JP2018047594A - Relative position detection method of recording head and image formation apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a relative position detection method of a recording head which can more properly and flexibly detect the relative position of a recording head, and provide an image formation apparatus.SOLUTION: A detection method of the relative position between recording heads in an image formation apparatus which has the plurality of recording heads arrayed with a plurality of recording elements, in which the adjacent recording heads partially overlap each other in the width direction range out of the array ranges of the recording elements, and which records an image on a recording medium relatively-moving in the direction orthogonal to the width direction with respect to the recording head includes: a step of recording a test image containing a reference line recorded by a prescribed recording element in the overlapping part of one recording head and a comparison line recorded by a prescribed number of recording elements relevant to the overlapping part of the other recording head; a step of calculating a first index indicating the degree of deviation between the reference line and the comparison line and a second index different from the first index respectively from the test image; and a step of identifying the relative position between the recording heads on the basis of the relationship between the first index and the second index.SELECTED DRAWING: Figure 7

Description

  The present invention relates to a recording head relative position detection method and an image forming apparatus.

  There is an ink jet image forming apparatus that forms an image by ejecting ink from a plurality of nozzles and landing on a recording medium in an appropriate pattern. In this image forming apparatus, the number of nozzles increases as the formed image becomes more accurate and faster. In particular, the nozzles are arranged over the entire recording width of the recording medium in the width direction perpendicular to the predetermined conveying direction of the recording medium, and only the recording medium is moved without moving the nozzle position. A line head type image forming apparatus that performs image formation at high speed by switching the presence or absence of ink ejection is known.

  As this line head type image forming apparatus, a configuration is widely used that covers the entire recording width by arranging recording heads in which a plurality of nozzles are arrayed in different positions in the width direction. In this case, if there is a deviation in the relative arrangement of the recording heads, there is a problem that stripes of density unevenness and image quality deterioration occur at the joints of the plurality of recording heads. Therefore, conventionally, a technique is known in which ink is ejected from nozzles near the joints of a plurality of recording heads, a relative position is detected by a sensor, and nozzles that eject ink are adjusted (Patent Document 1).

JP 2005-53167 A

  However, in the conventional technology, when there is a defect or variation in the nozzle itself at the joint portion of the recording head, and the desired test image is not formed at an accurate position, the relative position can be detected appropriately in a flexible manner. There is a problem that it cannot be done.

  An object of the present invention is to provide a recording head relative position detection method and an image forming apparatus capable of detecting the relative position of the recording head more appropriately and flexibly.

In order to achieve the above object, the invention according to claim 1
There are a plurality of recording heads in which a plurality of recording elements that perform operations related to image recording are arranged, and a range in a predetermined width direction in the arrangement range of the plurality of recording elements in the plurality of recording heads is in the width direction. An image recording unit provided with the plurality of recording heads so as to partially overlap between adjacent recording heads is provided, and the plurality of recording heads and the recording medium are relatively moved in a relative movement direction orthogonal to the width direction. A recording head relative position detection method for detecting a relative position of the plurality of recording heads in an image forming apparatus that moves and records an image on the recording medium,
A reference line recorded by the predetermined recording element in the overlapping portion of one recording head related to the overlapping portion and extending in the relative movement direction, and the reference line and the width direction in the overlapping portion of the other recording head A test image recording step for recording a test image including the predetermined number of comparison lines recorded by the predetermined number of the recording elements within a range in which the positions of the recording elements can coincide with each other and extending in the relative movement direction;
A first deviation degree for calculating a first index indicating the degree of deviation in the width direction between the reference line and the predetermined number of comparison lines for the predetermined number of comparison lines from the recorded test image. Calculation step,
A second deviation degree calculating step of calculating a second index indicating the degree of deviation in a method different from the first index for at least a part of the predetermined number of comparison lines;
A relative position identifying step for identifying a relative position in the width direction between the one recording head and the other recording head based on a relationship between the first index and the second index;
It is characterized by including.

According to a second aspect of the present invention, in the method for detecting the relative position of the recording head according to the first aspect,
Including an imaging step of imaging the recorded test image;
The calculation of the first index and the calculation of the second index are performed using data of the captured test image.

According to a third aspect of the present invention, in the method for detecting the relative position of the recording head according to the second aspect,
The test image is captured as a multi-valued image having a density gradation of 3 or more,
The degree of deviation is obtained based on a luminance distribution in the width direction.

According to a fourth aspect of the present invention, in the method for detecting the relative position of the recording head according to the third aspect,
At least one of the first index and the second index is a predetermined calculated value based on a luminance distribution in the width direction within a first range that includes the reference line and does not include the comparison line, and The width direction is the same as the first range, and is indicated by a difference from the predetermined calculation value in a second range including a single comparison line.

According to a fifth aspect of the present invention, in the method for detecting the relative position of the recording head according to the fourth aspect,
The predetermined calculated value is a value indicating a shift of the center of gravity position of the luminance distribution.

According to a sixth aspect of the present invention, in the method for detecting a relative position of a recording head according to any one of the third to fifth aspects,
At least one of the first index and the second index includes a luminance distribution in the width direction within a first range that includes the reference line and does not include the comparison line, and the first index in the width direction. And a predetermined similarity with the luminance distribution in a second range that is the same range as the first range and includes one comparison line.

According to a seventh aspect of the present invention, there is provided the recording head relative position detecting method according to the sixth aspect,
The predetermined similarity is a normalized cross-correlation.

The invention described in claim 8 is the recording head relative position detection method according to any one of claims 2 to 7,
In the imaging step, the test image is captured by an imaging sensor fixed in the width direction.

According to a ninth aspect of the present invention, in the method for detecting a relative position of a recording head according to any one of the first to eighth aspects,
In the relative position identification step, a regression equation indicating a relationship between the first index and the second index is obtained, and the relative position is identified based on the regression expression.

According to a tenth aspect of the present invention, in the method for detecting the relative position of the recording head according to any one of the first to eighth aspects,
At least one of the first deviation degree calculating step and the second deviation degree calculating step identifies a corresponding change range in which the degree of deviation changes according to the position of the recording element corresponding to the comparison line,
In the relative position identifying step, a regression equation indicating a relationship between the first index and the second index in the corresponding change range is obtained, and the relative position is identified based on the regression equation. .

The invention according to claim 11 is the relative position detection method of the recording head according to any one of claims 1 to 10,
In the relative position identification step, a value of the other index different from the one index when the value of one of the first index and the second index is a value indicating a minimal deviation amount is set. Based on a regression equation that identifies and indicates the correspondence between the value of the other index and the position of the recording element according to the comparison line, the recording element corresponding to the value of the identified other index The relative position is identified from the position.

A twelfth aspect of the present invention is the recording head relative position detection method according to any one of the first to eleventh aspects,
In the test image recording step, the predetermined number of comparison lines are recorded at different positions in the relative movement direction, and at least a part of the reference line is at a position different from the predetermined number of comparison lines in the relative movement direction. It is characterized by being recorded.

The invention according to claim 13 is the method for detecting the relative position of the recording head according to claim 12,
In the test image recording step, the reference line is recorded over a range in which the predetermined number of comparison lines are recorded in the relative movement direction.

According to a fourteenth aspect of the present invention, in the method for detecting a relative position of a recording head according to any one of the first to thirteenth aspects,
In the test image recording step, a plurality of the reference lines are recorded by a plurality of the recording elements.

Further, the invention of claim 15 is
There are a plurality of recording heads in which a plurality of recording elements that perform operations related to image recording are arranged, and a range in a predetermined width direction in the arrangement range of the plurality of recording elements in the plurality of recording heads is in the width direction. An image recording section provided with the plurality of recording heads so as to partially overlap between adjacent recording heads;
A relative movement unit that relatively moves the plurality of recording heads and the recording medium in a relative movement direction orthogonal to the width direction;
A control unit;
With
The controller is
A reference line recorded by the predetermined recording element in the overlapping portion of one recording head related to the overlapping portion and extending in the relative movement direction, and the reference line and the width direction in the overlapping portion of the other recording head A test image including the predetermined number of comparison lines recorded by the predetermined number of the recording elements within a range in which the positions of the recording elements can be matched and extending in the relative movement direction;
From the recorded test image, a first index indicating a degree of deviation of the reference line and the predetermined number of comparison lines in the width direction is calculated for each of the predetermined number of comparison lines,
Calculating a second index indicating the degree of deviation in a method different from the first index for each of at least a part of the predetermined number of comparison lines;
An image forming apparatus comprising: identifying a relative position in the width direction between the one recording head and the other recording head based on a relationship between the first index and the second index. is there.

  According to the present invention, there is an effect that the relative position of the recording head can be detected more appropriately and flexibly in the image forming apparatus.

1 is an overall schematic diagram illustrating an inkjet recording apparatus that is an embodiment of an image forming apparatus of the present invention. It is a bottom view which shows the surface facing the conveyance surface of a head unit. It is a block diagram which shows the function structure of the inkjet recording device of this embodiment. FIG. 6 is a diagram for explaining a positional relationship between nozzle openings in two recording heads. It is a figure which shows the example of the test image used for specification of positional offset amount with the inkjet recording device of this embodiment. It is a figure which shows the example of a detection of the positional offset amount of the reference line obtained from the reading result of a test image, and a comparison line in the inkjet recording device of this embodiment. It is a figure which shows the correspondence of the calculated | required positional offset amount and the similarity degree of luminance distribution. It is a flowchart which shows the control procedure of the relative position specific process performed in the inkjet recording device of this embodiment. It is a figure which shows the modification which concerns on the detection of the positional offset amount from the reading result of a test image.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
FIG. 1 is an overall schematic view showing an inkjet recording apparatus 1 which is an embodiment of an image forming apparatus of the present invention.

  The ink jet recording apparatus 1 includes a transport unit 10 (relative movement unit), an image forming unit 20 (image recording unit), an image reading unit 30, a control unit 40, and the like.

  The conveyance unit 10 includes a drive roller 11 and a conveyance belt 12. The rotation of the drive roller 11 causes the outer peripheral surface of the conveyance belt 12 to be a conveyance surface and a predetermined conveyance direction (relative movement direction) with respect to the image forming unit 20. The recording medium P placed on the transport surface is moved in the transport direction.

  The image forming unit 20 performs a recording operation of recording an image by ejecting ink from nozzles and landing on the upper surface of the recording medium P. Here, the image forming unit 20 has four head units 21Y, 21M, 21C, and 21K (hereinafter collectively referred to as a head unit 21), and yellow, magenta, and magenta are supplied from an ink storage unit (not shown), respectively. Cyan and black ink are ejected. Each of these head units 21 is provided with nozzles over the recordable width of the maximum size recording medium P that can be transported by the transport unit 10 in the width direction perpendicular to the transport direction, so that ink can be ejected. It has become.

FIG. 2 is a bottom view showing a surface facing the transport surface of the head unit 21K.
Since the head units 21C, 21M, and 21Y have the same configuration as the head unit 21K, description thereof will be omitted.

  The head unit 21K is provided with eight (plural) recording heads 211a to 211h (collectively referred to as recording heads 211) in which a plurality of nozzle openings are arranged at predetermined intervals in the width direction on the bottom surface. These are arranged in a staggered pattern to form a line head in which nozzle openings are arranged at uniform intervals over the maximum width (recordable width) that can be recorded on the recording medium P in the width direction. doing. That is, the head unit 21 </ b> K is fixed during image formation, and sequentially ejects ink to different positions in the transport direction according to the transport of the recording medium P, thereby recording an image by a one-pass method.

  The recording heads 211 are arranged so that the arrangement ranges of the nozzle openings in the recording heads 211 that are adjacent in the width direction partially overlap each other. The relative positions of the recording heads 211 are detected and held, and the overlapping portions are selectively adjusted based on the information on the relative positions so that ink is ejected by the nozzles of one of the recording heads 211. This makes it possible to form a uniform image.

  The image reading unit 30 is provided downstream of the image forming unit 20 in the conveyance direction of the recording medium P, and picks up an image formed (recorded) on the recording surface of the recording medium P by the image forming unit 20. And output as imaging data. The image reading unit 30 includes a line sensor 32 (see FIG. 3; imaging sensor) in which imaging elements are arranged over the width that can be recorded by the head unit 21 in the width direction. The line sensor 32 is fixed with respect to the recording medium P to be transported, and the transport unit 10 moves the recording medium P relative to the image reading unit 30 in the transport direction, while the primary within the imaging target range in the width direction. By sequentially acquiring the original image data by the line sensor 32, a two-dimensional image on the recording medium P can be obtained. As the line sensor 32, for example, a CCD sensor (Charge Coupled Device), a CMOS sensor (Complementary Metal Oxide Semiconductor), or the like is used. Normally, the arrangement interval in the width direction of the image sensor is wider than the arrangement interval in the width direction of the nozzle openings in the recording head 211. That is, the imaging resolution of the line sensor 32 is lower than the recording resolution of the image forming unit 20.

  The control unit 40 performs overall control of the operation of each unit of the inkjet recording apparatus 1.

  FIG. 3 is a block diagram showing a functional configuration of the inkjet recording apparatus 1 of the present embodiment.

  In addition to the control unit 40, the conveyance unit 10, the image forming unit 20, and the image reading unit 30, the inkjet recording apparatus 1 includes a communication unit 50, a storage unit 60, an operation display unit 70, and a bus 80. Etc.

  The control unit 40 performs a control operation that comprehensively controls the overall operation of the inkjet recording apparatus 1. In addition, the control unit 40 performs adjustments related to ink ejection based on the test image formed (recorded) by the image forming unit 20 and read by the image reading unit 30, and adjusts the overall image quality and the nozzle openings. Inspect and deal with the ink ejection.

  The control unit 40 includes a CPU 41 (Central Processing Unit), a ROM 42 (Read Only Memory), a RAM 43 (Random Access Memory), and the like. The CPU 41 performs arithmetic processing and executes various processes related to operation control. The ROM 42 stores a control program related to operation control. As the ROM 42, a mask ROM, a readable / writable nonvolatile memory such as a flash memory, or a combination thereof is used.

  The RAM 43 provides a working memory space to the CPU 41 and stores temporary data and various settings. As the RAM 43, various volatile memories such as SRAM and DRAM are used.

  The transport unit 10 includes a transport motor 14 and an encoder 15. The transport motor 14 rotates at a predetermined speed based on a control signal from the control unit 40 and rotates the driving roller 11 to rotate the transport belt 12 in the transport direction. The encoder 15 measures the conveyance speed. As the encoder 15, a rotary encoder that measures the rotational speed of the driving roller 11 or the transport motor 14 as well as the one that directly measures the moving speed of the transport belt 12 can be used. The conveyance speed is fed back to the control unit 40 and used for adjusting the set speed, or used for calculating the moving distance from a predetermined timing, and used for adjusting the ink discharge position on the recording medium P. Or

  The image forming unit 20 includes a head drive unit 22 and a correction unit 23. The head drive unit 22 outputs a drive signal for operating the ink discharge mechanism in the recording head 211 of each head unit 21, and discharges ink from the opening of the operation target nozzle at an appropriate timing. These drive signals are output in parallel to each head unit 21 (recording head 211). The drive signal is output in synchronization with the encoder 15 that measures the conveyance speed (position) of the recording medium P by the conveyance unit 10. As an ink discharge mechanism, for example, a voltage is applied to a piezoelectric element provided along an ink flow path communicating with a nozzle to deform the piezoelectric element, and pressure is applied to the ink in the ink flow path with a predetermined pressure pattern. In addition, a piezo type that ejects ink, or heat is generated by flowing current through a heating wire, and the ink in the ink flow path is heated and partly vaporized, causing a volume change and ejecting by applying pressure to the ink. A thermal type is used. Each nozzle, an individual ink flow path communicating with the nozzle, and an ink ejection mechanism corresponding to each combination of the nozzle and the ink flow path constitute a recording element.

  The correction unit 23 performs a setting operation related to the adjustment adjustment of the drive nozzles based on the head relative position information 61 related to the positional relationship of the overlapping portions of the nozzle opening array ranges in the recording heads 211 adjacent in the width direction.

  The image reading unit 30 includes an imaging drive unit 31 and a line sensor 32. The imaging drive unit 31 operates each image sensor of the line sensor 32 and detects the amount of incident light detected by the image sensor at a predetermined sampling rate, that is, reflected light in the reading range of the surface of the recording medium P by each image sensor. Imaging data (multi-valued image data) is generated from a luminance value represented by a predetermined density gradation (for example, multiple gradations such as 256 gradations), and is output to the control unit 40 (RAM 43) or the storage unit 60. Perform the action. The imaging data may be directly output to the RAM 43 or the storage unit 60 by DMA (Direct Memory Access) without being controlled by the CPU 41. Further, a predetermined calibration operation may be performed at the time of conversion from incident light amount data to imaging data. The line sensor 32 is arranged with wavelength filters and / or image sensors that can detect the luminance of each wavelength band of RGB. Further, the image reading unit 30 may include an illumination unit that irradiates the surface of the recording medium P with a predetermined amount of light.

  The communication unit 50 acquires image formation data and a print job from an external computer terminal or a print server according to a predetermined communication protocol, and outputs a status signal related to image formation.

  The storage unit 60 stores image formation data acquired through the communication unit 50 and processing data thereof. In addition, the storage unit 60 stores and holds positional relationship information relating to overlapping portions of the nozzle openings of the recording head 211 as head relative position information 61. The storage unit 60 may store various execution programs related to image formation, and the CPU 41 reads out and loads the execution program into the RAM 43 when the execution program is executed. As the storage unit 60, for example, an HDD (Hard Disk Drive) or a flash memory and a RAM (DRAM) are used in combination.

  The operation display unit 70 displays a user input operation acceptance screen and status information as the display unit 71, and accepts a user input operation as the operation acceptance unit 72 and outputs an operation signal to the control unit 40. The operation display unit 70 is provided with, for example, a touch sensor and a liquid crystal screen overlapped with each other, and includes these drivers. Alternatively, a display screen according to another display method such as an organic EL display may be used for display, or an LED lamp for status display may be used in combination. In addition, a push button switch, a rotation switch, or the like may be provided for accepting the operation instead of or in addition to the touch panel.

  The bus 80 is a path for transmitting and receiving signals between the control unit 40 and other components.

  Next, a relative position detection operation between a plurality of recording heads 211 according to an embodiment of the recording head relative position detection method of the present invention will be described.

As described above, in the head unit 21, the plurality of recording heads 211 are provided such that the arrangement range of the nozzle openings in the recording heads 211 adjacent to each other in the width direction partially overlaps in the width direction.
FIG. 4 is a diagram for explaining the positional relationship between the nozzle openings in the two recording heads 211. Here, the overlapping portions in the width direction of the recording heads 211a and 211b are shown, but the same applies to other overlapping portions.

  Here, the two recording heads 211a and 211b related to the overlapped portion are provided with Na nozzle openings arranged one-dimensionally in the width direction in units of Na. When the recording heads 211a and 211b are accurately attached to the standard position of the head unit 21, as shown in FIG. 4A, the array ranges of 128 nozzle openings overlap each other in the width direction. , K = 1 to 128, the “Na− (128−k)” th nozzle opening A (Na− (128−k)) of the recording head 211a and the “k” th nozzle opening B of the recording head 211b. (K) has the same position in the width direction. That is, the position of the “Na-127” -th nozzle opening A (Na-127) of the recording head 211a coincides with the first nozzle opening B (1) of the recording head 211b in the width direction, and the recording head 211a. The position of the Na th nozzle opening A (Na) coincides with the 128 th nozzle opening B (128) of the recording head 211b in the width direction.

  On the other hand, as shown in FIG. 4B, when at least one of the recording heads 211a and 211b is mounted shifted from the standard position, the arrangement range of the overlapping nozzle openings in the width direction increases or decreases (here D), and the correspondence relationship between the nozzle openings whose positions match in the width direction is different from that in FIG.

  For example, when a relative positional deviation within ± 380 μm is allowed between the recording head 211a and the recording head 211b when the head unit 21 is assembled, a nozzle arrangement of 1200 dpi (dots per inch) causes a deviation of less than ± 18 nozzles. Can occur. Accordingly, in the inkjet recording apparatus 1, an operation for detecting a positional deviation amount within the allowable relative positional deviation range is performed in advance, and an ink ejection operation is corrected in accordance with the detected positional deviation amount to perform a recording target. Ink can be ejected at a correct position according to image data.

FIG. 5 is a diagram illustrating an example of a test image used for specifying the positional deviation amount in the inkjet recording apparatus 1 of the present embodiment.
In the inkjet recording apparatus 1, as shown in FIG. 5A, as a test image, one of the adjacent recording heads 211 related to the overlapping portion (here, the recording head 211 a) corresponds to the allowable positional deviation amount. A plurality of reference nozzles are determined at a predetermined interval (here, an interval of 36 nozzles) (for example, each nozzle having the number “Na− (j−1) × 36”, j = 1 to 4), and the conveyance direction is determined by the reference nozzle. The reference lines L1 to L4 extending in the horizontal direction are recorded, and the other (here, the recording head 211b) causes ink landing by a plurality of nozzles (positions that can coincide with the reference nozzles (that is, the reference lines L1 to L4) in the width direction). Line segments of equal width and equal length are sequentially recorded as comparison lines at different positions in the transport direction depending on the position). Here, 37 (predetermined) comparison lines C101 to C137 are recorded with respect to the reference line L1. Similarly, 37 comparison lines are recorded for each of the reference lines L2 to L4. The comparison line C137 for the reference line L1 and the comparison line C201 for the reference line L2 are recorded by the same nozzle in the recording head 211b. That is, the range of the recording head 211b in which the positions of the four reference nozzles can coincide with each other in the width direction is the nozzle opening B (Na) = 1 + 36 × (j−1) to 37 + 36 for j = 1 to 4, respectively. It is the range of the position of x (j-1).

  At this time, the lengths of the reference lines L1 to L4 are determined to be longer than the range in which the corresponding 37 comparison lines are provided. Here, the reference lines L1 to L4 are included in the range in which only the reference lines L1 to L4 are recorded at both ends in the transport direction. Is recorded. That is, the reference lines L1 to L4 are recorded over a range in which 37 comparison lines are recorded in the transport direction, and a part of the reference lines L1 to L4 is recorded at different positions in the transport direction. .

  The test image is read by the image reading unit 30 and the amount of misalignment is identified using the data of the read (taken) test image. Here, first, any one of the reference lines L1 to L4 is included at the approximate center in the width direction, and one comparison line Ck (k = 101 to 137, 201 to 237, 301 to 337, 401) is included in the transport direction. ˜437, each area E (k) (second range) including at least a part, for example, a range of ± 5 to 10 around k = 119, 219, 319, 419, is set. The center-of-gravity position v (G (E (k))) in the width direction of the luminance value L distribution (luminance distribution) (that is, the ink density distribution) in the area is obtained. In each area, the luminance changes in the range of the reference line and the range of the comparison line with respect to the luminance of the background color. Therefore, the center of gravity position v (G (E (k))) depends on the position of the comparison line Ck. It is obtained by deviating from the position of the center of gravity of the reference line. Since the reference centroid positions v (G1) to v (G4) of only the reference lines L1 to L4 are obtained for each reference line from the reference areas F1 to F8 (first range) at both ends in the transport direction, If the two reference centroid positions are equal, only the reference areas F1 to F4 can be used, and the centroid position v (G (E (k)) of the luminance distribution in each area E (k) related to the comparison line C (k). ) Is a first index (predetermined calculated value based on luminance distribution, centroid position) where the deviation dv (k) = v ((G (E (k))) − v (Gj)) In the case where there is a slight deviation between the two reference centroid positions due to the inclination of the recording medium P, etc., the comparison line C (k) to be compared is in accordance with the position in the transport direction. Reference weight for comparison line C (k) by weighted average of both If there is a large deviation in .2 one reference centroid position can be determined the position, because there is some problem, it is possible to stop subsequent processing.

In the example of FIG. 5A, the recording heads 211a and 211b are all provided at the standard positions, and therefore, the gravity center positions of the areas E (119), E (219), E (319), and E (419). v ((G (E (k))) coincides with the reference centroid positions v (G1), v (G2), v (G3), and v (G4), respectively, and the positional deviation amount dv (k) is “0”. It becomes.
On the other hand, in the example of FIG. 5B, the recording head 211b is displaced from the recording head 211a in the direction in which the overlapping range becomes narrower in the width direction. As a result, the areas E (115) and E (215) are arranged. ), E (315), and E (415) are centroid positions v ((G (E (k))) as reference centroid positions v (G1), v (G2), v (G3), and v (G4), respectively. Match.

FIG. 6 is a diagram illustrating a detection example of the amount of positional deviation between the reference line and the comparison line obtained from the test image reading result in the inkjet recording apparatus 1 of the present embodiment.
As shown in FIG. 6A, the last two digits of k indicating the comparison line Ck on the horizontal axis (k% 100 = 1 to 37; where “%” is an operation symbol for obtaining the remainder of division), that is, comparison A value indicating the relative distance between the line Ck (nozzle opening B of the nozzle that records the comparison line Ck) and the reference line Lj (nozzle opening A of the nozzle that records the reference line Lj) corresponding to the comparison line Ck; When the positional deviation amount dv (k) is plotted on the vertical axis, the positional deviation amount dv (k) gradually approaches “0” according to the position of the comparison line Ck with respect to the reference line Lj, and the positive and negative signs are further inverted to “0”. "Go away."

  As described above, when the nozzles for recording the comparison line C137 and the comparison line C201 are the same, the area size is set so that both are included in the area (area E (137), area E (201)). Then, since these comparison lines C137 and C201 are also included in the adjacent areas E101 and E237, the size in the width direction of the area can be set smaller than this. In this case, only the reference lines L1, L2, etc. are included in the area, and the positional deviation amount dv (k) is a value of about “0”. Therefore, in this case, the range in which the comparison line is not included in the area is excluded, and thereafter, the range in which the positional deviation amount dv (k) changes according to the position of the comparison line (corresponding change range), that is, Only the result within the width W in FIG. As the setting of the width W, for example, the position shift amount dv (k) is first set toward both sides from the position where the center position (k% 100 = 19 position) and the position shift amount dv (k) are closest to “0”. The position where the value becomes equal to or greater than a predetermined reference value can be set as both ends, or more simply, the position deviation amount dv (k) can be set within a predetermined number of ranges on both sides from the position closest to “0”.

  Here, if ink is accurately ejected from all nozzles and landed at the correct position, and the line sensor 32 accurately detects the luminance distribution with sufficient accuracy, a value and a position indicating the relative distance. The displacement amount dv (k) has a proportional relationship, and the nozzle openings corresponding to the value indicating the relative distance at which the displacement amount dv (k) is “0” are at the same position in the width direction. However, in reality, since all points do not lie on a complete straight line due to variations in nozzle operation, etc., a regression line dv (k) between the value indicating the relative distance and the positional deviation amount dv (k). = A1 × (k% 100) + b1 is found to include some errors.

  In the ink jet recording apparatus 1 of the present embodiment, the relationship between the parameter corresponding to the positional deviation amount and the relative position (value indicating the relative distance) is obtained in a manner different from the above method.

  Here, as shown in FIG. 6B, for the eight reference areas F1 to F8 in which only the reference lines L1 to L4 are recorded, the luminance distribution Ls (p) for each pixel of the line sensor 32 in the width direction. ) (P indicates the pixel position) (reference profile; template) is acquired. The luminance distribution in this case is not necessarily acquired for the entire width of the reference areas F1 to F8. Similarly, the luminance distributions Lr (q) (q is the pixel position) in the width direction in the areas E (101) to E (437) related to the comparison lines C101 to C437 are compared, and the corresponding reference profiles Ls (p ) (Predetermined similarity) is calculated as a second index indicating the degree of deviation.

The similarity is not particularly limited. For example, the matching value (ΣLs (p) · Lr (q)) related to the cross-correlation of the luminance distribution or the sum of squares of the deviation of the luminance value (Σ (Lr (p) ) −Ls (q)) ² ) or the sum of absolute values (Σ | Lr (p) −Ls (q) |) is used. At this time, the luminance value is further normalized (NCC; normalized cross-correlation). ) (Σ (Ls (p) · Lr (q)) / √ (ΣLs (p) ² · ΣLr (q) ² )), or a deviation from the luminance average value (ZNCC; zero average normalized cross-correlation) ) (Σ (Ls (p) −av (Ls)) · (Lr (q) −av (Lr)) / √ (Σ (Ls (p) −av (Ls)) ² · Σ (Lr (q) −) ^{av (Lr)) 2);} av (Ls), av (Lr) is, Ls (p), respectively, the average value of Lr (q)), or the correlation coefficient of the two distributions is used Rukoto in, it is possible to reduce the influence of luminance unevenness of ink density and lighting.

  As shown in FIG. 6C, when the similarity is plotted against the value indicating the relative distance, the similarity is maximized when the reference line and the comparison line completely overlap, that is, the degree of deviation. Is minimized. The similarity decreases (the degree of deviation increases) as the comparison line moves left and right from the reference line. Also in this case, as in the example shown in FIG. 6A, each point does not completely lie on the regression curve due to variations in nozzle characteristics.

FIG. 7 is a diagram illustrating a correspondence relationship between the obtained positional deviation amount dv (k) and the similarity NCC of the luminance distribution.
In the inkjet recording apparatus 1 of the present embodiment, as described above, the correlation between parameters indicating the degree of deviation obtained by two types of methods is obtained for the areas including the respective comparison lines C101 to C437. Here, this correlation is obtained by a regression equation of a quadratic curve according to the change characteristic of the similarity (NCC) (or ZNCC, the same applies hereinafter). These parameters change (decrease) in correlation with the characteristic values according to variations in nozzle characteristics, so that the influence on the regression line is smaller than when the parameters change with respect to the relative distance.

  The degree of likelihood obtained based on the correspondence relationship between the positional deviation amount dv (k) and the similarity NCC, here, the similarity NCC (one index) is the maximum (minimum (minimal) deviation amount ( In the case of a value) indicating the degree of deviation), the positional deviation amount dv (G) (the other index) is identified, and the relative position corresponding to this positional deviation amount dv (G) is identified. For specifying the relative position, a regression line (regression equation) indicating the relationship between the positional deviation amount dv (k) and the relative position shown in FIG.

FIG. 8 is a flowchart showing a control procedure by the control unit 40 of the relative position specifying process executed in the inkjet recording apparatus 1 of the present embodiment.
This relative position specifying process is started by a predetermined input operation to the operation receiving unit 72 at the time of inspection before product shipment, at the time of shipping assembly, or after replacement of the recording head 211 (head unit 21).

  The control unit 40 (CPU 41) operates the head driving unit 22 and the transport motor 14 to record the above-described test image on the recording medium P (step S101; test image recording step). In addition, the control unit 40 captures the test image recorded by the imaging drive unit 31 and acquires imaging data (step S102; imaging step).

  The control unit 40 identifies the eight end portions of the four reference lines L1 to L4 from the imaging data, and determines the reference areas F1 to F8 (step S103). At this time, the control unit 40 confirms whether or not the positions of the reference lines L1 to L4 are shifted in the vertical direction, that is, between the reference areas F1 to F4 and the reference areas F5 to F8. In some cases, correction (such as image rotation processing) may be performed. Further, the control unit 40 acquires the brightness profile in the width direction in the determined reference areas F1 to F8 as template data (step S104).

The control unit 40 calculates the center of gravity position in the width direction using the luminance value of each area in the imaging data (step S105). The control unit 40 sets a regression line between “k% 100” (or relative position; “dx = d × (k% 100))” where d is the relative position; Is calculated (step S106).
Steps S105 and S106 constitute a first deviation degree calculating step.

  Based on the calculated regression line, the control unit 40 selects an area in a range where the relationship between the center of gravity position and the relative position is on the regression line at a predetermined level or more (step S107). The above-mentioned NCC is calculated between the luminance profile of the area and the luminance profile of the template (step S108; second deviation degree calculating step).

The control unit 40 obtains a correspondence relationship between the positional deviation amount dv (dx) of the selected area and the NCC using a quadratic regression curve (step S109). Further, the control unit 40 identifies the optimized positional deviation amount dv (G) at the maximum position of the NCC in the obtained quadratic regression curve. The control unit 40 substitutes this optimized positional deviation amount dv (G) for dv (dx) in the regression line obtained in step S106, and the corresponding relative position dx (or relative nozzle position “k% 100”), Deviation from the standard position “k% 100-19” or the like, or as long as the relative position can be identified, the absolute position of the nozzle that ejects ink at a predetermined reference position may be calculated. (Step S110).
A relative position identification step is configured by the processing of steps S109 and S110.
The control unit 40 stores the relative position dx in the storage unit 60 as the head relative position information 61 and causes the display unit 71 to display (step S111). Then, the control unit 40 ends the relative position specifying process.

[Modification]
In the above-described embodiment, as the two types of parameters indicating the degree of deviation, the ZNCC and the like can be used in addition to the NCC as the positional deviation amount of the center of gravity and the NCC are used. Other values can be used. For example, in each of the areas E (101) to E (437), the positions of the reference line and the comparison line may be identified, and the distance may be calculated and used as the amount of displacement.

FIG. 9 is a diagram illustrating a modification example related to detection of the amount of misalignment from the test image reading result.
As described above, when the distance obtained by identifying the positions of the reference line and the comparison line (that is, the degree of deviation) is plotted against the relative position, each point is distributed in a straight line, so that a regression line is obtained. The relative distance can be statistically identified with the above, but it can be affected by variations in nozzle characteristics, as in the case where the center of gravity position is used alone. Therefore, by using the obtained distance in combination with another index such as the similarity of the luminance distribution described above, it is possible to detect a flexible relative positional relationship that can cope with nozzle ejection defects and the like with more appropriate accuracy. I can do it.

  In this case, in the output of the test image shown in FIG. 5, the distance cannot be specified in a range where the reference line and the comparison line cannot overlap and cannot be separated. Therefore, the data of these areas is used for determining the regression line. I can't. Therefore, the reference lines are not recorded in the same area as the comparison lines, but are recorded in separate areas in the same range in the width direction, that is, the reference lines L1 to L4 are recorded only in the areas F1 to F8. The distance can be obtained by identifying the position of each line.

As described above, in the recording head relative position detection method in the inkjet recording apparatus 1 of the present embodiment, the recording head 211 includes a plurality of recording heads 211 in which a plurality of recording elements that perform operations related to image recording are arranged. An image forming unit provided with a plurality of recording heads 211 such that a range in a predetermined width direction among a plurality of recording element arrangement ranges in 211 partially overlaps between the recording heads 211 adjacent in the width direction. 20 (head unit 21), and a plurality of recordings in the ink jet recording apparatus 1 that records images on the recording medium P by relatively moving the recording heads 211 and the recording medium P in the transport direction orthogonal to the width direction. This is a recording head relative position detection method for detecting the relative position of the head 211, in which the one recording head 211a associated with the overlapping portion is detected. Reference lines L1 to L4 recorded by the reference recording element in the overlapping portion and extending in the transport direction, and a predetermined number within a range in which the positions of the reference lines L1 to L4 and the width direction can coincide with each other in the overlapping portion of the other recording head 211b. Test image recording for recording a test image including 37 comparison lines (C101 to C137, C201 to C237, C301 to C337, C401 to C437) recorded by (37 each) recording elements and extending in the transport direction From the test images recorded in the step, the 37 comparison lines using the positional deviation amount dv (k) indicating the degree of deviation in the width direction between the reference lines L1 to L4 and each of the 37 comparison lines as a first index. The first deviation degree calculating step for calculating each of the luminance distribution similarity degree (here, the degree of deviation in a method different from the positional deviation amount dv (k)) NCC) is calculated for each of at least a part of the 37 comparison lines, based on the relationship between the positional deviation amount dv (k) and the similarity (NCC). A relative position identifying step of identifying a relative position in the width direction with respect to the other recording head 211b.
As a result, an error that is likely to occur due to the influence of nozzle ejection failure or the like can be reduced with only one index, and the relative position between the recording heads 211 can be detected more accurately and reliably by an easy method.

  In addition, an imaging step of capturing the recorded test image is included, and the calculation of the positional deviation amount dv (k) and the similarity such as NCC are performed using the captured image of the test image. By using the imaged data in this way, it is possible to easily perform arithmetic processing such as normalization and zero average related to the calculation of similarity.

  The test image is picked up by the line sensor 32 that detects the luminance as a multi-valued image having three or more density gradations, and the degree of deviation is obtained based on the luminance distribution in the width direction. Since processing based on the distribution is performed using the multi-valued image in this way, it becomes easier to identify the position more accurately than using the binary image, particularly when the resolution of the line sensor 32 is rough.

  Further, the positional deviation amount dv (k) which is one of the two indexes is a reference centroid position v based on the luminance distribution in the width direction in the reference areas F1 to F8 including the reference lines L1 to L4 and not including the comparison line. (G1) to v (G8) and an area E that is in the same range as the reference areas F1 to F8 in the width direction and includes one of the comparison lines C101 to C137, C201 to C237, C301 to C337, and C401 to C437. (101) to E (137), E (201) to E (237), E (301) to E (337), and the center of gravity position v (k% 100) in E (401) to E (437) Indicated by the difference.

  In addition, in this way, by obtaining a value indicating the deviation of the center of gravity position of the luminance distribution, it is possible to identify a statistically accurate relative position without specifying the position of the reference line or the comparison line itself, It becomes difficult to be influenced by the position identification error according to the resolution of the line sensor 32 or the like.

  In addition, one of the two indexes is the luminance distribution in the width direction of the reference areas F1 to F8 including the reference lines L1 to L4 and not including the comparison line, and the same range as the reference areas F1 to F8 in the width direction. In the areas E (101) to E (137), E (201) to E (237), E (301) to E (337), E (401) to E (437) including one of the comparison lines The predetermined similarity with the luminance distribution at. Thus, by using the luminance tendency at each pixel position of the line sensor 32, it is possible to obtain an accurate positional relationship between a plurality of recording heads by utilizing more information.

  The predetermined similarity is normalized cross-correlation (including zero-averaged), which reduces and eliminates the effects of density unevenness due to differences in ejection characteristics among multiple nozzles. It is possible to quantitatively compare the similarity between the reference profile and the luminance distribution including each comparison line.

  Further, in the imaging step, the test image is captured by the line sensor 32 fixed in the width direction, so that the processing can be performed easily and at high speed without considering the position change of the line sensor 32 and the like.

  Further, in the process of step S109 (relative position identification step) in the relative position specifying process, a regression equation indicating the relationship between the positional deviation amount dv (k) that is two indexes (parameters) and the similarity (NCC) is obtained. Based on this regression equation, the relative position corresponding to the optimum value of the degree of deviation is identified. These indicators are all parameters according to the deviation between the reference line and the comparison line, and the influence of nozzle discharge failure etc. affects each of them, so the deviation direction (variation) with respect to the regression line shown in the regression equation The influence between these two parameters can be estimated with higher accuracy.

  Further, at least one of the first deviation degree calculating step for obtaining the positional deviation amount dv (k) and the second deviation degree calculating step for obtaining the similarity of the luminance distribution depends on the position of the recording element corresponding to the comparison line. A corresponding change range in which the degree of deviation changes is identified, and a regression equation indicating the relationship between the positional deviation amount dv (k) and the luminance distribution in this corresponding change range is obtained. That is, when there is a range where the deviation between the comparison line and the reference line is large and the comparison line protrudes from the detection area and the deviation amount does not correspond to the index value, the processing is performed by excluding the range. When a plurality of reference lines L1 to L4 are provided, it is possible to easily set an image range related to the calculation of the index value and obtain an appropriate value with a simple process.

Further, in the process of step S109 in the relative position specifying process, the positional deviation amount dv (k) that is the other index when the similarity that is one of the two indices is maximal (the degree of deviation is minimal). In the process of step S110, the identified positional deviation amount dv based on the regression equation indicating the correspondence between the value of the positional deviation amount dv (k) and the position of the printing element corresponding to the comparison line. The relative position between the recording heads is identified from the position of the recording element corresponding to the value of (k).
In this way, the correspondence between the plural parameters is used in particular according to their accuracy, etc., so that the value corresponding to the relative position between the recording heads can be obtained more accurately, and the relative position of the recording head is identified based on this value. Therefore, the relative position of the recording head can be obtained more stably and accurately than in the past.

  In the test image recording step, the predetermined number of comparison lines are recorded at different positions in the transport direction, and at least a part of the reference line is recorded at different positions in the transport direction. As described above, the area in which only the reference line is provided and the area in which each comparison line is provided are separately arranged in the transport direction, so that the line sensor 32 sequentially reads each area and compares them accurately. Cheap.

  Further, in the test image recording step, since the reference lines L1 to L4 are recorded over a range in which a predetermined number of comparison lines are recorded in the transport direction, the reference lines and the comparison lines are simultaneously recorded in the area, Thereby, the shift | offset | difference of a reference line and a comparison line can be acquired from each luminance distribution easily and reliably.

  In the test image recording step, a plurality of reference lines L1 to L4 are recorded by a plurality of recording elements. In statistical processing, the accuracy can be improved by increasing the number of processing points, and even if there is a discharge failure in any of the nozzles, the same processing covers the discharge failure between the print heads 211. Since the relative position can be calculated, a more accurate relative position can be obtained without complicating the process.

In addition, the inkjet recording apparatus 1 of the present embodiment includes a plurality of recording heads 211 in which a plurality of recording elements that perform operations related to image recording are arranged, and a plurality of recording elements (nozzle openings) in the plurality of recording heads 211. An image forming unit 20 (head unit 21) provided with a plurality of recording heads 211 such that a range in the predetermined width direction in the arrangement range is partially overlapped between adjacent recording heads 211 in the width direction. , A transport unit 10 that relatively moves the plurality of recording heads 211 and the recording medium P in the transport direction orthogonal to the width direction, and a control unit 40. The control unit 40 includes one recording head 211a related to the overlapping portion. The reference lines L1 to L4 that are recorded by a predetermined recording element in the overlapping portion and extend in the transport direction, and the reference line in the overlapping portion of the other recording head 211b 1 to L4 and a predetermined number of comparison lines C101 to C137, C201 to C237, and C301 to C337 that are recorded by a predetermined number (37 each) of recording elements within a range in which positions in the width direction can coincide with each other and extend in the transport direction. , C401 to C437 are recorded, and from this recorded test image, the widths of the reference lines L1 to L4 and a predetermined number of comparison lines C101 to C137, C201 to C237, C301 to C337, C401 to C437 A positional deviation amount dv (k) as a first index indicating the degree of deviation in the direction is calculated for each of a predetermined number of comparison lines, and the degree of deviation is indicated by a method different from the positional deviation amount dv (k). Similarity with the luminance distribution of the reference line as the index of 2 is calculated for at least a part of the predetermined number of comparison lines, and the relationship between the positional deviation amount dv (k) and the similarity is calculated. Based on, to identify the relative position of the width direction of the one of the recording head 211a and the other of the recording head 211b.
As described above, in the inkjet recording apparatus 1 provided with the plurality of recording heads 211, by using the plurality of parameters (indexes) to identify the relative positions between the plurality of recording heads 211, ejection failure, ejection unevenness, and the like. Therefore, the relative position of the recording head can be detected more appropriately and flexibly.

The present invention is not limited to the above-described embodiment, and various modifications can be made.
For example, in the above embodiment, the head unit 21 has been described as having nozzle openings arranged one-dimensionally in the width direction and a plurality of recording heads 211 arranged in a staggered pattern. May be a two-dimensional array (that is, the array range is a two-dimensional area), and the recording head 211 is disposed obliquely with respect to the width direction and the conveyance direction, so that the nozzle openings are partially formed. The positions may overlap in the width direction.

  Further, the two parameters (indexes) used for calculating the relative position are not limited to the similarity between the gravity center position and the luminance distribution. The positions of the reference line and the comparison line may be identified and the amount of displacement may be calculated, or other parameters may be used. In this case, not a multi-value image but a binary image may be captured and acquired.

  Also, any parameter may be used as a reference in the process of step S109, or a position shifted from a position indicating any minimum shift amount may be used as a reference in accordance with the relationship between both parameters.

  In the above embodiment, all the comparison lines in the range corresponding to the reference line (reference nozzle) are recorded. However, the relative position can be identified without necessarily recording all. In particular, when a nozzle with poor ejection is known in advance, for example, when ink is not ejected in the first place, or when the ejection direction is largely deviated in the transport direction, the comparison line is recorded by the nozzle. It is good also as not letting you do.

  In the above embodiment, the relative position between the plurality of recording heads 211 in the line head is detected based on the image data obtained by the line sensor 32. However, the plurality of recording heads 211 are partially (in the direction orthogonal to the transport direction ( The present invention is not limited to the line head as long as it is arranged with an overlapping range (not limited to 128 nozzles shown in the embodiment). Further, the imaging may be performed while moving in the width direction instead of the line sensor 32. In addition, the ink jet recording apparatus 1 does not have to include the line sensor 32, and the relative position may be detected based on the imaging data by performing imaging using an external imaging sensor. This relative position detection operation can also be performed by an external computer or the like.

  In the above embodiment, four reference lines are provided. However, the present invention is not limited to this. For example, the reference lines may be reduced to three so that the adjacent areas E (k) and E (k + 1) are completely separated. Further, the relative positions of the plurality of head units 21, that is, the configurations related to the ink ejection of the respective colors are separately detected. If the reference line and the comparison line are overlapped and recorded in the same range depending on the combination of the detection wavelength of the line sensor 32 and the ink color and can be separately detected separately, the plurality of colors within the same range. The reference line and the comparison line may be recorded by the recording head 211 related to the ink ejection.

  Further, in the above embodiment, the NCC is calculated and used only for the range selected in the process of step S107, but only the data in the selected range is used after mechanically calculating all the NCC. It is good also as performing this process.

In the above embodiment, the ink jet recording apparatus has been described as an example. However, in other image forming apparatuses that form an image by outputting each pixel by a plurality of recording elements, for example, an LED printer or the like. The present invention can be applied.
In addition, specific details such as the configuration, operation contents, and procedures shown in the above embodiments can be changed as appropriate without departing from the spirit of the present invention.

DESCRIPTION OF SYMBOLS 1 Inkjet recording device 10 Conveyance part 11 Drive roller 12 Conveyance belt 14 Conveyance motor 15 Encoder 20 Image formation part 21, 21C, 21M, 21Y, 21K Head unit 211, 211a-211h Recording head 22 Head drive part 23 Correction part 30 Image reading Unit 31 imaging drive unit 32 line sensor 40 control unit 41 CPU
42 ROM
43 RAM
50 Communication unit 60 Storage unit 61 Head relative position information 70 Operation display unit 71 Display unit 72 Operation reception unit 80 Bus P Recording medium

Claims (15)

There are a plurality of recording heads in which a plurality of recording elements that perform operations related to image recording are arranged, and a range in a predetermined width direction in the arrangement range of the plurality of recording elements in the plurality of recording heads is in the width direction. An image recording unit provided with the plurality of recording heads so as to partially overlap between adjacent recording heads is provided, and the plurality of recording heads and the recording medium are relatively moved in a relative movement direction orthogonal to the width direction. A recording head relative position detection method for detecting a relative position of the plurality of recording heads in an image forming apparatus that moves and records an image on the recording medium,
A reference line recorded by the predetermined recording element in the overlapping portion of one recording head related to the overlapping portion and extending in the relative movement direction, and the reference line and the width direction in the overlapping portion of the other recording head A test image recording step for recording a test image including the predetermined number of comparison lines recorded by the predetermined number of the recording elements within a range in which the positions of the recording elements can coincide with each other and extending in the relative movement direction;
A first deviation degree for calculating a first index indicating the degree of deviation in the width direction between the reference line and the predetermined number of comparison lines for the predetermined number of comparison lines from the recorded test image. Calculation step,
A second deviation degree calculating step of calculating a second index indicating the degree of deviation in a method different from the first index for at least a part of the predetermined number of comparison lines;
A relative position identifying step for identifying a relative position in the width direction between the one recording head and the other recording head based on a relationship between the first index and the second index;
A method for detecting the relative position of a recording head. Including an imaging step of imaging the recorded test image;
The method for detecting a relative position of a recording head according to claim 1, wherein the calculation of the first index and the calculation of the second index are performed using data of the captured test image. The test image is captured as a multi-valued image having a density gradation of 3 or more,
The recording head relative position detection method according to claim 2, wherein the degree of deviation is obtained based on a luminance distribution in the width direction.   At least one of the first index and the second index is a predetermined calculated value based on a luminance distribution in the width direction within a first range that includes the reference line and does not include the comparison line, and 4. The width direction is indicated by a difference from the predetermined calculation value in a second range that is the same range as the first range and includes a single comparison line. A method for detecting the relative position of the recording head.   The recording head relative position detection method according to claim 4, wherein the predetermined calculated value is a value indicating a shift of a gravity center position of the luminance distribution.   At least one of the first index and the second index includes a luminance distribution in the width direction within a first range that includes the reference line and does not include the comparison line, and the first index in the width direction. A predetermined similarity with the luminance distribution in a second range that is the same range as the first range and includes one of the comparison lines is indicated. The recording head relative position detection method described.   The method according to claim 6, wherein the predetermined similarity is normalized cross-correlation.   The method of detecting a relative position of a recording head according to claim 2, wherein in the imaging step, the test image is captured by an imaging sensor fixed in the width direction.   9. The relative position identifying step, wherein a regression equation indicating a relationship between the first index and the second index is obtained, and the relative position is identified based on the regression expression. The method for detecting the relative position of the recording head according to any one of the above. At least one of the first deviation degree calculating step and the second deviation degree calculating step identifies a corresponding change range in which the degree of deviation changes according to the position of the recording element corresponding to the comparison line,
In the relative position identification step, a regression equation indicating a relationship between the first index and the second index in the corresponding change range is obtained, and the relative position is identified based on the regression equation. The method for detecting a relative position of a recording head according to claim 1. In the relative position identification step, a value of the other index different from the one index when the value of one of the first index and the second index is a value indicating a minimal deviation amount is set. Based on a regression equation that identifies and indicates the correspondence between the value of the other index and the position of the recording element according to the comparison line, the recording element corresponding to the value of the identified other index The relative position detection method for a recording head according to any one of claims 1 to 10, wherein the relative position is identified from a position.   In the test image recording step, the predetermined number of comparison lines are recorded at different positions in the relative movement direction, and at least a part of the reference line is at a position different from the predetermined number of comparison lines in the relative movement direction. 12. The recording head relative position detection method according to claim 1, wherein recording is performed.   13. The relative position detection of a recording head according to claim 12, wherein, in the test image recording step, the reference line is recorded over a range in which the predetermined number of comparison lines are recorded in the relative movement direction. Method.   14. The method for detecting a relative position of a recording head according to claim 1, wherein a plurality of the reference lines are recorded by a plurality of the recording elements in the test image recording step. There are a plurality of recording heads in which a plurality of recording elements that perform operations related to image recording are arranged, and a range in a predetermined width direction in the arrangement range of the plurality of recording elements in the plurality of recording heads is in the width direction. An image recording section provided with the plurality of recording heads so as to partially overlap between adjacent recording heads;
A relative movement unit that relatively moves the plurality of recording heads and the recording medium in a relative movement direction orthogonal to the width direction;
A control unit;
With
The controller is
A reference line recorded by the predetermined recording element in the overlapping portion of one recording head related to the overlapping portion and extending in the relative movement direction, and the reference line and the width direction in the overlapping portion of the other recording head A test image including the predetermined number of comparison lines recorded by the predetermined number of the recording elements within a range in which the positions of the recording elements can be matched and extending in the relative movement direction;
From the recorded test image, a first index indicating a degree of deviation of the reference line and the predetermined number of comparison lines in the width direction is calculated for each of the predetermined number of comparison lines,
Calculating a second index indicating the degree of deviation in a method different from the first index for each of at least a part of the predetermined number of comparison lines;
An image forming apparatus comprising: identifying a relative position in the width direction between the one recording head and the other recording head based on a relationship between the first index and the second index.

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