JP5009041B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus such as a copying machine, a printer, and a facsimile having a function of correcting a positional deviation of a written image.

  2. Description of the Related Art Conventionally, an image forming apparatus that forms an image in color forms a color image by superimposing images of a plurality of basic colors. For this reason, in order to accurately superimpose the images of the respective basic colors on the recording medium, a process for aligning the positions of the images of the respective basic colors is required. The shift of the position of the image by each basic color without matching is referred to as a position shift. A positional shift occurs in the image of each basic color, so that a color shift occurs in the superimposed image. In order to prevent this color misregistration, a misregistration detection mark for each basic color is formed on an intermediate transfer medium or the like, and the position of this mark is detected to detect whether or not misregistration has occurred. For example, Patent Document 1 proposes a technique for preventing color misregistration by correcting the position of an image of each basic color when misregistration occurs.

This Patent Document 1 discloses that an image forming apparatus that can stably provide no color misregistration can be provided by a technique for accurately detecting a phase difference of a rotational speed variation of a photoreceptor.
Japanese Patent Laying-Open No. 2005-077939

  However, in the technique described in Patent Document 1, since the toner mark sensor is located behind the end photoconductor, at least four photoconductors + α are required until the alignment operation is started and the sensor reading operation is completed. There was a problem.

  Therefore, the problem to be solved by the present invention is to start the alignment operation and shorten the time until the sensor reading operation is completed.

In order to achieve the above object, the present invention provides a plurality of image carriers and an endless belt that functions as an intermediate transfer medium to which a toner image formed on the image carrier is transferred or a recording on which the toner image is transferred. A test pattern for correcting misregistration , which is provided on at least one of an endless belt for conveying paper and the image carrier, is formed on the image carrier, and is transferred onto the endless belt is detected. In the image forming apparatus comprising: a detection unit ; the detection unit detects a test pattern formed of a single color; a first measurement unit that detects a test pattern in which patterns of a plurality of colors are combined; A second measuring means for detecting an absolute deviation amount of the position where the test pattern is transferred on the plate on which the pattern has been transferred, at different positions in the sub-scanning direction between different image carriers. The first measuring means is provided on the scanning writing position side, detects the test pattern that has made a round over the secondary transfer position, reaches the detection means position again, reads the test pattern writing position, and When the alignment is performed based on the measurement result, the absolute deviation amount detected by the second measurement unit is stored. After that, when the alignment is performed using the second measurement unit, the storage is performed. The alignment is performed by calculating the correction amount with reference to the absolute displacement amount, and when the absolute displacement amount is measured by the second measuring unit, the alignment is performed from the signal related to the image formation inside the image forming apparatus. The time until pattern reading is measured, and a correction amount used for alignment is calculated from the time difference between the reference time and the measured time .

  In the embodiments described later, the image carrier is on the photosensitive drums 14Y, 14M, 14C and 14K, the intermediate transfer medium is on the intermediate transfer belt 13, the test pattern is on the reference numeral 150 or 1 dot line L1, and the detection means is a toner mark. The calculation means corresponds to the sensor (alignment sensor) 151 or the line sensor LS, and the calculation means corresponds to the control unit 101.

According to the present invention, it is possible to finish the reading of the early displacement data Ri yo, thereby starting the alignment operation, it is possible to shorten the time until the sensor reading operation is completed.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram schematically showing an overall configuration of a tandem type image forming apparatus according to an embodiment of the present invention. In the figure, an endless intermediate transfer belt 13 is stretched between a driving roller 11 and a driven roller 12. The intermediate transfer belt 13 is made of a synthetic resin such as polyimide.

  Above the intermediate transfer belt 13, four photosensitive drums 14Y and 14M of yellow (Y), magenta (M), cyan (C), and black (K) are arranged along the conveyance direction of the intermediate transfer belt 13. , 14C, 14K are disposed. The intermediate transfer belt 13 rotates clockwise in FIG.

  Primary transfer devices 15Y, 15M, 15C, and 15K are provided below the respective photosensitive drums 14Y, 14M, 14C, and 14K with the intermediate transfer belt 13 interposed therebetween. Around the photosensitive drums 14Y, 14M, 14C, and 14K, there are respectively neutralizing devices 16Y, 16M, 16C, and 16K that neutralize the photosensitive drums, and charging devices 17Y, 17M, 17C, and 17K that charge the photosensitive drums. Developing devices 18Y, 18M, 18C and 18K for developing the latent image on the photosensitive drum, and cleaning devices 19Y, 19M, 19C and 19K for cleaning the toner image remaining after being transferred to the intermediate transfer belt 13 by the primary transfer device. Has been placed.

  A secondary transfer roller pair 21 is disposed below the intermediate transfer belt 13. The secondary transfer roller pair 21 constitutes a secondary transfer device that transfers the toner image formed on the intermediate transfer belt 13 onto a transfer sheet as a recording medium. The intermediate transfer belt is supported by a support roller 22. A cleaning device 23 is provided between the support roller 22 and the secondary transfer roller pair 21 to remove residual toner remaining on the intermediate transfer belt 13 after the toner image is transferred onto the transfer paper. The toner image transferred to the transfer paper is fixed to the transfer paper by the fixing device 25.

  A light beam scanning device 30 is disposed above the photosensitive drums 14Y, 14M, 14C, and 14K. The light beam scanning device 30 forms yellow, magenta, cyan, and black single-color latent images on the photosensitive drums 14Y, 14M, 14C, and 14K. As a light source for irradiating a light beam, an LD, LED, EL or the like can be used. These latent images are visualized by the developing devices 18Y, 18M, 18C, and 18K. These single-color images are sequentially transferred onto the intermediate transfer belt 13 and superimposed to form a color image. The color image formed on the intermediate transfer belt 13 is transferred to the transfer paper by the secondary transfer roller pair 21 and fixed on the transfer paper by the fixing device 25. Since these configurations are conventionally known, detailed configurations and descriptions are omitted.

  Since this tandem method is likely to cause color misregistration, a predetermined test pattern is transferred onto an intermediate medium such as an intermediate transfer belt and a conveyor belt, read by an alignment sensor, and fed back to a writing control unit to determine the position between each color. Control to match.

FIG. 2 is a diagram showing an alignment sensor (toner mark sensor). FIG. 2A shows the case of the diffuse light sensor system, and FIG. 2B shows the case of the regular reflection light sensor system. When a diffused light sensor is used as the alignment sensor 151, as shown in FIG. 2A, a light source 151a composed of an LD or an LED and light from the light source 151a are applied to the alignment pattern 150 and reflected. The diffused light is detected by the diffused light sensor 151b arranged at a position not receiving light. When a regular reflection light sensor is used, the reflected light sensor 151c detects the light from the light source 151a reflected by the alignment pattern 150, as shown in FIG. Incidentally, the light source 151a and the diffused light sensor 151b, or referred to the reflected light sensor 15 1 c and the light source 151a with the toner mark sensor or TM sensor.

  Conventionally, the arrangement position of the toner mark sensor is located downstream and downstream of all the photoconductors.

  FIG. 3 is a block diagram showing a relationship between an alignment sensor (toner mark sensor), a flow of image data to be written on the photosensitive member, a control unit for controlling them, and a peripheral part thereof. In FIG. 3, the control unit 101 includes a CPU or its peripheral ASIC. The control unit 101 receives image data from the print controller 102 and modulates and transmits the image data to the LD driver 103 for each line or a plurality of lines or at a certain timing. Further, the control unit 101 must transmit image data to the LD driver 103 at a certain timing, and transmits image data to the LD driver 103 at a timing set in the control unit 101.

  The timing is automatically set by the machine itself by feeding back the detection data of the test pattern (for alignment). That is, the alignment pattern 150 transferred onto the intermediate medium (intermediate transfer belt) 13 is read by the alignment sensor (TM sensor) 151 and an analog signal is sent to the control unit 101. The control unit 101 quantizes the data by A / D to obtain misregistration data, or averages to obtain accurate color misregistration data from analog data. This calculation processing part may use a DSP or other CPU. This misalignment data is fed back to the control unit 101 again to reset the timing.

  The LD driver 103 drives the LD 31 according to the transmitted image forming signal. The light beam emitted from the LD 31 is deflected by a polygon mirror (not shown) and scanned on the photoconductor 14 to form an image. The (horizontal) synchronization sensor 32 is synchronized once or at a specific scan timing, so that an image can be formed at a constant timing.

  The image forming apparatus according to this embodiment is a color image forming apparatus. As described above, the LD driver 103 has four colors and is driven by the LD driver 103 in order to form an image by superimposing the four basic colors. The LD 31, the photoconductor 14, and the synchronization sensor 32 are also provided independently for four colors.

  Many color matching techniques in such a tandem full-color machine have been reported so far and will not be described in detail here.

  FIG. 4 is a diagram showing a specific example of the alignment pattern formed on the intermediate transfer belt 13. FIG. 9A shows an example of a main scanning deviation amount detection pattern, and FIG. 10B shows an example of a sub-scanning deviation amount detection pattern. These patterns are the alignment patterns for the regular reflection light and are conventionally used. Here, drawing is performed using four colors of C, M, Y, and K, and reading is performed by the toner mark sensor 151. In actual reading, an edge portion of a pattern formed with toner is read. The method for reading the deviation amount will be described below.

  The length (ΔSc, ΔSk, ΔSy, ΔSm) between the horizontal line pattern and the diagonal line pattern of the same color shown in FIG. 4A is measured by the timer of the control unit 101, and the time is converted into a length. The amount of deviation can be calculated by comparing the lengths. From the sub-scan correction pattern of FIG. 4B, ΔFy, ΔFc, ΔFm can be measured by the timer as deviations from the reference color K as shown in the figure, and this is converted into a length and compared with the ideal length. The shift amount can be calculated by From this, the amount of deviation of each color from the ideal distance is obtained and fed back to each device to correct the color deviation.

  Although the description of this embodiment has been made using a regular reflection sensor, it goes without saying that a diffused light sensor or another type of sensor may be used. Further, since these are well-known techniques, a detailed description thereof will be omitted.

  FIG. 5 is a diagram illustrating a relationship among the photosensitive drum, the intermediate transfer belt, and the toner mark sensor according to Example 1 of the present embodiment.

  In the first embodiment, as can be seen from FIG. 5, the four photosensitive drums 14Y, 14C, 14M, and 14K, which are image carriers, are arranged in parallel, and between the adjacent photosensitive drums 14C and 14M. In addition, a toner mark sensor (hereinafter also abbreviated as TM) is arranged. Front, center, and rear are defined from the front, and TM11, TM12, and TM13 are arranged from the front. Here, the four photoreceptors are prepared with the name YCMK, but any number of photoreceptors may be used as long as there are a plurality of photoreceptors. Three TM sensors, TM11, TM12, and TM13, are arranged from the front in the front, center, rear, and main scanning directions, but two or one may be used as long as the color matching accuracy is maintained. Or more, you may arrange | position with TM14, TM15 ....

  In the present embodiment, such a TM sensor 151 is set upstream of the conventional sensor, which is a feature of the present embodiment and the present invention.

  FIG. 6 is a diagram illustrating a test pattern of Example 1 in which an alignment pattern is formed for each of two colors and read to correct misalignment. When configured as shown in FIG. 6, Y-color and C-color patterns are formed on the photoconductor Y and the photoconductor C, respectively, and the toner images transferred to the intermediate transfer belt 13 can be read immediately by the TMs 11, 12, and 13. .

  Further, if a sensor is disposed between the photosensitive drum 14M and the photosensitive drum 14K, such as TM21, TM22, and TM23, the toner image formed by the photosensitive drums 14C and 14M and transferred to the intermediate transfer belt 13 is transferred. Can be read. Similarly, if sensors such as TM31, TM32, and TM33 are arranged on the downstream side of the photosensitive drum 14K, the toner images formed on the photosensitive drums 14M and 14K can be read quickly. Of course, the toner images formed on the photosensitive drums 14Y, 14C, and 14M may be read by the sensors TM21, TM22, and TM23.

  When the alignment pattern is formed and read by the toner mark sensor TM, TM11, TM12, and TM13 measure the color shift ΔCY between yellow Y and cyan C. In TM21, TM22, and TM23, a color shift ΔMC between magenta M and cyan C is measured. In TM31, TM32, and TM33, a color shift ΔKM between black K and magenta M is measured. For example, when K color is used as a reference, M color shift from ΔKM to K can be measured, and C color shift amount from M can be measured from ΔMC. As a result, C color shift amount from K can be measured, and similarly from ΔYC. In addition, the amount of Y color shift relative to K can be measured.

  The reference color need not be limited to the K color. In this case, the accuracy of color matching is improved by using the C or M color arranged in the center as a reference. Further, this method can be implemented by main scanning correction, sub-scanning correction, skew control, and bending correction. By performing such control, it is possible to quickly acquire color misregistration information even when performing alignment (color alignment) during printing of the first sheet.

The deviation amount can be obtained as follows, for example.
Here, the color misregistration amount measured in units of two colors is converted into the color misregistration amounts for the K colors of Y, M, and C when the K color is used as a reference. That is, if the displacement amount of the M color with respect to the K color read by TM31, TM32, and TM33 is ΔKM, ΔKM is
ΔKM = KM
And
M = K-ΔKM
It is represented by Here, if the displacement amount of the C color with respect to the M color read by TM21, TM22, TM23 is ΔMC, ΔMC is
ΔMC = MC
= K-ΔKM-C
It becomes. This
C = K-ΔKM-ΔMC
Because
ΔKC = K−C
= ΔMC + ΔKM
It becomes.

On the other hand, if the amount of deviation of Y with respect to C read by TM11, TM12, and TM13 is ΔCY, ΔCY is
ΔCY = CY
= K-ΔKM-ΔMC-Y
And ΔKY is
ΔKY = KY
= ΔCY + ΔKM + ΔMC
Thus, it can be seen that the amount of color misregistration between all two colors can be converted to the amount of color misregistration based on the K color.

  This makes it possible to perform color matching of other Y, C, and M colors based on K color (K color is not corrected). Of course, color matching can be performed based on M and C colors near the center instead of K color, and Y color can also be used as a reference.

  FIG. 7 is a timing chart showing the timing of measuring the color misregistration amount in the conventional example and this embodiment. In the conventional example, a TM sensor is arranged downstream of the final color of the photosensitive drum, and this embodiment is an example in which the amount of color misregistration is measured for each of the two colors shown in FIG. In both cases, when a start trigger signal for starting a pattern is input, FGATEs for the pattern are sequentially generated. While FGATE is being generated, it indicates that the color is being written in real time. Below that, the time for the pattern to pass the TM sensor is shown in the form of a gate.

In the prior art example, Y, C, M , and K and the pattern 150 are overlapped in the order of image formation and then read by the TM sensor 151. In contrast, in this embodiment, between the photosensitive drum 14C and 14M, between 14 M and 14K, since the TM sensor downstream of the 14K are arranged, superimposed pattern 150 every two colors, to be read it can. That is, as soon as a start trigger signal for starting the pattern 150 is input, an FGATE of the pattern 150 for three colors may be immediately generated, and then another corresponding FGATE may be generated. Thereafter, the TM sensor 151 reads the pattern.

  After measuring the color misregistration amount, the writing timing is reset, or the setting values of the drive and writing devices are reset. In this way, the first print can be performed at high speed while positioning before printing.

  FIG. 8 is a block diagram showing a circuit configuration of a signal generation circuit that generates the signal used in FIG. In the figure, the signal generation circuit comprises the control unit 101, the printer controller 102, and LD writing units 104Y, 104M, 104C, and 104K provided for each color. The start trigger signal is transmitted from the print controller 102 to the control unit 101 when there is a print request. In the control unit 101, / FGATE signals are sequentially generated in accordance with the timings of the LD writing units 104Y, 104M, 104C, and 104K. Similarly, when forming a test pattern for alignment, each / FGATE signal is generated after receiving a start trigger signal.

  FIG. 9 is a diagram illustrating the relationship among the photosensitive drum, the intermediate transfer belt, and the toner mark sensor according to Example 2 of the present embodiment.

  The second embodiment is an example in which the number of toner mark sensors is reduced as compared with the first embodiment shown in FIG. That is, in the second embodiment, TM12 is provided at the center between the photoconductive drums 14C and 14M, TM22 is provided at the center between the photoconductive drums 14M and 14K, and the front, center, rear on the downstream side of the photoconductive drum 14K. TM31, TM32, and TM33 are arranged respectively. In such an arrangement, TM12 detects the sub-scanning deviation amount between the photosensitive drums 14C and 14Y, TM22 detects the sub-scanning deviation amount between the photosensitive drums 14M and 14C, and TM31, TM32, and TM33. A sub-scanning deviation amount between the photosensitive drums 14K and 14M and a main scanning deviation amount between the photosensitive drums 14Y, 14M, 14C, and 14K are detected.

When the main scanning and the sub scanning are compared, the sub scanning needs to precisely drive each motor such as a photosensitive drum driving motor, an intermediate transfer belt driving motor, and a secondary transfer driving motor, and there are many problems. The main scan is driven by the polygon scanner motor and is relatively easy to control, and the alignment correction frequency of the main scan may be less than that of the sub-scan. Therefore, in the case of the configuration of the second embodiment, main scanning correction is not performed in many cases, and only the correction correction for calculating the sub-scanning deviation amount between two colors is performed using TM12, TM22, TM31, TM32, and TM33, particularly in the first print. By executing this, it is possible to execute printing while performing alignment in a shorter time. As described above, in the second embodiment, the number of toner mark sensors is reduced from nine to five compared to the first embodiment. It becomes possible to reduce to individual, and cost can be reduced.

  FIG. 10 is a diagram illustrating the relationship among the photosensitive drum, the intermediate transfer belt, and the toner mark sensor according to Example 3 of the present embodiment.

  In the third embodiment, the arrangement of the toner mark sensors is changed to further reduce the cost compared to the second embodiment. That is, in Example 3, TM12 is provided at the center between the photoconductive drums 14C and 14M, TM23 is provided at the rear between the photoconductive drums 14M and 14K, and TM31 is provided at the front downstream of the photoconductive drum 14K. It is arranged. In such an arrangement, TM12 detects the amount of sub-scanning deviation between the photosensitive drums 14C and 14Y, TM23 detects the amount of sub-scanning deviation between the photosensitive drums 14M and 14C, and TM31 detects the amount of sub-scanning deviation. And 14M are detected.

  As for the amount of deviation of the main scanning, after a pattern combining all colors is imaged and transferred, the pattern is not transferred by the secondary transfer device but sent to the downstream, and the belt cleaning unit goes around without cleaning and reaches the sensor position again. The amount of deviation of the main scanning position is detected by reading the pattern. In this method, it takes time to read the main scan. However, as described above, the alignment correction frequency of the main scan may be less than that of the sub-scan, so that the system is established.

  As described above, in the third embodiment, the number of toner mark sensors can be further reduced from five to three as compared with the second embodiment described above, and the cost can be further reduced with respect to the second embodiment. it can.

  FIG. 11 is a diagram illustrating the relationship among the photosensitive drum, the intermediate transfer belt, and the toner mark sensor according to Example 4 of the present embodiment.

  In the fourth embodiment, the arrangement of the toner mark sensors is changed from the second embodiment so that the writing position can be corrected. That is, in Example 4, the front TM11 between the photoconductive drums 14C and 14M, the TM21 at the front rear between the photoconductive drums 14M and 14K, and the front, center, rear on the downstream side of the photoconductive drum 14K. TM31, TM32, and T33 are arranged in the circuit. In this arrangement, TM11 detects the sub-scanning deviation between the photoconductor drums 14C and 14Y, TM21 detects the sub-scanning deviation between the photoconductor drums 14M and 14C, and TM31, TM32, and TM33 detect the photoconductor. A sub-scanning deviation amount between the drums 14K and 14M and a main scanning deviation amount between the YMCK photosensitive drums 14 are detected.

  Further, by using TM11, TM21, and TM31, it is possible to perform main-scan writing position correction in units of two colors. If there is a main scanning overall magnification, the color shift of each plate can be corrected by matching the main scanning writing position.

  As described above, in the fourth embodiment, since the writing start position can be corrected as compared with the second embodiment described above, the alignment of the main scanning can be performed more advantageously.

  FIG. 12 is a diagram illustrating a relationship among the photosensitive drum, the intermediate transfer belt, and the toner mark sensor according to Example 5 of the present embodiment.

  The fifth embodiment is an example in which toner mark sensors TM01 to TM33 are arranged at the front, center, and rear immediately after the downstream side of each of the photosensitive drums 14Y, 14M, 14C, and 14K. In this embodiment, the amount of sub-scanning deviation is detected, and the pattern shown in FIG. 4B is formed as a test pattern. In this example, laser writing is performed on the photosensitive drums 14Y, 14M, 14C, and 14K, and the test pattern including the formed toner image is formed and read by the alignment sensor (toner mark sensor) in the shortest period. Is. In this configuration, the test pattern 150 transferred from the photosensitive drums 14Y, 14M, 14C, and 14K to the intermediate transfer belt 13 is immediately read by the toner mark sensor.

In the example of FIG. 12, the test pattern is the pattern of the sub-scanning correction pattern 150 of FIG. One pattern may be used, but when a plurality of patterns are formed, data obtained by averaging a plurality of detection results is used as the positional deviation correction data. Further, when the toner image is transferred from the photoconductive drums 14Y, 14M, 14C, and 14K to the intermediate transfer belt 13, if the position does not shift so much, a toner mark is formed on each photoconductive drum 14Y, 14M, 14C, and 14K. The sensor TM may be arranged to read the positional deviation amount. As will be described later, when the line sensor is used, FIG. 13 is a timing chart showing the detection timing when the toner mark sensor is arranged as shown in FIG. 12 and this toner mark sensor is used. In this example, the toner mark sensor is used for position correction in the sub-scanning direction as described above. As can be seen from this timing chart, in the example of FIG. 12, / FGATE of each color is asserted by the start trigger signal. A test pattern for correcting the sub-scanning deviation is formed during the period when the / FGATE signal is asserted. Then, a time from when the / FGATE signal is negated to when the alignment pattern is read is measured by a timer. Therefore, the time from the / FGATE negation to the pattern reading is measured at the time of alignment between the two colors described above, and is stored in a memory (not shown) connected to the control unit 101.

  On the other hand, a line sensor is used as a toner mark sensor for detecting the absolute position of main scanning. FIG. 14 is a diagram showing a configuration for detecting an absolute position in the main scanning direction. When detecting the absolute position in the main scanning direction, the vertical 1 dot line L1 is imaged and transferred to the intermediate transfer belt 13, and the pattern transferred to the intermediate transfer belt 13 is transferred to a line sensor LS composed of a CCD, CMOS, or the like. To read the main scanning position. The line sensor LS is disposed at the same position as the toner mark sensor 151. The line sensor LS has a row of detectors that can detect 1 dot of an image, and can read the position of the pattern as described above. When the amount of light is insufficient, reflected light or diffused light is read using a light source such as an LED or a lamp.

  FIG. 15 is a flowchart showing a processing procedure for detecting (measuring) the amount of misalignment by the second detection means, and FIG. FIG. 5B shows a processing procedure for alignment correction by the second detection means. That is, in the flowchart of FIG. 15, the second detection means (single color pattern is used to detect positional deviation) in synchronization with the detection operation of the first detection means (detects the amount of positional deviation using a plurality of color patterns). The detection operation by detecting the amount) is shown.

  In the flowchart of FIG. 15A, the reference value of the absolute position of the main scanning position and the sub-scanning position is detected. For the main scanning position, the line sensor LS is used as the second detection unit, and for the sub-scanning position, the toner is used. The mark sensor 151 is used as the first detection means. First, a toner mark sensor (first detection means) 151 as shown in FIG. Alternatively, the shift amount is detected in units of four colors (full color machine using four colors of YMCK), and alignment correction is performed (step S101). Next, in the sub-scanning direction, the time from the FGATE negate to the pattern detection by the toner mark sensor 151 is measured by the control unit 101 and converted into a length. On the other hand, in the main scanning direction, the line sensor LS as shown in FIG. 14 is used, and the main scanning absolute position is detected using the 1 dot pattern L1 (step S102). Then, the detected main scanning and sub-scanning absolute positions are stored in the memory as reference values (step S103).

  Further, the alignment correction by the line sensor LS, which is executed by using the number of formed images or environmental data as a trigger, is performed as follows.

  First, each absolute position in the main scanning direction and the sub-scanning direction serving as a reference is loaded from the memory stored in step S103 (step S201). Next, in the sub-scanning direction, the control unit 101 measures the time from the FGATE negate to the pattern detection by the TM sensor 151 and converts it to a length. For the main scanning direction, the line sensor LS is used as the TM sensor, and the main scanning absolute position is detected using a 1 dot pattern (step S202). The loaded absolute reference value position data is compared with the detected absolute position data to calculate a correction amount (step S203), and finally the correction amount is set in the control unit 101 (step S204). Note that the number of image formations is managed by the print controller 102, and environmental data is obtained by, for example, the ambient temperature in the image forming apparatus, the temperature in the vicinity of the intermediate transfer belt, or the ambient humidity by a temperature sensor or humidity sensor (not shown). When the humidity exceeds a predetermined threshold value, alignment correction is executed.

  In this manner, the second detection means is executed in synchronization with the first detection means, and the absolute position reference value can be obtained.

  As a modification of FIG. 12, a configuration as shown in FIG. 16 can be adopted. FIG. 16 is a diagram showing a configuration for changing a part of the toner mark sensor 151 shown in FIG. 12 to the line sensor LS and detecting the main scanning absolute position by the line sensor LS. As can be seen from the figure, in this modification, TM01, TM03, TM11, TM13, TM21, and TM23 in FIG. 12 are changed to line sensors LS. In this example, the setting is that the black K color is the reference color, and since the respective colors are matched with the black K color, the black K toner mark sensor is not changed. Further, the toner mark sensors TM31, TM32, and TM33 at this position are conventionally installed. In this configuration, correction using the line sensor LS is possible in the main scanning direction and the sub-scanning direction. Naturally, the pattern of the location where the line sensor LS is used is the 1 dot pattern L1 shown in FIG. 14, and the test pattern at the positions of the toner mark sensors TM02, TM12, TM22, TM31, TM32, TM33 is the sub-scan in FIG. This is a correction pattern 150.

  FIG. 17 is a further modification of FIG. In the example of FIG. 17, TM01, TM03, TM11, TM13, TM21, and TM23 in FIG. 16 are deleted, and the sub-scan correction pattern 150 is detected by TM02, TM12, TM22, TM31, TM32, and TM33. Such a configuration can be adopted when only absolute position correction in the sub-scanning direction is performed without performing absolute position correction. In addition, TM02, TM12, and TM22 may be arranged on the writing position side so that the main scanning writing position is corrected. Deviations in the main scanning direction can be accurately handled by correcting the write timing of optical scanning, but positional deviations in the sub-scanning direction are related to motor rotation accuracy, roller diameter accuracy, backlash between the bearings and rollers, and the intermediate transfer belt. Since it is difficult to obtain accuracy due to complex errors such as the amount of expansion and contraction, it is performed for each color in the sub-scanning direction. Thus, by omitting the absolute position detection function in the main scanning direction, the cost can be further reduced.

As described above, according to this embodiment,
1) The time required to start the alignment operation and complete the sensor reading operation can be shortened.
2) Faster first printing can be realized even if alignment control is executed before printing.
3) Since at least one sensor disposed between the photosensitive drums is disposed far upstream from the conventional sensor, reading of the displacement data can be completed earlier.
4) As a result of combining these, it is possible to provide a color image forming apparatus in which the first print is fast and there is no positional deviation.
There are effects such as.

1 is a diagram schematically showing an overall configuration of a tandem type image forming apparatus according to an embodiment of the present invention. It is a figure which shows the alignment sensor (toner mark sensor). FIG. 3 is a block diagram illustrating a relationship between an alignment sensor (toner mark sensor), a flow of image data to be written on a photoconductor, a control unit that controls them, and a peripheral part of the control unit. FIG. 6 is a diagram illustrating a specific example of an alignment pattern formed on an intermediate transfer belt. FIG. 5 is a diagram illustrating a relationship among a photosensitive drum, an intermediate transfer belt, and a toner mark sensor according to Example 1 of the present embodiment. It is a figure which shows the test pattern of Example 1 which forms the alignment pattern for every 2 colors, reads and performs position shift correction. 6 is a timing chart illustrating timings of measurement of color misregistration amounts in a conventional example and Example 1. FIG. 8 is a block diagram illustrating a circuit configuration of a signal generation circuit that generates a signal used in FIG. 7. 6 is a diagram illustrating a relationship among a photosensitive drum, an intermediate transfer belt, and a toner mark sensor according to Embodiment 2. FIG. FIG. 10 is a diagram illustrating a relationship among a photosensitive drum, an intermediate transfer belt, and a toner mark sensor according to a third embodiment. FIG. 10 is a diagram illustrating a relationship among a photosensitive drum, an intermediate transfer belt, and a toner mark sensor according to a fourth embodiment. FIG. 10 is a diagram illustrating a relationship among a photosensitive drum, an intermediate transfer belt, and a toner mark sensor according to a fifth embodiment. 13 is a timing chart showing detection timing when a toner mark sensor is arranged as shown in FIG. 12 and this toner mark sensor is used. It is a figure which shows the detection structure of the absolute position of a main scanning direction. It is a flowchart which shows the process sequence when detecting the amount of position shifts by the 2nd detection means (measurement). It is a figure which shows the structure for changing a part of toner mark sensor shown in FIG. 12 into a line sensor, and detecting a main scanning absolute position with a line sensor. FIG. 17 is a diagram showing a configuration in which TM01, TM03, TM11, TM13, TM21, and TM23 in FIG. 16 are deleted and a sub-scan correction pattern is detected by another TM in the modification of FIG.

Explanation of symbols

13 Intermediate transfer belt 14Y, 14M, 14C, 14K, Photosensitive drum 15Y, 15M, 15C, 15K Primary transfer device 18Y, 18M, 18C, 18K Developing device 21 Secondary transfer device 30 Light beam scanning device 31 LD
101 Control Unit 102 Print Controller 103 LD Driver 114 LD
150 test pattern 151, TM toner mark sensor L1 1 dot pattern LS line sensor

Claims (7)

A plurality of image carriers;
An endless belt that functions as an intermediate transfer medium to which a toner image formed on the image carrier is transferred, or an endless belt that conveys a recording paper to which the toner image is transferred;
Detecting means provided on at least one of the image carriers, formed on the image carrier, and detecting a test pattern for correcting misregistration transferred onto the endless belt;
In an image forming apparatus comprising:
The detection means includes
First measurement means for detecting a test pattern in which patterns of a plurality of colors are combined;
A second measuring means for detecting a test pattern formed in a single color and detecting an absolute deviation amount of a position where the test pattern is transferred on a plate on which the test pattern is created;
Including
The test pattern is provided on the main scanning writing position side at different positions in the sub-scanning direction between different image carriers, and detects the test pattern that has made a round over the secondary transfer position and has reached the detection means position again. Read the export position of
When alignment is performed based on the measurement result of the first measurement unit, the absolute deviation amount detected by the second measurement unit is stored, and thereafter, the alignment is performed using the second measurement unit. When performing the adjustment, the correction amount is calculated based on the stored absolute deviation amount, and the alignment is performed.
When the absolute deviation amount is measured by the second measuring unit, the time from the signal related to image formation in the image forming apparatus to the reading of the alignment pattern is measured, and the time difference between the reference time and the measured time is measured. An image forming apparatus, wherein a correction amount used for alignment is calculated from the image forming apparatus. The image forming apparatus according to claim 1.
An image forming apparatus characterized in that the signal related to image formation is an image vertical synchronization signal . The image forming apparatus according to claim 1, wherein
The image forming apparatus according to claim 2, wherein the second measuring unit measures an absolute positional deviation amount by a line sensor . The image forming apparatus according to any one of claims 1 to 3,
An image in which the main scanning and sub-scanning absolute positions stored as reference values when alignment is performed by the first measuring unit is re-acquired by the second measuring unit and a correction amount is calculated. Forming equipment. 5. The image forming apparatus according to claim 1, wherein:
The image forming apparatus according to claim 1, wherein the color misregistration correction by the second measuring unit is performed based on the number of image forming sheets . 5. The image forming apparatus according to claim 1, wherein:
The image forming apparatus according to claim 1, wherein the color misregistration correction by the second measuring unit is performed based on environmental data . The image forming apparatus according to claim 6 .
The image forming apparatus, wherein the environmental data is temperature or humidity .

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