correction pattern in the state where the sweep is occurring, which is calculated by the above formulas (15) to (20), is corrected. As a result, it is possible to calculate the center position of the misregistration correction pattern in which the influence of sweeping is suppressed. For example, when the pattern width in the sub-scanning direction of the misregistration correction pattern is 300 dots, the center position can be obtained by the following equation.
Center position ty1'' of the first yellow developer pattern after sweep correction=(ty11+ty12')-(Terr_y×300)/2 (35)
Center position tm1'' of the first magenta developer pattern after sweep correction=(tm11+tm12')-(Terr_m×300)/2 (36)
Center position tc1'' of the first cyan developer pattern after sweep correction=(tc11+tc12')-(Terr_c×300)/2 (37)
Center position ty2'' of second yellow developer pattern after sweep correction=(ty21+ty22')-(Terr_y×300)/2 (38)
Center position tm2'' of second magenta developer pattern after sweep correction=(tm21+tm22')-(Terr_m×300)/2 (39)
Center position tc2'' of second cyan developer pattern after sweep correction=(tc21+tc22')-(Terr_c×300)/2 (40)
In this way, it is possible to calculate the detection error caused by the sweep occurring in the misregistration correction pattern. Further, by correcting the center position where the misregistration correction pattern is detected based on the calculated detection error, it is possible to suppress the detection error due to sweeping.

(Second embodiment)
In the first embodiment, a method of forming a sweeping amount correction pattern for detecting sweeping has been described. In this embodiment, a method of using part of the positional deviation correction pattern as the sweep amount correction pattern will be described. Detailed descriptions of the same contents as in the first embodiment, such as the configuration of the image forming apparatus, the configuration of the sensor unit, and the positional deviation correction control, will be omitted here.

[Sweeping amount correction pattern]
In this embodiment, in order to suppress an error in positional deviation correction due to sweeping, a pattern is formed that serves both as a positional deviation correction pattern and a sweeping amount correction pattern. FIG. 9 shows a pattern that serves both as a misregistration correction pattern and as a sweep amount correction pattern. A pattern group 901 is a misregistration correction pattern and also serves as a reference pattern for the sweep amount correction pattern. The pattern group 902 has a yellow developer pattern, a magenta developer pattern, and a cyan developer pattern whose widths are longer in the sub-scanning direction than those of the pattern group 901. The pattern group 902 is a misregistration correction pattern and a sweep amount correction pattern. It also serves as a comparison pattern. As for the black developer pattern, as an example, the sweep amount correction pattern is not formed here because it is less susceptible to sweeping. However, if it is also desired to correct the effect of the sweeping of the black developer, a comparison pattern using the black developer may be formed.

FIG. 10 is a diagram showing part of a pattern that serves both as a positional deviation correction pattern and a sweep amount correction pattern. An analog output signal and a digital output signal are also shown. A pattern group 902 including a comparison pattern has a longer width in the sub-scanning direction than a pattern group 901 including a sweep amount correction reference pattern. Therefore, as in the case described in the first embodiment, the influence of sweeping is different. The waveform peak values 104y, 104m, and 104c at the trailing edge due to the occurrence of sweeping when the comparison pattern of each color is detected are the waveform peak values 105y at the trailing edge due to the occurrence of sweeping when the reference pattern is detected, It becomes a larger value than 105m and 105c.

Each control unit 206 internally operates a timer in order to detect the formation position of the sweep amount correction pattern. Then, detection timings corresponding to rising and falling edges of the digital output signal of the sweep amount correction pattern are stored in the memory from the timer reference point.

Next, the pattern width time of the reference pattern of each color and the comparison pattern is calculated by the following equation.
Yellow reference pattern width time Tya=(tya2-tya1) (41)
Yellow comparison pattern width time Tyb=(tyb2-tyb1) (42)
The magenta reference pattern width time Tma=(tma2-tma1) (43)
The magenta comparison pattern width time Tmb=(tmb2-tmb1) (44)
Cyan reference pattern width time Tca=(tca2-tca1) (45)
Cyan comparison pattern width time Tcb=(tcb2-tcb1) (46)
Since the following is the same as the first embodiment, detailed description will be omitted. A difference time is obtained from the calculated pattern width times of the reference pattern and the comparison pattern. Then, the amount of detection error caused by sweeping is calculated from the difference time, and the result of detection of the misregistration correction pattern is corrected.

In this way, it is possible to calculate the detection error caused by the sweep occurring in the misregistration correction pattern. Further, by correcting the center position where the misregistration correction pattern is detected based on the calculated detection error, it is possible to suppress the detection error due to sweeping. Further, by forming a pattern that serves both as a positional deviation correction pattern and a sweeping amount correction pattern, the time required for detection can be shortened.

101 reference pattern 102 comparison pattern 206 control unit

Claims (8)

an image forming means for forming a misregistration correction pattern composed of developer images of a plurality of colors on an image carrier;
a detecting means for irradiating light toward the misregistration correction pattern formed by the image forming means and detecting reflected light of the irradiated light;
a control means for correcting a positional deviation based on the detection result detected by the detection means;
The image forming means forms, on the image carrier, a sweep correction pattern composed of developer images of a plurality of colors,
The sweeping correction pattern includes a first color reference pattern, a first color comparison pattern, a second color reference pattern, and a second color comparison pattern,
In the movement direction of the image carrier, the second width of the first color reference pattern is longer than the first width of the first color reference pattern, and the third width of the second color reference pattern is longer than the first width of the first color reference pattern. the fourth width of the second color comparison pattern is longer than the width of the
The control means performs the positional deviation correction based on a result obtained by correcting a first detection result of detecting the positional deviation correction pattern with a second detection result of detecting the sweeping correction pattern. image forming apparatus. an image forming means for forming a misregistration correction pattern composed of developer images of a plurality of colors on an image carrier;
a detecting means for irradiating light toward the misregistration correction pattern formed by the image forming means and detecting reflected light of the irradiated light;
a control means for correcting a positional deviation based on the detection result detected by the detection means;
The misregistration correction pattern includes a first color reference pattern, a first color comparison pattern, a second color reference pattern, and a second color comparison pattern,
In the movement direction of the image carrier, the second width of the first color reference pattern is longer than the first width of the first color reference pattern, and the third width of the second color reference pattern is longer than the first width of the first color reference pattern. the fourth width of the second color comparison pattern is longer than the width of the
The control means calculates a value related to sweeping from a first detection result of detecting the misregistration correction pattern, and calculates the positional deviation based on a result of correcting the first detection result with the value related to sweeping. An image forming apparatus characterized by correcting deviation. The control means obtains a value related to the amount of sweeping in the developer image of the first color by obtaining a difference between the reference pattern of the first color and the comparison pattern of the first color, and calculates the reference pattern of the second color. 3. The image forming apparatus according to claim 1, wherein a value relating to sweeping of the developer image of the second color is obtained by obtaining a difference between the pattern and the comparison pattern of the second color. Width of the reference pattern of the first color, width of the comparison pattern of the first color, width of the reference pattern of the second color, and width of the comparison pattern of the second color in the movement direction of the image carrier. 4. The image forming apparatus according to claim 1, wherein is larger than the spot diameter of said detecting means. The control means calculates a positional deviation amount of the developer image of the other color with respect to the developer image of a predetermined reference color based on the result of the correction, and performs the positional deviation correction based on the positional deviation amount. The image forming apparatus according to any one of claims 1 to 4, characterized by: 6. The apparatus according to claim 5, wherein said control means calculates said positional deviation amount according to a difference between a central position of a developer image of a predetermined reference color and a central position of a developer image of another color. image forming device. 7. The image forming method according to claim 1, wherein the controller corrects at least one of a main scanning direction deviation and a sub scanning direction deviation based on the result of the correction. Device. The detection means includes irradiation means for irradiating the developer image with light;
8. The image forming apparatus according to claim 1, further comprising a light receiving unit for receiving diffusely reflected light from the developer image.

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