JP2005271372A - Image forming device and method of correcting image forming position - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image forming device which detects the concentration distribution of a test pattern with high sensitivity by using a reflection-type optical sensor of a simple configuration, and corrects an image forming position of a recording head with high accuracy, and to provide a method of correcting the image forming position. <P>SOLUTION: According to the operation of the image forming device, it is determined at a step 400 whether or not print data for printing the test pattern are inputted, and if the print data are inputted, it is determined at a step 402 whether or not a yellow head 12Y is driven from the print data. If it is determined that the yellow head 12Y is driven, then a cyan head 12C is driven at a step 404, thereby printing a ground of pale blue. Then at a step 406, the test pattern is printed on the printed pale-blue ground. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an image forming apparatus and a method for correcting an image forming position, and more particularly to an image forming apparatus that corrects an image forming position of each recording head and an image forming position correction in an image forming apparatus including a plurality of recording heads. Regarding the method.

Conventional ink jet printers print a test pattern on paper and correct the print position of each recording head using the print result. For example, print a test pattern whose density distribution changes according to the recording head position deviation, detect the recording head position deviation from the density distribution read by the reflective optical sensor, and correct the printing position of each recording head. The method of doing is known (patent documents 1 and 2).

In the correction method described in Patent Document 1, a red LED or an infrared LED is used as an optical sensor, and a color excellent in light absorption characteristics for these colors is used in a test pattern. In the correction method described in Patent Document 2, a white LED having a high peak near a wavelength of 460 nm and a gentle peak around a wavelength of 560 nm is used for the optical sensor as shown in FIG. ing. Cyan is excellent in light absorption characteristics near a wavelength of 560 nm, and magenta and yellow are excellent in light absorption characteristics near a wavelength of 460 nm.
JP 11-291470 A JP 2002-347227 A

  However, if a red LED or the like is used for the optical sensor, sufficient density characteristics and S / N ratio cannot be obtained with magenta or yellow. In order to avoid this problem, Patent Document 1 discloses a method in which a blue LED and a green LED are mounted in addition to a red LED, and dot alignment is performed for each color (C, M, Y) with respect to black. Although proposed, this method requires control for switching two or more LEDs for each color of CMY, and also requires two types of LEDs, which complicates and enlarges the configuration of the optical sensor and is expensive. There is a problem of becoming.

  Further, even when the above-described white LED is used for the optical sensor, there is a problem in that there is no density difference between patterns when the test pattern is printed in yellow. This is because, as shown in FIG. 12, in the yellow spectral region, the difference in reflectance between the white background and the yellow print portion is only about 80%.

  The present invention has been made to solve the above problems, and an object of the present invention is to detect the density distribution of a test pattern with high sensitivity using a reflection type optical sensor having a simple configuration, and An object of the present invention is to provide an image forming apparatus and an image forming position correcting method capable of correcting an image forming position with high accuracy.

  In order to achieve the above object, a first image forming apparatus of the present invention includes a plurality of recording heads that record images on a recording medium using color materials of different colors, and has a density with respect to the ground color of the recording medium. After forming a ground on the recording medium using a second color material that is a complementary color to the first color material having a small difference, the recording head uses the first color material. Recording means for recording a plurality of pattern images whose density changes according to the positional deviation of each of the plurality of pattern images, and in each of the plurality of pattern images, a wavelength region in which a difference between the reflectance of the color material and the reflectance of the recording medium is large The pattern image is recorded based on the irradiation means for irradiating light having a peak to the light, the detection means for detecting the light quantity of the reflected light from each of the plurality of pattern images, and the light quantity detected by the detection means. Correcting the image forming position of the recording head A positive means, characterized by comprising a.

  In the first image forming apparatus, a recording unit including a plurality of recording heads that record images on a recording medium with color materials of different colors has a color with a small density difference with respect to the ground color of the recording medium. After forming a base on the recording medium using a second color material that is complementary to the first color material, the density changes according to the positional deviation of the print head using the first color material. A plurality of pattern images to be recorded are recorded. The irradiating means irradiates each of a plurality of pattern images (recording patterns) recorded by the recording means with light having a peak in a wavelength region where the difference between the reflectance of the color material and the reflectance of the recording medium is large, and detecting means Detects the amount of reflected light from each of the plurality of pattern images. Then, the correcting unit corrects the image forming position of the recording head on which the pattern image is recorded, based on the light amount detected by the detecting unit.

  In the present invention, since the irradiation means emits light having a peak in a wavelength region where the difference between the reflectance of the color material forming the recording pattern and the reflectance of the recording medium is large, the light intensity varies depending on the change in the density of the recording pattern. The reflectance changes by a predetermined value or more. In addition, in the present invention, for example, a blue pattern is printed on a white paper, and then a yellow pattern image is printed. For the first color material having a small density difference with respect to the ground color of the recording medium. After forming the background on the recording medium using the second color material of complementary color, the pattern image is recorded using the first color material, so that the reflectance at the background portion is improved and the pattern is recorded. The reflectance at the portion where the image is formed is relatively lowered.

  The reflectance from the pattern image changes according to the density of the pattern image. Therefore, according to the first image forming apparatus of the present invention, the density distribution of the test pattern, that is, the density of each of the plurality of recording patterns constituting the test pattern can be detected with high sensitivity. Thereby, the image forming position of each recording head can be corrected with high accuracy.

  In addition, since the light having a peak in the wavelength region in which the difference between the reflectance of the color material forming the recording pattern and the reflectance of the recording medium is large is emitted, the color of the light to be irradiated is changed according to the color on which the recording pattern is formed. It is not necessary to perform complicated control for switching, and it is possible to detect density differences between a plurality of recording patterns at a low cost with a simple configuration.

  In order to achieve the above object, a second image forming apparatus according to the present invention includes a plurality of recording heads that record images on a recording medium with different color materials, and the background color of the recording medium. And recording means for recording a plurality of pattern images whose density changes according to the positional deviation of the recording head using a color material of complementary color, and reflection of the color material on each of the plurality of pattern images An irradiating means for irradiating light having a peak in a wavelength range where the difference between the reflectance and the reflectance of the recording medium is large; a detecting means for detecting the amount of reflected light from each of the plurality of pattern images; and the detecting means And correcting means for correcting the image forming position of the recording head on which the pattern image is recorded based on the amount of light detected in step (b).

  In the second image forming apparatus, for example, the recording unit uses a color material having a color complementary to the ground color of the recording medium, such as printing a yellow pattern image on blue paper. Since a plurality of pattern images whose density changes according to the positional deviation of the head are recorded, the reflectance at the base portion is improved and the reflectance at the portion where the pattern image is formed is relatively lowered.

  Therefore, according to the second image forming apparatus of the present invention, as in the first image forming apparatus, the density distribution of the test pattern is detected with high sensitivity using a reflection type optical sensor having a simple configuration, and is recorded. The image forming position of the head can be corrected with high accuracy.

  In the image forming apparatus, the recording unit may include four types of recording heads that record images on a recording medium using cyan, magenta, yellow, and black color materials, respectively. The pattern image recorded by the recording means is preferably composed of one color selected from cyan, magenta, and yellow and black.

  The image forming apparatus preferably further includes a sensitivity adjusting unit that adjusts the detection sensitivity of the detecting unit. Examples of such sensitivity adjusting unit include an electronic volume.

  The irradiating means may irradiate light having peaks in at least two wavelength ranges of red light, green light, and blue light. The light from the monochromatic light source and the phosphor excited by the monochromatic light source may be used. What irradiates the light which mixed the emitted light may be used. The irradiating means may be composed of a white light emitting diode (LED), or may be configured to include three light emitting elements that independently irradiate each of red light, green light, and blue light.

  In the first image forming position correction method of the present invention, a color having a small density difference with respect to the ground color of the recording medium is obtained by using a plurality of recording heads that record images on the recording medium with different color materials. After forming a base on the recording medium using a second color material that is a complementary color to the first color material, the first color material is used to shift the position of the recording head. A plurality of pattern images having different densities are recorded, and each of the plurality of pattern images has a peak in a wavelength region where a difference between the reflectance of the first color material and the reflectance of the recording medium is large. , And the amount of reflected light from each of the plurality of pattern images is detected, and the image forming position of the recording head on which the pattern image is recorded is corrected based on the detected amount of light. .

  According to the second image forming position correcting method of the present invention, a color material having a color complementary to the ground color of the recording medium by a plurality of recording heads that record images on the recording medium with different color materials. Are used to record a plurality of pattern images whose density changes according to the positional deviation of the recording head, and the difference between the reflectance of the color material and the reflectance of the recording medium is recorded in each of the plurality of pattern images. A recording head that irradiates light having a peak in a large wavelength region, detects the amount of reflected light from each of the plurality of pattern images, and records the pattern image based on the amount of light detected by the detection means The image forming position is corrected.

  According to the first and second image forming position correction methods of the present invention, as with the first image forming apparatus, the density distribution of the test pattern is highly sensitive using a reflective optical sensor having a simple configuration. It is possible to detect and correct the image forming position of the recording head with high accuracy.

  According to the present invention, the density distribution of the test pattern can be detected with high sensitivity using a reflection type optical sensor having a simple configuration, and the image forming position of the recording head can be corrected with high accuracy. An effect is obtained.

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

  FIG. 1 is a schematic cross-sectional view of an image forming apparatus 10 according to the present embodiment. The image forming apparatus 10 includes a carriage 14, a reflective sensor module 16, a platen 18, a transport belt 19, a recording paper cassette 20, a guide plate 22, a pinch roller 26, a registration roller 28, and a discharge roller 30, and a discharge tray 32. Is installed.

  The carriage 14 is equipped with independent inkjet heads (hereinafter referred to as “heads”) 12K, 12Y, 12M, and 12C that eject black / cyan / magenta / yellow inks. The carriage 14 is installed at a position facing the surface on which the recording paper 34 of the platen 18 is placed so as to be separated from the platen 18 by a predetermined distance so as to be movable in a direction perpendicular to the paper transport direction W (hereinafter referred to as “carriage scan direction”). ing.

  The reflective sensor module 16 is installed on the downstream side of the carriage 14 in the paper conveyance direction W and is separated from the platen 18 by a predetermined distance. The nozzles (not shown) of the head 12 are arranged at a pitch of 800 dpi, and an image can be printed at a resolution of 800 dpi × 800 dpi. A recording sheet 34 as a recording medium is set in the recording sheet cassette 20 and is conveyed in the sheet conveying direction W based on a predetermined process, passes between the registration rollers 28, the guide rollers 24, and the pinch rollers 26, and then on the platen 18. It is conveyed to.

  Based on the input signal, the recording paper placed on the platen 18 by scanning in the paper conveyance direction W (hereinafter referred to as “carriage scanning direction”) by the carriage 14 and conveyance of the recording paper 34 by the conveyance belt 19. In 34, an image based on the input signal is formed. After the image is formed, the recording paper 34 passes between the paper discharge rollers 30 and is discharged to the paper discharge tray 32.

  FIG. 2 is a schematic sectional view of the reflective sensor module 16. The reflective sensor module 16 incorporates an LED light source 40 and a sensor 42. As the LED light source 40, a monochromatic (460 mm) light source and a white LED that emits white light by light emitted from a phosphor excited by the monochromatic light source are used. As the sensor 42, a visible light phototransistor or photodiode is used.

  Based on a predetermined input signal, the LED light source 40 emits light and irradiates the recording paper 34, and the reflected light from the recording paper 34 is received by the sensor 42 (see the optical path 44). In addition, a lens etc. can also be arrange | positioned in the middle of the optical path | route 44 from the light emission part of the LED light source 40 to the sensor 42 as needed.

  FIG. 11 shows the light emission characteristics of the white LED. As can be seen from the figure, the light from the white LED has a high peak near the 460 nm wavelength and a gentle peak around the 560 nm wavelength. For cyan, the emission wavelength component centered around the wavelength of 560 nm, for magenta and yellow, the emission wavelength component near the wavelength of 460 nm, and for black, the wavelength component near the two wavelengths of 560 nm and 460 nm. , Each becomes an effective wavelength component for a wavelength region having a low reflectance.

  As shown in FIG. 3, the control unit 46 for controlling the carriage 14, the head 12, and the reflective sensor module 16 includes a black head 12K, a yellow head 12Y, a magenta head 12M, and a cyan head mounted on the carriage 14. 12C, the LED light source 40, the sensor 42, a storage unit 48 for storing correction information, and an input unit 50 for inputting various instructions.

  The control unit 46 is connected to an electronic volume 51 that adjusts the detection sensitivity of the reflective sensor module 16. As shown in FIG. 4, when the UP (up) signal is input, the electronic volume 51 increases the output voltage by one step, and when the DN (down) signal is input, the electronic volume 51 decreases the output voltage by one step. In accordance with the photoelectric voltage obtained from the sensor 42, the electronic volume 51 is controlled to increase or decrease the output voltage stepwise. Thereby, the detection sensitivity of the sensor 42 can be finely adjusted.

  Next, a method for correcting the image forming position using the image forming apparatus will be described.

(Test pattern printing)
First, a test pattern for detecting the printing position deviation amount is printed.

  In the present embodiment, before the test pattern is printed, the background is printed with ink of a color complementary to the color of the ink for printing the test pattern. For example, when a pattern is formed with yellow ink, a light blue background is printed. With reference to the flowchart shown in FIG. 7, the processing routine of the base printing process executed by the control unit 46 will be described.

  In step 400, it is determined whether or not print data for printing a test pattern is input. When the print data is input, in step 402, it is determined whether or not to print with yellow ink based on the print data. To do. If it is determined to print with yellow ink, in step 404, the cyan head 12C is driven to print a light blue background. In step 406, a test pattern is printed on the printed light blue background. On the other hand, if it is determined not to print with yellow ink, in step 408, a necessary pattern is driven based on the print data to print a test pattern.

  Different test patterns are printed depending on the items to be detected. Items to be detected include, for example, the mounting inclination (tilt angle) of each color head, the amount of deviation between colors in the carriage scan direction and the paper transport direction, and the amount of deviation in the carriage scan direction during reciprocal printing with the same head. .

  In the present embodiment, a test pattern for detecting a shift amount in the carriage scan direction will be described with reference to FIGS. 5 and 6. This test pattern is configured as a set of five patches (A) to (E) each having a predetermined pattern. Each of the five patches (A) to (E) is composed of a plurality of lines having a width corresponding to two pitches in the carriage scan direction. The patches (A) to (E) are arranged at a predetermined interval along the carriage scan direction.

  Each patch is composed of a first line formed by the first head and a second line formed by the second head. Between each pattern, printing is performed such that the relative positional relationship of the second line with respect to the first line is sequentially shifted by one pitch in the carriage scan direction on the print data. The pattern is formed so that the brightness value of each dot to be printed is constant.

  For example, the test pattern includes a sparse pattern and a dense pattern. When both patterns are printed, after the coarse pattern is detected coarsely, the fine pattern is detected finely. In the case of a sparse pattern, 1 pitch is 4 dots (about 32 μm), and in the case of a dense pattern, 1 pitch is 1 dot.

  In this example, each patch is composed of a black line formed by the black head 12K and a yellow line formed by the yellow head 12Y, and is printed on a light blue ground.

  FIG. 5 shows a print example of the test pattern when the relative positional relationship between the two heads is normal. In this case, in the patch (A), a pattern is formed on the basis of print data in which the black line and the yellow line are exactly overlapped. In patches (B), (C), (D), and (E), the relative positional relationship of the yellow line with respect to the black line is sequentially shifted to the right by one pitch from the position of the patch (A) on the print data. A pattern is formed based on the data.

  Here, in the patch (C), the yellow line has just entered between the black lines, and the background (blue background) cannot be seen. In the patch (B) and the patch (D), the black line and the yellow line are overlapped by one pitch, and the background can be seen by one pitch. Further, in the patch (A) and the patch (E), the black line and the yellow line are just overlapping each other, and the background can be seen by two pitches.

  Accordingly, when the relative positional relationship between the black head 12K and the yellow head 12Y is normal, the density at the patch (C) is the highest in the test pattern.

  On the other hand, FIG. 6 shows a print example of a test pattern when the position of the yellow head 12Y is shifted in the carriage scan direction (right side in the figure) with respect to the black head 12K. In this case, in the patch (A), the black line and the yellow line should overlap on the print data, but the yellow line is shifted to the right by one pitch due to the relative displacement of the yellow head 12Y and printed. ing. In the patches (B), (C), (D), and (E), a pattern that is sequentially shifted to the right by one pitch from the pattern of the patch (A) is formed.

  Therefore, in this case, the state in which the yellow line has just entered between the black lines, that is, the pattern in which the background cannot be seen is the pattern of the patch (B), and the density of the pattern in the patch (B) is the darkest.

  As described above, when the position of the yellow head 12Y is shifted in the carriage scan direction, the position of the patch having the highest density is shifted. Accordingly, if one of the patches (A) to (E) having the darkest density (density distribution) is detected, it is possible to detect the amount of deviation of the print position in the carriage scan direction. The detected deviation amount is fed back to correct the print timing and print data.

  The reflection type sensor module 16 detects the amount of reflected light from each patch. As the patch density increases, the reflectance of the patch with respect to the irradiation light decreases. Therefore, it is only necessary to detect the position of the patch having the lowest reflectance. Here, if the difference in reflectance between the background and the print portion is small, the difference in reflectance between patches becomes small, and the patch with the lowest reflectance, that is, the patch with the highest density cannot be identified.

  In general, when the test pattern is printed in yellow on white paper, there is a problem that there is no density difference between patches. In the present embodiment, since the yellow test pattern is printed after the light blue background is printed, the reflectance of the background portion is improved, and in the same manner as when the blue filter is passed, The relative reflectance of the liquid crystal decreases relatively (the density increases). Accordingly, the difference in reflectance between the base portion and the print portion becomes large, and the density difference between patches becomes clear. Thereby, the position of the patch with the highest density is detected with high accuracy.

  In the above, an example of printing a test pattern with yellow ink after printing a light blue background has been described. However, when printing a pattern with magenta ink, a light green background is printed and a pattern is printed with cyan ink. When printing, print a light red background. Further, instead of printing a light blue background, a light blue recording paper may be used.

(Sensor sensitivity adjustment)
The detection sensitivity of the reflective sensor module 16 is usually different for each color of CMY. Therefore, it is preferable to perform sensitivity adjustment processing so that the sensor 42 can obtain a desired sensitivity after the test pattern is printed. A processing routine of sensitivity adjustment processing executed by the control unit 46 will be described with reference to a flowchart shown in FIG.

  That is, in step 100, it is determined whether or not a test pattern has been printed. If it is determined that the test pattern has been printed, the LED light source 40 of the reflective sensor module 16 is turned on in step 102, and in step 104, A detection signal from the sensor 42 is acquired. The photoelectric voltage (the amount of received light) from the sensor 42 is converted into a digital signal by an A / D converter (not shown) and taken into the control unit 46.

  Next, in step 106, the electronic volume 51 is adjusted based on the acquired detection signal. For example, UP / DOWN may be automatically determined and instructed according to the magnitude of the photoelectric voltage, or the operator may operate the input unit 50 to instruct UP / DOWN. In this embodiment, starting from 0 step, the output voltage of the electronic volume is increased step by step.

  Next, in step 108, the detection signal from the sensor 42 is acquired again, and it is determined whether or not the light amount of the sensor 42 has reached the target value. This target value is set in advance so as to obtain a desired detection sensitivity. If the light amount of the sensor 42 has reached the target value, in step 110, the voltage value is stored in the storage unit 48 as a light amount adjustment value (calibration value), and the routine is terminated. If the light quantity of the sensor 42 has not reached the target value, the process returns to step 106, the electronic volume 51 is adjusted again, and this process is repeated until the light quantity reaches the target value.

  By the sensitivity adjustment process described above, the detection process described later can be performed with uniform sensitivity regardless of the color on which the test pattern is formed.

(Acquisition of correction information)
Using the test pattern described above, the reflective sensor module 16 detects the position of the darkest pattern, obtains information on the printing position deviation, and stores this information as correction information. The detection processing routine executed by the control unit 46 will be described with reference to the flowchart shown in FIG.

  When the LED light source 40 is turned on in step 200, the printed test pattern is irradiated with light. In step 202, the light amount adjustment value of the sensor 42 is read from the storage unit 48 and set in the electronic volume 51. When the sensor 42 is driven in step 204, reflected light from each patch of the test pattern is received by the sensor 42. In the sensor 42, the received light is photoelectrically converted in accordance with the received light intensity and fed back to the control unit 46. Therefore, in step 206, the control unit 46 receives the photoelectrically converted signal.

  Here, since the voltage value that is photoelectrically converted and output from the sensor 42 is proportional to the intensity of the reflected light, the voltage value of the photoelectric conversion signal based on the reflected light from the patch having a low reflectance becomes low. Therefore, in order to extract a patch having a low reflectance, the received signal (voltage value) is sequentially stored in the storage unit 48 in step 208. The received signal is stored for each pattern, but pattern breaks are determined between patches when irradiation is transferred from one patch to the next when the voltage value during background irradiation continues for a certain time or longer. It is judged that the background is irradiated.

  In step 210, it is determined whether or not the storage of voltage values has been completed for all patches (A) to (E). If it is determined that the process has not ended, the process returns to step 200 and the above process is repeated. If it is determined that the processing has been completed, in step 212, the position of the patch having the lowest voltage value is detected from (A) to (E) based on the stored voltage value.

  Based on the detected position information, the amount of deviation of the print position of the head 12 used for printing the test pattern is determined. Thus, based on the detected position information, in step 214, the print timing of the head 12 used for printing the test pattern, correction information for correcting the print data is generated, and the generated correction information is stored in the storage unit 48. Store and end the routine.

(Image position correction)
Based on the correction information obtained as described above, the image forming process shown in FIG. 10 is performed. In step 300, information such as print data and print timing is corrected based on the correction information stored in the storage unit 48. In step 302, based on the corrected print data, print timing, transport distance, and the like, scanning by the carriage 14 and transport by the transport belt 19 are performed, an image is formed on the recording paper 34, and this processing ends.

  Actually, after printing the test pattern (see FIGS. 5 and 6) composed of the yellow line and the black line, the LED light source 40 of the reflective sensor module 16 is turned on to irradiate the test pattern and record it. When the reflected light from the paper 34 was read and the relative reflectance difference between the patterns was measured, it was possible to detect the pattern with the smallest reflectance.

  Further, the position information of this pattern is fed back to the print data to correct the print position, and when printing is performed, even if the relative position between the two heads is mounted with a slight shift, the head on the actual print pattern An image defect due to the positional deviation did not occur, and a good image could be obtained.

  As described above, according to the present embodiment, the background is printed with ink of a color complementary to the color of the ink that prints the test pattern, and the test pattern is printed thereon. The reflectance is improved, and the reflectance at the printed portion is relatively lowered. Therefore, the difference in reflectance between the base portion and the printed portion becomes large, and the density difference between patterns becomes clear. Accordingly, the position of the pattern having the highest density can be detected with high accuracy regardless of the color forming the test pattern.

  In addition, since a white LED is used, there is no need to perform complicated control such as switching the color of light emitted according to the color on which the test pattern is formed, and the difference in reflectance can be reduced at a low cost with a simple configuration. Can be detected. That is, the sensor module can be reduced in size and cost, and complicated control is not required, and the reliability of the sensor module is improved.

  Also, since the print timing of the head used for printing the test pattern and the correction information for correcting the print data are generated and stored based on the detected deviation amount, printing is performed based on this correction information. As a result, it is possible to form a good image with corrected printing deviation.

  In addition, since the test pattern is automatically read by the reflective sensor module, correction information is automatically stored, and feedback is performed during image formation, so that the print position deviation can be easily corrected without bothering the user. be able to.

  Also, print position shifts caused by hardware, such as head mounting position shifts, are eliminated by software by correcting the print timing and print data. The image forming apparatus can be manufactured at low cost.

(Modification)
In the above-described embodiment, the method of detecting and correcting the relative displacement between the black head 12K and the yellow head 12Y has been described. However, the black head 12K, the yellow head 12Y, the cyan head 12C, and magenta are described. A test pattern can be formed by a combination of any two of the heads 12M, and a relative positional deviation amount between the two heads can be detected and corrected in the same manner.

  In the above embodiment, the deviation amount in the carriage scanning direction is detected and corrected. However, as shown in FIG. 13, the deviation amount in the carriage scanning direction is used as a test pattern as shown in FIG. A test pattern formed by rotating the test pattern 90 degrees is detected, and the amount of deviation is detected in the same manner as described above, and the deviation in printing in the paper conveyance direction is corrected by correcting the paper conveyance amount and the like. can do. In addition, as shown in FIG. 14, with respect to the mounting inclination (tilt angle) of each color head, a test pattern in which the crossing angle of the yellow line with respect to the black line gradually increases and decreases is detected in the same manner as described above. can do.

  Further, the test pattern formed for detecting the shift amount is not limited to the above, but the line width, the interval between the lines, the length of the line, the shift amount between the color patterns, the pattern to be formed. Regarding the number, etc., there are various items such as the item to be detected (which head displacement amount, the direction of displacement, etc.), any detected amount, the accuracy to be detected, and the ink bleeding on the paper when printed. An appropriate pattern can be determined in consideration of the factors, and correction can be performed using the determined pattern.

  Further, the test pattern is not limited to a line pattern formed by a plurality of lines, and various patterns can be used in which the amount of deviation of the head mounting position can be detected as a density difference, that is, a reflectance difference. .

  Further, in the above description, the example using the white LED that emits white light by the light emitted from the phosphor excited by the monochromatic light source has been described, but the light source that is the irradiation unit is each of red light, green light, and blue light. It can be set as the structure provided with three LED elements which radiate | emit independently. With this configuration, it is possible to emit light by switching the peak wavelengths corresponding to at least two of red, green, and blue according to the application. In addition, as a light source, a white LED in which three types of LED chips each emitting red light, green light and blue light are housed in one package, and LED elements of independent red light, green light and blue light are combined. Can be used.

1 is a schematic sectional view of an image forming apparatus of the present invention. It is a schematic sectional drawing of a reflection type sensor module. FIG. 2 is a schematic block configuration diagram of a portion related to a reflective sensor module and a head of the image forming apparatus. It is a figure explaining operation | movement of an electronic volume. It is an example of the test pattern which detects the deviation | shift amount between the printing printed with the head of two colors of a carriage scanning direction. It is another example of the test pattern which detects the deviation | shift amount between the printing printed with the head of two colors of a carriage scanning direction. It is a flowchart which shows the routine of the base printing process which prints a base before printing of a test pattern. It is a flowchart which shows the routine of the sensitivity adjustment process which adjusts the sensitivity of a reflection type sensor module. It is a flowchart which shows the detection process routine which detects the position of a pattern with a high density. It is a flowchart which shows the procedure of the image formation process which forms an image based on correction information. It is a graph which shows the light emission characteristic of white LED, and the spectral reflectance characteristic of a cyan / magenta / yellow / black pattern. It is a graph which shows the reflective characteristic of a blank paper, and the spectral reflectance characteristic of a yellow pattern. It is an example of a test pattern for detecting a deviation amount in the paper transport direction. It is another example of the test pattern which detects a tilt angle.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Image forming apparatus 12 Inkjet head 14 Carriage 16 Reflection type sensor module 40 LED light source 42 Sensor 46 Control part 48 Storage part

Claims (12)

A plurality of recording heads for recording an image on a recording medium with different color materials, and a color complementary to the first color material having a low reflectance with respect to the ground color of the recording medium. Recording using a second color material to record a plurality of pattern images in which the density changes in accordance with the positional deviation of the recording head using the first color material after forming a base on the recording medium. Means,
Irradiation means for irradiating each of the plurality of pattern images with light having a peak in a wavelength range where the difference between the reflectance of the first color material and the reflectance of the recording medium is large;
Detecting means for detecting the amount of reflected light from each of the plurality of pattern images;
Correction means for correcting the image forming position of the recording head on which the pattern image is recorded, based on the amount of light detected by the detection means;
An image forming apparatus. A plurality of recording heads for recording an image on a recording medium with different color materials are used, and a color material that is a complementary color to the ground color of the recording medium is used to respond to a positional deviation of the recording head. Recording means for recording a plurality of pattern images whose densities change,
Irradiation means for irradiating each of the plurality of pattern images with light having a peak in a wavelength range where the difference between the reflectance of the color material and the reflectance of the recording medium is large;
Detecting means for detecting the amount of reflected light from each of the plurality of pattern images;
Correction means for correcting the image forming position of the recording head on which the pattern image is recorded, based on the amount of light detected by the detection means;
An image forming apparatus.   The image forming apparatus according to claim 1, wherein the recording unit includes four types of recording heads that record images on a recording medium using color materials of cyan, magenta, yellow, and black, respectively.   The image forming apparatus according to claim 3, wherein the pattern image includes one color selected from cyan, magenta, and yellow and black.   The image forming apparatus according to claim 1, wherein the irradiating unit irradiates light having peaks in at least two wavelength ranges of red light, green light, and blue light.   The image forming apparatus according to claim 1, wherein the irradiating unit irradiates light obtained by mixing light from a monochromatic light source and light emitted from a phosphor excited by the monochromatic light source.   The image forming apparatus according to claim 1, wherein the irradiation unit includes a white light emitting diode (LED).   The image forming apparatus according to claim 1, wherein the irradiation unit includes three light emitting elements that independently irradiate red light, green light, and blue light.   The image forming apparatus according to claim 1, further comprising a sensitivity adjustment unit that adjusts a detection sensitivity of the detection unit.   The image forming apparatus according to claim 9, wherein the sensitivity adjusting unit includes an electronic volume. A plurality of recording heads each recording an image on a recording medium with a different color material, a second color that is complementary to the first color material having a small density difference with respect to the ground color of the recording medium. After forming a background on the recording medium using the color material, the first color material is used to record a plurality of pattern images whose density changes according to the positional deviation of the recording head,
By irradiating each of the plurality of pattern images with light having a peak in a wavelength range where the difference between the reflectance of the first color material and the reflectance of the recording medium is large, from each of the plurality of pattern images Detect the amount of reflected light of
Correcting the image forming position of the recording head on which the pattern image is recorded, based on the detected light amount;
Image forming position correction method. A plurality of recording heads each recording an image on a recording medium with a different color material, and using a color material of a color complementary to the ground color of the recording medium, the density according to the positional deviation of the recording head Records multiple pattern images with varying
Reflecting light from each of the plurality of pattern images by irradiating each of the plurality of pattern images with light having a peak in a wavelength region where the difference between the reflectance of the color material and the reflectance of the recording medium is large. Detect the amount of light,
Correcting the image forming position of the recording head on which the pattern image is recorded, based on the amount of light detected by the detecting means;
Image forming position correction method.

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