JP5883632B2 - Image forming apparatus and color registration method thereof - Google Patents

Description

  The present disclosure relates to an image forming apparatus that forms a color image.

  There is known an image forming apparatus that transfers toner images of respective colors to an intermediate transfer belt and further transfers these toner images to paper or the like. Due to vibration and elongation of the transfer belt, deformation and eccentricity of a roller for driving the transfer belt, displacement of each color photosensitive drum that transfers the toner image to the transfer belt, and the like, displacement between the toner images of each color occurs. In order to print an accurate color, it is necessary to perform color registration for correcting such a shift (color shift). An example thereof is described in Patent Document 1.

Japanese Patent Laid-Open No. 2002-55502

  However, the printer of Patent Document 1 only adjusts the timing at which the delay of the photosensitive belts of the respective colors driven by the rollers is maximized. The period of change cannot be corrected. For this reason, highly accurate color registration cannot be performed.

  An object of the present invention is to perform color registration with higher accuracy.

An image forming apparatus according to an embodiment of the present disclosure is an image forming apparatus that forms a plurality of colors including a reference color. An image forming unit formed side by side, and the first pattern image and the second pattern image formed by the image forming unit are transferred, and the transferred first pattern image and second pattern image are transferred in the sub-scanning direction. An intermediate transfer belt that is transferred to the intermediate transfer belt, a first detection unit that detects elements of the first pattern image on the intermediate transfer belt, and a second detection unit that detects elements of the second pattern image on the intermediate transfer belt And the positions in the sub-scanning direction of elements included in the first pattern image of the plurality of colors and the second pattern image of the plurality of colors on the intermediate transfer belt, And a position calculation unit obtained based on a detection result of the second detection unit, and a rotational fluctuation component of the intermediate transfer belt based on the position obtained by the position calculation unit for the second pattern image. The position obtained for each of the colors and the position obtained for the first pattern image is corrected based on the rotation variation component obtained for the color of the first pattern image, and the reference color is obtained based on the corrected position. And a controller that performs color registration so as to reduce the offset based on the obtained offset. The first pattern image is an image for obtaining an offset of another color with respect to the reference color among the plurality of colors. For each of the plurality of colors, the second pattern image is in the main scanning direction. A plurality of the same color bar images are provided, and the plurality of the same color bar images are continuously arranged in the sub-scanning direction .

  According to this, using the same color pattern images arranged in the main scanning direction, an offset with respect to the reference color is obtained in consideration of the rotational fluctuation component. Since the rotational fluctuation component is taken into account, highly accurate color registration can be performed.

A method according to the present disclosure is a color registration method of an image forming apparatus that forms an image of a plurality of colors including a reference color, and for each of the plurality of colors, a first pattern image and a second pattern image of the same color are obtained. The first pattern image and the second pattern image that are formed side by side in the main scanning direction are transferred to an intermediate transfer belt, and the transferred first pattern image and second pattern image are transferred in the sub-scanning direction. Detecting the elements of the first pattern image on the intermediate transfer belt, detecting the elements of the second pattern image on the intermediate transfer belt, and detecting the elements of the plurality of colors on the intermediate transfer belt. The positions of the elements included in the first pattern image and the second pattern image of the plurality of colors in the sub-scanning direction are determined with respect to the elements of the first and second pattern images. The rotation variation component of the intermediate transfer belt is obtained for each of the plurality of colors based on the position obtained for the second pattern image and obtained for the first pattern image. The position is corrected based on the rotation variation component obtained for the color of the first pattern image, and an offset of another color with respect to the reference color is obtained based on the corrected position, and based on the obtained offset. Thus, color registration is performed so that the offset becomes small. The first pattern image is an image for obtaining an offset of another color with respect to the reference color among the plurality of colors. For each of the plurality of colors, the second pattern image is in the main scanning direction. A plurality of the same color bar images are provided, and the plurality of the same color bar images are continuously arranged in the sub-scanning direction .

  According to the present disclosure, the offset can be measured with higher accuracy, so that color registration can be performed with higher accuracy.

1 is an explanatory diagram illustrating a schematic configuration example of an image forming apparatus according to an embodiment of the present invention. It is explanatory drawing which shows the transfer belt of FIG. FIG. 2 is a block diagram illustrating a configuration example of a portion related to color registration of the image forming apparatus in FIG. 1. It is explanatory drawing which shows the structural example of the detection part of FIG. FIG. 2 is an explanatory diagram for measuring a position of a toner image on the intermediate transfer belt in FIG. 1. 3 is a flowchart illustrating an example of a flow of offset measurement processing in the image forming apparatus of FIG. 1. It is explanatory drawing which shows the example of the pattern image for color registration. 3 is a graph showing an example of measured values of rotational fluctuation components of the transfer belt in FIG. 1. It is a table which shows the example of a rotation fluctuation component. It is explanatory drawing about calculation of X-offset and Y-offset. It is explanatory drawing about calculation of W-offset. It is explanatory drawing regarding a distortion calculation process. 6 is a graph illustrating an example of an error in the position of a toner image after color registration when a rotation variation component is not taken into consideration. 3 is a graph showing an example of an error in the position of a toner image after color registration by the image forming apparatus of FIG. 1.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. Components shown with the same reference numbers in the drawings are identical or similar components.

  FIG. 1 is an explanatory diagram illustrating a schematic configuration example of an image forming apparatus 100 according to an embodiment of the present invention. The image forming apparatus 100 in FIG. 1 forms a color image by forming a plurality of color images including a reference color, and includes a recording medium transport unit 112, an image forming unit 120, and toner tanks 146Y and 146M. , 146C, 146K, a transfer unit 150, a fixing unit 160, and detection units 170L, 170R.

  The recording medium conveyance unit 112 accommodates a recording medium on which an image is finally formed and conveys the recording medium onto the recording medium conveyance path. The recording medium is, for example, paper P and is stacked and accommodated in a cassette. The recording medium transport unit 112 causes the paper P to reach the secondary transfer area at the timing when the toner image transferred to the paper P is formed and reaches the secondary transfer area.

  The transfer unit 150 conveys the toner image formed by the developing unit 140 to a secondary transfer region where the toner image is secondarily transferred to a recording medium. The transfer unit 150 includes an intermediate transfer belt (ITB) 152, suspension rollers 154A, 154B, 154C, and 154D that suspend the transfer belt 152, primary transfer rollers 156Y, 156M, 156C, and 156K, and secondary transfer. And a roller 158.

  FIG. 2 is an explanatory view showing the intermediate transfer belt 152 of FIG. The intermediate transfer belt 152 is an endless belt that is circulated and moved by suspension rollers 154A, 154B, 154C, and 154D. A toner image is formed on the surface of the intermediate transfer belt 152 by the image forming unit 120. Hereinafter, the intermediate transfer belt is also simply referred to as a transfer belt.

  As shown in FIG. 1, the primary transfer rollers 156Y, 156M, 156C, and 156K sandwich the transfer belt 152 between the corresponding photosensitive drums 134. The secondary transfer roller 158 sandwiches the transfer belt 152 together with the suspension roller 154D. The primary transfer rollers 156Y, 156M, 156C, and 156K are provided so as to press the photosensitive drum 134 and the like from the inner peripheral side of the transfer belt 152. The secondary transfer roller 156 is provided so as to press the suspension roller 154D from the outer peripheral side of the transfer belt 152. Although not shown in FIG. 1, the transfer unit 150 may further include a belt cleaning device that removes toner attached to the transfer belt 152.

  For example, for each of four colors of yellow (YL), magenta (M), cyan (C), and black (K), the image forming unit 120 includes a charging roller 132, a photosensitive drum 134, a cleaning unit 138, and a developing unit. Unit 140. The four photosensitive drums 134 are provided along the moving direction of the transfer belt 152. The image forming unit 120 further includes an exposure unit 122. Here, yellow is described as an example, but images of the respective colors are similarly formed for magenta, cyan, and black.

  As shown in FIG. 1, a charging roller 132, a cleaning unit 138, and a developing unit 140 are provided on the circumference of each photosensitive drum 134. The photosensitive drum 134 is an electrostatic latent image carrier on which an image is formed on its peripheral surface, and for example, an OPC (organic photo conductor) is used. The charging roller 132 uniformly charges the surface of the photosensitive drum 134 to a predetermined potential. The exposure unit 122 is, for example, an LSU (laser scanning unit), and exposes the surface of the photosensitive drum 134 charged by the charging roller 132 according to an image to be formed. As a result, the potential of the portion of the surface of the photosensitive drum 134 exposed by the exposure unit 122 changes, and an electrostatic latent image is formed. The developing unit 140 develops the electrostatic latent image formed on the photosensitive drum 134 with the toner supplied from the toner tank 146Y, and generates a toner image.

  The cleaning unit 138 collects the toner remaining on the photosensitive drum 134 after the toner image formed on the photosensitive drum 134 is primarily transferred to the transfer belt 152. For example, the cleaning unit 138 is provided with a cleaning blade, and is configured to scrape the remaining toner on the photosensitive drum 134 by bringing the cleaning blade into contact with the peripheral surface of the photosensitive drum 134. A neutralizing lamp (not shown) for resetting the potential of the photosensitive drum 134 is disposed on the circumference of the photosensitive drum 134 between the cleaning unit 138 and the charging roller 132 in the rotation direction of the photosensitive drum 134. May be.

  The developing unit 140 includes stirring and conveying units 142 and 143 and a developing roller 144. The developing roller 144 is a developer carrier that supplies toner to the electrostatic latent image formed on the peripheral surface of the photosensitive drum 134. The agitating / conveying units 142 and 143 agitate the magnetic carrier and the non-magnetic or weak magnetic toner constituting the developer to charge the carrier and the toner. The first agitating / conveying unit 142 is disposed to face the developing roller 144 in a substantially vertical direction, and supplies the mixed and agitated developer to the developing roller 144. The second agitating and conveying unit 143 has a role of mixing and agitating the developer to sufficiently charge the developer, and conveys the charged developer to the first agitating and conveying unit 142. The second agitating / conveying unit 143 is provided with a toner concentration sensor (not shown) for detecting the toner concentration. When the toner concentration in the conveying path decreases, a developer is introduced from the toner tank 146Y into the conveying path. Is supplied.

  The fixing unit 160 adheres and fixes the toner image secondarily transferred from the transfer belt 152 to the recording medium. The fixing unit 160 includes, for example, a heating roller 162 and a pressure roller 164. The heating roller 162 is a cylindrical member that can rotate around a rotation shaft that functions as a fixing roller, and a heat source such as a halogen lamp is provided therein. The pressure roller 164 is a cylindrical member that can rotate around the rotation axis, and is provided so as to press the heating roller 162. A heat-resistant elastic layer such as silicon rubber is provided on the outer peripheral surfaces of the heating roller 162 and the pressure roller 164. By passing the recording medium through a fixing nip, which is a contact area between the heating roller 162 and the pressure roller 164, the toner image is melted and fixed on the recording medium.

  A travel sensor 168 that detects the travel state of the recording medium is provided between the fixing unit 160 and the secondary transfer region in which the transfer is performed from the transfer belt 152 to the recording medium. The travel sensor 168 detects whether the recording medium has passed the position where the travel sensor 168 is provided. Further, the image forming apparatus 100 is provided with discharge rollers 104 and 106 for discharging the recording medium on which the toner image is fixed by the fixing unit 160 to the outside of the apparatus.

  First, when the image forming apparatus 100 is operated, image data of an image to be recorded is transmitted to the signal generation unit. Next, the control unit uniformly charges the surface of the photosensitive drum 134 to a predetermined potential by the charging roller 132, and then the surface of the photosensitive drum 134 by the exposure unit 122 based on the image data received by the signal generation unit. A laser beam is irradiated to form an electrostatic latent image.

  In the developing unit 140, the toner and the carrier are mixed and stirred to be sufficiently charged, and then the developer is carried on the developing roller 144. Then, when the developer is transported to a region facing the photosensitive drum 134 by the rotation of the developing roller 144, toner is formed on the peripheral surface of the photosensitive drum 134 among the developer carried on the developing roller 144. Move to the electrostatic latent image and develop the electrostatic latent image. The toner image formed in this way is primarily transferred from the photosensitive drum 134 to the transfer belt 152 in a region where the photosensitive drum 134 and the transfer belt 152 face each other. On the transfer belt 152, toner images formed on the four photosensitive drums 134 are sequentially stacked to form one stacked toner image. The laminated toner image is secondarily transferred to the recording medium conveyed from the recording medium conveyance unit 112 in the region between the suspension roller 154D and the secondary transfer roller 158.

  The recording medium on which the laminated toner image is secondarily transferred is conveyed to the fixing unit 160. By passing the recording medium between the heating roller 162 and the pressure roller 164 while applying heat and pressure, the laminated toner image is melt-fixed on the recording medium. Thereafter, the recording medium is discharged to the outside of the image forming apparatus 100 by the discharge rollers 104 and 106. After the laminated toner image is secondarily transferred to the recording medium, the toner remaining on the transfer belt 152 is removed by a belt cleaning device.

  FIG. 3 is a block diagram illustrating a configuration example of a portion related to color registration of the image forming apparatus 100 of FIG. As shown in FIG. 3, the image forming apparatus 100 includes a position calculation unit 182, a control unit 184, and a signal generation unit 186 in addition to the image forming unit 120, the transfer belt 152, and the detection units 170 </ b> L and 170 </ b> R in FIG. 1. Have The control unit 184 is a CPU, for example, and controls the entire image forming apparatus 100. This will be described with reference to FIG. 3 and other drawings.

  FIG. 4 is an explanatory diagram showing a configuration example of the detection unit 170L in FIG. As illustrated in FIG. 4, the detection unit 170L includes an LED (light emitting diode) 172 and photosensors 174 and 175. Instead of the LED 172, another light emitting element such as a laser diode may be used as the light source. The detection unit 170R is configured similarly to the detection unit 170L. The LED 172 irradiates a part of the transfer belt 152 with light, and the transfer belt 152 and the toner image formed thereon reflect or scatter the irradiated light. The photo sensors 174 and 175 receive light reflected or scattered by the transfer belt 152 or the like, and output a signal corresponding to the intensity of the received light. For example, the detection unit 170L outputs the sum of the output signals of the photosensors 174 and 175 to the position calculation unit 182 as the detection signal SS.

  FIG. 5 is an explanatory diagram for measuring the position of the toner image on the intermediate transfer belt 152 of FIG. The point SPL due to the light emitted from the LED 172 moves relatively in the lower direction of the drawing as the transfer belt 152 rotates. FIG. 5 shows an example of the detection signal SS output from the detection unit 170L in this case. The position calculation unit 182 binarizes the detection signal SS. That is, the position calculation unit 182 generates a signal SB that has a high potential when the detection signal SS is greater than or equal to a predetermined threshold value and that has a low potential when the detection signal SS is less than the predetermined threshold value.

  The position calculation unit 182 has a counter that counts the number of pulses of the synchronization signal HSY output from the image forming unit 120, and controls the count value of the counter at the timing of each pulse of the signal SB (for example, at the time of falling). Output to 184. The control unit 184 stores the count value. The synchronization signal HSY is a high-speed clock signal that serves as a reference for overall control of the image forming apparatus 100. Since the frequency of the synchronization signal HSY is much higher than the frequency of the signal SB, the position of the toner image on the transfer belt 152 can be represented by the count value.

  The control unit 184 generates a page synchronization signal, a line synchronization signal, a video clock signal, and the like, and outputs them to the signal generation unit 186. Further, the control unit 184 generates a motor clock for controlling the scanning motor of the exposure unit 122 and outputs it to the exposure unit 122. The signal generation unit 186 generates an image signal VD according to image data PD input from the outside of the image forming apparatus 100, and synchronizes with a page synchronization signal, a line synchronization signal, a video clock signal, and the like to the image formation unit 120. Output. The image forming unit 120 forms an image based on the image signal VD. The signal generation unit 186 stores pattern registration data for color registration.

  FIG. 6 is a flowchart showing an example of the flow of offset measurement processing in the image forming apparatus of FIG. In S12, the control unit 184 calibrates the LEDs 172 of the detection units 170L and 170R. Specifically, the control unit 184 sets the current of the LED 172 so that the position calculation unit 182 can determine from the detection signal SS whether the toner image is present on the surface of the transfer belt 152. If the presence or absence of the toner image cannot be determined, the control unit 184 sets the current of the LED 172 to a different value. If the presence / absence of the toner image cannot be determined even after changing the current of the LED 172 a predetermined number of times, the control unit 184 sets a flag indicating that the calibration could not be performed.

  In S14, the control unit 184 determines whether or not the calibration has been normally completed. If the process ends normally, the process proceeds to S16. If the process ends normally, the process proceeds to S32. In S32, the control unit 184 performs error processing. Specifically, the control unit 184 interrupts the color registration process, notifies the user or the like of error information indicating that the calibration process did not end normally, and ends the process. At this time, the control unit 184 may display the error information on a display (not shown), or may notify the management center of the error information via a communication line. If the calibration process does not end normally, the color registration process may be continued using the settings at the previous calibration as they are (that is, the process may proceed to S16).

  In S16, in accordance with an instruction from the control unit 184, the signal generation unit 186 reads the stored pattern image data for color registration, generates a corresponding image signal VD, and outputs the image signal VD to the image forming unit 120. . The image forming unit 120 forms a color registration pattern image in accordance with the image signal VD, and transfers the pattern image onto the transfer belt 152.

  FIG. 7 is an explanatory diagram illustrating an example of a pattern image for color registration. FIG. 7 shows an ideal toner image formed on the transfer belt 152, and this image moves upward from the bottom of FIG. 7 by the movement of the transfer belt 152. The horizontal direction in FIG. 7 is the main scanning direction (X axis), and the vertical direction is the sub scanning direction (Y axis). In the following description, it is assumed that black is the reference color, but the reference color may be another color.

  The pattern image of FIG. 7 includes first pattern images FK1, FC1, FM1, FY1, FK2, FC2, FM2, and FY2, which are images for obtaining an offset of another color with respect to a reference color among a plurality of colors. It includes second pattern images RK1, RC1, RM1, RY1, RK2, RC2, RM2, and RY2, which are images for determining the movement of the transfer belt 152 in the sub-scanning direction. The color shift is caused by the offset, and the offset includes an X-offset, a Y-offset, and a W-offset described later.

  The first pattern image FK1 includes, as elements, a bar-shaped horizontal bar image BH extended in the main scanning direction and a bar-shaped slant bar image BS extended in a direction rotated by 45 ° with respect to the horizontal bar image BH. . The same applies to the other first pattern images FC1, FM1, FY1, FK2, FC2, FM2, and FY2. The second pattern image RK1 has a plurality of bar-shaped horizontal bar images BR extended in the main scanning direction. The same applies to the other second pattern images RC1, RM1, RY1, RK2, RC2, RM2, and RY2. The number of horizontal bar images BR included in each of these second pattern images may be different from the example of FIG.

  The color of the first pattern images FK1, FK2 and the second pattern images RK1, RK2 is black, the color of the first pattern images FC1, FC2, and the second pattern images RC1, RC2 is cyan, the first pattern images FM1, FM2, and the second The colors of the pattern images RM1 and RM2 are magenta, and the colors of the first pattern images FY1 and FY2 and the second pattern images RY1 and RY2 are yellow.

  In the main scanning direction of the first pattern images FK1 and FK2, black second pattern images RK1 and RK2 having the same color as these are respectively arranged. In the main scanning direction of the first pattern images FC1 and FC2, cyan second pattern images RC1 and RC2 having the same color as these are arranged, respectively. In the main scanning direction of the first pattern images FM1 and FM2, magenta second pattern images RM1 and RM2 having the same color as these are arranged, respectively. In the main scanning direction of the first pattern images FY1 and FY2, yellow second pattern images RY1 and RY2 having the same color as these are arranged, respectively. As described above, the image forming unit 120 forms the first pattern image and the second pattern image of the same color side by side in the main scanning direction, and transfers them to the transfer belt 152.

  The slant bar image BS of the first pattern image FK1 and the slant bar image BS of the first pattern image FK2 are arranged in the same straight line. The same relationship exists between the first pattern image FC1 and the first pattern image FC2, between the first pattern image FM1 and the first pattern image FM2, and between the first pattern image FY1 and the first pattern image FY2. There is.

  FIG. 7 shows a region SPL irradiated by the detection unit 170L and a region SPR irradiated by the detection unit 170R. The first pattern image and the second pattern image shown in FIG. 7 are transferred to the transfer belt 152, and the transfer belt 152 transfers the transferred first pattern image and second pattern image in the sub-scanning direction. In FIG. 7, since the pattern image moves upward, the detection unit 170L detects elements of the pattern image on the straight line SL, and the detection unit 170R detects elements of the pattern image on the straight line SR. The distance between the straight line SL and the straight line SR is, for example, 176 mm.

  In S18, the position calculation unit 182 obtains the positions in the sub-scanning direction of elements included in the pattern image of FIG. 7 on the transfer belt 152 based on the detection results of the detection units 170L and 170R. Specifically, in accordance with an instruction from the control unit 184, the detection units 170L and 170R detect each element of the pattern image in FIG. 7, and the position calculation unit 182 counts the synchronization signal HSY at each detection timing (synchronization value). The number of pulses of the signal HSY) is stored as a measured value of the position in the sub-scanning direction. The position calculation unit 182 stores measurement values for the entire pattern image of FIG.

  In S <b> 20, the control unit 184 determines the rotation fluctuation component of the transfer belt 152 (that is, an error from the ideal movement in the sub-scanning direction) based on the position obtained by the position calculation unit 182 for the second pattern image. , Magenta, cyan, and black. FIG. 8 is a graph showing an example of measured values of rotational fluctuation components of the transfer belt 152 of FIG. FIG. 8 shows, as an example, the error EY between the position actually obtained by the detection units 170L and 170R and the ideal position of the elements included in the pattern image RK1.

The measured values in FIG. 8 include noise and higher-order fluctuation components. In order to remove these influences and obtain the fundamental component of the vibration of the transfer belt 152, the control unit 184 approximates the measured values in FIG. The control unit 184 is, for example,
f (t) = A * sin (2 * π * f * t + B) (1)
And find each coefficient. Here, A: amplitude, f: frequency, t: time (calculated from the distance and the moving speed of the transfer belt 152), and B: phase. The control unit 184 obtains each coefficient of Expression (1) by, for example, the least square method.

  FIG. 9 is a table showing an example of the rotation fluctuation component. The table in FIG. 9 shows the relationship between the count value of the synchronization signal HSY (corresponding to the position in the sub-scanning direction) and the rotation fluctuation component EY. Here, the rotational fluctuation component EY in the sub-scanning direction is shown in units of dots. The length per dot is determined from the resolution (for example, 600 dpi) of the image forming apparatus 100. One dot corresponds to, for example, 1024 pulses of the synchronization signal HSY. The control unit 184 obtains the table shown in FIG. 9 using Expression (1) and stores it in the position calculation unit 182.

  In S20, the control unit 184 performs the same processing for each of the pattern images RC1, RM1, RY1, RK2, RC2, RM2, and RY2, and the position calculation unit 182 uses these tables as shown in FIG. Stored for each pattern image.

  FIG. 10 is an explanatory diagram for calculating the X-offset and the Y-offset. The X-offset is a shift in the main scanning direction of a pattern image of a certain color with respect to the pattern image of the reference color on the transfer belt 152. The Y-offset is a shift in the sub-scanning direction of a pattern image of a certain color with respect to the pattern image of the reference color on the transfer belt 152. Here, as an example, offset of magenta with respect to black will be described. In FIG. 10, (1) is an ideal state where there is neither X-offset nor Y-offset, (2) is when the magenta pattern image is shifted to the upper left, and (3) is when the magenta pattern image is right The case where it has shifted | deviated below is shown.

  In S22, the control unit 184 corrects the measured value of the position in the sub-scanning direction of each first pattern image obtained in S18 by subtracting the value in the table of FIG. For a count value (position) that is not in the table of FIG. 9, a rotation variation component EY is obtained by interpolation, for example. Here, the control unit 184 corrects the position of the first pattern image FK1 using a table corresponding to FIG. 9 obtained from the second pattern image RK1. Similarly, the control unit 184 uses the table obtained from the second pattern image RC1 using the table obtained from the second pattern image RC1 and the position obtained from the second pattern image RM1 using the table obtained from the second pattern image RC1. Then, using the table obtained from the second pattern image RY1 for the position of the first pattern image FY1, and using the table obtained from the second pattern image RK2 for the position of the first pattern image FK2, the first pattern image Using the table obtained from the second pattern image RC2 for the position of FC2, and using the table obtained from the second pattern image RM2 for the position of the first pattern image FM2, the position of the first pattern image FY2 is set to the second. Correction is performed using a table obtained from the pattern image RY2.

In S22, the control unit 184 further uses the corrected measurement value to calculate the X-offset (ΔX),
ΔX = dK−dM (2)
Ask for. dK is the absolute value of the measured value difference between the black horizontal bar image BH and the slant bar image BS, and dM is the absolute value of the measured value difference between the magenta horizontal bar image BH and the slant bar image BS. is there. The control unit 184 sets the obtained ΔX as a correction value in the X direction.

In S24, the control unit 184 uses the corrected measurement value to calculate the Y-offset (ΔY),
ΔY = (CM−CK) −DMK (3)
Ask for. CK and CM are measured values of black and magenta horizontal bar images BH, respectively. DMK is a difference in position between the magenta pattern image and the black pattern image (difference in the count value of the synchronization signal HSY) in an ideal case. The control unit 184 sets the obtained ΔY as a correction value in the Y direction.

  FIG. 11 is an explanatory diagram for calculating the W-offset. The W-offset is an error in magnification in the main scanning direction of a pattern image of a certain color on the transfer belt 152 with respect to the pattern image of the reference color. Here, the offset of magenta with respect to black will be described as an example, but the same applies to yellow and cyan. In FIG. 11, (1) shows an ideal state without W-offset, (2) shows a case where the magnification of the magenta pattern image is small, and (3) shows a case where the magnification of the magenta pattern image is large.

In S26, the control unit 184 uses the corrected measurement value to calculate W-offset (ΔW),
ΔW = 1 + {(dMR−dKR) − (dML−dKL)} / LS (4)
Ask for. Regarding the pattern image on the straight line SR, dKR is an absolute value of a measured value difference between the black horizontal bar image BH and the slant bar image BS, and dMR is between the magenta horizontal bar image BH and the slant bar image BS. Is the absolute value of the measured value difference. Regarding the pattern image on the straight line SL, dKL is an absolute value of a measurement value difference between the black horizontal bar image BH and the slant bar image BS, and dML is between the magenta horizontal bar image BH and the slant bar image BS. Is the absolute value of the measured value difference. LS is a distance between the straight line SL and the straight line SR. The control unit 184 sets the obtained ΔW as a correction value for the magnification in the X direction.

  The processes of S22, S24, and S26 are similarly performed for yellow and cyan. When the angle of the slant bar image BS with respect to the horizontal bar image BH is not 45 °, ΔX or ΔW is obtained in consideration of the angle formed by both.

  In S28, the control unit 184 performs a distortion calculation process. FIG. 12 is an explanatory diagram regarding the distortion calculation processing. In FIG. 12, a point PK1 is an intersection of the extension lines of two elements of the pattern image FK1, a point PK2 is an upper right end point in the pattern image RK1, and a point PK3 is a lower right end point in the pattern image FK2. The point PC1 is the intersection of the extension lines of the two elements of the pattern image FC1, the point PC2 is the upper right end point in the pattern image RC1, and the point PC3 is the lower right end point in the pattern image FC2. Point PM1 is the intersection of the extension lines of the two elements of pattern image FM1, point PM2 is the upper right end point in pattern image RM1, and point PM3 is the lower right end point in pattern image FM2. Point PY1 is the intersection of the extension lines of the two elements of pattern image FY1, point PY2 is the upper right end point in pattern image RY1, and point PY3 is the lower right end point in pattern image FY2.

  A triangle TRK formed by connecting three points PK1, PK2, and PK3, a triangle TRC formed by connecting three points PC1, PC2, and PC3, a triangle TRM formed by connecting three points PM1, PM2, and PM3, and a point Consider a triangle TRY formed by connecting three points PY1, PY2 and PY3. The areas of these triangles in the ideal case are equal, and the control unit 184 stores this area in advance.

  The control unit 184 obtains the areas of the triangles TRK, TRC, TRM, and TRY using the measured values after correcting the positions of the toner images on the transfer belt 152 obtained in S22. The control unit 184 obtains a ratio of each of the obtained triangles TRK, TRC, TRM, or TRY to an ideal case.

  In S30, the control unit 184 determines whether or not the ratio obtained in S28 is within a predetermined range (for example, 0.8 to 1.2). If the ratio is within the predetermined range, the process of FIG. 6 is terminated. If the ratio is not within the predetermined range, it is considered that there is a problem with the image quality, and the process proceeds to S34.

  In S34, the control unit 184 performs error processing. Specifically, the control unit 184 notifies the user or the like of error information indicating a failure, and ends the process. At this time, the control unit 184 may display the error information on a display (not shown), or may notify the management center of the error information via a communication line.

  The control unit 184 stores the areas of the triangles TRK, TRC, TRM, and TRY in an ideal case for each of 0 ° C., 20 ° C., and 40 ° C., for example, when measuring the position of the toner image. An appropriate stored value may be used according to the temperature of the transfer belt 152 or the like at that time or the ambient temperature.

  In S28 and S30, a triangle formed by connecting the points PK1, PK2, and PK3 is used. However, a triangle formed by connecting the other three points may be used as long as it is a point on the same color toner image. A distance between two points on the same color toner image may be used.

  In accordance with the above processing results, the control unit 184 performs color registration by controlling the signal generation unit 186 and the like. Specifically, the control unit 184 changes the timing of the line synchronization signal and the page synchronization signal for each color, for example. When generating the image signal VD according to the image data PD, the signal generation unit 186 moves the position of the image so that the offsets ΔX and ΔY become small for each color. The control unit 184 also supplies the signal generation unit 186 with the frequency of the video clock signal multiplied by ΔW for each color in order to reduce the offset ΔW.

  FIG. 13 is a graph showing an example of an error in the position of the toner image after color registration when the rotation variation component is not taken into consideration. In this case, the error is about 220 μm. FIG. 14 is a graph showing an example of an error in the position of the toner image after color registration by the image forming apparatus 100 of FIG. In this case, the error is about 90 μm. As described above, the error of the position of the toner image is greatly improved.

  As described above, the image forming apparatus 100 in FIG. 1 performs the offset measurement process based on the toner image of the pattern image actually formed on the transfer belt 152. Since offset images are measured in consideration of rotational fluctuation components using pattern images of the same color arranged in the main scanning direction, highly accurate color registration can be performed. Since the pattern image for detecting the offset is detected while detecting the pattern image for obtaining the rotation fluctuation component, the processing time can be reduced to about half as compared with the case of processing each one in turn.

  For example, when the transfer belt 152 is replaced, when the power is turned on, when the environment changes (when the ambient temperature or the power supply voltage becomes a predetermined value, etc.), or when the number of printed sheets is predetermined, When the number is reached, the processing of FIG. 6 is performed. When an environmental change occurs or when the number of printed sheets reaches a predetermined number, the process of S20 may be omitted. In that case, a table of rotational fluctuation components obtained so far may be used.

  When an error is detected, the control unit 184 may perform color registration based on an offset obtained before that.

  Instead of the pattern image of FIG. 7, another pattern image may be used. For example, the pattern image FK1 or the like has been described as having the slant bar image BS extended in the direction rotated by 45 ° with respect to the horizontal bar image BH, but the angle between the slant bar image BS and the horizontal bar image BH is Other angles may be used (except 0 ° and 90 °).

In FIG. 7, the pattern image FK1 and the pattern image RK1 may be interchanged. The pattern image FC1 and the pattern image RC1 may be interchanged. The pattern image FM1 and the pattern image RM1 may be interchanged. The pattern image FY1 and the pattern image RY1 may be interchanged. The pattern image FK2 and the pattern image RK2 may be interchanged.
The pattern image FC2 and the pattern image RC2 may be interchanged. The pattern image FM2 and the pattern image RM2 may be interchanged. The pattern image FY2 and the pattern image RY2 may be interchanged. These replacements may be performed independently.

  Each functional block in this specification may typically be realized by hardware. For example, each functional block can be formed on a semiconductor substrate as part of an IC (integrated circuit). Here, the IC includes a large-scale integrated circuit (LSI), an application-specific integrated circuit (ASIC), a gate array, a field programmable gate array (FPGA), and the like. Alternatively, some or all of each functional block can be implemented in software. For example, such a functional block can be realized by a processor and a program executed on the processor. In other words, each functional block described in the present specification may be realized by hardware, may be realized by software, or may be realized by any combination of hardware and software.

  The many features and advantages of the present invention are apparent from the written description, and thus, it is intended by the appended claims to cover all such features and advantages of the invention. Further, since many changes and modifications will readily occur to those skilled in the art, the present invention should not be limited to the exact construction and operation as illustrated and described. Accordingly, all suitable modifications and equivalents are intended to be within the scope of the present invention.

DESCRIPTION OF SYMBOLS 100 Image forming apparatus 120 Image forming part 152 Intermediate transfer belt 170L, 170R Detection part 182 Position calculation part 184 Control part 186 Signal generation part

Claims (8)

An image forming apparatus for forming images of a plurality of colors including a reference color,
For each of the plurality of colors, an image forming unit that forms a first pattern image and a second pattern image of the same color side by side in the main scanning direction;
An intermediate transfer belt for transferring the first pattern image and the second pattern image formed by an image forming unit and transferring the transferred first pattern image and second pattern image in a sub-scanning direction;
A first detector that detects elements of the first pattern image on the intermediate transfer belt;
A second detector for detecting elements of the second pattern image on the intermediate transfer belt;
The first and second detectors detect positions of elements included in the first pattern image of the plurality of colors and the second pattern image of the plurality of colors on the intermediate transfer belt in the sub-scanning direction. A position calculation unit to be obtained based on the detection result of
Based on the position obtained by the position calculation unit for the second pattern image, the rotational fluctuation component of the intermediate transfer belt is obtained for each of the plurality of colors, and the position obtained for the first pattern image is determined. Correction is performed based on the rotation variation component obtained for the color of the first pattern image, an offset of another color with respect to the reference color is obtained based on the corrected position, and an offset is obtained based on the obtained offset. And a control unit that performs color registration so that the
The first pattern image is an image for obtaining an offset of another color with respect to the reference color among the plurality of colors.
For each of the plurality of colors, the second pattern image has a plurality of bar images of the same color extended in the main scanning direction, and the plurality of bar images of the same color are continuously arranged in the sub-scanning direction. that <br/> image forming apparatus. The image forming apparatus according to claim 1.
For each of the plurality of colors, the first pattern image is rotated by a predetermined angle with respect to the first bar image extended in the main scanning direction and the first bar image, and is extended in a direction other than the sub-scanning direction. Forming the second bar image. The image forming apparatus according to claim 1.
The image forming apparatus that obtains an offset of another color with respect to the reference color when the power is turned on. The image forming apparatus according to claim 1.
A signal generator that generates an image signal from the image data based on the synchronization signal;
The image forming unit forms an image based on the image signal,
The image forming apparatus that performs the color registration by changing the synchronization signal based on the corrected position. The image forming apparatus according to claim 1.
When an error is detected, the control unit performs the color registration based on an offset obtained before that. The image forming apparatus according to claim 1.
The image forming unit includes the plurality of colors of the second pattern images at the positions in the sub-scanning direction with respect to the plurality of colors of the first pattern images on the intermediate transfer belt. An image forming apparatus that forms an image so that the first pattern images of the plurality of colors are further transferred to positions in the sub-scanning direction with respect to the second pattern image . The image forming apparatus according to claim 6 .
The control unit has an ideal area of a triangle that connects one point on an element or one intersection of extension lines of elements in each of three of the first pattern image and the second pattern image of the same color. An image forming apparatus that calculates a ratio to the area of the case and performs error processing when the determined ratio is out of a predetermined range. A color registration method for an image forming apparatus for forming images of a plurality of colors including a reference color,
For each of the plurality of colors, a first pattern image and a second pattern image of the same color are formed side by side in the main scanning direction,
The formed first pattern image and the second pattern image are transferred to an intermediate transfer belt, and the transferred first pattern image and the second pattern image are transferred in the sub-scanning direction,
Detecting elements of the first pattern image on the intermediate transfer belt;
Detecting elements of the second pattern image on the intermediate transfer belt;
The positions of the elements included in the first pattern image of the plurality of colors and the second pattern image of the plurality of colors on the intermediate transfer belt in the sub-scanning direction are the positions of the first and second pattern images. Based on the detection results for the element,
Based on the position obtained for the second pattern image, the rotational fluctuation component of the intermediate transfer belt is obtained for each of the plurality of colors, and the position obtained for the first pattern image is determined as the first pattern image. Correction based on the rotation fluctuation component obtained for the color of the color, offset of the other color with respect to the reference color is obtained based on the corrected position, and the offset is reduced based on the obtained offset. Color registration,
The first pattern image is an image for obtaining an offset of another color with respect to the reference color among the plurality of colors.
For each of the plurality of colors, the second pattern image has a plurality of bar images of the same color extended in the main scanning direction, and the plurality of bar images of the same color are continuously arranged in the sub-scanning direction. that <br/> way.