JP2012194477A - Image forming apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To allow a high quality color image to be obtained by improving color matching accuracy.SOLUTION: A color image forming section causes a color matching pattern to be formed on an intermediate transfer belt as an endless moving member as follows. A reference color sub-scanning ends error detection overlapping pattern YK2, which is formed by overlapping a black pattern Kws as a reference pattern and a yellow pattern Yw1 as a monochrome pattern of color other than black, and a reference color sub-scanning ends error detection monochrome pattern Yws, which is formed by the yellow pattern as the monochrome pattern of color other than black, are formed on the intermediate transfer belt. The reference color sub-scanning ends error detection overlapping pattern YK2 and the reference color sub-scanning ends error detection monochrome pattern Yws are detected by an optical sensor, and based on the detected result, a reference color detection error is calculated, which is a detection error at end positions in the sub-scanning directions of the black pattern Kws. Then, according to the reference color detection error, a color shift amount of the image formation positions between the reference color and other colors is corrected.

Description

  The present invention relates to an image forming apparatus such as a printer or a copying machine capable of forming a color image, and more particularly to an image forming apparatus that performs color matching control on an endless moving member during color image formation.

  As an image forming apparatus as described above, image holding of a plurality of image forming units juxtaposed along the rotating direction (moving direction) of a transfer belt (also referred to as “intermediate transfer belt”) which is a single endless moving member A color image is formed by sequentially superimposing and transferring each color image (toner image) formed on the body onto an intermediate transfer belt (see, for example, Patent Document 1). .

In such an image forming apparatus, it is necessary to detect a positional deviation amount (color misregistration amount) of each color in order to accurately superimpose the images of the respective colors.
Therefore, as a color matching pattern for color matching of a color image on the intermediate transfer belt, for example, as shown in FIGS. 9A and 9B, a black color Kws and a monochrome pattern other than black (in this example, A superposition pattern YK2 that is a superposition of the yellow pattern) Yw1 and a monochromatic pattern (in this example, a yellow pattern) Yws composed of only a single color other than black are formed.

  The overlay pattern YK2 is formed by superimposing the black pattern Kws on the upper side and forming a width WS in the sub-scanning direction (hereinafter also referred to as “sub-scanning width”) WS, which is the rotation direction of the intermediate transfer belt, and the lower monochromatic color. The width in the sub-scanning direction of the pattern Yw1 is larger than WS, and the black pattern Kws and the edge in the sub-scanning direction of the monochrome pattern Yw1 (hereinafter also simply referred to as “sub-scanning edge”) do not overlap.

  Next, the overlay pattern YK2 and the single color pattern Yws formed on the intermediate transfer belt are detected by an optical sensor which is an optical element. Here, the detection period of the single color pattern Yws is Tyws. The superimposition pattern YK2 has a non-detection period due to the black pattern Kws after the start of detection, and a detection period occurs again. Therefore, the non-detection period can be regarded as the detection period of the black pattern Kws, and the detection period is defined as Tkws. And

  However, the monochrome pattern other than black can detect the reflected light reflected at the end portion in the sub-scanning direction (hereinafter, also simply referred to as “sub-scan end portion”), so the detection period Tyws of the monochrome pattern Yws is the monochrome pattern Yws. However, the black pattern Kws detection period Tkws includes a period during which the reflected light from the lower monochromatic pattern Yw1 is blocked by the upper black pattern Kws having a certain thickness. The non-detection period is started before the edge portion of T, and Tkws> Tyws. Therefore, there is a problem that an error occurs in the detection of the edge portion of the black pattern Kws, and color misregistration is caused by performing color matching control using the detection result of the color matching pattern including the error.

  The present invention has been made in view of the above points, and an object thereof is to improve color matching accuracy and obtain a high-quality color image.

  According to the present invention, each single-color image including black formed on the image carrier of a plurality of image forming units arranged in parallel along the sub-scanning direction that is the rotation direction of a single endless moving member is An image forming apparatus having color image forming means for forming a color image by sequentially superimposing and transferring the image onto an endless moving member, wherein the image forming apparatus is configured as follows to achieve the above object. .

  The image forming apparatus according to the present invention includes an optical element that emits a light beam to the endless moving member, detects reflected light from the endless moving member, and converts it into an electrical signal, and the endless movement by the color image forming unit. A color-matching pattern for color-matching the color image is formed on the member, and the amount of misregistration between the image forming positions of the reference color and the other colors based on the result of detecting the color-matching pattern by the optical element A positional deviation amount detecting means for detecting the color deviation, and an adjusting means for adjusting an image forming position of a color other than the reference color according to the positional deviation amount detected thereby. When the color matching pattern is formed on the endless moving member by the image forming means, the black pattern as the reference color pattern and a single color pattern of a color other than black And a reference color sub-scanning end error detection superposition pattern and a reference color sub-scanning end error detection single-color pattern consisting of a single color pattern other than black are formed on the endless moving member. And the reference color sub-scanning edge error detection overlay pattern and the reference color sub-scanning edge error detection single-color pattern based on the result of detection by the optical element, the end of the black pattern in the sub-scanning direction. Means for calculating a reference color detection error which is a part position detection error and correcting the positional deviation amount according to the reference color detection error is provided.

Further, the misregistration amount detection means forms a pattern Yws (for example, a yellow pattern) having a width WS in the sub-scanning direction in a single color other than black as the reference color sub-scanning end error detection single-color pattern. A pattern Ywl having a width WL in the sub-scanning direction (for example, a yellow pattern) is formed in the sub-scanning direction with a color in which the reference color sub-scanning end error detecting single-color pattern is formed as the color sub-scanning end error detecting overlapping pattern; A black pattern Kws (black pattern) is formed in black so as to overlap the pattern Ywl in the sub-scanning direction, and the pattern Kws is included in the pattern Ywl, and the end of the pattern Kws in the sub-scanning direction The portion of the pattern Ywl does not overlap the end of the pattern Ywl in the sub-scanning direction, and the pattern Yws and the pattern Ywl The distance between the ends of the serial sub-scanning direction may be set so that it can take a sufficient period for the optical element is not temporarily pattern detection.
Of the period Tywl in which the positional deviation amount detection unit detects the pattern Ywl with the optical element, a period Tkws in which reflected light is not detected by the pattern Kws (detection period in the sub-scanning direction of the pattern Kws). In addition to measurement, the detection period Tyws of the pattern Yws may be measured, and the reference color detection error period Terr may be derived from the detection periods Tkws and Tyws by an arithmetic expression (Terr = Tkws−Tyws).

Furthermore, the misregistration amount detection means derives a correction value C for correcting the misregistration amount from the reference color detection error period Terr, and the black pattern in the detection period of the black pattern of the color matching pattern is derived. The positional deviation amount may be corrected by delaying the detection start timing Ks by the correction value C.
The positional deviation amount detection means may derive the correction value C by an arithmetic expression (C = Terr * α (where α is a real number larger than zero)).

  Then, a superimposed black pattern density setting for setting the density of the black pattern to be superimposed on a single color pattern of a color other than black when forming the reference color sub-scanning edge error detection superimposed pattern in the positional deviation amount detection means And the superimposed black pattern density setting means forms N single-color patterns other than black with the same density (N is an integer equal to or larger than 2 and below the black density gradation setting value), and the N After superimposing the black patterns of different densities on the single color pattern, if the detection output of the optical element for the N single color patterns is equal to or greater than a preset black detection threshold, it is regarded as black detection, and the black color The lowest density of the monochrome pattern density corresponding to the detection output considered as the detection is the shape of the reference color sub-scanning edge error detection overlay pattern. Sometimes it is desirable to set the concentration of the black pattern superimposed on the monochromatic pattern of a color other than the black.

In this case, when the superimposed black pattern density setting unit superimposes the black patterns having different densities on the N monochrome patterns, the monochrome pattern at the end in the sub-scanning direction among the black patterns. It is preferable to set the density so that the density is gradually increased with respect to each monochrome pattern following the monochrome pattern.
The reference color sub-scanning edge error detection overlay pattern and the reference color sub-scanning edge error detection single color pattern may be included in the color matching pattern.

  According to the present invention, when the color matching pattern is formed on the endless moving member by the color image forming means, the reference color sub-scan in which the black pattern as the reference color pattern and the single color pattern of the color other than black are superimposed. A reference color sub-scanning end error detection is performed by forming an end error detection overlapping pattern and a reference color sub-scanning end error detecting single-color pattern composed of a single color pattern other than black on the endless moving member. The reference color detection error, which is the detection error of the end position of the black pattern in the sub-scanning direction, is calculated based on the result of detecting the overlay pattern for use and the single color pattern for detecting the reference color sub-scanning end error by the optical element. By correcting the amount of misalignment between the reference color pattern and the other color pattern according to the reference color detection error, the color matching accuracy is improved. It is possible to obtain a color image.

1 is a schematic configuration diagram illustrating an embodiment of an image forming apparatus according to the present invention. FIG. 2 is a diagram illustrating an optical device 102 viewed from the direction indicated by an arrow A in FIG. 1 together with an exposure control block and a photosensitive drum. FIG. 2 is a perspective view of relevant parts for explaining detection of a color matching pattern formed on an intermediate transfer belt 114 in FIG. 1. It is a block diagram which shows the structure of the exposure control block 300 shown in FIG. 2 in detail. FIG. 2 is a diagram illustrating an example of a color matching pattern formed on the intermediate transfer belt 114 in FIG. 1. Color patterns Mws, Cws, Yws, Kws corresponding to the color patterns 71M, 71C, 71Y, 71K constituting the horizontal line pattern 71, which is a part of the color matching pattern shown in FIG. It is the figure which looked at the sensor 30 from the horizontal direction.

It is a figure which shows an example of the pattern for a color matching in which a part pattern differs from FIG. It is a figure which shows the other example of the pattern for a color matching similarly. It is a figure for demonstrating the detection error of the subscanning direction position of the black pattern by the detection of the pattern for a conventional color matching. FIG. 10 is a diagram for explaining formation of a superposition pattern YK2 and a yellow pattern Yws that are single color patterns and detection of a reference color detection error shown in FIGS. 8 and 9; It is a figure for demonstrating formation of the superposition pattern YK1 shown in FIG. 7, the yellow pattern Yws which is a single color pattern, and the detection of a reference | standard color detection error. It is a figure for demonstrating correction | amendment of the detection error of the subscanning edge part of the black pattern Kws of each superimposition pattern YK2, YK1 shown in FIG. 10, FIG.

It is a figure for demonstrating the density setting change at the time of black pattern Kws formation in the superposition pattern YK2 of FIG. It is a figure for demonstrating the density setting at the time of forming the black pattern Kws in the superposition pattern YK2 of FIG. It is a figure which shows an example of the pattern for color matching containing the pattern for color matching YK1 which changed the density setting value of the black pattern Kws of FIG. It is a figure which shows an example of the pattern for color matching including the pattern for color matching YK2 which changed the density setting value of the black pattern Kws of FIG. It is a figure which shows the other example of the color matching pattern containing the color matching pattern YK1 which changed the density setting value of the black pattern Kws of FIG. It is a figure which shows the other example of the pattern for color matching containing the pattern for color matching YK2 which changed the density setting value of the black pattern Kws of FIG.

Hereinafter, embodiments for carrying out the present invention will be specifically described with reference to the drawings.
FIG. 1 is a schematic configuration diagram showing an embodiment of an image forming apparatus according to the present invention.
The image forming apparatus 100 is a tandem color image forming apparatus, and an optical device 102 that is an optical writing device including optical elements such as a semiconductor laser and a polygon mirror, and magenta (M), cyan (C), and yellow. A color image forming unit 112 including image forming process units (image forming units) 104, 106, 108, and 110 for each color of (Y) and black (K), an intermediate transfer belt 114 which is an endless moving member, and the like. The image forming apparatus includes the transfer unit 122, and forms a color image forming unit (color image forming unit).

  Each of the image forming process units 104, 106, 108, 110 of the color image forming unit 112 is a photoconductor drum 104a, 106a, 108a, 110a, which is a photoconductor indicated by adding a to 104, 106, 108, 110, respectively. Charging devices 104b, 106b, 108b, 110b, and charging units 104b, 106b, 110b, and c, which are charging units shown with b arranged around them, are shown with developing units 104c, 106c, 108c, 110c, and d that are developing units shown with c. Primary transfer rollers 104d, 106d, 108d, 110d and the like are provided.

  The optical device 102 is a multi-beam scanning device, and a laser beam emitted from a light source element such as a semiconductor laser (not shown) is deflected by a polygon mirror 102c, which is a deflection element, and is incident on an fθ lens 102b. In this embodiment, the number of laser beams corresponding to the colors M, C, Y, and K is generated, and after passing through the fθ lens 102b, reflected by the reflecting mirror 102a.

  Each of the laser beams is shaped through the WTL lens 102d, then deflected again by the plurality of reflecting mirrors 102e, and used as the laser beam L for exposure by the image forming process units 104, 106, 108, and 110. The surfaces of the photosensitive drums 104a, 106a, 108a, 110a are irradiated.

Irradiation of the laser beam L to the photosensitive drums 104a, 106a, 108a, and 110a is performed using a plurality of optical elements as described above, and therefore timing synchronization is performed in the main scanning direction and the sub-scanning direction.
The “main scanning direction” is defined as the laser beam scanning direction, and the “sub-scanning direction” is a direction orthogonal to the main scanning direction. In this image forming apparatus 100, the photosensitive drums 104a, 106a, 108a, 110a are The direction of rotation, that is, the moving direction of the surface of the photoreceptor is defined.

Each of the photosensitive drums 104a, 106a, 108a, and 110a includes a photoconductive layer including at least a charge generation layer and a charge transport layer on a conductive drum such as aluminum.
Each of the photoconductive layers is charged with a surface charge applied by chargers 104b, 106b, 108b, and 110b constituted by a corotron, a scorotron, a charging roller, or the like. The charged photoconductive layers of the respective photosensitive drums 104a, 106a, 108a, and 110a are image-wise exposed by the laser beam L from the optical device 102 to form a two-dimensional electrostatic latent image.

  The electrostatic latent images formed on the photosensitive drums 104a, 106a, 108a, 110a are respectively transferred to M, by developing units 104c, 106c, 108c, 110c including a developing sleeve, a developer supply roller, a regulating blade, and the like. Development is performed with toner that is a developer of each color of C, Y, and K, and a toner image of each color is formed. The toner images of the respective colors face the primary transfer rollers 104d, 106d, 108d, and 110d, which are transfer units to which the photosensitive drums 104a, 106a, 108a, and 110a are respectively applied with a transfer bias voltage across the intermediate transfer belt 114. In the primary transfer section, the images are sequentially transferred in the order of K, Y, C, and M on the intermediate transfer belt 114 which is a transfer medium moving in the arrow B direction.

The intermediate transfer belt 114 is stretched around the transport rollers 114a, 114b, and 114c, and one of the intermediate transfer belts 114 is rotated in the direction indicated by the arrow B by the transport roller 114a or 114c that is a driving roller. In a state where a full-color toner image superimposed and transferred is carried, the toner image is conveyed to the secondary transfer unit.
The secondary transfer unit includes a secondary transfer belt 118 that is transported in the direction of arrow C by transport rollers 118a and 118b. The conveyance roller 114b of the intermediate transfer belt 114 also functions as a secondary transfer counter roller.

  A sheet-like recording medium 124 such as high-quality paper or a plastic sheet is supplied to the secondary transfer unit from a recording medium storage unit 128 such as a paper feed cassette by a conveying roller 126. Then, a secondary transfer bias is applied to the conveying roller 114 b that also functions as a secondary transfer counter roller, and the full-color toner image carried on the intermediate transfer belt 114 is held by suction on the secondary transfer belt 118. Transfer to the recording medium 124.

The recording medium 124 onto which the full-color toner image has been transferred is conveyed to the fixing device 120 by the rotation of the secondary transfer belt 118 in the direction of arrow C.
The fixing device 120 is configured to include a fixing member 130 such as a fixing roller containing silicone rubber or fluorine rubber, and pressurizes and heats the recording medium 124 and the toner image together to fix the toner image to the recording medium 124. After that, the printed matter 132 is discharged to the outside of the image forming apparatus 100.
After the toner image is transferred, the intermediate transfer belt 114 is prepared for the next image forming process after the transfer residual toner is removed by a cleaning unit 116 including a cleaning blade.

FIG. 2 is a diagram showing the optical device 102 viewed from the direction indicated by the arrow A in FIG. 1 together with the exposure control block and the photosensitive drum.
The optical device 102 includes the polygon mirror 102c and the fθ lens 102b described above, a reflection mirror 208 and a photodiode for detecting the laser beam deflected by the polygon mirror 102c at a predetermined position before the main scanning writing position. And a synchronous detection sensor (photoelectric conversion element) 210 using an optical sensor such as the above. Further, an exposure control block 300 including a control circuit 202 including a CPU, a driver circuit 204 for lighting a semiconductor laser, and a semiconductor laser element (LA) 206 as a light source element is provided. The semiconductor laser element 206 is, for example, a surface emitting laser (VCSEL).

  The polygon mirror 102c is rotationally driven by a polygon motor (not shown) at a peripheral speed of several thousand to several tens of thousands rpm, irradiated with a laser beam from the semiconductor laser element 206, deflects it within a predetermined angle range, and fθ The photosensitive drums 104a, 106a, 108a, and 110a are irradiated through the lens 102b.

  The control circuit 202 uses image dot information (for example, 4800 dpi high resolution image) to be plotted by the semiconductor laser element 206 from image data (for example, 600 dpi or 1200 dpi resolution image data) from an image reading unit or image memory (not shown). Dot information). Further, the control circuit 202 performs laser output control for causing the semiconductor laser element 206 to emit light with a predetermined laser output, and outputs a PWM (Pulse Width Modulation) or PM (Power Modulation) signal to the driver circuit 204.

The driver circuit 204 supplies a lighting current to the semiconductor laser element 206 according to the received signal, and operates the semiconductor laser element 206 with a predetermined output. As a result, the semiconductor laser element 206 generates a laser beam bundle (light beam) with an output corresponding to the signal from the control circuit 202.
Each laser beam constituting the laser beam bundle forms an electrostatic latent image on the photosensitive drums 104a to 110a.
A laser beam detection signal from the synchronization detection sensor 210 is input to the control circuit 202 and becomes a reference for the writing timing of each main scan.
The control circuit 202 will be described in detail later.

FIG. 3 is a perspective view of relevant parts for explaining detection of a color matching pattern formed on the intermediate transfer belt 114 of FIG. The optical sensor 30 is shown in a perspective view so that the internal configuration can be seen.
In the example shown in FIG. 3, the intermediate transfer belt 114 serving as a transfer medium has a plurality of photosensitive drums 104a, 106a, 108a, 110a arranged in parallel, as described in FIG. It is arranged across the photosensitive drum.

An optical sensor which is an optical element for reading a color matching pattern (image pattern) P formed on the intermediate transfer belt 114 in the vicinity of the driving roller 114a which is one of the conveying rollers 114a to 114c shown in FIG. 30 is arranged.
The optical sensor 30 includes a light emitting element 32 made of LEDs or the like in a housing 31, and a lens for condensing illumination light (light flux) from the light emitting element 32 and irradiating the surface of the intermediate transfer belt 114. 33, and a light receiving lens 34 for condensing the reflected light from the surface of the intermediate transfer belt 114, and a light receiving lens 34 that receives (detects) the light collected by the light receiving lens 34 and converts it into an electric signal. Element 35 is incorporated.

  When the color matching pattern P enters a region illuminated by the light emitting element 32 and received by the light receiving element 35, a detection output (electric signal) by the light receiving element 35 according to the color matching pattern P. Therefore, the color matching pattern P can be detected (read) by the detection output of the light receiving element 35.

FIG. 4 is a block diagram showing the configuration of the exposure control block 300 shown in FIG. 2 in more detail.
The control circuit 202 in the exposure control block 300 includes a buffer RAM 21 that stores raster data, a RAM control unit 22 that controls the buffer RAM 21, an image processing unit 23 that performs image processing on image data read from the buffer RAM 21, and a color matching pattern. And the like, a lighting data control unit 25 that performs PWM conversion on the image data output from the image processing unit 23 and the pattern generation unit 24 as lighting data and outputs the data to the driver circuit 204, and the semiconductor laser element 206 Is provided with a main scanning / sub-scanning counter unit 26 that operates on the basis of a synchronization detection signal detected by a synchronization detection sensor (photoelectric conversion element) 210, and includes a register control unit and shading (not shown). A correction unit is also provided.

In this embodiment, the CPU 50 detects the detection state of the color matching pattern based on the output of the optical sensor 30. The CPU 50 detects the pattern formation position of the other color with respect to the reference color, derives a deviation amount with respect to the ideal value, derives a correction amount for controlling the image formation position of the other color, and sets a setting value to the control circuit 202. Send.
The control circuit 202 adjusts, for example, the sub-scan writing start timing of another color according to the setting value transmitted from the CPU 50, or transmits the image data to the control circuit 202 to a preceding control circuit (not shown). The writing control such as adjusting the generation timing of the image data output request signal is performed.
Here, the CPU 50 in the exposure control block 300 uses the optical sensor 30 and the control circuit 202 to control the color image forming unit, thereby functioning as a misregistration amount detection unit and an adjustment unit according to the present invention. .

Hereinafter, processing related to the present invention in the image forming apparatus according to this embodiment will be described. Prior to the description, processing according to the prior art will be described with reference to FIGS. . For convenience of explanation, it is assumed that the CPU 50 in FIG. 4 detects a color matching pattern formed on the intermediate transfer belt 114 using the optical sensor 30 and the control circuit 202.
5 to 8 are diagrams for explaining color matching based on detection of a color matching pattern.

FIG. 5 is a diagram illustrating an example of a color matching pattern formed on the intermediate transfer belt 114 in FIG. It is assumed that three optical sensors 30 are provided.
This color matching pattern is a color matching pattern for color matching (positioning) of a color image on the intermediate transfer belt 114 by the color image forming unit, and is a predetermined pattern for positioning for regular reflection light. A horizontal line pattern 71, a diagonal line pattern 72, and a horizontal line pattern 73, which are provided in the order of colors of M, C, Y, and K, are arranged in the sub-scanning direction and correspond to each optical sensor 30 as three columns. Yes.

  The horizontal line pattern 71 is composed of four color patterns 71M, 71C, 71Y, 71K which are four horizontal patterns having a predetermined width and a predetermined length in the horizontal direction with respect to the main scanning direction of the photosensitive drums 104a, 106a, 108a, 110a. The oblique line pattern 72 has four oblique lines having a predetermined width and a predetermined length with a predetermined inclination angle (for example, 45 °) with respect to the main scanning direction of the photosensitive drums 104a, 106a, 108a, and 110a. Each color pattern 72M, 72C, 72Y, 72K is a direction pattern. The horizontal line pattern 73 includes the same color patterns 73M, 73C, 73Y, and 73K as the horizontal line pattern 71.

  This color matching pattern forms a horizontal line pattern 71, a diagonal line pattern 72, and a horizontal line pattern 73 corresponding to the colors M, C, Y, and K on the photosensitive drums 104a, 106a, 108a, and 110a, respectively, and intermediate transfer is performed. By transferring and combining on the belt 114, it is formed on the intermediate transfer belt 114 in the arrangement as described above.

Conventionally, the color matching pattern shown in FIG. 5 is formed on the intermediate transfer belt 114, and each color pattern constituting the color matching pattern is detected by the optical sensor 30.
6 shows color patterns Mws, Cws, Yws, Kws corresponding to the color patterns 71M, 71C, 71Y, 71K constituting the horizontal line pattern 71, which is a part of the color matching pattern shown in FIG. 5, and an intermediate transfer belt. 114 and the optical sensor 30 as seen from the lateral direction, and the waveform of the output signal of the optical sensor 30 is also shown.
FIG. 7 and FIG. 8 are diagrams showing different examples of color matching patterns that are partially different from those in FIG. 6, and corresponding portions are denoted by the same reference numerals.

  For example, as shown in FIG. 6, the CPU 50 detects the color patterns Mws, Cws, Yws, and Kws formed on the intermediate transfer belt 114 by the optical sensor 30 and then detects the color patterns Mws, Cws, Yws, and Kws. The image formation start position in the sub-scanning direction is calculated. Further, for example, when the pattern of the reference color is a black pattern Kws, the image formation position of a color other than the reference color with respect to the reference color from the detection position and ideal value for each of the black pattern Kws and the other color patterns Mws, Cws, and Yws. The above-described writing control is performed so as to obtain a deviation amount and correct the positional deviation amount (adjust the image forming position of a color other than the reference color according to the positional deviation amount).

  In this case, if each color is formed as a single color pattern as shown in FIG. 6 above, for example, when the intermediate transfer belt 114 is formed of a black elastic belt, the light reflectance of the elastic belt is low. It becomes difficult to detect the pattern Kws. For this reason, instead of the black pattern Kws shown in FIG. 6, the black pattern Kws is superimposed on a single color pattern (in this example, a yellow pattern having a high light reflectance) Yw1 other than black as shown in FIG. The superimposed pattern YK1 formed, or the superimposed pattern YK2 formed so that the black pattern Kws overlaps the monochromatic pattern other than black as shown in FIG. 8 (in this example, the yellow pattern with high light reflectance) Yw1. By detecting with the optical sensor 30, the formation position of the black pattern Kws is detected.

FIG. 9 is a diagram for explaining a detection error of a black pattern position in the sub-scanning direction (position in the sub-scanning direction) due to detection of a conventional color matching pattern.
For example, as shown in FIG. 8, when the formation position of the black pattern Kws is detected by detecting the overlap pattern YK2 formed so that the black pattern Kws overlaps the yellow pattern Yw1 with the optical sensor 30. The monochromatic patterns Mws, Cws, and Yws other than black can detect the sub-scanning end, but the light flux emitted from the light emitting element 32 built in the optical sensor 30 is as shown in FIG. Since it is obliquely incident on the pattern surface, the black pattern Kws superimposed on the yellow pattern Yw1 is shielded from light, and as a result, the sub-scan end of the black pattern Kws is detected at a shifted position.
Therefore, for example, when the sub-scanning position of another color is derived using black as a reference color, the above-described deviation amount is included as an error, and color deviation occurs even if the image forming position of the other color is corrected.

  Therefore, in order to solve the problem, in the image forming apparatus of this embodiment, the CPU 50 in FIG. 4 controls the control circuit 202 and the like, and the color image forming unit forms a color matching pattern on the intermediate transfer belt 114. At this time, as shown in FIG. 9B, a superposition pattern in which a black pattern Kws as a reference color pattern and a yellow pattern Yw1 which is a single color pattern of a color other than black (yellow in this example) are overlaid. (Hereinafter also simply referred to as “reference color sub-scanning end error detection overlay pattern”) YK2 and yellow, which is a monochrome pattern of a color other than black (yellow in this example) as shown in FIG. A pattern (hereinafter also referred to as “standard color sub-scanning end error detecting single color pattern”) Yws is formed on the intermediate transfer belt 114.

Then, based on the result of detection of the overlay pattern YK2 and the yellow pattern Yws by the optical sensor 30, a reference color detection error (black) that is a detection error of the sub-scanning end position (end position in the sub-scanning direction) of the black pattern Kws. (Image formation position error) is calculated, and color image formation with reduced reference color detection error is realized by correcting the amount of misalignment between the reference color (black) pattern and other color patterns according to the reference color detection error can do.
The overlapping pattern and the single color pattern may be included in the color matching pattern, or may be formed separately from the color matching pattern and the reference color detection error may be calculated in advance.

FIG. 10 is a diagram for explaining the formation of the superposition pattern YK2 and the yellow pattern Yws that are single color patterns and the detection of the reference color detection error shown in FIGS.
The CPU 50 in FIG. 4 causes the color image forming unit to form the overlay pattern YK2 shown in FIGS. 8 and 9 as shown in FIG. 10, for example, and the black pattern based on the result detected by the optical sensor 30. The detection error of the Kws sub-scanning end can be detected.

Here, the sub-scanning width of the yellow pattern Yws which is a pattern made only of yellow and the sub-scanning width of the black pattern Kws of the overlay pattern YK2 are formed to be the same WS, and the yellow pattern Yw1 and the black pattern Kws Each color sub-scanning end portion of the superposition pattern YK2 is formed so as not to overlap.
The sub-scanning width WL (not shown) of the yellow pattern Yw1 in which the black pattern Kws of the superimposed pattern YK2 does not overlap is wide enough to be detected by the optical sensor 30, and the sub-scanning width WL between the yellow pattern Yw1 and the yellow pattern Yws. The distance R (not shown) between the end portions in the scanning direction is set in advance so that it can sufficiently take a period in which the optical sensor 30 does not detect the pattern once.

  Since the detection period Tkws of the black pattern Kws includes an error and becomes long, by taking the difference between the detection period Tkws of the black pattern Kws and the detection period Tyws of the yellow pattern Yws, the sub-scanning end of the black pattern Kws The detection error is obtained and stored in a non-volatile memory (not shown). From the detection result of the black pattern Kws of the color matching pattern shown in FIG. 8 as exemplified above, the detection position of the sub-scanning end of the black pattern Kws is delayed by the detection error of the sub-scanning end. to correct.

  Here, in the period Tywl in which the yellow pattern Yw1 is detected by the optical sensor 30, the non-detection period Tkws in which reflected light is not detected by the black pattern Kws is measured as the detection period Tkws of the black pattern Kws, and the yellow pattern Yws ( Yws), the detection period Tyws is measured. Then, a reference color detection error period Terr, which is a detection error (black image formation position error) at the sub-scanning end of the black pattern Kws, based on the difference between the measured black pattern Kws detection period Tkws and the yellow pattern Yws detection period Tyws. Tkws−Tyws) is calculated, and a correction value C (C = Terr in this case) for correcting the positional deviation amount is derived from the reference color detection error period Terr, and is stored in the nonvolatile memory.

  Therefore, the amount of misregistration is corrected by delaying the detection start timing Ks of the black pattern Kws in the detection period of the black pattern Kws of the color matching pattern by the correction value C (reference color detection error period Terr) (that is, By correcting the color misregistration detection result by detecting the color matching pattern including the black image formation position error), the black image formation position error can be reduced and the accuracy of the black image sub-scan formation position can be improved. become. Accordingly, it is possible to obtain the image formation positional deviation amount of each color with higher accuracy, and it is possible to form a higher-quality color image by performing writing control in which the obtained positional deviation amount is corrected.

FIG. 11 is a diagram for explaining the formation of the overlay pattern YK1 and the yellow pattern Yws that is a single color pattern shown in FIG. 7 and the detection of the reference color detection error.
The CPU 50 in FIG. 4 causes the color image forming unit to form the overlay pattern YK1 shown in FIG. 7 as shown in FIG. 11, for example, and subtracts the black pattern Kws based on the result detected by the optical sensor 30. It is also possible to detect a detection error at the scanning end.

  Here, the yellow pattern Yws, which is a pattern composed of only yellow, is formed so that the yellow pattern exposure width of the overlay pattern YK1 is the same WS, and each color sub-scan end of the overlay pattern YK1 is It is formed so as not to overlap. In addition, the distance between the end portions in the sub-scanning direction of the overlapping pattern YK1 and the yellow pattern Yws can sufficiently take a period in which the optical sensor 30 does not detect the pattern once.

  Since the detection period Tyw1 of the yellow pattern Yw1 of the superimposed pattern YK1 is short including an error, the difference between the detection period Tyws of the yellow pattern Yws and the detection period Tyw1 of the yellow pattern Yw1 is taken to obtain a subtraction of the black pattern Kws. A detection error at the scanning end is obtained and held in a non-illustrated nonvolatile memory. From the detection result of the black pattern Kws of the color matching pattern shown in FIG. 7 as exemplified above, the detection position at the sub-scanning end of the black pattern Kws is delayed by the detection error of the sub-scanning end. to correct.

  Here, during the period Tywl in which the yellow pattern Yw1 is detected by the optical sensor 30, the period during which the reflected light is detected by the black pattern Kws is measured as the detection period Tyw1 of the yellow pattern Yw1, and the yellow pattern Yws The detection period Tyws is measured. Then, a reference color detection error period Terr, which is a detection error (black image formation position error) at the sub-scanning end of the black pattern Kws, based on the difference between the measured detection period Tyw1 of the yellow pattern Yw1 and the detection period Tyws of the yellow pattern Yws. (Tyws−Tyw1) is calculated, and a correction value C (C = Terr in this case) for correcting the positional deviation amount is derived from the reference color detection error period Terr, and is stored in the nonvolatile memory.

Therefore, the black image formation position error is reduced by correcting the misregistration amount by delaying the detection start timing Ks of the black pattern Kws of the color matching pattern by the correction value C (reference color detection error period Terr). It is possible to improve the accuracy of the black image sub-scan formation position. Accordingly, it is possible to obtain the image formation positional deviation amount of each color with higher accuracy, and it is possible to form a higher-quality color image by performing writing control in which the obtained positional deviation amount is corrected.
It is desirable that the detection error detection at the sub-scanning end is performed before color matching control by color matching pattern detection.

FIG. 12 is a diagram for explaining correction of detection errors at the sub-scanning end portions of the black patterns Kws of the superimposed patterns YK2 and YK1 shown in FIGS.
When the detection of the yellow patterns Yws and Yw1 by the optical sensor 30 is expressed as ON (non-detection) and the non-detection is expressed as OFF (off), the ideal is obtained by removing the errors of the superimposed patterns YK2 and YK1 shown in FIGS. In the case of pattern detection, detection and non-detection of the yellow patterns Yws and Yw1 can be expressed as shown in FIG.
The start of the sub-scan end of the yellow pattern Yws, Yw1 is detected as “OFF → ON” and the end of the sub-scan end is detected as “ON → OFF”, whereas the start of the sub-scan end of the black pattern Kws Detects “ON → OFF” and the end of the sub-scanning end by “OFF → ON”.

  “ON → OFF” indicating the start of the sub-scan end of the black pattern Kws of the overlay patterns YK2, YK1 is affected by the thickness of the black pattern Kws overlaid on the yellow pattern Yw1, and is closer to the front than the actual end. However, in actuality, the black toner is not always formed in the shape as shown in the figure, and the thickness and shape change due to the influence of the temperature condition and the like, and the above detection error is also small. Will change. Further, since the reflectance varies depending on the color, the output state of the optical sensor 30 also changes.

Therefore, the CPU 50 in FIG. 4 multiplies the detection error (reference color detection error period Terr) at the sub-scanning end by the optimum coefficient α to correct the positional deviation amount. That is, a correction value C for correcting the positional deviation amount is derived from the reference color detection error period Terr and the basic coefficient α (= 1) by the following equation, and is stored in the nonvolatile memory to correct the positional deviation amount. .
C = Terr * α (where α is a real number greater than zero)

  For example, by changing conditions such as a temperature condition, a correction value C for correcting the positional deviation amount is derived from the reference color detection error period Terr and the basic coefficient α (= 1) (the correction value C is used as the reference color detection error). When the detection error at the sub-scanning end portion is small, the coefficient is set to be “0 <coefficient <1”, and the sub-scanning end portion is set. When the detection error of the part becomes large, the coefficient is set to be “1 <coefficient”, the correction value C is re-derived (recalculated), and overwritten in the nonvolatile memory. By correcting the misregistration amount using the correction value C re-derived by this coefficient, it is possible to improve the color matching accuracy corresponding to the influence of the temperature condition and the like, and form a higher quality color image. be able to.

FIG. 13 is a diagram for explaining the density setting change when the black pattern Kws is formed in the superimposed pattern YK2 of FIG.
4 reduces the influence of the thickness of the black pattern Kws on the detection of the detection error at the sub-scanning edge of the black pattern Kws in the superimposed pattern YK2 shown in FIG. 13B, for example. The density setting value is changed so as to suppress the thickness.

When the density of the black pattern Kws is lowered, the toner adhesion amount is reduced. As a result, as shown in FIG. 13C, the thickness of the black pattern Kws is reduced. When the thickness of the black pattern Kws is reduced, the period during which the light beam emitted from the optical sensor 30 is blocked at the sub-scanning end of the black pattern Kws is shortened, and the error can be reduced.
Therefore, the influence on color matching can be reduced by correction by reducing the error.

FIG. 14 is a diagram for describing density setting when forming the black pattern Kws in the overlay pattern YK2 of FIG.
When the CPU 50 in FIG. 4 forms the black pattern Kws of the overlay pattern YK2 in FIG. 10, the density is set such that the light emitted from the optical sensor 30 passes through the black pattern Kws and does not erroneously detect the yellow pattern Yw1 in the lower layer. There is a need to.

  Therefore, for example, as shown in FIG. 14, a plurality of superimposed patterns YK2 in which only the density of the black pattern Kws is gradually changed are formed on the intermediate transfer belt 114 by the color image forming unit, and the optical sensor 30 detects no erroneous detection. Find the density value above the threshold. In order to know which density setting value superimposition pattern YK2 is detected, each pattern YK2 is formed by splitting the lower yellow patterns Yw1 without connecting them, and all the sub-scanning widths of the yellow patterns Yw1 are all set. It is the same.

The process of setting the density of the black pattern Kws to be superimposed on the yellow pattern Yw1, which is a single-color pattern other than black when the superimposed pattern YK2 in FIG. 10 is formed, will be described in a little more detail.
The CPU 50 causes the color image forming unit to form N yellow patterns Yw1 with the same density on the intermediate transfer belt 114 (N is an integer of 2 or more and less than the black density gradation setting value), and the N yellow patterns Black patterns Kws having different densities are superimposed on the pattern Yw1.

At this time, among the black patterns Kws, the lowest density is set for the black pattern Kws at the end in the sub-scanning direction, and the density gradually increases with respect to each black pattern Kws following the black pattern Kws. Set the density so that
Then, after superimposing black patterns Kws of different densities on the N yellow patterns Yw1, the black output is detected when the detection output of the optical sensor 30 for the N yellow patterns Yw1 is equal to or greater than a preset black detection threshold. The lowest density of the black pattern Kws corresponding to the detection output regarded as black detection is regarded as the density of the black pattern Kws superimposed on the yellow pattern Yw1 when the superimposed pattern YK2 in FIG. 10 is formed. Set.

4 reduces the influence of the thickness of the black pattern Kws of the overlay pattern YK2 on the detection of the detection error at the sub-scanning end of the black pattern Kws, so that the density setting value is set to suppress the thickness of the black pattern Kws. The point of deriving the set value when changing is described with reference to FIG.
Although a detection threshold is provided so as not to erroneously detect the yellow pattern Yw1 in the lower layer, when a density setting value in the vicinity of the detection threshold is applied as shown by a broken line portion in FIG. If the level is not set, there is a possibility that the lower layer yellow pattern Yw1 is erroneously detected.

  It is clear that the effect of reducing the thickness of the black pattern Kws is the sub-scanning end portion of the black pattern Kws. Therefore, by gradually increasing the density from the sub-scanning end portion of the black pattern Kws, The influence on the detection error detection of the sub-scanning end due to the thickness of the black pattern Kws can be reduced, and false detection of the lower layer yellow pattern due to disturbance or the like in the density setting value near the detection threshold can be prevented.

FIG. 15 is a diagram illustrating an example of a color matching pattern including the color matching pattern YK1 in which the density setting value of the black pattern Kws in FIG. 7 is changed.
FIG. 16 is a diagram illustrating an example of a color matching pattern including the color matching pattern YK2 in which the density setting value of the black pattern Kws in FIG. 8 is changed.
FIG. 17 is a diagram illustrating another example of the color matching pattern including the color matching pattern YK1 in which the density setting value of the black pattern Kws in FIG. 7 is changed.
FIG. 18 is a diagram illustrating another example of the color matching pattern including the color matching pattern YK2 in which the density setting value of the black pattern Kws in FIG. 8 is changed.

Each black pattern Kws shown in FIGS. 15 and 16 is obtained by changing the density setting so that the thickness is uniformly reduced.
Each black pattern Kws shown in FIGS. 17 and 18 has a density setting such that the edge portion on the yellow pattern Yw1 side is thin (notched) so as not to block the reflected light from the yellow pattern Yw1. The changes were made.

  In this embodiment, the yellow (yellow) pattern is used as the reference color sub-scanning end error detection single color pattern, and the reference color sub-scanning end error detection is used as the reference color sub-scanning end error detection overlay pattern. A yellow pattern was formed in the sub-scanning direction with yellow with a single color pattern, but a magenta or cyan pattern was superimposed as a reference color sub-scanning edge error detection as a reference color sub-scanning edge error detection monochrome pattern. As a pattern, a magenta or cyan pattern may be formed in the sub-scanning direction using magenta or cyan in which a reference color sub-scanning end error detecting single-color pattern is formed.

  The present invention can be used for electrophotographic color image forming apparatuses such as copying machines, printers, facsimile machines, and digital multi-function peripherals (MFPs).

30: Optical sensor 32: Light emitting element 35: Light receiving element 100: Image forming apparatus 102: Optical apparatus 102a, 102e: Reflection mirror 102b: fθ lens 102c: Polygon mirror 102d: WTL lenses 104, 106, 108, 110: Image forming process Sections 104a, 106a, 108a, 110a: photosensitive drums 104b, 106b, 108b, 110b: chargers 104c, 106c, 108c, 110c: developing units 112: color image forming unit 114: intermediate transfer belts 114a, 114b, 114c: transport Roller 118: Secondary transfer belt 120: Fixing device 122: Transfer unit 124: Recording medium 130: Fixing member 132: Printed matter 202: Control circuit 204: Driver circuit 206: Semiconductor laser element 208: Reflection mirror 210: Synchronization detection sensor 300: Dew Control block

JP 2010-160349 A

Claims (8)

Each single-color image including black formed on the image carrier of the plurality of image forming units juxtaposed along the sub-scanning direction that is the rotation direction of the single endless moving member is displayed on the endless moving member. An image forming apparatus having color image forming means for forming a color image by sequentially superimposing and transferring to
An optical element that emits a light beam to the endless moving member, detects reflected light from the endless moving member, and converts it into an electrical signal;
A color matching pattern for color matching of the color image is formed on the endless moving member by the color image forming means, and the reference color and other colors are determined based on the result of detection of the color matching pattern by the optical element. A positional deviation amount detecting means for detecting a positional deviation amount of the color image forming position;
Adjusting means for adjusting an image forming position of a color other than a reference color according to the amount of misregistration detected by the amount of misregistration detecting means;
When the color image forming unit forms the color matching pattern on the endless moving member, the misregistration amount detection unit superimposes a black pattern as the reference color pattern and a single color pattern of a color other than black. A combined reference color sub-scanning end error detection overlay pattern and a reference color sub-scanning end error detecting single color pattern composed of a single color pattern other than black are formed on the endless moving member, and the reference Detection of the end position of the black pattern in the sub-scanning direction based on the detection result of the superposed pattern for color sub-scanning end error detection and the reference color sub-scanning end error detection single-color pattern by the optical element An image forming apparatus comprising: means for calculating a reference color detection error which is an error, and correcting the positional deviation amount according to the reference color detection error   The misregistration amount detecting means forms a pattern Yws having a width WS in the sub-scanning direction in a single color other than black as the reference color sub-scanning end error detecting single color pattern, and detecting the reference color sub-scanning end error. A pattern Ywl having a width WL in the sub-scanning direction is formed in the sub-scanning direction with the color formed as the reference color sub-scanning end error detecting single-color pattern as the overlay pattern for black, and the sub-pattern in black so as to overlap the pattern Ywl. A pattern Kws having a width WS is formed in the scanning direction, the pattern Kws is included in the pattern Ywl, and the end of the pattern Kws in the sub-scanning direction does not overlap the end of the pattern Ywl in the sub-scanning direction Thus, the distance between the end portions in the sub-scanning direction of the pattern Yws and the pattern Ywl is a period during which the optical element does not detect the pattern once. The image forming apparatus according to claim 1, characterized in that it is set so that it can take enough. The positional deviation amount detection means measures a period Tkws in which reflected light is not detected by the pattern Kws in the period Tywl in which the pattern Ywl is detected by the optical element, and measures a detection period Tyws of the pattern Yws. The image forming apparatus according to claim 2, wherein the reference color detection error period Terr is derived from the detection periods Tkws and Tyws by the following expression.
Terr = Tkws-Tyws The misregistration amount detection means derives a correction value C for correcting the misregistration amount from the reference color detection error period Terr,
4. The positional shift amount is corrected by delaying the black pattern detection start timing Ks in the black pattern detection period of the color matching pattern by the correction value C. Image forming apparatus. The image forming apparatus according to claim 4, wherein the misregistration amount detection unit derives the correction value C by the following equation.
C = Terr * α (where α is a real number greater than zero) The misregistration amount detection means includes a superimposed black pattern density setting means for setting a density of the black pattern to be superimposed on a single color pattern of a color other than black when the reference color sub-scanning end error detection overlay pattern is formed. Have
The superimposed black pattern density setting means forms N monochrome patterns other than the black with the same density, superimposes the black patterns with different densities on the N monochrome patterns, When the detection output of the optical element for a single color pattern is equal to or higher than a preset black detection threshold, it is regarded as black detection, and the lowest density of the density of the single color pattern corresponding to the detection output regarded as black detection is 6. The density of a black pattern to be superimposed on a single color pattern of a color other than black at the time of forming the reference color sub-scanning end error detection overlay pattern. The image forming apparatus described.   The superimposing black pattern density setting means applies the black pattern having different densities on the N single color patterns to the monochromatic pattern at the end in the sub-scanning direction among the black patterns. 7. The image forming apparatus according to claim 6, wherein the lowest density is set, and the density is set so that the density gradually increases with respect to each monochrome pattern following the monochrome pattern.   8. The color matching pattern includes the reference color sub-scanning edge error detection overlay pattern and the reference color sub-scanning edge error detection single color pattern. The image forming apparatus described in 1.